Department of Chemistry, Moscow State University , 1/3, Lenin Hills, Moscow 119991, Russia.
National Research Centre "Kurchatov Institute" , 1, Akademika Kurchatova pl., Moscow 123182, Russia.
ACS Appl Mater Interfaces. 2017 Oct 4;9(39):34325-34336. doi: 10.1021/acsami.7b09666. Epub 2017 Sep 20.
Uniaxial tension accompanied by the orientation and crystallization of polymer chains is one of the powerful methods for the improvement of mechanical properties. Crystallization of amorphous isotropic polylactide (PLA) at room temperature is studied for the first time during the drawing of films in the presence of liquid adsorption-active media (ethanol, water-ethanol mixtures, and n-heptane) by the solvent crazing mechanism. The crystalline structure arises only under simultaneous actions of a liquid medium and a tensile stress and does not depend on the nature of the environment. The degree of polymer crystallinity increases nearly linearly with the growth in the fraction of the fibrillar material and reaches a maximum value of 42-45%. It has been stated that polymer crystallization happens in crazes involving nanofibrils with a diameter of about 10-20 nm without affecting the bulk polymer parts. Wide-angle X-ray scattering has been used to confirm that the crazing-induced crystallization is accompanied by the formation of the α'-crystalline phase with crystallite sizes (X-ray coherent scattering region) of 3-5 nm, depending on the nature of the liquid medium. After stretching in liquid media to a high tensile strain, the strength of a PLA film has increased to 200 MPa.
单轴拉伸伴随着聚合物链的取向和结晶是改善力学性能的有效方法之一。通过溶剂微纤化机制，首次研究了在室温下通过拉伸薄膜时，在具有液体吸附活性介质（乙醇、水-乙醇混合物和正庚烷）存在下，无定形各向同性聚乳酸（PLA）的结晶。只有在液体介质和拉伸应力的同时作用下，才会出现结晶结构，而与环境的性质无关。聚合物结晶度随纤维状材料分数的增加几乎呈线性增加，达到 42-45%的最大值。已经指出，聚合物结晶发生在涉及直径约为 10-20nm 的纳米纤维的银纹中，而不会影响聚合物本体部分。广角 X 射线散射已被用于证实，微纤化诱导的结晶伴随着形成α'-晶相，其晶粒尺寸（X 射线相干散射区）为 3-5nm，取决于液体介质的性质。在液体介质中拉伸至高拉伸应变后，PLA 薄膜的强度增加到 200MPa。
