Sängerlaub Sven, Kucukpinar Esra, Müller Kajetan
Fraunhofer Institute for Process Engineering and Packaging IVV, Giggenhauser Strasse 35, 85354 Freising, Germany.
TUM School of Life Sciences Weihenstephan, Chair of Food Packaging Technology, Technical University of Munich, Weihenstephaner Steig 22, 85354 Freising, Germany.
Materials (Basel). 2019 Jul 18;12(14):2304. doi: 10.3390/ma12142304.
Silica gel is a well-known desiccant. Through dispersion of silica gel in a polymer, films can be made that absorb and desorb water vapor. The water vapor absorption becomes reversible by exposing such films to a water vapor pressure below that of the water vapor pressure during absorption, or by heating the film. The intention of this study was to achieve a better understanding about the water vapor absorption, permeability (HO, N, O, CO), and mechanical properties of films with dispersed silica gel. Low-density polyethylene (PE-LD) monolayer films with a nominal silica gel concentration of 0.2, 0.4, and 0.6 g dispersed silica gel per 1 g film (PE-LD) were prepared and they absorbed up to 0.08 g water vapor per 1 g of film. The water vapor absorption as a function of time was described by using effective diffusion coefficients. The steady state (effective) water vapor permeation coefficients of the films with dispersed silica gel were a factor of 2 to 14 (8.4 to 60.2·10 mg·cm·(cm²·s·Pa), 23 °C) higher than for pure PE-LD films (4.3·10 mg·cm·(cm²·s·Pa), 23 °C). On the other hand, the steady state gas permeabilities for N, O, and CO were reduced to around one-third of the pure PE-LD films. An important result is that (effective) water vapor permeation coefficients calculated from results of sorption and measured by permeation experiments yielded similar values. It has been found that it is possible to describe the sorption and diffusion behavior of water by knowing the permeability coefficient and the sorption capacity of the film (Peff.≈Seff.·Deff.). The tensile stress changed only slightly (values between 10 and 14 N mm²), while the tensile strain at break was reduced with higher nominal silica gel concentration from 318 length-% (pure PE-LD film) to 5 length-% (PE-LD with 0.6 g dispersed silica gel per 1 g film).
硅胶是一种广为人知的干燥剂。通过将硅胶分散在聚合物中，可以制成能吸收和解吸水蒸气的薄膜。通过将此类薄膜暴露在低于吸收过程中水蒸气压力的水蒸气压力下，或通过加热薄膜，水蒸气吸收变得可逆。本研究的目的是更好地了解含有分散硅胶的薄膜的水蒸气吸收、渗透性（H₂O、N₂、O₂、CO₂）和机械性能。制备了标称硅胶浓度为每1克薄膜（低密度聚乙烯（PE-LD））含有0.2、0.4和0.6克分散硅胶的PE-LD单层薄膜，它们每1克薄膜最多吸收0.08克水蒸气。利用有效扩散系数描述了水蒸气吸收随时间的变化。含有分散硅胶的薄膜的稳态（有效）水蒸气渗透系数比纯PE-LD薄膜（4.3×10⁻¹²毫克·厘米/(厘米²·秒·帕)，23℃）高2至14倍（8.4至60.2×10⁻¹²毫克·厘米/(厘米²·秒·帕)，23℃）。另一方面，N₂、O₂和CO₂的稳态气体渗透率降低到纯PE-LD薄膜的三分之一左右。一个重要的结果是，根据吸附结果计算并通过渗透实验测量的（有效）水蒸气渗透系数得出了相似的值。已经发现，通过了解薄膜的渗透系数和吸附容量（Peff.≈Seff.·Deff.），可以描述水的吸附和扩散行为。拉伸应力仅略有变化（值在10至14牛/毫米²之间），而断裂伸长率随着标称硅胶浓度的增加从318长度%（纯PE-LD薄膜）降低到5长度%（每1克薄膜含有0.6克分散硅胶的PE-LD）。
