New Concept of Co-Agents for Scorch Delay and Property Improvement in Peroxide Vulcanization

Abstract

Peroxide cure is an important and widely used cure system for rubber. Several properties obtained via peroxide vulcanization are superior and not achievable with sulfur vulcanization, e.g.: aging resistance, no reversion and low compression set. However, other properties such as tensile strength and dynamic properties, are inferior to those of sulfur vulcanizates. The use of co-agents in peroxide cure leads to a certain extent to improvement in mechanical properties such as tensile strength. Nevertheless the properties are still inferior with respect to mechanical/dynamical properties of sulfur-cured articles. If these properties can be improved, the range of applications of peroxide cure in the rubber industry can be significantly broadened.Scorch is a common problem in peroxide cure, especially for injection molding and extrusion applications. Several additives can help to improve scorch safety, however, they always result in a lower peroxide efficiency, thus inferior vulcanizate properties.In the present study a new concept of co-agents for peroxide vulcanization is introduced. This new concept consists of the use of a combination of a bismaleimide type co-agent, like N,N'-m-phenylenedimaleimide (BMI-MP), and a sulfur containing compound, like dipentamethylenethiuram tetrasulfide (DPTT). This combination provides scorch safety and at the same time improves the mechanical properties of the vulcanizates. Within the bismaleimide type co-agents N,N'-p-phenylenedimaleimide (BMI-PP) provides better mechanical properties than BMI-MP. The concentration of coagent and sulfur containing compound have a big influence on the scorch time and on the mechanical properties. Optimal properties are reached with 4 phr of co-agent and 0.7 to 0.96 phr of sulfur containing compound. * Corresponding

Cure retardation of peroxide‐cured silica filled natural rubber influenced by organosilane

“…Typically, at high curing temperatures, TESPT would release sulfur that is capable of increasing the cure efficiency in sulfur vulcanization system . In this work where peroxide is used as a curing agent, the formation of crosslinks through the free radicals might be obstructed by the released sulfur from TESPT, giving rise to a decrease in cure efficiency with increasing TESPT content . In addition, the crosslink density results measured via equilibrium swelling technique are presented in Fig.…”

“…The result may be explained by the reduced crosslink density as a consequence of the consumption of peroxy radicals in the presence of TESPT as mentioned earlier. It has been reported that every mole of the elemental sulfur would destroy about 1 mole of peroxide . Although the increase of TESPT content results in the reduced crosslink density and modulus, other mechanical properties such as tensile strength, elongation at break and tear strength are improved.…”

TPVs PA/NBR: sistema de reticulação e propriedades

“…A morfologia é definida durante a vulcanização dinâmica e depende, entre outros fatores, do sistema de cura que, além do agente principal, pode envolver coagentes [1,23,24] . Grimma et al [25] ao reticular borracha EPDM da forma convencional, com peróxido de dicumila (DCP) combinado com enxofre ou agentes doadores de enxofre, como o 2-mercapto benzotiazol (MBT), obtiveram uma borracha termofixa com alto módulo e alta resistência à ruptura. Observaram, no entanto, que um dos inconvenientes para este sistema, é uma redução na resistência ao envelhecimento da borracha em temperaturas elevadas [26] , atribuída as pontes sulfídicas.…”

“…Só o aumento significativo do DCP combinado com o aumento no teor de BMI, TPV DB 3.4_1.1 resultou em um material com bom desempenho mecânico, apresentando uma tensão de ruptura de 11,4 MPa e alongamento de 175%. Estes resultados estão em concordância com os publicados por Grimma et al [25] , onde o mesmo abordou a importância do enxofre e BMI na reticulação da borracha termofixa de EPDM com peróxido de dicumila. tamanho dos domínios da fase elastomérica dispersa na matriz plástica, melhor é o desempenho mecânico do TPV.…”

Influence of a crosslinked system on the morphology and properties of TPVs based on PA/NBR

“…In some cases, coagents are the alternatives applied to improve the crosslinking3 in thermoset rubbers manufacturing, for which sulfur is an adequate choice because of its low cost. With respect to physical mechanical properties, it was observed that the use of sulfur or the sulfur donor agent MBT (2‐mercaptobenzothiazole) as a coagent for dicumyl peroxide (DCP) contributes to the curing process, resulting in TPVs with high modulus and tensile strength but with less resistance to aging 8. A more recent work8 described the use of bismaleimide and sulfur or a sulfur donor as coagents of dicumyl peroxide in the crosslinking of EPM rubber.…”