Toughness improvement of LLDPE/PP blend by GTR incorporation

Abstract

Introduction: Approximately 80 % of waste rubber comes from end of life tires. Land filling causes serious environmental troubles due to the impermeability and hollowed shape of tires. The global concern about the continue accumulation of discarded tires and the developing ecological awareness demand new ways and regulations to solve this problem, encouraging the scientific community to explore alternative solutions to reuse this waste material. However, the reuse or recycling of tires is not a simple task. Besides the several materials that tires are constructed from, rubbers used in tires are vulcanizated, having a cross-linked structure that makes them elastic, insoluble and infusible thermoset materials that cannot be reprocessed, as is the case of thermoplastic materials. It is therefore of critical importance to find technologically feasible and cost-effective methods for tires recycling. A possible industrial recycling method of tires is their downsizing to obtain a powder called ground tyre rubber (GTR). On the other side, a commonly used practice in industry to improve mechanical behavior and toughness of a polymer is to incorporate rubber particles into it (1). Then, adding GTR to a polymeric material, so high-quality products can be shaped at an acceptable cost, seems to be an attractive option. Compound of waste tire rubber with polymers allows to lower the cost of the final products while contributing to the world’s 3R (reduce, reuse, and recycle) notion: reducing the amount of virgin polymer used, reusing the tire rubber, and recycling the waste tires (2). In this work, we report results of adding GTR to a LLDPE/PP blend (the most abundant thermoplastics in municipal waste), with the aim of obtaining a completely recycled composite with improved toughness. Methods: GTR particles in different size ranges – lower than 300 µm, 300-500 µm and 500-800 µm – and in various percentages – 5, 10 and 15% – were incorporated to a 75% LLDPE / 25% PP blend in a twin screw extruder, and plaques obtained by injection molding. Materials were characterized by several techniques such as Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), conventional uniaxial tensile testing, and fracture tests. Results & Discussions: We found that GTR particles did not affect the microstructure of the thermoplastic matrix. The tensile behavior of the ternary materials was slightly affected by the composition of the mixture: the mechanical behavior became less rigid and more ductile; this being directly related to the elastic nature of the rubber particles. However, large differences were found in the fracture performance of the ternary blends, when compared with the matrix blend. In addition, different mechanical behaviors were observed that varied according to the relative percentage of the particles and their size. GTR greatly influenced both energies involved in crack initiation and in crack propagation, as well as mechanisms developed during deformation and crack evolution. Conclusions: Fracture tests seem to be a sensitive and adequate tool to estimate the influence of particles in polymer blends, much more than simple tensile tests. The fracture behavior of LLDPE/PP blends can be modified by the sole incorporation of GTR particles, leading to a toughness increase in the ternary blends, because of the diversification of deformation mechanisms. Keywords: Fracture toughness, fracture mechanisms, recycled tires, thermoplastic blend References Karger-Kocsis, J., L. Meszaros, and T. Barany. Ground Tyre Rubber (GTR) in Thermoplastics, Thermosets, and Rubbers. Journal of Materials Science. 2013; 48(1): 1-38. Ramarad, S., M. Khalid, C. T. Ratnam, A. Luqman Chuah, and W. Rashmi. Waste Tire Rubber in Polymer Blends: A Review on the Evolution, Properties and Future. 2015. Progress in Materials Science 72:100–140.