Multifunctional Peroxidegas Alternative Crosslink Agents for Dynamically Vulcanized Expoxidized Natural Rubber/Polypropylene Blends

Commonly used dicumyl peroxide (DCP) in combination with coagent, triallyl cyanurate (TAC), as a crosslinking agent is well acceptable for dynamically vulcanized rubber phase of thermoplastic vulcanizates (TPVs). However, it generally produces volatile decomposition products, which cause a typical unpleasant smell and a blooming phenomenon. In this work, influence of two types of multifunctional peroxides: 2,4-diallyloxy-6-tert-butylperoxy-1,3,5-triazine (DTBT) and 1-(2-tert-butylperoxyisopropyl)-3-isopropenyl benzene (TBIB), on properties of TPVs based on epoxidized natural rubber (ENR)/polypropylene (PP) blends were investigated. The conventional peroxide/coagent combinations, i.e., DCP/TAC and tert-butyl cumyl peroxide (TBCP)/-methyl styrene (-MeS) were also used to prepare the TPVs for a comparison purpose. The TPVs with multifunctional peroxide, DTBT, provided good mechanical properties and phase morphology of small dispersed vulcanized rubber domains in the PP matrix which were comparable with the DCP/TAC cured TPVs. However, the TPVs with TBIB/-MeS and TBCP/-MeS showed comparatively low values of the tensile properties as well as rather large phase morphology. The results were interpreted by three main factors: the kinetic aspects of the various peroxides, solubility parameters of respective peroxide/coagent combinations in the ENR and PP phases, and the tendency to form unpleasantly smelling byproducts

NR/PP Thermoplastic Vulcanizates: Selection of Optimal Peroxide Type and Concentration in Relation to Mixing Conditions

Thermoplastic vulcanizates (TPVs) from natural rubber (NR) and polypropylene (PP) were studied, prepared by dynamic vulcanization during melt mixing, using various peroxides to crosslink the rubber phase. The objective was to find a proper balance between degree of crosslinking of the rubber and degradation of the PP-phase, and the tendency of the peroxide to form smelly by-products, in particular acetophenone. Four types of peroxides were investigated: 2,5-dimethyl-2,5-di(tert-butyl-peroxy) hexyne-3 (DTBPHY), 2,5-dimethyl-2,5-di(tert-butyl-peroxy) hexane (DTBPH), di(tert-butylperoxyisopropyl) benzene (DTBPIB), and dicumyl peroxide (DCP), at two mixing temperatures: 160 and 180°C for a 60/40 NR/PP TPV. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 160°C, whereas the other two require a higher temperature of 180°C. The best mechanical properties, tensile strength, elongation at break and compression set are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the NR and PP. Unfortunately, these two peroxides form more smelly by-products than DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these NR/PP TPVs

Thermoplastic vulcanizates based on epoxidized natural rubber/polypropylene blends: Selection of optimal peroxide type and concentration in relation to mixing conditions

A proper balance between degree crosslinking of ENR and degradation of PP-phase, and the tendency of peroxide to form smelly by-products, in particular acetophenone are investigated on a 60/40 ENR/PP TPV. Four types of peroxides were used at two mixing temperatures: 160 and 180 oC. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 160 °C, whereas the other two type of peroxides require a higher temperature of 180 °C. The best mechanical properties are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the PP and ENR. Unfortunately, these two types of peroxides form more smelly by-products and blooming than those of the DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these ENR/PP TPVs

Effect of different types of peroxides on rheological, mechanical, and morphological properties of thermoplastic vulcanizates based on natural rubber/polypropylene blends

Influences of various types and concentrations of peroxides on the properties of thermoplastic vulcanizates based on natural rubber/polypropylene (PP) blends were investigated. The objective was to find a proper balance between the influences of degree of crosslinking of the rubber and degradation of the PP phase on the rheological, mechanical, and morphological properties. The typical crosslinking temperature and crosslink efficiency and also relative amounts of decomposition products of each peroxide play an important role in the properties of the TPVs. In this work, the TPVs prepared with DCP or DTBPIB give a superior overall balance of properties relative to the TPVs crosslinked with DTBPH or DTBPHY