Crosslink Density Of Vulcanizates Research Articles

Peroxide curing systems applied for cross-linking of rubber compounds based on SBR

Abstract The work was aimed at the investigation of influence of peroxide curing system on cross-linking and properties of rubber compounds based on SBR. First, the temperature of vulcanization and the amount of dicumyl peroxide on curing process and physical-mechanical properties were investigated. Then, co-agents Type I and Type II were added to the rubber formulations cured with peroxide. The results revealed that the increase in temperature leads to the acceleration of curing process while both, curing kinetics and physical-mechanical properties were influenced by the amount of peroxide. The application of Type I co-agents resulted in the acceleration of curing process and increase in cross-link density of vulcanizates, which was reflected in the increase of hardness and decrease of elongation at break. The influence of Type II co-agents on curing kinetics was negligible, while most of them caused the reduction in cross-linking degree of vulcanizates. Type I co-agents contributed to the improvement of tensile strength of vulcanizates, while the influence of Type II co-agents on tensile strength was of minor importance.

Influence of trans-polyoctylene rubber content on styrene-butadiene rubber properties

Abstract The study was focused on the investigation of trans-polyoctylene (TOR) influence on cross-linking as well as mechanical and rheological properties of rubber compounds based on styrene-butadiene rubber (SBR). SBR was compounded with different proportions of TOR in the concentration range from 0 to 30 phr. Integration of TOR into rubber leads to the prolongation of the optimum curing time and scorch time and thus the decrease of the curing rate. Higher content of TOR led to less viscous rubber due to the plasticizing effect. Cross-link density of vulcanizates was reduced, which correlates with higher elongation at break. Tensile strength and hardness of vulcanizates increased with the increasing TOR content, probably due to the increasing amount of the crystalline phase.

Study on the preparation of graphene oxide/silica/natural rubber latex composites by different processes

In this study, the graphene oxide/silica/natural latex composites were prepared by four different processes, including spray sputtering drying method, dry-ice–expansion predispersion method, mechanical stirring method, and traditional drying method. Compared to the other three methods, the spray sputtering method had higher physical mechanical properties and better silica dispersion in the rubber matrix. Meanwhile, the cross-linking density of vulcanizates prepared by the spray sputtering drying method is the largest. Compared with the compound prepared by mechanical stirring, the tensile strength, tear strength, and wear resistance property of the compound prepared by spray sputtering drying method increased by 13.6%, 31.5%, and 16.7%, respectively. The tensile strength, tear strength, and wear resistance property of the compound prepared by spray sputtering drying method increased by 27.2%, 43.6%, and 24.6%, respectively, than those prepared by dry mixing method.

Insight into vulcanization mechanism of novel binary accelerators for natural rubber

A novel TU derivative, N-phenyl-N′-(γ-triethoxysilane)-propyl thiourea (STU), is prepared and its binary accelerator system is investigated in detail. Compared to the control references, the optimum curing time of NR compounds with STU is the shortest, indicating a more nucleophilic reaction occurs. The Py-GC/MS results present that the phenyl isothiocyanate fragment still remains in the NR/STU compounds with or without extracting treatment, but no silane segment can be found in the vulcanizate with extracting treatment. Vibrations of C=S, NH and aromatic ring in FTIR experiments and a new methyne carbon peak, as well as the peaks of phenyl group of STU, in the solid state 13C-NMR experiments are found in the NR/STU vulcanizate with extracting treatment. Moreover, the crosslinking density of vulcanizates with STU evolves to lower level, indicating the sulfur atom of STU does not contribute to the sulfur crosslinking. Therefore, a new vulcanization kinetic mechanism of STU is propounded that the thiourea groups can graft to the rubber main chains as pendant groups by chemical bonds during the vulcanization process, which is in accordance with the experimental observations quite well.

Effect of Epoxidized Palm Oils Loading on the Crosslink Density and Rebound Resilience Characteristic of SBR Vulcanizates

The study about natural oils as processing aids in rubber was reported by several researchers for the past few years. The natural oils like rice bran oils, soybean oils, sunflower oils, vegetables oils and palm oils can be used as processing oils in rubber compounding [1-3]. These natural oils have been reported to have certain advantages compared to the petroleum based processing oils. In this study the potential of epoxidized palm oils (EPO) as additive and processing oils in carbon black filled styrene butadiene rubber was investigated. The main ingredients used were butadiene rubber (SBR), epoxidized palm oil (EPO) and carbon black. The vulcanized SBR rubber is then undergo several testing like swelling test, hardness and rebound resilience. An attempt was made to see whether the amount of EPO added to the SBR vulcanizates will affect the rebound resilience and swelling behaviour of the SBR vulcanizates. From this study, it was found that the compound contained higher EPO content tend to have lower rebound resilience, similar trend can be observed for hardness properties. While the crosslink density of the vulcanizates is decrease as the EPO content increases.

Investigation of electrically conductive acrylonitrile‐butadiene rubber

AbstractElectrically conductive acrylonitrile‐butadiene rubbers (NBRs) containing carbon black (CB) as conductive filler were prepared in order to investigate their electrical and mechanical properties. The effects of conductive CB loading, temperature, acrylonitrile content, crosslinking density of vulcanizates, and plasticizer on conductivity were studied. The change in electrical conductivity of NBRs with different amounts of CB showed that there is a certain critical point (percolation threshold) where a significant decrease in electrical resistivity (increase in conductivity) is observed. Mechanical properties such as tensile strength, elongation to break, and surface hardness of vulcanized NBRs were measured. It was found that the percolation threshold was 5 phr of CB for the NBR/CB composites. J. VINYL ADDIT. TECHNOL., 13:71–75, 2007. © 2007 Society of Plastics Engineers.

Thermal Aging Behaviors of Rubber Vulcanizates Cured with Single and Binary Cure Systems

Rubber compounds are crosslinked by a sulfur, peroxide, or resole cure system. The sulfur vulcanization is the most popular method. In general, an accelerated sulfur cure system consists of elemental sulfur (S8), one or two cure accelerators, and cure activators. Crosslink density of a rubber vulcanizate determines the physical properties. By increasing the crosslink density, the modulus, hardness, resilience, and abrasion resistance increase, whereas the elongation at break, heat build-up, and stress relaxation decrease. Sulfur linkages are composed of monosulfide, disulfide, and polysulfides. Sulfur linkages, especially polysulfides, are dissociated by heating and this brings about decrease of the crosslink density. Curatives remained in a rubber vulcanizate make new crosslinks and this results in increase of the crosslink density. Crosslink density of a rubber vulcanizate is changed by thermal aging. In general, crosslink density of a sulfur-cured rubber vulcanizate increases with increase of the aging temperature. However, for a rubber vulcanziate with an elemental sulfur-free cure system, the crosslink density after thermal aging at high temperatures decreased. In the present work, we studied the thermal aging behaviors of the rubber vulcanizates with single and binary cure systems which have one and two cure accelerators, respectively. The single cure system had one cure accelerator of N-tert-butyl-2-benzothiazole sulfenamide (TBBS) and binary cure system had two cure accelerators of TBBS and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane (DBTH). Scheme 1 shows the chemical structures of TBBS and DBTH. The binary cure system has faster cure rate and better reversion resistance than the single cure system. The NR vulcanizates with different crosslink densities were prepared to investigate the influence of the initial crosslink density on the thermal aging behaviors. The aging temperatures (50-90 C) and aging times (4 and 8 days) were also varied to investigate the influence of the aging temperature and time on the thermal aging behaviors. Figures 1 and 2 show variations of the crosslink density changes by the thermal aging as a function of the aging temperature. The crosslink density change was calculated by dividing the difference in the crosslink densities of the vulcanizates after and before the thermal aging by the initial crosslink density; ΔXc (%) = 100 × (Xc aged – Xc )/Xc , where the Xc aged and Xc ini indicate the crosslink densities of the vulcanizates after and before the thermal aging, respectively. The crosslink densities after the thermal aging at 50-90 C on the whole increased. The increased crosslink density after

Effects of some phenylethynylsilicon compounds on heat-curable silicone rubber—IV. Tetraphenylethynylsilane

The effects of tetraphenylethynylsilane (TPSI) as a crosslinker on heat-curable silicone rubber (HCSR) are reported. Mechanical properties, sol fractions and crosslinking density of vulcanizates have been measured. The experimental results indicate that TPSI is a good crosslinker of HCSR.