PREPARATION OF NEW RUBBER MATERIALS FROM HIGHLY DEPROTEINIZED NATURAL RUBBER

采用高氨天然橡胶（HDPNR）乳胶与蛋白水解酶在表面活性剂存在下孵育，然后离心两次，制备了高脱蛋白天然橡胶（HDPNR）乳胶。HDPNR的含氮量小于0.02%，完全去除了橡胶中的蛋白质。以低分子量天然橡胶（HDPNR）为原料，在K_2S_2O_8和丙烷的存在下，在60℃的温度下振荡，氧化降解低分子量天然橡胶（LNR）和LNR乳胶。仅含K_2S_2O_8的HDPNR的特性粘度[eta]在2 h后由7.2降至5.5,3 h后又上升至6.5。添加丙醛后，HDPNR的[eta]在反应5小时后显著降低至0.5，而高氨天然胶乳制得的橡胶[eta]略有降低。胶乳的浓度和用于稳定胶乳的表面活性剂的种类对HDPNR胶乳的降解率影响不大。LNR胶乳具有稳定的乳胶形态，由胶乳凝结而成的干燥橡胶透明无色。经核磁共振和分子量分析，LNR是一种两端含有醛和酮基团的远螺旋聚合物。以HDPNR胶乳为原料，以过氧化叔丁基/四乙烯五胺（TBHPO-TEPA）为有机氧化还原引发剂，制备了天然橡胶与苯乙烯的接枝共聚物，经脱蛋白处理后，接枝聚苯乙烯的苯乙烯含量、接枝效率和分子量均显著提高。HDPNR胶乳接枝共聚物的接枝位点数比未经处理的天然胶乳接枝共聚物的接枝位点数大3倍左右。HDPNR与未经处理的天然橡胶之间的反应性差异被解释为由于未经处理的天然橡胶中存在的蛋白质和天然抗氧化剂的去除。

Highly deproteinized natural rubber (HDPNR) latex was prepared by incubation of commercial high-anmonia latex with a proteolytic enzyme in the presence of a surfactant, followed by centrifugation twice. The nitrogen content of HDPNR was less than 0.02%, suggesting the complete removal of protein in the rubber.Low molecular-weight natural rubber (LNR) and LNR latex were prepared by oxidative degradation of HDPNR latex in the presence of 1 phr of K_2S_2O_8 and 15 phr of propanal, by shaking at 60ﾟC.The intrinsic viscosity [eta] of HDPNR with only K_2S_2O_8 decreased from 7.2 to 5.5 after 2 hr and then increased to 6.5 after 3 hr. By the additaion of propanal, HDPNR showed a significant decrease in[eta]to give 0.5 after 5 hr of the rection, while rubber from high-ammonia nataural rubber latex showed a slight decrease in[eta]. The concentration of latex and the kind of surfactant used for stabilizing latex gave no much effect on the degradation rate of HDPNR latex. The LNR latex is stable as latex form and the dried rubber coagulated from latex is transparent and colorless. The LNR was a telechelic polymer containging aldehyde and ketone groups at both terminals by NMR and molecular weight analyzes.A graft copolymer of natural rubber with stirene was made from HDPNR latex with tert-butyl hydroperoxide/tetra ethylene pentamine (TBHPO-TEPA) as an organic redox initiator, The stirene content, graft efficiency and molecular weight of grafted polystirene were significantly increased by deproteinization. The unber of grafting sites for graft copolymer from HDPNR latex was about three-times larger than that determined for graft copolymer from untreated natural rubber latex. The differences of reactivity between HDPNR and untreated natural rubber were explained to be due to the removal of protein and naturally occurring antioxidant present in untreated natural rubber.