11/03/2023
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation defense by Shawn Martey on "Reactive processing and melt compounding of plastic waste by incorporating catalysts and nanoparticles."

Candidate Name: Shawn Martey
Degree: Doctoral
Defense Date: Friday, Nov. 17, 2023
Time: 1-3 p.m.
Location: ETIC 345

Committee:

  • Advisor: Margaret Sobkowicz-Kline, Professor, Plastics Engineering, University of Massachusetts Lowell
  • Co-Advisor: Wan-Ting (Grace) Chen, Assistant Professor, Plastics Engineering, University of Massachusetts Lowell
  • Carol Barry, Professor, Plastics Engineering, University of Massachusetts Lowell
  • Jo Ann Ratto, Ph.D., Research Materials Engineer, U.S. Army Combat Capabilities Development Command

Brief Abstract:
This dissertation explores the role of selected catalysts and nanoparticles including clay, aramid nanofiber and nanoclay in polyethylene and polyolefin-based immiscible waste polymer blends during melt extrusion. The overall goal was to seek improvements to mechanical recycling of waste plastics in pursuit of a circular economy.

The first part of this work investigates the role of y-zeolites and MCM-41 catalysts in reactive extrusion of LDPE at low and high shear. LDPE extruded with microporous y-zeolite shows lower degradation temperature and increased short chain branching. Mesoporous MCM-41 also induces increased branching but has no effect on the degradation temperature. Structural and chemical properties of the catalysts are correlated to the effects on the polymer.

The second part presents the role of clay, polymer grafted aramid nanofibers and nanoclay in improving the properties of ocean bound waste plastics and waste polypropylene/poly(ethylene terephthalate) immiscible blends. Ocean bound waste plastics consisting of high-density polyethylene (HDPE) and polypropylene (PP) were blended with virgin LDPE while incorporating ethylene propylene rubber (EPR) and custom clay filler. The polymer blend containing EPR showed improved elasticity. Incorporating additives such as rubber could improve the mechanical properties of polymer blends for recycling purposes.

Nanofibers have the tendency to improve properties of polymers; however, nanoscale fillers tend to agglomerate in the polymer matrix due to their high surface energy and incompatibility with polymers. To improve dispersion of nanofibers like aramid nanofiber in immiscible PP/PET blend, PP and PET were grafted separately onto aramid nanofiber and melt blended with immiscible PP/PET waste blend. Droplet size distributions of 0.1-6.2 μm, 0.5-7.4 μm and 0.2-2 μm were observed when 1 wt.% of ANF, PET_ANF and PP_ANF were added to PP/PET blends respectively. Smaller droplet size and good dispersion suggests improvement in mechanical properties of the blend. This was evident in the increase in the tensile modulus of the blend when 5% of PP_ANF was added.

Nanoclay has been identified to reduce the droplet size of the dispersed phase in an immiscible polymer blend. The mechanism for this phenomenon is poorly understood. The last part of this project seeks to understand the role of montmorillonite in immiscible PP/PET blend. When PP and PET were compounded with modified montmorillonite (cloisite 20A), it was observed that cloisite 20A reduced the droplet size of PET in the PP matrix by suppressing coalescence of the droplets. Additionally, smaller droplets size of PET (0.7-2.7 μm) in the blend enhanced the mechanical properties of PP/PET blend as compared to unfilled PP/PET blend with droplets size ranging from 0.7-14.2 μm.

The investigations presented in this dissertation reveal the role of various catalysts and nanoparticles in improving the properties of plastic waste and can help in the exploration of other nanoparticles and catalysts for mechanical recycling.