Effect Of Epitaxial Crystallization On The Structural Evolution Of Poly(?-caprolactone) Nanocomposites During Tension

In this work,poly(?-caprolactone)(PCL)and reduced graphene oxide(RGO)as well as PCL and carbon nanotubes(CNT)nanocomposites were selected as the research objects to explore the effects of epitaxial crystallization and soft epitaxy mechanisms on the structural evolution of nanocomposites during tensile process.The mechanism of structural evolution was fully characterized and analyzed by small angle X-ray scattering(SAXS),wide angle X-ray diffraction(WAXD),ex-situ differential scanning calorimetry(DSC)and density measurements.The structural evolution of pure PCL during tension and the effect of epitaxial crystallization on the structural evolution of PCL/RGO nanocomposites during tension and the effect of soft epitaxy on the structural evolution of PCL/CNT nanocomposites during tension were studied in detail.The main contents and results are as follows:1.PCL/RGO nanocomposites with different RGO content and PCL/CNT nanocomposites with different CNT content were prepared.2.Pure PCL undergoes strain-induced melting-recrystallization during tension with relatively low velocity at room temperature.During the tensile process,the tension of the amorphous region causes the long period to become large,the degree of orientation and crystallinity are basically unchanged before yielding.Crystal melting occurs around yielding,while the crystallinity decreases.And continuous tension causes molecular chains to be aligned along the tensile direction,some of the original folded chains are transformed into straight chains,forming a fibril structure with some cavities.3.For PCL/RGO nanocomposites,due to the influence of flow field during the injection moulding process and the space restriction of RGO,the order of PCL molecular chains has been improved,and due to the epitaxial crystallization between RGO and PCL forms larger thickness crystals,so the degree of orientation and crystallinity are higher than Pure PCL.During the tensile process,the long period increases before yielding,while the degree of orientation and crystallinity remain unchanged.After yielding,the long period decreases rapidly,the degree of orientation increases gradually,and the crystallinity decreases firstly and then increases gradually.With the increase of RGO content,PCL/RGO nanocomposites exhibit a hysteresis phenomenon in longperiod,the degree of orientation and crystallinity.Generally speaking,PCL/RGO nanocomposites undergo strain-induced melting-recrystallization during tension with relatively low velocity at room temperature.And epitaxial crystals limit the structural evolution of PCL during tensile process,and more cavities formed than Pure PCL.4.For PCL/CNT nanocomposites,Due to the different structure from the two-dimensional planar RGO,the surface curvature of one-dimensional CNT is extremely large,so the the epitaxial crystallization is neglected,mainly occurs soft epitaxy by surface-induced between CNT and PCL.The soft epitaxy between CNT and PCL forms nanohybrid shish-kebabs,which improve the degree of orientation and crystallinity of PCL.During the tensile process,the long period increases before yielding,while the degree of orientation and crystallinity remain unchanged.After yielding,the long period decreases rapidly,the degree of orientation increases gradually,and the crystallinity decreases firstly and then increases gradually.Although the same melting-recrystallization and fibrillation process take place,the nanohybrid shish-kebabs in PCL/CNT nanocomposites change a little during the tensile process,only a small part of them melts,and more tension and fibrillation originated from amorphous region,thereby generating more cavities between the crystalline region and the amorphous region.