Volatile extractives effects of pine wood on PP/pine wood compounds on rheological properties

Pine wood (PW) filled polypropylene (PP) compounds, PP/PW [90/10 (PP10), 75/25 (PP25), and 50/50 wt% (PP50)], were investigated upon rheological property, morphology, spherulite formation, and mechanical property. As the concentrations of the PW particles were increased, the complex shear and the steady shear viscosities were increased; however the elongation stresses were decreased. The complex viscosity of the PP10 and the PP25 compounds was slightly lower than that of the PP; however, that of the PP50 was higher than that of the PP, i.e., eta*[PP50 > PP > PP25 > PP10]. At a low shear rate range, the order of steady state viscosity was eta[PP50 > PP25 > PP > PP10], while at a high shear rate range, it was eta[PP > PP10 > PP25 > PP50]. Spherulites were locally developed at the interface between the PW and the PP. The amount of volatile extractives in the PW was decreased as the drying temperature of the wood was increased. The most volatile extractives were evaporated out during the processing; however, some of them were remained on the PW surface and then led to a poor interfacial adhesion between the PW surface and the PP matrix. Some fatty acids seemed migrated to the metal surface of the wall and this resulted in the viscosity drop of the PP10 and the PP25 compounds lower than the PP one.