03/19/2026
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation defense by Nicholas Bowen on: "Processing and Rheology of Recycled Cellulose Fiber-Reinforced Polymer Composites for Injection Molding."

Candidate Name: Nicholas Bowen
Degree: Doctoral
Defense Date: Friday, March 27, 2026
Time: 11 a.m. - 1 p.m.
Location: ETIC 445

Committee:

  • Advisor: Davide Masato, Ph.D., Associate Professor, Department of Plastics Engineering, UMass Lowell
  • Amir Ameli, Ph.D., Associate Professor, Department of Plastics Engineering, UMass Lowell
  • Margaret J. Sobkowicz-Kline, Ph.D., Professor, Department of Plastics Engineering, UMass Lowell
  • Peng Gao, Ph.D., Assistant Professor, Department of Engineering and Design, Western Washington University

Abstract:
As the plastics industry increasingly incorporates recycled and bio-based materials, injection molding processes must accommodate materials with greater variability, thermal sensitivity, and processing instability. These challenges complicate the ability to reliably achieve consistent structure and mechanical performance in molded products. This research investigates the processing–structure–property relationships governing recycled polymer composites during injection molding, with particular emphasis on how thermal history, rheology, and processing conditions influence crystallization behavior, degradation mechanisms, and final mechanical properties. Through a series of experimental studies combining injection molding trials, material characterization, and in-mold rheological analysis, this work evaluates how processing parameters influence the performance of recycled polypropylene and cellulose fiber–reinforced polypropylene composites.
Results demonstrate that recycled polymers exhibit different sensitivities to processing conditions compared to virgin materials due to accumulated thermal history and compositional variability. Additionally, thermal degradation behavior in fiber-reinforced systems can be monitored through rapid color analysis, providing a practical method for defining stable processing windows. This research also introduces an in-mold rheological characterization approach capable of capturing non-isothermal flow behavior during injection molding. Significant differences were observed between conventional isothermal rheometry and in-process behavior due to frozen-layer formation and thermal gradients, highlighting the importance of process-relevant rheological measurements. Overall, this work establishes an integrated framework linking processing conditions, rheology, morphology, and mechanical performance in recycled polymer systems. The findings provide guidance for improving process robustness and enabling broader industrial adoption of sustainable polymer materials in injection molding applications.