Preparation Of Novel Multifunctional Rubber Additives And Their Effects On Structure And Properties Of Rubber Composites

With development in the rubber industry and strengthening awareness of environmental protection, preparation of rubber agents with innocuity, high-performance, functionalization and low-cost has been a new way for the advance in the rubber industry. Therefore, it is theoretical and realistic to understand the preparation of novel functional rubber agents and their effects on structure-property relationship of rubber/filler composites essentially.In this work, two kinds of novel multifunctional rubber agents, lanthanum glutamic dithio-carbamate (La-GDTC) and N-phenyl-N'-(γ-triethoxysilane)-propyl thiourea (STU), were prepared and their effects on the structure-property relationship of rubber composites had been investigated systematically.The rubber-sulfur crosslinking reaction occurred in the SBR/La-GDTC compounds easily, in the absence of zinc oxide and stearic acid, indicating the good accelerated curing property of La-GDTC. As compared to SBR/La-GDTC compounds, the crosslinking reaction energies of SBR/SiO2/La-GDTC compounds were lower by adding SiO2particles, which demonstrated that the SiO2particles can activate the accelerated curing property of La-GDTC by some chemical reactions, leading to a much easier sulfur crosslinking reaction in the SBR/SiO2/La-GDTC compounds. The addition of La-GDTC could restrain the formation of filler network effectively by the presentation of hydrogen-bonds and coordination bonds between La-GDTC and SiO2particles under heating, resulting in a lower processing modulus and well-dispersion of SiO2particles in the SBR/SiO2/La-GDTC compounds. This is because one side of La-GDTC, containing dithio-carbamate group, could graft to the SBR molecular chain by poly-thiol dithiocarbamate; on the other hand, the other side of La-GDTC, carboxyl groups and lanthanum cation, could anchor on the surface of SiO2particles by reacting with silanol group. The La-GDTC play a role of "bridge-binding" bonds between the SBR matrix and SiO2particles, facilitating the compatibility between the rubber matrix and filler and improving the inter-phase adhesion, as well as the chemical crosslinking density, in the SBR/SiO2/La-GDTC composites by the formation of immobilized polymer layer on the surface of SiO2particles. The La-GDTC multifunctional addivtive exhibited the reinforced behavior for SBR/SiO2/La-GDTC composites. When the external stress was applied to SBR/SiO2/La-GDTC composites, the molecular chain could orientate along the stretching direction and relax by undergoing the process of "deformation of silica aggregation-cavitation-debonding-cavitation development-destruction of silica aggregation" leading to the "over-strain" of SBR molecular chain. Mechanical properties of SBR/La-GDTC/SiO2composites are largely improved and better than those of the SBR/ZDC(Zinc diethyl dithiocarbamate)/SiO2composites.The property of accelerated vulcanization of STU, as well as the surface modification and reinforcement effect, for NR compounds has been investigated thoroughly. Researches have been carried out on the accelerated curing property of STU as a second accelerator for NR compounds. The vulcanization velocity of NR/STU compounds were enhanced by a large scale under lower temperature (133℃), i.e., a decrease in the optimal curing time, which was a advantage for energy conservation and environmental protection. This was because STU favoured the cleavage of S-S, S-C, or S-N bonds in primary accelerators at low temperature and promoted the formation of more active crosslinking precursors, which owed to the polarization of C=S group by the electron-withdrawing effect of the benzene ring. Meanwhile, a conclusion could be drawn that the optimal ratio of STU and primary accelerator N-Cyclohexyl-2-benzothiazole sulfonamide (CZ) for NR compounds was1:1, based on the vulcanization parameters of NR compounds with different ratios of STU and CZ. Another find was the sulfur of STU did not lose to participate in the sulfur crosslinking reaction between sulfur element and rubber and, at the end of vulcanization process, STU decomposed into two parts, one grafted to the rubber molecular chain to form a poly-thiol dithiocarbamate group, and anther parts was y-Aminopropyl triethoxysilane (KH550), which was consistent with the results calculated from simulation equation of vulcanization process.The effect of STU on the behavior of strain-induced crystallization of NR vulcanizates was taken into consideration. A decrease in the glass transition temperature was observed in the NR/STU vulcanizates, as well as a larger size of three-dimensional network mesh and a wider dispersion of crosslinking density, as compared with NR vulcanizates without STU. Under the uniaxial stretching, the absorbed peak of C-H of-C(CH3)=CH-gourp, associated with the crystal structure of NR, shifted to higher wavenumber at lower strain by extracting from the FTIR spectra. Also, the strain-induced crystallization behavior of NR/STU vulcanizates occurred at low strain of about A=3revealed by XRD analysis. Based on the Classical Elastomer Theory and Tube Model Theory, the results mentioned-above originated from the modification reaction of rubber molecular chain by STU, improving the local motion of molecular chain and the diameter of entanglement tube and favoring the orientation along the stretching direction and configuration rearrangement of the molecular chain, which facilitated the occurence of strain-induced crystallization of NR/STU vulcanizates under lower strain.On the other hand, the influence of SiO2particles modified by STU on the structure-properties relationship of NR vulcanizates was investigated systematically. STU could react with silanol groups on the surface of SiO2particles under heating to form a covering layer, restraining the crosslinking-block effect of SiO2particles for NR compounds effectively and promoting the dispersion of SiO2particles in NR vulcanizates and inter-phase adhesion between rubber and filler. Based on the XRD experiment and Mooney-Rivlin mechanical theory model, the regularity of the rubber molecular chains was introduced by the physical adsorption of rubber molecular segments to the surface of SiO2particles. These physical links exhibit freedom of movement under stretching, leading to the orientation of rubber molecular chain along the stretching direction and relaxation, which advanced the "over-strain" of molecules and accelerated the strain-induced crystallization of vulcanizates to take place under lower strain. Considering the crystallization index, loading of filler and crosslinking density in the NR composites, the mechanical properties of rubber-filler composites depended on the rubber-filler inter-phase adhesion strongly under high strain. The stronger the inter-phase adhesion was, the good mechanical properties of composites may be achieved.