Polyolefin crystallinity, crosslinking

Crosslinking reduces the polyolefin crystallinity. Crosslinks play the role of defect centres which impede the folding of macromolecules and thus decrease the sizes of the lamellar crystals. Even a small number of crosslinks reduces the crystallinity of low density polyethylene provided that it is performed above the melting tonperature of the polymer crystallites. The linkage of polymer chains impedes their independoit displacement and the degree of crystallinity is distinctly Iowa even when only one macromolecule involves one crosslink [160]. 

Polyolefin based thermoplastic elastomers are either made by reactor copolymerization or physical blending of crystalline polypropylene with EPDM in an extruder under conditions where the optimum level of chemical crosslinking of the EPDM phases could be promoted. 

Crystalline polyethyelene (Marlex EHM 6006) and Neoprene W crosslinking agents PEGDMA, TAC, TAP and TMPTMA. NR, crumb rubber from The Rubber Institute of India, Kottayam PE (HDPE), Hostalen GA 7260 from Polyolefin Industries, Bombay. 

EPR random copolymers are inherently thermoplastic and rubbery in nature but to give them useful levels of strength, creep resistance, heat resistance, and solvent resistance, they are commonly blended, or block or graft copolymerized, with crystalline polyolefins, particularly polypropylene, which on cooling separate as crystalline domains and act as thermoplastic crosslinks and reinforcing fillers. ... 

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