Ecocompatible Blends and Composites Based on Biodegradable Polymeric Materials

The research activity implemented in the present Doctorate Thesis was focused on polymeric materials based on polyolefins that are the predominant polymers mostly used for consumer packaging. These polymers are not biodegradable and management of waste of relevant plastic items represents a serious environmental challenge world-wide. Attempts were made to develop several ecocompatible blends and composites utilizing polyolefins in conjunction with other biodegradable polymeric materials. Research on those efforts will be presented here. Much attention was focused on novel ecocompatible materials based on blends of polyhydroxybutyrate (PHB) and polystyrene (PS). The selection of PS was made due to its large use in current commercial packaging and also because of recent efforts to impart oxo-biodegradable functionality to this polymer. PHB is well known biodegradable bacterial polyester emerging as a viable substitute for synthetic, semi-crystalline non-biodegradable polymers. Polystyrene-co-methylmethacrylate P(S-MMA) and polystyrene-co-maleic anhydride P(S-MAn) copolymers were selected as compatibilizers due to the intrinsic immiscibility between PS and PHB. The films produced by compression molding were characterized by means of thermal analysis (TGA and DSC), scanning electron microscopy (SEM) and tensile tests. The effect of thermal and sunlight degradation behavior of the blend films of PS with PHB using P(S-MAn) as compatibilizer were also investigated. PS-PHB-P(S-MAn) blends were formulated with or without pro-degradant additives to influence the initial rates of degradation. This family of materials were subjected to a thermal aging for 90 days followed by sunlight exposure for 120 days. Thermally aged PS-PHB-P(S-MAn) blends showed no significant changes in weight increase when evaluated by FTIR, TGA and GPC. On the other hand, sunlight exposure led to some degradation in the sample after 120 days. Additionally, a new strategy was planned to compatibilize PS-PHB based blends through the synthesis of an A-B copolymer from PHB by using Atom Transfer Radical Polymerization (ATRP) of styrene. The copolymer was prepared in a three-step procedure which consisted of (i) a transesterification reaction between diethylene glycol and a high molecular weight PHB (ii) synthesis of PHB-derived macroinitiator and (iii) ATRP polymerization to synthesize PS-PHB block copolymer. The latter step was carried out at 115°C in an anisole solution with CuBr and 2,2-bipyridyl as the initiating system. FTIR, GPC, 1H- and 13C-NMR spectroscopy were used for the assessment of structural features and/or end-group functionality at each step of the adapted procedure. Moreover, PHB and PS based blends were prepared by the method of casting using a previously synthesized PHB-PS copolymer as a compatibilizer. Blends were analyzed for their morphology and thermal properties. Blends showed good miscibility and had well defined morphological structure. Also, blends of poly(lactic acid) (PLA) and PHB with a plasticizer (Lapol) were developed and evaluated by TGA, DSC, XRD, SEM and mechanical testing. PLA/PHB blends showed a good distribution and absence of phase separation. Another investigation undertaken in the present thesis work is the preparation and characterization of composites based on lignin, a renewable resource-based in conjunction with PHB. The work aimed at the application of low cost lignin extracted from pine nut shells (PNS) as filler with a high cost PHB in order to obtain composites with improved economics and ecological performance. New types of eco-friendly composite materials that are suitable for short-term packaging and disposable applications based on rhyolite as filler in polyethylene (PE), polypropylene (PP) and poly(lactic acid) (PLA) matrices were investigated. Additionally, a novel and facile method for surface modification of bacterial cellulose nanowhiskers (BCNW) was developed by graft copolymerization of glycidyl methacrylate by redox-initiated free radical method. These modified BCNW were subsequently introduced into a PLA polymeric matrix to produce fully biodegradable nanocomposites. This Ph.D. thesis is divided into ten chapters reporting on the different topics investigated during the implementation of the research activities: • PS/PHB using P(S-MMA) as compatibilizer • PS/PHB using P(S-MAn) as compatibilizer • PS/PHB/P(S-MAn) blends with pro-degradant • Synthesis of PS-PHB block copolymer using ATRP • PS/PHB compatibilized with a synthesized PS/PHB copolymer • Plasticized PLA-PHB blends • PHB/lignin blends compatibilized with PVAc • HDPE and PP rhyolite composites • PLA Rhyolite composites • PLA/bacterial cellulose nanowhiskers modified