Дисертації з теми "Adhesive performance"

The increasing environmental concern has reawakened an interest in materials based on renewable resources as replacement for petroleum-based materials. The main objective of this thesis was to explore plant proteins, more specifically wheat gluten, as a binder in wood adhesives intended for typical solid wood applications such as furniture and flooring. Alkaline and acidic dispersions of wheat gluten were used as wood adhesives to bond together beech wood substrates. Soy protein isolate was used as a reference. The tensile shear strengths of the substrates were measured for comparison of bond strength and resistance to cold water. AFM in colloidal probe mode was used to investigate nanoscale adhesion between cellulose and protein films. Wheat gluten was divided into the two protein classes; glutenins and gliadins, and their adhesive performance was compared with that of wheat gluten. Heat treatment and mild hydrolysis were investigated as means for improving bonding performance of wheat gluten. The treated wheat gluten samples were analysed by SE-HPLC and 13C-NMR to correlate molecular size distribution and structural changes with bonding performance. Soy protein isolate is superior to wheat gluten, especially in regards to water resistance. However, the bond strength of wheat gluten is improved when starved bond lines are avoided. The AFM analysis reveals higher interfacial adhesion between soy protein isolate and cellulose than between wheat gluten and cellulose. These results partly explain some of the differences in bonding performance between the plant proteins. Soy protein isolate contains more polar amino acid residues than wheat gluten and possibly interacts more strongly with cellulose. Furthermore, the bond performances of wheat gluten and glutenin are similar, while that of gliadin is inferior to the others, especially regarding water resistance. The extent of penetration of the dispersions into the wood material has a large impact on the results. The bonding performance of gliadin is similar to the others when over-penetration of the dispersion into the wood material is avoided. Moreover, the bond strength of the wheat gluten samples heated at 90°C was in general improved compared to that of wheat gluten. A small improvement was also obtained for some of the hydrolyzed wheat gluten samples (degree of hydrolysis: 0-0.6 %). The improvements in bonding performance for the heat treated samples are due to polymerization, while the improvements for the hydrolyzed samples are due to denaturation. The 13C-NMR analysis of the treated samples confirms some degree of denaturation.
QC 20120514

In this dissertation, four test approaches were developed to characterize the adhesion performance and durability of adhesive bonds for specific applications in areas spanning from structural adhesive joints to popular confectionaries such as chewing gum. In the first chapter, a double cantilever beam (DCB) specimen geometry is proposed for combinatorial fracture studies of structural adhesive bonds. This specimen geometry enabled the characterization of fracture energy vs. bondline thickness trends through fewer tests than those required during a conventional "one at a time" characterization approach, potentially offering a significant reduction in characterization times. The second chapter investigates the adhesive fracture resistance and crack path selection in adhesive joints containing patterns of discreet localized weak interfaces created using physical vapor deposition of copper. In a DCB specimen tested under mode-I conditions, fracture energy within the patterned regions scaled according to a simple rule of mixture, while reverse R-curve and R-curve type trends were observed in the regions surrounding weak interface patterns. Under mixed mode conditions such that bonding surface with patterns is subjected to axial tension, fracture energy did not show R-curve type trends while it was observed that a crack could be made to avoid exceptionally weak interfaces when loaded such that bonding surface with defects is subjected to axial compression. In the third chapter, an adaptation of the probe tack test is proposed to characterize the adhesion behavior of gum cuds. This test method allowed the introduction of substrates with well-defined surface energies and topologies to study their effects on gum cud adhesion. This approach and reported insights could potentially be useful in developing chewing gum formulations that facilitate easy removal of improperly discarded gum cuds from adhering surfaces. In the fourth chapter we highlight a procedure to obtain insights into the long-term performance of silicone sealants designed for load-bearing applications such as solar panel support sealants. Using small strain constitutive tests and time-temperature-superposition principle, thermal shift factors were obtained and successfully used to characterize the creep rupture master curves for specific joint configurations, leading to insights into delayed failures corresponding to three years through experiments carried out in one month.
Ph. D.

A study has been carried out regarding the possibility for application of UV-cured coatings on different pretreated galvanized steel, in coil coating application. In order to address the questions about whether the adhesion will be affected and how, when combining respective coating with a steel substrate. Two types of UV-curable formulations have been applied respectively, acrylate-based free radical formulation and epoxy-based cationic formulation, on five types of steel substrates. In addition, UV-LED was also investigated as an alternative energy source. The aim is to explore the curing of the coatings, the surface topology and hydrophilicity, the material and mechanical properties of coatings and coated systems respectively. It was found that the acrylate coating gives a hydrophilic surface while the epoxy coat is hydrophilic but is more hydrophobic than acrylate. The acrylate resin is not compatible with Standard Ti-pretreatment from PO substrates and the curing of epoxy is inhibited by pretreatment primer in PP substrates. Curing using UV-LED is possible and should be investigated further. No comparison could be made between coating systems acrylate and epoxy, regarding the adhesive performance, due to the failure of obtaining the right thickness for the acrylate coating.
I denna studie undersöktes möjligheten att applicera UV-härdande lacker på olika förbehandlade galvaniserade stålsorter för bandlackering. Detta för att förstå mer om vidhäftningen påverkas av, och på vilket sätt, kombinationen av respektive UV-lack med olika metallsubstrat. Två olika UV-formuleringar, akrylat and epoxy, applicerades på fem olika stålsubtrat och även screeningsstudie på UV-LED utfördes. Målet är att undersöka uthärdning av lackeringar, topologin och hydrofilicitet, material och mekaniska egenskaper hos färglacken och de lackade systemen, samt möjlighet att använda LED-lampa som UV-källan. Resultatet visar att akrylat ger en hydrofil yta medan epoxy är hydrofil men är mer hydrofob än akrylat. Akrylatet är inte kompatibelt med Standard Ti-pretreatment från PO substrat och uthärdning av epoxy inhiberas av förbehandlade primer på PP-prover. Uthärdning med UV-LED är möjligt och bör undersökas ytterligare. Det gick inte att jämföra mellan de två UV-formuleringarna, akrylat och epoxy, på grund av fel tjocklek hos akrylatfilmerna.

The performance of connections and full-scale shear walls constructed with acrylic foam pressure sensitive adhesive (PSA) tape is the focus of this thesis. The objectives of this study were first to investigate the bonding characteristics of adhesive tape to wood substrates and then to expand this investigation to cover adhesive-based shear walls subjected to high wind and seismic loadings. A total of 287 monotonic connection tests and 23 reversed cyclic wall tests were performed to achieve these objectives. Connection tests were performed in accordance with ASTM D 1761-88 (2000), and walls were tested using the CUREE (Consortium of Universities for Earthquake Engineering) general displacement-based protocol.

Variables investigated within the main study were the following: the use of OSB versus plywood sheathing, the effect of priming and surface sanding on adhesion, and the comparison of connections involving mechanical fasteners with those that utilized only adhesive tape or a combination of the two. It was found that an application pressure of 207 kPa (30 psi) or greater was needed to form a sound bond between the acrylic foam adhesive tape and a wood substrate. Properly bonded OSB and plywood connections provided fairly ductile failure modes. Full-scale walls constructed with adhesive tape performed similarly to traditional wall configurations, while walls constructed with a combination of adhesive tape and mechanical fasteners provided significant gains in strength and toughness. The results of this study serve to provide a foundation for expanding the engineering uses of acrylic foam adhesive tape for structural applications.
Master of Science

Cellulose nanocrystals (CNCs) are attractive nanomaterials due to their superior mechanical properties, renewability, and natural abundance. Their surface hydroxyl groups, along with surface charges induced during their production, allow CNCs to be easily dispersed in an aqueous medium, especially with sustainable water-based production methods such as emulsion polymerization. Moreover, their surface functionality makes them highly suitable for modification, thereby making them even more versatile. Emulsion polymer latexes are heterogeneous mixtures, having a continuous aqueous phase along with a dispersed organic phase. Latex polymers are used in a wide range of applications such as in coating and adhesive films. Because of the bi-phasic nature of emulsion polymerizations, the surface properties of CNCs play a crucial role in their location relative to the organic phase, and how well-dispersed they are in the cast films. In this thesis, three grades of CNCs (Celluforce Inc.) with either hydrophilic, partially-hydrophobic, or hydrophobic surface properties, were combined with conventional emulsion and miniemulsion polymer formulations to investigate their effect on the properties of pressure sensitive adhesive (PSA) films. In the first instance, hydrophilic CNCs were tested in a seeded semi-batch emulsion polymerization. Using a sequential experimental design, the effects of polar comonomer, surfactant, chain transfer agent, and CNC loading on latex stability and PSA properties were studied. By increasing polymer chain entanglements and the work of adhesion, the hydrophilic CNCs were observed to simultaneously improve the three key properties of acrylic-based PSA films, i.e., tack, peel strength and shear strength. In the second part of this project, we compared the role of hydrophilic and partially-hydrophobic CNCs in PSA property modification. Viscosity measurements and atomic force microscopy revealed differences in the degree of association between the two types of CNCs and the latex particles. Dynamic strain-sweep tests showed that hydrophilic CNC nanocomposites softened at lower strains than their partially-hydrophobic counterparts. This behaviour was confirmed via dynamic frequency tests and modelling of the nanocomposites’ storage moduli, which suggested the formation of CNC aggregates of, on average, 3.8 and 1.3 times the length of CNCs. These results confirmed that the partially-hydrophobic CNCs led to improved CNC dispersion in the PSA films and ultimately, enhanced PSA properties. In the third part of the project, mini-emulsion polymerization (MEP) was used to embed the hydrophobic CNCs within the polymer particles in contrast to the hydrophilic and partially-hydrophobic CNCs which resided mainly in the aqueous phase or near the water-particle interface. Higher CNC loadings led to increased particle size, decreased polymerization rate and number of particles, while only slightly increased the viscosity and the work of adhesion. PSA film properties decreased upon the incorporation of hydrophobic CNCs. Transmission electron microscopy showed that CNCs were expelled from the latex particles at higher loadings, suggesting the incompatibility of the acrylic polymer and the CNCs’ modifying agents. The ability to modify CNCs enables one to achieve a range of hydrophilicity/hydrophobicity. This makes them extremely versatile in a heterogeneous mixture such as in an emulsion polymerization. Because emulsion polymers are used in a wide range of applications with a broad spectrum of properties (i.e., not only as adhesives but as non-tacky coatings), our ability to control CNC location relative to the polymer particles in the latex opens the door to a world of high value-added sustainable polymer products.

It was the objective of this research to develop high temperature and high performance polyimides that also display (a) thermal stability; (b) crystallinity in the initial material and ability to crystallize from the melt; (c) fast crystallization kinetics and (d) melt processability. This unique combination of properties is presently unavailable in any other polyimide. In this regard, the present work investigates the crystallization, morphology and thermal stability of two novel semicrystalline polyimides based on the same diamine, 1,3-bis (4-aminophenoxy) benzene (TPER), but two different dianhydrides, 3,3',4',4'-biphenyltetracarboxylic dianhydride (BPDA) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). Phthalic anhydride was used as an endcapper to improve the thermal stability of the polyimides. The BPDA based polyimide was also tested extensively as a structural adhesive using Ti-6Al-4V coupons. Additionally, these polyimides are based on monomers, that are presently commercially available. The bulk thermal stability of the polyimides was first evaluated using dynamic and isothermal thermogravimetric experiments. DSC was utilized to test the ability of the polyimides to crystallize from the melt after exposures to varying melt times and temperatures. Exceptional thermal stability was demonstrated by BPDA based polyimide with no change in the melting behavior after 40 min at 430°C or 30 min at 440°C. The semicrystalline morphology of the material was studied using hot stage polarized optical microscopy (OM) and atomic force microscopy. The spherulitic growth rates were determined as a function of crystallization temperature after quenching from various melt times and temperatures. The effect of crystallization temperature, previous melt time and melt temperature on the morphology was considered. The spherulitic growth rates increased with increasing undercooling in the temperature range studied (nucleation controlled), while the growth rate at a specific crystallization temperature decreased on increasing the previous melt time and temperature. The melting behavior was studied after different crystallization times and temperatures and also as a function of different heating rates. Crystallization kinetics was followed both isothermally and non-isothermally using DSC and OM. Avrami analysis was performed for TPER-BPDA and the obtained results were correlated with microscopic observations. Melt viscosity measurements were carried out as a function of melt temperature, melt time and frequency. The adhesive investigations for TPER-BTDA utilized lap-shear test, wedge test and double cantilever beam tests. The durability of the adhesive and the fracture surface was studied after exposure to various solvents and after high aging and testing temperatures. The polyimide demonstrated very high average room temperature lap-shear strengths (8400 psi or 59 MPa), excellent solvent resistance and durability of strengths at high aging and testing temperatures.
Ph. D.

The primary differences between the solventborne and waterborne epoxy printed circuit board (PCB) impregnating resins arise from the distinct physical compositions and drying characteristics of the polymer solution and the latex emulsion. The presence of residual surfactant from the waterborne epoxy emulsion poses a concern for dielectric performance and adhesive durability. Another problem involves the crystallization of insoluble solid dicyandiamide (DICY), which is significantly different in morphology than that found in solution cast resins. A two-stage drying model was employed to gain a better understanding the drying and coalescence processes. The process of surface DICY crystal formation during the drying of glass prepreg sheet was related to a threshold concentration of the curing agent in the impregnating latex resin formulation. Conditions favoring faster drying lead to the rapid formation of a coalesced skin layer of latex resin, thereby trapping the curing agent in the bulk and reducing the surface deposition of DICY by percolating water. Surfactant is believed to remain concentrated in a receding wet zone until it is driven to the surfaces of the glass fibers upon the completion of drying. The copper foil/laminate interface was evaluated by a 90° peel test as part of two different studies: an analysis of the viscoelastic response of the interface during peel and a study of the thermal durability of the copper/laminate interfacial peel strength. The surfactant acted as a plasticizer to toughen the fiber/matrix interphase, resulting in larger observed peel strengths in the latex resin impregnated materials relative to the solventborne system. Surfactant segregated to the fiber surface during coalescence to form a plasticized fiber/matrix interphase; surfactant migrated into the bulk during postcure to yield a more homogeneously plasticized epoxy matrix. Dielectric measurements of neat resin and laminate materials revealed that the dielectric constants of the model resin-impregnated laminates met the performance criteria for PCB substrates of their class, regardless of surfactant content. Overall, the adhesive performance, adhesive durability, and dielectric properties of PCB systems fabricated with model latex epoxy resin, containing native surfactant (5 wt %), met or exceeded the performance of an equivalent solventborne resin impregnated system.
Ph. D.

The cure kinetics of a high performance epoxy adhesive system based on TGDDM/DGEBA/DDS/DICY and toughened with carboxy terminated poly(acrylonitrile-co-butadiene) rubber with aluminum filler was investigated using differential scanning calorimetry. Three different sets of experiments were performed to follow the cure kinetics of the adhesive in a multi-step cure cycle. Three-dimensional plots of data entered into a surface-fitting software allowed for the interpolation of the degree and rate of cure as functions of heating rate and temperature, time and temperature, or time and initial degree of cure. Isothermal cure was modeled successfully using the kinetic model of Kamal. The gel point of the adhesive was measured using dynamic shear rheometry under isothermal conditions. Methods were developed to combine ramp and soak segments so that both the conversion (α) and rate of cure (dα/dt) can be followed through a two-step cure cycle of the type used to cure composite prepreg and adhesive in an industrial setting.
Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry.
"July 2006."

Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry.
"July 2006." Title from PDF title page (viewed on Nov. 4, 2007). Thesis adviser: William T. K. Stevenson. Includes bibliographic references (leaves 95-99).

Il lavoro svolto ha avuto come obiettivo la verifica l’applicabilità della tecnologia adesiva su componenti edilizi innovativi. L’impiego degli adesivi strutturali rappresenta la traduzione costruttiva del principio della “semplificazione tecnologica”, ovvero della possibilità di realizzare prodotti industrializzabili con elevate prestazioni ed un numero limitato di componenti, riducendo le emissioni ambientali nelle loro fasi di vita. In particolare, è stata verificata la fattibilità tecnico-costruttiva di un solaio tensegrale in acciaio e vetro, sviluppando l’idea brevettuale del brevetto n. 00014426973, inventore Prof. P. Munafò. L’attività di ricerca si è sviluppata con la sperimentazione di diverse tipologie di giunti adesivi con aderendi in acciaio, alluminio, vetro e adesivi sia dopo maturazione in condizioni di laboratorio che dopo invecchiamento artificiale accelerato. È stato poi definito costruttivamente il giunto adesivo tra sottostruttura in acciaio e l’impalcato in vetro per rendere strutturalmente collaborante l’impalcato con la sottostruttura tensegrale. Costruito il prototipo di solaio si è passati alla verifica delle prestazioni meccaniche con prove di carico. Parallelamente all’attività sperimentale sono state condotte analisi numeriche sull’elemento costruttivo, per verificare le ipotesi assunte. Il risultato ottenuto ha validato l’assunto alla base dell’idea brevettuale validando le previsioni dell’analisi numerica. In-fatti, dalle prove di carico si è riscontrato un significativo incremento della rigidezza del solaio grazie alla giunzione adesiva tra impalcato in vetro e sottostruttura tensegrale.
The aim of the present work was to examine the applicability of adhesive bonding technology to innovative building components. The use of structural adhesives represents the constructive implementation of the principle of “technological simplification”, that is, the possibility of assembling industrially manufactured products with high performance and a limited number of components, reducing environmental emissions during their life phases. In particular, the technical-constructive feasibility of a steel and glass tensegrity floor was verified, developing the idea of Patent No. 00014426973 (inventor Prof. P. Munafò). The research activity developed with the testing of different types of adhesive joints with steel, aluminium, glass, and adherends both after curing in laboratory conditions and after artificial accelerated ageing. The adhesive joint between the steel substructure and the glass deck was then determined by design to allow the deck to structurally cooperate with the tensegrity substructure. The prototype of the floor was assembled, and the mechanical performance was verified by load tests. In parallel with the experiments, numerical analyses were performed on the structural element to verify the hypotheses adopted. The results obtained confirmed the assumption underlying the patent idea by validating the predictions of the numerical analysis. In fact, the load tests showed a significant increase in the stiffness of the floor thanks to the adhesive joint between the glass deck and the tensegrity substructure.

Chapter 1 is an introduction to lithium disilicate: its glass ceramic nature, its characteristics, its mechanical properties. The possibility to be etched allows lithium disilicate to be adhesively luted on dental tissues, influencing both the final properties of restoration and the clinical protocol of cementation. The aim of this thesis was investigate the adhesive interface between lithium disilicate, resin cement and dental tissues from different points of view: retention, fracture strength and survival rate. In Chapter 2 the retention of lithium disilicate crowns cemented using two different cementation systems was measured. Twenty extracted mandibular premolars were prepared. Anatomic crowns were waxed and hot pressed using lithium disilicate ceramic. Teeth were divided into two groups (n = 10): (1) self- curing luting composite and (2) glass-ionomer cement (GIC). After cementation, the crowns were embedded in acrylic resin block with a screw base. Each specimen was pulled along the path of insertion in Universal Testing Machine. Failure load in Newtons (N) and failure mode were recorded for each specimen. Failure mode was classified as decementation or fracture. Failure load data were analyzed using one-way analysis of variance (ANOVA). Failure modes were compared using Pearson’s Chi-square test. Mean failure load was 306.6(±193.8) N for composite group and 94.7(±48.2) N for GIC group (p = 0.004). Disilicate crown cemented with luting composite most often failed by fracture; otherwise, crown cemented with glass-ionomer cement most often failed by decementation (p = 0.02). Disilicate full crown cemented with luting composite showed higher failure load compared with conventional cementation with glass-ionomer cement. The interface between tooth, luting composite and lithium disilicate surface was also qualitatively evaluated using a scanning electron microscope (SEM). An extracted restoration-free human molar was stored in physiological solution until it was embedded in an autopolimerysing acrylic resin. A standard preparation for onlay was completed and after preparation an anatomic onlay was waxed on the tooth and then hot pressed using lithium disilicate ceramic. After cementation the sample was dissected using an Automatic Micromet (Remet s.a.s) and the section was analyzed using a SEM. SEM evaluation of the tooth showed the three layers seamlessly; by increasing the enlargement the interface did not change. In Chapter 3 the fracture strength of human teeth restored with lithium disilicate onlays, with and without fiber post build-up, was measured. Twenty human mandibular molars were horizontally sectioned and divided into two groups (n = 10). No treatment was applied in group A. Teeth in group B were endodontically treated, built-up using fiber post and composite core and prepared with a circumferential chamfer providing a 1 mm circumferential ferrule. Lithium disilicate onlays were pressed and luted on teeth using dual-curing luting composite. Teeth were tested under static load. Failures were classified as restorable or not restorable. Failure loads were analyzed with ANOVA. Failure modes were compared using Pearson’s Chi-square tests. The mean fracture loads were 1383.5 N for group A and 1286.3 N for group B. No difference was found (p = 0.6). Ninety per cent of fractures were classified as not restorable in both groups, with no difference (p = 0.8). It was concluded that, for teeth restored with adhesive procedures and lithium disilicate onlays, the presence of build-up with fiber post to provide retention and resistance form (as traditionally stated) does not influence the fracture strength. Finally, in Chapter 4, a retrospective study was conducted to assess the clinical performance of lithium disilicate single restorations adhesively cemented on natural teeth. All patients who received lithium disilicate single restorations between 2009 and 2013 at the dental clinic of the University of Ferrara were recalled for clinical evaluation. A total of 43 partial and total restorations in 17 patients were evaluated from a minimum of 36 months follow-up to a maximum of 81 months follow-up, with a mean follow-up of 51 months. The cumulative survival rate was 97.7%, and the cumulative success rate was 94.2%. Lithium disilicate can be successfully used for single-tooth restorations in both anterior and posterior regions, provided that an adhesive luting protocol is applied.

Background and objectives: TISSIUM light-activated adhesive was investigated as an alternative to tissue-penetrating products to fix meshes in intraperitoneal laparoscopic ventral hernia repair. The objective of this study was to ensure efficient polymer light activation through commercial meshes and to assess the acute and chronic fixation strength of the light-activated adhesive in a porcine model in comparison to commercial fixation products. Methods: A spectroscopic analysis was conducted on the light-activated adhesive through three different meshes (1, 2, and 3) to quantify the acrylate conversion associated with the level of polymer cross-linking. Two setups were implemented: a static (light source fixed over a drop of polymer) and a dynamic (light source rotated around a pattern of polymer to mimic the surgical procedure). Hernia defects were created in porcine models and repaired either using the light-activated adhesive or a commercial product (A, B, C, and D) to fix a mesh. For each tested condition, the acute and chronic (3 months) fixation strength performances were assessed using burst ball and t-peel mechanical tests. Results: The light activation proved to be effective (more than 90% of the acrylates converted) in static in 7 seconds through the three meshes and in dynamic between 3 min and 5 min 32 sdepending on the considered mesh. In a burst ball test, the light-activated adhesive reached between 42 and 84% of the commercial products’ acute performance with the three meshes (between 75,9 and 95,9 N) and reached 88% of the commercial product A’s chronic performance with mesh 1 (610,1 N). A t-peel test demonstrated similar strength of ingrowth for the repairs using the light-activated adhesive or the commercial product A at the 3-month timepoint with mesh 1 (2,55 and 2,37 N/cm respectively). Conclusions: Data suggest the light-activated adhesive has the potential to be used in intraperitoneal laparoscopic ventral hernia repair. In a reasonable time, the adhesive is efficiently light-activated through commercial meshes. The light-activated adhesive’s performances to fix commercial meshes, both acute and chronic, are similar to commercial products, but with a strong advantage of not being tissue penetrating.

Le collage structural est une technique d’assemblage de plus en plus demandée aujourd’hui dans beaucoup de domaines comme l’automobile, l’aéronautique, l’aérospatial, l’industrie navale et ferroviaire. La qualité d’un adhésif est un important paramètre pour garantir la fiabilité et la durabilité d’un assemblage collé. On sait qu’une fausse conception d’un joint collé, un mauvais choix d’adhésif ou même un traitement de surface mal réalisé pourra avoir des conséquences spectaculaires voire dramatiques. En termes de performance, l'ajout de nanoparticules à base de carbone à l'adhésif peut contribuer à améliorer les performances des assemblages collés. Dans cette étude, des adhésifs renforcés par trois types de nanacharges sont développés. En effet, l'adhésif DGEBA a été renforcé avec des nanotubes de carbone (CNT), des nanoplaquettes de graphène (GNP) et du noir de carbone (CB) avec différentes fractions massiques (1wt.%, 2wt.% et 5wt.%). L'objectif global est l'étude de l'influence du type, de la fraction massique et des dimensions des nanocharges sur le comportement mécanique de la colle et de l’assemblage collé. Les résultats ont montré que chaque type d'adhésif renforcé par des nanocharges possède un bon potentiel en termes de comportement mécanique sous des sollicitations statiques et dynamiques. Cependant, la présence d'une fraction massique élevée de nanoparticules a tendance à entraîner une dégradation par rapport à l'adhésif pur en raison du changement de morphologie de la microstructure et des interactions physico-chimiques. Et afin de quantifier la résistance à l’endommagement de l’adhésif dopé par des nanocharges et démontrer la compatibilité de l'adhésion avec divers substrats, des essais DCB et ENF ont étaient réalisés sur des assemblages Aluminium/aluminium et Composite/composite. De plus, des modèles numériques avec prise en compte de l’endommagement de la colle dopée ont été développés et validés avec les résultats expérimentaux. Cette étude démontre que le type, la fraction massique, la taille et la forme des nanocharges jouent un rôle important dans l'amélioration des performances des assemblages collés
Adhesively bonded joint is a joining technique that is increasingly in a request today in many fields such as the automotive, aerospace, and naval. The adhesive selection is an important parameter to guarantee the reliability and durability of an adhesively bonded joint. It is well known that the wrong design of a bonded joint, the wrong choice of adhesive, or even a poorly executed surface treatment can have dramatic consequences. In terms of performance, the incorporation of carbon-based nanoparticles into the adhesive improves the performance of bonded joints. In this study, DGEBA adhesive doped by three kinds of nanofillers is established. Indeed, the adhesive has been doped with carbon nanotubes (CNT), graphene nanoplatelets (GNP), and carbon black (CB) with different mass fractions (1wt.%, 2wt.%, and 5wt.%). The overall objective is to study the influence of the type, mass fraction, and dimensions of the nanofillers on the mechanical behavior of the adhesive and the bonded joint. The results showed that each type of adhesive reinforced with nanofillers has a good potential in terms of mechanical behavior under static and dynamic loadings. However, the presence of a high mass fraction of nanoparticles tends to lead to degradation compared to the neat adhesive due to the transformation in microstructure morphology and physicochemical interactions. In addition, to quantify the damage resistance of the nanofiller-doped adhesive and demonstrate the adhesion compatibility with various kinds of substrates; DCB and ENF tests were performed on aluminum/aluminum and composite/composite bonded joints. Besides, numerical models taking into account the damage of the doped adhesive were developed and validated with the experimental results. This study demonstrates that the type, mass fraction, size, and shape of nanofillers play an important role in improving the performance of the adhesively bonded joints

The structural adhesives widely used in structural strengthening applications are thermoset ambient cure adhesive polymers. At ambient temperatures, these polymers are in a relatively hard and inflexible state. At higher temperatures, the material becomes soft and flexible. The region where the molecular mobility changes dramatically is known as the glass transition temperature Tg and often is presented as a single value. Epoxy polymers exhibit a significant reduction in mechanical properties near glass transition temperature Tg when they are exposed to elevated temperatures. Glass transition temperature Tg is used to characterise the change in epoxy adhesive properties with changing temperature. The mechanical properties of epoxies tend to improve with curing temperature. This is because the crosslink density between the adhesive molecular structures increases during the curing process consequently the Tg improves. The aims of this work are first to demonstrate the importance of curing temperature. Second, to investigate the influence of glass transition temperature !! improvement on the performance of EB-FRP strengthened steel structures in flexure at ambient and elevated temperatures. Third, to compare analytical results with experimental results from the flexure tests results. Finally, to compare the current design guideline recommendations with the flexure tests results. The most commonly used methods to evaluate Tg Dynamic Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC) were used to study Tg. Two off-shelf structural adhesives were investigated to understand their property variation with temperature. Epoxy coupons were cured at different elevated temperature and humidity environments up to 28 days. A combination of two extreme relative humidity of 0 and 100% and variable curing temperatures between 15 to 80°C were considered. From a test matrix of 300 DMA and over 250 DSC coupons these conclusions were drawn. First, ambient cured thermosets have a linear relationship between Tg and curing temperature, but Tg is reduced if a certain temperature is reached. Second, a fully cured adhesive requires heating treatment. Without a curing regime, designed Tg may never be achieved. Finally, curing time is crucial at the low curing temperatures while it is less significant at the higher curing temperature. The results of Tg investigation were used to select appropriate curing temperature that the adhesives resistance to temperature can be maximised without damaging the mechanical properties. The study helps designs to understand and assess the behaviour of these two adhesives when they are exposed to extreme temperatures. The study increases the awareness that a fully cured adhesive may never be achieved at ambient or low temperatures. It is important to find the mechanical properties and Tg when the coupons are exposed to the same curing temperature. To investigate the influence of glass transition temperature Tg improvement on the performance of EB-FRP strengthened steel structures in flexure at ambient and elevated temperature, nine three metre length beams were designed to behave as a concrete-steel composite bridge deck. The beams were tested in four-point bending. Lap shear, DMA test, and pull-off adhesion samples were prepared and cured at the same conditions and tested at ambient temperature. Six beams were tested under only mechanically loading at ambient temperature, including the control specimen. Five beams were tested at ambient temperature to show the effects of adhesive curing on FRP strengthened sections. A significant increase of load capacity of the adhesive joints was achieved due to the curing of the joints at elevated temperature. The failure occurred was in the same manner. An increase in the load capacity was observed with increasing curing temperature. An increase of approximately 25% was noticed in the ultimate load capacity of the specimens cured at 50°C compared to the specimens cured at 30°C. The load capacity of lap-shear specimens cured at 50°C was 28% higher than the specimens cured at 30°C. Three specimens were tested under mechanical and thermal loading. A bespoke thermal chamber was designed and fabricated to apply a controlled thermal loading. The beams were loaded mechanically up to 350kN, first. The temperature of the specimens was then increased at a rate of 0.8°C/min. The sustained load 350kN remained constant during the heating phase. Digital Image Correlation (DIC) technique was used to detect the slippage of the tip of the FRP plates. The only specimen cured at 30°C showed relatively poor performance compared to the two specimens cured at 50°C. The plate ends started to slip when the adhesive storage modulus from the DMA runs reduced approximately by 15 and 18% for the beams cured at 30 and 50°C respectively. Pull-off adhesion tests confirmed that adequate surface preparation of over 25 MPa was achieved The flexural model for the composite steel section represented to predicate load-deflection behaviour of the specimens using semi-experimental constitutive material law. The model successfully predicts the load-deflection behaviour of specimens, considering the strain hardening contribution. A bond stress analysis is also presented, which counts for the effect of FRP plate moment effect. The experimental and theoretical FRP plate slippage assuming only adhesive degradation with temperature are compared. The analytical bond models cannot predict the experimental failure because the linear elastic material properties were assumed and the failure was adhesion.

Orientador: Luis Alexandre Maffei Sartinni Paulillo
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: A microscopia confocal de varredura a laser (MCVL) é um recurso de visualização microscópica que permite a análise de materiais ou estruturas com requisitos mínimos de preparação de amostras de modo não destrutivo. Assim, os objetivos deste estudo foram: avaliar a influência da incorporação do corante fluorescente Rodamina B (R) nas propriedades mecânicas resistência coesiva (RC), módulo de elasticidade (ME) e resistência à flexão (RF) de 2 sistemas adesivos, o autocondicionante Clearfil SE Bond e o convencional Scotchbond Multi-Purpose (estudo 1); validar o método modificado de microtração (?TBS), em que micro-amostras de secção transversal de 0,09 mm2 foram testadas e verificar a influência da R na resistência à união a dentina e integridade interfacial através de microscopia confocal (estudo 2). Para avaliar a influência do corante, 0,16 mg/ml de R foram incorporados aos adesivos constituindo assim dois grupos para cada adesivo: grupos dos adesivos corados e não corados totalizando 4 grupos experimentais. Para a análise da RC, E e RF, os corpos de prova foram confeccionados a partir de uma matriz de silicone por adição. Sobre a matriz, foram dispensados 10 ?L de adesivo variando de acordo com cada grupo de adesivos corados e não corados. RC (n= 10), E e RF (n= 5) foram avaliadas em máquina de ensaio universal a 0,5 mm/min, até a ruptura da amostra. Para visualização em microscopia confocal e análise da resistência à união os adesivos foram aplicados à superfície plana da dentina oclusal de 32 pré-molares humanos. Após a realização dos procedimentos adesivos, realizaram-se as restaurações (blocos de 16 mm2) com Charisma Opal (Kulzer - cor A3). Em seguida, para a realização do teste modificado de microtração, micro-amostras em forma de palito (secção transversal 0,09 mm2) foram confeccionadas. Previamente ao ensaio mecânico, foi realizada através de MVCL a análise micromorfológica das microamostras dos grupos de adesivos corados. Posteriormente a resistência à união foi mensurada através do ensaio modificado de microtração a velocidade de 0,5 mm/min em máquina de ensaio universal. Os dados de todos os testes avaliados foram submetidos à análise de variância dois fatores. Os resultados mostraram que o comportamento dos sistemas adesivos investigados não se modificou, independente da presença do corante, pois não foram observadas diferenças significativas nas propriedades mecânicas estudadas: resistência à união, resistência coesiva, resistência flexural, módulo de elasticidade, bem como a integridade interfacial. A preparação de micro-amostras não comprometeu os resultados do ensaio de resistência adesiva. De acordo com os resultados obtidos e análise dos parâmetros: coeficiente de variação, porcentagem de padrão de fratura e incidência de falhas prematuras, concluiu-se que o teste modificado de microtração foi considerado um método confiável para a avaliação da resistência à união de sistemas adesivos. A técnica de visualização microscópica confocal produziu informações detalhadas da interface adesiva e pode ser bem indicada para a avaliação da efetividade de união de sistemas adesivos. Desta forma, é possível associar ambas as metodologias obtendo-se uma avaliação mais realista e confiável dos materiais restauradores
Abstract: The confocal laser scanning microscopic (CLSM) is a tool of visualization that allows microscopic analysis of materials or structures labeled with fluorescent dyes with minimal requirements of specimen's preparation nondestructively. The aims of this study were: to evaluate the influence of incorporation of fluorescent dye Rhodamine B (R) in the properties mechanical: cohesive strength (CS), elastic modulus (E) and flexural strength (FS) of the selfetching Clearfil SE Bond and etch-and-rinse Scotchbond Multi-Purpose (Study 1); validating the modified microtensile method using micro-specimens cross section of 0.09 mm2 (?TBS) and evaluate the influence of R in bond strength in dentin and interfacial integrity by confocal microscopy (study 2). To evaluate the influence of the dye, 0.16 mg/ml of R were incorporated into adhesives thus forming two groups for each adhesive: groups of labeled adhesives and no-labeled totaling 4 experimental groups. For the analysis of CS, E and FS the specimens were made from a silicone matrix. About the matrix were 10 ?L dispensed adhesive varying according to each group of adhesives stained or not. CS (n = 10), E and FS (n = 5) were evaluated in a universal testing machine at 0.5 mm/min until failure of the specimen. For visualization in confocal microscopy and bond strength analysis (n = 8), the adhesives were applied to the occlusal dentine surface 32 of human premolars. After procedures adhesives, composite crowns approximately (16 mm2) were built up with Charisma Opal (Kulzer - color A3). Then for testing modified microtensile, micro-specimens beam-shaped were prepared. Prior to mechanical testing micromorphological analysis of micro-sticks of the groups of labeled adhesives was performed using CLSM. Subsequently bond strength was measured using the modified microtensile test in a universal testing machine speed of 0.5 mm/min. The results showed that the behavior of the adhesive systems investigated did not change regardless of the presence of the dye, as there were no significant differences in mechanical properties studied: bond strength, tensile strength, flexural strength, modulus of elasticity, as well as interfacial integrity. The preparation of micro-specimens did not affect the results of the bond strength test. According to the analysis results and parameters: coefficient of variation percentage of fracture pattern and incidence of early failures, it is concluded that the modified microtensile test was considered a reliable method for evaluating the bond strength of adhesive systems. The confocal microscopic visualization technique yielded detailed information of the adhesive interface and can be well suited for evaluating the effectiveness of adhesive systems. Thus, it is possible to associate both methods give a more realistic and reliable adhesive restoration on the presence of fluorescent dye
Doutorado
Dentística
Doutora em Clínica Odontológica

L’obiettivo del presente lavoro è verificare l’applicabilità di materiali innovativi, quali compositi (GFRP - Glass Fibre Reinforced Polymer) e colle strutturali, per la realizzazione di facciate continue ad alte prestazioni meccaniche e termiche e a basso impatto ambientale. Tale obiettivo è stato verificato anche tramite l’applicazione del principio della “Semplificazione tecnologica” che rappresenta il filo conduttore alla base dello studio e delle sperimentazioni svolte dal gruppo di ricerca, coordinato dal Prof. P.Munafò, che ha sviluppato il brevetto “Sistema per la realizzazione di facciate di edifici” (n.102015000087569) di cui il Professore è inventore. Con tale filosofia di approccio è possibile realizzare componenti edilizi altamente prestazionali e semplici nella loro concezione essendo costituiti con un numero limitato di pezzi implicando così un minor consumo di energia nella produzione, assemblaggio, manutenzione e smaltimento del prodotto, classificandolo quindi come eco-sostenibile. In questa tesi viene verificata la fattibilità di un sistema costruttivo per la realizzazione di facciate continue per edifici studiando preventivamente, con test sperimentali e analisi sul ciclo di vita dei componenti, le prestazioni meccaniche dei profili in GFRP e degli adesivi strutturali in condizioni di invecchiamento accelerato (durabilità) e non, e l’interazione del componente edilizio con l’ambiente, dalla produzione alla dismissione finale (LCA - Life Cycle Assessment). I metodi principalmente usati in questo studio sono di tipo sperimentale al fine di testare le proprietà meccaniche dei materiali, in condizioni ambientali e dopo invecchiamento (accelerato in camera climatica ad elevata umidità e temperatura (ISO 6270-2) e sotto esposizione ai raggi UV (ASTM D904–99)). In seguito ai singoli test di invecchiamento precedentemente citati, sono stati condotti ulteriori sperimentazioni riguardanti il trattamento di campioni a condizioni di invecchiamento combinato (camera climatica ed esposizione ai raggi UV - Tcc+Tuv - e viceversa - Tuv+Tcc -). Al fine di validare i risultati ottenuti dalle sperimentazioni effettuate sono stati eseguiti test numerici e analitici. Il risultato più significativo è dato proprio dalla validazione dell’idea brevettuale dimostrando la possibilità di industrializzare componenti (facciate continue) che utilizzano tale materiale composito (pultruso - GFRP), mediante l’accoppiamento a materiali come l’acciaio che possono conferire al componente alte prestazioni meccaniche, soprattutto per quanto riguarda il contenimento delle deformazioni sotto carico. Le soluzioni tecniche studiate inoltre evitano il problema della rottura fragile delle giunzioni bullonate che è uno dei problemi che riguardano le giunzioni di questo tipo su profili in pultruso. La deformabilità e la rottura fragile delle giunzioni bullonate dei profili in pultruso ne hanno limitato l’utilizzo nel settore dell’ingegneria edile per la realizzazione di facciate continue specie di grandi dimensioni. A tal fine l’attività di ricerca è stata prevalentemente incentrata a verificare la possibilità di inserire nei montati in pultruso di tali facciate, una lamina d’acciaio incollata per contenere la deformazione e per migliorare la qualità della giunzione bullonata in modo da evitare rotture di tipo fragile raggiunto il carico di collasso. Le risultanze dei test sperimentali condotti dimostrano le buone performance del sistema ibrido GFRP-acciaio anche in seguito all’esposizione a differenti condizioni di invecchiamento artificiale e verificano la fattibilità di realizzazione di una facciata continua ad alte prestazioni meccaniche e termiche.
The aim of this work is to demonstrate the applicability of innovative materials, such as Glass Fibre Reinforced Polymer (GFRP) industrialized components (profiles), structural adhesives, for the realization of curtain walls with high mechanical and thermal performances and low environmental impact. This objective with the “Technological Simplification” principle is verified. This latter is the guiding principle to the base of the search and experimental tests carried out by the research group. The teamwork coordinator and patent inventor is Prof P.Munafò, with him I developed a “System for the realization of building façade” (n. 102015000087569). The “Technological Simplification” principle allows the building components realization with high performance and easy to assemble, by using a limited number of pieces. All this involves lower energy consumption in the production, assembly, maintenance and disposal phases. For this reason, the construction element can be considered environmentally sustainable. In this thesis, the feasibility of the constructive system for the realization of building façade, through the experimental tests and component life cycle analysis, is verified. The components and materials properties both in laboratory conditions and after different types of ageing conditions (durability) are tested. The interaction between building components and environment, from the production to ultimate disposal (LCA - Life Cycle Assessment) are analysed. The methods used were mostly of the experimental type. The material mechanical properties both in environmental conditions and in different types of ageing conditions were analysed, such as continuous condensation (ISO 6270-2) and UV irradiation (ASTM D904–99). Additional test with combined artificial ageing (climatic chamber and exposure to UV radiation - Tcc+Tuv – and the other way around - Tuv+Tcc) were tested. The numerical and analytical studies were carried out, with the objective to check and validate the results obtained through experimental tests. The main outcome was the validation of the patents basic ideas, which is a key point in the industrialization process of the construction elements (Structural Member). The aim of this work is to demonstrate the feasibility of the use of pultruded Glass Fiber Reinforced Polymers (GFRP) profiles, adhesively joined with other materials (i.e. steel), in the construction sector. The objective is both to reduce the GFRP profiles deformation under loading conditions, and to avoid the brittle fractures that could occur in bolted joints. In the building engineering field, in fact, these issues (deformations and brittle fractures) prevent the use of pultruded materials. In the research activity, the possibility to adhesively join a steel laminate on the pultruded profile mullion for curtain walls was verified. The containment of the deformations and the prevention of brittle fractures in the bolted joint were checked, in order to verify the pultruded curtain wall feasibility, both constructively and for its structural and energy performances. Experimental results, in fact, demonstrated that the use of GFRP profiles, bonded with structural adhesives and combined with steel, is successful on curtain walls, even when they are exposed to adverse environmental conditions. The feasibility of the curtain wall implementation with high performance is verified.

Fiber reinforced polymer (FRP) composites are considered very promising for infrastructure applications such as repair, rehabilitation and replacement of deteriorated bridge decks. However, there is lack of proper understanding of the structural behavior of FRP decks. For example, due to the localization of load under a truck tire, the conventionally used uniform patch loading is not suitable for performance evaluation of FRP composite deck systems with cellular geometry and relatively low modulus (compared to concrete decks). In this current study, a simulated tire patch loading profile has been proposed for testing and analysis of FRP deck. The tire patch produced significantly different failure mode (local transverse failure under the tire patch) compared to the punching-shear mode obtained using the conventional rectangular steel plate. The local response of a cellular FRP composite deck has been analyzed using finite element simulation and results are compared with full scale laboratory experiment of bridge deck and structure. Parametric studies show that design criteria based on global deck displacement is inadequate for cellular FRP deck and local deformation behavior must be considered. The adhesive bonding method is implemented for joining of bridge deck panels and response of structural joint analyzed experimentally. Strength, failure mode and fatigue life prediction methodologies for a cellular FRP bridge deck are presented in this dissertation.
Ph. D.

Les systèmes d’ancrages adhésifs sont utilisés dans plusieurs applications en génie civil, notamment en réhabilitation et réparation des ouvrages d’infrastructure tels que des dalles de ponts, chaussées, tunnels, barrages, murs, poteaux, ainsi que dans certains travaux d’exploration géologique et minière. Un système d’ancrage adhésif comprend trois composants : l’élément d’ancrage : une barre d’armature ou une tige filetée ; le matériau adhésif : polymérique, cimentaire ou hybride ; et le substrat : en béton ou en maçonnerie. Les charges imposées sur les barres d’ancrage sont transmises au substrat par adhérence chimique (réactions) et liaison mécanique (interlock) entre les composants mentionnés. Le modèle de design d’adhérence uniforme établit que la performance structurale d’un système d’ancrage adhésif est déterminée par la contrainte de l’adhérence (τ), développée sur toute la surface de contact, entre les composants à l’intérieur du trou d’ancrage. Ce projet, en partenariat avec l’entreprise AMBEX, étudie et évalue la performance des systèmes d’ancrage avec adhésifs en matériau cimentaire, par rapport au comportement sous chargement continu. Pour ce faire, on a ancré des barres d’armature dans un substrat en béton conventionnel. Les deux adhésifs étudiés sont les cartouches d’ancrage AAC et ARC. On a tenu compte des paramètres géométriques et d’installation en assurant la rupture de l’adhérence lors des essais d’arrachement. On a évalué deux conditions en service: température ambiante (21ºC) et élevée (43ºC). On a effectué des essais statiques de traction et des essais sous chargement soutenu. Les résultats sont présentés dans des graphiques « chargedéplacement-temps », afin d’établir des prédictions futures de comportement. Le projet montre les avantages des ancrages adhésifs en matériau cimentaire, tels que le taux de fluage très faible sous chargement soutenu, et quelques limitations aussi, comme la variabilité des résultats à l’arrachement pour les ancrages avec la cartouche AAC.
Abstract : Adhesive anchoring systems are used in many civil engineering applications, including rehabilitation and repair of infrastructure such as bridge decks, roadways, tunnels, dams, walls, columns, and in some geological explorations and mining. An adhesive anchoring system consists of three components: the anchor: a reinforcing bar or a threaded rod; the adhesive material: polymeric, cementitious or hybrid; and a substrate of concrete or masonry. The loads applied on the anchor rods are transmitted by a chemical adhesion to the substrate (reactions) and mechanical interlock between the components mentioned. The design pattern of uniform adhesion establishes that the structural performance of an adhesive anchoring system is determined by the bond strength (τ) developed across the contact surface, between the components within the anchor hole. This project, in partnership with AMBEX, investigates and assesses the performance of an anchoring system, with an adhesive of cementitious material, related to the creep behaviour. To achieve this, steel rebars were anchored in a conventional concrete substrate. Two adhesives were evaluated: AAC and ARC cartridges. Geometrical and installation parameters were taken into account, to ensure bond failure during pullout tests. Two service conditions were studied: room temperature (21ºC) and high temperature (43ºC). Static tensile tests and creep tests were performed. The results are presented in graphs “load-displacement-time”, in order to make predictions of future behavior. The project shows the advantages of adhesive anchors made of cementitious material, as a feeble creep rate at sustained load, and also some limitations, as the variability of tension test results for anchors tested with AAC cartridge.

Un nouveau système réactif de type phénolique plus respectueux de l’environnement, c’est-à-dire sans phénol, résorcinol ou formaldéhyde a été caractérisé lors de ces travaux de thèse. Ce système implique la copolymérisation du phloroglucinol et du téréphthalaldéhyde (TPA) en solution aqueuse très diluée. Dans un premier temps, une recherche bibliographique a permis de sélectionner les techniques expérimentales pertinentes pour suivre l’avancement de ces systèmes évolutifs complexes en solution. La combinaison d’analyses chromatographiques et spectroscopiques a été nécessaire pour la caractérisation de la partie soluble du système phloroglucinol-TPA. Un mécanisme de polymérisation conduisant à des espèces linéaires a été proposé pour des temps courts de réaction. L’augmentation de la fraction insoluble lors de la réaction dans les analyses nécessitant une étape de solubilisation met en évidence un second mécanisme de réaction des oligomères entre eux. Une méthode de suivi de l’état du système par mesures rhéologiques a été également développée pour le contrôle de production. Dans un deuxième temps, ce système a été utilisé pour la conception d’un adhésif Phloroglucinol-TPA-Latex. Celui-ci a été étudié à l’état liquide lors du ‘mûrissement’ et à l’état solide après réticulation sous la forme de films libres pour différentes situations modèles. La stabilité de l’adhésif lors du ‘mûrissement’ a été vérifiée même si des réactions de condensation au sein du système Phloroglucinol-TPA se poursuivent. Après réticulation, la morphologie à deux phases des films observée est spécifique à la nature de la phase latex. Il a été conclu que le nouveau système phloroglucinol-TPA a un comportement similaire à celui du système résorcinol-formaldéhyde en termes de mécanismes de réaction et lors de son utilisation en présence de latex. Celui-ci a donc la capacité de remplacer le système initial dans l’élaboration d’un nouvel adhésif plus respectueux de l’environnement
A new phenolic-type reactive system more environment friendly, namely phenol-, resorcinol- or formaldehyde-free, was characterized during this Ph.D. This system consists in the copolymerization of Phloroglucinol and Terephthalaldehyde (TPA) in highly diluted water solution conditions. First, a literature study allowed a selection of relevant experimental technics in order to follow the advancement of these complex systems in solution. The combination of chromatographic and spectroscopic analyses is required to characterize the soluble part of the Phloroglucinol-TPA based system. A mechanism of reaction to synthesize linear oligomers was proposed for short reaction times. The increase of the non-soluble part during the reaction in the analyses made after a solubilization step leaded to the conclusion of another type of mechanism where the oligomers are involved. A monitoring method to follow the state of the system by rheological measurement was also developed for the production process. Secondly, this system was used in the preparation of an adhesive based on Phloroglucinol, TPA and Latex. This adhesive was studied in a liquid state during it ‘maturation’ and in a solid state after curing resulting in films from several model systems. The stability of the system during maturation was checked even if condensation reactions of the Phloroglucinol-TPA still took place. After curing, a two-phase morphology of the films was observed which was found to be specific to the nature of the latex phase. It was concluded that the new Phloroglucinol-TPA system has a similar behavior to the one of Resorcinol-Formaldehyde in terms of mechanism and use in presence of latex. It showed the capability to replace the initial system in the preparation of a new adhesive more environment friendly

Electrically conductive adhesives (ECAs) are one of the lead-free interconnect materials with the advantages of environmental friendliness, mild processing conditions, fewer processing steps, low stress on the substrates, and fine pitch interconnect capability. However, some challenging issues still exist for the currently available ECAs, including lower electrical conductivity, conductivity fatigue in reliability tests, limited current-carrying capability, poor impact strength, etc. The interfacial properties is one of the major considerations when resolving these challenges and developing high performance conductive adhesives. Surface functionalization and interface modification are the major approaches used in this thesis. Fundamental understanding and analysis of the interaction between various types of interface modifiers and ECA materials and substrates are the key for the development of high performance ECA for lead-free interconnects. The results of this thesis provide the guideline for the enhancement of interfacial properties of metal-metal and metal-polymer interactions. Systematic investigation of various types of ECAs contributes to a better understanding of materials requirements for different applications, such as surface mount technology (SMT), flip chip applications, flat panel display modules with high resolution, etc. Improvement of the electrical, thermal and reliability of different ECAs make them a potentially ideal candidate for high power and fine pitch microelectronics packaging option.

The use of adhesively-bonded joints instead of the traditional types of joining can give reduced weight and increased stiffness in a structure. However, most industries have concerns about the use of adhesive joints in anything other than secondary structures, due to uncertainties over the long-term service life. This thesis discusses the prediction of the lifetime of adhesively-bonded composite structures. A fracture mechanics approach was used to characterise the fracture behaviour of an epoxy film adhesive, Cytec FM-300M, mainly using composite substrates prepared using wet peel ply, removing the need for any additional surface treatment. Aluminium alloy substrates were also used for some tests. Tapered double cantilever beam and double cantilever beam specimens were used to determine the mode I critical strain energy release rate, GIC, and end loaded split specimens were tested to obtain the mode II critical strain energy release rate, GIIC. Lastly, fixed ratio mixed mode specimens were used to obtain the relationship between GIC and GIIC when a joint undergoes mixed mode failure. For validation purposes, single lap joint and double scarf joint specimens were also tested. These data were then applied in finite element models using Abaqus. Two different modelling techniques were used, the virtual crack closure technique and cohesive zone modelling, CZM. Simulations of the tests performed were executed, in the process obtaining the CZM fitting parameters. Good agreement with the experimental data was verified for each of the models tested. Fatigue tests were also performed in order to obtain the mode I and mode II threshold values of the fracture energy below which crack growth did not occur, by executing double cantilever beam and end loaded split tests, respectively. For validation purposes, single lap joint fatigue tests were also performed to determine the threshold maximum load the joint could withstand without failure. Finally, using the CZM fitting parameters obtained in the quasi-static tests and the experimentally obtained threshold values of the fracture energy, modelling of single lap and double scarf joints was performed in order to predict the maximum load value for which no failure would occur when subject to cyclic loading. These predictions showed excellent agreement with the experimental results, showing that this simpler model can obtain good results.

Thesis (Ph.D.)(Civil and Biosystems Engineering)--University of Pretoria, 2005.
Includes bibliographical references. Includes bibliographical references. Available on the Internet via the World Wide Web.

Pressure sensitive adhesives (PSAs) are polymeric materials with versatile applications in industrial and consumer products such as protective films, product labels, masking tape, and sticky notes, to name a few applications. World demand for emulsion–based products is on the rise due to worldwide legislation on solvent emissions. In order to completely replace emulsion-based PSAs with their solvent-based counterpart, the property modification of emulsion-based PSAs is required. The use of nanomaterials to modify polymer properties is well established. The aim of this thesis was to use cellulose nanocrystals (CNCs) as property modifiers for emulsion-based PSAs. CNCs are recognized as a highly efficient reinforcement nanofiller. Owing to their environmentally friendly characteristics, low density, high aspect ratio, non-toxicity, and abundant availability, the application of CNCs in composite materials is gaining increasing attention. In this thesis, the inclusion of CNCs in emulsion-based PSAs was carried out through in situ emulsion polymerization and blending technique. To the best of our knowledge, there is limited information about the synthesis of CNC/PSAs nanocomposites via in situ emulsion polymerization and the evaluation of their mechanical performance. The addition of CNCs to the polymerization formulation caused latex instability due to the negatively charged surfaces of the CNCs. After numerous attempts to overcome the stability issues, a stable polymerization formulation and protocol were developed. CNC/PSAs were synthesized via in situ seeded-semi batch emulsion polymerization, which is a common commercial production pathway for PSAs. The mechanical performance of the resulting PSA nanocomposite films, namely, shear strength, tack, and peel strength, was evaluated at several CNC loadings. All three PSA adhesive properties were simultaneously enhanced with increasing CNC loading. The inclusion of CNCs into the films increased their hydrophilicity. Consequently, the PSA films’ improved wettability on a stainless steel substrate imparted greater tack and peel strength. The blending of the CNCs with a base latex also led to improved adhesive properties. However, the property modification through blending was not as effective as that for the CNC/PSA films synthesized via in situ emulsion polymerization. Thus, CNCs are safe nanomaterials that have been shown to provide remarkable property enhancement of emulsion-based PSA films at low loadings (1wt%).

The mechanical property of polymeric materials changes over time, especially when they are subjected to long-term loading scenarios. To predict the time-dependent viscoelastic behaviors of epoxy-based adhesive materials, it is imperative that reliable accelerated tests be developed to determine their long-term performances under different exposed environments. A neat epoxy resin system and a commercial structural adhesive system for bonding aluminum substrates are investigated. A series of moisture diffusion tests have been performed for more than three months in order to understand the influence of the absorbed moisture on creep behavior. The material properties, such as elastic modulus and glass transition temperature, are also studied under different environmental conditions. The time-temperature superposition method produces a master curve allowing the long-term creep compliance to be estimated. The physics-based Coupling model is found to fit well the long-term creep master curve. The equivalence of the temperature and moisture effect on the creep compliance of the epoxy adhesives is also addressed. Finally, a methodology for predicting the long-term creep behavior of epoxy adhesives is proposed.

Doctor of Philosophy
Department of Biological and Agricultural Engineering
Donghai Wang
Sorghum distillers dried grains with solubles (DDGS), canola and camelina meals are the main co-products resulting from grain-based ethanol or oil production. The main objective of this research was to study physicochemical properties of proteins isolated from DDGS, canola and camelina meals and their adhesion performance. Acetic acid-extracted sorghum protein (PI) from DDGS had superior adhesion performance in terms of dry, wet and soak adhesion strength compared to acetic acid-extracted sorghum protein (PF) from sorghum flour and aqueous ethanol-extracted sorghum protein (PII) from DDGS. PI had a significantly higher wet strength (3.15 MPa) than PII (2.17 MPa), PF (2.59 MPa), and soy protein without modification (1.63 MPa). The high content of hydrophobic amino acids in PI (57%) was likely the key factor responsible for high water resistance. Canola protein was extracted from canola meal and modified with different concentrations of NaHSO3 (0 to 15 g/L) during protein isolation. Unmodified canola protein showed the highest wet shear strength of 3.97 MPa cured at 190 °C. Adhesion strength of canola protein fractions extracted at pH 5.5 and pH 3.5 (3.9-4.1 MPa) was higher than the fraction extracted at pH 7.0. NaHSO3 slightly weakened adhesion performance of canola protein; however, it improved handling and flow-ability due to breaking of disulfide bonds in proteins. Albumin, globulin, and glutelins were isolated from camelina meal. Adhesion performance of globulin fraction behaved better than glutelin fraction. The greatest wet shear strength of globulin was 3.3 MPa at curing a temperature of 190 °C. Glutelin had a more protein aggregation compared with globulin, as indicated by higher crystallinity and thermal stability, and dense protein aggregate. This compact structure of glutelins may partially contribute to lower adhesion strength as compared to globulin.

En service, les pièces aéronautiques en matériaux composites et structures sandwiches subissent des dommages qui nécessitent des réparations. Les réparations par patch interne en biseau, en escalier ou par combinaison des deux offrent une excellente restauration de la résistance mécanique pour ces structures composites. Cependant, l’environnement de réparation peut se révéler être un défi de taille quant à leur mise en œuvre, au choix des paramètres géométriques (angle de biseau, nombre de plis extra), à leur comportement mécanique sous différents chargements ainsi qu’à leur processus d’endommagement. Cette thèse présente une étude expérimentale et numérique (éléments finis) du comportement mécanique de réparations par patch interne effectuées sur des structures avec des peaux en composites à renforts tissés fabriquées hors autoclave et âme en Nomex en nid d’abeille. Afin de déterminer l’effet de différents paramètres géométriques sur la résistance de la réparation et de comprendre son comportement mécaniqueet son processus d’endommagement, une série de tests de caractérisation sous différents chargements (traction, compression, flexion) a été effectuée sur des structures sandwiches faite avec deux matériaux composites tissés pour la peau : soit du composite tissé taffetas (PW) ou satin de 8 (8HS) Des simulations numériques ont été effectuées afin de prédire le comportement mécanique de la réparation. Cette étude numérique a été effectuée en plusieurs étapes. Un premier modèle 2D qui suppose que la colle ait un comportement linéaire élastique a été développé et permet d’étudier la distribution des contraintes dans le joint de colle pour différentes configurations de réparation rectangulaire. Ensuite, le modèle 2D est modifié pour tenir compte du comportement élastoplastique de la colle et ceci permet de prédire le comportement mécanique d’une réparation rectangulaire jusqu’à la rupture. Par la suite, un modèle 3D est développé pour prédire le comportement de réparations circulaires sous des chargements de compression. Ce modèle tient compte de l’endommagement progressif des peaux en composite. Les résultats de ces simulations numériques sont comparés par la suite aux mesures expérimentales. Les modèles par éléments finis, avec une loi de comportement élastoplastique pour le joint de colle, permettent une estimation adéquate de la résistance ainsi que de l’endommagement des structures sandwiches réparées. Une étude paramétrique a eu lieu afin d’étudier l’effet de différents paramètres géométriques sur la résistance de la réparation. La mise en œuvre et la détermination de la performance mécanique des réparations par patch interne des structures sandwiches est une tâche complexe avec de multiples paramètres de matériaux et de procédés. D’une manière générale, cette thèse contribue à une meilleure compréhension du comportement mécanique des structures sandwiches réparées et de leur processus d’endommagement. Les modèles par éléments finis développés dans ces travaux ont été validés expérimentalement et des simulations paramétriques ont contribué à une meilleure compréhension de l’influence des différents paramètres géométriques sur la résistance de la réparation par patch interne.
En service, les pièces aéronautiques en matériaux composites et structures sandwiches subissent des dommages qui nécessitent des réparations. Les réparations par patch interne en biseau, en escalier ou par combinaison des deux offrent une excellente restauration de la résistance mécanique pour ces structures composites. Cependant, l’environnement de réparation peut se révéler être un défi de taille quant à leur mise en œuvre, au choix des paramètres géométriques (angle de biseau, nombre de plis extra), à leur comportement mécanique sous différents chargements ainsi qu’à leur processus d’endommagement. Cette thèse présente une étude expérimentale et numérique (éléments finis) du comportement mécanique de réparations par patch interne effectuées sur des structures avec des peaux en composites à renforts tissés fabriquées hors autoclave et âme en Nomex en nid d’abeille. Afin de déterminer l’effet de différents paramètres géométriques sur la résistance de la réparation et de comprendre son comportement mécaniqueet son processus d’endommagement, une série de tests de caractérisation sous différents chargements (traction, compression, flexion) a été effectuée sur des structures sandwiches faite avec deux matériaux composites tissés pour la peau : soit du composite tissé taffetas (PW) ou satin de 8 (8HS) Des simulations numériques ont été effectuées afin de prédire le comportement mécanique de la réparation. Cette étude numérique a été effectuée en plusieurs étapes. Un premier modèle 2D qui suppose que la colle ait un comportement linéaire élastique a été développé et permet d’étudier la distribution des contraintes dans le joint de colle pour différentes configurations de réparation rectangulaire. Ensuite, le modèle 2D est modifié pour tenir compte du comportement élastoplastique de la colle et ceci permet de prédire le comportement mécanique d’une réparation rectangulaire jusqu’à la rupture. Par la suite, un modèle 3D est développé pour prédire le comportement de réparations circulaires sous des chargements de compression. Ce modèle tient compte de l’endommagement progressif des peaux en composite. Les résultats de ces simulations numériques sont comparés par la suite aux mesures expérimentales. Les modèles par éléments finis, avec une loi de comportement élastoplastique pour le joint de colle, permettent une estimation adéquate de la résistance ainsi que de l’endommagement des structures sandwiches réparées. Une étude paramétrique a eu lieu afin d’étudier l’effet de différents paramètres géométriques sur la résistance de la réparation. La mise en œuvre et la détermination de la performance mécanique des réparations par patch interne des structures sandwiches est une tâche complexe avec de multiples paramètres de matériaux et de procédés. D’une manière générale, cette thèse contribue à une meilleure compréhension du comportement mécanique des structures sandwiches réparées et de leur processus d’endommagement. Les modèles par éléments finis développés dans ces travaux ont été validés expérimentalement et des simulations paramétriques ont contribué à une meilleure compréhension de l’influence des différents paramètres géométriques sur la résistance de la réparation par patch interne.
In service, aeronautical components made of composite materials and sandwich structures are subject to type of damages that require repairs. Adhesively bonded repairs (scarf-scarf, step-step or scarf-step) offer an excellent mechanical strength recovery for these composite structures. However, the repair environment can be a significant challenge in terms of the choice of geometrical parameters (scarf angle, addition of an overply), damage process parameters and mechanical behavior under different loads.This thesis presents both experimental and numerical investigations of the mechanical behavior of internal patch repairs carried-out on Nomex honeycomb composite sandwich structures. The skins use an out-of-autoclave woven fabric made of carbon-epoxy composite materials. In order to determine the effect of different geometric parameters on the resistance of the internal patch repair and to better understand its mechanical behavior and damage processes, a series of mechanical tests under different loads (tensile, compression, bending) is conducted on the repaired sandwich panels made with either plain weave or 8 harness satin textile composites. Numerical simulations were carried out, in several stages, in order to determine the mechanical behavior of the repair. First, a 2D model that assumes a linear elastic behavior of the adhesive film was developed. This simple model allows to study the distribution of the stresses in the adhesive joint for different configurations of rectangular patch repair. Then, the 2D model is modified in order to account for the elastoplastic behavior of the adhesive film. The latter allows to predict the mechanical behavior of a rectangular internal patch repair until rupture. Subsequently, a 3D model is developed to predict the mechanical behavior of circular internal patch repairs under compressive loadings. This model takes into account the progressive damage and failure of the woven fabric skins. The results of these numerical simulations are validated by comparing them to experimental measurements. The finite element models that account for the elastoplastic behavior law for the adhesive joint allow predictions of the strength as well as the damage morphology of the repaired sandwich structures. A parametric study has also been conducted in order to determine the influence of the geometrical design parameters in the repair strength. Processing and assessment of the mechanical performance of internal patch repairs on sandwich structures is a complex task with multiple material and process parameters. In general, this thesis contributes to a better understanding of the mechanical behavior of adhesively bonded repaired sandwich structures and their damage process. The finite element models developed in this work and validated experimentally have contributed through parametric numerical simulations to an economical better understanding of the influence of different geometric parameters on the strength and failure of internal patch repaired sandwich panels.
In service, aeronautical components made of composite materials and sandwich structures are subject to type of damages that require repairs. Adhesively bonded repairs (scarf-scarf, step-step or scarf-step) offer an excellent mechanical strength recovery for these composite structures. However, the repair environment can be a significant challenge in terms of the choice of geometrical parameters (scarf angle, addition of an overply), damage process parameters and mechanical behavior under different loads.This thesis presents both experimental and numerical investigations of the mechanical behavior of internal patch repairs carried-out on Nomex honeycomb composite sandwich structures. The skins use an out-of-autoclave woven fabric made of carbon-epoxy composite materials. In order to determine the effect of different geometric parameters on the resistance of the internal patch repair and to better understand its mechanical behavior and damage processes, a series of mechanical tests under different loads (tensile, compression, bending) is conducted on the repaired sandwich panels made with either plain weave or 8 harness satin textile composites. Numerical simulations were carried out, in several stages, in order to determine the mechanical behavior of the repair. First, a 2D model that assumes a linear elastic behavior of the adhesive film was developed. This simple model allows to study the distribution of the stresses in the adhesive joint for different configurations of rectangular patch repair. Then, the 2D model is modified in order to account for the elastoplastic behavior of the adhesive film. The latter allows to predict the mechanical behavior of a rectangular internal patch repair until rupture. Subsequently, a 3D model is developed to predict the mechanical behavior of circular internal patch repairs under compressive loadings. This model takes into account the progressive damage and failure of the woven fabric skins. The results of these numerical simulations are validated by comparing them to experimental measurements. The finite element models that account for the elastoplastic behavior law for the adhesive joint allow predictions of the strength as well as the damage morphology of the repaired sandwich structures. A parametric study has also been conducted in order to determine the influence of the geometrical design parameters in the repair strength. Processing and assessment of the mechanical performance of internal patch repairs on sandwich structures is a complex task with multiple material and process parameters. In general, this thesis contributes to a better understanding of the mechanical behavior of adhesively bonded repaired sandwich structures and their damage process. The finite element models developed in this work and validated experimentally have contributed through parametric numerical simulations to an economical better understanding of the influence of different geometric parameters on the strength and failure of internal patch repaired sandwich panels.

Le travail présenté dans ce mémoire avait pour objectif d'étudier le processus de la pénétration d'eau dans les composites en carbone/époxyde dans un premier temps, et dans un deuxième temps, d'étudier l'effet de la prise en eau par ces matériaux sur les performances mécaniques des composites et leur joints collés. L'intégration de ces phénomènes physiques dans la modélisation numérique est d'une grande importance dans la prédiction de la durabilité d'une structure en composite subissant un vieillissement hygrothermique. Par conséquent, ce travail consiste non seulement en des observations expérimentales, mais aussi en des simulations numériques. Des corrélations entre les résultats obtenus permettent d'une part de mieux comprendre ce qui se passe dans un système composite avec l'assemblage collé soumis à des charges mécaniques, de l'initiation d'endommagement jusqu'à la rupture finale ; d'autre part, de valider un modèle numérique robuste dans le but de la conception et de l'optimisation. Les originalités de ce travail se situent à différents niveaux en proposant : 1. un nouveau modèle de diffusion à deux-phases permettant de mieux décrire l'effet de l'épaisseur des stratifiés sur la pénétration de l'eau; 2. un nouveau modèle RPM " Residual Property Model " afin de prévoir la dégradation des propriétés mécaniques due à la prise en eau ; 3. une nouvelle loi de traction-séparation linéaire-exponentiel pour décrire la courbe-R observée dans les essais DCB en mode I pur sur les composites stratifiés afin de les intégrer plus facilement dans les modèles numériques

La caractérisation et l’évaluation des propriétés physiques, chimiques, physico-chimiques et mécaniques sont un point important dans la compréhension du comportement des assemblages collés polymère/substrat. La spectroscopie diélectrique est une méthode de caractérisation efficace permettant d’étudier la dynamique moléculaire, et permettre aussi un suivi in situ de joints collés. La modélisation mathématique de résultats expérimentaux par la méthode de l’analyse par intervalle permet de s’affranchir de nombreux défauts de logiciels utilisés couramment (erreur expérimentale prise en compte dans les calculs du modèle, permet d’accepter ou de rejeter un modèle, …). Il a été démontré qu’en présence d’un substrat métallique, une compétition avait lieu entre la réaction de polymérisation et des réactions entre les monomères et les substrats métalliques, menant à une interphase (i.e. interface d’épaisseur non nulle) ayant des propriétés différentes des propriétés du même polymère en volume. Ces propriétés influent sur l’adhérence entre le polymère époxydeamine et le substrat d’aluminium. L’adhérence sera caractérisée par un test normé et reliée aux propriétés de l’interphase par diverses techniques. Des vieillissements de systèmes DGEBAanime/ aluminium ont été effectués. Durant ces vieillissements, des tests destructifs et non destructifs ont été effectués afin d’avoir un suivi sur les propriétés des interphases et interfaces de ces joints collés. Les résultats obtenus ont été mis en corrélation afin de pouvoir être capable par l’utilisation de tests non destructifs in situ, de pouvoir prévenir une rupture à l’interphase/interface entre l’adhésif et le substrat
Characterization and evaluation of physical, chemical, physico-chemical and mechanical properties are an important point in the comprehension of the behavior of bonded polymer/substrate assemblies. Dielectric spectroscopy is an effective method of characterization to study molecular dynamics, and also allow in situ monitoring of bonded joints. Mathematical modeling of experimental results by the method of interval analysis overcomes many shortcomings of commonly used software (experimental error taken into account, accept or reject a model ...). It has been shown that in the presence of a metal substrate, a competition was held between the polymerization reaction and the reactions between the monomers and metal substrates, leading to an interphase (i.e. non-zero thickness of interface) having properties different than these of the bulk. These properties influence the adhesion between the epoxy-amine polymer and the aluminum substrate. Adhesion will be characterized by a standardized test and related to the properties of the interphase by various techniques. The aging of DGEBA-anime/aluminum system have been done during this study. During the aging, destructive and non-destructive tests were carried out in order to have a follow-up on the properties of interfaces and interphases of these bonded joints. The results were correlated in order to be able to use an in situ non-destructive testing to prevent the rupture at the interphase/interface between the adhesive and the substrate