Mechanical Properties Of Natural Rubber Vulcanizates Research Articles

Effect of Nonisoprene Degradation and Naturally Occurring Network during Maturation on the Properties of Natural Rubber.

It well-known that the superior performance of natural rubber (NR) compared to its synthetic counterpart mainly derives from nonisoprene components and naturally occurring network, which varies during the progress of the maturation and thereby results in technically graded rubber with different properties. However, identifying the roles of these two factors in the forming of excellent performance of NR is still a challenge as they change simultaneously during the maturation process. Here, influences of naturally occurring networking and nonisoprene degradation on the components, structures and properties of NR were systematically investigated by tailored treatments of maturation. It was found that the maturation-induced formation of natural network structure contributes to the increase in initial plastic value, Mooney viscosity and gel content for un-crosslinked NR, while the decomposition of nonisoprene components plays a dominant role in improving the mechanical properties of vulcanized NR. Stress-strain curve and Mooney-Rivlin analysis demonstrate that the biodegradation of the nonisoprene components significantly boost the vulcanization process, which significantly increases the number of chemical cross-link networks and effective cross-link density of the material, greatly improving the mechanical properties of NR vulcanizates. This resulted in the tensile strength of TSR 10CV being able to reach 22.6 MPa, which is significantly improved compared to 15.8 MPa of TSR 3CV. Evidenced by tubular model fitting, the increase in chemical cross-linking points effectively reduces the movable radius of the molecular chain under dynamic loading, making the molecular chain more difficult to move, which suppresses the entropy change under dynamic loading and consequently endows NR excellent dynamic mechanical properties. This resulted in a significant decrease in the temperature rising of TSR 10CV to 3.3 °C, while the temperature rising of TSR 3CV was still as high as 14.5 °C. As a minor factor, the naturally occurring network improves the mechanical properties of vulcanizates in the form of sacrificial bonds.

Impacts of filler covalent and non‐covalent modification on the network structure and mechanical properties of carbon–silica dual phase filler/natural rubber

The carbon–silica dual phase filler (CSDPF) was modified by bis (3‐triethoxy‐silylpropyl) tetrasulphane (Si69) and 1‐allyl‐3‐methyl‐imidazolium chloride (AMI), respectively. The natural rubber (NR) vulcanizates filled with modified CSDPF were fabricated through mechanical mixing followed by a high‐temperature cure process. The impacts of filler surface modification on the curing characters, crosslinked junctions, network structure, and mechanical properties of NR vulcanizates were investigated. The results showed that the Si69 interacted with CSDPF through covalent bond, while the interaction between AMI and CSDPF was hydrogen bond. Both modifications increased the cure rate of CSDPF/NR compounds as well as the crosslinked degree, compared with those of pristine CSDPF/NR compound. The modifications improved the dispersion of CSDPF in NR matrix. The covalent modification by Si69 caused a limited movement of NR chains in the CSDPF surface, which contributed to a greater tensile modulus of Si69‐modified CSDPF/NR. However, the higher content of mono‐sulfidic crosslink and the poorer content of strain‐induced crystallization in the NR matrix led to a slight increase of tensile strength and tear strength of Si69‐modified CSDPF/NR, compared with those of CSDPF/NR. The tensile modulus of AMI‐modified CSDPF/NR had a lower value due to a faster polymer chain motion on the CSDPF surface. However, the tensile and tear strength of AMI‐modified CSDPF/NR increased significantly because of the increase of mono‐sulfidic crosslink, strain‐induced crystallization, and the existed hydrogen bond between CSDPF and NR. Copyright © 2015 John Wiley & Sons, Ltd.

Structure and Thermal Stability of Natural Rubber Reinforced with <i>In Situ</i> 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.

Smart Green Composite: Effect of Cuttlebone Particle on the Mechanical Properties of NR Vulcanizates

The purpose of this study was to investigate the reinforcement effect of the cuttlebone particle on the mechanical properties of natural rubber (NR) vulcanizates. The extraction of organic compound from the cuttlebone was prepared demineralization and deproteinization methods. The obtained chitin had been characterized by Fourier Transform Infrared Spectroscopy (FTIR). The mechanical and thermal properties of NR composite materials were investigated. The reinforcement effect of cuttlebone particle in NR composite was comparable with that of commercial CaCO3 as a reference. After thermal aging, the tensile properties of composite material were decreased. The presence of organic component was speculated to give a good interaction effect of cuttlebone particles to NR as revealed by Scanning Electron Microscopy (SEM).

Properties and Application of Low‐Molecular‐Weight High‐Trans‐1,4‐Polyisoprene

A low‐molecular‐weight trans‐1,4‐polyisoprene (LMTPI) was synthesized with hydrogen as a molecular weight regulator. The effect of hydrogen pressure on the molecular weight of TPI was investigated. Increasing the H2 pressure effectively reduced the molecular weight of TPI. When LMTPI was used as plasticizer in styrene‐butadiene rubber (SBR), the scorch time and optimum‐curing time of the SBR compounds increased compared with that of SBR compounds containing aromatic oil. The rebound resilience and anti‐fatigue of SBR vulcanizates were improved. The effect of pelletized sulfur (LMTPI as carrier) on the mechanical properties of natural rubber (NR) vulcanizates was studied and compared with that of powder sulfur and a commercial pelletized sulfur (Rhenogran S‐80). The pelletized sulfur could improve the processing properties of the NR compound. It also could effectively improve the flexing resistance and retain good mechanical properties of NR vulcanizates.

Effect of Kenaf Fibres on the Properties of Natural Rubber Vulcanizates

The mechanical properties and swelling behaviour of natural rubber (NR) vulcanizates loaded with kenaf fibres were studied using (hydrated silica, resorcinol and hexamethylene tetramine) as the adhesion system and compared with those of NR vulcanizates loaded with synthetic polyester short fibres (viscose). The effect of fibre content on the afore mentioned mechanical properties of NR vulcanizates was also studied before and after ageing. The kenaf fibres showed a higher reinforcing effect than that of synthetic polyester fibres and improved the rheological properties. Scanning electron microscopy was used to investigate the surface texture of unreinforced and reinforced vulcanizates.