Water-swellable thermoplastic vulcanizates based on ethylene–vinyl acetate copolymer/chlorinated polyethylene/cross-linked sodium polyacrylate/nitrile butadiene rubber blends

A novel water-swellable rubber (WSR) has been prepared by dynamically vulcanized ethylene–vinyl acetate copolymer (EVA)/chlorinated polyethylene (CPE)/nitrile butadiene rubber (NBR) blends where the cross-linked poly(sodium acrylate) (CPNaAA) was used as a super water-absorbent resin and dispersed in the NBR rubber. The mechanical properties, water-swelling behavior, weight loss and crystallization behavior of the prepared WSRs were investigated systemically. When the CPNaAA content was 20 phr above, the increase in CPNaAA dosage contributed to the decrease in mechanical properties. However, the WSRs showed strong water-swelling behaviors and the water-swelling ratio of WSRs with 50 phr CPNaAA was 669.3% at 120 h. The WSRs with 60 phr CPNaAA showed high water-swelling rate and achieved the equilibrium swelling at about 566.3% in 23 h. The secondary and third water-swelling behaviors of WSRs showed significantly rapid equilibrium swelling and remarkable decrease in weight loss. X-ray diffraction results revealed the increase in CPNaAA content would result in the reduction of crystalline structure content in EVA. Morphological study of etched surface showed that the CPNaAA particles were dispersed evenly in the WSRs and coated with cross-linked NBR rubber; moreover, field-emission scanning electron microscopic graphs showed the crystalline structure of EVA and clusters of flakes were dispersed on the etched surface of WSRs.