Universidad Nacional del Centro de la Provincia de Buenos Aires (UNCPBA), Facultad de Ciencias Exactas, Instituto de Física de Materiales Tandil (IFIMAT), Grupo Positrones "Prof. Alfredo Dupasquier", Pinto 399, 7000 Tandil, Buenos Aires, Argentina; CIFICEN, UNCPBA-CICPBA-CONICET, Tandil, Buenos Aires, Argentina.
Instituto de Investigación e Ingeniería Ambiental (IIIA), CONICET, Universidad Nacional de San Martín, (3iA), Campus Miguelete, 25 de mayo y Francia (1650), San Martín, Buenos Aires, Argentina.
Carbohydr Polym. 2023 Jun 15;310:120739. doi: 10.1016/j.carbpol.2023.120739. Epub 2023 Feb 23.
The effect of citric acid (CA) concentration and water content on the free hole volume of thermoplastic cassava starch films (TPS) was studied. To this aim, continuous in situ positron annihilation lifetime spectroscopy measurements were performed at fixed moisture content and during water desorption. The results show that the increase in CA concentration leads to wider free hole volume distributions with lower mean values. During water desorption, the mean values and width of such distributions systematically decrease with the exposure time, and the evolution of the hole volumes was well-described using the Kohlrausch-Williams-Watts function. The water vapour permeability was significantly higher in films incorporating 5 % (w/w) of CA, in line with the more open network of this material that was revealed in the hole volumes distribution. The Young's modulus of all the developed films increased significantly after partial water desorption, which was attributed to the plasticizer loss reflected in a decrease in the mean hole volume value (between 4 % and 13 %). This work evidences that the control and report of the relative humidity are essential when testing TPS-based films, as their nanostructures are strongly dependent on external conditions.
研究了柠檬酸（CA）浓度和含水量对热塑性木薯淀粉薄膜（TPS）自由孔体积的影响。为此，在固定水分含量和水分解吸过程中进行了连续的原位正电子湮没寿命谱测量。结果表明，CA 浓度的增加导致更宽的自由孔体积分布，平均值更低。在解吸过程中，这些分布的平均值和宽度随暴露时间系统地减小，孔体积的演化可以用 Kohlrausch-Williams-Watts 函数很好地描述。含有 5%（w/w）CA 的薄膜的水蒸气透过率显著提高，与该材料的更开放网络一致，这在孔体积分布中得到了揭示。在部分水分解吸后，所有开发的薄膜的杨氏模量都显著增加，这归因于增塑剂损失，反映在平均孔体积值（4%至 13%之间）的降低。这项工作表明，在测试基于 TPS 的薄膜时，控制和报告相对湿度是必不可少的，因为它们的纳米结构强烈依赖于外部条件。
