Abstract

ROJAS, Héctor et al. INFLUENCE OF THE DEGRADATION DURING THE PROCESSING ON THERMAL, RHEOLOGICAL AND TENSILE PROPERTIES OF POLY(LACTIC ACID) COMPOSITES. Rev. LatinAm. Metal. Mater. [online]. 2014, vol.34, n.1, pp.118-135. ISSN 0255-6952.

Poly (lactic acid) (PLA) composites with corn starch were prepared in a corotating twin-screw extruder. The influence of incorporating different proportions of filler was studied in terms of intrinsic viscosities, oscillatory shear flow, thermogravimetric analysis (TGA), scanning electron microscopy and tensile properties. Results showed that the kinetics of the thermo-oxidative reaction of the PLA and also of the PLA phase in the composites with corn starch under isothermal conditions in the dynamic rheometer was mainly a random chain splitting process. The thermal and hydrolytic degradation of the PLA phase in the composites with corn starch during their processing were fitted in an autocatalyzed carboxylic group degradation model. Also, several models were employed to predict the viscosity ratio at constant frequency and temperature, the tensile strength and elongation at break ratios and it was found that the experimental values in the composites lie close to those of the Maron-Pierce and Thomas, Nicolais and Narkis, and Nielsen models, respectively. Additionally, results showed that the composites of PLA with corn starch have higher susceptibility to thermal and hydrolytic degradation during its processing than the PLA processed only by injection molding due to higher water absorption of the corn starch while in the extruder feeding. However, the enhanced degradation of composites with corn starch increased the crystallinity degree due to a higher molecular mobility which produced similar tensile strength and modulus values to those of injection-molded PLA. Nonetheless, the complex viscosity and storage modulus at low frequencies, the elongation at break and thermal and stability both in inert atmosphere (TGA) and in air (in the rheometer) under isothermal conditions are lower.

Keywords : Poly (lactic acid) composites; corn starch; thermal-oxidative degradation..

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