Fillers are often incorporated in polymer matrices in order to improve cost, mechanical, thermal, and transport properties. This work explores the hypothesis that pollen, a natural particle, has the potential to be an effective biorenewable reinforcing filler due to its unique surface architectures, high strength, chemical stability, and low density. Pollens from sources such as ragweed plants are ubiquitous natural materials that are based on sustainable, non-food resources. Pollen is a remarkable example of evolutionary-optimized microscale particle with structures and/or chemistries tailored for effective adhesion to a variety of surfaces and protection of genetic material under different dynamic and environmental conditions. The pollen shell is perhaps the most chemically resistant naturally occurring material. As many pollens achieve pollination simply by being carried by wind, they are very light-weight. These properties make pollen an attractive option as a natural filler for polymers. This research aims to characterize pollen interfacial properties and utilize pollen as an effective reinforcing filler in polymer materials. In this work, interfacial properties are characterized using Fourier transform infrared spectroscopy (FTIR), the BET method, and inverse liquid chromatography (ILC). These techniques were useful in determining the effect of surface treatments and further chemical modifications on pollen interfacial properties. Characterizing these properties allowed for improved understanding and utilization of pollen as a filler by revealing the enhanced surface interactions and surface properties of acid-base treated pollens when compared to as received untreated pollens. Epoxy and polyvinyl acetate (PVAc) matrices were used to demonstrate the effectiveness of pollen as a filler, as a function of pollen loading and surface treatments/chemical modifications. Scanning electron microscopy (SEM) was used to determine interfacial morphology, a high throughput mechanical characterization device (HTMECH) was used to determine mechanical properties, and differential scanning calorimetry (DSC) was used to determine glass transition behavior. In epoxy, pollen was an effective load bearing filler only after modifying its surface with acid-base hydrolysis. In PVAc, pollen was an effective load bearing filler only after an additional functionalization with a silane coupling agent. Finally, the species of pollen incorporated in PVAc matrices was varied in order determine the effect of the size of surface nano- and micro- structures on wetting, adhesion, and composite properties. Composites containing pollen displayed enhanced wetting and interfacial adhesion when compared to composites with smooth silica particles. Additionally, it was observed that pollen with smaller surface structures were wetted more effectively by the polymer matrix than pollen with larger structures. However, mechanical properties did not suggest significant changes in interfacial adherence with varied pollen microstructure size. The results of this work highlight the feasibility and potential of utilizing pollen as a natural filler for creating high strength, light-weight polymer composites with sustainable filler.

Cellulose nanocrystals (CNCs) are crystalline nanoparticles that are extracted from renewable sources such as trees or bacteria through mechanical or chemical treatments of their source. CNCs are of interest to several research communities concerned with sustainable technologies. Specifically, CNCs have attracted great interest in the polymer composite community given their high theoretical specific strength and modulus. Two key obstacles surround the use of CNCs in polymer composites, namely their comparatively lower thermal stability and hydrophilicity render their dispersion, and therefore mechanical reinforcement, in polymer matrices challenging. This research considered a waterborne epoxy and a polyurethane elastomer for CNC/polymer composites since these composites are seldom reported in literature or often suffer from degraded mechanical properties. In the epoxy/CNC composites, samples were prepared by two methods, first an epoxy emulsion was mixed with an amine crosslinker and an aqueous based CNC suspension (1-step mixing), and second, the epoxy emulsion was premixed with the aqueous based CNCs and the amine crosslinker was added some time later (2-step mixing). Both composites were mixed by magnetic stirring, however the samples prepared by the 2-step mixing method exhibited enhanced dispersion and mechanical properties, specifically the storage modulus (E’), tensile strength, and work of fracture. Zeta potential measurements and chemical analysis by FTIR indicated that the dispersion mechanism was physical in nature, rather than chemical. In the second composite system, CNCs were chemically modified with an isophorone diisocyanate (IPDI) monomer having unequally reactive isocyanate groups. The goal of the modification step was to react only one isocyanate group with the CNC surface and have a free isocyanate group available for further modification. The chemical structure of one linked isocyanate (urethane bond) and one free isocyanate was confirmed by FTIR and 13C NMR. The particles modified by IPDI (m-CNC) and the neat particles (um-CNC) were incorporated into a polyurethane matrix based on IPDI and a triol crosslinker. Upon visual inspection of the cured composites, it was clear that the modification step produced homogeneously dispersed nanoparticles in the polyurethane while the um-CNCs were aggregated. When the mechanical properties were tested by uniaxial tensile testing, it was determined that the m-CNC composites resulted in improvements in the tensile strength and work of fracture without degradation of the elongation of break property when compared to the neat matrix. Overall the findings in this research highlight important considerations for designing CNC/thermoset composites with enhanced dispersion and mechanical performance.

Nanoporous (NP) metals are a unique class of materials that are characterized by extremely high surface-to-volume ratios and possess such desirable properties of metals as high electrical conductivity, catalytic activity, and mechanical strength. At the same time, understanding of their physical properties is often lacking, especially for hierarchical NP metals where individual struts and joints that make up open cell 3D network are nanocrystalline. The aim of this work is to employ a dedicated experimental campaign to understand the structure property relation of nanostructured nanoporous metals. Towards this goal, NP Pt and NP Cu have been synthesized for a range of strut sizes and their mechanical properties have been investigated via ex-situ and in-situ nanoindentation experiments. Both NP Pt and NP Cu exhibit relatively high hardness in the range of 0.2 to 1.3 GPa. The relative role of material effects arising from small dimensions of the struts/joints and the geometrical features of NP metals are discussed. Selected applications of the systems synthesized during this work in electrochemistry and catalysis are demonstrated. In the examined applications the NP metals exhibited catalytic activity comparable to or significantly exceeding the best available alternative systems, while offering superior stability.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Dentistry / Master / Master of Dental Surgery

published_or_final_version / Civil Engineering / Master / Master of Philosophy

A novel method for isolating fish proteins by shifting pH to high acid or high alkali pH was the focus of the study. Biochemical and physicochemical properties of various pH-treated soluble fish proteins as a function of ionic strength were determined. Effect of ionic strength and various storage conditions on gelation properties and stabilization of fish protein isolate (FPI) were also elucidated. At low ionic strength (IS 10 mM NaCl), the solubility of Pacific whiting (PW) proteins was low between pH 5 and 10, but increased significantly as the pH was shifted to either acidic or alkaline pH. The isoelectric point (pi) shifted toward acidic direction as IS increased to 600 mM. High IS (600 mM NaCl) resulted in protein aggregation at low pH but improved myosin heavy chain (MHC) solubility at pH 6 - 10. Changes in total sulfhydryl (SH) content and surface hydrophobicity (S [subscript o]) were associated with the different molecular weight distributions of the soluble proteins. At pH 4 and IS 10-100 mM, MHC was soluble but degraded. At pH 10, the formation of high MW polymers was observed at IS [greater than or equal to] 150 mM. Gels obtained from FPI prepared at pHl1/IS150 and conventional surimi (CS) were superior to FPI prepared at pH 3 and/or other IS levels. There was no correlation between protein solubility and gel properties of FPI. Gelation mechanisms of acid and alkali-treated FPI were identical under the same IS condition. FPI prepared at pH 3 or 11 could be partly refolded at pH 7. No significant difference in texture was observed between alkali-treated protein isolates (AKPI, pH 11) kept frozen at pH 5.5 and 7.0. Strongest gel was found for AKPI with cryoprotectants (C) and without freeze/thaw (FT) cycles at both pH storage (5C & 7C), while poor gel was obtained from AKPI without cryoprotectants (NC) and with FT (5NC-F & 7NC-F). 5NC-F & 7NC-F demonstrated the lowest S [subscript o] and total SH probably suggesting that proteins were more aggregated as a result of hydrophobic interactions and disulfide bonds. Scanning electron microscope (SEM) revealed the most discontinuity of gels from AKPI without cryoprotectants and with FT and showed less protein stability when stored at pH 5.5 than at neutral pH. Raman spectral analysis demonstrated that refolding of AKPI by pH adjustment to 7.0 was achieved, but not identical to the native protein. CS contained higher α-helix content (~50%) than AKPI (~20-30%). Frozen storage induced a decrease and an increase in the α-helix of CS and AKPI samples, respectively. Alkali-treated proteins were slightly less stable than CS during frozen storage. / Graduation date: 2005

The issue on variability of mechanical properties within wood has found to be increasingly prominent in recent years. On the other hand, it is known that uniformity of wood properties is essential in quality control in the timber manufacturing such as manufacturing of Glued Laminated (Glulam) timber. The AS/NZS 1328 P2 specified that the overall mechanical properties of Glulam timber can be estimated based on the MOE of the finger jointed laminates and the arrangement of the corresponding laminates. In relating to the above standard, optimisation in the arrangement of shooks’ location along the finger jointed laminate will enable determination of the overall MOE of laminates, as well as optimise the utilisation of feedstocks. In this study, a deterministic model was developed in relating the local shook’s modulus of elasticity (MOE) with the overall MOE of the corresponding finger jointed timber based on the principle of the Moment of Curvature. The projected overall MOE is calculated as a function of lengths and MOEs of individual shooks in the finger joint timber. The effect of shooks’ location can also be determined from the model. Numerical derivation of the model was addressed and the analyses of the relationships between the local shook MOEs, the overall MOE, and bending strength (MOR) were assessed. Experimental results showed that the model can effectively predicts the overall MOE, particularly on shook combinations with random and large standard deviations in shook MOEs. The errors of the predictive model were ranged from -8.17% to +0.81%. Results from the assessment on the relationships between the overall MOE and bending MOR indicated that wood failure in the combinations of small standard deviations shook MOEs was most likely to occur at the weakest point, however, wood failures may not necessarily occur in the shook with the lowest MOE in the asymmetrical MOE arrangements. This also applies to the finger jointed timber with combinations of shooks with large standard deviations for local MOEs. In addition, the relationship between dynamic MOE of shooks and the static bending overall MOE were assessed. A linear regression has been suggested for the adjusted shooks dynamic MOE at 36 mm thickness. The predictability of the model could further improve when the shook MOEs were sorted according to sawing pattern and the proposed model for quarter sawn is suggested. Lastly, economic analysis was performed based on the models available in literature and the developed model in this study. Models reported in the literature including the arithmetic mean model and model based on the shook’s minimum MOE. The results from economic analysis showed that the study’s model was most cost effective in predicting the cost of shooks based on the predicted overall finger jointed MOE using the model as compare to the arithmetic mean and the minimum shook MOE method. In conclusion, the proposed model has demonstrated to be unique, simple, effective and robust in predictive applications.

The issue on variability of mechanical properties within wood has found to be increasingly prominent in recent years. On the other hand, it is known that uniformity of wood properties is essential in quality control in the timber manufacturing such as manufacturing of Glued Laminated (Glulam) timber. The AS/NZS 1328 P2 specified that the overall mechanical properties of Glulam timber can be estimated based on the MOE of the finger jointed laminates and the arrangement of the corresponding laminates. In relating to the above standard, optimisation in the arrangement of shooks’ location along the finger jointed laminate will enable determination of the overall MOE of laminates, as well as optimise the utilisation of feedstocks. In this study, a deterministic model was developed in relating the local shook’s modulus of elasticity (MOE) with the overall MOE of the corresponding finger jointed timber based on the principle of the Moment of Curvature. The projected overall MOE is calculated as a function of lengths and MOEs of individual shooks in the finger joint timber. The effect of shooks’ location can also be determined from the model. Numerical derivation of the model was addressed and the analyses of the relationships between the local shook MOEs, the overall MOE, and bending strength (MOR) were assessed. Experimental results showed that the model can effectively predicts the overall MOE, particularly on shook combinations with random and large standard deviations in shook MOEs. The errors of the predictive model were ranged from -8.17% to +0.81%. Results from the assessment on the relationships between the overall MOE and bending MOR indicated that wood failure in the combinations of small standard deviations shook MOEs was most likely to occur at the weakest point, however, wood failures may not necessarily occur in the shook with the lowest MOE in the asymmetrical MOE arrangements. This also applies to the finger jointed timber with combinations of shooks with large standard deviations for local MOEs. In addition, the relationship between dynamic MOE of shooks and the static bending overall MOE were assessed. A linear regression has been suggested for the adjusted shooks dynamic MOE at 36 mm thickness. The predictability of the model could further improve when the shook MOEs were sorted according to sawing pattern and the proposed model for quarter sawn is suggested. Lastly, economic analysis was performed based on the models available in literature and the developed model in this study. Models reported in the literature including the arithmetic mean model and model based on the shook’s minimum MOE. The results from economic analysis showed that the study’s model was most cost effective in predicting the cost of shooks based on the predicted overall finger jointed MOE using the model as compare to the arithmetic mean and the minimum shook MOE method. In conclusion, the proposed model has demonstrated to be unique, simple, effective and robust in predictive applications.

Fatigue has been observed to affect lower extremity mechanics during the cutting maneuver. However, there is a lack of research examining the effect of fatigue and limb dominance on lower extremity mechanics during unanticipated sidecutting. Objectives: This research sought to assess mechanical differences pre- and post-fatigue and with respect to limb dominance. Design: Repeated measures. Methods: Thirteen female collegiate soccer and field hockey players performed right and left unanticipated sidecutting following the Yo-Yo Intermittent Recovery test (Yo-Yo IR), a two minute treadmill run at a predicted VO2max, and maximum vertical jumps. Mechanical measures of ankle, knee, and hip motion were obtained during the stance phase of the cut. Repeated measures 2x2 ANOVAs were performed to look at fatigue and limb differences. Alpha level set a priori at 0.05. Results: At initial contact and peak stance, significant changes pre- to post-fatigue were observed. At initial contact there was a reduction in knee flexion angles along with increased ankle dorsiflexion angles postfatigue. At peak stance: increased knee adductor moments post-fatigue; greater ankle eversion moments on the dominant limb (DL) as well as increased eversion moments post-fatigue for both limbs. There was a differential effect of fatigue on peak hip abduction angles and hip internal rotation angles at initial contact which were altered in the DL only; decreased hip adductor moments occurred post-fatigue as well as decreased power absorption. Conclusions: Results from this study indicate that lower extremity mechanics are altered as an effect of fatigue such that injury risk may be elevated. / School of Physical Education, Sport, and Exercise Science