ON THE STABILITY OF NATURAL-RUBBER LATEX ACIDIFIED BY ACETIC-ACID AND SUBSEQUENT EPOXIDATION BY PERACETIC-ACID

Natural rubber (NR) latex having up to 54% dry rubber content (drc), stabilized by 1.65-5.0 parts of nonionic surfactant [(fatty alcohol)/(ethylene oxide) condensate type] per hundred of rubber can be acidified by acetic acid to pH ca 4, retaining good aggregative stability. It was shown that this stability depends on drc, surfactant level and final pH. The stabilized latex of medium-to-high drc (25-48%) could be successfully subjected to epoxidation at moderate temperature, using preformed peracetic acid. The epoxidation proceeds rapidly and effectively, leading to pure ENR of up to 60-70 mol% epoxide content as checked by i.r. and H-1-NMR. By swelling test and sol-gel fractionation, it was shown that the epoxidation reduces the solubility of rubber in nonpolar solvents and increases its sensitivity to polar solvents. The long lasting and highly acidic medium of reaction lead to increase in the gel content of ENR samples compared with the original NR.