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The aim of this work was to synthesise poly(butyleneterephthalate) (PBT) poly(dimethylsiloxane) (PDMS) block copolymers, containing the hydrolytically stable Si-C linkage. A number of routes involving mutually reactive oligomers were studied. Once synthesised the effect of the copolymer as a toughening agent for the PBT matrix was investigated. Siloxane copolymer precursors were synthesised by an equilibration reaction. The relative molar mass (RMM) of the precursor was governed by the initial ratio of end blocker to cyclic species. The functionality of the precursor determined by the end blocker. alpha, to hydroxy PBT oligomeric precursors were chemically modified, if necessary, to form mutually reactive species. Initial block copolymer synthetic routes concentrated on chloroplatinic acid catalysed hydrosilations in solution. This involved alpha, to di (hydrosilane) PDMS and alpha, to divinyl functionalised PBT. The lack of a suitable common solvent together with competing side reactions limited the progress of this route. Melt hydrosilation reactions proved ineffective also, because of the thermal instability of the catalyst. Further block copolymer experiments involving mutually reactive oligomers were performed in the melt. The most promising of these was one of transesterification. This used alpha,o-hydroxypropyl PDMS (RMM 1000) and alpha,o-hydroxy PBT (RMM 2000) precursors. Analysis indicated successful reaction to form a copolymer of low RMM. A higher RMM copolymer was desirable, for improved mechanical properties, and a number of approaches to achieve this were followed. Problems of competing reactions and ineffective catalysis were encountered. However, a material with promising mechanical properties was formed when using a diisocyanate as a chain extender. A PBT-PDMS copolymer was blended by itself, and also together with high RMM PDMS, in the PBT matrix. The mechanical properties of the blends were studied and compared. An improvement in impact properties, as compared to PBT, was achieved when the copolymer was used as an emulsifying agent in a PBT-PDMS blend.

Powder bed fusion (PBF) is one of seven technology modalities categorized under the term additive manufacturing (AM). Beyond the advantages of fabricating complex geometries and the "tool-less manufacturing" paradigm common to all types of AM, polymer PBF shows potential for significant industrial relevance through exploiting the technique's characteristic powder-filled bed (a.k.a. build piston) to utilize the full printer volume for batch-style production. Although PBF should be a suitable processing technique for all semi-crystalline polymers, the polyamide family currently occupies around 90% of the commercial market for polymer PBF. This commercial dominance of polyamides is mirrored in the focus of research publications. The lack of chemical variety in published research questions the universality of reported Structure-Property-Process and Process-Structure-Property relationships for PBF. This dissertation presents the findings from identifying Structure-Property-Process relationships critical to fabricate multi-layer parts for poly(phenylene sulfide) (PPS) by PBF towards expanding PBF material selection and evaluating universality of relationship guidelines. PPS is an engineering thermoplastic used for its high strength, rigidity, dielectric properties, and chemical resistance at elevated temperatures. These properties are attributed to PPS' highly crystalline morphology. Its current use in the automotive and aerospace industries, which are early adopters of AM technologies, makes PPS a prime candidate for AM applications. Therefore, the goal of this work is to demonstrate PPS printing by PBF, study its behavior throughout the PBF lifecycle, and abstract general trends in polymer PBF relationships. First, theoretical ranges for print parameter values are determined from properties of an experimental grade PPS powder feedstock. Successful printing of PPS by PBF is demonstrated in a way contrary to published empirical polymer-PBF relationships. Low temperature printing (i.e., bed temperature more than 15 °C lower than polymer peak melting temperature) of PPS successfully fabricated dimensionally accurate parts with reasonable mechanical properties compared against injection molding values. This distinct PPS behavior does not follow empirical guidelines developed for either polyamides or poly(aryl ether ketones). The unique success of low-temperature PBF prompted further investigation into potential benefits of low-temperature printing. Structure-Property-Process relationships were characterized over the course of simulated powder reuse to show that low-temperature printing prolonged the time when PPS powder properties remained in the "printable" range. Significantly re-used PPS powder was shown to be printable when print parameters were adjusted to accommodate structure and property changes. Successful prints from reused powder is uncommon among published reports of PBF printing of high-performance engineering thermoplastics. Observations of a change in molecular architecture through branching and crosslinking during simulated powder reuse motivated investigating if similar reactions occur in printed parts. PPS is commonly used at elevated temperatures in the presence of oxygen, which is the ideal environment for branching and crosslinking. Structural changes manifested in increased glass transition temperature and high temperature storage modulus. The relative change in structure when printed parts were thermo-oxidatively exposed was observed to be significant for parts printed from new powder, but minimal for parts printed from reused powder. This is a result of the structural changes occurring as powder feedstock during reuse over multiple builds. The changing architecture of reused PPS exposed shortcomings with print parameter value selection based solely on polymer thermal properties. Branching and crosslinking reduced crystallinity, resulting in calculated less energy required to melt; however, it also increased melt viscosity. This negative impact on coalescence behavior was not reflected in the methodology for process parameter value determination because current guidelines neglect rheological properties. These observations motivated proposing a method for selecting print settings based on polymer coalescence behavior. Because it is based on coalescence, this method can predict the transition in governing physics from viscous coalescence to bubble diffusion, which is accompanied by a change in the dependence of mechanical properties on laser energy density. Most work in polymer PBF has focused on "printed part triad'" Process-Property relationships. Work presented in this dissertation contributes to the "printability triad'" of Structure-Property-Process relationships and does so using the novel-to-PBF polymer, PPS. Additional polymers must be explored to continue to discern which polymer-manufacturing relationships are universal among all polymers and which are specific to one subset. The observations and connected interpretation to principles of polymer physics add to the body of knowledge for the polymer PBF field. These contributions will help pave the way for investigations into other polymer families and will re-shape the field's normative logic use when answering the question "what makes a polymer printable by PBF?" Understanding the connection between polymer properties and physical stimuli characteristic of PBF manufacturing will result in parts tailored for specific applications and more sustainable manufacturing, thus realizing additive manufacturing's full potential. / Doctor of Philosophy / Powder bed fusion (PBF) is one of seven distinct additive manufacturing (AM, also known as ``3D printing'') technologies. The manufacturing process creates solid, three-dimensional shapes through selectively heating, melting, and fusing together polymer powder particles in a layer-by-layer manner. Currently, organizations are interested in complementing existing manufacturing technology with PBF for one of three general reasons: (1) "complexity is free" PBF has the ability to make shapes that are difficult or expensive to fabricate using other manufacturing technologies. (2) "tool-less manufacturing" PBF only requires a digital design file to fabricate objects. This enables small changes to be easily made via computer-aided design (CAD) programs without the need to invest time and money into tooling (e.g., molds, jigs, fixtures, or other product-specific tools). This enables "mass customized" products (e.g., custom-fit medical devices and implants) to be economically feasible. (3) "material efficiency" AM is attractive as it often generates less waste than subtractive manufacturing techniques like milling. This is particularly a concern for organizations that manufacture parts from expensive, high-performance polymers, such as in the aerospace and medical industries. Despite these benefits, the state of the art for polymer PBF has room for improvement. Specifically, there are many details regarding material behavior during PBF manufacturing that are unknown; any unknown behaviors present challenges to building confidence in production quality. Additionally, approximately 90% of current PBF use is nylon-12 or else another material in the polyamide family of semi-crystalline thermoplastics. This limited selection of commercially available materials compared against other forms of manufacturing contributes to PBF's circular quandary: the manufacturing process physics are not robustly understood because most experimentation and research has been carried out on one family of polymers; however, a wider variety of polymers has not been developed because there is a limited understanding of the process physics. This dissertation presents research toward answering both PBF challenge areas. The first three chapters present investigations into relationships between the properties of a novel, experimental grade poly(phenylene sulfide) (PPS) semi-crystalline thermoplastic polymer powder, the stimuli imposed on this polymer during PBF processing, and the resultant properties of printed parts (i.e., "property-process-property relationships"). The target polymer, poly(phenylene sulfide), is a high-temperature, high-performance polymer that is traditionally melt processed, but has not yet been commercialized for PBF. Prior literature has established mathematical representation for the interaction between manufacturing energy input and the thermal response of the polymer resulting in melting. This framework has been created through studying the polyamide family. Work presented in this dissertation evaluates existing guidelines for PBF process parameter selection using measured thermal behavior of PPS (i.e., a polysulfide, not a polyamide) to predict the range of manufacturing energies affecting geometrically accurate printed parts of high density and strength. In addition, the impact of thermal exposure from repeated PPS powder reuse over the course of multiple PBF prints was evaluated on powder, thermal, and rheological properties identified as critical for PBF printing. Changes to the molecular structure and properties of reused PPS powder were observed to follow different trends than those reported for other materials traditionally used. The effect of thermal exposure on printed parts was also investigated to determine if the observed changes in molecular structure occurring during thermal exposure of the powder would result in changes to mechanical performance properties of printed parts. The importance of rheological flow properties in dictating printed part performance was observed to be a common theme throughout working with PPS. The final chapter presents a novel method for quantitatively predicting particle fusion during PBF and connecting the extent of particle fusion to mechanical properties of printed parts. The presented method is "polymer agnostic" and advances the state of the art in understanding the physics guiding polymer response to stimuli imposed during PBF AM.

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Nos travaux sont consacrés à la fabrication, à la mise en œuvre et aux caractérisations de mélanges de polymères thermoplastiques thermostables destinés à des applications aéronautiques hautes températures. Le Poly(éther cétone cétone) PEKK, polymère semi-cristallin, a été choisi pour sa température de transition vitreuse (Tg) et son point de fusion (Tf) élevés. Les polyimides amorphes utilisés pour leur Tg élevée, sont le Poly(éther imide) PEI et le (polyimide) PI. Le but de ces mélanges est d’augmenter la Tg du PEKK, sans augmenter sa température de fusion. Ces travaux ont abouti à la caractérisation thermique, mécanique et rhéologique de chacun des polymères purs ainsi qu’à la définition d’un protocole de fabrication des mélanges. Les propriétés des mélanges ont alors été caractérisées par analyses thermomécaniques, par balayage calorimétrique différentiel et par des essais de traction afin de faire ressortir les meilleurs candidats pour les applications visées. Les modèles empiriques classiques de variation de la Tg prennent en compte seulement la composition des mélanges. Dans ce travail, nous proposons de corriger ceux-ci par la prise en compte de la variation du taux de cristallinité qui influe sur la composition de la phase amorphe et ainsi permettre une prévision plus fine de ce paramètre. La tenue au vieillissement à court terme des différents polymères dans un fluide aéronautique a aussi été abordée, et a montré que le PEKK a un effet protecteur sur les mélanges. / This PhD work presents the fabrication, processing and characterizations of thermoplastic thermostable polymer blends. It aims at finding new materials useable at high temperatures for aeronautical applications. Poly(ether ketone ketone), PEKK, a semi-crystalline polymer, has been chosen for its high glass transition temperature (Tg) and high melting point (Tf). Amorphous polyimides, that have been used for their high Tg, are Poly(ether imide), PEI, and Polyimide, PI. The aim of these blends is to increase the Tg of the PEKK without increasing its Tf. We have measured the thermal, mechanical and rheological properties of each neat polymer and the processing conditions of the blends have been defined. The properties of the blends have been characterized by thermomechanical analyses, differential scanning calorimetry and tensile tests to focus on the better candidates for the aimed applications. The classical empirical models of the Tg composition dependence take only into account the blends composition. We propose to correct them taking into account the crystallinity level, that affects the blends composition and predict a better prediction of the Tg . The short term ageing of these polymer blends specimens in a commonly used aeronautic fluid has also been studied, and showed the protection effect of the PEKK polymer in the blends.

Yes / A novel process chain for serial production of polymer-based devices incorporating both micro- and nano-scale features is proposed. The process chain is enabled by the use of Zr-based bulk metallic glasses (BMG) to achieve the necessary level of compatibility and complementarity between its component technologies. It integrates two different technologies, namely laser ablation and focused ion beam (FIB) milling for micro-structuring and sub-micron patterning, respectively, thus to fabricate inserts incorporating different length scale functional features. Two alternative laser sources, namely nano-second (NS) and pico-second (PS) lasers, were considered as potential candidates for the first step in this master-making process chain. The capabilities of the component technologies together with some issues associated with their integration were studied. To validate the replication performance of the produced masters, a Zr-based BMG insert was used to produce a small batch of micro-fluidic devices by micro-injection moulding. Furthermore, an experimental study was also carried out to determine whether it would be possible by NS laser ablation to structure the Zr-based BMG workpieces with a high surface integrity whilst retaining the BMG's non-crystalline morphology. Collectively, it was demonstrated that the proposed process chain could be a viable fabrication route for mass production of polymer devices incorporating different length scale features.

Structures made of the thermoplastic polymer polyether ether ketone (PEEK) are widely used in dynamically-loaded applications due to their high-temperature resistance and high mechanical properties. To design these dynamic applications, in addition to the well-known stiffness and strength properties the vibration-damping properties at the given frequencies are required. Depending on the application, frequencies from a few hertz to the ultrasonic range are of interest here. To characterize the frequency-dependent behavior, an experimental approach was chosen and applied to a sample polymer PEEK. The test setup consists of a piezoelectrically driven base excitation of the polymeric specimen and the non-contact measurement of the velocity as well as the surface temperature. The beam’s bending vibrations were analyzed by means of the Timoshenko theory to determine the polymer’s storage modulus. The mechanical loss factor was calculated using the half-power bandwidth method. For PEEK and a considered frequency range of 1 kHz to 16 kHz, a storage modulus between 3.9 GPa and 4.2 GPa and a loss factor between 9 103 and 17 103 were determined. For the used experimental parameters, the resulting mechanical properties were not essentially influenced by the amplitude of excitation, the duration of excitation, or thermal degrad.ation due to self-heating, but rather slightly by the clamping force within the fixation area.