Cyclized natural rubber (CNR) was synthesized through the acid-catalyzed reaction of natural rubber (NR) latex using sulfuric acid as a catalyst and stabilized with a non-ionic surfactant. Cyclization was evaluated by iodine numbers under varying reaction times, temperatures, and NR-to-acid ratios. Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance spectroscopy (¹H-NMR) confirmed the formation of cyclic structures in CNR molecules. Differential scanning calorimetry (DSC) showed that the glass transition temperature (T_g) of CNR increased with cyclization, indicating greater rigidity and less chain flexibility. CNR was then blended with NR and used as a compatibilizer in NR/acrylonitrile butadiene rubber (NBR)blends. It increased blend viscosity, hardness, and dimensional stability but reduced tensile strength and elongation due to its rigid cyclic domains. In NR/NBR blends, CNR outperformed a commercial homogenizer in enhancing interfacial interactions, leading to superior shear flow properties, curing behavior, and mechanical performance. This is attributed to the polar groups in CNR, which enhance intermolecular interactions and phase compatibility, resulting in finer phase morphology. This study highlights the potential of CNR as a versatile material for enhancing the performance of rubber compounds, with promising applications in advanced industrial formulations.

In this research, heat-triggered triple-shape memory polymers (TSMPs) based on the ethylene-methyl acrylate copolymer (EMA)/chloroprene rubber (CR) thermoplastic vulcanizates (TPVs) were prepared by dynamic vulcanization successfully; meanwhile, an effective and facile triple-shape memory strategy was designed to realize the efficient and stable shape fixity and recovery of two temporary shapes. The field-emission scanning electron microscope images showed that EMA/CR TPV surface was a sea-island structure with the CR particle size ranging from 3 to 6 μm. Differential scanning calorimeters and X-ray diffraction were used to investigate the crystallization behavior of both EMA and CR. These served as a significant basis for the two temporary shapes: fixity and recovery. The results of triple-shape memory tests showed that the EMA/CR TPV had excellent triple-shape memory properties, where the first shape fixity ratio was higher than 89% and both the first shape recovery ratio and second shape recovery ratio could be higher than 95%. It can be observed that the EMA/CR TPV exhibited rapid shape recovery speed with the first shape recovery time of 10 s and the second shape recovery time of 20 s, respectively. This research presents a novel approach to extending the application of TPV in the field of smart devices, endowing them with excellent mechanical and triple-shape memory properties.

Natural rubber (NR) composites reinforced with sepiolite and crosslinked with phenolic resin were prepared. Effects of compatibilizer types and contents, namely 3-aminopropyl triethoxysilane (APTES) or epoxidized NR (ENR50), on curing, tensile, strain-induced crystallization, and stress relaxation were investigated. Compared to APTES, ENR50 provided a greater compatibilizing effect in the NR composites. The ENR50 introduced strong physical and chemical interactions between sepiolite and NR, while only physical interaction was present in the APTES compatibilized composites. Stronger interaction between rubber and sepiolite improved filler dispersion, swelling resistance, and tensile strength; and delayed stress relaxation of the composite. Increased addition of ENR50 improved the modulus and tensile strength, and the greatest tensile strength was achieved at 2 phr ENR50 with a 15% improvement over composite without compatibilizer. In the case of APTES, 2 phr level enhanced tensile strength, but a further increase in APTES content degraded tensile, swelling resistance, and stress relaxation responses, due to its plasticizing effect. Moreover, ENR50 enhanced the strain-induced crystallization and delayed stress relaxation of the composites more than APTES. Weaker interaction between rubber and filler in APTES filled composites was due to having only hydrogen bonds formed between rubber and filler, in addition to crosslinks.

This work presents the use of natural rubber (NR) grafted with poly(vinyl propionate) (NR-g-PVP) as an alternative compatibilizer in silica-filled NR compounds. The effects of NR-g-PVP with 10, 20 and 30% grafting on the properties of NR compounds were studied and compared with a commercial coupling agent (bis[3-(triethoxysilyl)propyl] tetrasulfide, TESPT). NR-g-PVP was compatible with silica and NR. The NR-g-PVP reduced filler-filler interactions and increased fillerrubber interactions. The crosslink density decreased with the percentage of grafting due to the steric hindrance. The compatibilization affected the physical and mechanical properties. The interactions of NR-g-PVP with silica via hydrogen bonding and subsequent vulcanization prevented undesirable filler-filler interactions and reduced the absorption of accelerators or basic materials. It caused a good dispersion of silica in the NR matrix and improved physical and mechanical properties. A 10% grafting (G10) was suitable for the compatibilizer in a silica-filled NR compound, showing the largest improvements in tensile properties, tear strength, and hardness. However, TESPT provided better properties than G10.

Thermoplastic vulcanizates (TPVs) were prepared by blending natural rubber (NR) and polypropylene (PP) using dynamic sulfur curing systems with varying accelerator/sulfur ratios: 0.5/2.5, 1.5/1.5, and 2.5/0.5 phr, categorized as conventional (CV), semi-efficient (semi-EV), and efficient (EV). The onset of dynamic vulcanization closely corresponded with scorch time in statically cured NR compounds. Mixing torque decreased over time, reflecting reversion patterns in static curing. The CV system exhibited the highest reversion tendency due to polysulfide linkage breakdown, forming stronger but shorter crosslinks. Dynamic vulcanization induced higher reversion than static curing, influenced by shear and extensional forces. Curing systems caused crosslinking rates, reversion, and crosslink density and distribution variations. Unlike statically cured NR, PP-extracted TPVs exhibited an inverse trend in total crosslink densities and distributions; TPVs primarily comprised shorter crosslinks with opposed total crosslink densities ranked EV > semi-EV > CV. This trend is strongly correlated with superior mechanical strength, toughness, storage modulus, viscosity, and rubber elasticity in the EV-cured TPV. EV system also had the smallest vulcanized NR domains in the PP matrix.