Fiber-spun polypropylene/polyethylene terephthalate microfibrillar composites with enhanced tensile and rheological properties and foaming ability

- Conventional fiber spinning is used for the in situ fibrillation of polyethylene terephthalate (PET) in a polypropylene (PP) matrix.
- The effect of draw ratio during fiber spinning on the PP/PET morphology is characterized.
- The PP/PET (95/5 wt%) fibrillar blend exhibits strain hardening in uniaxial extensional flow.
- Extrusion foaming is used to demonstrate enhancements in foaming ability of PP after fiber spinning with 5 wt% PET.

Modification of the mechanical and rheological properties of polypropylene (PP) is accomplished through the in-situ generation of polyethylene terephthalate (PET) fibrils via fiber spinning of PP/PET (95/5 wt%). This modification increases the tensile strength of PP fibers by up to 46% and elongation at break by up to seven-folds. The change in the tensile properties is governed by the draw ratio. Uniaxial extensional viscosity measurements show a strain-hardening behavior in the fiber-spun PP/PET, not observed in the neat PP or in the melt-blended PP/PET. The oscillatory shear behavior in the linear viscoelastic region is studied to understand the percolation properties of PET fibrils in PP. When the PET domains are fibrillated, the storage (G′) and loss (G″) moduli increase and their slopes decrease at low frequencies compared to neat PP or melt-blended PP/PET, indicating that the fibril network responds elastically over long timescales. The wide-angle X-ray scattering (WAXS) data shows the presence of γ-polymorph crystals of PP in both PP and the fiber-spun PP/PET. Foam extrusion is used as a model polymer process to study the effect of the PET fibrils on the processability of PP. Results reveal that the presence of PET fibrils in PP yields foams that exhibit up to two orders of magnitude higher cell densities and up to a five-fold increase in the expansion ratio relative to the neat PP. Enhancing the foaming ability of polymer blends by fibrillating the dispersed phase using fiber spinning is technologically promising.

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