Thermal stability of organo‐montmorillonite‐modified wood flour/poly(lactic acid) composites

Abstract

In this research, wood flour (WF) was modified using sodium–montmorillonite (Na‐MMT) at four different concentrations (0.5, 1.0, 2.0, and 4.0 wt%, respectively) and didecyl dimethyl ammonium chloride (DDAC) in a two‐step process to form organo‐montmorillonite (OMMT) inside the WF or attached to the WF surface. The thus‐modified WF was then mixed with poly(lactic acid) (PLA) to produce WF/PLA composites. The thermal stability of these composites with respect to their resistance against both thermal deformation and thermal decomposition was characterized by stress relaxation, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. Besides, the activation energies for thermal decomposition of the composites were calculated. The results showed the following: (1) The modification of WF by OMMT improved the resistance against thermal deformation of the composites at appropriate OMMT loadings (lower than 1 wt% in this study). However, after introducing excessive OMMT, the enhancements in thermal stability diminished. Composite containing WF modified by 0.5 wt% of OMMT showed the optimal thermal deformation stability in this study, reflected in the highest values of thermal properties such as the glass transition temperature, melting temperature, crystallization temperature, and slowest stress relaxation rate. (2) OMMT showed a negative effect on the resistance against thermal decomposition. Namely, OMMT accelerated the thermal decomposition of the composites, probably by the easier degradation of the organic surfactant used for the WF modification. However, this behavior might be favorable for achieving fire retardancy. POLYM. COMPOS., 37:1971–1977, 2016. © 2015 Society of Plastics Engineers