Composition dependence of flow-induced crystallization in high-density polyethylene/isotactic polypropylene blends

Published

October 2, 2024

Author(s)

McKenzie Coughlin, Derek Huang, Caitlyn Edgar, Anthony Kotula, Kalman Migler

Abstract

Polyolefins, including high density polyethylene (HDPE) and isotactic polypropylene (iPP), account for over half of the worldwide plastics market and have wide-ranging applications. Recycling of these materials is hindered due to separation difficulties as co-mingled blends of HDPE and iPP often exhibit brittle mechanical behavior because phase separated domains detach under stress due to low interfacial adhesion. Motivated to improve mechanical properties of mixed recyclates during processing, this work examines the effect of shear on the crystallization kinetics and rheological properties of HDPE-iPP blends utilizing a combination of differential scanning calorimetry (DSC), rheo-Raman spectroscopy, polarized optical microscopy, and scanning electron microscopy (SEM). In the quiescent experiments, the crystallization temperature as a function of blend composition exhibits a distinct decrease when the iPP forms the droplet phase, as expected, due to fractionated crystallization. In the presence of shear, we find elongated domains due to high capillary number. Unexpectedly we find a compositional dependence to the flow-induced crystallization (FIC) of iPP: stronger FIC is observed in all blends compared to the pure iPP. Moreover, the flow completely counteracts the reduced crystallization arising from fractionated crystallization, indicating that the flow is able to induce nucleation in droplets to an extent such that it offsets the reduction in active nucleating agents in finite size droplets. We attribute these effects to differing micro flow fields in the various morphologies as the iPP domains deform under shear.

Citation

Macromolecules

Volume

57

Issue

20

Pub Type

Journals

Download Paper

https://doi.org/10.1021/acs.macromol.4c01952

Local Download

Keywords

Polymer blends, polyolefins, mixed recyclates, flow-induced crystallization

Citation

Coughlin, M. , Huang, D. , Edgar, C. , Kotula, A. and Migler, K. (2024), Composition dependence of flow-induced crystallization in high-density polyethylene/isotactic polypropylene blends, Macromolecules, [online], https://doi.org/10.1021/acs.macromol.4c01952, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=956680 (Accessed October 25, 2024)