Cold drawing of semicrystalline polymers causes complex morphological changes due to molecular alignment and crystal rearrangements. These processes are intimately related to the mechanical properties such as strain hardening and tear. Small- and wide- angle X-ray scattering (SAXS and WAXS) have been widely used to investigate structural changes of the crystalline lamellar and lamellar superstructures during drawing. However these techniques cannot directly probe molecular alignment, which is key to fully understand the deformation processes from a molecular basis. Small angle neutron scattering (SANS) provides information about molecular dimensions as well as orientation and alignment induced by external fields such as shear flow or elongation. We performed in-situ SANS measurements during cold drawing of LLDPE blends composed of deuterated and hydrogenated commercial LLDPEs. We found that most of the molecular alignment occurs during the initial stage of deformation and slows down after the yield point. No further alignment occurs after the onset of strain-hardening. Fractionation of the deuterated LLDPE allows us to compare the alignment of the low molecular weight (MW) chains to that of the high MW chains. Although both fractions are well distributed in both the crystalline lamellar and the amorphous phases, we found that the high MW chains align significantly more that the low MW chains. Combining these results with in-situ SAXS/WAXS and polarized Raman measurements during deformation allows us to generate a complete picture of the microstructure evolution in relation to the stress-strain behavior of commercial polyethylenes. Complementary in-situ small angle light scattering and microscopy measurements will also be presented.

Molecular alignment of LLDPE during cold drawing: An <i>in-situ</i> tensile-SANS study

251st National Meeting (2016)

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Molecular alignment of LLDPE during cold drawing: An in-situ tensile-SANS study