To maximize value recovery from post mountain pine beetle - wood (MPB wood) for the manufacture of wood composite products, it is desirable to use completely MPB wood as OSB, MDF or particleboard furnish. The objective of this study in the first fiscal year was to determine and quantify the chemical properties, bondability and wettability of grey stage MPB wood in order to minimize or reduce the impact of beetle-killed wood on composite panel manufacturing. Investigation of the chemical and physical properties of grey stage MPB wood, such as wood pH and buffer capacity, wettability and bondability was conducted. Green lodgepole pine and aspen were used to compare the test results. Various wood furnish derived from MPB wood and green lodgepole pine have been prepared for the manufacturing testing of OSB, MDF and particleboard panels in the next fiscal year. The test results indicated that some basic chemical and physical properties of lodgepole pine, particularly in the sapwood area, had undergone changes associated with MPB infestation.
Based on the test results so far, the following conclusions are made:
1. The pH values of both the MPB heartwood and sapwood were lower and their acid and base buffer capacities were higher than those of the green lodgepole pine. As a result, the curing rate of pH sensitive adhesives such as UF and MUF may be affected.
2. MPB sapwood showed extremely fast and high water absorption but its thickness swell was lower than those of the MPB heartwood, green pine sapwood and heartwood regardless of water temperatures.
3. Thickness swell of the MPB sapwood almost reached to the maximum in the first two hours of water soaking at 20°C.
4. The water absorption of sapwood was higher but the thickness swell was lower than that of heartwood in both MPB wood and green lodgepole pine. The rates of water absorption and thickness swell of these woods were fast in the first several hours and slowed down thereafter.
5. Both the MPB heartwood and the green pine heartwood behaved very similarly in terms of water absorption rate and percentages. It appeared that the beetle infestation did not significantly affect the water absorption property of the MPB heartwood.
6. Edge thickness swell and center thickness swell of the MPB sapwood behaved very similarly in terms of the rates and percentages, which were quite different from those of the other woods and suggest that the blue stained MPB sapwood had probably undergone profound changes.
7. Higher temperatures led to faster and more water absorption. The water temperature affected the MPB sapwood more than the MPB heartwood.
8. Thickness swell reached to the equilibrium faster at higher temperatures.
9. Water pH had little influence on water absorption but affected thickness swell. The thickness swell of both MPB wood and lodgepole pine decreased under both acidic and alkaline conditions.
10. The bonding strength of MPB and green lodgepole pine with liquid PF, powdered PF and liquid UF were generally comparable to that of aspen at high press temperatures. Both the MPB wood and green pine showed lower bonding strength than aspen at low press temperatures. This may have significant implications on the bonding quality of the core layer of panels.
11. At high temperature (200°C), green pine produced substantially higher MDI bonding strength while MPB wood and aspen gave lower and similar bonding strength. This was also the case at low press temperature (140ºC), particularly in longer press time. The MDI bonding strength of MPB wood was close to that of aspen under all these press time and temperature conditions. However, aspen appeared to be less sensitive to low press temperature in terms of bonding with MDI. Therefore, green lodgepole pine may be more suitable as a core furnish material than the MPB wood in the manufacture of OSB, where MDI resin is widely used as a core layer adhesive. Grey stage MPB wood may be more suitable as an OSB face furnish material. This hypothesis will be carefully tested in the 2nd fiscal year of this project.
Insect killed wood - Utilization
Insect-killed wood - Recovery
Pinus contorta Dougl. var. latifolia - North America
Good resin distribution is key to the manufacture of high quality composite panels at low cost. An effective, reliable and non-destructive method for the detection and measurement of urea-formaldehyde (UF) resin content and distribution in furnish and panels is highly desirable in scientific research and in the medium density fibreboard (MDF) and particleboard industry, but up to now it has not been available.
In the Forintek laboratory, a novel non-destructive test method has been developed to allow the effective tracing of UF resin with a copper (2+) ion labeling agent throughout the board manufacturing process. Experiments using Scanning Electron Microscope (SEM) coupled with Energy Dispersive Analysis of X-rays (EDAX) have produced conclusive evidence that the copper (2+) label stays with the UF resin molecules at all times (even at high temperatures), which is essential to the effectiveness of UF resin labeling. X-ray fluorescence experiments have demonstrated that UF resin in MDF fibre can be detected and measured with great precision by using this method, as shown by the calibration curves (copper readings vs. UF resin add-on rates). A linear relationship between UF resin loading levels and the labeling agent quantities was observed. The reproducibility of each sample measurement is so good that variations of copper readings among different samples of the same batch of blending can effectively and quantitatively reflect the quality of the blending. This method can be used to measure UF resin not only in MDF furnish but also in MDF panels.
An MDF mill trial of this new method to measure melamine-urea-formaldehyde resin was successful. The trial showed that it is a practical tool for monitoring resin loading levels and uniformity and it is also a useful tool for on-site troubleshooting and process optimization. It can be used for fast analysis on an off-line basis. It is a non-destructive test method and hence has the potential for on-line applications.
Lab experiments showed that this method is also applicable to the detection and measurement of UF resin distribution in particleboard furnish and panels. Combining with Tyler screen analysis, this method is capable of showing quantitatively how UF resin is distributed among different wood particle sizes. Therefore, it is an effective tool to guide the optimization of furnish particle geometry and the reduction of resin usage.
Low copper concentration in the sample negatively influences the precision of the x-ray fluorescence measurement. At low resin loading levels, higher copper addition rate may be required. This would be a more important consideration in the case of particleboard because resin loading levels of particleboard are usually lower than those of MDF.
Sample density has a great influence on the XRF measurement. Therefore, it should be kept as constant as possible when comparing measurement results among different samples.
Transformative Technologies - Development of "Green" Wood Adhesives for Wood Composite Products
Chitosan is an amino polysaccharide obtained from the deacetylation of chitin, which is naturally occurring in the shells of a large number of marine crustaceans. Chitosan is soluble in weakly acidic aqueous solutions and possesses adhesive properties. Chitosan has received much attention for medical and industrial applications; however, only limited studies have been conducted on the application of chitosan as a wood adhesive, because its bonding properties on wood are poor. To improve the adhesive quality of chitosan resin, an innovative study on chitosan adhesives has been conducted to use selected fungal species to modify chitosan and improve its bonding properties, to synthesize non-formaldehyde resins with the fungus-modified chitosan, and to enhance urea-formaldehyde (UF) and phenol-formaldehyde (PF) resin performance with the fungus-modified chitosan.
The bonding properties of wood composites made with these chitosan-based green wood adhesives were significantly improved, in terms of lap-shear strength. Unmodified chitosan solution was not compatible with ammonium lignosulfonate, liquid PF resin, soybean resin, powder PF resin, or soybean flour, but was compatible with UF resin, polyvinyl acetate (PVA) resin, and phenol. With the addition of chitosan in UF and PVA resins, both the dry and wet shear strengths of plywood panels were improved, compared with those of panels bonded with the control UF and PVA resins, i.e. without chitosan. A number of chitosan and chitosan-reinforced UF resins were prepared as a binder for particleboard panel manufacturing. Six (6) types of particleboard panels with different levels of resin loadings and press conditions were manufactured. The resulting boards were tested to evaluate the bond quality of the chitosan and chitosan-reinforced UF resins. The test results showed that particleboard panels with good visual quality could be produced with all formulations of chitosan-UF adhesives, even with resin systems made with 1% of chitosan resin only. All chitosan resins used alone or added to UF resins yielded panels with better internal bond (IB) strength than those made with the UF control resin. The panels made with 1% chitosan resin plus 66% UF resin in a 1:1 ratio yielded panels with the highest IB strength and the best overall mechanical properties.
Chitosan is an amino polysaccharide deacetylated from chitin, which is naturally occurring in large amount in shells of marine crustaceans. Chitosan is soluble in weakly acidic aqueous solutions and possesses an adhesive property. Chitosan has received much attention for medical and industrial applications; however, only limited studies have been conducted on the application of chitosan as a wood adhesive because of its bonding properties on wood are poor. To improve the adhesive quality of chitosan resin, an innovative study on chitosan adhesives has been conducted to use selected fungal species to modify chitosan and improve its bonding property, to synthesize non-formaldehyde resin with the fungus-modified chitosan and to prepare UF and PF resins enhanced with the fungal modified chitosan. Bonding properties of wood composites made with these chitosan-based green wood adhesives in terms of lap-shear strength were significantly improved in this study. Unmodified chitosan solution was not compatible with ammonium lignosulfonate liquid, liquid PF resin, soybean resin, PF powder, or soybean flour, but was compatible with UF resin (liquid), PVA resin, or phenol. With addition of chitosan in UF and PVA resins, both dry and wet shear strengths of plywood panels were improved comparing with the use of the control UF and PVA resins without chitosan. A number of chitosan and chitosan-reinforced UF resins as binder for particleboard manufacturing have been prepared. Six (6) types of particleboards with different levels of resin loadings and press conditions were manufactured and evaluated for the bond quality of chitosan and chitosan-reinforced UF resins. The results showed that all formulations of chitosan-UF adhesives were able to produce particleboards with nice appearance, even those made of only with 1% of chitosan resin alone. All chitosan resins, alone or added to UF resins, had a better IB strength than UF control resin. The panels made of 1% of chitosan resin plus 66% of UF resin in a 1:1 ratio had the highest IB strength.
The fire resistance of cross-laminated timber (CLT) could be improved by treating the lamina with fire retardants. The major issues with this technology are the reduced bondability of the treated lamina with commercial adhesives. This study assessed several surface preparation methods that could improve the bondability and bond durability of fire-retardant treated wood with two commercial adhesives. Four surface preparation methods, including moisture/heat/pressure, surface planing, surface chemical treatment, and surface plasma treatment were assessed for their impact on the bondability and bond durability of lodgepole pine lamina. The block shear test results indicated that all surface preparation methods were somewhat effective in improving bond performance of fire-retardant treated wood compared to the untreated control wood samples, depending on the types of fire retardants and wood adhesives applied in the treatment process and bonding process. The selection of surface preparation, fire retardant, and wood adhesive should be considered interactively to obtain the best bond properties and fire performance. It may be possible to effectively bond the treated lamina with PUR adhesive without any additional surface preparation for the fire retardant used in the treatment at FPInnovations.
Phenolic glue extenders/fillers from mountain pine beetle (MPB)-attacked wood (sander dust, bark and wood particles) were developed as substitutes for corncob to reduce the costs of plywood manufacturing. Laboratory tests of the bonding performance of plywood panels produced with these new glue mixes generally exceeded the standard requirements for Canadian plywood in terms of wood failure percentage under both vacuum-pressure and boil-dry-boil conditions. All alternative extenders/fillers, except one: mountain pine beetle bark, increased the viscosity of glue mixes. The glue mix formulations may need to be adjusted in commercial production to minimize the impact on the glue application process.
Among these alternative glue extenders/fillers, sander dust is the most promising substitute for corncob since it is a by-product from the production of medium density fiberboard (MDF) production or particleboard, and as such has little value. With little treatment, it can be applied in a phenol-formaldehyde (PF) glue mix to partially or fully substitute for corncob. This will reduce cost and ensure a steady supply of extenders/fillers.
It is recommended that a mill trial be conducted to confirm and quantify the economic benefits.
A literature review was conducted to identify potentially effective nano-based technology for improving wood attributes in order to develop competitive specialty wood products. The review covered both conventional chemical treatment methods and nano-based methods. Traditional chemical treatments have shown to be effective in improving wood hardness, dimensional stability, stiffness, fire resistance, UV resistance, biological resistance and aesthetic appeal. However, nanotechnology offers new opportunities for further improving wood product attributes due to some very unique and desirable properties of chemical materials in the form of particles in nano scale. The advantages of nanotechnology appear to be particularly obvious when applied to create polymer nanocomposites such as wood coatings. Polymer nanocomposites consist of a continuous polymer matrix which contains inorganic particles of a size below approximately 100 nm at least in one dimension. Due to the material nature of solid wood products, creating a continuous polymer matrix with effective inorganic nanoparticles inside wood cells and lumens would be very difficult. The most promising areas of applying nanotechnology to create improvement opportunities would be wood coatings and wood adhesives. It is recommended that research be carried out to explore the potential of nanotechnology in wood coatings and adhesives and their applications in B.C. wood species and wood products.
This report as Part I of the series of the experimental work carried out in the Forintek Eastern Laboratory. Medium density fibreboard (MDF) was produced in the pilot plant with two different treatment of chemical agent at two different dosages. The chemicals were sulphur dioxide (SO2) and sodium bisulphite (NaHSO3). Preliminary test results indicate that:
With the dosage used in the experiment (0.1 – 0.2% of SO2 or 0.16 – 0.8% of NaHSO3 on dry wood fibre), no improvement in dimensional stability (TS and WA) and mechanical properties (IB, MOR and MOE) can be observed.
The results suggest that the dosage used for SO2 or NaHSO3 was higher than required and better result might be achieved with lower dosage as increasing the dosage from lower level to higher level for both SO2 and NaHSO3 reduced the panel strength and dimensional stability.
Based on general observation in the experiment, the runability was good with the introduction of either chemicals. However, SO2 was introduced into the system easier than NaHSO3 without extra process procedures.
The experimental work was verified that it is feasible to inject SO2 into the preheater without the gas leakage or contamination to the atmosphere.
Further experimental work is required to identify the optimal chemical dosage for the treatment and their interaction with different resin systems and wood species.
Experimental work was carried out to investigate the effect of chemical pre-treatment of wood strands for the manufacture of OSB. The chemicals used for the pre-treatment included low molecular weight liquid PF, low molecular weight poly(ethylene glycol) and hydrogen peroxide. These chemicals were tested at two dosage levels. The untreated strands and chemically pre-treated strands were characterized for their pH, acid buffer capacity, base buffer capacity and PF resin gel time. Eighteen OSB panels were made with different chemically pre-treated wood strands and compared with the untreated OSB panels as a control using PF or MDI resins. A total of 27 OSB panels were made in this study.
The results suggested that the moisture resistance and dimensional stability of the OSB made from chemically pre-treated wood strands were generally better than the control panels made from untreated wood strands and 3.5% PF resin (C1). However, no obvious improvement was made when comparing to the control OSB panels using untreated wood strands bonded with 7% PF resin (C2) or 3.5% MDI resin (C3). The three different chemicals studied performed differently. The low molecular weight liquid PF performed better than hydrogen peroxide, followed by the low molecular weight poly(ethylene glycol). It was found that the wood pH and acid and base buffer capacities were changed after the chemical treatments. However, there was no obvious correlation between these changes and the corresponding PF gel times.
Experimental work was carried out to investigate the effect of chemical pre-treatments and refining process conditions on the panel properties of high density fibreboard (HDF) using typical mountain pine beetle (MPB) infested lodgepole pine sawdust and shavings from a Western Canadian MDF mill as raw materials. The characterisation of the raw materials was conducted in terms of pH, acid buffer capacity, UF resin gel time, and peak temperature and reaction heat tested by the differential scanning calorimetry (DSC). Three different combinations of chemical pre-treatment and refining process condition were studied. HDF panels were made from these three differently treated fibres with 20% urea-formaldehyde resin content on oven dry wood.
The results of the experiment indicated that wood shavings and the wood sawdust present different acid buffer capacities. While the sawdust has the lowest acid buffer capacity and close to both the fresh lodgepole pine and 100% beetle-killed wood studied previously, the acid buffer capacity of the shavings was the highest. Both edge thickness swell and thickness swell of the HDF panels reduced with increasing fibre refining temperature. However, internal bond strength, MOR and MOE of the panels were reduced. The chemical pre-treatment of wood furnish using 0.5% hydrogen peroxide did not improve the dimensional stability of the panel.