Research on the mechanical and morphological properties of microfibrillar reinforced PET/PP blends at various processing routes

Polypropylene (PP) is one of the commodity polymers used in a number of industries including packaging, automotive, infrastructure, and textile. However, because of its low mechanical properties, there are some restrictions in its application ranges. Compounding with functional fillers like glass fiber can greatly enhance the mechanical properties of PP. However, this kind of filler is abrasive for production line, not eco-friendly and expensive. Because of that in today's market conditions, producers have been looking for a way to provide more economic and eco-friendly solutions. In recent years, polymer blending has become an economic way for preparing new materials. Some advantages of blending can be listed as below; • Blending can offers customer-driven product design opportunity. • The properties of matrix polymer such as flame resistance, toughness or dimensional stability can be improved. • Blending can offers a way for recycling of industrial plastic wastes. • Blending with low viscosity polymer can improve processability. • Blending can provide to increase of productivity. • Additionally, blending technology can be also used in multi-layer structures. In plastic industry, different ways are used to prepare polymer blends such as melt blending, block or graft copolymerization, melt solution. However, among of these techniques, melt blending is the most commonly used method to achieve desired properties. This method offers opportunity to prepare polymer blends in more economically. As known, most of polymers are thermodynamically incompatible due to differences in their chemical structure. Therefore, during the mixing numerous types of phase morphologies such as fibrillar, droplet or laminar occur and, final properties of blend strongly depend on this morphology. For example, laminar structure of the dispersed phase which is often generated via film extrusion or blow molding improves the barrier properties of blend, whereas fibril structure enhances the mechanical properties. In resent years, a new type of material named as microfibrillar reinforced composites (MFCs) based on blending of two immiscible polymers have been developed. In this materials, to achive higher mechanical performance, minor phase is dispersed in fibrillar form in the matrix polymer. In contrast to the common composites, MFC materials can prepare without any inorganic additives. Additionally, this technology offers opportunity to weight reduction and easy recyclability in comparison to glass fibre reinforced composites. The main aim of thesis study is to produce microfibrillar reinforced PET/PP blends and investigate the effects of various parameters such as screw speed, process temperature, drawing method, drawing ratio, PET content and compatibilizer on the morphological and mechanical properties. In study, microfibril reinforced composites were prepared by a three step process. In the first step, two polymers were blended in a twin screw extruder. In second step, to obtain PET fibers, the extrudate was stretched. In last step, to achive MFC material, drawn PET/PP blends (MFB) were pelletized and molded by injection molding. After each stage of MFC production, analyzes were carried out by scanning electron microscopy (SEM), wide angle X-Ray diffraction (WAXD) and mechanical tests. At the beginning of study, to determine appropriate screw rate for blending, PET and PP were mixed at various screw rates. It was observed from the SEM images that lower or higher screw speeds than 300 rpm were not suitable to obtain homogeneously dispersed blend morphology. In second step of study, to generate microfibril reinforced blend (MFB), two different stretching methods were used. In the first method, the extruded blend was stretched between the first godet and extruder die by increasing rotation speed of first godet. In the second method, the extruded blend was stretched between the two godets. According to the analysis results, reinforcer polymer was able to successfully distributed in fibrillar shape in both methods. However, in second method higher mechanical properties were achieved as a result of well orientation of both component of blend. Depend on the PET concentration and applied draw ratio, the tensile properties of MFB samples greatly increased almost 6-7 times higher than extruded blends. In study, the influence of compatibilizer and its amount on the blend properties were also investigated. SEM images showed that after adding of compatibilizer, maleic anhydride grafted polypropylene (PP-g-MA), more uniform blend morphology was occured. Additionally, adhesion between the PET fibers and PP matrix was improved through compatibilizer and thus, mechanical properties increased. In the last step of study, in order to achive microfibril reinforced PET/PP composites, drawn blend samples were molded at different injection temperatures. SEM images showed that even though injection temperature was set to temperature which is lower than melting temperature of PET, many of fibers lost their shapes and returned into droplet structure. Despite this, better impact resistance and tensile properties were observed in comparison with extruded blend. In conclusion, when take into consideration three stage of microfibrillar reinforced polymer composites (extrusion, drawing and injection molding), the presence of PET fibers caused to increased mechanical properties of extruded blends but the highest increase was obtained in drawn blend samples. Therefore besides of MFC materials, MFBs may also offer an opportunity for industrial applications. For example, it can be weaved like technical textiles or it can be directly winding on products like plastic pipe. On the other hand, MFCs can be used in injection molded plastic pipe parts called as fittings.