Rheology in the Presence of Carbon Dioxide (CO2) to Study the Melt Behavior of Chemically Modified Polylactide (PLA)
Rheology in the Presence of Carbon Dioxide (CO2) to Study the Melt Behavior of Chemically Modified Polylactide (PLA)
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DOI：
10.3390/polym12051108
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发表时间：
2020-05-01
期刊：
影响因子：
5
通讯作者：
Altstaedt, Volker
中科院分区：
文献类型：
--
作者：
Doerr, Dominik;Standau, Tobias;Altstaedt, Volker
为了制备聚乳酸（PLA）基泡沫，通常需要增加聚合物的熔体强度。添加剂如扩链剂（CE）或过氧化物通常用于在反应性挤出期间通过支化或甚至交联来增加分子量。此外，在发泡过程中引入具有低分子量的发泡剂，例如二氧化碳（CO2），这可能影响挤出过程中的反应性。离线流变测试可以帮助测量和更好地理解反应动力学，特别是聚合物和化学改性剂之间的反应。然而，流变学测量主要在惰性氮气气氛中进行，而没有聚合物熔体的等效气体负载，如在相应的反应性挤出过程中。因此，在这些标准流变测量中不考虑发泡剂本身的影响。因此，在这项研究中，配备有压力单元的流变仪用于在高达40巴的压力下在CO2的存在下进行纯聚合物和化学改性聚合物的流变测量。研究和比较了在高压下CO2对聚合物和化学改性剂（有机过氧化物和作为第二选择的环氧基CE）之间的反应性的具体影响。流变实验表明，在CO2存在下，扩链剂的反应性降低，而过氧化物的影响较小。最后，可以通过流变仪中的扭矩最大值检测未改性和未支化的样品的重结晶温度T-rc，该扭矩最大值代表印模从样品上撕下。T-RC是约13 K低，在CO2负载的样品。此外，可以同时检测分支和气体负载的影响。在这里，与气体负载相比，分支对T-rc的影响要高得多。
For the preparation of polylactide (PLA)-based foams, it is commonly necessary to increase the melt strength of the polymer. Additives such as chain extenders (CE) or peroxides are often used to build up the molecular weight by branching or even crosslinking during reactive extrusion. Furthermore, a blowing agent with a low molecular weight, such as carbon dioxide (CO2), is introduced in the foaming process, which might affect the reactivity during extrusion. Offline rheological tests can help to measure and better understand the kinetics of the reaction, especially the reaction between the polymer and the chemical modifier. However, rheological measurements are mostly done in an inert nitrogen atmosphere without an equivalent gas loading of the polymer melt, like during the corresponding reactive extrusion process. Therefore, the influence of the blowing agent itself is not considered within these standard rheological measurements. Thus, in this study, a rheometer equipped with a pressure cell is used to conduct rheological measurements of neat and chemical-modified polymers in the presence of CO2 at pressures up to 40 bar. The specific effects of CO2 at elevated pressure on the reactivity between the polymer and the chemical modifiers (an organic peroxide and as second choice, an epoxy-based CE) were investigated and compared. It could be shown in the rheological experiments that the reactivity of the chain extender is reduced in the presence of CO2, while the peroxide is less affected. Finally, it was possible to detect the recrystallization temperature T-rc of the unmodified and unbranched sample by the torque maximum in the rheometer, representing the tear off of the stamp from the sample. T-rc was about 13 K lower in the CO2-loaded sample. Furthermore, it was possible to detect the influences of branching and gas loading simultaneously. Here the influence of the branching on T-rc was much higher in comparison to a gas loading.