08/13/2025
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation Proposal defense by Pongkhun Prommart on: "Recycling Challenging Waste Streams: Solvent-based Recycling of Poly(vinyl alcohol) and Hydrothermal Liquefaction of Mixed PE."

Candidate Name: Pongkhun Prommart
Degree: Doctoral
Defense Date: Monday, August 25, 2025
Time: 10 a.m. - 1noon
Location: ETIC 445

Committee:

  • Advisor: Wan-Ting Chen, Associate Professor, Plastics Engineering, University of Massachusetts Lowell
  • David Kazmer, Professor, Plastics Engineering, University of Massachusetts Lowell
  • Margaret SobkowiczKline, Professor, University of Massachusetts Lowell
  • Jo Ann Ratto, Retired Polymer Research Engineer, U.S Army Natick Soldier Research, Development and Engineering Center

Brief Abstract:
The global production rate of plastic products has risen quickly while recycling rates have stagnated. Mechanical recycling remains the dominant method of recycling and has been shown to have the lowest environmental impact in many lifecycle assessments (LCAs). However, it struggles to recycle highly contaminated or complex waste streams. Solvent-based recycling and chemical recycling can complement mechanical recycling by handling these challenging waste streams or upcycling plastic waste into value added chemicals. This PhD dissertation aims to increase the circularity of plastic waste through two approaches: solvent-based recycling of multi-layer film and hydrothermal liquefaction (HTL) of mixed waste. Firstly, Chapter 1 investigates the dissolution and recovery of polyvinyl alcohol (PVOH) in PVOH/poly(butylene adipate-co-terephthalate) (PBAT) - poly(lactic acid) (PLA) multi-layer films to better understand the dissolution behavior of PVOH and the effects of solvent-based recycling on the mechanical properties of PVOH. The effect of temperature, time, agitation, and film size on the dissolution behavior were investigated. Additionally, the chemical, physical, and barrier property differences between virgin PVOH and recovered PVOH were evaluated. Secondly, Chapter 2 extends this approach to the dissolution of PVOH in PVOH/polyethylene (PE) multi-layer films with a focus on the scale up potential of the process. The film loading will be maximized to increase the process efficiency, and the kinetics of dissolution as a function of film loading, agitation, temperature, size, and presence of a tie layer will be investigated to guide the scaling up of the process. Thirdly, Chapter 3 investigates HTL of real mixed polyethylene terephthalate (PET) and polypropylene (PP) waste to produce terephthalic acid (TPA) and oil at different temperatures, times, pressures, and polymer loadings. First, the oil yield and TPA yield from HTL of PET and PP will be examined separately. Then, HTL of mixed PET and PP at different ratios will be optimized for producing either the oil or TPA products. With optimized conditions, real PET and PP waste will be tested to evaluate the effect of real waste on the HTL process.