Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)
Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)
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DOI：
10.3390/ma13061371
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发表时间：
2020-03-02
期刊：
影响因子：
3.4
通讯作者：
Altstaedt, Volker
中科院分区：
文献类型：
--
作者：
Standau, Tobias;Long, Huan;Altstaedt, Volker
在这项综合研究中，研究了(I)材料特性(例如，相对分子质量、零剪切粘度、D-含量)和(Ii)工艺参数(例如，饱和温度、-时间、-压力和压降速率)对线性聚乳酸(PLA)级高压灭菌器发泡过程中的膨胀行为的影响，以识别和评估发泡相关参数。其较差的流变性经常被认为是聚乳酸的一个缺点，这限制了其发泡能力。因此，系统地选择了9个不同熔体强度和零剪切粘度的聚乳酸牌号，以确定这些因素是否是影响泡沫膨胀的主要因素，以及是否存在超过这些流变性参数的临界值，以获得具有细孔的低密度泡沫。通过压降诱导间歇发泡实验表明，所研究的所有聚乳酸牌号都可以在没有常用的化学改性的情况下发泡，尽管具有不同的膨胀程度。有趣的是，聚乳酸的发泡行为相当复杂，由于其特殊的性质，可以受到许多其他因素的影响。低分子量与高结晶能力相结合，只会导致中等密度的降低。相反，较高的相对分子质量(即增加的零剪切粘度)会显著增加膨胀性，而不依赖于D-含量。然而，D-含量在发泡温度和结晶方面起着至关重要的作用。此外，所应用的工艺参数控制泡沫膨胀、泡孔大小和结晶。
In this comprehensive study, the influence of (i) material specific properties (e.g., molecular weight, zero shear viscosity, D-content) and (ii) process parameters (e.g., saturation temperature, -time, -pressure, and pressure drop rate) on the expansion behavior during the autoclave foaming process were investigated on linear Polylactide (PLA) grades, to identify and evaluate the foam relevant parameters. Its poor rheological behavior is often stated as a drawback of PLA, that limits its foamability. Therefore, nine PLA grades with different melt strength and zero shear viscosity were systematically chosen to identify whether these are the main factors governing the foam expansion and whether there is a critical value for these rheological parameters to be exceeded, to achieve low density foams with fine cells. With pressure drop induced batch foaming experiments, it could be shown that all of the investigated PLA grades could be foamed without the often used chemical modifications, although with different degrees of expansion. Interestingly, PLAs foaming behavior is rather complex and can be influenced by many other factors due to its special nature. A low molecular weight combined with a high ability to crystallize only lead to intermediate density reduction. In contrast, a higher molecular weight (i.e., increased zero shear viscosity) leads to significant increased expandability independent from the D-content. However, the D-content plays a crucial role in terms of foaming temperature and crystallization. Furthermore, the applied process parameters govern foam expansion, cell size and crystallization.