Preparation of environment-friendly hydrophilic rubber from natural rubber grafted with sodium acrylate by reactive melt mixing

In this research, we present an easy way to prepare environment-friendly hydrophilic rubbers derived from natural rubber (NR) grafted with sodium acrylate (NaAA) through reactive blending using an internal mixer operated at a rotor speed of 80 rpm and 150 degrees C. The key parameters affecting the grafting efficiency of NR-g-NaAA were investigated in terms of the fill factor (FF) of the chamber, mixing time, and NaAA content. Lastly, the grafted sample (with a suitable grafting efficiency) was crosslinked using peroxide curing to produce X(NR-g-NaAA) as a hydrophilic NR sample. Results showed that grafting efficiency of the NR-g-NaAA samples tended to decrease with increasing FF and NaAA contents owing to the higher chain-scission reaction rather than the free-radical generation on the NR molecules in the mastication step, while the optimal mixing time was only 4 min. The remarkable improvement in the hydrophilicity of NR by grafting with NaAA was established via the presence of C = O vibration of the ionized carboxylate group (-COO-) of NaAA located at 1559 cm(-1). Increasing the grafting efficiency up to 69% resulted in a marked decrease in the water contact angle from 103 degrees to 72 degrees and enhanced the water swelling of the X(NR-g-NaAA) sample.