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Abstract

Natural rubber latex (NRL) is often stored for a certain period of time before the grafting of poly(methyl methacrylate) (PMMA) to natural rubber (NR). It is well known that the properties of NRL change as a function of storage time. This paper describes the influence of storage time of NRL on its mechanical stability, followed by the effect on grafting efficiency of PMMA onto the NR backbone in NRL. The mechanical stability time (MST) of NRL decreases dramatically after 30 days of storage, implying that there is an increase in volatile fatty acid content leading to lower MST. Quality control tests [i.e., total solid content (TSC), alkalinity, pH, viscosity and MST] show that the alkalinity, viscosity and pH of NRL slightly fluctuate as a function of time in both NRL that fails the MST test and the NRL after addition of potassium oleate. Both NRLs having low and high MST at fixed period of storage time were used for the grafting of PMMA onto the NR in NRL.

Correlation between storage time of NRL in low and high MST and the grafting efficiencies was studied. Results suggest that there is no significant change in the grafting efficiency, which ranges from 84 - 88% for all samples, as well as MMA monomer conversion to PMMA for NRL with low and high MST at fixed storage time. The grafting of PMMA onto NRL backbone is confirmed using Fourier-transform infrared (FTIR) spectroscopy.

Keywords: Natural rubber latex; methyl-methacrylate, NR-g-PMMA; grafting, storage period

(ProQuest: ... denotes formulae omitted.)

1. Introduction

Hevea brasiliensis tree has been the object of research for the past few decades. The dry phase of latex [known as natural rubber (NR)] from the Hevea tree consists of 93 - 95 wt% 67.s'-1,4-poly(isoprcnc) [1, 2], NR possesses excellent physical properties such as high mechanical strength, excellent flexibility, and resistance to impact and tear [3, 4], but the unsaturated and non-polar nature of the chain makes it susceptible to flame, chemicals, solvents, ozone and weather [5, 6], Investigations of NR modified by graft-copolymerization with a second monomer such as vinyl benzene [7, 8], methyl methacrylate (MMA) [9-11], acrylonitrile [12, 13], phosphonate [12, 14] have been reported. Among these, NR grafted with MMA [methyl-grafted (MG) rubber or NR-g-PMMA]...

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