General properties toughness

Effects of Density. Decreasing the o -olefin comonomer content increases the amount of crystallinity in LLDPE. Increasing the amount of crystallinity increases the density of the pol5mier and has a significant effect on polymer properties. As crystallinity increases, LLDPE becomes stiffer and in general, less tough. Table 3 shows the effect of increasing density in LLDPE blown films. 

For reasons that are not fiiUy understood, PPSF exhibits generally improved compatibiUty characteristics over either PSF or PES in a number of systems. An example of this is blends of PPSF with polyaryletherketones (39,40). These blends form extremely finely dispersed systems with synergistic strength, impact, and environmental stress cracking resistance properties. Blends of PPSF with either PSF or PES are synergistic in the sense that they exhibit the super-toughness characteristic of PPSF at PSF or PES contents of up to 35 wt % (33,34). The miscibility of PPSF with a special class of polyimides has been discovered and documented (41). The miscibility profile of PPSF with high temperature (T > 230° C) polysulfones has been reported (42). 

Ba.inite. In a given steel, bainite microstmctures ate generally found to be both harder and tougher than peadite, although less hard than martensite. Bainite properties generally improve as the transformation temperature decreases. Lower bainite compares favorably with tempered martensite at the same hardness and can exceed it in toughness. Upper bainite, on the other hand, may be somewhat deficient in toughness as compared to fine peadite of the same hardness (33). 

Generally the harder the ceramic, the better its wear resistance however, other properties such as fracture toughness may play the dominant role. If a ceramic is mated with a metal hardness is the determining factor, but when a ceramic is mated with another ceramic fracture toughness appears to determine the wear rate (54). 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

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