据认为,冻干无定形材料的表面熔化和膨化与材料的表面温度(Tsur)和冷冻浓缩玻璃化转变温度(Tg')之间的差异有关。尽管Tg\'是特定于材料的参数,Tsur受溶质的类型和数量以及冷冻干燥条件的影响。因此,如果可以仅使用最小的必要参数来计算Tsur,这对于防止表面熔化和膨化实际上是有用的。本研究旨在根据计算的Tsur建立冻干无定形材料表面熔化和膨化的预测模型。首先,在热力学平衡假设下,提出了一个Tsur预测模型。第二,具有各种蔗糖溶质质量分数的溶液,麦芽糊精,制备蔗糖-麦芽糊精混合物,和三个材料特定参数(Tg',未冻结的水含量,和真实密度)是通过实验确定的。根据所提出的模型和参数,在13、38和103Pa的腔室压力下计算样品的Tsur。样品在腔室压力下冷冻干燥,并观察到它们的外观。不出所料,在计算的Tsur>Tg\'时发生表面熔化和膨化,但有一些例外。冻干样品的水活度(aw)随着Tsur-Tg'的增加而增加。这将是表面熔化和膨化的结果,制作了一个覆盖膜,从而防止随后的脱水。观察结果表明,所提出的模型也可用于预先确定冷冻干燥的无定形材料的干燥效率和储存稳定性。
It is thought that surface melting and
puffing of freeze-dried amorphous materials are related to the difference between the surface temperature (Tsur) and freeze-concentrated glass transition temperature (Tg\') of the materials. Although Tg\' is a material-specific parameter, Tsur is affected by the type and amount of solute and freeze-drying conditions. Therefore, it will be practically useful for preventing surface melting and
puffing if Tsur can be calculated using only the minimum necessary parameters. This study aimed to establish a predictive model for the surface melting and
puffing of freeze-dried amorphous materials according to the calculated Tsur. First, a Tsur-predictive model was proposed under the thermodynamic equilibrium assumptions. Second, solutions with various solute mass fractions of sucrose, maltodextrin, and sucrose-maltodextrin mixture were prepared, and three material-specific parameters (Tg\', unfrozen water content, and true density) were experimentally determined. According to the proposed model with the parameters, the Tsur of the samples was calculated at chamber pressures of 13, 38, and 103 Pa. The samples were freeze-dried at the chamber pressures, and their appearance was observed. As expected, surface melting and
puffing occurred at calculated Tsur > Tg\' with some exceptions. The water activity (aw) of the freeze-dried samples increased as the Tsur - Tg\' increased. This will have resulted from surface melting and
puffing, which created a covering film, thereby preventing subsequent dehydration. The observations suggest that the proposed model is also useful for predetermining the drying efficiency and storage stability of freeze-dried amorphous materials.