Preparation of constant viscosity natural rubber with mercaptan

Constant viscosity natural rubber has been prepared using mercaptan. The accelerated storage tests indicate that the storage hardening phenomenon of natural rubber can be inhibited by mercaptan. The amount of mercaptan (2-mercaptobenzothiazole) of 0.14 phr is sufficient to prepare constant viscosity natural rubber and the storage hardening numbers of constant viscosity NR in both Mooney viscosity and Wallace plasticity are less than 4. The processing properties and anti-oxidative behavior of CV-NR can be improved, although the mechanical properties of vulcanizates decreased slightly as compared to those of natural rubber. The results further support the hypothesis that the abnormal groups in natural rubber molecules are aldehyde groups and are responsible for the hardening of natural rubber.

Structure and thermal stability of natural rubber reinforced with in situ generated zinc sorbate

In situ prepared zinc disorbate (ZDS) in natural rubber (NR) by the reaction of zinc oxide and sorbic acid was used to reinforce the dicumyl peroxide-cured NR vulcanizate. The changes in mechanical properties of NR vulcanizates after ageing and were determined and the structures and thermal stability of vulcanizates were also analyzed using scanning electron microscope and thermal gravimetric analyzer. The change ratios in tensile strength and elongation at break of NR vulcanizate with theoretic formation of ZDS of 21phr can be increased to -33 from -44 and -27 from -38 after ageing and the initial weight loss temperature of NR vulcanizate can be increased for about 7°C as compared to un-reinforced NR vulcanizate, indicating that the antioxidative behavior and thermal stability of NR can be improved significantly with theoretic formation of ZDS of 21phr.

Reinforcement of natural rubber with core-shell structure silica-poly(Methyl Methacrylate) nanoparticles

A highly performing natural rubber/silica (NR/SiO2) nanocomposite with a SiO2 loading of 2 wt% was prepared by combining similar dissolve mutually theory with latex compounding techniques. Before polymerization, double bonds were introduced onto the surface of the SiO2 particles with the silane-coupling agent. The core-shell structure silica-poly(methyl methacrylate), SiO2-PMMA, nanoparticles were formed by grafting polymerization of MMA on the surface of the modified SiO2 particles via in situ emulsion, and then NR/SiO2 nanocomposite was prepared by blending SiO2-PMMA and PMMA-modified NR (NR-PMMA). The Fourier transform infrared spectroscopy results show that PMMA has been successfully introduced onto the surface of SiO2, which can be well dispersed in NR matrix and present good interfacial adhesion with NR phase. Compared with those of pure NR, the thermal resistance and tensile properties of NR/SiO2 nanocomposite are significantly improved.

Rubber latex yield and physiology of rubber tree with tea tree oil treatments

To examine the effects of tea tree oil on rubber latex yield and the resulting latex physiological parameters of rubber tree （Hevea brasiliensis），clean water and 20%，40%，60%，80% and 100% of tea tree oil were applied on the tapping cut of rubber trees. The data were analyzed by Duncan test and its results showed that when compared to clean water （ck），80% and 100% of tea tree oil stimulation significantly promoted rubber latex yield（P＜0.05）. In addition，the latex physiological parameters changed with the sucrose content（P＜0.01），magnesium ion content （P＜0.01） and inorganic phosphorus content （P＜0.01） of latex significantly increasing and thiol content significantly deceasing （P＜0.01）. The effect of tea tree oil treatments on rubber yield was similar to the impact of 0.5% ethrel stimulation. However，compared to ethrel stimulation，100% tea tree oil treatment significantly increased dry rubber and sucrose contents （P＜0.01） and decreased thiol content （P＜0.01）. Thus，tea tree oil treatment involved different latex yield promotion mechanisms than that of ethrel stimulation.

Thermal degradation kinetics and mechanism of epoxidized natural rubber

Thermal resistance is one of the most dominative properties for polymer materials. Thermal degradation mechanisms of epoxidized natural rubber (ENR) and NR are studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The results show that, the introduction of epoxy groups into the NR molecular main chain leads to a remarkable change in the degradation mechanism. The thermal stability of ENR is worse than that of NR. For the first thermooxidative degradation stage, the thermal decomposition mechanism of ENR is similar to that of NR, which corresponds to a mechanism involving one-dimensional diffusion. For the second stage, the thermal decomposition mechanism of ENR is a three-dimensional diffusion, which is more complex than that of NR. Kinetic analysis showed that activation energy (E?), activation entropy (?H) and activation Gibbs energy (?G) values are all positive, indicating that the thermooxidative degradation process of ENR is non-spontaneous.

Preparation and characterization of natural rubber/silica nanocomposites using rule of similarity in latex

Rule of similarity and latex compounding techniques were combined for the first time to prepare natural rubber/nanosilica (NR/SiO2) nanocomposite with core-shell nanosilica-poly (methyl methacrylate) (SiO 2-PMMA) particles and PMMA-modified natural rubber matrix (NR-PMMA). The microstructure of SiO2 and nanocomposites with different SiO 2 contents was characterized by fourier transform infrared spectroscopy (FTIR); the morphology of nanocomposites was investigated with scanning electron microscopy (SEM); the tensile strength was characterized by tensile testing machine and the thermal stability of composites was studied by thermal gravimetric analysis. Results showed that PMMA chains have successfully grafted onto the surface of SiO2, and the core-shell SiO 2-PMMA nanoparticles and NR-PMMA latex have been perfectly incorporated. SiO2-PMMA nanoparticles are evenly distributed over the NR matrix with an average size in the range of 60-100 nm at the low content (SiO2? 3 wt%), while aggregations are apparently observed when 5 wt% SiO2 is loaded. In addition, NR/SiO2 composities possess a considerable improvement in ageing resistance compared with the pure NR. The tensile strength of composite increases from 6.99 to 12.72 MPa, reaching the highest value at a 0.5 wt% SiO2 loading, and then the figure decreases gradually because of the aggregation of SiO2 nanoparticles. It is anticipated that the reported process is to provide a simple and economic way for preparing NR composites.

Effect of ultrasonic wave on latex production and quality of rubber tree

The effects of ultrasonic wave on tapping surface of ‘PR107’ rubber tree were studied. Daily production and cumulative production of latex were measured to estimate the effects of ultrasonic wave on latex production. The solid substance content, dry rubber content and mechanical stability of latex were determined to study the effects of ultrasonic wave on latex quality. Results showed that ultrasonic wave could increase both daily and cumulative production of latex and maintain latex basic quality. The daily production of latex was increased and appeared two peaks both in the ultrasound-treated rubber tree and the one with no treatment. The first peak appeared on the fifth day, and the latex production by ultrasound was 212.34 ml and the control was 141.75 ml The second peak appeared with the production 266.59 ml on the seventeenth day by ultrasound, while the control appeared on the thirteenth day with production of 193.5 ml. The latex cumulative production of ultrasound-treated trees was 209.56 ml higher than that of control in one month. There was little change in solid substance content and dry rubber content between different ultrasonic time. The best mechanical stability of latex was obtained by ultrasound-treating the rubber tree for 4-6 min. it was proved that the ultrasound was helpful in improving the latex production and quality. The application of ultrasonic wave on rubber tree is novel, and its mechanism is worth further research.