Garofalo Emilia, Taurino Leonardo, Di Maio Luciano, Neitzert Heinz C, Incarnato Loredana
Department of Industrial Engineering, University of Salerno, 84084 Fisciano, Italy.
Polymers (Basel). 2023 Apr 13;15(8):1858. doi: 10.3390/polym15081858.
The emission of off-odors from mechanically recycled plastics severely limits their re-introduction into the market for the production of new objects, for the same use or even for less demanding applications, thus hindering the implementation of an effective circular economy for plastics. The addition of adsorbing agents during the extrusion of polymers represents one of the most promising strategy to reduce the odorous emissions of plastics, due to its characteristics of cost-effectiveness, flexibility and low energy consumption. The novelty of this work lies in the assessment of zeolites as VOC adsorbents during the extrusion of recycled plastics. They appear more suitable than other types of adsorbents, due to their ability to capture and "hold" the adsorbed substances at the high temperatures of the extrusion process. Moreover, the effectiveness of this deodorization strategy was compared with the traditional degassing technique. Two types of mixed polyolefin wastes, coming from completely different collection and recycling processes, were tested: Fil-S (Film-Small), deriving from post-consumer flexible films of small size, and PW (pulper waste), which is the residual plastic waste obtained from the paper recycling process. The melt compounding of the recycled materials with two micrometric zeolites (zeolite 13X and Z310) resulted as more effective in the off-odors removal with respect to degassing. In particular, the highest reduction (-45%) of the Average Odor Intensity (AOI) was measured for both PW/Z310 and Fil-S/13X systems at 4 wt% of the zeolites' amount, compared with the corresponding untreated recyclates. Finally, by combining degassing and melt compounding with zeolites, the best result was obtained for the composite Fil-S/13X, whose Average Odor Intensity resulted as quite close (+22%) to the one of the virgin LDPE.
机械回收塑料散发的异味严重限制了它们重新进入市场用于生产新物品，无论是用于相同用途还是要求较低的应用，从而阻碍了有效的塑料循环经济的实施。在聚合物挤出过程中添加吸附剂是减少塑料异味排放最有前景的策略之一，因为它具有成本效益、灵活性和低能耗的特点。这项工作的新颖之处在于评估沸石作为回收塑料挤出过程中的挥发性有机化合物（VOC）吸附剂。由于它们能够在挤出过程的高温下捕获并“保留”被吸附物质，因此它们似乎比其他类型的吸附剂更合适。此外，还将这种除臭策略的有效性与传统的脱气技术进行了比较。测试了两种来自完全不同收集和回收过程的混合聚烯烃废料：Fil-S（薄膜-小），来自消费后小尺寸的柔性薄膜；以及PW（碎浆机废料），它是纸张回收过程中产生的残余塑料废料。将回收材料与两种微米级沸石（13X沸石和Z310）进行熔融共混，在去除异味方面比脱气更有效。特别是，在沸石用量为4 wt%时，PW/Z310和Fil-S/13X体系的平均气味强度（AOI）相较于相应的未处理回收物降幅最大（-45%）。最后，通过将脱气与沸石熔融共混相结合，复合Fil-S/13X取得了最佳效果，其平均气味强度与原始低密度聚乙烯（LDPE）的相当接近（+22%）。
