Poly(lactic acid) and acrylonitrile−butadiene−styrene blends: Influence of adding ABS−g−MAH compatibilizer on the kinetics of the thermal degradation

Abstract

Square plates (nominal thickness: 3 mm, nominal width: 100 mm) of different rheologically modified PLA/ABS blends were manufactured through injection molding, with or without adding ABS grafted with maleic anhydride (MAH). During processing, the properties of the melt were stabilized and enhanced by the addition of a styrene-acrylic multi-functional-epoxide oligomeric reactive agent (SAmfE). PLA-REX was obtained by reactive extrusion of PLA. A general analytical equation was used in order to evaluate the kinetic parameters of the thermal degradation of PLA−REX/ABS and PLA−REX/ABS/ABS−g−MAH blends through thermogravimetric analysis. The thermal degradation of these blends occurred through two different reaction steps. Various empirical and theoretical solid-state mechanisms were tested to elucidate the best kinetic model. In order to reach this goal, plots of standardized conversion functions were constructed. Given that it is not always easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, a recently proposed index was determined to quantitatively identify the best mechanism. By doing that, it has been possible to determine the right activation energy of the thermal degradation. It has been demonstrated that the best mechanisms for these materials were R2 (i.e. phase-boundary-controlled reaction (contracting area)) for the first step (α < 60%) and F3 (i.e. three order reaction) for the second one (α > 70%). The thermal stability of PLA−REX/ABS blend was greatly improved by adding the ABS−g−MAH compatibilizer. These findings were also confirmed by means of morphological characterization through scanning electron microscopy.