Development of biodegradable materials by reactive extrusion

Plastic materials produced from petrochemicals are used in a wide range of applications, such as, packaging, automotive, healthcare application, industry and communication or electronic industries. Most of these plastics are extremely durable, requiring more than 100 years for their degradation. Therefore, they may accumulate in the environment and became a significant source of environmental pollution. A possible solution to solve this problem, could be to replace commodity synthetic nonbiodegradable polymers by biodegradable ones. Reactive extrusion (REX) has been used as an attractive method to prepare new polymeric materials. It allows to prepare new materials, in the melt, by blending, polymerization, grafting, branching and functionalization. Polymerization or chemical modifications reactions in the melt were identified as an efficient and economic way for low cost production, which enhances the commercial viability and costcompetitiveness of these materials. Thus, the main goal of this thesis is to investigate new routes to prepare biodegradable polymers by reactive extrusion. Blends of biodegradable polymers (starch-based thermoplastics (TPS), poly(-caprolactone (PCL) and polylactide (PLA)) and non-biodegradable synthetic polymers, such as, polyolefins were investigated. High density polyethylene/polyethylene-grafted-maleic anhydride (HDPE/PE-g-MA) blends and biodegradable polymers (PCL, PLA and TPS) with different compositions were prepared. The blends were characterized using several techniques and different standard methods were used to evaluate the aerobic biodegradation. The results showed that even though biodegradability can increase, due to lower compatibility between the polymers, the specified final mechanical properties were not achieved. A different approach used to prepare biodegradable/bio-based polymers was based on the synthesis of copolymers of non-biodegradable and biodegradable polymers. One procedure was based on the synthesis of grafted copolymers, by in situ polymerization of lactide (LA) and -caprolactone (-CL) in the presence of molten EVA, using titanium phenoxide (Ti(OPh)4) as catalyst. The method used allowed copolymer formation, which even in small amount, promote an enhancement of thermal and mechanical properties of EVA and an increase of its biodegradability. Therefore, in situ polymerization is a promising route to produce biodegradable/bio-based materials with mechanical properties similar to conventional polymers. The other route used to prepare biodegradable/bio-based copolymers was through transesterification reactions between EVA and PLA or PCL, catalysed by titanium propoxide (Ti(OPr)4) leading the formation of EVA-g-PLA or EVA-g-PCL copolymers, respectively. The effect of the grafted copolymer amount on physical properties, mechanical properties and biodegradability was investigated. The results obtained show that both, in situ polymerization of monomers and/or transesterification reactions, are promising routes to produce biodegradable/bio-based materials with mechanical properties similar to conventional polymers and higher biodegradability, which can be used in technological applications.