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.

Automated summary

This research introduced a simple method to prepare environmentally friendly hydrophilic rubbers by grafting sodium acrylate onto natural rubber. Key parameters affecting the grafting efficiency were investigated, showing that grafting efficiency tended to decrease with higher fill factor and NaAA content. The improvement in hydrophilicity of the rubber through grafting was established, leading to decreased water contact angle and enhanced water swelling.