3SPack, CREPEC, Chemical Engineering Department, Polytechnique Montreal, Montreal, Canada.
3SPack, CREPEC, Chemical Engineering Department, Polytechnique Montreal, Montreal, Canada.
Waste Manag. 2021 May 1;126:239-246. doi: 10.1016/j.wasman.2021.03.005. Epub 2021 Mar 26.
Mechanical recycling is a promising approach to reduce the environmental impact of plastic packaging waste. However, the presence of defects in recycled materials results in final products with relatively poor visual and/or mechanical properties. In this work, the origin of the visual defects in post-consumer recycled HDPE (PCR HDPE), as well as the effects of processing method, processing condition and the addition of antioxidants on the visual defects were studied in multilayer flexible polyethylene films. The nature of the defects in the film samples were investigated by combining optical microscopy, energy dispersive X-ray (EDX), hot stage microscopy, solvent extraction, and differential scanning calorimetry (DSC) techniques. It was found that the defects in PCR film samples can be mainly categorized as fiber defects and point gels. Hot stage microscopy results show that point gels can be subcategorized in two groups: (a) non-melting, non-deformable gels, and (b) melting, deformable defects. In addition, it was found that deformation of molten, deformable defects increased at higher temperatures specifically above 200 °C. Further characterizations showed that the observed deformable defects are highly entangled high molecular weight HDPE. The effect of processing temperature, processing with a twin-screw extruder and the addition of antioxidant on the visual defects in film samples were also discussed in detail. It was shown that increasing processing temperature and using twin-screw extruders were two approaches that could reduce considerably the number of defects. The addition of antioxidants was also shown to improve the film quality especially at lower processing temperatures.
机械回收是减少塑料包装废物环境影响的一种很有前途的方法。然而，回收材料中存在缺陷会导致最终产品的视觉和/或机械性能相对较差。在这项工作中，研究了消费后回收高密度聚乙烯（PCR HDPE）中可见缺陷的起源，以及加工方法、加工条件和添加抗氧化剂对多层柔性聚乙烯薄膜中可见缺陷的影响。通过结合光学显微镜、能量色散 X 射线（EDX）、热台显微镜、溶剂萃取和差示扫描量热法（DSC）技术，研究了薄膜样品中缺陷的性质。结果发现，PCR 薄膜样品中的缺陷主要可以分为纤维缺陷和点凝胶。热台显微镜结果表明，点凝胶可以分为两类：（a）不熔化、不可变形的凝胶，和（b）熔化、可变形的缺陷。此外，还发现可变形缺陷的熔融变形在较高温度下（特别是在 200°C 以上）增加。进一步的表征表明，观察到的可变形缺陷是高度缠结的高分子量 HDPE。还详细讨论了加工温度、使用双螺杆挤出机和添加抗氧化剂对薄膜样品中可见缺陷的影响。结果表明，提高加工温度和使用双螺杆挤出机是两种可以大大减少缺陷数量的方法。添加抗氧化剂也显示出可以改善薄膜质量，特别是在较低的加工温度下。
