Effect Of Protein On The Properties Of Constant Viscosity Natural Rubber

In this paper, the alkaline proteinase2709was applied to remove the protein in natural rubber latex, and the amount of protein for the viscosity-maintaining effect of constant viscosity natural rubber (CVNR) as well as its properties were studied in which2-Mercaptobenzothiazole (MBT) as a type of viscosity stabilizer was adopted to prepare constant viscosity natural rubber.The results show that NR has a lower plasticity (Po), Mooney viscosity (Mv), average molecular weight (Mw) and gel content, while the plasticity retention index (PRI) is higher. And with the decrease of protein content in NR, the Po, Mv, Mw, PRI and gel content decreased.The viscosity-maintaining effect of NR which was treated with the viscosity stabilizer-MBT after accelerated storage hardening were investigated. The results show the MBT-CVNR has good viscosity-maintaining effect and aging resistance. Aging resistance of MBT-CVNR is bound up with storage time and protein content, it will be getting worse with the extension of storage time, but getting worse gradually with the protein content decreased.Thermo-gravimetric analysis (TG) and differential thermal analysis (DTA) were utilized to study thermal degradation of MBT-CVNR. The results show that the thermal degradation reaction of MBT-CVNR is a first-order reaction, and use of MBT and lower protein content will cause adverse effects on heat resisting property. Even the Ct of NR-a, NR-b, NR-c, NR-d and NR-e is95.59%,96.40%,95.77%,96.07%,95.53%, respectively, they can be almost degraded completely.Frequency sweep tested by rubber process analyzer indicate that the elastic modulus(G’) increase with frequency’s increase while loss factor (tan8) decrease. And the use of MBT and lower protein content will lead to lower G’and higher tan8. And the Flow index and consistency tell us that the MBT-CVNR has better flow properties with protein content decrease, when samples used to test temperature sweep,G’and tan8have the same tendency with frequency sweep.The stress relaxation sweep show that the MBT-CVNR has the shorter stress relaxation with the protein content decrease.In terms of the vulcanizates performance, the torque increase rate (VM), cure rate index (Vc), the maximum torque(MH) and the minimum torque(ML) of NR-b are higher and vulcanization time (t90) is smaller than NR-a, which indicate that the MBT-CVNR has better vulcanization characteristics and higher crosslinking densities compared with NR vulcanizate. At the same time, the lower protein content in MBT-CVNR, the higher vulcanization rate and crosslinking densities it have.The result is consistent with the test result of NMR. The results show that the influence on mechanical properties of vulcanized natural rubber, the viscosity stabilizer-MBT and protein content are all obviously. Compared with NR-a, the vulcanized NR of NR-b has better modulus, tensile strength, tearing strength and the elongation at break is higher. All of these will be increased after the protein content is decreased.