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

Abstract

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.

Cross-Linking Characteristics, Morphology, Dynamics, and Mechanical and Thermal Properties of Polychloroprene/Polybutadiene/Nano-Zinc (CR/BR/nZn) Compositions with Reduced Fire Hazard

“…It was expected that these silica properties and the presence of functional groups on its surface would enable the generation of filler-elastomer matrix interactions (especially silica-CR). The differences between highly active silica and biofillers (chalcedonite and sillitin) are a very interesting aspect of this paper, which is a continuation of our earlier published research [32]. In conclusion, the aim of this work was to produce new compositions of polychloroprene with polybutadiene (CR/BR), which is unconventionally cross-linked in the presence of nano-zinc (nZn) and characterized by increased flame resistance.…”

“…The test was performed according to PN-ISO 4589-2. The oxygen index (OI) was calculated from Formula (7) [23][24][25][26][28][29][30][31][32]:…”

“…The standard uncertainty of the measured heat release rate was ±10%. Based on the results, the fire hazard was calculated as the fire propagation rate (1/t flashover ) from Formula (8) [30,32]:…”

“…The toxicity of gaseous products of thermal decomposition of the CR/BR/nZn vulcanizates was determined using a laboratory set. The method used to determine toxicity (toxicometric indices) is described in detail in the previous articles of this study's authors [32,41,42].…”

“…In addition, through the appropriate selection of rubbers, it is possible to obtain better processability of rubber blends, as well as to reduce the production costs of elastomeric goods. The unique properties of polychloroprene mean that it is often mixed with such rubbers as natural rubber [18,19]; carboxylated acrylonitrile-butadiene rubber [20]; styrene-butadiene rubber [21][22][23]; and, recently, with butadiene rubber as well [24][25][26][27][28][29][30][31][32]. Vulcanizates made of polychloroprene are characterized by their good tensile strength, resistance to weather conditions, thermal resistance up to 100 • C, and good resistance to ozone and non-polar solvents.…”