The role of oxidized polyethylene wax in processing and crystallization of isotactic polypropylene in WPC composites

Isotactic polypropylene (iPP), in connection with its good processability, provides a matrix of composites applied in many industries. An influence of additives on iPP supermolecular structure, and consequently on its properties, should not be overlooked. The matter of inappropriate adhesion between a non-polar iPP matrix and polar fillers tends towards analyses and implementations of new kinds of coupling agents, e.g., polar polymeric waxes. Moreover, the presence of waxes in the composite matrix will change the MFR and may affect the iPP crystallization. To this day, literature has confirmed some beneficial effects observed during the application of polymer (e.g., polyethylene or polypropylene) waxes in the iPP composites technology, but did not demonstrate the result of its presence on iPP nucleation and crystallization. In the current paper, we focused on the simultaneous influence of lignocellulosic filler and coupling agent on crystallinity of iPP. Various research methods were applied, such as: WAXS, DSC, FTIR or PLM. Two oxidized polyethylene waxes (acid numbers: 23 and 89, respectively), as well as commercial non-oxidized polyethylene wax, were used as coupling agents. We found that an addition of 3% (by wt) of PE waxes drastically changes the processing parameters of the composites. The influence of waxes was observed in changes of crystallization kinetics, melting temperatures and in the degree of crystallinity. The percentage of crystalline phase in materials was decreased each time after waxes application. Moreover, the shear stress applied during crystallization changed the PE waxes role on iPP crystallization in WPC composite. The beneficial effect of flowing rapeseed straw powder was decreased by the presence of PE waxes. Graphical abstract: [Figure not available: see fulltext.].