Date of Award
Doctor of Philosophy (PhD)
Rhett C. Smith
With a globally increasing population and largely unchecked consumption of raw materials, human society is on track for devastating consequences. Two industries responsible for utilizing massive amounts of raw materials and generating equally gargantuan quantities of waste are the packaging and infrastructure sectors. In 2017 in Europe, for example, packaging reached a record 173 kg of packaging waste per capita. One of the largest packaging consumers is the food industry, in which 40% of packaging is made of petroleum-derived single-use plastic, leading to a massive carbon imbalance. “The Built Environment,” on the other hand, is responsible for about 50% of all extracted raw material from the earth. In the EU the construction industry accounts for more than 35% of all waste that is generated while also being responsible for 5–12% of greenhouse gas emissions.
Unfortunately, society’s reliance on packaging and infrastructure is only forecast to increase, and at a staggering rate. It is currently estimated that global materials consumption will double in the next forty years with an attendant 70% increase in waste generation. This situation demands a restructuring of globally packaging and infrastructure strategies. An important part of this restructuring will be the development of novel technologies wherein products are designed to be degraded or recycled — a concept referred to as the circular economy.
A centerpiece for creating a circular economy is the use of biopolymers rather than petroleum-derived polymers. As opposed to petroleum-derived polymers, biopolymers are readily recycled by various microorganisms. Like synthetic polymers, however, biopolymers and their composites are capable of remarkable strength and resilience. This dissertation focuses on strategies that can be employed to valorize biopolymers to reduce the consumption of raw materials in support of a more circular economy.
Chapter 1 focuses on the recent advances that have been made to develop starch-based films towards food packaging applications. Included in this analysis are the various strategies and additives that can be utilized to endow films with enhanced mechanical or functional applications as well as discussing how up-and-coming technologies can be used concomitantly to accelerate this basic-research field towards real industrial applications.
The remaining chapters contribute to an overarching approach employing synthetic manipulation of biopolymers or biomass in order to endow them with functional groups capable of reacting with sulfur (a waste product of petroleum refining) through an inverse vulcanization pathway. The impact of the biopolymer/biomass source as well as attributes like degree of modification and biopolymer crystallinity on the resultant morphological and mechanical properties of biopolymer/biomass-sulfur composites is explored.
Chapters 2–3 more specifically focus on the synthesis and characterization of various starch derivatives and their subsequent reactions with elemental sulfur in order to develop strong thermoplastic materials.
In Chapter 4 a novel method for the modification of cellulose with 3-bromo-2-methylpropene is discussed. The resultant cellulose derivative is characterized and reacted with sulfur in order to develop the first polysaccharide-sulfur composites. The morphology and mechanical properties of these composites are thoroughly characterized.
Chapter 5 discusses the green synthesis of a terpinol-cellulose derivative. Similarities in the degree of modification of these terpinol-cellulose derivatives to cellulose derivatives in Chapters 4 and 5 allow the importance of biopolymer crystallinity as well as the type and quantity sulfur-reactive functional groups is highlighted.
In Chapter 6 raw waste material from peanut processing (peanut shell powder) is modified and reacted with sulfur to generate composites with up to twice the compressive strength required for residential Portland cement.
Chapter 7 aims to determine the impact of each component of the complex peanut shell waste material by utilizing more basic model systems for comparison. This work displays the impact of residual peanut oil, the importance of cellulose-lignin crosslinking/inclusion, and the importance of feed ratio in determining structure-property relationships of prepared composites.
Chapter 8 focuses on determining how the particle size of peanut shell powder impacts the resultant mechanical properties of biomass-sulfur composites. This is done by preparing fractions having narrowly-defined particle sizes and reacting each fraction with sulfur to yield a series of composites. Various prescient trends are revealed that inform on properties required to affect improved particle-reinforced sulfur composites in next-generation materials.
Lauer, Moira, "Valorization of Biopolymers and Biomass to Produce Materials for a More Circular Economy" (2022). All Dissertations. 3036.