Blended polymers toughness enhancement

Liu, Y. H., and Zumbrunnen, D. A., Toughness enhancement in polymer blends due to the in-situ formation by chaotic mixing of fine-scale extended structures, J. Mater. Sci. 34, 1921-1931 (1999). 

Co-continuous morpholoey A different type of morphological structure, cocontinuity of the phases, can prove beneficial by drawing on properties of both constituents stiffness from a rigid polymer and high strain at break from a ductile one. This is illustrated by Kyu et al. (1991) who studied the toughness enhancement of PC/PMMA blends. The blends were prepared using three different procedures ... 

T. Kyu, J.M. Saldanka, M.J. Kiesel, Toughness enhancement in polycarbonate/polymethyl-methacrylate blend via phase separation, in Two-Phase Polymer Systems, ed. by L.A. Utracki (Hanser Publishers, Munich, 1991), pp. 259-275 J. Laatsch, G.-M. Kim, G.H. Michler, T. Arndt, T. Sufke, Polym. Adv. Technol. 9,716-720 (1998)... 

Polypropylene block and graft copolymers are efficient blend compatibilizers. These materials allow the formation of alloys, for example, isotactic polypropylene with styrene-acrylonitrile polymer or polyamides, by enhancing the dispersion of incompatible polymers and improving their interfacial adhesion. Polyolefinic materials of such types afford property synergisms such as improved stiffness combined with greater toughness. 

A group of new, fully miscible, polymer blends consisting of various styrene-maleic anhydride terpolymers blended with styrene-acrylonitrile copolymer and rubber-modified versions of these materials have been prepared and investigated. In particular the effects of chemical composition of the components on heat resistance and the miscibility behavior of the blends have been elucidated. Toughness and response to elevated temperature air aging are also examined. Appropriate combinations of the components may be melt blended to provide an enhanced balance of heat resistance, chemical resistance, and toughness. 

Blending of polymer with ABS offers certain significant property enhancement opportunities such as resistance to chemical attack which increases with increasing AN content, toughening, and modification of processability characteristics. However, such opportunities can only be realized if sufficient miscibility of the glassy (matrix) components is achieved to retain or enhance toughness and predictable variation of properties with blend ratio is to be expected only for largely or fully miscible matrix components. For this reason, a study of the miscibility... 

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. 

Polycarbonate (PC), an amorphous polymer, provides the toughness for both blends. The crystallinity of PBT and PET contributes the chemical resistance. The shorter methylene groups in PET relative to PBT (2 vs. 4) enhance chain stiffness and hence high-temperature rigidity in PET. 

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