Polyisoprene, with a high degree of polymerization, is the main component of natural rubber. In the industrial production process, it is necessary to adjust the length of the macromolecule of polyisoprene to improve its plasticity. It is thus of vital importance to explore the effect of the degree of polymerization of polyisoprene on its properties, e.g., mechanical property and thermal property. Molecular dynamics simulations link microstructure to macroscopic properties. In this paper, Moltemplate was used to establish polyisoprene models with different degrees of polymerization, and the mechanical properties of polyisoprene under uniaxial tension were analyzed under an OPLS all-atom force field. The results showed that the strength and elastic modulus of the material increased with the increase in the degree of polymerization of the molecular chain. In the process of tensile loading, the non-bonded potential energy played a dominant role in the change of the total system potential energy. Then, the thermal conductivity of polyisoprene with different degrees of polymerization was calculated by the non-equilibrium molecular dynamics method (NEMD). The thermal conductivity of PI was predicted to converge to 0.179 W/(m·K). The mechanism of thermal conductivity of the polymer containing branched chains was also discussed and analyzed. The research content of this paper aims to provide theoretical support for improving the mechanical and thermal properties of natural rubber base materials.

In order to solve the problem of poor interfacial adhesion between aramid fibers and a rubber matrix, an efficient and mild modification method was proposed via polydopamine and mercapto functionalized graphene oxide (GO) and carbon nanotube (CNTs) hybrids synergistically modifying aramid fibers. GO and CNTs were firstly stacked and assembled into unique 3D GO-CNTs hybrids through π-π conjugation. Then, the mercapto functionalization of the assembled 3D GO-CNTs hybrids was realized via the dehydration condensation reaction between the hydroxyls of GO and the silanol groups of coupling agent. Finally, the mercapto functionalized 3D GO-CNTs hybrids were grafted onto the aramid fibers, which were pre-modified by polydopamine through the Michael addition reaction mechanism. The surface morphology and chemical structures of GO-CNTs hybrids and fibers and the interfacial adhesion strength between fibers and rubber matrix were investigated. The results showed that the modification method had brought about great changes in the surface structure of fibers but not generated any damage traces. More importantly, this modification method could improve the interfacial strength by 110.95%, and the reason was not only the reactivity of functional groups but also that the 3D GO-CNTs hybrids with excellent mechanical properties could effectively share interfacial stress. The method proposed in this paper was universal and had the potential to be applied to other high-performance fiber-reinforced composites.

The binding amount of rubber and reinforcing filler directly affects the quality of rubber products. The effect of aromatic solvent oil (S-150) on the binding amount of rubber and reinforcing filler was studied. In order to determine the suitability of rubber after adding S-150, the curing characteristics, physical performance and tensile properties of rubber samples were tested and analyzed. Meanwhile, the microstructure of the composite was analyzed by scanning electron microscopy (SEM). The test results showed that the binding amount of rubber and reinforcing filler was increased after adding S-150. The density and Shore A hardness were decreased. When carbon black was 80 phr, after adding 40 phr of S-150, the rebound resilience of rubber increased by 13% on average, and the elongation at break increased by 88% on average. When white carbon black was between 10-70 phr, after adding 65 phr of S-150, the rebound resilience of rubber increased by 9% on average, and the elongation at break increased by 51% on average. Modulus at 100% and tensile strength were decreased. Meanwhile, it could be judged from the microstructure results that the reticulation space inside the rubber was increased, the agglomerate particles were relatively uniform, and no bubbles or holes were observed. The mechanism that S-150 could increase the binding amount of rubber was analyzed according to the like-dissolves-like principle. This research achievement could lead to improvements in the quality of rubber products and promote their practical application.