Improvement in strain-induced crystallization and physicochemical property of natural rubber by protease treatment

Natural rubber (NR) distinguishes itself from a synthetic one in that it contains non-rubber components and is subject to strain-induced crystallization (SIC). Non-rubber components may have a great influence on the physicochemical properties and SIC behavior of NR. However, the underlying mechanisms remain poorly understood. This work uses protease to treat the non-rubber components so as to control their content. The mechanical properties, dynamic properties, and crystallization kinetics of the resulting NR are compared. The protease treatment shortens the solidification time of latex. Thus, a higher phospholipid content is retained. A higher protease content yields better mechanical and dynamic properties. Protease-treated NR shows a SIC behavior at lower strain and a higher crystallinity at the same strain. This indicates that phospholipids have a greater impact on the properties than proteins, namely they better speed up vulcanization and SIC.