Dissertations / Theses on the topic 'Physical foaming'

There is a growing need for synthetic bone graft materials, which is particularly apparent for procedures requiring impaction bone grafting (IBG), such as revision hip arthroplasty. Currently allograft bone is used that has limited supply and associated risks of transmission of infectious agents. Porous bioresorbable polymeric scaffolds can be created using supercritical carbon dioxide (scCO2). This thesis investigated the use of these scaffolds for impaction bone grafting procedures. Building on previous research within the literature poly(D,L-lactide) (PDLLA) and poly(D,L-lactide-co-glycolide) (PDLLGA) scaffolds of high molecular weight (100 kDa) were investigated for this use. Scaffolds were milled using a standard bone mill and impacted to create porous milled chips of bioresorbable scaffolds and impacted for mechanical shear testing and biocompatibilities. The impaction process used forces equivalent to those experienced during IBG. In vitro cell experiments were used to assess the proliferation and osteoblastic differentiation of mesenchymal stem cells (MSCs) on impacted scaffolds to identify the most promising scaffold compositions. These compositions included pure polymer and polymer:HA microparticle composites. Further experiments using animals (murine and ovine) were then used to investigate the in vivo performance of the scaffolds. A critical sized ovine femoral condyle defect established the osteoinductive and osteoconductive potentials of milled scCO2 foamed PDLLA + 10 wt.% hydroxyapatite (HA) microparticle scaffolds in vivo. The scale-up potential of scCO2 foaming of bioresorbable scaffolds was established using a 1 L vessel. Scaffolds scCO2 foamed using either a 60 ml autoclave or a 1 L vessel were characterised using scanning electron microscopy and micro computed tomography. Scaffolds from different batches were characterised and compared to ensure process repeatability was accounted for. The final chapter investigated differences in the osteoblastic differentiation of MSCs on PDLLA and PDLLGA scaffolds observed in experiments at the start of the study. Spincoated and dipcoated flat films of PDLLA, PDLLGA, and PDLLA:PDLLGA (50:50) were used for in vitro cell culture to remove the effect of morphological differences that affected scCO2 foamed scaffold experiments. Additionally, this chapter investigated the effect of the form of HA using HA nanoparticles andHA microparticles in scCO2 foamed PDLLA:HA composites for in vitro studies.

Travaux portant sur le moussage physique par adjonction de CO2 supercritique de polyoléfines et thermoplastiques vulcanisés (TPV) que ce soit par procédé continu (extrusion) ou par procédé discontinu (réacteur).Grâce à la formulation, l’étude rhéologique et le moussage de polymères existants et inédits un critère rhéologique permettant de définir la capacité à mousser a été démontré et étendu au mélange complexe de polymère (TPV). Plus spécifiquement l’étude de la formulation des TPV sur le moussage a été investigué et des conclusions concernant la chimie de réticulation ainsi que l’ajout de charges ont pu être déterminées.La modélisation numérique et la mise en œuvre de l’extrusion moussage ont été réalisées et ont permis de démontrer la possibilité d’obtenir une mousse régulière et homogène ainsi que de prédire, en fonction des paramètres d’entrés, les caractéristiques finales de la mousse
Work on the physical foaming of vulcanised polyolefins and thermoplastics (TPV) by the addition of supercritical CO2, whether by continuous process (extrusion) or by batch process (reactor).Through the formulation, rheological study and foaming of existing and new polymers, a rheological criterion for defining the ability to foam was demonstrated and extended to complex polymer blends (as TPV). More specifically, the study of TPV formulation on foaming was investigated .Conclusions regarding cross-linking chemistry and addition of fillers were determined.Numerical modelling and implementation of extrusion foaming were carried out and demonstrated the possibility of obtaining a regular and homogeneous foam as well as predicting, depending on the input parameters, the final characteristics of the foam

The viscosities of a set of silicone oils containing different size ranges of charcoal or paraffin particles as well as the viscosities of silicone oil foams were measured at room temperature in order to determine the effect of dispersed phase on the viscosity of a liquid and its effect on foaming ability. The effective viscosity of the samples increased with volume fraction of the second phase. The foaming ability was improved by the presence of the particles. The improved foaming effect was for the most part not a result of the increased viscosity. No connection between the particle size and the effective viscosity could be determined. On the other hand particle morphology and the particle size distribution had effect on the effective viscosity. The viscosity data were compared with a number of existing equations for the estimation of effective viscosity. Einstein-Roscoe equation is suitable for two-phase mixtures containing globular particles with narrow particle size distribution and low interfacial tension. New mathematical models are required for effective viscosity prediction, where the suspending phase viscosity, effect of the interfacial tension, as well as the particle morphology should be taken in consideration.

碩士
逢甲大學
纖維與複合材料學系
105
In this study, using calcium carbonate, talc and white carbon black add to EVA, and studied its physical properties after foaming by supercritical fluid carbon dioxide, In view of the traditional chemical foaming system requires high temperature and a long time to achieve the complete reaction decomposition of chemical foaming agent，This experiment mainly uses less than the traditional chemical foaming of the processing temperature and time on different formulations to foaming it. By changing the amount of different powder added, discussion the effect of tensile strength, tear strength, elongation, density, expansion ratio, and surface hardness, under different content, the relationship between the expansion ratio and the above physical properties is also discussed, and the surface condition and cell structure were observed by optical microscope and SEM. The first step in this article use calcium carbonate, talc, white carbon black for the addition of different content, measure the relationship between the amount of change and the various physical properties, and then according to the different expansion ratio to explore its trend with a variety of physical properties and observing its surface structure and bubble structure in the same time. The second part is compare that the selection of calcium carbonate filled with 10 unit of the foam material and the EVA630 chemical foam materials that refer by literature, Compare the two similarities and differences. The results show that under supercritical fluid, foaming can be successfully performed at low temperature and low pressure, the comprehensive conditions and performance are better than ADC chemical foaming. The different nucleating agents also have different effects on the foamed material, filled with talc and white carbon black, both in tensile strength, tear strength, elongation properties, reinforcement effect and extension performance Comprehensive performance observation, mostly better than the calcium carbonate system, especially the addition of white carbon black in the tensile strength has especially good performance, Talc powder in the tear performance has a good cost-effective. No matter what kind of powder to add, the expansion ratio is negatively correlated with mechanical strength and surface hardness, has a positive correlation with elongation. Optical microscopy and SEM analysis of the observation can be seen that the addition of powder can significantly help the nucleation and growth of bubbles, among them, white carbon black system added to the material let the bubble to achieve the smallest and ideal case, but whether the material surface or internal observation, can be found reunion occurred.

There is significant industrial interest in the development of innovative and efficient materials for thermal insulation applications. Indeed, the energy issues are becoming more and more important because of possible energy shortage in the future compounded by global warming. Moreover, regulations on thermal insulation in the household sector, building trade, aeronautics and gas transport are becoming ever stricter. One of the solutions to these issues is to fabricate materials with very low thermal conductivity. Many cellular materials are used in thermal insulation to take advantage of the good insulation capacity of some gases, in particular rigid polyurethane foams. The thermal conductivity of these polymers can become lower than the relevant gas, because of the Knudsen effect that limits the heat conduction via a confined gaseous phase. Fabrication of low density material within which the gas mobility is restricted is a challenge in terms of obtaining a very low thermal conductivity material. In this dissertation, the foaming of rigid polyurethanes by using high pressure carbon dioxide (CO2) as physical blowing agent was investigated starting from the knowledge of the behavior of the whole system in the presence of CO2. The study of CO2 sorption in the polymeric precursors of rigid polyurethane foam (polyol and isocyanate), by using a coupled gravimetry-Axisymmetric Drop Shape Analysis, was conducted to design the process and the equipment and to optimize the foaming. In particular, to address the recent interest in combining the gas (physical) foaming with the classical (chemical) polyurethane foaming, a novel instrumented pressure vessel was designed for studying: i) gas sorption under high pressure on the different reactants, kept separate and ii) synthesis under high gas pressure, upon mixing, by spectroscopic investigation and iii) foaming upon release of the pressure. In the literature, no papers addressed the use of CO2 as a physical blowing agent in polyurethane foams (as well as in other thermosetting polymers), where CO2 solubilization is conducted in both the reactants before mixing in lab-scale. Furthermore, in industrial processes, typically liquid CO2 is mechanically mixed (not solubilized) under pressure in polyurethane foam reactants to froth the mixture by release pressure. The two novelties, shown in this thesis, are the possibility to solubilize the gas (1) as physical blowing agent (2) in both the reactants of a polyurethane foam before the mixing. As results, from sorption measurements the maximum value of CO2 pressure usable for foaming experiments was defined, in order to avoid extraction of low molecular weight fractions of the polymeric precursors in CO2. Rigid polyurethane foams obtained during this Ph.D. are described in terms of their morphology. In conclusion, the developed lab-scale apparatus allows to obtain rigid polyurethane foams by solubilizing CO2, as physical blowing agent, both in polyol and isocyanate. By optimizing some chemical and processing parameters is possible to control the morphology and so the thermal conductivity of the final foam. In the first part of this thesis, an overview of the current chemistry and foaming processes used in the production of rigid polyurethane foam are reported. The main part will be occupied by the description of CO2 solubility measurements, of the new equipment to study sorption, synthesis and foaming of rigid polyurethane foams and of experimental results.

碩士
國立高雄科技大學
化學工程與材料工程系
107
SEBS usually needs to be added with processing oil and then to be easily pelletized or formed by processing method. Usually, SEBS can be blended with other copolymer to adjust and control the crosslinking and foaming physical properties to achieve comfort and light weight to expand its application fields. In this study, a new type of SEBS 6014 developed by TSRC CORPORATION, which can be processed without adding oil, was added with different melting temperatures of polyolefin elastomers (POE) to explore the effects on blending physicals, crosslinking-foaming kinetics, and crosslinking-foaming physical properties of different proportions of POE mixed with SEBS 6014. In experiments, the RPA (Rubber Process Analyzer) was used to determine the crosslinking-foaming kinetics, and the Tb (Tensile Strength at Break) and Eb (Elongation at Break) of the unfoamed and foamed test pieces were measured by a universal tensile machine. The results showed that the blends of unfoamed SEBS 6014 and POEs such as DF110, DF810 and DF610 with three different melting temperatures exhibit the additive rule, synergistic effect and anti-synergistic effect phenomenon. From the foaming-crosslinking curve of SEBS blend, it was found that with the increasing of POE amount, the crosslinking speed of the three blends showed an upward trend while the foaming speed showed a downward trend. However, the tensile strength and elongation results of the foaming-crosslinking SEBS blends show that the foaming-crosslinking blends formed by SEBS 6014 and DF110, DF810 and DF610 exhibit only additive rule instead of synergistic and anti-synergistic effect.

碩士
國立中興大學
化學工程學系所
107
This study explores the foaming properties of EVA copolymer materials by the combination of using the original ADCA azo dimethyl hydrazine C2H4N402 foaming agent and the microcapsule foaming agent. Keeping the hard density does constant, efforts were made to enhance the rigidity between the foaming pores, improve the shock absorption and higher buffering capacity of the foam material to protect human movement or collision and reduce different sports injuries. Therefore, under the same system, in different doser of microcapsule foaming agent were added to the study, and the structure, physical properties and energy absorption of the foaming materials were evaluated by vulcanization test, SEM observation, physical testing, simulations helmet test (EN1077, EN1078, NOCSAE). In research (I), the microcapsule foaming agent was added in EVA copolymer, it was found that the EVA copolymer added with the microcapsule foaming agent without ADCA foaming agent had a vulcanization time (TC90) of 9.07 min in the vulcanization test at the addition ratio of only 3 phr and MAX foaming pressure was 266.74 lbf/in. Minimum curing time and MAX foaming pressure are obtained for 3 phr dosage in the three test formulations. For this foaming ratio, the microcapsule expansion agent is insufficient due to insufficient foaming power of microcapsule foaming agent. The cell structure of EVA copolymer was opened and the final expansion ratio was only 1.1 times. For the EVA copolymer with 3 phr microcapsule foaming agent and 3 phr ADCA foaming agents added, the vulcanization time (TC90) was 10.71 min and the MAX foaming pressure was 476.28 lbf/in. Increasing obvious vulcanization time will increase MAX foaming pressure . In the physical property test, the rebound was 11% and compressive strength was 1.2 kg/cm² that are better but compression deformation of 8.73% is worse. Shrinkage test at 70 ° C for 24 hours period for -2 cm X -2 cm X 0.37 mm specimen, shrinkage gave the relatively good value. In the impact test, impact strength was measured as 15.09 KN and the shock absorption strength was also better . In research (II), the microcapsule foaming agent was added in an amount of 3, 5, 7, 10 phr and 3phr ADCA foaming agent was added in the EVA copolymer. In the vulcanization test, the vulcanization time (TC90) was 11.56 min~12.48 min and the foaming pressure was 562.61 lbf/in〜630.9 lbf/in . In the physical property test, the rebound was 11.5 %〜11.9 % and compression strength was 1.20 kg/cm² to 1.24 kg/cm² that are better, but the compression deformation is worse. Shrinkage gave the relatively good value in the 24 hour shrinkage test at 70 ° C. The shock absorption strength also appears a linear mode in the impact test, since the increase in the addition of microcapsule foaming agent is not much, the data change is small. The impact height was 910 mm, microcapsule foaming agent was added in an amount of 3, 5, 7, 10 phr, impact strength was measured as 15.09 KN, 13.59 KN, 13.37 KN, 11.54 KN. The impact height was 1526mm, microcapsule foaming agent was added in the amount of 3, 5 7, 10 phr, impact strength was measured as 41.45 KN, 41.20 KN, 40.11 KN, 39.86 KN. In research (III), effect of impact energy on the addition of microcapsule foaming agent EVA copolymer, Addition of 3 phr ADCA foaming agent in EVA Copolymer, compared with adding 3 phr ADCA and 3 phr microcapsules foaming agents . Test discovery at different impact Heights 910 mm, 1115 mm, 1320 mm, 1520 mm, the effect of adding microcapsule foaming agent is better than that without adding microcapsule foaming agent, which is superior to 910 mm : 27.6 %, 1115 mm : 33 %, 1320 mm : 14.7 % and 1520 mm : 4.49 % of shock absorption effect. Therefore, when the impact energy exceeds a certain value, the strength of microcapsule can not disperse the impact force effectively, and the shock absorption effect will become worse.

碩士
國立交通大學
應用化學系所
92
The purpose of the present study is to establish an analytical program for spiral die with physical foaming agent. First, we predict the viscosity of melt polymer with foaming agent mathematically, and establish the flow model by fluid dynamics. Applying the Sanchez-Lacombe equation, we can calculate the weight percentage of foaming agent in melt polymer at any pressure and temperature. As predicted, more foaming agent can be dissolved into melt polymer at a high pressure or low temperature. The parameters of spiral die include DEPTH, WCHAN, GIBC, HBC, NOSEC, θ and α. Second, we use the Tguchi method to search several optimal sets of die geometric parameters by assessing the flow uniformity(UNI) and mixing degree(MD) isothermally and create ANOVA tables. From ANOVA tables, we realize that the seven parameters can totally describe the flow situation in spiral die. At the same time, we find that whatever the number of channels is, the most relevant parameters with respect to MD are DEPTH,WCHAN and GIBC; with respect to UNI, WCHAN and NOSEC are the most relevant parameters; furthermore, with respect to pressure gradient, GIBC及ALFAR are the most relevant. During polymer foaming, if the local die pressure cannot reach the critical pressure, prefoaming occurs. Therefore, at the outlet of spiral die, we narrow down the channel depth to increase the local pressure, which is thus greater than critical pressure. Finally, with die lip being attached to spiral die, we examine the non-isothermal condition, so that an analytical program for spiral die with physical foaming agent can be established.

碩士
國立交通大學
應用化學系所
94
Coat-hanger dies were widely used in the production of films and sheets. In many cases, foam extrusion was necessary to be utilized. In this thesis, two different types of coat hanger die was proposed for the extrusion foaming process with a physical blowing agent. A flow model of two-dimensional control volume method was utilized to simulate the non- isothermal and non-Newtonian flow behavior in a coat-hanger die used for the extrusion foaming process. The research works included the development of mathematical models for the direct prediction of shear viscosity of a molten polymer containing a dissolved gas and of the critical pressure under a certain temperature and solubility of gas in the melt. Based on this prediction, the aforementioned control volume method is then used to establish the flow model of a coat hanger die. In addition, a Taguchi method was coordinated to establish a software for the analysis and optimal design of a coat-hanger die for the foam extrusion which requires a high foaming ratio with a physical blowing agent. Finally, in this thesis, an optimal design of coat-hanger die used for the LDPE/CO2 system will be also investigated to predict the position of pre-foaming, pressure distribution, flow homogeneity and temperature homogeneity.

碩士
中原大學
化學研究所
94
Abstract In this study, the organophilic clay used as intercalation agent was prepared by cation exchange method, which is a reaction occurred between the sodium cation of MMT clay and quaternary alkylammonium ions of hexadecyltrimethylammonium bromide. As a typical procedure for the preparation of nanocomposite systems with 0.5, 1.0, 3.0 wt-% clay, an appropriate amount of organophilic clay was first suspended in BMA-St monomer to proceed bulk polymerization. At the end of polymerization, the PBS/clay nanocomposite materials were thus obtained. Subsequently, a series of corresponding nanocomposite foamed materials were prepared by “ Physical Foaming Process ”. The foamed characterization on the structure of the nanocomposite and nanocomposite foams was evaluated by XRD measurements to show changes in the d spacing of the clay and by TEM to image the indivdual clay layers. The cell size & cell density was observed by SEM. TGA、DSC and DMA were employed to investigate the thermal stability of as-prepared specimens. Thermal transport parameters such as the thermal conductivity, thermal diffusively and specific heat were measured by a HOT DISK analyzer under room temperature.