03/20/2026
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation defense by Saeed Alanazi on: "Effect of Nucleating Agents on Thermal and Mechanical Properties of PLA under Quiescent and Injection Molding Conditions."

Candidate Name: Saeed Alanazi
Degree: Doctoral
Defense Date: Friday, April 3, 2026
Time: 10 a.m.-noon
Location: Perry Hall 315

Committee:

  • Advisor: Davide Masato, Associate Professor, Department of Plastics Engineering, University of Massachusetts Lowell
  • Carol Barry, Professor, Department of Plastics Engineering, University of Massachusetts Lowell
  • Amir Ameli, Associate Professor, Department of Plastics Engineering, University of Massachusetts Lowell
  • Peng Gao, Assistant Professor, Department of Engineering and Design, Western Washington University

Abstract:
Poly (lactic acid) (PLA) is a widely studied bio-based thermoplastic valued for its renewable origin and biodegradability. However, its inherently slow crystallization kinetics remain a fundamental processing limitation, frequently resulting in amorphous molded parts with compromised thermal stability, dimensional accuracy, and mechanical performance. This dissertation addresses this limitation through a progressive, three-study framework aimed at establishing a coherent processing-structure-property understanding for nucleated PLA systems.

The first study examined quiescent isothermal crystallization of PLA with orotic acid (OA) and ethylene bis-stearamide (EBS) across 80–140°C. Both agents accelerated crystallization kinetics, reduced incubation time, and produced smaller, more uniformly distributed spherulitic domains. The most effective condition was 1 wt.% EBS at 110 °C, yielding the fastest crystallization rate and most densely packed lamellae. Critically, both agents enabled substantial crystallinity development at 80 °C, well below conventional processing temperatures, highlighting their potential to reduce thermal requirements during processing.

The second study investigated velocity-controlled versus pressure-controlled injection molding of neat PLA and PLA/EBS blends. Material composition was the most significant factor, with EBS increasing crystallinity by approximately 41%. However, under short cooling times, EBS particles acted as matrix discontinuities rather than nucleation sites, introducing interfacial weakness and reducing mechanical performance. Pressure-controlled molding offered a process efficiency advantage by delivering comparable crystallinity at reduced nozzle pressure. Higher injection settings most significantly improved stiffness through enhanced molecular orientation, while ultimate tensile strength remained unaffected across all conditions.
The third study evaluated mold temperature and cycle time across four systems (neat PLA, PLA/EBS, PLA/OA, and dual-nucleated PLA/EO) using a full factorial design. Cycle time was the most significant driver of crystallinity and stiffness across all formulations. Nucleated systems suppressed post-molding cold crystallization at cycle times of 150 s and beyond, reaching crystallinity levels up to 55%. Each nucleating strategy produced a distinct crystallization pathway: EBS favored efficient nucleation-dominated behavior; OA promoted growth-dominated crystallization with high stiffness but reduced ductility; and PLA/EO exhibited regime-dependent behavior that moderated the penalties of either single-agent extreme.

Collectively, these studies demonstrate that the effectiveness of organic nucleating agents in PLA is fundamentally conditional on thermal history, processing time, and the crystallization pathway they promote. Crystallinity alone is an insufficient predictor of mechanical performance; what matters is how, when, and under what conditions crystallization is allowed to develop. These findings offer a practical and transferable framework for processing nucleated PLA under industrially relevant conditions, with direct implications for reducing cycle times, improving part consistency, and advancing the broader adoption of bio-based polymers in performance-driven applications.