Kaiser Katharina M A, Ewender Johann, Welle Frank
TUM School of Life Sciences Weihenstephan, Technical University of Munich, Weihenstephaner Steig 22, 85354 Freising, Germany.
Fraunhofer Institute for Process Engineering and Packaging IVV, Giggenhauser Strasse 35, 85354 Freising, Germany.
Polymers (Basel). 2020 Dec 15;12(12):2988. doi: 10.3390/polym12122988.
Lacking recyclability of multilayer packaging can be overcome by using a thermoreversible crosslinking adhesive consisting of maleimide- and furan-functionalized polyurethane-(PU-)prepolymers, reacting in a Diels-Alder-reaction. Here, the furan-functionalized PU-prepolymer carries furan-side-chains to avoid the usage of an additional crosslinking agent. Thus, ‑(2‑hydroxyethyl)maleimide and furfurylamine are the only two chemicals contained in the adhesive that are not listed in the appendix of EU Regulation 10/2011. Using migration modelling, it could be shown that, at 23 °C, both chemicals have lag-times of only a few minutes if 45 µm PE is used as a barrier. However, if the residual content is below 30 mg/kg, the legally specified maximum amount of 0.01 mg/kg food is not reached. After determining the diffusion coefficients and the activation energy of diffusion through ethylene-vinyl alcohol copolymer (EVOH), it could be determined that the lag-time of the migrants can be extended to at least 9 years by the use of 3 µm EVOH. From a food law point of view, the use of the described adhesive is possible if the above‑mentioned measures are complied.
多层包装缺乏可回收性的问题可以通过使用一种热可逆交联粘合剂来克服，该粘合剂由马来酰亚胺和呋喃功能化的聚氨酯（PU）预聚物组成，它们通过狄尔斯-阿尔德反应进行反应。在此，呋喃功能化的PU预聚物带有呋喃侧链，从而避免使用额外的交联剂。因此，粘合剂中仅含有的两种化学物质-（2-羟乙基）马来酰亚胺和糠胺未列入欧盟法规10/2011的附录中。通过迁移模型可以表明，在23°C下，如果使用45μm的聚乙烯（PE）作为阻隔层，这两种化学物质的滞后时间仅为几分钟。然而，如果残留量低于30mg/kg，则不会达到法定规定的0.01mg/kg食品的最大含量。在确定了通过乙烯-乙烯醇共聚物（EVOH）的扩散系数和扩散活化能之后，可以确定通过使用3μm的EVOH，迁移物的滞后时间可以延长至至少9年。从食品法律的角度来看，如果遵守上述措施，则可以使用所述粘合剂。
