Guayule natural rubber composites: impact of fillers on their cure characteristics,dynamic and mechanical behavior

Guayule natural rubber (GNR) is an alternative resource of Hevea natural rubber (HNR) with 99.9% cis content in its 1,4-polyisoprene chemical backbone. In this study, compounds were formulated independently with four different reinforcing fillers such as carbon black (HAF), precipitated silica (VN3), fume silica (FUM) and nanofly ash (NFA) for the advancement of GNR based products. The cure characteristic, dynamic-mechanical performance and mechanical properties of GNR composite were studied with the reinforcing effect of different fillers on GNR. The cure characteristic results demonstrated that HAF and FUM silica filled compounds had more processing safety than VN3 and NFA filled compounds. Viscoelastic parameters of the vulcanizates were studied by dynamic mechanical analysis to estimate the glass transition characteristics and dynamic behavior. The higher storage modulus of FUM silica vulcanizate was an indication of superior filler reinforcing nature and improved rolling resistance than other filled systems. Additionally, HRTEM analysis also proved the better filler dispersion ability of FUM silica in GNR matrix. The mechanical properties were studied with a variation of each filler loading of 8, 16, and 32 phr in GNR vulcanizates. The tensile strength of each filled system increased with an increase of filler content from 8 to 32 phr. In comparison, FUM silica GNR vulcanizates exhibited better mechanical properties, therefore, it was considered as a better structure-performance composite than those of HAF, VN3 and NFA filled composites.

     

Phosphorylated cardanol prepolymer grafted guayule natural rubber: an advantageous green natural rubber

Natural rubber (HNR), produced from Hevea Brasiliensis, is being considered as the major source of 99.9% 1,4-cis-polyisoprene. Till date, this grade of natural rubber is not manufactured synthetically even using sophisticated solution polymerization techniques and utilizing the most advanced catalyst systems. Rubber industries have been continuously thriving for an alternative as well as an additional source of natural rubber to compensate for the reduction in production of Hevea natural rubber and to reduce the consumption of petroleum-based rubbers. The present study deals with chemical grafting of phosphorylated cardanol prepolymer (PCP) onto the main chain of guayule natural rubber (GNR), which could impart inherent multifunctional characteristics to the rubber. The grafting of PCP onto GNR was carried out successively using benzoyl peroxide as a free radical initiator in the solution stage and the grafting parameters have been optimized through the Taguchi method using grafting efficiency and percent grafting. Grafting of PCP onto GNR (PCP-g-GNR) was confirmed through UV–Visible, FTIR, NMR and GPC analysis. Thermal behavior of PCP-g-GNR indicates a significant increase in thermo-oxidative stability and it also displays a slight depression of glass transition temperature as compared to GNR. The viscoelastic characteristics of GNR also alter and cure characteristic improves drastically in giving rise to improved processability after grafting of the PCP. The unfilled PCP-g-GNR vulcanizates show approximately similar physico-mechanical properties with 5 phr processing oil as plasticized GNR vulcanizates. Therefore, PCP-g-GNR can be used in rubber industries as gum rubber materials as it reduces the usage of processing aids significantly.     

Improved dispersion and physico-mechanical properties of rubber/silica composites through new silane grafting

3-Octanoylthio-1-propyltriethoxysilane (a new silane) grafted styrene butadiene rubber/ silica composites were prepared in the present work, where grafting weight percentage of the base rubber (0%, 2%, 4%, and 6%) and filler content of the composites (0, 5, 15, 35, and 50 phr) were varied to investigate dispersion of the filler in the rubber. A detailed quantitative study of morphology-physical property relationship of the composites using dispersion degree parameter was carried out. Pronounced improvement of dispersion was observed with increasing grafting weight percentage of the base rubber. A mechanism of polymer to filler interaction was shown by Fourier transform infrared spectroscopy. The dispersion rate constant from the torque-time curve increased with the grafting percentage. Bound rubber content and Payne effect measurement indicated improved rubber-filler interaction for the grafted rubber compound. A relation between low strain modulus of the composites and grafting percentage was proposed. The nanoindentation studies gave further insight into the results. Other physico-mechanical properties at different grafting weight percentages at particular filler loading (50 phr) and at different filler loadings at a particular grafting weight percentage (4%) were evaluated. The improved mechanical and dynamic mechanical properties with increasing grafting weight percentage are an indication that this methodology could be used in green tire application.