The study of this thesis was focused on materials based on polyethylene (PE), which remains as the largest polymer used in the field of packaging. This polymer is not biodegradable and its waste represents a serious problem to the environment. A proposal of eco-compatible PE based materials will be presented. This is bound to the enhancement of the polyethylene oxo-biodegradability through the blending with biodegradable polymers of biosynthetic origin, [poly(hydroxybutyrate) (PHB) or starch] and commercial prodegradant additives.
This work was structured in three chapters. In the first chapter, the compatibilization between PE and PHB was studied. For this purpose, a screening statistical design experiment (DEX) was preformed, in order to assist in the selection of the better compatibilizer and materials proportions. The variables selected were three copolymers, containing both PE and polar segments, and their amount in the blend, which was constrained at the limits of 10 wt-% and 40 wt-% depending on the compatibilizer. These compatibilizers were poly(ethylene-co-vinyl acetate) (EVA), poly(ethylene-co-glycidyl methacrylate) (EGMA) and poly(ethylene-co-methyl acrylate (EMAC). The films were characterized by means of thermal analysis (TGA and DSC), scanning electron microscopy (SEM), wide angle x-ray scattering (WAXS), Photoacoustic Fourier Transform Infrared Spectroscopy (PAS-FTIR), dynamic mechanical thermal analysis (DMTA) and tensile tests (Instron). EGMA was chosen as the compatibilizer to formulate a new series of materials. This compatibilizer promoted the better adhesion between PE and PHB than the others two tested copolymers did. The best formulation was found for PE matrix with 10 wt-% of EGMA (68E22B10G).
In the second chapter, PE-PHB-EGMA blends were formulated in presence or not of prodegradant additives (Totally Degradable Plastics Additives - TDPA®) DCP562 (T6) and DCP571 (T7). The formulation strategy followed a central composite design (CCD) where the independent variables were the amount of the biodegradable polymer PHB and of the prodegradant additives T6 and T7. Films were characterized by means of SEM, TGA, DSC, FTIR and Instron. This family of materials was submitted to a thermal aging experiment at three temperatures (45, 55 and 65 °C). Gravimetry, FTIR, SEC, TGA, DSC and Instron were carried out to characterize the thermal aged samples. The prodegradants were effective in promoting PE oxidation. Thermal aged PE-PHB-EGMA-TDPA blends samples showed significant changes on weight gain and carbonyl index (COi) measured in FTIR spectra. By means of COi were evaluated the activation energy (Ea) of thermal degradation applying the Arrhenius equation. Blends containing PHB presented lower values of activation energy (54 kJ/mol for 2B3T6) compared to the equivalent blend without PHB (81 kJ/mol for 3T6). Samples from thermal aging were biodegraded in both aquatic media and soil burial. The biodegradation of the blends in both ambient showed low mineralization. For example, the maximum mineralization of 2B3T6t (85.5PE-9.5EGMA-2PHB-3T6) sample was ca. 4 % after 140 days in soil burial, probably as a consequence of the large extent of crosslinking occurred during the thermal aging, which in this case increased up to 76 %.
The last chapter of this thesis comprises two series of experiment concerning PE-Starch composites. In the first one, the compatibilization of compression moulded PE-Starch materials was studied. In the second part, selected composites of compatibilized PE-Starch were prepared by melt blow extrusion. Two different types of starches and two compatibilizers were defined as variables: thermoplastic corn-starch (TPS) and natural corn starch (CS) as fillers and EVA and EGMA as compatibilizers. The results obtained showed that: i) PE-TPS films resulted in very distinct phase separation even when higher amounts of EVA and EGMA were used; ii) In the PE-CS films the compatibilizer EGMA at 20 wt-% provided a good dispersion of starch granules. In addition, blends containing CS produced films more homogeneous than that with TPS. The best compatibilized formulation was used to prepare by melt blow extrusion PE-CS based composites and PE-Biopar blends containing or not T6 and T7 prodegradants, whose films were mechanically tested. The mechanical properties of PE family of materials containing CS and Biopar presented similar values for Young modulus (100-200 MPa). However, films with Biopar presented higher values of tensile strain (ca. 200 %) than films with CS (ca. 100%).