Thermoplastic elastomers blends based on linear low density polyethylene, ethylene-1-octene copolymers and ground rubber tire

http://dx.doi.org/10.4322/polimeros.2014.033 Maria Elena Leyva Instituto de Química, Departamento de Físico-Química, Universidade Federal de Itajubá Marcia Gomes de Oliveira Divisão de Processamento e Caracterização de Materiais, Instituto Nacional de Tecnologia Abstract: Blends of linear low density polyethylene (LLDPE) ethylene-1-octene copolymers (EOC), with different 1-octene (OC) content, and ground rubber tire (GRT) were prepared by melt mixing in a twin screw extruder. Five different compositions of LLDPE/EOC/GRT blends were processed in the extruder to evaluate the effect of EOC addition to the LLDPE/GRT blends. The addition of EOC to LLDPE/GRT blends improves the mechanical properties. Besides, the replacement of 5% of GRT by EOC grades (OC = 20 or 30 wt %) in the 50/50 LLDPE/GRT blend, leads to a significant increase of ultimate tensile properties. The EOC comonomer content affects the properties of LLDPE/EOC and LLDPE/EOC/GRT blends. Dynamical-mechanical analyses showed that, with the addition of EOC to LLDPE/GRT blends, the Tg of GRT and the Tg of EOC are closer. This effect is more pronounced when the EOC with the highest content of comonomer (30 wt %) is added to LLDPE/GRT blend. In this case, only one peak related to the Tg of the rubber phase can be visualized in the amorphous region. These findings indicate that EOC may act as compatibilizer agent for LLDPE/GRT blends. Keywords: Blend, linear low density polyethylene, ground rubber tire, ethylene-1-octene copolymers, compatibilizer, mechanical properties. Introduction Nowadays, there is a great concern over the environment protection and biodiversity conservation. Consequently, new policies and techniques related to energy conservation, substitution of materials obtained from non-renewable sources and adequate solid waste management have been introduced in most countries. There is a big amount of discarded tires every year in the world. In order to maintain ecological balance, it is necessary to reduce the serious environmental problem caused by waste rubber. The main recycling approach of waste rubber is to make powdered rubber[1]. Vulcanized rubber tire is available in different sizes and can be obtained by cryogenic or room temperature methods. The cryogenic process allows smaller particles to be obtained, resulting in materials with better properties with respect to those obtained through grinding at room temperature[2,3]. Ground rubber tire (GRT) is mostly used in less demanding applications. There is a need to find some value-added applications for GRT based products. Recycling of GRT by mixing with thermoplastic polymers is a perspective branch of rubber recycling. It has been used for preparation of polymer blends with thermoplastic resins in order to obtain impact-resistant plastics. However, the resulting compositions exhibit poor mechanical properties due to the insufficient adhesion between the rubber particles and the polymer matrix. Several approaches have been used in order to improve the adhesion between GRT and the thermoplastic resin[2,4,5]. Ground rubber tire has also been used for preparing thermoplastic elastomers (TPEs) and thermoplastic vulcanizates (TPVs). The major criterion for the formation of thermoplastic elastomers is that the two components must be thermodynamically incompatible, but not so dissimilar that intermixing cannot be accomplished. In order to achieve this condition, one or more compatibilizers should be introduced into the system. As incorporated into the mixture, compatibilizers can reduce the surface tension between the matrix and the disperse phase by reducing its particle size. They can also enhance adhesion between the blends components[6]. Methods of reactive and non-reactive compatibilization have been described in the literature. Reactive methods require the compatibilizers and blends components to have a reactive group which can form in situ primary chemical bonds. The formed compatibilization agent reduces the interfacial tension between the immiscible blend components, enhances the adhesion between the phases and, as a consequence imparts to the blend satisfactory mechanical properties. In physical blending, the compatibilizing agent is chemically synthesized prior to the blending operation and added to the blend as a non-reactive component. Due Corresponding author: Marisa Cristina Guimarães Rocha, Instituto Politécnico, Universidade do Estado do Rio de Janeiro, CP 97282, CEP 28601-970, Nova Friburgo, RJ, Brazil, e-mail: Polímeros, vol. 24, n. 1, p. 23-29, 2014 23 - Marisa Cristina Guimarães Rocha Departamento de Materiais, Instituto Politécnico, Universidade do Estado do Rio de Janeiro TECHNICAL-SCIENTIFIC PAPERS Thermoplastic Elastomers Blends Based on Linear Low Density Polyethylene, Ethylene-1-Octene Copolymers and Ground Rubber Tire Rocha, M.C.G. et al. - Thermoplastic elastomers blends based on linear low density polyethylene, ethylene-1-octene copolymers and ground rubber tire to its chemical and molecular characteristics it is able to locate at the interface, reduces the interfacial tension between the blends components and promotes adhesion between the phases[6]. Several attempts have been made in order to compatibilize GRT and thermoplastic blends. Reactive and non-reactive compatibilization methods, GRT surface modifications based on acid treatments, UV or gamma irradiation, plasma or corona charge, and new methods for preparation of these blends such as: solid-state shear pulverization and solid state mechanochemical millings have been described in the literature[2,7,8]. The resulting materials present mechanical properties more or less similar to those presented by thermoplastic elastomers. Various thermoplastics have been investigated, either neat or scrap. Polyethylene is one of the most used polymers in these blends. Hrdlicka et al.[9] tested several approaches in order to improve the mechanical properties of the GRT and low density polyethylene (LDPE) blends. Combination of mastication of ground rubber prior to use and incorporation of ethylene-propylene-diene terpolymer (EPDM) for compatibilization led to obtaining properties similar to those presented by thermoplastic vulcanizates materials. Partial crosslinking of LDPE employing dicumyl peroxide and a sulfur system was also studied. Peroxide cure gave positive results only for basic blend of ground rubber and LDPE and sulfur cure system led to a moderate increase of the tensile strength. Nevatia et al.[10] found that utilization of a sulfuraccelerator system provides better results than a peroxide system for dynamic crosslinking of scrap LDPE and reclaimed rubber blends. Kumar et al.[11] investigated TPEs based on GRT untreated or thermomechanically decomposed, LDPE and fresh rubber prepared with and without dynamic curing via sulfur or peroxide. The best performance was achieved by recipes containing decomposed GRT and EPDM after dynamic vulcanization with sulfur. (...truncated)