Nitrosamine-safe thiuram disulfide and benzothiazole sulfenamide as a synergistic pair of accelerators for the vulcanization of rubber

The Morphology, Mechanical and Dynamic Properties, Fire Hazard and Toxicity of Chloroprene and Butadiene Rubber Composites Cross-Linked with Zinc

This paper presents the influence of zinc on the cross-linking process, mechanical and dynamic properties, morphologies and balance of thermal degradation of blends containing chloroprene rubber (CR) and butadiene rubber (BR). The novel aspect of this research is a comprehensive approach presenting a new curing agent for the CR/BR blends to increase their cross-linking density and final properties, including non-flammability and low fire hazard. This is due to the need to find an alternative to zinc oxide, which is the standard curing agent for chloroprene rubber. The regulations of the European Union enforce a significant limitation on the use of this compound in elastomer technology, due to its harmful effect on aquatic organisms. In this paper, the CR/BR composites were cured with zinc and filled with natural silica fillers (sillitin or chalcedonite) or synthetic silica filler (aerosil). The investigation focused on the morphology characterization of the obtained compounds, their cross-linking degree, swelling, mechanical and dynamic properties, fire hazard and toxicity. The structure of cured CR/BR blends was characterized via scanning electron microscopy (SEM). The fire resistance studies were performed using cone calorimetry or oxygen index methods, whereas toxicity tests were performed with the use of the FB-FTIR (fluidized bed reactor coupled with FTIR analyzer) method. The results showed that obtained CR/BR products were characterized by satisfactory final properties. The properties determined by the oxygen index and cone calorimetry methods, including the behaviors of the tested CR/BR vulcanizates in fire conditions, showed that the produced compounds were characterized by a low fire hazard and can be classified as non-combustible rubber products. However, the toxicity of the decomposition products, determined at 450, 550 and 750 °C, was very high.

Renewable Vanillin-Based Thermoplastic Polybutadiene Rubber: High Strength, Recyclability, Self-Welding, Shape Memory, and Antibacterial Properties

The vast majority of traditional vulcanized rubber products are insoluble and infusible, which is difficult to reprocess and biodegrade, resulting in black pollution. In addition, although most rubber materials based on covalent adaptive networks (CANs) can achieve structural reconstruction, the lack of traditional vulcanization system leads to a decline in strength. In this study, biobased vanillin derivatives (PV) were synthesized to cross-link the commercially available 1,2-polybutadiene rubber precursor to construct imine-based CANs, thereby fabricating a resource-renewable, recyclable, and degradable high-performance rubber material. Due to the rigid tripod structure of the PV, the tensile strength of the material can achieve as high as 16.24 MPa, ranking among the best in the field of recyclable polybutadiene-based materials. Benefiting from the dynamic imine unit, the "dynamic covalent bridge" can be re-established to repair the damaged network and endow the material with excellent weldability. And, shape memory faculty of the material was proved and depicted. Moreover, this material displayed excellent antibacterial property originates from the introduced Schiff-base structure. By mixing with graphene, the application of action sensors can also be achieved.

Two-Layer Rubber-Based Composite Material and UHMWPE with High Wear Resistance

The aim of the study is the development of two-layer materials based on ultra-high-molecular-weight polyethylene (UHMWPE) and isoprene rubber (IR) depending on the vulcanization accelerators (2-mercaptobenzothiazole (MBT), diphenylguanidine (DPG), and tetramethylthiuram disulfide (TMTD)). The article presents the study of the influence of these accelerators on the properties and structure of UHMWPE. It is shown that the use of accelerators to modify UHMWPE leads to an increase in tensile strength of 28–53%, a relative elongation at fracture of 7–23%, and wear resistance of three times compared to the original UHMWPE. It has been determined that the introduction of selected vulcanization accelerators into UHMWPE leads to an increase in adhesion between the polymer and rubber. The study of the interfacial boundary of a two-layer material with scanning electron microscopy (SEM) and infrared spectroscopy (FTIR) showed that the structure is characterized by the presence of UHMWPE fibrils localized in the rubber material due to mechanical adhesion.

Toward Mechanically Robust Crosslinked Elastomers through Phase Transfer Agent Tuning the Solubility of Zn2+ in the Organic Phase

Zinc oxide (ZnO), which is toxic to aquatic organisms, is widely used as an activator in the rubber industry. The reduction of ZnO content is one of the efficient ways to tackle ecological environment impacts induced by ZnO. However, the incompatibility between Zn2+ and organic matrix inhibits the solubility and activity of Zn2+ in the organic matrix, causing the heavy use of ZnO. This work develops a phase transfer agent with Zn2+-philic structure and oleophilic structure to increase the solubility of Zn2+ in the organic matrix. The phase transfer agent and Zn2+ form coordination interactions, while the hydrophobic chains of phase transfer agent and organic matrix form hydrophobic interactions. The above two interactions improve the solubility and activity of Zn2+ in the organic matrix, contributing to the formation of crosslinking network. Through the phase transfer agent strategy, we obtain the mechanically robust elastomers, and the samples with low ZnO content still maintain the superior properties. This work provides an efficient way to reduce ZnO content without sacrificing the performance of elastomers.

The Synergistic Effect of Dibenzyldithiocarbamate Based Accelerator on the Vulcanization and Performance of the Silica-Filled Styrene-Butadiene Elastomer

This work focused on studying the effect of dibenzyldithocarbamate vulcanization accelerator on the curing characteristics and performance of styrene–butadiene elastomer (SBR) filled with nanosized silica. A dibenzyldithocarbamate derivative was applied as an additional accelerator to enhance the efficiency and the rate of sulfur vulcanization in the presence of two other accelerators, i.e., N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and/or 1,3-diphenylguanidine (DPG). Furthermore, the possibility of reducing the amount of zinc oxide (ZnO) and the elimination of CBS and DPG from elastomer compounds using dibenzyldithiocarbamate accelerator was tested. Dibenzyldithocarbamate derivative applied with other accelerators (especially CBS) effectively enhances the efficiency of SBR vulcanization by reducing the optimal vulcanization time and increasing the crosslink density of the vulcanizates despite the lower amount of ZnO. Moreover, vulcanizates with dibenzyldithocarbamate demonstrate higher tensile strength while having a smaller content of CBS or DPG compared to the reference SBR composites. Thus, the synergistic effect of dibenzydithiocarbamate derivative on the vulcanization and performance of SBR was confirmed. Furthermore, dibenzyldithocarbamate derivative enables the amount of ZnO to be reduced by 40% without harmful influence on the crosslink density and performance of the vulcanizates. Finally, it is possible to replace CBS with a dibenzyldithiocarbamate derivative without the crosslink density and tensile strength of the vulcanizates being adversely affected, while improving their resistance to thermo-oxidative aging.