Improving the Mechanical Performance of LDPE/PP Blends through Microfibrillation

Polyolefins (polyethylene (PE) and polypropylene (PP)) are the most abundant polymers found in plastic solid waste. They are expensive to separate, and recycling them in the form of blends is not viable due to their immiscibility and incompatibility. Following the idea of the circular economy where waste is turned into raw materials for manufacturing technological products using minimum energy, a solution is proposed for the poor behavior of immiscible PE/PP blends by taking advantage of their immiscibility to transform them into microfibrillar composites (MFCs). PE/PP blends with an 80:20 content ratio were studied, emulating the ratio found in municipal waste. A microfibrillar structure was achieved through an unusual combination of common industrial processing techniques: extrusion, drawing, and injection. The performance of the resulting fibrillar materials was evaluated by means of tensile, fracture, and impact tests, and the results were compared with those of unstretched blends (UBs) with droplet morphology. The effect of adding a compatibilizer was also evaluated. The results were promising as the performance of the MFCs was much better than that of the nonfibrillated blends, and a synergistic effect between the addition of the compatibilizer and microfibrillation process was observed. It seems that this type of processing has great potential for large-scale application in immiscible recycled polyolefin blends in which the final properties can be improved by modifying their morphology, obviating the need to separate these polymers in mixed waste streams.