Effect of MAPP on interfacial compatibility of wood flour/polypropylene composite evaluated with dielectric approach

To quantitatively evaluate the effect of maleic anhydride grafted polypropylene (MAPP) as a coupling agent on interfacial compatibility between wood and polymer in wood/polypropylene (PP) composite, the dielectric constant and dielectric loss factor were measured for poplar (Populus tomentasa Carr.) wood flour/polypropylene (PP) composites prepared with six MAPP loading levels (0.5, 1.0, 1.5, 2.0, 4.0, and 8.0%), and the Cole–Cole plots, the dielectric relaxation strength, the distribution of relaxation time and the activation thermodynamic quantities of the dielectric relaxation based on the reorientation of the methylol groups (CH₂OH) in the amorphous region of wood cell wall were further analyzed. The results showed that the dielectric relaxation strength decreased with the MAPP loading and dropped to the lowest at MAPP loading of 2.0%, after which it kept almost constant. It suggested that the internal bonding between wood and PP molecules was the strongest at 2.0% MAPP, therefore the reorientation of the methylol groups in wood became very difficult under the strong hindrance from the long‐chained PP molecules and the physical or/and chemical bonds between MAPP, wood flour, and PP in the composites. The activation free energy ΔE could be served as the indicator to quantitatively evaluate the effect of MAPP on interfacial compatibility of the wood/PP composites. ΔE of 2.0% MAPP modified composites showed the maximal value among all the tested conditions, which was 33.52 kJ mol⁻¹; while the values for 1.5 and 4.0% MAPP modified were 23.35 and 21.75 kJ mol⁻¹. Therefore, excessive MAPP was not beneficial to improve the internal compatibility of wood/PP composites, but had negative effect. POLYM. COMPOS., 35:489–494, 2014. © 2013 Society of Plastics Engineers