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

Comparative properties of silica- and carbon black-reinforced natural rubber in the presence of epoxidized low molecular weight polymer

This work investigates the effect of epoxidized low molecular weight natural rubber (ELMWNR) in silica- and carbon black-filled natural rubber (NR) compounds on processing and mechanical and dynamic mechanical properties. The ELMWNRs with different mol% epoxide content were prepared from depolymerization of epoxidized NR using periodic acid in latex state to have a molecular weight in a range of 50 000–60 000 g/mol. Their chemical structures and actual mol% of epoxide were analyzed by 1H NMR. The ELMWNRs were added to the filled NR compounds as compatibilizers at varying loadings from 0 to 15 phr. The addition of ELMWNR decreases compound viscosity and the Payne effect, that is, filler–filler interaction, of the silica-filled compound. In the silica–silane compound and the compound with 28 mol% epoxide (ELMWNR-28), the compound viscosities are comparable. The optimal mechanical properties of silica-filled vulcanizates are obtained at the ELMWNR-28 loading of 10 phr. In contrast, the addition of ELMWNR to a carbon black-filled compound shows only a plasticizing effect. The incorporation of ELMWNR into NR compounds introduces a second glass transition temperature and affects their dynamic mechanical properties. Higher epoxide contents lead to higher loss tangent values of the rubber vulcanizates in the range of the normal service temperature of a tir

Degradation behavior during mixing of silica-reinforced Natural Rubber: Changes of the dynamic responses

High shearing forces and temperature are applied during mixing of silica filled natural rubber (NR) for tire tread applications, in order to achieve the best possible filler-rubber interactions and a sufficient silanization reaction of the silica. Both thermal and mechanical conditions in the mixing process can lead to polymer degradation. The present work investigates NR degradation during mixing via monitoring changes of its viscoelastic behavior. Silica-filled NR compounds prepared by using various dump temperatures were investigated taking pure NR and gum or unfilled NR compounds as references. Chain scission and chain recombination as two competitive reactions affect the molecular weight and chain architecture. Chain scissions most likely contribute more to the viscous response whereas chain recombination and interactions contribute to the elastic component of viscoelasticity. Increasing viscous responses of masticated pure NR and gum compounds are observed with higher dump temperature as measured by Mooney stress relaxation rates, changes of storage and loss moduli, resp. tan delta with frequency, and large amplitude oscillatory shear (LAOS). Chain scission causes a lower molecular weight, but a broader molecular weight distribution and more branching. For silica-filled NR compounds, the elastic response rises at high dump temperatures above 150 degree C due to crosslinking and/or branching. The long-chain branching index (LCB) rises with increasing dump temperature. Furthermore, deterioration of tensile properties of the corresponding vulcanizates are observed which is attributed to degradation and chain modifications