The role of solubility and critical temperatures for the efficiency of sorbitol clarifiers in polypropylene
作者:Zsuzsanna Horváth、Benjámin Gyarmati、Alfréd Menyhárd、Petar Doshev、Markus Gahleitner、József Varga、Béla Pukánszky
DOI:10.1039/c4ra01917b
日期:——
The optical properties of polypropylene (PP) were modified by nine different sorbitol type clarifiers available commercially or synthesized in the study. The solubility of the clarifiers in PP was estimated by thermodynamic model calculations. The results showed that the solubility of these additives in PP is small, a few 1000 ppm at most. Solubility is determined by the chemical structure of the sorbitol, and the heat of fusion of the latter changes solubility by at least one order of magnitude. Solubility can be estimated reasonably by the Flory–Huggins lattice theory. The morphology of most sorbitols transforms at a temperature much below their melting point upon heating. This transformation, which is accompanied by crystal perfection, seems to influence melting and solubility. A fibrillar structure forms upon the cooling of molten sorbitols, but the diameter of the fibrils is much larger than those forming in the polymer melt. The nucleating effect of the clarifier depends on solubility, but also on processing conditions. Nucleus density is related to the amount of dissolved clarifier. A close correlation was found between the Flory–Huggins interaction parameter of sorbitols and the smallest achievable haze, which can be explained by the effect of solubility and nucleus density.
本研究利用市售或合成的九种不同山梨醇型澄清剂改变了聚丙烯(PP)的光学特性。通过热力学模型计算估算了这些澄清剂在 PP 中的溶解度。结果表明,这些添加剂在聚丙烯中的溶解度很小,最多只有几千 ppm。溶解度由山梨醇的化学结构决定,而山梨醇的熔融热会使溶解度发生至少一个数量级的变化。溶解度可以通过弗洛里-哈金斯晶格理论进行合理估算。加热时,大多数山梨醇的形态会在远低于熔点的温度下发生转变。这种转变伴随着晶体的完善,似乎会影响熔化和溶解度。熔融山梨醇冷却后会形成纤维状结构,但纤维的直径要比聚合物熔体中形成的纤维大得多。澄清剂的成核效应不仅取决于溶解度,还取决于加工条件。成核密度与澄清剂的溶解量有关。研究发现,山梨醇的 Flory-Huggins 作用参数与可达到的最小雾度之间存在密切联系,这可以用溶解度和晶核密度的影响来解释。