Full definition
Organic peroxides are a crucial class of chemical curing agents used primarily in the rubber industry as an alternative to traditional sulfur curing methods. These agents are effective in creating thermally stable carbon-carbon (C-C) bonds, which are significantly shorter and stronger than the polysulfidic bonds formed during sulfur vulcanization. The use of organic peroxides results in compounds that exhibit improved heat resistance, a higher reversion temperature, and superior compression set properties. Moreover, they provide enhanced electrical insulation without causing sulfur bloom, which can lead to discoloration in finished products. This makes them particularly suitable for applications where aesthetic and functional integrity is paramount, such as in food-grade, medical, and electrical components.
Commonly used organic peroxides include dicumyl peroxide (DCP), di-tert-butyl peroxide (DBPH), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (BIPB). DCP is the most widely utilized, containing 40-45% active ingredients and decomposing at temperatures around 150-170°C. In contrast, DBPH offers a higher decomposition temperature, making it ideal for continuous vulcanization processes. BIPB is often employed in the curing of fully saturated rubbers like EPDM and silicone, where traditional sulfur curing is ineffective due to the absence of double bonds.
Despite their advantages, organic peroxides come with certain limitations. They typically exhibit lower tear and fatigue resistance compared to sulfur-cured rubbers. Additionally, the curing process is susceptible to oxygen inhibition, necessitating the use of positive pressure or an inert atmosphere to achieve optimal results. The incorporation of co-agents such as TAC, TAIC, or TMPTMA is common to enhance cross-link density and overall efficiency. The typical dosage of organic peroxides during the curing process ranges from 1 to 5 parts per hundred rubber (phr), depending on the specific application and desired characteristics of the final product.