Elastomer vulcanizates based on natural rubber (NR), NR reclaim (NRR) and layered silicates were compounded in an internal mixer and cured on a two-roll mill. Cure characteristics and mechanical properties of samples based on 50NR/50NRR reinforced with Cloisite 20A, Cloisite 30B and Nanolin DK1 were compared to those of conventional NR/NRR/kaolin microcomposites. Due to the light/soft nature of organoclays suppressing the friction forces, the minimum torque values decreased in the presence of organoclays, whereas the crosslink density, evidenced by the difference between the maximum and minimum torque values, increased in all samples and scorch times shortened by 37% to a minimum in the presence of Nanolin alkaline/catalytic role in the cure reaction. Fatigue resistance improved by about 10% benefiting the crack tips blunting/energy consuming hysteresis mechanisms motivated by the organoclays among which Nanolin DK1 provides the most efficient dispersion/distribution of nanolayers by faster intragallery crosslinking reactions that pushes the stacks apart. Higher states of dispersion in this sample would also promote strain-induced crystallization under deformation responsible for the improvements seen in the modulus and elongation-at-break. Two-step mixing sequence further improved the compound performance due to the dispersion state progress confirmed by X-ray diffraction and transmission electron microscopy (20% in fatigue resistance and 53% in tensile modulus). In-situ compatibilization through bis(triethoxysilylpropyl)tetrasulfide bi-functional silane coupling agent also promoted modulus and fatigue resistance. However, a prolonged scorch time was observed due to the blinded NR cure-reactive sites as well as steric hindrance of large functional groups in the presence of this coupling agent.

The effects of solvent, temperature, time, weight percent of catalyst on the rate and mechanism of cyclization of natural rubber (NR) was studied in toluene and xylene solutions having tin tetra chloride catalyst (SnCl4). Iodometric titration show, with 8% SnCl4 (based on polymer weight) cyclization occurs, leaving 27.4% of the total unsaturation. Infrared spectra of cyclized NR show decreased absorption intensity at 840 and 780 cm-1 which are characteristic bands of the linear polymer and the appearance of absorption band at 890 cm-1 as cycles were formed By using this chemical modification, NR is transformed into a resinous thermoplastic, hard, non rubbery cyclized material with much less unsaturation than the original rubber, which could find commercial applications as adhesives, printing inks, industrial and ship paints.

Compatibility is a serious problem in silica-added natural rubber (NR) because of the difference in the polarities of silica and NR. Thus, a coupling agent, such as silane, or a compatibilizer must be incorporated. In this work, amine-functionalized NR was synthesized by an in situ epoxidation process using performic acid and later modified with hexamethylene diamine (HMDA) by a ring-opening reaction. The effects of amine-modified epoxidized NR (ENR-HMDA) content on the cure characteristics, physical and mechanical properties of various NR blends (NR/ENR-HMDA) without filler were studied. ENR-HMDA enhanced the vulcanization process. The maximum torque of compounds increased with the corporation of ENR-HMDA and scorch time and cure time decreased. The cure rate index of NR/ENR-HMDA increased by 98%. All vulcanized rubber blends showed the strain-induced crystallization at high extension. Mechanical properties and crosslink density of the blends were higher than those of NR and NR incorporated with unmodified ENR. Tensile strength was 61% and 43% higher than that for NR and NR/ENR, respectively. The NR/ENR-HMDA blends showed a single Tg that indicated the miscibility of both components. The developed ENR-HMDA compound can be used to improve the compatibility of NR and fillers which would enable the fabrication of a wide range of rubber products.

Biocomposites have received a great deal of attention in academic research and industry because they are environmentally friendly and produce less carbon footprint, especially with the use of natural fibers. Nevertheless, compatibility issues require complexity to overcome the field of composite materials. Biocomposites based from poly(lactic acid) (PLA), natural rubber (NR) and kenaf were prepared by melt blending in an internal mixer. PLA/NR composition was fixed at 90/10 (wt/wt), while kenaf loading varied from 0 to 20 phr. The aim of this work was to study the effect of epoxidized natural rubber (ENR) and poly(methyl methacrylate) (PMMA) addition as co-compatibilizers in the biocomposites. Rheological behavior during mixing showed higher processing torque and stabilization torque after compatibilization. The mechanical properties deteriorated with increasing kenaf loading in biocomposites. Incorporation of rigid kenaf particles within matrix resulted in poor stress transfer and restricted chain movement. Addition of compatibilizer increased the tensile strength, elongation-at-break, tensile modulus and impact strength. Upon compatibilization, the interfacial interaction between kenaf and matrix is improved, enabling more efficient stress transfer, thus higher mechanical properties. Water absorption of biocomposites was studied by immersion in distilled water for 30 days. At high kenaf loading, water absorption percentage increased due to hydrophilic nature of kenaf. After compatibilization, water absorption decreased due to better interfacial adhesion. Morphological study of tensile fractured and impact fractured surface of biocomposites was investigated using scanning electron microscopy. Less fiber pull-out, more work of fracture and less interfacial gap between fiber and matrix were observed for compatibilized biocomposites, indicating enhanced interfacial adhesion. Addition of ENR and PMMA in PLA/NR/KF biocomposites was able to pare down the compatibility issues, contributing to improvement of overall properties.

The role of various vulcanizing systems on the curing characteristics, mechanical properties, morphology and dynamic mechanical analysis of natural rubber and recycled ethylene-propylene-diene rubber blends was investigated. Accelerated sulfur-vulcanizing systems (semi-EV and EV), peroxide, and mixed sulfur/peroxide-vulcanizing systems (semi-EV/peroxide and EV/peroxide) were observed and compared. The blends were processed on a two-roll mill, and a fixed amount of carbon black was also incorporated. Amongst the blends, accelerated sulfur-vulcanizing systems exhibited higher torques, state of cure, tensile strength and elongation-at-break, in comparison with the peroxide-vulcanizing system, whereas the tensile modulus, hardness and cross-link density showed lower trend. In the mixed sulfur/peroxide-vulcanizing systems, it showed intermediate behavior to the individual sulfur- or peroxide-vulcanizing systems. This was associated to the interference of peroxide during the cross-linking formation. SEM micrographs of semi-EV-vulcanizing system exhibited more roughness and cracking path indicating that higher energy was required towards the fractured surface. The high cross-link density observed from the swelling study could be verified from the storage modulus (E′) where peroxide vulcanized blends provided a predominant degree of cross-linking followed by semi-EV, semi-EV/peroxide, EV and EV/peroxide-vulcanizing systems, respectively. The glass transition temperature (Tg) depicted at maximum peak of mechanical loss factor (tand max), indicating that semi-EV-vulcanizing system showed highest Tg value. The Tg values can be ordered as semi-EV>peroxide>semi-V/peroxide>EV>EV/peroxide-vulcanizing systems. The Tg of rubber vulcanizates can be increased due to the restriction of molecular movement such as cross-link density.