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In recent years, the growing sensibility about environmentally friendly products has pushed the Wood Polymer Composites (WPC) market along an increasing trend. On the other hand, the presence of the wood flour determines a few problems, two of which are particularly significant. First, WPC products are often used in a large range of temperature and moisture conditions that can be demanding for the material. Further, large quantities of wood filler promote the embrittlement of the composite and often cause failure in the finite products. The aim of this work was to evaluate the hygrothermal degradation effects on the tensile properties of a polypropylene based WPC toughened with a thermoplastic elastomer. Santoprene improves the elongation at break, as revealed by tensile tests, but increases porosity, as shown by SEM analysis. In wet conditions, the presence of the thermoplastic elastomer reduces the negative effect of the hygrothermal degradation. For these reasons, the addition of Santoprene is suggested only for applications in humid environment.

A method used to determine whether plastics should be described as high-temperature thermoplastics, that is, those capable of being used at ≥150 °C, based on values of heat distortion temperature and continuous use temperature, has been proposed. These all have substantially aromatic structures and high-temperature properties, as well as generally having good oxidation resistance, good mechanical properties, good chemical resistance, and usually good fire retardancy. It has been shown that polyphthalamides hold an intermediate position between conventional engineering thermoplastics, and the high-temperature group. This group of polymers is the most expensive plastics material, so are used in niche applications where their excellent performance is required. Monomer production, and the production, structure, properties, processing, and applications of six groups of high-temperature thermoplastics are discussed. These are polysulfones, polyphenylene sulfides, imide polymers, polyaryletherketones, polybenzimidazole, and liquid-crystal polymers. Commercial examples of these plastics are included.

Often, fillers are added to polymers in order to improve stiffness and inadvertently reduce toughness. This is not unexpected, as it is almost impossible to have a stiff material and still retain considerable level of toughness, especially in a poorly dispersed system. However, if the particles are well dispersed, it is quite possible to have a “win-win” situation, whereby the process will simultaneously improve toughness and stiffness. Fillers can be well dispersed and on a micro-scale agglomerate. If they are well dispersed, they will be well attached to the matrix and will remain so, even at large deformations. Of course agglomerated fillers will be prone to debonding, causing an internal fracture, leading to the formation of voids and hence, eventual deformation. However, brittle polymers can be toughened, significantly, by the addition of miscible amorphous polymers and/or a thermoplastic elastomer. In this chapter, the various mechanisms suitable for toughening nanostructured polymer blends will be succinctly reviewed. The interparticle distance and the interfacial adhesion of the filler to the polymer account for the extent of toughening achievable in the system. By far, toughening (with particulate fillers) immiscible blends has been more successful with semicrystalline than with amorphous polymers. Quite obviously, the toughening mechanism synonymous to conventional polymer blends is expected to be different from the mechanisms based on the nanophase-separated structures, since the latter represents a specific morphology-toughness correlation. This is because; toughness modification in polymer blends results in a specific toughness-morphology correlation and this is even more so, when nano-additives are factored into the system.

Rubber toughening mechanisms in acrylonitrile-butadiene-styrene (ABS) may be affected by the dispersed phase size, structure and content and by the characteristics of the styrene-acrylonitrile copolymer (SAN) matrix, namely by its molecular weight distribution and acrylonitrile (AN) content. In this work a series of ABS samples having different matrix average molecular weights and AN contents, and different dispersed rubber-phase content were prepared. For all materials time to fracture initiation and crack speed as a function of the stress intensity factor were determined under cyclic loading, while J-resistance curves were determined under static loading. Directly compared, the results obtained indicate that fatigue fracture is positively affected by molecular weight, but scarcely or, sometimes, negatively by the rubber content; on the contrary, static J-resistance is higher for higher rubber contents, but is not significantly affected by matrix molecular weight. However, a proper consideration of the time scale in which fracture occurs in the two loading modes, and of the strain energy release rates involved in fatigue testing, shows that these results are only apparently contrasting.

The basis for the phenomenon of spherulitic crystallization is the tendency for the polymer to reject non-crystallizable material during their formation. As a result, the boundaries between adjacent spherulites contain a high concentration of non-crystallizable material composed of low molecular weight chains, atactic polymer, and various impurities. As expected, the segregation of non-crystallizable material at spherulite/lamellar boundaries results in mechanical weakness in these regions of the polymer. This chapter is directed towards developing a scheme for increasing interspherulitic and interlamellar strength in polypropylene (PP) while maintaining, as much as possible, the original crystallinity and melt flow characteristics. The approach this chapter takes towards this objective is to blend isotactic polypropylene homopolymer with a copolymer that segregates at spherulite boundaries and interlamellar regions like a non-crystallizable impurity during primary crystallization, but then co-crystallizes across adjacent spherulites/lamellae during secondary crystallization. Isotactic–atactic polypropylene block copolymer is shown to be an effective spherulite boundary-strengthening additive. Toughness, as measured by Izod impact testing, has been found to significantly increase through blending with this copolymer. Perhaps more significantly, the toughness enhancement is not accompanied by a significant stiffness decrease as is generally evident in conventional rubber toughening schemes.

Stereorubbers were toughened by sillica in-situ formed with a sol-gel method. The introduction of water into hydrophobic rubber was carried out by alloy formation of rubber with poly(ethylene-co-vinylalcohol) (EVAL) in the presence of compatibilizer. Tetraethylorthosilicate (TEOS) dissolved in rubber reacted with water during blending and curing to form sillica particles in rubber matrix, which were identified by FTIR, EDX and EPMA. Mechanical properties of alloy rubber vulcanizate were superior to those of the corresponding pure rubber vulcanizate. Silica particles formed by sol-gel reaction further reinforced alloy rubber.

Publisher Summary This chapter provides an overview on the rubber modification of plastics that includes a chemical method of achieving improved toughness, elongation of fracture, ductility, or enhanced propensity to yield. The focus is kept on rubber modification by polyblend approach. Also, the chapter gives a brief description of the use of thin layers of soft polymers, encapsulating fibers, or mineral fillers. The mechanism of rubber toughening is categorized into various theories, such as energy absorption by rubber particles, ductility enhanced, shear yielding and crack termination, stress distribution and relief, and craze termination and prevention of crack propagation. The coefficient of thermal expansion of rubbery polymers is considerably higher than that of the glassy polymers in which they are dispersed. Such polyblends are usually formed or molded at temperatures significantly higher than those at which they are used, and the cooling process results in radial tension. The chapter also highlights properties of particular systems, such as cross-linked amorphous glasses, crystalline and amorphous polymers, and semi crystalline polymers of low glass temperature.

Rubber toughening is one of the key inventions in the history of the plastics industry. The first commercial exploitation of the invention took place in the late 1940s, when the US Rubber Company began melt-blending nitrile rubber with styrene-acrylonitrile (SAN) copolymer to make an early form of ABS (acrylonitrile–butadiene–styrene copolymer),1 and Dow Chemical launched a toughened grade of polystyrene–high-impact polystyrene (HIPS); early developments in HIPS have been reviewed by Amos2 and by Pohlemann and Echte.3 The success of these products led to the development of improved grades of ABS and HIPS, and a growing realization that the principle could be applied to virtually all types of thermoplastics and to many thermosets. There is still considerable scope for further research and development, and the field is a very active one, with many papers and patents appearing each year.

Publisher Summary The principal application of polymer blends is in the manufacture of fracture-resistant plastics, a fact that testifies to the practical importance of fracture properties to the user of plastics products. The fracture resistance of polystyrene can be increased substantially by adding a small proportion of rubber to obtain high-impact polystyrene (HIPS). This chapter describes general features of a variety of rubber-toughened plastics and the relationship between structure and fracture resistance. Study of rubber-toughened plastics shows that phase separation is an essential feature in which the rubber must be dispersed randomly like small discrete particles in the continuous-matrix phase. Other necessary features of the rubber phase are: (a) low shear modulus in relation to the matrix polymer; (b) good adhesion to the matrix; (c) adequate cross-linking; (d) average particle diameter near the optimum value for the material; and (e) low glass transition temperature. The chapter also highlights principles of fracture mechanics that begins with the assumption that all materials contain intrinsic cracks, flaws, and other defects. Four important techniques have been developed for studying rubber toughening. Each technique is capable of yielding quantitative information, therefore, placing the subject on a proper scientific foundation. The techniques are osmium staining, scanning electron microscopy, volumetric strain measurement, and fracture mechanics.