Gradient Nanostructure\nand its Relationship with the\nMechanical Properties of Injection-Molded PBAT Studied Using SAXS-CT

The difference in the polymer processing conditions can\nlead to\na significant difference in the polymer performance. Structural characterization\nplays an important role, but it is challenging to determine the relationship\nbetween polymer processing and performance. An unprecedented new method\nin development, small-angle X-ray scattering microtomography (SAXS-CT)\nshows powerful prospects for revealing the polymer microstructures.\nThis study has been used to analyze the gradient nanostructures of\npoly(butylene adipate-<i>co</i>-terephthalate) (PBAT) produced\nby an oscillation shear injection molding (OSIM) with various parameters.\nThe significant benefit of using this approach is that a sample of\nseveral millimeters can be virtually divided into thousands of voxels\nwhile the nanostructure information in each voxel is extracted nondestructively.\nFor each sample produced by specific OSIM processing, nearly 10,000\ntwo-dimensional scattering patterns are reconstructed, and the detailed\nthree-dimensional distribution of structural parameters, including\nthe long period, lamella thickness, amorphous layer thickness, crystallinity,\nand orientation are drawn one by one according to the tremendous scattering\ndata. Interestingly, the distribution of these parameters shows a\nvery clear ring band in the cross-section of the sample, and the size\nof this band varies with the preparation conditions of the samples.\nSuch a phenomenon has never been observed in previous studies using\nother characterization methods. The results reveal that a high shear\ntime is beneficial for the formation of lamellae in the OSIM-made\nsamples. It also suggests that compared to conventional injection\nmolding (CIM), OSIM processing can generally enhance Young’s\nmodulus of PBAT, and low temperature and high shear duration will\ngreatly boost its tensile strength. The accurate and detailed nanostructure\nobtained by SAXS-CT paves a new way to establish the relationship\nbetween the process technology and the structure of the injection-molded\npolymer.