Crosslinking Density Of Natural Rubber Research Articles

Study on Crosslink Density of Natural Rubber with Different Initial Moisture Contents Dried by Microwave

In this work, the crosslink density of uncured natural rubber with different initial moisture contents, 3.80%, 10.05%, 19.76%, 23.68%, respectively, dried by microwave at frequency of 2450MHz was studied using nuclear magnetic resonance spectrometer. Seen from the results, the effect of initial moisture content of wet natural rubber on crosslink density and processability were obvious. With the increment of initial moisture content of wet natural rubber, the crosslink density of natural rubber after microwave dried with the frequency of 2450MHz decreased gradually. The crosslink density and A(Mc) of natural with the lower initial moisture content was bigger compared with natural rubber with the higher initial moisture content.

Influence of Carbon Black on Crosslink Density of Natural Rubber

Vulcanization and reinforcement are two important factors contributing to the properties of vulcanized rubber. In order to investigate the influence of carbon black (CB) on chemical crosslinking, three groups of samples with different crosslink densities were prepared. In each group with the same crosslink density, different amounts of CB were introduced. Data fitting showed that delta torque (ΔM = M H–M L, the difference between the highest and lowest torques during curing) in the cure curves of each group had a good linear relationship with CB load and extrapolation of the fitting lines almost intercepted the x coordinate at the same value, which indicated that CB had no influence on the chemical crosslinking of the rubber. To verify the above result, a series of nonfilled natural rubber (NR) vulcanizates with different crosslink densities were studied using equilibrium swelling and the swelling ratios were compared with those of corresponding CB filled rubbers with the same sulfur and accelerator amount. The results of both the equilibrium swelling and NMR relaxation parameter measurements showed that CB filled vulcanizates had higher apparent crosslink densities than those of unfilled ones due to the strong interaction between rubber molecules and the surface of the CB particles. The swelling ratios of filled rubbers had a parallel relationship with those of the unfilled ones which indicated that CB had little influence on chemical crosslink density introduced by chemical vulcanization.

Effect of 3‐propionylthio‐1‐propyltrimethoxylsilane on structure, mechanical, and dynamic mechanical properties of NR/silica composites

AbstractBlocked mercaptosilane possessing two functionally active end groups can chemically react with both silica and rubber leading to significant improvement in silica‐filled vulcanizate products. The effect of the novel blocked mercaptosilane (3‐propionylthio‐1‐propyltrimethoxylsilane) (called hereafter PXT) on the structure, mechanical, and dynamic mechanical properties of NR/silica composite were studied. Equilibrium swelling test and scanning electron microscope (SEM) indicate that PXT is able to enhance the crosslinking density of natural rubber (NR)/silica composites and the dispersion of silica in matrix. Mechanical measurement of properties show that PXT can strengthen the reinforcement of silica for NR vulcanizate. In the presence of PXT, the resistance to flex cracking, abrasion and dynamic compression fatigue, and heat build‐up of NR/silica composites can be improved substantially. For the application of automotive tire, it also obtains high‐skid resistance and low‐rolling resistance simultaneously at 2 phr of the PXT concentration. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers

Multispin moments edited by multiple-quantum NMR: application to elastomers

The spin system response to the five-pulse sequence used for measurements of double-quantum and triple-quantum buildup curves is evaluated in the initial excitation/reconversion regime. The multispin dipolar network that is present also in many soft solids like elastomers was considered. It is proved rigorously that the relevant quantity for analysis of double-quantum build-up curves in the initial regime is the second van Vleck moment. The higher-order moments edited by double-quantum as well as higher-order coherences in the multiple-quantum build-up experiments are different from van Vleck moments. These results can be applied to compare 1H residual moments edited by double-quantum and triple-quantum experiments with those measured by other NMR methods. The sensitivity of multiple-quantum coherences to the changes in the values of residual dipolar couplings for cross-linked natural rubber under uniaxial elongation is also discussed. Under such conditions 1H second van Vleck moments were measured for different elongation ratios of a cross-linked natural rubber. Moreover, 1H triple-quantum edited moments were also measured for the same sample under uniaxial compression. The dependence of the second van Vleck moment and the time of the maximum of the double-quantum buildup curve on the cross-link density of natural rubber measured at low magnetic field was also investigated.

Kinetics of Diffusion of Styrene Monomer Containing Divinyl Benzene through Vulcanized Natural Rubber

Diffusion and sorption of styrene monomer containing divinyl benzene as crosslinker through vulcanised natural rubber were studied in a temperature range of 25-45°C. this study is the primary step in the preparation of an interpenetrating network (IPN) based on natural rubber (NR) and polystyrene (PS) by the sequential technique, where NR is swollen in styrene monomer and its crosslinker and initiator, which is then polymerised in situ. The mechanism of diffusion was analysed and was found to follow an anomalous trend. The influence of the nature of crosslinks and crosslinking density of NR on the transport properties was examined. The diffusion coefficient was calculated and was found to be concentration dependent. Arrhenius parameters for diffusion and permeation processes and other thermodynamic parameters of sorption were estimated. The influence of the cure system, the nature of crosslinks, crosslink density, and temperature on the diffusion process were examined in detail. In the presence of crosslinker, the monomer uptake was lowered, whereas an increase in temperature activated the diffusion process. Finally, the experimental sorption results were compared with theoretical predictions.