Effect of chemical and physical foaming additives on the properties of PP/wood flour composites

Low weight is an important property of polymer composites used in applications such as construction, the automotive industry, etc. Focusing on fabricating lighter materials, PP/wood flour composites were expanded using different chemical and physical foaming agents. The goal of the investigation was to compare the effect of these additives on the density, mechanical and morphological properties of the expanded composites by means of density determinations, tensile tests and scanning electron microscopy analysis. The foaming agents used were based on azodicarbonamide, sodium bicarbonate and expansive polymer spheres. It was verified that the effect of the chemical foaming agents reflected its degradation behaviour determined by thermogravimetry. Closed cells with varied sizes and more or less regular shapes were found in the materials according to the foaming system used. Among them, Hydrocerol 1004 (a masterbatch of sodium bicarbonate and citric acid in PE), produced the expanded PP/wood flour composites with the finest morphology, significant density reduction and acceptable loss of mechanical properties.