Composites, polymer-based filler, mechanical properties

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

It is known, that physical and mechanical properties of carbonic composites on the base of this polymer (UPA 6-15,. .., UPA 6-40), where carbon fibrous materials Ural and Viskum are applied as a filler, depend on its weight fraction and uniformity of the filler distribution in the composite. 

The use of polymer-based composites has been Increasing rapidly in recent years. Mica has been an important mineral filler in the evolution of composites, its use being favored particularly in mechanical and in electrical insulation applications because of its well-proven insulating properties, its relative abundance, low cost and environmental safety. 

Recently, Vaia et al. [8] reported a new process for direct polymer intercalation based on a predominantly enthalpic mechanism. By maximization of the number of polymer host interactions, the unfavorable loss of conformational entropy associated with intercalation of the polymer can be overcome leading to new intercalated nanostructures. They also reported that this type of intercalated polymer chain adopted a collapsed, two-dimensional conformation and did not reveal the characteristic bulk glass transition. This behavior was qualitatively different from that exhibited by the bulk polymer and was attributed to the confinement of the polymer chains between the host s layers. These types of materials have important implications not only in the synthesis and property areas, where ultrathin polymer films confined between adsorbed surfaces are involved. These include polymer filler interactions in polymer composites, polymer adhesives, lubricants, and interfacial agents between immiscible phases. 

This chapter considers a study of two types of composites based on polyhydroxyether and graphite with various amounts of a filler. Using various methods it is possible to estimate the adhesion characteristics and interfacial layer, including its thickness and tensile strength and the interdependence between these values and the adhesion properties. The results were treated on the basis of the theory of irreversible aggregation, cluster theory of the polymer structure and fractal analysis. It was established that all the important characteristics of adhesion, the interfacial layer and mechanical properties are interconnected by the fractal dimensions of the surface of the aggregates of filler particles and of the polymer matrix, whose structure is distorted under the influence of the filler surface. 

Wood-filled PVC has inferior mechanical properties because of lack of interaction. Treatment of wood filler with aminosilane improves acid-base interaction between filler and polymer to the extent that impact strength and tensile properties of composite are improved over unfilled PVC. Tensile properties of PVC were deteriorated when leather particles were used as a filler. But, after filler particles were treated with ethylene-vinyl acetate copolymer, a coating was produced on the surface of filler particles that promoted adhesion with PVC and improved mechanical properties.These are some recent examples of many applications of filler preparations to improve its interaction with PVC. 

In the case of polymer-based materials, composites are often preferred because the mechanical properties of the pure polymer phase are inadequate for the proposed application [4]. To overcome this problan, polymeric materials are reinforced in some way, typically by incorporating a substantial amount of rigid filler. For some polymers, the problem may be that they lack the toughness required for a particular application, and for these materials, elastomeric fillers are used. These fillers have the effect of increasing toughness and the concomitant effect of reducing brittleness. However, this approach is not used for restorative dental materials. 

Fibers have been widely used in polymeric composites to improve mechanical properties. Cellulose is the major substance obtained from vegetable fibers, and applications for cellulose fiber-reinforced polymers have again come to the forefront with the focus on renewable raw materials. Hydrophilic cellulose fibers are very compatible with most natural polymers. The reinforcement of starch with ceUulose fibers is a perfect example of a polymer from renewable recourses (PFRR). The reinforcement of polymers using rigid fillers is another common method in the production and processing of polymeric composites. The interest in new nanoscale fillers has rapidly grown in the last two decades, since it was discovered that a nanostructure could be built from a polymer and layered nanoclay. This new nanocomposite showed dramatic improvement in mechanical properties with low filler content. Various starch-based nano-composites have been developed. 

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