Reports from various institutions claim that garbage management in Rwanda has had diverse effectson both the natural environment and human society. Such claims prompted for an exploratory study to find outan optimal system to handle solid waste in Kigali City.The study considered a literature review and primary data from 400 randomly selected citizens. They weresurveyed about their opinions on which system they perceived to be the optimal to handle garbage in KigaliCity. The computer software Web-Hipre was used to analyze data on the three systems considered to handlesolid waste in Rwanda: briquetting, composting, and incineration.The results indicate briquetting as the optimal alternative to handle solid waste from homesteads and workplacesof Kigali City. Briquetting considers production of solid fuels that may reduce destruction of forests for fuel.Other major reasons for briquetting, highlighted by respondents, include improved kitchen hygiene andsanitation and replacement of charcoal for a less dusty fuel.Economic factors governed surveyed participants to prioritise briquetting system to handle solid waste in Kigali.Composting may be considered for transforming organic materials into mulch to support farming activities inrural areas as well as gardening in the towns. However, a centralised incineration system is presently notsuitable. The private sector has so far not fully been engaged in the transformation of solid waste into bioenergyin Rwanda.

Poly(beta-amino esters) are photopolymerizable and biodegradable polymers prepared by the combination of amines with diacrylates. This study aims to fundamentally understand the polymer network formed by poly(ethylene)glycol diacrylate (PEGDA) MW 700 and 3-methoxypropylamine (3MOPA) as well as to characterize the degradation response of this material with and without cyclic loading. The networks were formed by a two-step process; (1) the synthesis of amine-co-peg diacrylate macromers through a step growth reaction, followed by (2) UV initiated chain growth network formation of the diacrylated macromers. Macromer reaction chemistry was confirmed by 1H NMR measurements. UV calorimetric analysis revealed that network formation was dependent on molecular weight of the PEGDA monomer and light intensity, but not temperature in the range of 20 °C to 40 °C. The glass transition temperature of all networks was measured to be in the range of -40 °C to -30°C with a rubbery moduli ranging from 4 to 10 MPa, depending on the molecular weight of the PEGDA monomer. Partial crystallization was discovered to occur in the networks containing higher molecular weight PEGDA only in the presence of humidity and high frequency cyclic loading. Degradation studies were performed with and without applied cyclical stress, and in both cases elastic modulus decrease and mass loss occurred steadily over a 24-hour period. Increasing frequency of applied compressive stress during degradation served to slightly lower degradation rates, especially in samples cycled at high frequency, which crystallized. In all materials, applied cyclic load resulted in catastrophic fracture of the material prior to an appreciable decrease in modulus. The experiments reveal that degradation rate and failure mode can be influenced by the addition of cyclic loading and this should be considered when screening biodegradable polymers for applications that include mechanical loading.

Conventional urea-based moulding compounds for investment casting patterns are manufactured using a slow “cooking” process. Nowadays in industrial processes the use of a faster process is highly recommended to increase throughput levels. At the same time, for quality control purposes, the requirements of an investment caster must be met. This study is therefore focused on: <ul><li> Finding the appropriate conventional process and conditions to prepare urea-based investment casting moulding compounds. </li><li> Optimising the composition variables to meet the mechanical, thermal, surface, flow and cost properties needed in investment casting. </li><li> Characterising the moulding compounds to meet the requirements of an investment caster by comparing them with an industrial, “cooked” urea-based compound. </li></ul> Polyvinyl alcohol (PVOH) and ethylene vinyl acetate (EVA) urea-based moulding compounds were prepared using a two-roll mill and a conventional extrusion processes respectively. It was possible to injection mould PVOH urea-based moulding compounds with a urea content of up to 90 wt % which had been compounded using a two-roll mill. Using the conventional extrusion process, it was also possible to compound and injection mould EVA urea-based moulding compounds containing up to 70 wt % urea. The effects on composition variables on the properties of the moulding compound were studied and compared to those of the existing “cooked” urea-based moulding compound (Benchmark). The mechanical properties were characterised using the three-point bending test and Charpy impact test. The thermal properties were determined using simultaneous differential thermal analysis and thermogravimetric analysis (SDTA/TGA) and differential scanning calorimeter (DSC). The thermo-mechanical and visco-elastic properties were determined using a dynamic mechanical analyser. A scanning electron microscope was used to study the surface texture of the mouldings. The EVA urea-based moulding compounds showed two endothermic melting peaks and multiple exothermic crystallisation peaks in the DSC curves. The peak at ca. 55 - 66°C corresponds to the melting of the wax/EVA blend, while the large peak at 130 - 132°C corresponds to the melting of the urea. The DSC heating curve of the PVOH urea-based moulding compounds showed two endothermic peaks. The small peak corresponds to the melting of the wax, while the large peak corresponds to the melting of the urea/PVOH blend. PVOH urea-based moulding compound had better mechanical properties than the industrial benchmark. The mechanical properties of the EVA urea-based compound were generally lower. The effect of the wax and polymer content on the mechanical properties was as follows: <ul><li> Increasing polymer content produced weaker but tougher moulding compounds. </li><li> Increasing wax content improved the strength and stiffness but gave compounds that were less tough. </li><li> Two-way Analysis of Variance (ANOVA) indicated significant polymer-wax interactions. </li></ul> The urea content determined the stiffness (elastic modulus) of the compounds. PVOH mouldings had superior stiffness compared with the EVA and cooked urea-based mouldings. The Dynamic mechanical analysis (DMA) results confirmed the result obtained from the modulus of elasticity determination in the three-point bending test. The impact strength increased with an increase in polymer content and reduced with an increase in wax content. The linear thermal expansion coefficient decreased as the urea content was increased. Measured values (100 to 156x10-6°C) were comparable to those of the benchmark. The cooked urea-based moulding compound had the lowest melt viscosity at 110°C, as indicated by its melt flow index (MFI). Fluidity increased with the polymer content. The thermo gravimetric analysis (TGA) results confirmed that both the PVOH and EVA urea-based moulding compounds decomposed readily and left less than 1 wt % ash after combustion. From the SEM results apparent surface roughness appeared to increase with wax content. The EVA urea-based moulding compound had an irregular surface texture. Based on the criteria of cost-effectiveness and environmental friendliness, the synthesis of PVOH urea-based patterns is preferable. The use of a conventional extrusion process to prepare PVOH urea-based patterns is recommended. / Thesis (PhD)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

$EVWUDFW Application of radionuclides due to their unique nature is still attracting the interest of professionals from different branches of science. In this thesis, the unifying topic is the utilization of various radioactive labels on polymeric carriers for biomedicinal purposes. In the introductory part, the area of use of the investigated substances - in terms of their possible application in nuclear medicine, is presented to the reader. The experimental work is divided into three main sections dealing with synthesis and studying properties of appropriate selected polymers, their metal chelates and radiolabeling. First part of the study describes development of new strategies for labeling of polymeric carriers with radiometal cations and radioiodine, whereas in the following sections of the study synthesis and investigation of biocompatible polymer materials is discussed. New possible approaches in the diagnostics and therapy of cancer by using polymeric chelates as carriers are presented as well as the use of macroporous metal chelating polymer beads as potential therapeutics intended for radioembolization of liver malignancies and for the therapy of Wilson's disease. Investigated polymers have been shown to be non-toxic, to have good in vitro stability and to have the ability to be radiolabeled in...

Thesis advisor: Jeffery A. Byers / Chapter 1. Poly(lactic acid) (PLA) is a biodegradable polymer derived from renewable resources that has garnered much interest in recent years as an environmentally friendly substitute to conventional petroleum-derived engineering polymers. PLA has many applications in textiles, packaging, compostable consumables, and biomedical devices, as PLA displays excellent biocompatibility. This polymer is primarily produced from the ring-opening polymerization of lactide, a cyclic dimer of lactic acid. This introductory chapter highlights mechanistic features of this ring-opening polymerization reaction as well as metal-based catalysts that have been reported for lactide polymerization. In addition, switchable catalysis is an emerging field that has gained interest with polymer chemists for the potential of creating original polymer compositions and architectures. The utilization of redox-switchable catalysis to control lactide polymerization is discussed in this chapter. Chapter 2. Bis(imino)pyridine iron bis(alkoxide) complexes have been synthesized and utilized in the polymerization of (rac)-lactide. The activities of the catalysts were particularly sensitive to the identity of the initiating alkoxide with more electron-donating alkoxides resulting in faster polymerization rates. The reaction displayed characteristics of a living polymerization with production of polymers that exhibited low molecular weight distributions, linear relationships between molecular weight and conversion, and polymer growth observed for up to fifteen sequential additions of lactide monomer to the polymerization reaction. Mechanistic experiments revealed that iron bis(aryloxide) catalysts initiate polymerization with one alkoxide ligand, while iron bis(alkylalkoxide) catalysts initiate polymerization with both alkoxide ligands. Oxidation of an iron(II) catalyst precursor lead to a cationic iron(III) bis(alkoxide) complex that was completely inactive towards lactide polymerization. When redox reactions were carried out during lactide polymerization, catalysis could be switched off and turned back on upon oxidation and reduction of the iron catalyst, respectively. In addition, preliminary investigations of copolymerization reactions of lactide with ethylene are reported. Chapter 3. A cationic iron(III) complex is active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex is inactive. Cyclohexene oxide polymerization could be "switched off" upon in situ reduction of the Fe(III) complex and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the complex: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY-NMR studies.  Chapter 4. Formally iron(I) bis(imino)pyridine monoalkoxide complexes were synthesized through protonolysis of a bis(imino)pyridine iron alkyl species with p-methoxyphenol or neopentyl alcohol. The resulting complexes were characterized by X-ray crystallography, 1H NMR, EPR, and Mössbauer spectroscopy, and preliminary characterization of the electronic structure of these complexes is discussed. These iron complexes were found to be highly active catalysts for the polymerization of various cyclic esters and carbonates, with the iron mono(neopentoxide) complex being much more active and giving more narrow molecular weight distributions than the mono(aryloxide) complex. The bis(imino)pyridine iron neopentoxide complex was highly active in particular for the polymerization of ε-caprolactone (CL), giving full conversion within 10 minutes at room temperature in toluene, making it one of the most active iron complexes reported for this transformation ([Fe]:[CL] = 1:2000). Comparison of the polymerization activity of these iron mono(alkoxide) complexes with the analogous iron(II) bis(alkoxide) complexes is reported. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Foram desenvolvidas embalagens biodegradáveis ativas tipo espuma, obtidas a partir de fécula de mandioca, capazes de aumentar a vida-de-prateleira de frutas minimamente processadas. Para tanto, agentes ativos que evitam a proliferação de fungos, a perda de peso e, também, forneçam uma indicação visual (mudança de cor da embalagem) da qualidade do produto embalado, foram adicionados às embalagens de fonte renovável. As espumas foram obtidas pelos processos de extrusão e termoprensagem de uma massa de fécula, gel (fécula suspensa em água) e aditivos (plastificantes e/ou agentes ativos). As formulações de espumas variaram quanto: ao tipo e concentrações de plastificantes (glicerol e polietilenoglicol PEG 300); às quantidades de sólido (fécula de mandioca em pó); aos diferentes tratamentos da fécula (modificações química por acetilação e físicas irradiação e pré-gelatinização); à procedência da fécula (da Bahia e do Paraná); ao reaproveitamento de espumas descartadas; às diferentes concentrações de agentes ativos (ácido l-ascórbico, cloreto de cálcio, sorbato de potássio e permanganato de potássio) e quanto à adição de corantes naturais (extratos de beterraba e repolho roxo). Foram avaliadas, principalmente, as propriedades mecânicas e de barreira das diferentes formulações de espumas de fécula de mandioca. Os resultados indicaram que quanto maior a concentração de fécula mais resistente é a espuma. As espumas contendo o plastificante PEG 300 se mostraram bastante flexíveis, apresentaram boa resistência à ruptura e absorveram pouca água. A pré-gelatinização da fécula proporcionou melhores propriedades mecânicas e de barreira para as espumas em relação aos outros tratamentos dados à fécula de mandioca. Já a adição de agentes ativos à massa não proporcionou tais melhoras às embalagens. As espumas de fécula de mandioca produzidas pelo processo de extrusão seguido de termoprensagem foram mais resistentes à ruptura do que as produzidas somente por termoprensagem. / Active biodegradable packaging foams type were developed, obtained from cassava starch, to increase the shelf-life of minimally processed fruits. For this, active agents that prevent the proliferation of fungi, weight loss and, still, provide a visual indication (change of packaging color) of the packaged product quality, were added to the renewable packaging. The foams were obtained by extrusion and thermopressing processes of a mixture of starch, gel (starch suspended in water) and additives (plasticizers and/or active agents). The foams formulations varied as: the type and concentrations of plasticizers (glycerol and polyethylene glycol PEG 300); the concentrations of solid (cassava starch powder); the different treatments of starch (chemical, for acetylation, and physical modifications radiation and pre-gelatinization); the starch suppliers (from Bahia and Paraná); the reuse of discarded foams; the different active agents (l-ascorbic acid, calcium chloride, potassium sorbate and potassium permanganate) and the addition of natural dyes (beet and cabbage extracts). It was evaluated, mainly, the mechanical and barrier properties of the different formulations of cassava starch foams. The results indicated that the higher starch concentration more resistant become the foam. The foams containing the plasticizer PEG 300 proved to be very flexible, had good tensile strength and absorbed less water. The pre-gelatinization of starch provided better mechanical and barrier properties to foams in comparison with other treatments of cassava starch. The addition of active agents to the mix did not provide such improvements to packaging. The cassava starch foams produced by extrusion followed by thermopressing were more resistant to breakage than those produced only by thermopressing.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nos últimos 20-30 anos polímeros biodegradáveis vêm sendo estudados e desenvolvidos e atualmente já são comercializados. Contudo, o custo, a processabilidade e algumas propriedades ainda dificultam a penetração desses polímeros no mercado e a competição com as chamadas commodities. Não são poucos os autores que se dedicam a desenvolver aditivos e formulações para superar essas limitações. Desta forma, esta Tese se dedicou ao desenvolvimento de compósitos de Ecobras, fabricado pela Basf e comercializado pela Corn Products, utilizando como carga mineral resíduo da extração da bauxita, no município de Santa Luzia/PB, o qual consiste em sua totalidade de vermiculita. Esta vermiculita foi quimicamente modificada com sais de alquil fosfônio para melhorar a compatibilidade com a matriz polimérica e também espaçar as camadas de aluminossilicato. De fato, a modificação com o brometo de hexadecil tributil fosfônio resultou na esfoliação da vermiculita tornando-a potencialmente apropriada para a obtenção de nanocompósitos. A preparação dos compósitos foi realizada pelo método de intercalação no estado fundido e foram comparadas a utilização da câmara interna de mistura e da mini extrusora de dupla rosca, sendo esta última mais eficaz na dispersão da vermiculita, conforme revelado pela microscopia eletrônica de varredura, difração de raios-X e reometria de placas. O grau de dispersão também foi influenciado pela estrutura química do modificador da vermiculita e pelo teor dessa carga incorporada à matriz. Teores mais elevados levaram a formação de aglomerados, enquanto a modificação da carga implicou na formação de micro e nanocompósitos. Ainda houve alterações das propriedades térmicas com aumento dos valores da temperatura de transição vítrea, de cristalização e fusão, embora o grau de cristalinidade tenha sido mantido. Nitidamente, foram obtidos materiais mais rígidos, com maior módulo e menor capacidade de deformação. Cerca de 58% de perda de massa foi observada para os micro e nanocompósitos obtidos após 17 semanas de enterro em solo simulado para avaliação da biodegradabilidade, valor bem próximo ao Ecobras puro. De modo geral, a incorporação das diferentes vermiculitas retardou nas primeiras semanas a biodegradação, provavelmente em função de modificações na estrutura cristalina, conforme sugerido pelos maiores valores de temperatura de fusão observados durante o acompanhamento do processo de biodegradação. No entanto, após 7 semanas os perfis de biodegradação dos micro e nanocompósitos se aproximaram bastante do Ecobras puro. Desta forma, foi possível nesta Tese obter um nanocompósito de Ecobras com vermiculita modificada com brometo de hexadecil fosfônio utilizando ferramentas comuns de processamento no estado fundido com biodegradabilidade próxima ao polímero de partida, porém mais rígido e menos deformável / In the last 20-30 years biodegradable polymers have been studied and developed and currently are already commercialized. However, cost, processability and some properties still avoid the penetration of such polymers on the market and the competition with the so-called commodity. There are few authors who are dedicated to developing additives and formulations to overcome these limitations. Thus, this thesis is devoted to the development of Ecobras composites, blend of PBAT and starch manufactured by BASF and commercialized by Corn Products, using as mineral filler a residue of bauxite extraction from Santa Luzia / PB, which consists entirely of vermiculite. The vermiculite was chemically modified with alkyl phosphonium salts to improve compatibility with the polymer matrix, and also to increase the space between aluminosilicate layers. In fact, its modification with hexadecyl tributyl phosphonium bromide promoted the exfoliation of vermiculite making it potentially suitable for obtaining a nanocomposite. The preparation of the composites was performed by the melt intercalation technique. Internal mixing chamber and a twin screw mini-extruder were compared as processing tool, the latter was more effective in dispersing the vermiculite, as revealed by scanning electron microscopy, X-ray diffraction and plate rheometry. The degree of dispersion was also influenced by the amount and chemical structure of the vermiculite. Higher filler levels led to formation of agglomerates, while filler modification led to formation of micro and nanocomposites. There were changes in the thermal properties with increasing temperature values of glass transition, crystallization and melting, although the degree of crystallinity has been retained. Clearly, stiffer materials were obtained, with a higher modulus and low strain capacity. About 58% of weight loss was observed for micro and nanocomposites after 17 weeks of burial in simulated soil for evaluation of biodegradability, very close to pure Ecobras value. Generally, the incorporation of different vermiculite delayed biodegradation in the first weeks, probably due to changes in crystalline structure as suggested by the higher melting temperature values observed during the monitoring of the biodegradation process. However, after seven weeks of the micro and nanocomposites biodegradation profiles approached quite to pure Ecobras. Thus, it was possible in this work obtain a Ecobras nanocomposite with hexadecyl tetrabutyl phosphonium bromide modified vermiculite prepared by melt intercalation technique using common processing tools and with biodegradability close the starting polymer, but more rigid and less deformable

Due to the excellent properties of biodegradability and biocompatibility, aliphatic polycarbonate and polyesters are very promising either as biomaterials or as environmentally friendly materials to address growing ecological concerns. The first chapter describes an overview of ring-opening polymerization, enzymatic polymerization and their application on the polymerization of cyclic carbonate and lactones. The second chapter describes the synthesis of enantiomerically pure functional polycarbonate from a novel seven-membered-cyclic carbonate (5S, 6S)- Dimethyl 5,6- isopropylidene-1,3-dioxepin-2-one (ITC) derived from naturally occurring L-tartaric acid. The monomer was synthesized in three steps and screened for polymerization with four commercially available lipases. Block co-polymerization of ITC with ε-caprolactone in 'one-shot feeding' is reported in the third chapter. It is the first report of 'one-shot' block copolymerization of ε-caprolactone with a cyclic carbonate monomer. The deprotection of the ketal groups resulted in copolymers containing free hydroxy groups in the polymer backbone. In chapter four, star-shaped poly(ε-caprolactone)'s (PCL) series based on two tetra-hydroxy resorcinarenes initiators were reported. These polymers were synthesized by the ring-opening polymerization. The data suggest that the initiator core directed the PCL-arms toward more interactions resulting in increasing in the rigidity of star-polymers compare to linear-PCL.

A magnetic target drug delivery system consisting of biodegradable polymeric microspheres (poly D, L-lactic acid) loaded with magnetite nanoparticles (10-100 nm) and anticancer drug (paclitaxel) was studied. The magnetite nanoparticles were synthesized by chemical precipitation. The as-synthesized magnetite nanoparticles were subsequently introduced into a mixture of polymer magnetic polymeric composite particles were investigated and further correlated with the reaction parameters. It was found that the size and characteristics of the polymeric composite particles depended on the viscosity of the polymer solution. Preliminary drug release experiments showed that the loaded drug was released with the degradation of the polymer. The release rates could be enhanced by an oscillating external magnetic field. / Singapore-MIT Alliance (SMA)

Thesis (M.Ch.E.)--University of Delaware, 2006. / Principal faculty advisor: Annette D.Shine, Dept. of Chemical Engineering. Includes bibliographical references.