Biodegradable polyesters are considered as one of the most cost effective and environmentally friendly solutions to waste-disposal problems associated with traditional thermoplastics. The technologies for converting the resins into useful items require knowledge about the rheological properties of these materials. Adequate rheological models are essential for the design and optimization of the process technologies. Rheological properties of two commercial biodegradable polyesters- poly(lactic acid) (PLA) and aliphatic-aromatic co-polyester (AAC) Ecoflex -have been investigated using parallel plate and capillary rheometers. Results from a study on the extrusion instabilities of biodegradable polymers are reported for the first time. The experimental studies found that the biodegradable polyesters exhibit pseudoplastic (shear-thinning) behaviour and the Cox-Merz rule is obeyed. A Cross model was proposed to describe their shear-thinning behaviour. The viscosity of both PLA grades is more temperature sensitive than the viscosity of Ecoflex. It was observed that the extensional viscosity of Ecoflex is larger than that of PLA and that the extensional viscosity of biodegradable polymers is similar to that of LLDPE. The experimental results indicate that biodegradable polymer melts slip at the die wall. It was observed that with increasing shear rate PLA exhibits sharkskin and gross melt fracture while Ecoflex exhibits only gross melt fracture. With regards to flow instabilities PLA behaves like linear polyolefins, however without exhibiting stick-spurt phenomenon. While Ecoflex behaves like branched LDPE, its gross melt fracture starts at higher values of wall shear stress than LDPE. Both biodegradable materials exhibit small extrudate swell: up to 28% for PLA and up to 34% for Ecoflex, which is comparable to that of rigid PVC. It was observed that biodegradable polymers substantially degrade during extrusion processing. It was also found that blending PLA and Ecoflex produced immiscible blends. Melts of these blends exhibited sharkskin and gross melt fracture at higher shear stresses than the neat resins. This effect was attributed both to degradation during blending and to some sort of lubricating effect. / Thesis / Master of Applied Science (MASc)

Master of Science / The accumulation of plastic waste has long been a problem and requires a multifaceted approach to address the complexity of this issue. Two heavy contributors are single-use plastics in the form of food packaging, and medical packaging. Conventionally, these are made of petroleum-based plastics as their production is well-established and low-cost, but a big disadvantage is their negative environmental effects, as they are almost always nondegradable. Biodegradable polysaccharides have a high potential to replace current plastics while bringing about a much better end of life, specifically as a biodegradable film that exhibits similar materials properties as typical plastics. However, these materials can be difficult to process and achieve suitable mechanical properties. The primary goal of this research was to develop and optimize a polysaccharide-based formula and test its capability to perform at the same level as traditional single-use plastics, as well as compare the introduction of crosslinkers and their enhancement. The fabricated films with or without crosslinkers were tested to determine their mechanical and thermal properties, anti-bacterial activity, water swelling, and soil degradation. A medical-grade plastic barrier film was used as a standard for comparison. Results demonstrate this product yields comparable necessary properties to plastics in current use and could serve as a viable degradable replacement.

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The rheological properties of polymer melts and polymer/blowing agent (BA) solutions are determined experimentally and the influences of material rheological properties and crystallization on low-density foaming behaviour of polylactic acid (PLA) are investigated. Understanding the rheological properties of foaming polymers allows the optimization of polymer chemical structure and the development of technologies that produce desired cell morphologies. Although the technology for producing CO2-blown polystyrene (PS) foams is well established, the rheological properties of a PS/CO2 solution, especially its extensional property, are not well understood. In this study, these properties are determined with an in-house developed, online technique, and the measured data are compared with those from commercial rheometers. The online measurement system consists of a tandem foam extrusion system and a die for measuring pressure drops. Shear viscosity is determined from the pressure drop over a straight rectangular channel, while planar extensional viscosity from the pressure drop over a thin hyperbolic channel, taking into account the pressure drop due to shearing. Measured viscosities of the polystyrene without CO2 compare well with those from commercial rheometers. With the presence of dissolved CO2, both the shear and extensional viscosities of the polystyrene are significantly reduced. The influence of CO2 on the two viscosities is found to be similar to an increase of temperature. Polylactic acid is the first mass-produced biodegradable polymer, and has potential to replace petroleum-based polymers in foaming applications. In this study, the influences of material rheological properties and crystallization on the low-density, microcellular extrusion foaming behaviour of polylactic acids (PLAs) are investigated. Comparisons are made between linear and branched PLAs and between amorphous and crystalline PLAs. The branched PLAs are found to produce foams with higher expansion ratios and reduced open-cell content compared to the linear PLA. The foaming behaviour of the linear PLA, then, is significantly improved by adding a small amount of long-chain-branched PLA. The improved cell structure with branched PLAs is attributed to their relatively high melt strength and strain to break. For the first time, it is shown that crystallization, induced by cooling and macroscopic flow during processing, increases melt strength, which aids the production of low-density foams.

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The aim of this study was to design and synthesise thermoplastic biodegradable and biocompatible polyurethanes for tissue engineering applications. A secondary aim was to tailor a range of degradation rates of the polyurethanes to suit a broad spectrum of tissue engineering applications. Various factors were systematically investigated in order to provide a means of controlling mechanical, thermal and degradation properties of the polyurethanes. The factors investigated included variation of the hard segment percentage, the diisocyanate, the soft segment macrodiol as well as the chain extender. Soft segment macrodiols were synthesised for this study including a poly(γ-butyrolactone) macrodiol which has been used to make biodegradable aliphatic poly(ester-urethane) for the first time. A novel range of degradable chain extenders was also developed and has been reported. The polymers were characterised using Gel Permeation Chromatography (GPC), Instron tensile testing, Differential Scanning Calorimetry (DSC) and Shore hardness. Cell culture testing was performed as was a three-month degradation study which showed the polyurethanes to be biocompatible and biodegradable respectively. Selected materials were shown to be suitable for scaffold fabrication using Fused Deposition Modelling (FDM), and the scaffolds made were further shown to support primary fibroblast growth in vitro.

Since their inception and invention, plastic materials have taken on an essential role in numerous applications within the lives of human beings for years now. Each year, the global figure for production of plastic is estimated to be more than 100 million tons. The major reason for the existence of such an enormous amount is due to plastics’ supremacy over other materials with their exceptionally useful properties. According to Hong Kong’s Environmental Protection Department, 13,458 tons of waste was disposed in Hong Kong’s landfills per day during 2011. Such an amount is very large in quantity, and it is predicted that the three strategic landfills of Hong Kong will be fully saturated in 2015-16 if the waste generation rate remains similar as present time and business as usual. Plastics made up approximately 19% of the overall composition of Hong Kong’s disposed municipal solid waste in 2011. Plastic material does not degrade efficiently, and since it has only been in production during the most current century, plastic specialists have not been able to conclude the final life span of the material before it completely degrades. Estimates for different plastic polymers range from 20 years to 400 years and above. To solve these increasingly serious environmental issues, the society has raised its demands and directed many researches into biodegradable polymers (i.e., plastics). They have now become more seriously considered as alternative solutions for conventional, non-biodegradable plastics. However, the creation of such biodegradable materials, the efficiency and cost of that creation and the true biodegradability of those materials is under much scrutiny and debate. The purpose of this study was multi-faceted. It primarily focused on (1) the status and production of biodegradable products in Hong Kong and (2) assessment of the general public’s receptiveness towards using such products. This study aimed to evaluate the above two aspects via literature review and interviews of representatives from biodegradable plastics companies in Hong Kong as well as students and general working-class citizens. This element inquired whether the general public would be willing to pay extra money to use biodegradable plastic products, and whether they thought that these products had beneficial effects towards environmental conservation and protection. Also, the general public would be asked their opinion on a duty for biodegradable products and whether they would be adverse to a policy implementation involving such a duty. A large portion of this project’s critically significant data was generated from random, systematic sampling of different people, asking them about the aforementioned monetary scenarios. Results were insightful and informative giving evident trends that represented the public’s attitude towards biodegradable plastics. Overall, the public was positively supportive of biodegradable technology, which is relatively new. Concurrently, extensive literature review was conducted to assess foreign practices and policies regarding biodegradable plastics, as well as the life-cycle of a primary biopolymer called polylactic acid. A concluding recommendation was constructed to envision the future waste management infrastructure in Hong Kong. That infrastructure could build off of the special region’s budding development of incinerators, composting facilities, waste-to-energy facilities, and sorting technologies. Then, to supplement biodegradable polymer production and post-use handling facilities, the Hong Kong SAR Government could implement strong waste management policies to motivate its society to aim for a more sustainable way of life. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management