The Effects Of Betaine And Micro-coagulation On Natural Rubber Structure And Properties

Compared with natural rubber coagulated by acid (NR-a) , the effects of betaine and micro-coagulation on natural rubber (NR) structure and properties were studied by employing the Nuclear Magnetic Resonance Crosslink-density spectrometer (NMR-CDS) and Rubber Processing Analyzer (RPA) . Some basic properties such as vulcanization process, curing kinetics, the crosslink-density, the physical properties and the dynamic properties of the NR were investigated.The results of vulcanization characteristics showed that the natural rubber added with betaine (NR-b) had the shortest tc10, tc50 and tc90, NR-a had the longest, but MH of NR-b was the biggest, MH of natural rubber coagulated by microorganisms (NR-m) was bigger than NR-a. The betaine and non-rubber components had a promotional effect on vulcanization process.The physical properties indicated betaine and micro-coagulation enhanced tensile strength, hardness and resilience. For unfilled NR, when the added amount of betaine was 1.0 g, tensile strength reached to 23.82 MPa and tearing strength reached to 33.88k N/m, increased by27.04 % and 28.92 % respectively compared with NR-a. Betaine made accelerant zinc salt have a better solubility in NR, sulphur was well-distributed, cross-linked network was more completed and had fewer defects, so NR-b performed excellent properties.The results of NMR showed that Physical XLD of NR-m was the biggest, Physical XLD of NR-b was near to NR-a. Chemical XLD and Total XLD of NR-b were the biggest. Under the same curing time, Total XLD and AMc of NR-b were bigger than NR-a, AT₂, Mc and T₂ of NR-b were smaller than NR-a. NR-m compound had the shortest relaxation time and the comparison of vulcanizates relaxation time was NR-b<NR-m<NR-a.For unfilled NR, the TG/DTA results showed that all the thermal degradations of three kinds of NR in nitrogen were an one-step reaction. The initial degradation temperature and the temperature at the maximum degradation rate of three kinds of NR were close to each other. The DSC results showed Tg of NR-b was the lowest.The results of curing kinetics showed that curing kinetics coefficients (k) of three kinds of NR compounds increased with curing temperature and under each temperature, the k of NR-b was the biggest. This indicated that betaine could promote vulcanization and increase k.The dynamic performances tests on carbon black filled NR by RPA indicated that the dynamic modulus (G') of three kinds of NR compounds increased with tear frequency while the loss factor (tanδ) decreased. Through temperature sweep we found NR-b began to crosslink at 110℃. The dependence of dynamic properties of NR vulcanizates on the tear frequency, temperature and tear strain varied with the XLD. NR-b vulcanizate had the biggest XLD, the range of its tanδwith tear frequency, temperature and tear strain was smaller than others.