Carbon black migration between ground tire rubber (GTR) and rubber matrix is essential in developing high-performance rubber/GTR composites. In this work, carbon black N220 (surface area: 107.1 m²/g, particle size: 20–25 nm) and N660 (surface area: 33.1 m²/g, particle size: 49–60 nm) were used as the reinforcement fillers for styrene-butadiene rubber (SBR) blended with reclaimed GTR. The combined effects of GTR devulcanization level and carbon black grade on the properties of SBR/GTR composites were investigated considering curing characteristics, thermal stability, physico-mechanical properties, dynamic mechanical properties, swelling behavior, and morphology. The results showed that, regardless of GTR devulcanization level and carbon black grade, application of GTR resulted in deterioration of mechanical properties compared to a reference sample without GTR. It was observed the reinforcement effect of carbon black in SBR/GTR composites was more visible with higher devulcanization level of GTR and lower particle sizes of carbon black fillers. SBR/GTR composites reinforced with carbon black N220 were characterized by tensile strength in the range of 15.3–16.3 MPa and abrasion resistance in the range of 120–123 mm³, which justify their potential application in the manufacturing of technical rubber goods or footwear.

Epoxidized natural rubber with 50 mol% epoxide (ENR-50) was compounded with zinc chloride (ZnCl₂) and subjected to torque response analysis using a moving die rheometer. It was found that different ZnCl₂ concentrations (3, 5, 7, 9, and 12 millimoles (mmol)) mixed in ENR-50 exhibited positive torque responses, prompting further molecular characterization using Fourier transform infrared spectroscopy. The results indicated distinct absorption peaks at wavenumbers of 442 and 809 cm^–1, which signify the presence of –O–Zn–O– coordination linkages. The curing characteristics of ENR and ZnCl₂ compounds showed that increasing ZnCl₂ content resulted in higher minimum and maximum torque values, but also led to a decrease in scorch time and cure rate index (CRI). Moreover, higher ZnCl₂ concentrations enhanced the strength properties (tensile strength, moduli, stiffness, toughness, and hardness), crosslink densities, dynamic shear moduli, initial modulus during relaxation experiments, and thermal resistance, as evidenced by temperature scanning stress relaxation (TSSR), thermogravimetric analysis, and dynamic mechanical analysis. However, an increase in ZnCl₂ content led to a reduction in elongation at break due to the higher crosslink density within the coordination networks in the ENR matrix, which resulted in the movement constraint of the rubber vulcanizate.

Research into sustainable packaging materials has gained increasing importance due to the pressing environmental concerns related to plastic waste. The present study focused on developing a sustainable paper coating based on modified natural rubber (NR) latex filled with gelatin (GT). The graft copolymer latex of NR and poly(vinylbenzyl chloride) bearing quaternary ammonium groups, abbreviated as NR-g-QPVBC, was first synthesized. GT was then incorporated into the latex, and the combination of these materials resulted in a heat-sealable film with good tensile properties and a water barrier. The ionic crosslinking of the latex film was achieved by the reaction with ethylenediaminetetraacetic acid (EDTA). Heat-sealing studies of the NR-g-QPVBC latex film filled with GT (NR-g-QPVBC/GT) revealed its heat-sealability at 160 °C. Scanning electron microscope (SEM) analysis further confirmed the diffusion of the chains across the interface during heat sealing. Dip coating was a method for depositing latex film on kraft paper. The paper coated with the NR-g-QPVBC/GT latex showed a significant increase in dry and wet-tensile strength compared to the uncoated paper. The sealing process was optimized to achieve a heat-seal strength of 755.31 N/m at a dwell time of 3 s and a temperature of 160 °C. The research's practical application was demonstrated by transforming the coated paper into various heat-sealable bags using a handheld bag sealer.

The structure and property relationships of graft copolymers from natural rubber (NR) and polymethyl methacrylate (PMMA) crosslinked with a phenolic resin were investigated. The NR grafted with PMMA (NR-g-PMMA) having different grafting levels was initially prepared by emulsion polymerization before compounding and vulcanization. Then, proton nuclear magnetic resonance and transmission electron microscopy were used to verify the resultant NR-g-PMMAs. The graft copolymers crosslinked with phenolic resin exhibited improvements in various properties. Tensile modulus and tensile strength increased at least 18 and 95%, respectively, over the un-grafted counterpart and further improved with grafting percentage, while the elongation at break decreased accordingly. Storage modulus in rubbery plateau increased while tanδ peak height decreased with PMMA content. Moreover, the thermal stability of the graft copolymers was also improved over that of the plain NR at least 23 °C, depending on MMA contents. These improvements are tentatively attributed to the strong adhesion between NR and PMMA phases, based on interactions between the functional groups of PMMA and hydrogen bonding between phenolic resin crosslinker and PMMA. The results clearly suggest that the phenolic resin could be an effective crosslinker for NR-g-PMMA.

The influence of the type of mechanical recycling of waste rubber particles on the tensile properties of waste/natural rubber blends has been investigated. The wastes originating from ground tyre rubber (GTR) had been treated by two distinct processes: cryo-grinding and high shear mixing (HSM). For both processes, the resulting composites show enhanced stiffness and strength for all strain rates and temperatures tested. This is attributed to both the reinforcing effect of the waste as well as the nucleation ability of the wastes on strain induced crystallization (SIC) in the natural rubber (NR) matrix. Cryo-grinding was shown to provide the finest particle size with an average diameter of 34 μm, while the HSM process was found to show an elastic modulus of aggregated GTR powder of 7 MPa at 1 Hz at room temperature. Within these characteristics, the NR/GTR blends using the HSM process show the best tensile performance under single loading, with the highest strength and highest ability to crystallize under strain. Under cyclic loading, NR/GTR blends using cryo-ground GTR particles show the best performance, which we ascribed to their ability to better distribute and accommodate the stress from one cycle to another owing to their finest size. Both explored recycling techniques provide the natural/waste rubber blends interesting properties such as mechanical reinforcement and strain-induced crystallization ability under various testing conditions.