Odor reduction and mechanical properties of natural rubber latex/sepiolite films

Abstract

The bacterial action on non-rubber components and thermal degradation lead to offensive odor in natural rubber. This study aims to investigate the odor reduction, mechanical and morphological properties of the natural rubber latex (NRL)/sepiolite films with sepiolite from Tolsa (sepiolite-T), and sepiolite from China (sepiolite-C). The NRL/sepiolite films were prepared by heating of the NRL and curatives with various sepiolite content, from 0 to 2.0 parts per hundred rubber (phr), in a water bath at 70 ±1 °C. Then, casting the prevulcanized latex onto the glass mold. The results of nitrogen adsorption-desorption isotherms and pore size distribution show that sepiolite-T is a mesoporous material with high specific surface area (Sb e t ) and total pore volume, while sepiolite-C is a macroporous material with low Sb e t and total pore volume. The presence of volatile organic compounds (VOCs) included volatile fatty acids, alcohol, amide, hydrocarbon, terpene, and piperidines in neat NRL films and NRL/sepiolite films has been confirmed by using gas chromatography-mass spectrometry. The results show that the mesoporous sepiolite-T adsorbed more odorous VOCs compared to macroporous sepiolite-C in the neat NRL films. The result of dynamic olfactometry analysis also shows a negative correlation between odor concentration and the sepiolite content. Besides that, the odor concentration of NRL/sepiolite-T samples was much lower than NRL/sepiolite-C samples and the lowest odor concentration was achieved by adding 2.0 phr sepiolite-T (T2.0). The addition of 2.0 phr sepiolite in NRL/sepiolite-T and NRL/sepiolite-C reduced the odor concentration of NRL films by 69.1% and 59.4%, respectively. The morphological studies of NRL/sepiolite films reveal that the defects including sepiolite agglomerate, free volume and sepiolite pull-out were evident in NRL/sepiolite films. It was found that the tendency of defects formation increased with sepiolite content and consequently led to a decrease in tensile strength of NRL/sepiolite films. The rubber/sepiolite interaction in NRL/sepiolite-C films was proven by the ratio of the volume fraction of rubber in unfilled rubber sample to the volume fraction of rubber in a filled rubber sample (Vr/Vf). Therefore, NRL/sepiolite-C films demonstrated a higher tensile strength than NRL/sepiolite-T films. The increase in modulus at 300% elongation (M300) and decrease in elongation at break of NRL/sepiolite films show that the sepiolite provided stiffness to NRL/sepiolite films. The tear strength of NRL/sepiolite-T films was found to increase with sepiolite-T content due to the improvement of crack propagation resistance conferred by sepiolite-T. However, no significant changes of tear strength have been noticed in NRL/sepiolite-C films. Thus it can be concluded that sepiolite-T is a promising deodorizer for NRL films due to its higher odorous VOCs adsorption potentials. However, the high stiffness of the NRL/sepiolite films may not be appropriate for the thin rubber products except T0.5 and T1.0, which has the high elongation at break and low M300.