La recherche actuelle est entreprise dans l’optique de la révision complète du design chimique et des principes d’élaboration des photocatalyseurs composites supportés (PCCS) afin d’améliorer considérablement leurs capacités réactionnelles, la durabilité de leur action en temps et de résoudre le problème de pollution secondaire des milieux à traiter. Les travaux effectués ont permis la mise en œuvre d’un nouveau modèle de PCCS interactifs dont les composants photosensibles sont en fortes interactions chimiques avec leurs supports appartenant au groupe d’acides de Lewis. Cette particularité assure une grande sélectivité d’action des produits développés, leur fonctionnement durable en régime stationnaire, évite la pollution secondaire des effluents à traiter et garanti une performance photocatalytique comparable à celle du produit de référence Degussa P25.Les travaux réalisés ont permis d’acquérir de nouvelles connaissances scientifiques concernant le rôle de l’acidité de surface dans l’action photocatalytique et du taux de dissociation de l’eau adsorbée sur le produit actif. De plus, un ensemble de huit paramètres principaux assurant les meilleures conditions d’exploitation des PCCS a été établi.Les PCCS développés peuvent être appliqués, tout d’abord, dans le domaine de l’incinération photocatalytique des COV. Un prototype de filtre dynamique capable de traiter 50 m3/h de l’air avec une consommation d’énergie modérée, est conçu. Un nouveau type de matériaux composites à vocation germicide à base de polymères synthétiques fait également l’objet de la partie applicative de ces travaux de thèse. / The current research is undertaken in the context of the complete reconsideration of the supported composite photocatalysts (SCPC) chemical design and elaboration principles in order to improve their reaction capacities, to assure the sustainability of their action in time and to resolve the secondary pollution problem for the media to treat. This work enabled the implementation of a new model of interactive SCPC in which the photosensitive components occur in a strong chemical interaction with their supports belonging to the Lewis acid group. This feature provides the developed products with high selectivity, allows them to function in the stationary conditions, avoids the secondary pollution effect and guarantees the photocatalytic performance comparable with the one of the reference industrial photocatalyst Degussa P25. An important scientific knowledge on the role of the surface acidity in the photocatalytic action and on the dissociation state of the water adsorbed over the active product was acquired. Apart from this, a set of eight main parameters ensuring the best SCPC operation properties was established. The developed SCPC are forecasted to be firstly applied in the photocatalytic VOC oxidation processes. A prototype of such filter capable to treat 50 m3/h of air, having modest energy consumption, was designed. A new composite material with germicidal properties elaborated using synthetic polymer supports, also constitutes a subject of the applications part of this thesis.

Résumé : Des feuillets de graphène fonction-nalisés FGSx avec un rapport C/O~x ont été post-fonctionnalisés avec des dérivés de tétrazine (3,6-bis(2-pyridyl)-1,2,4,5-tétrazine) par cycloa-ddition de Diels-Alder à demande inverse. Des applications potentielles de ces graphènes fonctionnalisés ont été explorées sur le stockage d'énergie (supercondensateur) et l’électrocatalyse (réaction de réduction de l'oxygène).Pour les applications de supercondensateurs, des nanocomposites constitués de FGS20 fonction-nalisé et de polypyrrole ont été synthétisés en deux étapes en incorporant d’abord les fonctions pyridine-pyridazine à la surface du FGS20 par cycloaddition suivie de l’électropolymérisation du pyrrole dans l’acétonitrile. La capacité spéci-fique du matériau a été mesurée par des cycles de charge-décharge galvanique et la stabilité au cyclage a été étudiée dans divers milieux électro-lytiques (acétonitrile, liquide ionique, eau acide et eau neutre) et les résultats comparés par rapport au FGS20 non fonctionnalisé avec ou sans polypyrrole. Alors que l'acétonitrile révèle un comportement capacitif pur pour tous les matériaux étudiés, l'eau acide est le milieu où les valeurs de capacité sont les plus élevées et, de manière surprenante, où les nanocomposites contenant du polypyrrole présentent une meilleure rétention de capacité lors du cyclage que le graphène seul. Un impact positif de la fonctionnalisation du graphène avant l'électropoplymérisation a été mis en évidence dans tous les milieux électrolytiques (pertes de capacité limitées à moins de 8% après 1500 cycles dans tous les milieux sauf l'eau neutre), soulignant l'intérêt du contrôle d'interface dans ce type de nanocomposites. / Abstract: Functionalized graphene sheets with a ratio C/O~x (FGSx) was further functionalized with a tetrazine derivatives (3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) by inverse demand Diels-Alder cycloaddition reactions. Functionalized FGS20 and FGS13 potential applications were explored on energy storage (super-capacitor) and catalysis (oxygen reduction reaction).In supercapacitor applications, nanocomposites made of functionalized FGS20 with polypyrrole were synthesized in two steps by first incorporating pyridine-pyridazine functions on FGS20 surface through cycloaddition followed by electropolymerization of pyrrole in acetonitrile. The specific capacitance of the material was measured by galvanic charge-discharge cycles and the stability upon cycling investigated in various electrolytic media (acetonitrile, ionic liquid, acidic, and neutral water) in comparison with non-functionalized FGS20 with or without polypyrrole. While acetonitrile reveals pure capacitive behaviour for all investigated mate-rials, acidic water is the medium where the capacitance values are the highest and surprisingly where nano-composites with polypyrrole show better capacitance retention upon cycling than graphene alone. A positive impact of graphene functionalization prior to electropolymerization was demonstrated in all electrolytic media (capacitance losses limited to less than 8% after 1500 cycles in all media but neutral water), highlighting the interest of interface control in this kind of nanocomposites.

Polymer nanocomposites are a going part of Materials Science and Engineering. These new composite materials exhibit dimensional and thermal stability of inorganic materials and toughness and dielectric properties of polymers. Development of nanocomposites become an important approach to create high-performance composite materials. In this study silica, fly ash, silica nanotubes and carbon black particles have been added to modify polyurethane foam and thermoplastic polyurethanes. It has been found that the addition of silica can diminish the size of foam bubbles, resulting in an increased stiffness of the material, increase of the compressive strength, and greater resistance to deformation. However, the uniformity of bubbles is reduced, resulting in increased friction of the material. Fly ash added to the foam can make bubbles smaller and improve uniformity of cells. Therefore, the material stiffness and compressive strength, resistance to deformation, and has little impact on the dynamic friction of the material. Adding nanotubes make bubble size unequal, and the arrangement of the bubble uneven, resulting in decreased strength of the material, while the friction increases. After the addition of carbon black to the polyurethane foam, due to the special surface structure of the carbon black, the foam generates more bubbles during the foaming process changing the foam structure. Therefore, the material becomes soft, we obtain a flexible polyurethane foam. The results of mechanical properties determination of the thermoplastic polyurethane that adding particles may increase the stiffness and wear resistance of the thermoplastic polyurethane, while the tensile properties of the material are reduced. This phenomenon may be due to agglomeration of particles during the mixing process. Possibly the particles cannot be uniformly dispersed in the thermoplastic polyurethane.

Le développement de nanocomposites thermoconducteurs à base de caoutchouc est une tâche difficile pour diverses technologies modernes, allant des appareils électroniques à l'industrie du pneu. La présente étude est concentrée sur les propriétés thermiques et mécaniques de composites de caoutchouc naturel chargés avec des additifs à base de carbone, notamment du noir de carbone, des nanotubes de carbone, de l'oxyde de graphène réduit et des nanoplaquettes de graphène. En raison de la faible conductivité thermique du caoutchouc, des concentrations élevées de divers additifs thermoconducteurs sont nécessaires. Cependant, cela a un impact significatif sur le comportement mécanique des matériaux finaux, ce qui limite leur application. Dans ce scénario difficile, nous avons cherché à améliorer la conductivité thermique et les propriétés mécaniques (y compris les propriétés en traction, la dureté, les propriétés dynamiques, etc.) de nanocomposites à base de caoutchouc en exploitant des systèmes de charges hybrides à base de carbone. Nous avons aussi modifié la surface de ces charges pour améliorer leur interaction avec la matrice en caoutchouc dans le but de créer un réseau continu de charges à travers la matrice. La première partie de la thèse (chapitre 2) décrit l'effet de l'ajout de l'oxyde de graphène réduit (RGO) sur la conductivité thermique et les propriétés mécaniques de caoutchouc. Le RGO a d'abord été synthétisé en utilisant la méthode Hummer améliorée. Ensuite, il a été pré-dispersé dans du latex naturel en utilisant la technique de co-coagulation puis mélangé à la formulation de référence à différentes teneurs (0-2 parties pour cent en caoutchouc (phr))à l'aide d'un mélangeur interne. Pour une concentration de RGO de 2 phr, les résultats ont montré que la densité de réticulation des nanocomposites caoutchouc/RGO développés avait augmenté de 65% par rapport à la formulation de base. Une augmentation significative de la résistance à la traction (53%) et du module de Young (31%) a été observée pour la même concentration en RGO. Enfin, il a été observé que l'ajout de seulement 0.5 phr de RGO avait entraîné une amélioration considérable (26%) de la conductivité thermique. Dans la deuxième partie de la thèse (chapitre 3), l'effet d'un système de charges hybride (noir de carbone/nanotubes de carbone multi-parois, MWCNT) sur les propriétés mécaniques et la conductivité thermique des nanocomposites développés a été étudié. En raison de la différence de forme entre le noir de carbone et les MWCNT, ainsi que de l'adsorption des agents de réticulation à la surface des MWCNT, il a été observé que le temps de cuisson (vulcanisation) (t₁₀) et celui de cuisson optimal (t₉₀) de la matrice en caoutchouc augmentaient progressivement avec l'augmentation de la teneur en MWCNT. Enfin, en remplaçant 5 phr de noir de carbone par la même concentration en MWCNT, des améliorations significatives de la conductivité thermique et des propriétés mécaniques ont été obtenues grâce aux propriétés intrinsèques des MWCNT et à leur synergie avec le noir de carbone. En outre, les modules à 100% et 300% de déformation (M@100 et M@300) des nanocomposites développés ont respectivement augmenté de 72% et 54%. Dans la troisième partie de la thèse (chapitre 4), la modification de surface des MWCNT a été réalisée pour améliorer le comportement mécanique dynamique des nanocomposites correspondants et trouver un ratio optimal de charges menant à des propriétés mécaniques et thermiques améliorées. Les résultats ont montré l'effet positif de l'oxydation de la surface des MWCNT sur la dispersion des charges et les propriétés thermiques et mécaniques des nanocomposites. La dernière partie de la thèse (chapitre 5) a été consacrée à l'étude de l'effet synergique des systèmes hybrides de charges (noir de carbone/nanoplaquettes de graphène, GNPs) dans lequel les GNPs (GNP-M25, GNP-C300 et GNP-C750) présentaient différentes surfaces spécifiques et différents rapports d'aspect. Les résultats ont montré que la surface spécifique de la charge et son rapport d'aspect jouent un rôle vital dans la production d'un réseau de charges conducteur. L'incorporation du GNP-M25 ayant une dimension latérale la plus élevée parmi les trois GNPs étudiés permettait de développer un nanocomposite ayant une conductivité thermique plus élevée. D'autre part, à une concentration élevée (5 phr), la synergie entre GNPs-M25 et le noir de carbone était élevée, entraînant une meilleure dispersion des charges et une plus faible dissipation d'énergie. / Creating effective thermally conductive rubber nanocomposites for heat management is a challenging task for various modern technologies, from electronic devices to the tire industry. This study focused on the thermal and mechanical properties of natural rubber nanocomposites filled with carbon-based fillers, including carbon black, carbon nanotubes, reduced graphene oxide (RGO), and graphene nanoplatelets. Due to the poor thermal conductivity of rubber materials, high loadings of various thermally conductive fillers are required. However, this significantly impacts the final materials' mechanical behavior, limiting their application. In this challenging scenario, we aimed to enhance the thermal conductivity and mechanical properties (including tensile properties, hardness, dynamic mechanical properties, etc.) of rubber-based nanocomposites by exploiting hybrid carbon-based filler systems and suitable filler surface modification to improve the formation of continuous filler's network through the natural rubber (NR) matrix. The first part of the thesis (chapter 2) describes the effect of adding RGO to the natural rubber's thermal conductivity and mechanical properties. RGO was first synthesized using an improved Hummer method. Then, RGO pre-dispersed in natural rubber latex using the co-coagulation technique was added to a reference formulation in various contents (0-2 parts per hundred rubber (phr)), and compounded using an internal mixer. It was observed that the crosslink density of the developed natural rubber/RGO nanocomposites increased by 65% for RGO concentration of 2 phr. A significant increase in tensile strength (53%) and Young's modulus (31%) was observed for the same RGO concentration. Ultimately, the addition of only 0.5 phr of RGO resulted in a considerable improvement (26%) in thermal conductivity. In the second part of the thesis (chapter 3), the effect of the carbon black/multiwall carbon nanotubes (MWCNT) hybrid filler system on the mechanical properties and thermal conductivity of the nanocomposites was studied. Because of the shape difference between carbon black and MWCNT and the adsorption of curing agents onto the MWCNT, the scorch time (t₁₀) and optimum curing time (t₉₀) gradually increased with increasing MWCNT content. Finally, by substituting 5 phr of carbon black with MWCNT, significant improvements in thermal conductivity and mechanical properties were achieved due to the intrinsic properties of MWCNT and its synergy with carbon black. Moreover, the modulus at 100% and 300% strain (M@100 and M@300) increased by 72% and 54%, respectively. In the third part of the thesis (chapter 4), the surface modification of MWCNT was carried out to improve the dynamic mechanical behavior of the natural rubber/MWCNT nanocomposites to find an optimum fillers ratio having suitable mechanical and thermal properties. The results showed the positive effect of MWCNT surface oxidation on the fillers' dispersion and nanocomposites' properties. The last part (chapter 5) focused on the synergistic effect between carbon black and GNPs hybrid fillers with different surface areas and aspect ratios (GNPs-M25, GNPs-C300, and GNPs-C750). The results showed that the specific surface area of filler and its aspect ratio play a vital role in producing a conductive filler network. GNPs-M25 with a higher lateral dimension led to the highest consistency and denser conductive network inside the NR nanocomposite compared to GNPs-C300 and GNPs-C750. On the other hand, higher substitution increased the synergy of hybrid fillers, resulting in better filler dispersion and less energy dissipation.

Composites of multi-walled carbon nanotubes (MWCNTs) with polypropylene (PP) and thermoplastic olefins (TPOs) were prepared by melt compounding. Two non-covalent functionalization methods were employed to improve nanotube dispersion and the resulting composite properties are reported. The first functionalization approach involved partial coating of the surface of the nanotubes with a hyperbranched polyethylene (HBPE). MWCNT functionalization with HBPE was only moderately successful in breaking up the large aggregates that formed upon melt mixing with PP. In spite of the formation of large aggregates, the samples were conductive above a percolation threshold of 7.3 wt%. MWCNT functionalization did not disrupt the electrical conductivity of the nanotubes. The composite strength was improved with addition of nanotubes, but ductility was severely compromised because of the existence of aggregates. The second method involved PP matrix functionalization with aromatic moieties capable of π-π interaction with MWCNT sidewalls. Various microscopy techniques revealed the addition of only 25 wt% of PP-g-pyridine (Py) to the neat PP was capable of drastically reducing nanotube aggregate size and amount. Raman spectroscopy confirmed improved polymer/nanotube interaction with the PP-g-Py matrix. Electrical percolation threshold was obtained at a MWCNT loading of approximately 1.2 wt%. Electrical conductivity on the order of 10-2 S/m was achieved, suggesting possible use in semi-conducting applications. Composite strength was improved upon addition of MWCNTs. The matrix functionalization with Py resulted in a significant improvement in composite ductility when filled with MWCNTs in comparison to its maleic anhydride (MA) counterpart. Preliminary investigations suggest that the use of alternating current (AC) electric fields may be effective in aligning nanotubes in PP to reduce the filler loading required for electrical percolation. Composites containing MWCNT within PP/ethylene-octene copolymer (EOC) blends were prepared. Microscopy revealed that MWCNTs localized preferentially in the EOC phase. This was explained by the tendency of the system to minimize interfacial energy when the MWCNTs reside in the thermodynamically preferential phase. A kinetic approach, which involved pre-mixing the MWCNTs with PP and adding the EOC phase subsequently was attempted to monitor the migration of MWCNTs. MWCNTs began to migrate after two minutes of melt mixing with the EOC. The PP-g-Py matrix functionalization appears to slightly delay the migration. A reduction in electrical percolation threshold to 0.5 wt% MWCNTs was achieved with a co-continuous blend morphology, consisting of a 50/50 by weight ratio of PP and EOC. / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-09-30 13:22:24.499

This thesis looks at the study of nanocomposites of Poly(ethylene terephthalate) and organoclays. Two methods of materials blending are investigated for the production of the nanocomposites: solvent blending and melt blending. The main objectives were the investigation of the influence of organoclays and processing conditions on morphological, rheological, mechanical properties, crystal structure and isothermal crystallization kinetics of the nanocomposite and a comparison with unfilled PET. In solvent blending, the use of long sonication time and epoxy led to the formation of a two-dimensional network structure of long, thin particles in a solvent blended PET nanocomposite at low clay loading. The clay network structure seemed not to affect the tensile properties. The long, thin particles were able to be separated and dispersed further by high shear in a twin screw extruder, resulting in a high level of separation and dispersion. The crystallization of the solvent blended nanocomposite was not only influenced by the nanoclay but also by the residual solvent. The extent of clay dispersion did not affect the crystallization of the solvent blended sample. Both solvent blended and melt blended nanocomposites showed that increasing the amount of surfactant improved the degree of nanoclay dispersion in the PET that led to an enhancement in the tensile properties of the nanocomposite compared to the unfilled polymer. The degradation of the organoclay during melt blending did not limit the nanoclay dispersion in the PET. The low thermal stability of the organoclay reduced the strength of the crystalline nanocomposite but it did not affect the strength of the amorphous nanocomposite. In contrast to the solvent blended sample, the extent of clay dispersion influenced the crystallization of the melt blended sample. The poorly dispersed particles were more efficient in nucleating PET crystallization than the well dispersed particles. The crystallization rate of PET increased as the surfactant concentration decreased.

Polymer nanocomposites have garnered incredible promise in the field of material science due to the excellent mechanical strength, thermal and electrical conductivities of the nanoparticles and the extension of these properties to the processing flexibility inherent to plastics. However, practical realization of these nanoparticle-based materials has been hindered by the tendency of these nanoparticles to aggregate as a result of strong inter-particle forces. In this dissertation, we investigate the formation of non-covalent charge transfer interactions between polymers and single-walled carbon nanotubes (SWNTs) with the goal of optimizing interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites of SWNTs and three sets of polymer matrices with varying composition of electron donating or electron accepting functional groups were prepared. In the first part of this dissertation, quantitative characterization by optical microscopy and Raman spectroscopy and qualitative results through thick film composite visualization show that the existence of a moderate amount of interacting moieties along the polymer chain results in an enhanced intermolecular interaction with SWNT, which translates to an optimum nanoparticle homogeneity. Calculations from density functional theory and Flory-Huggins theory correlate with the experimental results, which illustrate that chain connectivity is critical in controlling the accessibility of the functional groups to form intermolecular interactions. Thus, controlling the amount of interacting functional groups throughout the polymer chain such that an adequate distance between them is realized will direct the extent of charge transfer interaction, which enables tuning the SWNT dispersion. The second part of this dissertation focuses on the elucidation of the morphology of these nanoparticle entities in a polymer matrix. The observance of microphase-separated peaks in the scattering patterns of polyacrylonitrile (PAN) nanocomposites indicate an ordering of the PAN polymer induced by the carbon nanotube cage, which could either be due to a thermodynamically bound layer around the SWNT or the occurrence of SWNT-induced PAN crystallization. Finally, UV-Vis measurements were performed on SWNT-polymer suspension in order to comprehend the interactions that occur during nanocomposite fabrication. These results demonstrate that SWNT dispersions in pure N,N-dimethyl formamide (DMF) are stabilized by the adsorption of polymers onto the SWNTs.

Biopolymers from renewable resources are of interest for packaging applications as an alternative to conventional petroleum-based polymers. One of the major application areas for biopolymers is food packaging, where a candidate polymer should meet critical requirements such as mechanical and oxygen barrier performance, also in humid conditions. Starch has long been used in certain packaging applications, either in plasticized state or blended with other polymers. However, native starch has high sensitivity to water and low mechanical and barrier performance. Recently, wood-derived hemicelluloses have been extensively studied as oxygen barrier films, but suffer from low film-forming ability and mechanical performance. In the present study, xyloglucan (XG) from tamarind seed waste is explored as an alternative high-performance biopolymer in packaging applications. The obstacles of polysaccharides in terms of moisture sensitivity and processability are addressed in this thesis. In Paper I, film properties of XG were studied. XG has a cellulose backbone, but unlike cellulose, it is mostly soluble in water forming highly robust films. Moisture sorption isotherms, tensile tests and dynamic mechanical thermal analysis were performed. Enzymatic modification (partial removal of galactose in side chains of XG) was performed to study the effect of galactose on solubility and filmforming characteristics. XG films showed lower moisture sorption than starch. Stiffness and tensile strength were very high of the order of 4 GPa and 70 MPa respectively, with considerable ductility and toughness. The thermomechanical performance was very high with a softening temperature near 260 ºC. In Paper II, several plasticizers were studied in order to facilitate thermal processing of XG films: sorbitol, urea, glycerol and polyethylene oxide. Films of different compositions were prepared and studied for thermomechanical and tensile properties. Highly favorable characteristics were found with XG/sorbitol system. A large drop in glass transition temperature (Tg) of XG of the order of 100 ºC with 20 - 30 wt% sorbitol was observed with an attractive combination of increased toughness. In Paper III, XG was chemically modified and the structure-property relationship of modified XG studied. XG modification was performed using an approach involving periodate oxidation followed by reduction. The oxidation is highly regioselective, where the side chains of XG are mostly affected with the cellulose backbone well-preserved as noticed from MALDI-TOF-MS and carbohydrate analysis. Films were cast from water and characterized by dynamic mechanical thermal analysis, dynamic water vapor sorption, oxygen transmission analysis and tensile tests. Property changes were interpreted from structural changes. The regioselective modification results in new types of cellulose derivatives without the need for harmful solvents. In Paper IV, moisture durability of XG was addressed by dispersing montmorillonite (MTM) platelets in water suspension. Oriented bionanocomposite coatings with strong in-plane orientation of clay platelets were prepared. A continuous water-based processing approach was adopted in view of easy scaling up. The resulting nanocomposites were characterized by FE-SEM, TEM, and XRD. XG adsorption on MTM was measured by quartz crystal microbalance analysis. Mechanical and gas barrier properties were measured, also at high relative humidity. The reinforcement in mechanical properties and effects on barrier properties were remarkable, also in humid conditions. In Paper V, cross-linked XG/MTM composite was prepared with high clay content (ca. 45 vol%) by an industrially scalable “paper-making” method. Instead of using cross-linking molecules, cross-linking sites were created on the XG chain by selective oxidation of side chains. The in-plane orientation of MTM platelets were studied using XRD and FE-SEM. The mechanical properties and barrier performance were evaluated for the resulting 'nacre-mimetic' nanocomposites. The elastic modulus of cross-linked nanocomposites is as high as 30 GPa, one of the stiffest bionanocomposites reported. / <p>QC 20121107</p>

Polymer nanocomposites are already a part of many important of worldwide businesses: automotive (molded part in cars), electronics and electrical engineering, household products, packaging industry, aircraft interiors, appliance components, security equipments. Among many nanocomposite precursors, TiO₂ nanopowder is increasingly being investigated due to its special properties. <br /><br /> The objective of this work is to synthesize and characterize polymer-TiO₂ hybrid nanocomposites. When dispersed at the nanoscale level TiO₂ could act as visually transparent UV filters and high-thermomechanical-performance materials. The synthesis strategy involved two steps. Firstly, aggregated TiO₂, as received, was modified by 3-trimethoxysilyl propylmethacrylate aimed at altering its surface characteristics. The effect of modifier concentration on changing the physicochemical properties of TiO₂ surface was evaluated. Size distribution of unmodified and modified TiO₂ nanopowders was measured using a particle size analyzer. The qualitative and quantitative grafting of vinyl groups on TiO₂ surface was investigated with Fourier transform-infrared (FTIR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Secondly, styrene monomer was then added to carry out copolymerization with vinyl groups on the modified TiO₂ by free radical initiator 2,2-azobis isobutyronitrile (AIBN) in bulk medium. FTIR spectra confirmed the formation of nanocomposites with polystyrene chains chemically linked to the surface of TiO₂ nanopowders. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated that the resulting nanocomposites displayed higher thermal stability and maintained similar glass transition temperatures (T_g) compared with pure PS. Ultraviolet ?visible spectroscopy (UV-Vis) investigated that these nanocomposites have improved optical properties potentially acting as visually transparent UV filters. Such incremented properties were attributed to the nancoscale dispersion (20-50nm size) of TiO₂ into polystyrene matrix, which morphology was observed by scanning electron microscopy (SEM).

Polymer nanocomposites are already a part of many important of worldwide businesses: automotive (molded part in cars), electronics and electrical engineering, household products, packaging industry, aircraft interiors, appliance components, security equipments. Among many nanocomposite precursors, TiO₂ nanopowder is increasingly being investigated due to its special properties. <br /><br /> The objective of this work is to synthesize and characterize polymer-TiO₂ hybrid nanocomposites. When dispersed at the nanoscale level TiO₂ could act as visually transparent UV filters and high-thermomechanical-performance materials. The synthesis strategy involved two steps. Firstly, aggregated TiO₂, as received, was modified by 3-trimethoxysilyl propylmethacrylate aimed at altering its surface characteristics. The effect of modifier concentration on changing the physicochemical properties of TiO₂ surface was evaluated. Size distribution of unmodified and modified TiO₂ nanopowders was measured using a particle size analyzer. The qualitative and quantitative grafting of vinyl groups on TiO₂ surface was investigated with Fourier transform-infrared (FTIR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Secondly, styrene monomer was then added to carry out copolymerization with vinyl groups on the modified TiO₂ by free radical initiator 2,2-azobis isobutyronitrile (AIBN) in bulk medium. FTIR spectra confirmed the formation of nanocomposites with polystyrene chains chemically linked to the surface of TiO₂ nanopowders. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated that the resulting nanocomposites displayed higher thermal stability and maintained similar glass transition temperatures (T_g) compared with pure PS. Ultraviolet ?visible spectroscopy (UV-Vis) investigated that these nanocomposites have improved optical properties potentially acting as visually transparent UV filters. Such incremented properties were attributed to the nancoscale dispersion (20-50nm size) of TiO₂ into polystyrene matrix, which morphology was observed by scanning electron microscopy (SEM).