Material Property Modeling of Ground Tire - Recycled Polymer - Natural Fiber Composite

Book excerpt: Composites made of thermoplastic with ground tire rubber (GTR) have attracted increasing interest as recycled rubber with reclaimed polymer offer advantages of better tensile properties, better toughness, low energy requirement for molding, more economical, and provides an opportunity to add value to disposed material. Thermoplastic material studied herein is primarily recycled linear low-density polyethylene (RLLDPE) from agricultural films with 10% being virgin LLDPE. The agricultural plastic obtained from scrap grain bags contain naturally oxidized macromolecules that provides better adhesion with GTR. In addition, hemp fiber processed from crop residue provides reinforcement to enhance the tensile strength and stiffness of the composite. The research characterizes the behavior of a value-added thermoplastic elastomer (TPE) of varying compositions of recycled thermoplastic, virgin thermoplastic, GTR, and natural fiber formed under different processing parameters. From the literature review examining value-added thermoplastic elastomer composites, sufficient data was obtained for conducting further analysis. Tensile properties (tensile strength (TS), elongation at break (EB), Young's modulus (YM)) were identified as dependent variables. Processing parameters including GTR percentage (RP), fiber percentage (FP), GTR particle size (RS), compatibiliser percentage (CO%), type of blending (BT), type of specimen procedure (SP) along with properties of matrix material were identified as independent variable. Using multiple regression analysis with stepwise regression, statistical model with continuous and categorical independent ii variables having significant effect on the outcome variable were derived. Models were derived that explain the variations in each dependent variable with minimum error and higher correlation. Model verification was two-fold using test data from literature as well as experimental data. Both set of data compared favorably with values predicted by the model having coefficient of determination value higher than 0.75 for each property. The derived equations suggest that tensile properties have nonlinear relationship with the property parameters. Inverse correlation of tensile properties with GTR percentage and rubber size proves varying detrimental effect. Incorporating natural fiber up to 30% enhances the stiffness and tensile strength at the expense of about 90% reduction in elongation at break. Tensile properties of thermoplastic matrix were found to explain about 15% variation in tensile strength and stiffness of composite material. To validate the model with experimental data, tensile specimens were prepared by compression molding with GTR percentage ranging from 10% to 70%. The required properties were achieved by performing the tensile test following the ASTM D412-16 standard. The evaluation of experimental data revealed conformity with predicted data within the allowable error range. This research investigated the mechanical properties of value-added thermoplastic elastomer material and created statistical models for tensile properties. Using the well derived equation, engineers can select the material, their composition, and different processing parameters to achieve desired properties to manufacture products for various applications.