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首页> 外文会议>The 8th International Symposium on the Properties of Water, 8th, Sep 16-21, 2000, Zichron Yaakov, Israel >Plasticization and Antiplasticization of Starch Glasses by Water
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Plasticization and Antiplasticization of Starch Glasses by Water

机译：水对淀粉玻璃的增塑和抗塑化作用

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Water is able to reduce by plasticization the glass transition temperature, Tg, of many hydrogen bonded biopolymers. Simultaneously, low water concentrations appear to improve the barrier property of amorphous starch by increasing its density and by lowering its compressibility, thermal expansion and free volume. This counter-intuitive effect of low solvent concentrations on polymer glasses is called antiplasticization because the opposite volumetric and mechanical behavior is typically observed upon plasticization. The thermodynamic data of starch-water systems shows that antiplasticization and plasticization occur simultaneously in systems exhibiting sigmoidal type IV vapor sorption. The linear decrease of Tg with increasing mole fraction of water reported here suggests that the whole water content of the system is involved in its plasticization. The dual sorption approach combining the Flory model of polymer solutions with a generalized Freundlich adsorption model suggests further that only the Freundlich part is involved in antiplasticization whereas both parts are involved in plasticization. The analysis suggests thus that antiplasticization is not an intrinsic property of water but a general feature occurring whenever a solvent has the size and the affinity required to occupy the excess free volume available within polymers frozen in a glassy state. Antiplasticization occurs thus spontaneously whenever a dry polar polymer glass is exposed to ambient moisture as indicated by water sorption phenomenology. The apparent correlation of antiplasticization and sigmoidal sorption can highlight how plasticizers are able to minimize the excess free volume of glassy polymers used in controlled release applications.
机译：水可以通过增塑来降低许多氢键生物聚合物的玻璃化转变温度Tg。同时，低水浓度似乎通过增加其密度并降低其可压缩性，热膨胀性和自由体积而改善了无定形淀粉的阻隔性能。低溶剂浓度对聚合物玻璃的这种反直觉的影响称为抗塑化，因为在塑化时通常会观察到相反的体积和机械性能。淀粉-水系统的热力学数据表明，在表现出S型IV型蒸汽吸附的系统中，抗塑化作用和增塑作用同时发生。 Tg随水的摩尔分数增加而线性降低，表明该系统的整个含水量都与它的增塑有关。将聚合物溶液的弗洛里模型与广义Freundlich吸附模型结合起来的双重吸附方法进一步表明，只有Freundlich部分参与了抗塑化，而两个部分都参与了塑化。因此分析表明，抗塑化不是水的固有特性，而是每当溶剂具有一定尺寸和亲合力，以占据以玻璃态冷冻的聚合物中可用的过量自由体积时，就会发生的一般特征。因此，每当干燥的极性聚合物玻璃暴露于环境湿气时，就会自动发生抗塑化作用（如吸水现象）。抗塑化和S形吸附的明显相关性可以突出显示增塑剂如何最大程度地减少控释应用中使用的玻璃状聚合物的过量自由体积。

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