The ambivalent effects of heavy metals present in natural rubber latex

Abstract

Accumulation of heavy metals in plant parts due to environmental uptake may have repercussions on the plant's health and integrity. In this study, we quantified various heavy metals in natural rubber (NR) latex collected from Mantin, Negeri Sembilan, Malaysia (sub-urban area) and Batu Embun, Pahang, Malaysia (rural area) for 12 consecutive months. Acid digestion as sample pre-treatment was performed prior to detection and quantification of the heavy metals, namely Cr, Cu, Fe, Mn, Pb, and Zn, using inductively coupled plasma–optical emission spectrometer (ICP-OES). Then, plasticity test and preparation of polystyrene/natural rubber (PS/NR) blends were conducted to investigate the effects of heavy metals on the integrity of NR. It was found that the plasticity retention index (PRI) was inversely proportional to the concentration of heavy metals in NR. Conversely, high levels of heavy metals in latex had acted as an excellent compatibilizer in PS/NR blends with improved properties of tensile strength and impact energy. The most deposited heavy metals (4391.2 ppm) compatibilized PS/NR blends with the highest tensile strength of 27.4 MPa and impact energy of 17.55 kJ/m². In contrast, the least accumulated heavy metals (18.8 ppm) resulted in PS/NR blends with the lowest tensile strength (2.61 MPa) and impact energy (2.70 kJ/m²). The phase distribution of PS/NR was observed to be more uniformed when high levels of heavy metals were available in the blends. Our discovery has indirectly demonstrated the role of NR in eliminating heavy metals from the environment which in turn, acting as a good compatibilizer in the blending of PS/NR.