11/04/2025
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation defense by Sixtus Nzeh on: "Architected designs of industrial recycled post-consumer polyolefins with enhanced properties."

Candidate Name: Sixtus Nzeh
Degree: Doctoral
Defense Date: Wednesday, November 12, 2025
Time: 3:30 - 5:30 p.m.
Location: Emerging Technologies and Innovation Center (ETIC) 345

Committee:

  • Advisor: David Kazmer , Professor, Department of Plastics Engineering ,University of Massachusetts Lowell
  • Margaret J. Sobkowicz-Kline , Professor, Department of Plastics Engineering, University of Massachusetts Lowell
  • Ramaswamy Nagarajan , Professor, Department of Plastics Engineering University of Massachusetts Lowell
  • Vicky Nguyen , Professor, Department of Mechanical Engineering, Johns Hopkins University, Baltimore

Abstract:
The increasing demand for sustainable materials has intensified interest in the reuse of post-consumer polyolefins (rPOs), particularly polyethylene (PE) and polypropylene (PP), which make up about 60% of post-consumer plastic waste globally.

However, their industrial recyclability is challenged by poor mechanical performance, inconsistent melt behavior, and severe extrusion instabilities resulting from degraded chain structures, contamination, and molecular heterogeneity. This dissertation addresses these challenges through a multi-pronged research strategy involving advanced material characterization, architected processing techniques, and compatibilization approaches aimed at transforming low-value rPOs into high-performance polymer blends suitable for functional applications.

In the first phase, industrial rPOs were comprehensively characterized using rheological, thermal, spectroscopic, and morphological analyses to evaluate their compositional variability and intrinsic processing limitations. In the second phase, the materials were processed using Layer Multiplying Elements (LMEs) integrated into a co-extrusion line to generate architected multilayer structures. This approach not only enhanced mechanical integrity by improving interfacial adhesion and stress distribution but also mitigated flow instabilities typically observed in recycled polyolefins. The third phase explores the strategic incorporation of polypropylene-grafted-maleic anhydride, polyethylene-grafted-maleic anhydride, and block copolymer as compatibilizers targeting both morphological refinement and stabilization of interfacial dynamics, thereby further improving melt strength and mechanical properties.

Overall, this work demonstrates that combining multilayer processing with molecular level compatibilization provides a scalable and effective route to upgrade recycled polyolefins. The findings contribute to the development of high-value, circular polymer systems, bridging the gap between recyclability and functional performance in industrial polymer processing.