Improved toughness

Mechanical loading —> cavitation in rubber particles —> promotion of shear bands in matrix —> toughness improvement... 

Table 3. The toughness improvement induced by the -modification, rationalized in terms of the ratio Gt0t(/ -nuclcalcd)/Gtot (non-nucleated), is markedly stronger for the series tested under biaxial conditions. As both sets of investigated samples were injection molded, the skin-core structure (discussed in Sect. 3.2.3) could be inferred to be at least partly responsible for this feature. This was, however, confirmed in a recent work, where impacted /3-PP samples (tested at 5 ms-1, T = 23 °C and - 20 °C) with or without skin layers showed the same fracture performance within the limits of the experimental error [116].

Acrylic emulsions (or acrylic latices) are characterised as high-solids polymers having a film-forming temperature at or below room temperature (Lavelle, 1986). They have excellent hydrolysis resistance compared with other resins and are well suited as modifiers for portland cement mortars. Studies have shown that certain acrylic latices impart excellent workability at lower water demand, thin section adhesion and toughness, improved flexural strength and tensile strength and outstanding adhesion (Lavelle, 1983). 

The properties of thermosetting and thermoplastic resin systems are continually improved to meet increasing performance requirements of end users. One way to enhance material properties is to incorporate nano-modifiers, based on elastomeric silicone particles, which are optionally grafted with other (acrylic) polymers to control dispersibility, viscosity, and other parameters. As an example, epoxy resin formulations have been modified with silicone nanospheres to improve low-stress behavior. Table 1 shows the outstanding fracture toughness improvement of silicone coreshell nanospheres, even at very low particle loading levels. 

PPS Blends PPS/PDMS, trialcoxy silane and PO PPS/PBT, silane and GF PPS with silicone and acrylate elastomer lattices PPS-g-amine with PDMS-g-epoxy processability and impact strength chemical resistance and toughness improved heat- and impact- resistance improved tensile elongation and strength Liang, 1987 Serizawa et al., 1992 Koshirai etal., 1992, 1994 Han, 1994... 

PC/LDPE, PC/elastomer, etc.) Improve low temperature toughness Improve thermal-aging resistance... 

ABS/Polycarbonate Improve low temperature toughness Improve processability Lower cost... 

Features Permits prod, of higher m.w. condensation polymers with flexibility, toughness, improved impact resist., low moisture absorp., hydrolytic resist. 

Jan Jang, J.-S., Shin, S.-H. Toughness improvement of tetrafunctional epoxy resin by using hydrolysed poly (ether imide). Polymer 36 (1995) 1199-1207. 

Koh Koh, J. S., Kang, D. W., Park, H. S. Synthesis and toughness improvement of amino-ethylpi-perazine terminated polydimethylsiloxane tetrafunctional epoxy resin network. Korea Polym. J. 4 (1996) 39 4. 

Earlier Rowe and co-workers (37) had discussed improved toughness of cured epoxy polymers having a bimodal distribution of rubber particles embedded in the matrix—especially in light of failure mechanisms and what they suggest or mean. Similar models were addressed by Bascom and Hunston (38,39) and Ting (40,41) to show that such toughness improvements are carried over to the adhesive joint or to the fiber-reinforced composite. 

Combination of cross-linkable resins with biodegradable polyesters may result in various structures. Distribution of the polyester as dispersed phase in thermosets is the usual prerequisite of toughness improvement. The dispersion is generated by phase separation upon curing. Such systems may show SM properties although this is not yet reported for systems with biodegradable polyesters. 

Poly(phenylene sulfide), PPS, is an expensive, high-performance but brittle specialty resin. Blending can offer a good alternative both in toughness improvement and cost reduction (Nadkami and Jog 1991). 

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