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In 2012, a new type of lignin, catechyl (C)-lignin was found in the seed coat of vanilla orchid (Vanilla planifolia) and Melocactus cacti, and later in the nutshell of Aleurites moluccana (candlenut). This caffeyl alcohol homopolymer is the exclusive lignin in vanilla seed coat but separated in time and/or location with guaiacyl (G)-lignin in candlenut. Unlike conventional guaiacyl/syringyl (G/S-lignins) with alkyl-aryl ether linkages, intermonomer linkages in C-lignin are connected by benzodioxane linkages which are stiffer than alkyl-aryl ether linkages. C-lignin is unusually stable against acid-catalyzed cleavage. Tissues with C-lignin are expected to exhibit high glass transition temperature (Tg) compared to tissues with G/S/H-lignin. C-lignin also probably shows high crystallinity due to its highly linear-homopolymer structure. The ability of some seed coats/nutshells in angiosperms to synthesize a new type of lignin is another level of lignin evolution. However, the role of C-lignin related to the function of the seed coat is unclear while it exhibits different behaviors to the regular G/S/H-lignin. These points motivated us to conduct cell-wall structure/property studies in the context of plant evolution, using microscopy, X-ray diffraction (XRD) and dynamic mechanical analysis (DMA). Light and electron microscopes were used to identify cell's size and type of intact and macerated vanilla seed coat and candlenut shell. Vanilla seeds are tiny, sized approximately 300μm and the surface is covered with dark-colored seed coat. Candlenut is slightly smaller than walnut, with uneven, hard, dark brown shell covering the nut. Microscopy observations indicated that both seed coat and nutshell are dominated by highly lignified cells, known as sclereids. The types of sclereids in vanilla seed coat and candlenut shell are different; vanilla seed coat has ostoesclereid-type cells, while candlenut shell has macrosclereid-type cells. XRD was used to study tissue with C-lignin crystallinity by comparing diffractograms of vanilla seed coat and candlenut shell to Southern Yellow Pine wood diffractograms. The Southern Yellow Pine wood diffractogram corresponds to a typical native cellulose in higher plants, that is cellulose I allomorph. Diffractogram XRD analysis on vanilla seed coat and candlenut shell shows similarities to Southern Yellow Pine native cellulose, suggesting that cellulose is the contributor for crystallinity in seed coat and nutshell, and this also indicated that tissues with C-lignin is not crystalline. Crystallinities of vanilla seed coat and candlenut shell determined using peak deconvolution methods were about half of Southern Yellow Pine crystallinity. DMA was used to measure Tg in vanilla seed coat and candlenut shell. Measurements were conducted in solvent-submersion mode using organic plasticizers to reduce the Tg to non-damaging temperatures. DMA measurement of vanilla seed coat and candlenut shell is challenging due to specimen size and shape. Specimen preparation for DMA measurement included seed coat purification for vanilla and cutting/milling for candlenut shell followed by specimen saturation in plasticizers. Compressive-torsion DMA was used to allow tiny specimens gripping. Vanilla seed coats exhibited higher glass transition temperature compared to wood, while candlenut shells exhibited various Tgs depending on specimen type/size. / Doctor of Philosophy / Lignin is a complex organic material that constructs higher plant cell walls. Lignin provides stiffness and strength and is the landmark of plant evolution to terrestrial life. Typically, lignin in hardwood/softwood has guaicayl and/syringyl (G/S) units derived from coniferyl/sinapyl alcohols. ln 2012, a new type of lignin, catechyl (C)-lignin, was found in the seed coat of vanilla orchid (Vanilla planifolia) and Melocactus cacti, and later in the nutshell of Aleurites moluccana (candlenut). C-lignin is a caffeyl alcohol homopolymer and is exclusive in vanilla seed coat but coexists with guaiacyl (G)-lignin in candlenut shells. This new type of lignin exhibits different behavior than G/S-lignin. C-lignin is unusually stable against acid-catalyzed hydrolysis. Intermonomer linkage in C-lignin is stiffer than G/S lignin(s); it is likely to have higher glass transition temperature (Tg) than normal lignin. Due to its linearity, tissue with C-lignin is also expected to be highly crystalline. C-lignin's roles are not well known and therefore, these are merit for structure/property studies in the context of plant evolution as bio-inspired new materials. Microscopy, X-ray diffraction (XRD), and dynamic mechanical analysis (DMA) were used to study vanilla seed coat and candlenut shell morphology, crystallinity, and glass transition temperatures (Tg), respectively. It was observed that the two tissues have different types of sclereids, but this is not associated with why vanilla seed coats exhibit only C-lignin while candlenut shells have both C /G-lignins. XRD scans revealed that C-lignin is not crystalline due to similarity of their diffractograms to those of wood. DMA measurements revealed that vanilla seed coat tissues exhibit higher Tg than tissue with G/S lignin as expected, while the Tg candlenut shells varied among specimen type and particle sizes.

The focus of this research project was to investigate morphological and mechanical properties of both extruded and dispersion-cast Nafion® membranes. The project can be divided into three primary objectives; obtaining a fundamental understanding of the glass transition temperature of Nafion®, determining the effect of thermal annealing treatments on the morphology and mechanical properties of dispersion-cast Nafion®, and examination of dispersion-cast Nafion® subjected to an ex-situ, Fenton's chemical degradation test. Nafion®, a perfluorosulfonate ionomer, is considered a commercially successful semi-crystalline ionomer with primary applications in chlor-alkali cells and proton exchange membrane fuel cells. With the aid of dynamic mechanical analysis (DMA) and dielectric spectroscopy (DS), we were able to provide definitive evidence for a genuine glass transition in Nafion®. DMA of Nafion® samples that were partially neutralized with tetrabutylammonium counterions showed a strong compositional dependence suggesting that the β-relaxations of H+-form Nafion® and the neutralized ionomers have the same molecular origin with respect to backbone segmental motions. Building upon our previous studies of the molecular and morphological origins of the dynamic mechanical relaxations of Nafion® neutralized with a series of organic ions, the glass transition temperature of H+-form Nafion® is now confirmed to be the weak β-relaxation centered at -20 °C. Dielectric spectra also showed this transition from the perspective of dipole relaxation. The signature of cooperative long range segmental motions in dielectric spectra was seen here, as with other polymers, mainly through the excellent agreement of the β-relaxation time-temperature dependence with the Vogel-Fulcher-Tammann equation. We have also discovered that new dispersion-cast H+ form Nafion® membranes are susceptible to disintegration/dissolution when subjected to boiling methanol. In this work, we have achieved significant decreases in the percent solubility of H+-form Nafion® by either thermally annealing above 175 °C or solution-processing at 180 °C using a high boiling point solvent. Small Angle X ray Scattering (SAXS) displayed a change in the morphology of H+ form membranes with increasing annealing temperature by a shift in the crystalline scattering peak (q â 0.05 Ã 1) to lower q values. Counterion exchange of Nafion® from H+ to Na+ form had no influence on the membrane's susceptibility to disintegration in boiling methanol. In order to achieve mechanical stability in boiling methanol, Na+ form membranes had to be annealed at 275 °C for at least fifteen minutes. The SAXS data of annealed Na+ form membranes showed a dramatic decrease in crystalline order with annealing temperature, ultimately leading to the disappearance of the crystalline scattering peak after fifteen minutes at 275 °C. The onset of methanol stability with the melting of Nafion® crystallites suggests that chain entanglement is an important parameter in obtaining solvent stability. With respect to chemical stability, we performed studies aimed at examining the effects of Fenton's Reagent on the resistance to radical attack of new generation, dispersion-cast Nafion®. Changes in the 19F solid-state NMR spectra of dispersion-cast Nafion® before and after chemical degradation via Fenton's Reagent predicts a rather random attack by ·OH and ·OOH radicals. Several membranes were also thermally annealed between 100-250 °C in an attempt to correlate crystallinity with chemical degradation kinetics of Nafion® via Fenton's Reagent. The results indicate that the effect of counterion exchange into the Na+ form was minimal, but the degree of thermal degradation had a tremendous effect on the fluoride release rate and chemical degradation kinetics. By exchanging the membranes into the Na+ form, thermal degradation was avoided, allowing us to study the role of crystallinity as a function of fluoride release. Ultimately, Nafion® crystallinity was deemed an important factor in deterring peroxide radical attack. As the percent crystallinity decreased with annealing temperature, the fluoride concentration in the resulting Fenton's media increased accordingly, indicating that the amorphous regions of the polymer are more susceptible to chemical degradation via peroxide radical attack. / Ph. D.

In the effort to improve oil production riser performance, new materials are being studied. In the present case, a Polymer Matrix Composite (PMC) is being considered as a replacement for carbon steel in flexible risers manufactured by Wellstream Inc., Panama City, Florida. The Materials Response Group (MRG) at Virginia Tech had the primary responsibility to develop the models for long-term behavior, especially remaining strength and life. The MRG is also responsible for the characterization of the material system with a focus on the effects of time, temperature, and environmental exposure. The present work is part of this effort. The motivation to use a composite material in a non-bonded flexible riser for use in the offshore oil industry is put forth. The requirements for such a material are detailed. Strength analysis and modeling methods are presented with experimental data. The effect of matrix crystallinity on composite mechanical properties is shown. A new method for investigating matrix behavior at elevated temperatures developed. A remaining strength life prediction methodology is recalled and applied to the case of combined fatigue and rupture loading. / Master of Science

Polyesters are an attractive class of polymer that can be readily modified with a wide range of different comonomers, during polymerization or with melt blending, to achieve a wide variety of physical properties. This research primarily focuses on polyesters that incorporate rigid aromatic structures that have excellent potential to enhance thermal and mechanical properties. Copolyesters were prepared through melt polycondensation of diesters and diols in the presence of an exchange catalyst. Monomer incorporation was verified with nuclear magnetic resonance (NMR) and molecular weights were obtained by measuring inherent viscosity (ninh). Physical properties were assessed with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and rheology. Mechanical properties were assessed with tensile and impact testing. Copolyesters of poly(ethylene terephthalate) (PET) were synthesized by substituting dimethyl terephthalate (DMT) with dimethyl 4,4'-biphenyldicarboxylate (4,4'BB) resulting in enhanced glass transition (Tg) temperatures relative to PET while affording melting temperatures (Tm) low enough to allow facile melt processing. Further modification with dimethyl isophthalate (DMI) or dimethyl 3,4'-biphenyldicarboxylate (3,4'BB) slowed crystallization sufficiently to allow biaxial orientation, leading to further studies assessing the permeability of oriented films. Novel amorphous polyesters were synthesized with 3,4'BB or 4,4'BB in combination with neopentyl glycol (NPG), 1,4-cyclohexandimethanol (CHDM) and ethylene glycol (EG). Use of multiple diols produced clear, amorphous copolyesters with Tgs as high at 129 C. A series of novel high temperature(Tm) copolyesters were synthesized from dimethyl 2,6-naphthalenedicarboxylate (DMN) and 4,4'BB combined with CHDM. Studies were performed with standard DSC and thin film calorimetry to show the convergence of multiples melting endotherms in an effort to determine their origin. Preliminary work was performed on the modification of poly(1,4-cyclohexylenedimethylene terephthalate) (PCT), poly(1,4-cyclohexylenedimethylene 2,6-naphthalate) (PCN) and poly(1,4-cyclohexylenedimethylene 4,4'-bibenzoate) (PCB) with dimethyl p-terphenyl-4,4''-dicarboxylate. / PHD / Polyesters have a unique balance of properties that sets them apart from other polymers formed by step growth reactions. The transesterification reaction that forms polyesters occurs continually at reaction temperatures, making it easy to randomly distribute a mixture of different comonomers along the backbone during the polymerization process, or even when blending two different polyesters. Poly(ethylene terephthalate), commonly referred to as PET, is the most important polyester currently in production, and is prized for its transparency, chemical resistance, and recyclability. PET was first made by John Whinfield and James Dickson at Calico Printers’ Association of Mansfield, in 1941 and was eventually licensed to DuPont in the 1970s. It has since become a valuable resource for producing synthetic textiles and replacing heavier materials, such as glass and metal, to produce lightweight containers, especially for food storage. Many of the polyesters, such as PET, that we see on a daily basis are actually copolyesters that contain low levels of additional comonomers that have been added to improve some property of the final polymer or to facilitate processing. In research, modification of polyesters with different comonomers broadens our understanding in how the molecular structure of comonomers affects polyester properties. This makes it possible to tune a copolyester’s physical properties in a way that can enhance its suitability for a wide range of applications. The research described in this dissertation is focused on exploring how rigid monomer structures containing multiple aromatic rings might be used to produce polyesters with improved performance relative to current commercial polyesters. Materials that demonstrate good barrier to gases such as CO₂ and O₂ are important for packaging that can seal in and preserve food and beverages. In our research, we modified PET with bibenzoate structures to produce films that showed improved gas barrier when stretched in a manner that imitates the stretch blow molding process used to produce bottles. These materials showed good promise for packaging capable of preserving food for longer periods of time. Clear, food safe plastics that do not deform at the boiling temperature of water are important for baby bottles and durable dishwasher safe containers, which are commonly sterilized with boiling water. Until recently, such materials were produced from bisphenol-A polycarbonate (BPA PC), which fell out of favor for food safe applications over concerns that BPA, believed to have endocrine disrupting activity, may leach into food and beverages. Bibenzoate monomers, which increases the application temperature of many polyesters, were combined with different combinations of diol monomers to produce transparent copolyesters that are usable at higher temperatures. These materials demonstrated excellent potential as food safe alternatives to BPA containing materials. Crystalline plastics that resist distorting at high temperatures are important for applications in the electronics and automotive industry. Semicrystalline polyesters provide less expensive alternatives to the costly liquid crystalline polymers commonly used for high temperature applications. We explored the properties of a number of semicrystalline copolyester compositions capable of exceeding the application temperature of semicrystalline polyesters currently on the market.

Polylactic acid (PLA) is an aliphatic polyester, derived from sustainable natural sources that is biodegradable and can be industrially composted. This material has been in the spotlight recently due to its sustainability and properties. However it has been invented in 1932 by Carothers and then patented by DuPont in 1954 (Standau et al. 2019). The properties of this material though limit its use for applications mainly in the medical sector and in some cases single use packaging. In this research, PLA based blends with improved rheological and thermomechanical properties are investigated. The focus is based in proposing strategies in improving these properties based on commercial methods and processing techniques. In this work, commercial grade PLA has been blended with polycaprolactone (PCL) and polybutylene succinate (PBS) in binary and ternary formulations via twin screw extrusion. PCL has been known to act as an impact modifier for PLA, but to cause a corresponding reduction in strength. Results showed that the binary PLA blends containing PBS and PCL, had reduced viscosity, elastic modulus and strength, but increased strain at break and impact strength. Morphological and thermal analysis showed that the immiscibility of these additives with PLA caused these modifications. Incorporation of a small loading of PBS had a synergistic effect on the PLA-PCL blend properties. Miscibility was improved and enhanced mechanical properties were observed for a ternary blend containing 5wt% of both PBS and PCL compared to binary blends containing 10% of each additive. To increase heat resistance of PLA, the material’s crystallinity has to be increased. However PLA has a relatively slow crystallisation rate making it difficult and expensive to be used in commercial applications where heat resistance is needed. For this reason the chiral nature of PLA has been used to investigate the effect of stereochemistry of PLA in crystallisation. Optically pure PDLA was added to its enantiomer in small amounts (up to 15%) and the properties and crystallisation mechanism of these blends was investigated. Results showed that the addition of PDLA accelerated crystallinity and developed a stucture that increased heat resistance, melt strength and stiffness. Finally, a processing model of developing a fully stereocomplex PLA part based in commercial techniques is proposed. Injection moulded PLA showed even higher heat resistance without the need of further processing the product (increasing crystallinity). / Floreon

Doctor of Philosophy / Department of Grain Science and Industry / Praveen V. Vadlani / The purpose of this study was to investigate micro- and macro-scale aspects of solid state fermentation (SSF) for production of cellulolytic enzymes using fungal cultures. Included in the objectives were investigation of effect of physicochemical characteristics of substrate on enzymes production at micro-scale, and design, fabrication and analysis of solid-state bioreactor at macro-scale. In the initial studies response surface optimization of SSF of soybeans hulls using mixed culture of Trichoderma reesei and Aspergillus oryzae was carried out to standardize the process. Optimum temperature, moisture and pH of 30ºC, 70% and 5 were determined following optimization. Using optimized parameters laboratory scale-up in static tray fermenter was performed that resulted in production of complete and balanced cellulolytic enzyme system. The balanced enzyme system had required 1:1 ratio of filter paper and beta-glucosidase units. This complete and balanced enzyme system was shown to be effective in the hydrolysis of wheat straw to sugars. Mild pretreatments– steam, acid and alkali were performed to vary physicochemical characteristics of soybean hulls – bed porosity, crystallinity and volumetric specific surface. Mild nature of pretreatments minimized the compositional changes of substrate. It was explicitly shown that more porous and crystalline steam pretreated soybean hulls significantly improved cellulolytic enzymes production in T. reesei culture, with no effect on xylanase. In A. oryzae and mixed culture this improvement, though, was not seen. Further studies using standard crystalline substrates and substrates with varying bed porosity confirmed that effect of physicochemical characteristics was selective with respect to fungal species and cellulolytic activity. A novel deep bed bioreactor was designed and fabricated to address scale-up issues. Bioreactor’s unique design of outer wire mesh frame with internal air distribution and a near saturation environment within cabinet resulted in enhanced heat transfer with minimum moisture loss. Enzyme production was faster and leveled within 48 h of operation compared to 96 h required in static tray. A two phase heat and mass transfer model was written that accurately predicted the experimental temperature profile. Simulations also showed that bioreactor operation was more sensitive to changes in cabinet temperature and mass flow rate of distributor air than air temperature.

Micronisation of active pharmaceutical ingredients (APIs) to achieve desirable quality attributes for formulation preparation and drug delivery remains a major challenge in the pharmaceutical sciences. It is therefore important that the relationships between crystal structure, the mechanical properties of powders and their subsequent influence on processing behaviour are well understood. The aim of this project was therefore to determine the relative importance of particle attributes including size, crystal quality and morphology on processing behaviour and the characteristics of micronised materials. It was then subsequently intended to link this behaviour back to crystal structure and the nature of molecular packing and intermolecular interactions within the crystal lattice enabling the identification of some generic rules which govern the quality of size reduced powders. In this regard, different sieve fractions of lactose monohydrate and crystal variants of ibuprofen and salbutamol sulphate (size, morphology and crystal quality) were investigated in order to determine those factors with greatest impact on post-micronisation measures of particle quality including particle size, degree of crystallinity and surface energy. The results showed that smaller sized feedstock should typically be used to achieve ultrafine powders with high crystallinity. This finding is attributed to the reduced number of fracture events necessary to reduce the size of the particles leading to decreases in milling residence time. However the frequency of crystal cracks is also important, with these imperfections being implicated in crack propagation and brittle fracture. Ibuprofen crystals with a greater number of cracks showed a greater propensity for comminution. Salbutamol sulphate with a high degree of crystal dislocations however gave highly energetic powders, with reduced degree of crystallinity owing to the role dislocations play in facilitating plastic deformation, minimising fragmentation and extending the residence of particles in the microniser. Throughout these studies, morphology was also shown to be critical, with needle like morphology giving increased propensity for size reduction for both ibuprofen and salbutamol sulphate, which is related to the small crack propagation length of these crystals. This behaviour is also attributed to differences in the relative facet areas for the different morphologies of particles, with associated alternative deformation behaviour and slip direction influencing the size reduction process. Molecular modelling demonstrated a general relationship between low energy slip planes, d-spacing and brittleness for a range of materials, with finer particle size distributions achieved for APIs with low value of highest d-spacings for identified slip planes. The highest d-spacing for any material can be readily determined by PXRD (powder x-ray diffraction) which can potentially be used to rank the milling behaviour of pharmaceutical materials and provides a rapid assessment tool to aid process and formulation design. These studies have shown that a range of crystal properties of feedstock can be controlled in order to provide micronised powders with desirable attributes. These include the size, morphology and the density of defects and dislocations in the crystals of the feedstock. Further studies are however required to identify strategies to ensure inter-batch consistency in these attributes following crystallisation of organic molecules.