Mayrhofer Anna, Kopacic Samir, Bauer Wolfgang
Institute of Bioproducts and Paper Technology, Graz University of Technology, 8010 Graz, Austria.
Polymers (Basel). 2023 Aug 8;15(16):3336. doi: 10.3390/polym15163336.
The vast amount of synthetic polymers used in packaging is putting a strain on the environment and is depleting finite, non-renewable raw materials. Abundantly available biopolymers such as alginate, chitosan and microfibrillated cellulose (MFC) have frequently been suggested in the literature to replace synthetic polymers and their barrier properties have been investigated in detail. Many studies aim to improve the properties of standalone biopolymer films. Some studies apply these biopolymers as barrier coatings on paper, but the solids content in most of these studies is quite low, which in turn would result in a high energy demand in industrial drying processes. The aim of this study is to suggest a laboratory procedure to investigate the suitability of these biopolymers at higher and such more industrially relevant solids content as potential coating materials for paper and board in order to improve their barrier properties. First, biopolymer solutions are prepared at a high solids content at which the viscosity at industrially relevant higher shear rates of 50,000 s (1000 s for MFC) is in the same range as a synthetic reference material (in this case ethylene vinyl alcohol EVOH) at 10 wt%. These solutions are analyzed regarding properties such as rheology and surface tension that are relevant for their coatability in industrial coating processes. Then, free-standing films are cast, and the films are characterized regarding important properties for packaging applications such as different surface, mechanical and barrier properties. Based on these results suitable biopolymers for future coating trials can be easily identified.
用于包装的大量合成聚合物正在给环境带来压力，并消耗有限的不可再生原材料。文献中经常建议使用诸如藻酸盐、壳聚糖和微纤化纤维素（MFC）等大量可得的生物聚合物来替代合成聚合物，并且已经详细研究了它们的阻隔性能。许多研究旨在改善独立生物聚合物薄膜的性能。一些研究将这些生物聚合物用作纸张上的阻隔涂层，但大多数这些研究中的固体含量相当低，这反过来会导致工业干燥过程中的高能量需求。本研究的目的是提出一种实验室程序，以研究这些生物聚合物在更高且更具工业相关性的固体含量下作为纸张和纸板潜在涂层材料的适用性，从而改善它们的阻隔性能。首先，以高固体含量制备生物聚合物溶液，在该固体含量下，在50,000 s（MFC为1000 s）的工业相关较高剪切速率下的粘度与10 wt%的合成参考材料（在这种情况下为乙烯 - 乙烯醇EVOH）处于相同范围。对这些溶液进行分析，考察其在工业涂布过程中与可涂布性相关的流变学和表面张力等性能。然后，浇铸独立的薄膜，并对薄膜进行表征，考察其对于包装应用重要的性能，如不同的表面性能、机械性能和阻隔性能。基于这些结果，可以轻松确定适合未来涂布试验的生物聚合物。
