Gregory Smith
Relevant Thesis-Based Degree Programs
Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
The focus of this study was to investigate flax shive and hemp hurd as alternate residue for particleboard production, investigate the lowest percentage of the pricier polymeric diphenyl methane diisocyanate (pMDI) resin that can be used to effectively bond the residues and evaluate an acrylic-based resin for particleboard manufacture.The flax shive and hemp hurd had lower bulk densities and higher aspect ratios compared with wood. Their higher aspect ratios offered greater overlap in bonding leading to consistently higher bending properties that exceeded American National Standards Institute (ANSI) requirements for low density (LD2) particleboard and in some cases, medium density (M2) particleboard. Because of their particle geometry, the flax shive and hemp hurd particleboards also showed minimal linear expansion with changes in moisture content between 50% and 90% relative humidity (at 20 ± 3°C) and were within ANSI requirements. The high absorption capacity of the residues resulted in higher thickness swell and water absorption properties in contrast to wood. Improvements in bending strength above 40% and stiffness properties above 25% was achieved for wood, hemp hurd and flax shive particleboards by incorporating 15 weight % flax and hemp fiber in continuous mat form at the points of maximum tensile and compressive stresses in particleboard. Test results confirmed the possibility of using 2.5% pMDI resin load, a percentage lower than the commercially viable 3%–6% addition levels that are commonly used with wood residues. The results further demonstrated that based on 2.5% pMDI resin load and as much as 20% mass lignin substitution boards with satisfactory mechanical properties that exceed LD2 grade requirements could be manufactured from hemp hurd and flax shive. Dynamic scanning calorimetry results and the current cost of the acrylic-based resin suggests that it is not suited for particleboard manufacture from flax shive and hemp hurd.Overall, based on mechanical performance flax shive and hemp hurd residues can be considered as alternate biomass for particleboards of greater performance to wood for use in shelving and furniture applications. But the high cost of the residues compared to wood does not currently make it economical for particleboard manufacture.
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Currently used energy absorbers in transportation industries are made of synthetic fiber/polymer composites as an alternative to their metal counterparts. These composites are stiff and strong but are somewhat brittle when subjected to impact load which limits their application when high energy absorbing ability is required. Wood, in contrast, has a high stiffness and strength to weight ratio and exhibits a higher deflection before failure. Despite the extensive research on the mechanical properties of synthetic fiber/polymer composites few researches are available on the effects of wood composite configuration and densification and its lamination set-up on its impact and compressive properties. This research focused on the use of wood in the form of thin veneer to reinforce polyester and composites of them were fabricated using hand lay-up and compression molding, in different thicknesses. Various wood configurations were used to create unidirectional, cross-ply, and woven mats. The effects of each mat configuration on the impact properties of wood/polyester composites and the lamination and curing processes were investigated and discussed. The gap of knowledge on the wettability of wood to the polyester resin was informed in this dissertation using contact angle measurements and roughness tests. Energy absorbing behavior and dominant fracture mechanisms of wood/polyester laminates subjected to quasi-static compression and shear loading were examined and the results were compared with the lab-made glass fiber/polyester composites. Findings of this study demonstrated that the effect of wood configuration on the impact properties of the polyester composites was significant. Wood densification improved the impact performance of composites but this improvement was not statistically significant. It was found that wood composites had an impact energy equivalent to that of glass fiber laminates.
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Particleboard (PB) is the most utilized reconstituted wood composite panel for furniture production. However, edge smoothness and screw withdrawal resistance (SWR) have been limiting factors in some of its applications. In view of mounting wood and resin costs, this study focused on benchmarking the mechanical properties of Canadian-made furniture grade Ready-To-Assemble MS and M2 particleboard. Of the five plants surveyed, over 80% of the 30 furniture grade particleboards tested were below the ANSI A208.1 standard for edge SWR of 900N. Particle geometry was examined by hydrolyzing samples from the commercial panels to disintegrate them into individual particles which were then characterized in terms of particle length, aspect ratio (AR), and slenderness ratio (SR). Based on maximum likelihood estimation a 2-parameter lognormal distribution function was found to be the best fit for particle length, AR, and SR followed by the 2-parameter Gamma distribution function. AR was found to be the best indicator of edge SWR. A novel particle mixture was formulated by repartitioning the core particles of commercial, as-received PB furnish into core-fine, medium, and coarse particles, which were then remixed in different proportions for the core furnish to fabricate low density panels: the IB strength was 40% higher than the control panels and the edge SWR 18% higher. A response surface model based on a mixture design was developed for macro-voids in the core of simulated particle mats and the macro-voids ratio in pressed panels was also found to increase exponentially with the void fraction in randomly packed loose particle mats. The study concluded that there are too many fine particulates and dust in the core of commercial PB. Increasing the amount of fines in the panel surface by decreasing fine and dust in the panel core through repartitioning the particles into fine, medium, and coarse has the potential of increasing surface smoothness, IB strength, SWR, and consequently reducing density and raw material cost. Keywords: aspect ratio, gamma distribution, lognormal distribution, mixture design, particle, particle distribution, particle mixture, particleboard, random packing, response surface methodology, slenderness ratio, X-ray CT.
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During the manufacturing of wood composites, mats of resinated fibers, particles or strands are consolidated under heat and pressure to produce panels with the necessary strength and stiffness properties. As the mat consolidates a vertical density profile (VDP) is established and it has a significant impact on panel properties. In order to tailor the VDP of the panel to various end-use applications, a means of describing of the effect of pressing variables on the development of the VDP is needed.This study examined the role of environmental factors, i.e., temperature and moisture content (MC), on the compression and viscoelastic behavior of wood strands. The strand stress-strain relationship during hot pressing was modeled using a modified Hooke’s law, in which the compression modulus as a function of temperature and MC was quantitatively obtained using a regression approach. Similarly, the viscoelastic behavior of strands was investigated for various temperatures and MCs and the results were used to develop a model for predicting the stress relaxation response of the strands. The results showed that the relaxation modulus as a function of time follows a linear relationship on a log-log plot; it is important to note that the response was affected by strain level and environmental conditions.Based on the strand compression properties and mat structure, a comprehensive model was established that simulated the VDP development and was found to be a good description of the experimental results. The effects of mat elastoplasticity and springback on the formation of the VDP were also discussed. In addition, a generalized model based on the beam bending of the wood elements was developed to predict the mat pressure-density relationship of wood composites. This is valuable for improving the fundamental understanding of the relationship between pressing variables and panel properties for process optimization.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
This thesis studied the optimization of the pressing parameters for producing oriented strandboard (OSB) panels with a uniform vertical density profile (VDP) for furniture purpose. In order to identify the key parameters and press cycle that produces a uniform VDP, four experiments were developed by two hot pressing methods were considered (conventional hot pressing and steam injection hot pressing). Two main variables (strand thickness and closing position) were considered. The performed tests included internal bond (IB), bending and elastic moduli (MOR/MOE), vertical density profile (VDP), and face and edge screw withdrawal resistance (SWR).Results suggested the optimization of pressing parameters for conventional hot pressing to achieve a uniform VDP is creep closing schedule, which is the press platens stopped at 19.8 mm in 5s during closing segment and then continued closing with a slower rate to target thickness 18 mm in 10s. The total cooking time was 235s, ended with two degas segments (20s respectively) and a 20s opening segment. Compared to traditional hot pressing, the optimized pressing schedule can achieve a more uniform VDP panel. This means it can achieve a higher edge SWR strength which is the key to OSB suitability for upholstered furniture. In addition, examination of the SWR results showed that both face SWR and edge SWR are not affected by the strand thickness.
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Bamboo (Poaceael/Graminaceae) has great potential for use in improving the properties of wood-based strand composite building materials. In previous work it has been shown that replacement of aspen surface strands with Moso bamboo (Phyllostachys pubescens Mazel) strands significantly improves the strength and water resistance of oriented strand board (OSB) of the same density made from Aspen. Guadua (Guadua andustifolia Kunth) is one of the most commercially cultivated and used timber bamboo genera in Latin America. In this study, three experiments were designed. Six sets of 6 three-layer OSB (737 x 737 x 11.1 mm) were made with bamboo strands in the face layers and Aspen strands in the core layer. Measured board properties included internal bond, flexural properties (modulus of rupture, MOR; and modulus of elasticity, MOE), and water resistance (% thickness swell, TS; and % water absorption, WA). The 50% Guadua -50% Aspen boards (type GM) was compared with 50% Moso -50% Aspen boards (type MM) to examine the effects of bamboo species. Guadua hybrid OSB had a weaker IB strength and a higher MOE in the parallel direction. No other significant difference was found. To examine the effect of reducing board density down to an acceptable level, three board types were compared. 1) 50% Moso - 50% Aspen boards (type MM) with target density of 760 kg/m³, 2) 25% Moso - 75% Aspen boards (type ML1) with target density of 720 kg/m³, and 3) 25% Moso - 75% Aspen boards (type ML2) with lower target density of 628 kg/m³. The lowest density group had the lowest mechanical properties and water resistance ability but met the Canadian Standards Association (CSA) standards for industrial OSB. Another two board types were designed to examine the effect of the nodes on Guadua OSB products’ properties. 50% Guadua Node – 50% Aspen boards (type GN) showed weaker IB strength and weaker flexural properties than 50% Guadua Internode – 50% Aspen boards (type GI).
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A survey of Canadian and US particleboard (PB) and medium density fiberboard (MDF) manufacturers was performed to identify potential candidates for the mechanical and physical properties comparison study. Sixty-three plants across Canada and the United States were contacted and 19 plants participated in the survey. In order to obtain and compare data on mechanical and physical properties of boards from PB and MDF manufacturers, samples were collected from 10 different manufacturing facilities across Canada and the United States (5 PB and 5 MDF). The performed tests included internal bond (IB), bending and elastic moduli (MOR/MOE), thickness swell (TS), linear expansion (LE), vertical density profile (VDP), and face and edge screw withdrawal resistance (SWR). Each manufacturing facility provided 5 full-sized (2440 by 1220 mm) panels that were tested according to North American standards. For particleboard, 4 out of 5 press lines exceeded the American National Standards Institute (ANSI) A208.1-2009 recommendation for IB. Only one of the tested particleboard sets reached the recommended ANSI standard for MOR. Results for the edge SWR showed that none of the tested particleboard manufacturers reached the ANSI recommended value. For MDF, all but one press line exceeded the ANSI standard A208.2-2009 recommended minimum value for MOE. The results for the modulus of rupture for MDF showed two manufacturers exceeding the recommended value, and three failing to meet the recommended value.
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The objective of this research is to investigate the effect of nanoclay additions to particleboard resins on the properties of particleboard made with those resins. Two nanoclays, Cloisite30B, a modified nanoclay and Nanofil16, an unmodified clay, were blended with the two resins used to produce particleboard: Urea Formaldehyde (UF) and Melamine Formaldehyde (MF). Coupling agent was added to nanoclays to facilitate clay dispersion into the resin. X-ray diffraction tests showed that mechanical mixing was sufficient to exfoliate Closite30B into both resin types and enable the intercalation of Nanofil116/resin mixtures. Addition of nanoclays and coupling agents had small to severe adverse effects on resin curing: Cloisite30B slightly delayed the curing process of both UF and MF resin and reduced the reaction heat of curing, and the addition of coupling agent together with Closite30B further compounded this effect. Nanofil116 significantly delayed the curing reaction of both resins and decreased the heat of reaction. The coupling agent had a significant further detrimental effect on the resin cure.In order to test whether nanoclays had a positive or negative effect on the adhesive strength of UF and MF resins, the shear strength of clay-modified resin were tested and compared with that of unadulterated resin. Regardless of whether coupling agent was used, the clay-modified UF resin had lower bonding strength than pure UF resin. In contrast, three kind of clay-modified MF resin had higher bonding strength then pure MF resin. Based on these findings those MF resins which have higher shear strength were blended with furnish to fabricate particle board using different clay loading rates. Most clay treatments had no significant effect on particleboard physical or mechanical properties. The only significant improvement was for internal bond strength which increased when using either 2% Closite30B or Nanofil116 with or without coupling agent. Higher clay loading rates tended to decrease board strength properties. In conclusion, the modified Closite30B nanoclay and the unmodified Nanofil116 nanoclay had only a minor effect on improving UF and MF resin strength and the particle board properties.
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Proteinaceous surface layers (S-layers) have been identified in hundreds of different species belonging to all major phylogenetic groups of Bacteria and most Archaea and form a geometrically arranged paracrystalline lattice. Despite their wide abundance, few structural and functional studies have been performed on S-layers. Obtaining high-resolution structural models has been hampered by the aggregation properties of S-layers, whereas only a few functions have been identified. This thesis focuses on the structure and the function of the hexagonal S-layer of the environmental bacterium Caulobacter crescentus. In the first part of my thesis, an array of new methods was devised and tested to stabilize the S-layer protein (RsaA). Protein concentrations of an N-terminally truncated protein (RsaAΔ0-222) could be increased up to 7 mg/mL while maintaining the protein in the monomeric form. Stable protein samples were found to crystallize in the presence of Ca²⁺ and Sr²⁺. However, crystals were not thick enough (mainly formed in two dimensions), as x-ray diffraction experiments showed diffraction patterns with low resolutions. Hence, obtaining high-quality crystals remains a challenge. The second part of my thesis demonstrates that the S-layer serves as a resistance mechanism to cationic antimicrobial peptides, which are produced by virtually all living organisms, including bacteria, fungi, plants and animals. S-layer positive strains were shown to be less susceptible to antimicrobial peptides than S-layer negative strains in MIC and killing assays. This protective effect was also observed when S-layer positive and negative strains were grown in biofilms. S-layer mediated resistance to antimicrobial peptides was further confirmed using epifluorescence microscopy. Addition of exogenous S-layer protein significantly increased the resistance of an S-layer negative strain to antimicrobial peptides. Overall, these results identify a new, previously unrecognized role for the S-layer as a resistance mechanism against antimicrobial peptides.
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An ongoing shortage of suitable woody waste materials due to the many recent saw-mill closures in Canada has been a major concern for particleboard manufacturers. The existing particleboard plants are currently competing with other industries for the scarce fiber resources available and facing significant competition from the cheap lower grade substitutes being imported from China. This thesis presents a solution through the development of hollow core sandwich panels for modular furniture components that serve the same function as solid slabs of particleboard but with reduced amounts of raw material inputs (wood and resin).Through a series of preliminary experiments, prototype honeycomb sandwich panels were fabricated with a variety of face and core materials. The characteristic effects of different types of Kraft paper honeycomb materials, its cell size, orientation and cell wall height as well as the influence of different wood-based face materials on the sandwich strength and stiffness properties were established.The results indicate that by combining thicker (6 mm) face sheet materials with Kraft paper honeycomb with cell size less than 16 mm, cell wall height 38 mm and oriented with the core ribbon direction perpendicular to the long axis of the panel, a sandwich panel with significant strength properties can be produced. The findings also imply that the performance of the honeycomb sandwich panels can further be improved through the application of edge rail enforcements and edge band application. The outcome of this study has the potential of reducing the total weight of finished products for the furniture manufacturers and provides avenues for product differentiation.
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