Polylactic acid (PLA) is a well-known biodegradable and sustainable polymer, derived from renewable agricultural sources. Its high price in the past limited its applications to mainly biomedical materials such as bone fixation devices. As the growth of awareness in global environment protection and sustainable development, PLA has attracted increased attention and development. Nowadays, the applications of PLA have been broadened into plastics, textiles and composites etc. Composites have been widely used in industrial applications for several decades, due to their high strength-to-weight ratio and good structural properties. However, most traditional composite materials are composed of two distinct fossil fuel based components. They are not eco-friendly and are difficult to recycle. This study aims at the development of PLA biodegradable composites and the optimisation of the processing parameters to achieve the best mechanical properties of PLA self-reinforced composites (PLA-SRC) for various end-uses. A variety of polymer analytical techniques were used to evaluate crystallinity, thermal properties, and chemical structures of the PLA reinforcement and matrix. Further study was carried out to assess the effects on mechanical properties of PLA-SRC caused by the processing temperature, pressure and holding time. The composites produced at high temperature and/or high pressure have significantly better matrix penetration (fibre wetting), which enhances mechanical properties. However, holding time was found to have no significant effect on the properties of PLA-SRC.

En av dagens miljöproblem är den stora mängd plast som idag används och kommer att användas i framtiden. Det ryktas mycket om vad som ska göras när bomullen når den punkten att det inte finns arealer kvar för att odla men det diskuteras inte vad som ska ersätta polyester när oljan börjar ta slut. Idag har polyester gått om bomull i kampen om den populäraste textilfibern. Tillsammans med snabbare modesvängar i butikerna tillverkas polyester som aldrig förr och har därefter börjat påverka naturen negativt. Därför anses det vara väsentligt att ett passande material utvecklas som kan ersätta polyestern till viss del. Studien fokuserar på att förklara den komposterbara fiber, polylactic acid (PLA) som är gjord av majsglukos. Att börja använda en fiber som kan brytas ner med hjälp av naturen kan hjälpa med aktuella och framtida miljöproblem. Fibern har bra egenskaper så som fukttransport och UV-resistens som gör den passande för till exempel sportkläder. Att tillverka fibern kräver inga extra maskiner eller processer utan kan göras på samma vis som när polyester tillverkas. När sedan tillverkningsprocessen för plagg ska göras bör uppmärksamhet riktas mot de moment där materialet kommer i kontakt med värme då PLA har lägre smältpunkt. Även där den kan tänkas ligga i vatten bör tas med försiktighet då materialet kan börja brytas ner med rätt förutsättningar som värme, fukt och pH. Således är det väsentligt att även se hur relaterade företag ser på att börja produktutveckla plagg gjorda av PLA. Då det idag inte finns många klädföretag som tillverkar komposterbara plagg av PLA blev ett mål med studien att se om diverse företag har börjat fundera på att använda sig av materialet. Då PLA för tillfället är en dyr fiber på grund av småskalig produktion har merparten av företagen inte funderat på att börja använda PLA. Därför hade inte heller majoriteten av företagen funderat på vilka plagg eller hur deras produktutveckling skulle se ut för dessa plagg. Intresset för fibern är dock stor och alla företag var öppna till att börja använda sig av fibern i framtiden. Då med förutsättningen att fibern blir billigare och att tillverkarna inte använder sig av genmodifierad (GMO) majs som används idag.

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People's experience of space is quite different because we experience our environment with all senses available to us. Environmental pollutions can affect everybody's experiences of space. Noise is one of the environmental pollutions that long-term exposure to high noise levels can cause sleep disruption, reduction of performance, permanent hearing loss, and the inability to enjoy the space. This research presents an assessment of noise levels on the main campus of the University of Arizona, based on noise measurements and noise maps, and defines problems associated with the high noise levels in specific areas. Then, strategically develops an acoustic panel, by using an environmentally friendly material which is called Polylactic Acid. PLA is a kind of biopolymers and it is biodegradable material made from renewable raw materials like corn starch. In addition, the University of Arizona's campus is surrounded by four streets with intense vehicle traffic, which contribute to causing the noise level to exceed the legal limits established for some of the educational areas. There are many methods for mitigating noise in urban areas, including the formation of the city, the geometry of buildings, vegetation, and sidewalk design, building façade design and using acoustic materials. All these responses for noise mitigation should be considered as environmentally friendly design concepts. The manufacturing of many materials can cause severe environmental pollutions, but by using Polylactic acid material we will save our planet.

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The focus of this study was to explore process-structure-property relationships in biodegradable polymer nanocomposite films in order to eliminate the commonly used trial and error approach to materials design and to enable manufacturing of composites with tailored properties for targeted applications. The nanofiller type and concentration, manufacturing method and compounding technique, as well as processing conditions were systematically altered in order to study the process-structure-property relationships. Polylactic acid (PLA) was used as the polymer and exfoliated graphite nanoplatelets (GNP), carbon nanotubes (CNT), and cellulose nanocrystals (CNC) were used as reinforcement. The nanocomposite films were fabricated using three different methods: 1) melt compounding and melt fiber spinning followed by compression molding, 2) solution mixing and solvent casting, and 3) solution mixing and electrospinning followed by compression molding. Furthermore, the physical properties of the polymer, namely the crystallization characteristics were altered by using two different cooling rates during compression molding. The electrical response of the composite films was examined using impedance spectroscopy and it was shown that by altering the physical properties of the insulating polymer matrix, increasing degree of crystallinity, the percolation threshold of the GNP/PLA films is significantly reduced. Additionally, design of experiments was used to examine the influence of nanofiller type (CNT versus GNP), nanofiller content, and processing conditions (cooling rate during compression molding) on the elastic modulus of the composite films and it was concluded that the cooling rate is the primary factor influencing the elastic modulus of both melt compounded CNT/PLA and GNP/PLA films. Furthermore, the effect of nanofiller geometry and compounding method was examined and it was shown that the high nanofiller aspect ratio in the CNT/PLA films led to decreased percolation threshold compared to the GNP/PLA films. The melt compounded GNP/PLA films displayed a lower percolation threshold than the solution cast GNP/PLA films most likely due to the more homogeneous distribution and dispersion of GNP in the solution cast films. Fully biodegradable and biorenewable nanocomposite films were fabricated and examined through the incorporation of CNC in PLA. Through the addition of CNC, the degree of crystallinity of the matrix was significantly increased. Focusing the design space through investigation of process-structure-property relationships in PLA nanocomposites, can help facilitate nanocomposites with tailored properties for targeted applications.

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.

The chemistry of the tetrameric low-valent aluminium compoud (Cp*Al)4 (Cp* = 1,2,3,4,5- pentamethylcyclopentadienyl) is relatively undeveloped compared to its monomeric cousin dippNacNacAl (dippNacNac = 2,6-diisopropylphenyl-β-diketiminate). Given that the former can be formed by the reductive elimination of Cp*H from Cp*2AlH, a process common to transition metals yet rare with light main-group elements, using the Cp* ligand could unlock an abundance of unexpected reactivity for aluminium. An overview of the literature regarding the synthesis and reactivity of low oxidation state aluminium compounds is provided in chapter 1, as well as an introduction to relevant magnesium chemistry for this work. Chapter 2 studies the mechanism of C-H reductive elimination from Cp*2AlH to form (Cp*Al)4, and the properties which allow reductive elimination to take place are revealed. A transition state is identified where the Cp* group has a higher hapticity than in the starting material, a process which is thought to enable the reductive elimination. Using this insight, aluminium hydride and halide complexes featuring 9-methylfluorenyl ligands are synthesised and reduction of the aluminium centre is investigated. The reactivity of (Cp*Al)4 is considered in chapter 3 of this thesis. The formal cycloaddition reaction between (Cp*Al)4 and diphenylacetylene produces a Lewis acidic 1,4- dialuminacylohexadiene derivative. The inner Al2C4 ring of this complex is stable, with onward reactions happening at the complex's periphery. Insertion reactions in the Al-CCp* bonds are observed with unsaturated C-N species. With 2,6-dimethylphenylisonitrile the Al2C4 complex forms a zwitterionic aluminate, featuring a stable carbocation derived from the Cp* group. An amidinate complex with an unusual Cp* backbone is formed from the insertion of carbodiimides into the Al-CCp* bond of the 1,4-dialuminacyclohexadiene. Extending this, the insertion of carbon dioxide into the same bond is explored. The use of amidine ligands is common in main-group chemistry, however literature relating to the related phosphaamidinate ligands ([RPC(R)NR]-) is only reported sporadically. They have not been applied in a general manner to main-group chemistry thus far. Chapter 4 describes the synthesis of five new phosphaamidinate pro-ligands where the steric bulk of both the phosphorus and nitrogen components is increased systematically. To evaluate these new ligands, their coordination chemistry with magnesium was investigated. Three examples of heteroleptic LMgnBu (L = phosphaamidinate) complexes are synthesised, which all show high activity for the ring-opening polymerisation of racemic lactide. The resulting polylactide chains show good molecular weights and polydispersity indices. The synthesis of homoleptic L2Mg complexes is also described. Chapter 5 applies these new phosphaamidinate ligands to aluminium chemistry. An aluminium hydride species is isolated, which is shown to form via a probable lithium aluminate intermediate. The lifetime of this intermediate is found to be heavily dependent on the reaction solvent.