Littérature scientifique sur le sujet « Bio-nanocomposite Coating »

This paper presents a spin-coating layer-by-layer assembly process to prepare multilayered polyelectrolyte-clay nanocomposites. This method allows for the fast production of films with controlled layered structure. The preparation of a 100-bilayer film with a thickness of about 330 nm needs less than 1 h, which is 20 times faster than conventional dip-coating processes maintaining the same hardness and modulus values. For validation of this technique, nanocomposite films with thicknesses up to 0.5 μm have been created with the common dip self-assembly and with the spin coating layer-by-layer assembly technique from a poly(diallyldimethylammonium)chloride (PDDA) solution and a suspension of a smectite clay mineral (Laponite). Geometrical characteristics (thickness, roughness, and texture) as well as mechanical characteristics (hardness and modulus) of the clay-polyelectrolyte films have been studied. The spin-coated nanocomposite films exhibit clearly improved mechanical properties (hardness 0.4 GPa, elastic modulus 7 GPa) compared to the “pure” polymer film, namely a sixfold increase in hardness and a 17-fold increase in Young’s modulus.

In this study, the novel exopolysaccharide (EPS) produced by the marine bacterium Alteromonas macleodii Mo 169 was used as a stabilizer and capping agent in the preparation of selenium nanoparticles (SeNPs). The synthesized nanoparticles were well dispersed and spherical with an average particle size of 32 nm. The cytotoxicity of the EPS and the EPS/SeNPs bio-nanocomposite was investigated on human keratinocyte (HaCaT) and fibroblast (CCD-1079Sk) cell lines. No cytotoxicity was found for the EPS alone for concentrations up to 1 g L−1. A cytotoxic effect was only noticed for the bio-nanocomposite at the highest concentrations tested (0.5 and 1 g L−1). In vitro experiments demonstrated that non-cytotoxic concentrations of the EPS/SeNPs bio-nanocomposite had a significant cellular antioxidant effect on the HaCaT cell line by reducing ROS levels up to 33.8%. These findings demonstrated that the A. macleodii Mo 169 EPS can be efficiently used as a stabilizer and surface coating to produce a SeNP-based bio-nanocomposite with improved antioxidant activity.

Innovative post-harvest technologies are in demand to meet the requirements of farmers and agricultural industries to ensure global food security and to avoid food wastage. Edible coatings that can prevent food spoilage and/or enhance shelf life have taken on increasing importance. This work involves the development of edible coatings based on easily available bio resources, chitosan and nanocellulose, and utilizing their unique properties as an effective coating material. Aloe vera, known for its antioxidant and antimicrobial properties, has been proposed as an active ingredient that can be incorporated into the biodegradable film. Varying volumes of Aloe vera (0.25 ml, 0.35 ml, 0.5 ml, and 2.5 ml) were added to fabricate nanocomposite films by solvent casting. Transparent films were obtained, and their morphology was analysed using scanning electron microscope (SEM). The incorporation of Aloe vera was confirmed in various spectroscopic studies, which clearly show reduction in light transmittance for the nanocomposite films containing Aloe vera. The contact angle study showed an increase in hydrophobicity initially. Maximum tensile strength was obtained with 0.25 ml of Aloe vera. The potential use of nanocomposite solution as edible films was demonstrated in green chillies, which showed lower weight loss after 3 days when compared with uncoated chillies. In the first phase of this study, chitosan/nanocellulose nanocomposites enriched with Aloe vera have been proposed as a potential edible food coating material

The purpose of this study is to immobilize GOPEI on a spongin skeleton coated with an alginate coating layer in order to generate a cohesive composite that is very efficient in removing Hg and can be easily recovered from remediated water.

<p class="Abstract"><span lang="EN-US">ZnO is a semiconductor that has found wide application in the optics and electronics areas. Moreover, it is widely used in different technological areas </span><span lang="EN-US">due to its beneficial qualities (high chemical stability, non-toxicity, high photo-reactivity, and cheapness). Based on its antibacterial activity, recently it has found also application to prevent bio-deterioration of cultural heritage buildings. As many authors suggested, doped ZnO nano-structures exhibit better antibacterial properties than undoped analogues. In the present work, ZnO nanoparticles doped with ZrO₂ have been prepared by a sol-gel method in order to enhance the photocatalytic properties as well as the antibacterial activity of ZnO. Then, ZrO₂-ZnO-PDMS nanocomposite (PDMS, polydimethylsiloxane used as the binder) was synthesized by in-situ reaction. The resulting nanocomposite has been investigated as a possible protective material for cultural heritage building substrates. The performances of newly prepared coating were evaluated in three different stones (Lecce stone, Carrara Marble and Brick) and compared with Plain PDMS as a reference coating. </span></p>

In this study, polyethylene glycol (PEG) and polyurethane (PU)-based shape-stabilized copolymer nanocomposites were synthesized and utilized for developing low-cost and flexible temperature sensors. PU was utilized as a flexible structural material for loading a thermosensitive phase change PEG polymer by means of physical mixing and chemical crosslinking. Furthermore, the introduction of multi-walled carbon nanotubes (MWCNT) as a conductive filler in the PEG-PU copolymer resulted in a nanocomposite with thermoresistive properties. MWCNT loading concentrations from 2 wt.% to 10 wt.% were investigated, to attain the optimum conductivity of the nanocomposite. Additionally, the effect of MWCNT loading concentration on the thermosensitive behavior of the nanocomposite was analyzed in the temperature range 25 °C to 50 °C. The thermosensitive properties of the physically mixed and crosslinked polymeric nanocomposites were compared by spin coating the respective nanocomposites on screen printed interdigitated (IDT) electrodes, to fabricate the temperature sensor. The chemically crosslinked MWCNT-PEG-PU polymeric nanocomposite showed an improved thermosensitive behavior in the range 25 °C to 50 °C, compared to the physically mixed nanocomposite. The detailed structural, morphological, thermal, and phase transition properties of the nanocomposites were investigated using XRD, FTIR, and DSC analysis. XRD and FTIR were used to analyze the crystallinity and PEG-PU bonding of the copolymer nanocomposite, respectively; while the dual phase (solid–liquid) transition of PEG was analyzed using DSC. The proposed nanocomposite-based flexible temperature sensor demonstrated excellent sensitivity, reliability and shows promise for a wide range of bio-robotic and healthcare applications.

This PhD thesis dealt with the extraction of cellulose and cellulose nanocrystals (CNCs) from three different lignocellulosic agro-waste feedstocks, that is, corncob, giant cane cut-up and garlic stalk through a customized and standardized chemical procedure. In particular, for giant cane cut-up original biomass, a process optimization was performed aimed both to reduce the impact of the usage of organic solvents and to make the extractive conditions more ‘environmental-friendly’ in both cellulose and CNCs extractions. Moreover, the extracted cellulose and CNCs from giant cane cut-up were subsequently compared with bacterial cellulose (BC) and bacterial CNCs (BCNCs), produced by acetic acid bacteria, which represent the pure counterparts. Therefore, a comparison between the structural features of both the extracted plant-based cellulose and BC by means of 13C Cross-Polarization Magic Angle Spinning Nuclear Magnetic Resonance (13C CP MAS NMR), Fourier Transform Infrared Spectroscopy (FT-IR) and by optical microscopy analyses, was performed. As same, the top-down approaches of the agro-waste-derived cellulose in the production of cellulose nanocrystals, involved the use of both chemical and enzymatic methods. Nowadays, cellulose nanocrystals are one of the most promising alternatives to synthetic fillers, while representing an important field of investigation within numerous research groups due to its attractive properties such as high crystallinity, purity, non-toxicity, dimensional and origin. The most commonly employed method for the extraction of CNCs, is represented by the chemical hydrolysis (by means of concentrated acids solution, such as HCl, H2SO4 and HF), but enzymatic hydrolysis by using e.g. cellulase and endoglucanase, represents today a sustainable and more environmental-friendly approach than chemical procedures. As for giant cane-derived cellulose, a characterization of the extracted CNCs was performed, as well as a detailed comparison with the bacterial counterpart, mainly in terms of size distribution, morphology and yield of the extraction process. Moreover, because the enzymatic hydrolysis is time-consuming, in order to investigate the possibility to introduce a ‘booster’ during the enzymatic process, an expansin-like cerato-platanin (CP) protein as a pre-treatment for the enzymatic hydrolysis of BC was used. Up to now, the pre-treatment was performed only on cellulose from bacterial origin (which represents the pure counterpart) but, according to the literature, the testing of CP protein on giant cane cut-up-derived cellulose will represent an upcoming priority. CNCs were used as organic nanofiller to form a bionanocomposite coating deposited on plastics (polyethylene terephthalate – PET and biaxially oriented polypropylene – BOPP) and bioplastics (polylactic acid – PLA and starch-based compound – Mater-Bi) intended for food packaging applications, where the main biopolymer phase is represented by both polysaccharides and proteins (i.e., chitosan, pullulan and gelatin). The final coated packaging films exhibited enhanced oxygen barrier, surface and optical properties, which can expand the use of plastics and bioplastics for food packaging applications. Due to the pronounced difference in size distribution and morphological features between giant-cane derived CNCs and BCNCs, both the characterization and the overall performance evaluation of a cellulose nanocrystals/pullulan-based nanocomposite coating on PET, were discussed.

L’objectif de ces travaux a été de développer des vernis acrylate photo-polymérisables à 100% d’extrait sec, destinés à protéger des pièces thermoplastiques en polycarbonate contre les endommagements mécaniques, en particulier contre la rayure. Les relations entre la composition, la structure et les propriétés de ces revêtements ont été explorées. Pour ce faire ont été étudiées la morphologie, les propriétés thermomécaniques ainsi que la résistance à la rayure des matériaux. Cette dernière a été évaluée par des tests de micro-scratch. La cinétique de formation des réseaux polymères a elle aussi été étudiée, par photo-DSC. Tous les matériaux étudiés présentent, en analyse thermomécanique dynamique, un module élevé à l’état caoutchoutique ainsi qu’une large relaxation mécanique. Un vernis pétro-sourcé à 100% d’extrait sec, qualifié de standard, a servi de point de départ à ces travaux. Il a tout d’abord été comparé à un vernis commercial solvanté photo-polymérisable, spécialement conçu pour la protection de pièces thermoplastiques. Celui-ci s’est avéré être plus efficace en termes de résistance à la rayure. Dans un deuxième temps, a été étudiée l’influence sur les propriétés du vernis standard pétro-sourcé d’un monomère multicyclique entrant dans sa composition. La modification de son pourcentage n’a permis d’apporter aucun bénéfice en termes de résistance à la rayure. Des nanoparticules de silice, d’alumine ou de zircone, disponibles sous forme de dispersion dans un monomère acrylate, ont ensuite été incorporées dans le vernis standard pétro-sourcé. Une organisation particulière de la nano-silice et de la nano-alumine au sein des matériaux étudiés a pu être observée par microscopie électronique en transmission. Il a été constaté que le taux de charge doit être élevé pour observer une augmentation du module élastique et une amélioration de la résistance à la rayure du vernis (≥15% massique dans le cas de la nano-silice). Par ailleurs, l’ajout de 5% massique de nano-silice dans le vernis n’a conduit à aucune modification de sa cinétique de photo-polymérisation. Enfin, une partie des composés acrylate pétro-sourcés du vernis standard a été substituée par des acrylates bio-sourcés disponibles industriellement. La cinétique de photo-polymérisation des deux types de vernis est similaire. Les conclusions de la comparaison entre les vernis bio-sourcés et le vernis standard pétro-sourcé en termes de résistance à la rayure dépendent de l’épaisseur des revêtements étudiés. L’ajout d’un composé monoacrylate bio-sourcé à la formulation des vernis tend à améliorer la recouvrance élastique des revêtements de faible épaisseur. L’acrylate d’isobornyle est en particulier intéressant, car il a aussi tendance à retarder l’apparition des craquelures au cours de la rayure
The aim of this work was to develop 100% solids photo-polymerizable acrylate coatings, intended to protect thermoplastic pieces made of polycarbonate against mechanical damage, in particular scratches. The relationships between the composition, the structure and the properties of these coatings were examined. For this purpose the morphology, the thermomechanical properties and the scratch resistance of the materials, assessed by micro-scratch tests, were studied. The kinetics of the polymer network formation was also studied by photo-DSC experiments. All the materials feature a high elastic modulus and a broad mechanical relaxation in dynamic thermomechanical analysis. A 100% solids petro-based coating (standard) constituted the starting point of this work. First it was compared to a commercial photo-polymerizable coating containing solvents, specially designed to protect thermoplastic pieces. This commercial coating turned out to be more efficient against scratches. In a second time was studied the influence of the percentage of a multicyclic monomer, taking part in the composition of the standard petro-based coating, on the properties of the latter. The modification of its proportion does not bring any advantage concerning the scratch resistance. Silica, alumina and zirconia nanoparticles, dispersed in an acrylate monomer, were then incorporated in the standard petro-based coating. A particular organization of the silica or alumina nanoparticles in the materials could be observed by transmission electron microscopy. A high filler content is required to observe an increase in the elastic modulus and an enhancement of the scratch resistance of the coating (≥15% by weight for the nano-silica). Moreover, no change of the photo-polymerization kinetics was noticed through the addition of 5% by weight of nano-silica in the coating. Finally, some of the petro-based acrylate compounds of the standard coating were substituted by commercially available bio-based acrylate monomers. Both types of coatings feature similar polymerization kinetics. The conclusions concerning the comparison of the scratch resistance of the bio-based and standard petro-based coatings depend on their thickness. The incorporation of a bio-based monoacrylate compound in low thickness coatings tends to improve the elastic recovery. Isobornyl acrylate is particularly interesting since it also tends to delay the apparition of cracks along the scratch

AbstractBiobased polymers are of great interest due to the release of tension on non-renewable petroleum-based polymers for environmental concerns. However, biobased polymers usually have poor mechanical and barrier properties when used as the main component of coatings and films, but they can be improved by adding nanoscale reinforcing agents (nanoparticles - NPs or fillers), thus forming nanocomposites. The nano-sized components have a larger surface area that favors the filler-matrix interactions and the resulting material yield. For example, natural fibers from renewable plants could be used to improve the mechanical strength of the biobased composites. In addition to the mechanical properties, the optical, thermal and barrier properties are mainly effective on the selection of type or the ratio of biobased components. Biobased nanocomposites are one of the best alternatives to conventional polymer composites due to their low density, transparency, better surface properties and biodegradability, even with low filler contents. In addition, these biomaterials are also incorporated into composite films as nano-sized bio-fillers for the reinforcement or as carriers of some bioactive compounds. Therefore, nanostructures may provide antimicrobial properties, oxygen scavenging ability, enzyme immobilization or act as a temperature or oxygen sensor. The promising result of biobased functional polymer nanocomposites is shelf life extension of foods, and continuous improvements will face the future challenges. This chapter will focus on biobased materials used in nanocomposite polymers with their functional properties for food packaging applications.

The AC electrothermal effect can improve the pumping rate by multiple folds compared to other eletrokinetic techniques in micro/nano scale. In this research, the AC electrothermal micropump velocity will be optimized by surface modification using a biocompatible hydrophobic nanocomposite monolayer. This coating will modify the micropump surface to a hydrophobic surface and reduce the friction losses at the liquid-solid interface, and eventually increase the micropumping velocity. The advent of microfabrication and integrated miniature pumps has applications on biomedical devices such as implantable glucose sensors. These micropumps require the transport of small amounts of fluids (μL range). When utilized in biomedical applications, micropumps can be used to administer small amounts of medication (e.g. insulin) at regular time intervals. These micropumps can also be integrated with the lab-on-a-chip devices and can provide inexpensive disposable devices. To demonstrate the fluid manipulation in high conductive bio-fluids, we have developed an optimized AC electrothermal micropump using symmetrical electrode arrays.