A Lightweight, Abrasion-Resistant Polybutadiene Rubber/Styrene Butadiene Rubber Foam Prepared by Three-Step Process for Footwear Outsole Applications

Herein, a developed microcellular foam from polybutadiene rubber (BR) and styrene butadiene rubber (SBR), which is prepared by prevulcanization, supercritical foaming, and secondary vulcanization processes is reported. It has excellent abrasion resistance and with low density. The foaming process is successfully achieved with the assistance of eco-friendly supercritical nitrogen (sc-N 2 ). The microstructural analysis of BR/SBR foams indicates that the cell structure of BR/SBR foams has an obvious effect with the increased prevulcanization time. The thickness of solid skin on the foam surface is observed using scanning electron microscope, which revealed that the prevulcanization time is also a direct factor influencing the thickness of solid skin, where the fundamental cause is explained from two aspects, i.e., gas escape and rubber vulcanization. The prevulcanization time to meet the abrasion resistance characteristics has determined based on the cell structure and abrasion solid skin thickness of BR/SBR foams at different time zone of prevulcanizations. As a result, BR/SBR foams prepared by this process have a low relative volume loss (62.6–117.1 mm 3 ) and a desirable density (0.50–0.71 g cm −3 ) at a prevulcanization time of 15–17 min.