Rubber Research Institute

In this study, the effects of halogen-free flame retardant additives aluminum hydroxide (ATH) and zinc borate (ZnB) on the mechanical and fire resistance properties of glass fiber-reinforced unsaturated polyester (GF/UP) composites were systematically investigated. ATH and ZnB additives (5%, 10% and 15%) were added to the polymer matrix both alone and as hybrids (1:1). The composites were produced by hand lay-up method and characterized by flexural strength, Charpy impact strength and UL-94 horizontal burning tests. In terms of mechanical performance, while addition of ATH and ZnB decreased the flexural strength, increased the impact strength of the composites. 5% ATH additive provided the highest flexural strength (479.98 MPa) among the fire retardant added composites. As the ATH additive increased, the impact strength also increased and a value of 241.03 kJ/m2 was reached with 15% ATH addition. While horizontal burning rate of the composite without additive was about 20.15 mm/min, it decreased with the use of flame retardant additives. Moreover, composite with hybrid additives exhibited the best burning rate performance as 10.23 mm/min. Post-combustion analyses revealed that ATH formed a porous alumina structure and ZnB formed a glassy and dense borate phase. The combination of these two structures formed a more compact and crack-resistant surface residue, limiting heat and oxygen transfer. Overall, the UL-94 horizontal burning results indicate a synergistic trend for the ATH/ZnB hybrid formulations, evidenced by the lowest burning rate and a more coherent post-combustion residue, offering significant potential for the design of sustainable and fire-resistant composite materials for automotive, structural and electrical applications.

Fungal leaf anthracnose, caused by Colletotrichum species, is a major leaf disease of rubber trees, significantly reducing global natural rubber yields. To explore sustainable and safe biological control strategies, eight bacterial strains were isolated from rubber tree tissues, demonstrating antagonistic activity against Colletotrichum pathogens (C. siamense and C. australisinense). Among these, WSR1 exhibited the most pronounced antifungal effect, with inhibition rates of 87.64% and 89.03% against C. siamense and C. australisinense, respectively. Genomic analysis identified WSR1 as Bacillus velezensis. In pot experiments, WSR1 exhibited preventive efficacy of 77.24% and 73.42% for C. siamense and C. australisinense induced anthracnose, respectively, with therapeutic efficacy of 42.28% and 45.57%. WSR1 compromised the integrity of the cell walls and membranes of both C. siamense and C. australisinense, while inducing reactive oxygen species (ROS) accumulation within the hyphae. Additionally, WSR1 enhanced rubber tree resistance to anthracnose by activating defense-related enzymes, including phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD). Plate assays and genomic analysis revealed that WSR1 secretes fungal cell wall-degrading enzymes (cellulases, pectinase, and protease) and siderophores. Furthermore, LC-MS and gene cluster analysis confirmed the synthesis of antagonistic secondary metabolites, such as surfactin, macrolactin H, and fengycin. This study represents the first identification of Bacillus velezensis as a potential biocontrol agent against rubber tree anthracnose, offering a promising candidate for the eco-friendly management of rubber tree diseases.

The homeobox transcription factor (TF) superfamily includes the WUSCHEL-RELATED HOMEOBOX (WOX) family, which plays a critical role in adaptive plant growth. Specifically, WOX regulates stem growth in plants, with stems serving as the structural framework for laticifers in Euphorbia hirta. However, the number of WOX gene family members in the E. hirta genome has not been reported. In this study, we identified 14 EhWOX genes in E. hirta and characterized their physicochemical properties, chromosomal locations, phylogenetic relationships, conserved motifs, gene structures, promoter cis elements, gene ontology (GO) enrichment, tissue-specific expression patterns, and subcellular localization. Chromosomal mapping indicated their distribution across nine chromosomes. Phylogenetic analysis classified these genes into three evolutionary clades. Promoter cis-element analysis identified abundant light-responsive, hormone-responsive, and stress-responsive elements. GO enrichment suggested their broad involvement in diverse biological processes. Additionally, RNA-seq revealed high expression levels of EhWOX4-6 and EhWOX14 in stems. Furthermore, RT-qPCR confirmed tissue-specific expression in stems. Moreover, experimental evidence confirmed the subcellular localization and autoactivation capability of some WOX proteins that may be involved in stem development. Overall, this study provides a comprehensive characterization of the candidate EhWOX genes and provides a foundational resource for future functional investigations into their possible roles in stem and laticifer biology.

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Natural rubber is a polymer that has been widely used in various industrial applications because of its high flexibility. In this study, vulcanizates were developed from SiO2-reinforced natural rubber with added Gd₂O₃. Vulcanizate composites containing 0, 5, and 10 phr of Gd₂O₃ were fabricated to evaluate the combined effect of inorganic fillers and gamma irradiation. All composites were irradiate with gamma rays at a dose of 100 kGy and were evaluated for their chemical characteristic, swelling behavior, and crosslink density. Fourier Transform Infrared (FTIR) analysis showed that gamma irradiation induces significant structural changes in the natural rubber vulcanizate. These changes were confirmed by the emergence of new absorption peaks assigned to O-H and C=C groups in the FTIR spectra. Swelling and crosslink density measurements showed that gamma irradiation increased the vulcanizate’s crosslink density, indicating the formation of a stiffer polymer network. On average, the crosslink density increased by approximately 11%, accompanied by a 9.07% decrease in swelling. These finding highlight the synergistic role of SiO2 and Gd₂O₃ under gamma irradiation in improving the integrity of natural rubber based composites.

Abstract Binders are crucial for polymer‐bonded explosives (PBX), directly impacting their properties. While synthetic polymer binders perform well, their high cost limits large‐scale application. In contrast, natural rubber offers abundant availability and low cost as an alternative binder, significantly reducing preparation costs. This study employed molecular dynamics methods to systematically investigate the physical compatibility between natural rubber and various plasticizers. It also quantitatively analyzed how plasticizer content affects the glass transition temperature ( T g ) and mechanical properties. Results indicated that dioctyl sebacate (DOS) had the best compatibility with natural rubber. Furthermore, the system's T g decreased significantly with increasing plasticizer content. Both the bulk modulus (K) and shear modulus (G) decreased, though K's reduction was less pronounced than G's. This resulted in an increase in the K/G ratio and Poisson's ratio. This phenomenon indicates that plasticizers significantly enhance natural rubber's ductility by weakening intermolecular forces and reducing friction between molecular chains. Simultaneously, the lowered T g increases material flexibility, thereby improving impact resistance. This study provides valuable guidance for developing low‐cost, high‐performance PBX binder systems.