Effect of two types of plasticizers on the properties of biodegradable polyester blends

MELINA HANKOVITS; ANTONELLA GIACOMINI; DAVID D'AMICO; VIVIANA CYRAS; LILIANA MANFREDI

Mar del Plata

Simposio; XVI LATIN-AMERICAN POLYMER SYMPOSIUM (SLAP); 2018

ABSTRACTINTRODUCTIONIn recent years, the interest on the use of biodegradable polymers has increased because of their lower environmental impact compared to the commodity plastics. Polyhydroxybutyrate (PHB) is a thermoplastic biodegradable polymer produce by microorganisms. It presents good barrier properties to water vapor, oxygen and UV light; however, it is highly crystallineand brittle1. In order to improve their processing and mechanical properties, plasticizers and/or another polymer could be added2,3. Polylactic acid (PLA) is other biodegradable polyester which has mechanical properties comparable to commodities polymers. It has better mechanical resistance and is cheaper than PHB. Nevertheless, PLA has poor barrier properties4,5.In this work, the development of biodegradable blends based on PHB and PLA with improved properties compared to the pure polymers was proposed. Two types of plasticizers, one of low molecular weight (glyceryl tributyrate, TB) and other polymeric (polydiethyleneglycol adipate, A) were added to the blends in order to study their influence on the structure and the mechanical properties of the final materials.EXPERIMENTAL METHODSBlends with different ratio PLA (Nature Works)/PHB (PHB Industrial) (80/20, 70/30 and 60/40), plasticized with 10 and 15 wt% of TB (Fluka) and A (Sigma), were obtained in a Haake mixer (185ºC and 50 rpm) and then pressed at 15 kg/cm2 and 190ºC.The films were characterized by X-Ray diffraction (XRD), uniaxial tensile test and UV-vis spectroscopy.RESULTS AND DISCUSSIONIt was observed that the formulation 80/20 presented the best mechanical properties regarding uniaxial tensile tests, showing a good balance between stiffness and deformation capacity. Figure 1 shows the stress vs strain curves obtained from tensile test for the 80/20 blends with and without plasticizers. It was observed that the blends without plasticizer showed a brittle behavior, with a Young?s modulus of 1,4 GPa and 5% of elongation at break. A typical plastification effect was observed in the samples with both plasticizers, showing Young?s modulus reduction and an increase in the elongation at break. This effect was more significant with the addition of 15% of the low molecular weight plasticizer, by reaching 121% of elongation.In addition, the DRX pattern of the blends reveals no changes in the position of the characteristic reflection peaks for PHB and PLA. Then, it could indicate that the polymers crystallize separately, which implies a polymer phase separation in the blends. All blends are translucent and present an homogeneous aspect macroscopically. When UV-vis test was performed a more pronounced translucent behavior for blends was observed compared to the pure plasticized polymers. This could be related to the phase separation, observed by X-ray patterns, and to the variation in the global crystallinity degree of the samples.CONCLUSIONBlends containing fully biodegradable polyesters and plasticizers were successfully obtained. It was possible to reach an optimal blend formulation with improved mechanical properties, broadening the polymers processing window thus, the applications of both matrices.REFERENCES1. D?Amico, D.A. et al., Thermochim Acta, 544, 47? 53, 2012.2. Cyras, V.P. et al., Polymer, 50, 6274?6280, 2009.3. Bordes, P. el at., Progr Polym Sci, 34, 125-155, 2009.4. Arrieta, M.P., et al., J Agric Food Chem, 62, 10170 - 10180, 2014.5. Gerard, T., et al., Eur Polym J, 48, 1110?1117, 2012.ACKNOWLEDGMENTSThe authors gratefully acknowledge the support from the CONICET, ANCyPT and the National University of Mar del Plata.