Mercapto-modified copolymers in polymer blends. III. The effect of functionalized ethylene-propylene-diene rubber (EPDM) on curing and mechanical properties of NBR/EPDM blends

Ethylene-propylene-diene with ethylene norbornene as the diene (EPDM) sampl es functionalized with thioacetate (EPDMTA) or mercapto groups (EPDMSH) wer e employed as compatibilizing agents for nitrile rubber (NBR)/EPDM blends. The cure rate of the blend was affected by the presence of a small portion of these compounds. EPDMTA decreases the cure rate of the blends, whereas E PDMSH was able to decrease the scorch time and increase the cure rate when employed in a proportion as high as 5.0 phr. The compatibilization effect w as influenced by the nature of the EPDM employed in the blends. Blends cons isting of an EPDM sample with lower viscosity display better dispersion of the EPDM phase inside the NBR matrix and also better mechanical performance with the compatibilization. The compatibilization with EPDMSH is reactive, with the formation of chemical bond between the mercapto groups of the com patibilizing agent and the double bond of the diene rubber. The compatibili zation with EPDMTA is also considered to be reactive because the vulcanized blends containing this functionalized copolymer contain a higher amount of cross linked material, as indicated by the lower weight loss after swellin g experiments. A scanning electron micrograph demonstrated that these funct ionalized copolymers led to a filler phase morphology, mainly in NBR/EPDM57 C blends. The compatibilization increases the dynamic elastic modulus witho ut affecting the damping. An improvement of thermal aging resistance of the studied blends was also achieved with the presence of the functionalized c opolymers. (C) 2001 John Wiley & Sons, Inc.