Philip David Evans


Relevant Degree Programs


Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - April 2022)
Effects of adhesive z-connections on the properties of a model wood composite (2017)

Adhesive is a costly and critical component of wood composites. The relationship between adhesive distribution and properties of wood composites has been explored, but few studies have attempted to alter the distribution of adhesive in wood composites as a way of improving their properties. In this thesis, I hypothesize that creating a 3-dimensionally inter-connected adhesive network by introducing adhesive Z-connections will improve two key properties of wood composites (thickness swelling and fracture toughness). Both experiments and computer simulation (finite element analysis) were carried out to test this hypothesis. I developed a methodology to precisely perforate veneer to facilitate the creation of adhesive Z-connections when the composite was pressed. Adhesive Z-connections are defined as the cured adhesive distributed in the Z- (thickness) direction (in addition to the X-Y directions) of the laminated wood composite due to the perforation in veneer. I examined factors affecting the ability of Z-connections to improve dimensional stability and fracture toughness of a model wood composite. I visualized the adhesive distribution in the composite in 2D and 3D using macro-photography, X-ray micro-computed tomography and scanning electron microscopy. Significant improvements in dimensional stability and fracture toughness of some of the composites were observed. Key parameters affecting the ability of adhesive Z-connections to reduce thickness swelling were diameter and spatial arrangement of Z-connections, adhesive level and wood species used to make the composite. Key parameters affecting the ability of adhesive to increase the fracture toughness of a model wood composite were area-density of Z-connections and reinforcement of the adhesive in the composite. I conclude that introducing adhesive Z-connections can reduce thickness swelling and enhance fracture toughness of wood composites, but the effectiveness of such an approach is affected by wood species, area-density and spatial arrangement of the Z-connections. I discuss the implications of my findings for the development of wood composites with enhanced dimensional stability and fracture toughness and further research needed to capitalize on the concept of creating an inter-connected 3D adhesive network in wood composites by introducing adhesive Z-connections.

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Etching of wood by glow-discharge plasma (2012)

In this thesis I hypothesize that plasma will etch wood surfaces, produce new cell wall microstructures, and change the surface chemistry of wood because of differential etching of wood’s polymeric constituents. I also examine factors affecting the etching of wood by plasma, and applications of plasma etching for wood processing. Scanning electron and light microscopy and white light confocal profilometry were used to examine etching of wood surfaces. Wet chemical analysis, FTIR and XPS spectroscopy were used to analyze chemical changes at the surface of plasma-treated wood. Experiments were also performed to examine the effect of plasma treatments on the color of blue-stained wood, the morphology of fungal hyphae and the adhesion and performance of coatings on hot-oil modified wood. Exposure of wood to plasma caused etching of wood cell walls and created new surface microstructures. Regions of cell walls that were rich in lignin such as the middle lamella were etched more slowly by plasma. Confocal profilometry of wood exposed to plasma revealed a strong relationship between plasma treatment time and etching of cell walls, and same technique found that lignin pellets were etched more slowly than cellulose pellets. Plasma reduced the levels of carbohydrate at the surface of modified wood, which resulted in a relative increase in lignin content. Plasma treatment improved the effectiveness of hypochlorite bleach at removing blue-stain from wood and it prevented the discoloration of a white acrylic paint on hot-oil modified wood exposed to natural weathering. However, plasma treatment of hot-oil modified wood did not have positive effects on the adhesion and exterior performance of a range of other coatings (mainly semi-transparent stains). I conclude that prolonged exposure to plasma can etch wood cell walls, but cell wall layers that are rich in lignin are degraded more slowly. Plasma etching of wood mainly depends on treatment time and also on the structure and chemical composition of wood. Plasma treatment is an efficient pre-treatment for bleaching of blue-stained wood and reducing the discoloration of white acrylic paint on hot-oil modified wood.

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Role of Non-Decay Fungi on the Weathering of Wood (2012)

In this thesis I hypothesized that the graying of wood exposed outdoors is due to the presence of melanized fungi that are relatively resistant to UV-light. To test this hypothesis I examined the color and chemical changes at wood surfaces exposed to the weather and filtered solar radiation, isolated and identified fungi colonizing wood samples by DNA analysis and microscopy and examined the survival, growth and melanin production of staining fungi under UV, visible or no light. The ability of isolated fungi to decay wood was also tested by evaluating changes in the microstructure, mechanical, viscoelastic and chemical properties of spruce and lime wood incubated with fungi. Finally, I tested a novel non-biocidal approach to reduce the staining of wood by fungi, which employed melanin biosynthesis inhibitors (MBIs). My results support the general hypothesis (above) and reveal that weathered wood surfaces are grayed by the interactive effects of solar radiation and fungal colonization. UV-radiation increased the production of melanin by the fungus most frequently isolated from weathered wood (Aureobasidium pullulans), which leads to darker weathered wood surfaces. Decay tests showed that species of Cladosporium, Coniochaeta, Epicoccum, Lewia, Mollisia and Phialocephala, were able to degrade wood tissues. In artificial media, MBIs in combination with UV-radiation blocked the growth of staining fungi, but at wood surfaces MBIs reduced fungal staining irrespective of the type of light that samples were exposed to. I conclude that UV-radiation and melanized fungi interact to influence the color of weathered wood surfaces. Degradation of wood by surface fungi is possible, but the extent of damage probably depends on the presence of conditions that favor microbial decay. Finally, the use of MBIs is a promising approach to control graying of weathered wood surfaces, but further research is required to optimize the treatments and test them outdoors.

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Master's Student Supervision (2010 - 2021)
Optimizing profile geometry to reduce the checking, shelling and cupping of profiled softwood deck-boards exposed to natural weathering (2021)

Wooden deck-boards are susceptible to surface checking and distortion during weathering. Surface profiling is an effective physical pre-treatment to reduce the checking of boards, but it is less effective at reducing cupping, unless it is also used on the underside of boards. I hypothesize that the checking and cupping of softwood deck-boards exposed outdoors can be significantly reduced by optimizing the geometries of surface and sub-surface profiles. To test this hypothesis, I examine the effect of profile geometry and growth ring orientation on the checking and cupping of western larch deck-boards exposed outdoors. Standard and tall rib profiles were significantly more effective at restricting checking than other profile types, particularly when profiled boards were oriented pith-side-up. However, such growth ring orientation made larch deck-boards more susceptible to shelling, a severe defect caused by the separation of growth rings. Confocal profilometry and macro-photography were used to characterize the projection of separated latewood at deck-board surfaces. A negative correlation was revealed between the heights of protruding latewood and growth ring angle to the weathered surface of flat larch boards oriented pith-side-up. The number of shelled lanceolate-shaped tips at the peaks of profiled boards was more common in boards with rib profiles particularly those oriented pith-side-up. I conclude that profiled larch boards should be oriented bark-side-up rather than pith-side-up. Hence, there was a need to develop different sub-surface profiles to distinguish pith- and bark-sides of boards so that boards can be correctly oriented in decks with their bark-side facing uppermost. Pacific silver fir and western hemlock boards were chosen to test sub-surface grooving as an alternative to sub-surface profiling because previous studies had optimized surface profiles for both species. There was an unexpected effect of number of grooves on the cupping of hem-fir boards. Boards machined with an odd number of grooves that included a groove running down the centre-line of the underside of boards were less prone to cupping compared to boards with an even number of grooves. In conclusion, results demonstrate that checking and cupping of softwood deck-boards can be reduced by a combination of surface profiling and sub-surface grooving.

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Shape optimization of wooden bats using genetic algorithm and artificial intelligence (2020)

Cricket and baseball are popular and increasingly wealthy bat-and-ball sports. The bat is the key instrument used to score runs in both sports. In professional cricket and baseball leagues, the bats are made from a single piece of wood. Wooden cricket and baseball bats are the focus of increasing scientific research, and in this thesis, I describe an innovative approach to improving the performance-related geometry. I use parametric finite element (FE) modelling in combination with genetic algorithm (GA) to optimize the dynamic and vibrational properties of cricket and baseball bats. Parametric FE modelling enables an algorithm to tailor the mass distribution and mechanical properties of bats to converge the location of two points on a bat that are associated with increased velocity of a ball rebounding off bats: vibrational nodal points and center of percussion (COP). Modelling was able to reduce the distance between nodal points and COP from 174.5 to 98.1 mm and from 166.0 to 52.1 mm for cricket and baseball bats, respectively. This change occurred as a result of modifications to the geometry of the bats notably shifting cricket bat’s mass towards its end, and shifting baseball bat’s mass towards the center of the barrel and removing mass from the very end of the barrel.The combination of modelling and GA optimization required a powerful computer and long computational times. I further showed in this thesis that an artificial neural network (ANN) can be trained to replace the FE modelling component of my optimization system, which was the bottle-neck for bat optimization. I conclude that: (1) the combination of parametric modelling and GA optimization is an effective tool for altering the geometry and mass distribution of bats which could improve the rebound velocity of a ball hitting these bats; (2) my approach can reveal new performance-related geometries for both cricket and baseball bats; (3) GA-ANN optimization is a more computationally efficient approach for optimizing the design of bats.

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Envelope protection of preservative-treated pine decking with modified low molecular weight phenol formaldehyde resin (2018)

Preservative-treated pine is commonly used for outdoor decking in Canada and the United States, but its attractive appearance is lost when it is exposed to the weather. Wood can be protected from ‘weathering’ using low molecular weight phenol formaldehyde (LMW PF) resin. In this thesis, I combine preservative treatments and modification of wood with PF resin to try to develop wood decking with superior resistance to weathering. My hypothesis is that shallow ‘envelope’ modification of treated wood with LMW PF resin containing photostabilizers and wax additives will protect the appearance of preservative-treated pine decking exposed to natural weathering. I first screened different additives for their ability to protect wood from the adverse effects of weathering. The best additives were selected for further testing. Preservative-treated Scots and southern pine boards were modified by dipping or vacuum impregnation with modified PF resins, and modified and treated boards were exposed to the weather. Envelope modification restricted checking of untreated pine boards weathered for two years. Degradation of modified boards was shallow and easily cleaned off. Underneath the weathered grey layer, the colour of PF-modified wood was retained. Envelope modification with different PF resin formulations also protected treated boards weathered for six months. Ferric chloride was a more effective additive than a lignin stabilizer for most substrates (treated or untreated). The dark colour of PF/ferric-modified wood masked mould. The different PF resins I tested improved the performance of treated wood to varying degrees, but their effectiveness depended on the substrate they were applied to. I conclude that: (1) envelope modification with PF and modified PF resins is able to protect treated decking from the adverse effects of weathering; (2) vacuum impregnation with PF resin is a better method than dipping at creating an effective weather-resistant envelope at the surface of treated wood decking; (3) PF and additives need to be tailored to suit different preservative-treated woods; (4) PF modification shows promise as a finishing process to enhance weathering resistance of treated wood.

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Photoprotection of wood using metal acetylacetonates (2018)

Wood is a versatile material with a pleasant appearance that is widely used in architectural and interior applications. However, wood (including clear-coated wood) undergoes degradation when it is exposed outdoors. Wood can be protected from surface photodegradation (weathering) using reactive metal ions that are able to cross-link wood’s molecules and create complexes that are resistant to photodegradation. Metal acetylacetonates are coordination complexes of metal ions and the acetylacetonate anion. Metal acetylacetonates are used by industry to cross-link chemicals, and they have also been used as photostabilizers for polymers. One study has shown that titanium acetylacetonate can reduce the photodegradation of radiata pine veneers exposed to natural weathering. My general hypothesis is that metal acetylacetonates will be able to protect wood from photodegradation on their own or in combination with other protective systems, including clear finishes, oils and UV absorbers. I compared the photoprotective effects of six metal acetylacetonates on yellow cedar veneers and clear-coated yellow cedar and Scots pine panels. I found that the ability of metal acetylacetonates to photostabilize yellow cedar veneers varies depending on the metal in the coordination complex. Nickel, manganese, titanium and iron acetylacetonate were more effective than cobalt acetylacetonate at photostabilizing wood, based on the different measures I used to assess the degradation of weathered veneers. Iron acetylacetonate was more effective at photostabilizing lignin in weathered veneers than the other metal acetylacetonates. Manganese and titanium acetylacetonate had some positive effects on the performance of a clear polyurethane coating on Scots pine and particularly yellow cedar panels exposed to artificial accelerated weathering. Oils when combined with titanium acetylacetonate provided additional protection to wood surfaces, most notably water repellency, but the oils had negative effects (mould growth) on the appearance of panels exposed to natural weathering. I conclude that metal acetylacetonates can photostabilize wood surfaces and improve the performance of a clear polyurethane coating on wood, However, the effectiveness of metal acetylacetonates depends on the metal in the coordination complex and the wood species that are treated with the acetylacetonate. Finally, I conclude that metal acetylacetonates have potential as protective treatments, particular photoprotective primers for coatings.

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Effects of moisture-induced thickness swelling on the microstructure of oriented strand board (2017)

When wood becomes wet and then dries, restraint of shrinkage at the surface of wood by wetter surface and also sub-surface layers causes tensile stresses to develop resulting in micro-checking. Wood elements in composites such as oriented strand board (OSB) also swell and shrink when they become wet and dry. Furthermore, some wood elements are large enough to develop unbalanced surface and sub-surface tensile stresses. Hence, moisture changes and swelling and shrinkage of OSB might result in micro-checking. I test this hypothesis in this thesis. I also examine whether micro-checking contributes to thickness swelling of OSB. I used macro-photography, X-ray micro-computed tomography, and field emission scanning electron microscopy to probe the microstructure of OSB exposed to wetting and drying. These techniques were used to visualize and quantify the thickness swelling of OSB and the dimensions of micro-checks and other voids in OSB during and after wetting and drying. The spatial micro-distribution of a zinc borate biocide in OSB was also examined before and after samples were exposed to wetting and drying. Numerous surface and internal micro-checks developed in OSB exposed to wetting and drying as I hypothesized. Micro-checks developed during wetting, unlike the pattern of checking found in solid wood. Enlargement of voids was also observed during wetting and drying. Micro-checks occurred at the interface between latewood and earlywood and in the rays of softwood flakes and, less commonly, in the rays of aspen flakes. My results indicate that the pattern of micro-checking of OSB is different in some respects to that of solid wood, and suggest that micro-checking contributes to the irreversible thickness swelling of OSB. I briefly discuss the implications of my findings for the development of treatments designed to reduce the irreversible thickness swelling of OSB.

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Reducing the Surface Checking of Deck-Boards Exposed to Natural Weathering: Effects of Wood Species and Surface Profiling (2015)

Surface checking is a defect in wood decking that is highly disliked by consumers. Surface checking can be reduced by selecting species that are more resistant to checking, or profiling deck-boards with a series of V(rib) or U(ripple) shaped grooves. Most literature on checking of decking focuses on species that are already used as exterior products. This provides an opportunity to investigate the use of other under-utilized species as deck-boards. Surface profiling has been applied to deck-boards to reduce checking, but there is little research on why it is effective. I hypothesize that both species and the geometry of surface profiles will significantly influence checking of deck-boards exposed to natural weathering. To test this hypothesis I exposed deck-boards made from 9 untreated softwoods and 8 untreated hardwoods outside for one year and measured the checking of the boards. None of the species performed as well as western red cedar and ipe, durable species that resist checking. However, some diffuse porous hardwoods performed quite well and further improvements might be achieved with chemical or physical treatments. Profilometry was used to classify and identify the geometry of commercially profiled deck-boards. The ratio of the surface grooves (R1) to those of peaks (R2) classified profiles into two categories mentioned in the literature (rib and ripple). A new category of profile (ribble) was also identified that had intermediate characteristics of both rib and ripple profiles. New profiles with various R1/R2 and height to width (H/W) ratios of profile peaks and grooves were tested to examine the effect of profile geometry on the checking of Pacific silver fir boards exposed to natural weathering. Profiling reduced the width of checks but increased cupping of the boards. There was no consistent trend of R1/R2 and H/W ratios on checking, but rib profiles were better than ribble or ripple profiles at restricting checks. Therefore, I conclude that species and profile geometry influence checking. Furthermore, some of the rib profiles could be used with diffuse porous hardwoods and some softwoods to enable them to compete more effectively with decking made from durable wood species or wood plastic composites.

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Molten Wax Spray Treatment Makes Oriented Strandboard (OSB) More Water Repellent and Reduces Thickness Swelling (2014)

When oriented strandboard (OSB) absorbs moisture its compressed wood strands swell up and recover strains that were induced during hot pressing. Adhesive bonds that hold the strands together rupture and permanent thickness swelling occur. Few post-treatments are able to effectively reduce the thickness swelling of OSB. OSB is porous, with inter-strand voids up to 1.5 mm in diameter. Surface coatings are less effective at restricting moisture ingress into OSB than into solid wood, because of the irregular surface of OSB. Molten wax has a low viscosity and may be able to flow into and block the inter-strand voids of OSB. In this thesis I hypothesize that the water repellency and dimensional stability of OSB may be improved by spraying molten wax onto the hot surface of the board. Furthermore, I hypothesize that polar and low melting point waxes will form more effective water repellent barriers than nonpolar or high melting point waxes. The properties of 13 different waxes and five custom made wax blends were characterized with emphasis on properties likely to influence the water repellency of OSB. Molten waxes were sprayed onto the surface of hot OSB and the water absorption and thickness swelling of the samples were measured. Wax treatments were able to reduce the rate of water absorption and the rate of thickness swelling, but not the extent thickness swelling. I conclude that wax treatments are able to increase the water repellency of OSB and reduce the thickness swelling during short-term periods of exposure to water. Waxes with high melting point temperatures tended to form more effective water-repellent barriers, especially for short-term exposure periods, contrary to my hypothesis. Blends of pure beeswax, which contains polar functional groups, and strongly hydrophobic waxes, such as paraffin wax, formed excellent water-repellent barriers. The results suggest that a combination of polar and nonpolar wax is more effective at reducing the thickness swelling of wax-treated OSB than waxes that contain only hydrophobic components. Errata:

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High performance clear-coat systems for wood used outdoors (2011)

Wood is one of the main materials of choice to reduce the environmental footprint of the building and construction sector. Wood is aesthetically pleasing and hence there is great demand for finishing systems that do not mask wood’s color and texture. Unfortunately, clear coatings used on wood outdoors fail within one to two years mainly because of photodegradation of the underlying wood substrate. Theperformance of clear coatings on wood can be enhanced by photostabilizing thewood before coating or by modifying the clear coating to improve its photostability and flexibility. However, these approaches have seldom been combined. In this thesis I hypothesized that pre-treatments that can photostabilize wood without adversely affecting coating performance could, when combined with state-of-the-art clear coatings, create coating systems that are a significant improvement on those that are currently available. I compared the ability of nine different chemical treatments to photostabilize wood. I examined the effect of the same wood pretreatments on coating properties (wettability and adhesion) and the permeability of three different coating types. The most effective photostabilizing pre-treatments were benzoyl chloride, vinyl benzoate and chromic acid, and a PF-resin containing a hindered amine light stabilizer. The solvent based polyurethane was more compatible than the water-based acrylic and alkyd coatings with treated wood surfaces. Wood treatments had no effect on coating adhesion, but coating adhesion was highest for the polyurethane. Subsequently, I examined the outdoor performance of seven different clear coatings on photostabilized wood substrates. Benzoyl chloride, vinyl benzoate, chromic acid and the PF-resin/HALS treatments effectively enhanced the clear coat performance during a year-long weathering trial in Australia. Clear coat performance was also improved by using coatings with double the amount of UVA/HALS additives. My findings confirm that clear coat performance on wood exposed outdoors depends on the combination of wood retreatment and coating type. I conclude that superior clear coat systems (pretreatment plus coating) for wood can be developed by combining very effective treatments that can photostabilize wood together with state-of-the-art photostableand flexible clear coatings.

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Plasma modification of wood to improve the performance of clear coatings (2011)

Wood is susceptible to photodegradation, particularly by ultraviolet (UV) light which triggers photochemical reactions in wood up to 100 µm from the surface. Painting may protect the wood from sunlight, however, consumers prefer clear-coatings because they reveal wood’s grain. Unfortunately, clear finishes on wood used outdoors fail within 1-2 years because sunlight transmitted through the clear-coating degrades the underlying wood. I hypothesized that the performance of clear-coatings on wood used outdoors would be improved if the clear-coating could penetrate deeply into the wood and bond with sub-surface layers of wood that are less affected by UV light. Glow discharge plasma derived from water was used to etch and open up flow paths at the surface of the refractory wood species, black spruce. Image analysis was used to assess the penetration of two polyurethane clear-coatings into wood, and the adhesion (pull-off) of clear-coatings to unweathered wood was measured. A second experiment examined the changes in color, gloss and integrity of clear-coats on plasma treated and coated specimens subjected to artificial accelerated weathering. Plasma treatment of black spruce for 20 min significantly increased the penetration of clear coatings into sub-surface layers of wood (50-75 µm). However, the adhesion of the polyurethane clear coatings on wood depended much more on coating type (adhesion of the water-borne was better than that of the oil-borne coating). Plasma pre-treatments decreased film failure of coatings on flat-sawn specimens exposed to artificial weathering, but increased the surface yellowing of coated wood specimens. The oil-borne polyurethane performed better in terms of three performance criteria (redness, yellowness and gloss), while the water-borne was superior in terms of changes in lightness. I conclude that plasma treatment can increase the penetration of coatings into wood if the plasma can etch the wood and open up important flow-paths. However, plasma treatments have no positive effect on the adhesion of polyurethane coatings to black spruce wood and adhesion is influenced more by the type of coating. Finally, plasma treatments can have positive and negative effects on the exterior performance of coatings on wood depending on the criteria used to assess performance.

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Use of confocal profilometry to quantify erosion of wood and screen chemicals for their ability to photostabilize wood (2011)

Optical confocal profilometry is a new technology for characterizing the surfaces of materials. In this thesis, I hypothesize that confocal profilometry will be able to more accurately measure the erosion of wood during weathering than optical microscopy. Confocal profilometry may be able to screen photoprotective chemicals, and in this thesis I use confocal profilometry to test the hypothesis that PF resin can photostabilize wood. Confocal profilometry was used to measure the erosion of untreated western red cedar wood exposed to natural and artificial weathering. The erosion of western red cedar specimens increased with time. Specimens exposed in a xenon-arc weatherometer eroded significantly faster than specimens exposed in a QUV weatherometer. The profilometer was able to measure the erosion of specimens exposed for only 100 h in a xenon-arc weatherometer. There was a positive correlation between the size of the area of wood exposed to weathering and the erosion of wood during artificial and natural weathering. The erosion rate was about 2-20 times faster during artificial weathering compared to natural weathering. Profilometry was able to discern differences in the erosion of untreated specimens and specimens treated with PF resin. However, profilometry was not able to detect differences in erosion of specimens treated with different PF resin formulations. In contrast, the thin strip technique, which measured weight and tensile strength losses of treated wood veneers exposed to weathering, was able to discern differences between formulations. I conclude from measurements on western red cedar that confocal profilometry is a more accurate and less labor-intensive way of measuring the erosion of wood during weathering than optical microscopy. The exposure time required to produce erosion that can be measured using the profilometer is much less than that needed when using an optical microscope. But specimens need to be flat, free of checks and have eroded areas that are distinct from unweathered areas. Low molecular weight PF resin shows great promise as a treatment for photostabilizing wood.

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