Date of Award
Spring 5-16-2025
Document Type
Thesis
Degree Name
Master of Science in Chemistry (MSChem)
Department
Chemistry
First Advisor
Jeanne Norton jnorton@pittstate.edu
Second Advisor
Charles Neef cneef@pittstate.edu
Third Advisor
Paul Herring pherring@pittstate.edu
Abstract
THE EFFECTS OF REPROCESSING, POST-PROCESSING CONDITIONS, AND ENVIRONMENTAL EXPOSURE ON THE PHYSICAL PROPERTIES OF POST-INDUSTRIAL AND POST-CONSUMER POLYETHYLENE
An Abstract of the Thesis by
Grant Howard
Plastic pollution is a rapidly growing problem. Globally, millions of tons of plastic waste are produced, and that amount is projected to increase each year. To address this, recycling of commodity thermoplastics like polyethylene, polypropylene, and polyethylene terephthalate, have become a point of emphasis in industry. Companies have started to investigate the use of recycled plastics instead of virgin plastics in their products. The advantages of using recycled material are to receive tax breaks, to increase a company’s reputation, reduce material costs, and to reduce environmental impact. There are several tax breaks for companies using recycled material such as the IRS recycling tax credits, grants offered by the Department of Energy, and state tax incentives. As more consumers of plastic products are becoming more aware of sustainability, the image of companies that use recycled materials and highlight that use in their product marketing tends to rise for the general public. When a company uses recycled material, they are reducing their material costs, like using a small percentage of scrap material, which allows them to produce their products more inexpensively and decrease their material overhead. When producing virgin plastics, there are significant environmental impacts including water pollution, global warming, resource depletion, and microplastics pollution. By using recycled plastic, carbon emissions are reduced compared to virgin materials.
A recycled material undergoes size reduction when being recycled, which applies stress and shear that may affect the physical properties of the material. Changes in the physical properties of a plastic as a result of recycling could impact the ability of that company’s product to function as intended. In order to maximize the use of recycled material, companies must research the effects of mechanical recycling, environmental exposure, and successive rounds of reprocessing and ensure that the materials still have the desired mechanical, thermal, and chemical properties required for the products application.
After being processed, products undergo several different conditions. These conditions could be intentional and are made by the plastic manufacturer for the purpose of modifying final crystallinity. By controlling the rate of cooling in an ice bath, crystallization can be slowed or stopped, while annealing at the crystallization temperature enhances crystallization and ensures greater dimensional stability in the finished part, due to reducing the shrinkage. Some of the conditions in which a recycled plastic has been exposed are not intentional, but a result of typical wear and tear that a product may experience in its normal service life. A product that is exposed to the weather can experience a wide variety of exposure conditions such as moisture, UV radiation, chemical exposure, and extreme temperatures. These hazards could have negative impacts on the recycled plastic’s physical properties, making it unsuitable for reprocessing into products for certain applications.
To gain a more comprehensive understanding of recycled materials, we must investigate how reprocessing post-industrial and post-consumer materials changes physical properties when compared to virgin materials. We will examine how post-processing conditions, will impact the physical properties of the plastic material. Post-industrial materials are plastics that are scrap (including flash, part trimmings, sprues, start-up parts, purgings, and runners) or sub-standard parts which cannot be sold, but can be reprocessed. Post-consumer materials have been subjected to similar processing conditions to the post-industrial materials, but have also been exposed to environmental conditions. These exposures over time lead to additional changes in a plastic’s physical properties that exceed those experienced by post-industrial plastics.
The goal of this study is to gain a more comprehensive understanding of how recycled material properties are affected by different conditions and exposures. To study how these materials’ properties have been changed, we will use post-industrial and post-consumer materials to injection mold samples and compare them to a commonly used polyethylene material and to virgin material supplied by an industrial partner. We will demonstrate how post-industrial and post-consumer materials are affected by being re-processed, post-processing conditions, multiple rounds of reprocessing, and accelerated weather testing. Samples will then be subjected to mechanical testing (tensile, impact, and flexural testing), thermal analysis (differential scanning calorimetry and thermogravimetric analysis) and rheological characterization by melt flow indexing. When analyses are completed, we will be able to guide industry recommendations on how recycled plastics can be implemented to a much wider degree in consumer goods without sacrificing product performance.
Recommended Citation
Howard, Grant m., "THE EFFECTS OF REPROCESSING, POST-PROCESSING CONDITIONS, AND ENVIRONMENTAL EXPOSURE ON THE PHYSICAL PROPERTIES OF POST-INDUSTRIAL AND POST-CONSUMER POLYETHYLENE" (2025). Electronic Theses & Dissertations. 777.
https://digitalcommons.pittstate.edu/etd/777
