Date of Thesis

Spring 2022

Description

Plastics play a vital role in global materials industries, but they contribute to environmental and ecological toxicity effects that accelerate climate change. One important category of plastic material is polymer foams, which have widespread applications in insulation, packaging, and storage. Current bio-based plastic foams that originate from natural, non-petroleum feedstocks are potential solutions but do not yet have adequate properties to supplant petrochemical-based plastic foams. This project aims to generate, test, and analyze bio-based polylactic acid (PLA) polymer foams developed through methods involving solid-state processing such as solid-state shear pulverization (SSSP) and cryogenic milling. SSSP has previously been shown to enhance crystallization kinetics of PLA. This study aims to determine whether this and other properties enhanced by SSSP support foaming of PLA in the direction of chemical foaming, which has proved difficult to date.

Specifically, this honor's thesis investigates the effects of pre-foaming solid-state processing method and chemical foaming agent (CFA) weight percent on the void fraction, dynamic mechanical properties, heat flow characteristics, and morphological properties of PLA foams. The instrumental procedures of density reduction measurement, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) respectively are used to determine those properties of the foams.

SSSP and cryomill-processed foams are compared against a control set of foams that did not undergo solid-state processing. It was concluded through this study that solid- state processing of PLA before foaming can greatly increase the extent of PLA foaming by achieving void fractions approximately twice as high of the control foams. This is due to the solid-state processing methods being able to significantly enhance PLA's ability to crystallize, which was displayed through both DMA and DSC. The solid-state-processed foams are also shown to have higher dampening factors, leading to better energy absorption properties. Despite the cell size distribution and cell density of the PLA foams not changing noticeably due to solid-state processing, SSSP and cryogenic milling still showed significant promise in achieving improved chemical foaming to warrant continued investigation as viable methods for implementation into PLA foam production.

Keywords

polymer, foam, sustainable, PLA, SSSP, crystallization

Access Type

Honors Thesis

Degree Type

Bachelor of Science in Chemical Engineering

Major

Chemical Engineering

First Advisor

Katsuyuki Wakabayashi

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