Semicrystalline polymers toughness enhancement

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). 

G.H. Michler, Micromechanical mechanisms of toughness enhancement in nanoslnictured amorphous and semicrystalline polymers, in Mechanical Properties of Polymers Based on Nano-Structure and Morphology, ed. by F.J. Balta Calleja, G.H. Michler (Taylor and Francis, London, 2005), pp. 375-428... 

Enhancement of impact toughness in some semicrystalline polymers is similar to techniques used for some glassy polymers. Usually an elastomeric phase is melt-blended into the host polymer, resulting in a dispersion of spheroidal elastomeric particles or a network. Compatibilization is obtained by copolymerization or chemical reaction at the interface. The toughening mechanisms may include both massive crazing and cavitation-plastic deformation, depending on the... 

Enhancement of mechanical properties is of interest only if it is not accompanied by a loss of other important properties of the blend. Of particular concern for such polymer blends is stiffness, because most means of increasing impact strength also reduce stiffness (14-19). But this is not the case for the iPS-fc-iPP-iPS-iPP blends studied here as seen in Table II. It is clear that the enhancement in toughness just described is not accompanied by a loss of stiffness, but it is essentially unaffected by the compatibilizer. And the stiffness of iPS-fc-iPP-iPS-iPP is higher than that of iPP and HIPS. The impact-modulus behavior seems to be due to the tough (or rigid) characteristics, morphologies of phases, and semicrystalline isotactic structure of each block in the iPS-b-iPP diblock copolymer. 

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