Guo Jinyang, Wagner Willi, Atamaniuk Iryna, Chong Zhi Kai, Alassali Ayah, Kuchta Kerstin
Circular Resource Engineering and Management (CREM), Hamburg University of Technology (TUHH), Blohm Str. 15, 21079 Hamburg, Germany.
Polymers (Basel). 2024 Nov 21;16(23):3234. doi: 10.3390/polym16233234.
Printing inks, composed of binders, pigments, and additives, are essential components in plastic packaging but complicate recycling due to plastic contamination and degradation. While polyolefins are resistant to hydrolytic degradation, moisture generated from upstream cleaning processes, which is often ignored, can accelerate the degradation of ink binders, affecting the recyclate quality. This study has examined the impact of 3 wt.% moisture, introduced before extrusion, on the degradation of nitrocellulose (NC), polyurethane (PU), polyvinyl butyral (PVB), and cellulose acetate propionate (CAP) binders mixed with virgin, low-density polyethylene (LDPE) at varying concentrations to simulate contamination levels. Control samples were prepared by extrusion under dry conditions and using p-xylene to compare with degradation-free conditions. Analyses, including the measurement of the melt-flow index (MFI), tensile testing, FTIR (Fourier transform infrared spectroscopy), TGA (thermogravimetry analysis), and gas chromatography mass spectroscopy (GC-MS) have established that NC is fully degraded, causing discoloration and altering the MFI. Moreover, PU degrades mainly in the presence of moisture, contrary to previous findings. In contrast, PVB does not degrade but exhibits modified mechanical properties; whereas, CAP shows minimal impact. The findings of this research demonstrate the critical role of moisture in determining recyclability, informing strategies for ink selection and recycling processes to facilitate plastic packaging circularity.
由粘合剂、颜料和添加剂组成的印刷油墨是塑料包装中的重要组成部分，但由于塑料污染和降解，会使回收复杂化。虽然聚烯烃耐水解降解，但上游清洗过程中产生的水分（这一点常常被忽视）会加速油墨粘合剂的降解，影响回收物质量。本研究考察了在挤出前引入3 wt.%的水分对硝化纤维素（NC）、聚氨酯（PU）、聚乙烯醇缩丁醛（PVB）和醋酸丙酸纤维素（CAP）粘合剂降解的影响，这些粘合剂与不同浓度的原生低密度聚乙烯（LDPE）混合以模拟污染水平。对照样品通过在干燥条件下挤出并使用对二甲苯制备，以与无降解条件进行比较。包括熔体流动指数（MFI）测量、拉伸试验、傅里叶变换红外光谱（FTIR）、热重分析（TGA）和气相色谱 - 质谱联用（GC - MS）在内的分析表明，NC完全降解，导致变色并改变MFI。此外，与先前的研究结果相反，PU主要在有水的情况下降解。相比之下，PVB不会降解，但机械性能有所改变；而CAP的影响最小。本研究结果表明水分在决定可回收性方面的关键作用，为油墨选择和回收工艺策略提供了依据，以促进塑料包装的循环利用。
