Mechanical Properties of Hybrid Composites of Pet/poly(ethylene-co-methyl Acrylate-co- Glycidyl Methacrylate) Elastomer / Glass Fiber

A series of glass fiber-reinforced and rubber-toughened poly(ethylene terephthalate) hybrid composites were twin-screw extrusion compounded with varying total and relative concentrations of a reactive terpolymer of poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate) (E-MA-GMA) as the elastomeric impact modifier (10-1520 wt.%) and short glass fiber – SGF (20-25-30 wt.%). Haake torque rheometry mixing data of these composites indicate preferential interactions between the terminal carboxyl groups of the matrix PET with epoxy functionalities of E-MA-GMA. Tensile tests on these hybrid PET composites, at a given SGF content, indicated that the elastic modulus and tensile strength reduce monotonically and Izod impact strength increases substantially, as higher volume fractions of E-MA-GMA substitute PET matrix in the composite. Using the mechanical tests data (tensile and Izod impact) and microscopy analysis (MEV), a discussion is presented on the contributions of the fiber-reinforcement and rubbertoughening mechanisms to the balance in modulus/toughness behaviour of this model hybrid ternary composite of PET, as the total volume concentration of the hybrid reinforcement of SGF/E-MA-GMA increases in the polymer matrix. Introduction Waste bottle-grade PET as a hybrid thermoplastic composite system for “up-graded” applications such as engineering grade PET can be an attractive industrial proposition, if sufficient elastomeric impact modifier and short glass fiber (SGF) can be incorporated as distinct dispersed phases into the matrix thermoplastic polyester during its recycling process. In order to assure a good balance between engineering properties such as high impact resistance and toughness, high strength and stiffness in this hybrid PET composite, it is important to avoid SGF encapsulation by the elastomer, so that both efficient fiber-reinforcement and rubber-toughening mechanisms can simultaneously prevail in the matrix polymer and, thereby, counter-balancing the drastic deterioration of PET properties, leading to problems such as low melt viscosity, reduced impact strength and tensile ductility [1, 2]. Much of the recent growth in glass fiber reinforced PET (thermoplastic polyester for injection molding) has been found in various industrial applications such as automotive, appliances, furniture, and so on, where PET made parts and structures are gradually replacing steels, light alloys, and in some cases expensive, thermoplastics and thermosets [3]. Many studies dealing with short-fiber reinforced engineering plastics, such as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) have been reported [4-9], where different aspects related to the correct choice of the silane coupling agent of glass fibers, use of nucleating agents and optimized processing conditions contribute towards improved mechanical performance of these glass-reinforced thermoplastic composites. Recently, there has been active research interest in the study of rubber toughened polymer blends based on poly(ethylene terephthalate) (PET) as the matrix material [3,10-11,12-15]. By blending of PET with rubber in a suitable manner, materials with high toughness can be produced. The effects of compatibility between rubber and PET matrix have been observed to play an important role in the resulting blends behaviour [11, 14-15]. With different rubber types, it has been observed that maleic anhydride grafted styrene-ethylene-butadiene-styrene (SEBS-g-MA) rubber [3], ethylene-propylene-diene elastomer (EPDM) [16] and random terpolymer of ethylene-methyl acrylate–glycidyl methacrylate (E-MA-GMA) [17-18] are effective in the toughening of PET, where higher quantities of impact modifier (20%) and smaller particle size of less than 200 nanometers (at an interparticle distance of 50 nanometers) are required to induce “supertoughness” in polymers such PET [17]. However, the addition of rubber particles decreases the strength and stiffness of PET. For this purpose, recycled PET was extrusion compounded with varying concentrations of SGF pre-treated with epoxisilane “supposedly” and also with a reactive terpolymer of poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate) (E-MA-GMA), used as the elastomeric impact modifier. During the melt compounding process of PET composite, it is expected that the epoxi functional groups of E-MA-GMA should preferentially react with the terminal carboxyl and hydroxyl groups present in the matrix PET, rather than with the epoxide organic functionalities of the siloxane deposited on SGF surface. Under such conditions, it is expected that no SGF encapsulation by the elastomer should occur and, thereby, leading to a mechanically efficient hybrid PET composite system. The main goal of this investigation was to promote a better understanding on the structure-mechanical properties relationships existing in a model hybrid ternary composite of PET, where the contributions of the fiber-reinforcement and rubber-toughening