The Influence of Fines Material on the Mechanical Performance of Wood Fiber Polypropylene Composites

With an increasing interest in a wider scope of biomass feedstocks for biocomposite production, the potential influence of a possibly higher proportion of fines material needs to be addressed. In the pulp and paper industry, at least two major classes of fines material are identified; blocky fines and fibrillar fines. These differ in their aspect ratio, with the later having substantially higher aspect ratio. In this study, the physical impact of blocky fines (from CTMP refining) and fibrillar fines (produced via Super® Masscolloider refining) on a wet formed compression molded polypropylene (PP) matrix biocomposites were compared. The results indicated that in wet formed compression molded polymer matrix composites, both blocky (CTMP) and fibrillar (SMC) fines have a significant negative impact on modulus of rupture (MoR). Additionally, blocky CTMP fines also have a significant negative impact on modulus of elasticity (MoE). It is postulated that this is due to fibril agglomeration, in the case of fibrillar fines, and low aspect ratio in combination with some agglomeration, in the case of blocky CTMP fines. The indication is that fines material that has not been treated to minimize agglomeration has limited benefits as a reinforcing agent, and only a negative impact on most properties in wet formed compression molded polymer matrix composites.