Microfibrillar reinforced composites from PET/PP blends: processing, morphology and mechanical properties

Microfibrillar reinforced composites (MFC) based on blends from recycled poly(ethyleneterephthalate) (PET), polypropylene (PP) and a compatibilizer (ethylene-glycidyl methacrylate (E-GMA)) were prepared under industry-relevant conditions by melt extrusion, followed by continuous cold drawing. The PET/PP/E-GMA weight rations amounted to 40/60/0, 40/59/1, 40/57/3, 40/54/6 and 40/51/9, respectively. Test specimens were prepared by compression- and injection molding (CM and IM) at processing temperatures either below or above the melting temperatures of PET. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide-angle X-ray scattering (WAXS), and mechanical testing. SEM and WAXS showed that the extruded blends are isotropic, but become highly oriented after drawing, and they are converted into MFC structured polymer-polymer composites during CM and IM. The MFC structures are characterized by an isotropic PP matrix, which contains reinforcing PET fibrils of different orientations after IM or of uniaxial orientation in the case of CM. The flexural modulus and the flexural strength of the IM samples are by 50% better than those of the neat PP, without expressing any clear effect of the amount of E-GMA in the blend. This was different from the CM samples, in which both the flexural modulus and the flexural strength increased with an increase of E-GMA part.