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
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.
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.
Lignin or lignin residue by-product can be produced from black liquor of pulping process or from cellulosic ethanol process. This project studied these lignin by-products as a substitute for corncob/Superbond fillers in PF glue mixes for plywood production. Two types of lignins were evaluated in the lab tests and one of them was used in the mill trial production. PF glue mixes with up to 50% corncob/Superbond substituted with lignin were produced and evaluated for plywood production. The test glue mixes were comparable to the control in viscosity, stability and bond performance. It is technically viable that lignin or lignin residue by-product be used as a substitute for corncob/Superbond fillers in the plywood industry. Caution must be taken to ensure that all particles of lignin pass a 100-mesh screen and the glue mix passes a 40-mesh screen in order for the glue mix to be smoothly transferred from the storage tank to the glue mix applicator.
LignoForce lignin, a product obtained in a specific stage of kraft lignin production from black liquor of the pulping process, possesses unique characteristics and is cheaper than ordinary kraft lignin. This project studied this particular lignin as a substitute for corncob/Superbond fillers in PF glue mixes for plywood production. The lignin was evaluated in lab tests and in plywood mill production trial. PF glue mixes with 50% corncob/Superbond substituted by the lignin were produced and evaluated for plywood production. The test glue mixes were found to be comparable to the control in viscosity, stability and bond performance. This project demonstrated that LignoForce lignin is a viable substitute for corncob/Superbond fillers in the plywood industry. It should be noted that the procedure to incorporate LignoForce lignin into the glue mix is simple but different from the traditional mixing procedure during the glue mix preparation. The test glue mix with LignoForce lignin has the potential to be applied by different methods, such as glue spreader, curtain coater, and glue spray line.
To develop a method to economically produce MDF and particleboard products with ultra low formaldehyde emissions (<0.05 ppm), different accelerators for PF resins and a formaldehyde scavenger / hardener for UF resins were evaluated by means of gel time tests, lap shear tests and panel tests. The following conclusions and recommendations are made:
1. Particleboard and MDF products with formaldehyde emissions well below 0.05 ppm can be produced with a phenol-formaldehyde adhesive. These products can easily meet the most stringent formaldehyde emission standards for wood composite panel products such as the Japanese F**** standard (or E0). The products also have excellent durability in water, being suitable for both interior and exterior applications. These advantages effectively solve the two difficult problems commonly associated with today’s UF-bonded PB and MDF products: high formaldehyde emission and low water durability. The disadvantages of using PF adhesives are darker color on panel surface and higher water absorption.
2. Phenol-formaldehyde resin is a more efficient wood adhesive than urea-formaldehyde resin. Using PF at slightly more than one half of the UF loading rate, PF-bonded particleboard and MDF showed better mechanical properties than UF-bonded particleboard and MDF, and about the same thickness swell after 24-hour water soak.
3. The cure speed of phenol-formaldehyde resin can be dramatically improved with the use of resorcinol as an accelerator. At 205°C (400°F, normal OSB press temperature) and a resorcinol loading rate of 2% of liquid PF resin weight, a commercial OSB face phenolic resin used for MDF manufacturing showed comparable cure speed to that of an uncatalyzed commercial UF resin of E2 type at 182°C (360°F, normal MDF press temperature in a multi-opening press). At 2% resorcinol loading rate and 205°C, the same PF resin showed slightly slower cure speed to that of the same UF resin catalyzed by 0.5% ammonium chloride at 182°C during particleboard production.
4. The experiments revealed that there is potential to reduce PF resin consumption to one half of the normal UF resin consumption in particleboard and MDF manufacture and still maintain the desirable physical and mechanical properties. The cost of using PF adhesive to produce particleboard and MDF should be substantially lower than previously thought. Given the fact that the current oil price is high and PF resin cost is sensitive to oil price, the economic viability of using PF adhesive for particleboard and MDF production should be evaluated carefully. Nonetheless, the findings from this project have provided the basis for a more optimistic view on the economic viability of PF-bonded MDF and particleboard.
5. Ethylene carbonate, propylene carbonate and triacetin are well known PF accelerators in the literature but it was revealed in this research project that these esters cause substantial loss of bonding strength, particularly in the case of PF resin with higher alkalinity. Therefore, they are not recommended for the manufacture of PF-bonded MDF and particleboard. On the other hand, resorcinol is not only an effective PF accelerator but also preserves most of the bonding strength.
6. Ethylene carbonate, propylene carbonate and triacetin are very effective in reducing PF resin gel times. The gel time reduction is pH-dependent. Higher pH leads to shorter gel time.
7. Combining gel time test with lap shear test is a far more reliable approach to evaluate and predict PF adhesive (and conceivably UF adhesive) cure speed in wood composite panel manufacturing than using gel time test alone.
8. SUH-511M is an effective formaldehyde scavenger and hardener for UF resins but it seemed to produce lower board bending strength and increase thickness swell and water absorption.
9. A mill trial of producing MDF using resorcinol-accelerated phenolic resin as an adhesive is recommended.
10. A mill trial of producing particleboard using resorcinol-accelerated phenolic resin as an adhesive is recommended.
This report examines various aspects of the formaldehyde emission issue facing the wood composite panel industry in order to help Forintek member companies best navigate this extremely important but increasingly complex problem. It is a state-of-the-art review of fundamentals associated with the formaldehyde emission problem, various standards and regulations, and known technologies for the reduction of formaldehyde emissions. It has distilled and concentrated a vast amount of information based on the literature review, international conferences, known industrial practices and experiences of the authors.
Due to its hydrolytic instability, urea-formaldehyde (UF) adhesive is the main source of formaldehyde emissions from UF-bonded particleboard, medium density fiberboard (MDF), high density fiberboard (HDF) and hardwood plywood through out their service life. There are various technologies available to reduce formaldehyde emission. These are:
1. Chemical modifications of UF resin (lower formaldehyde/urea (F/U) molar ratios, improved resin synthesis procedures, condensed with small amounts of melamine, use of formaldehyde scavengers, use of catalysts/hardeners, cross-linked with methylene diphenyl diisocyanate (MDI) or various combinations of these);
2. Panel post-treatments (anhydrous ammonia treatment, panel overlay, coating, etc.);
3. Manipulation of production process conditions;
4. Using alternative adhesives to replace UF resin;
5. Making binderless panel products.
Some of these technologies can meet the challenges of the most stringent regulations, but likely at higher cost or lower productivity. The most promising options are using commercially available alternative wood adhesives (phenol-formaldehyde (PF), MDI, melamine-formaldehyde (MF), polyvinyl acetate (PVA) or soy) to replace UF. Depending on end use and target market, using ultra-low formaldehyde emitting UF or urea-melamine-formaldehyde/melamine-urea-formaldehyde (UMF/MUF) in combination with an effective catalyst/hardener and/or formaldehyde scavenger can also be a practical option.
Soybean resins, as protein-based wood adhesives, have been extensively examined in this study. Hydrolysis and modification of soy flour to produce soybean-based resins were evaluated in terms of desired resin attributes and bonding performance as wood adhesives. End use performance was determined in selected wood composite products. Two methods were applied to modify soy flour for improving the curing speed, bond strength and water resistance. One method was to directly mix a hydrolyzed soy solution with a synthetic resin. Another method was to first hydrolyze soy flour, followed by reacting with other chemicals.
Soybean-based resins produced from low hydrolyzed soy flour modified with melamine resins were successfully applied to plywood production. There is potential for these resins to be used for interior grade plywood and possibly for exterior grade plywood products provided cost effective ways to improve the applicability and stability of the target resins during plywood manufacturing can be found. A pilot plant study would be required to determine the relationship between performance and costs.
Hydrolysis was an effective method under alkaline conditions for reducing the viscosity of soy resins. However, hydrolysis also reduced the bond strength of soy resins. Soybean-based resins produced from highly hydrolyzed soy flour modified with various synthetic resins showed comparable bond strength to the control phenol-formaldehyde (PF) resin in the lap shear test. However, plywood products bonded with these resins showed low percentage wood failure even under dry conditions, and also low water resistance. The particleboard product bonded with one of these resins showed very low formaldehyde emissions, but the bond performance was poor compared to the control urea-formaldehyde (UF) resin. Therefore, soybean-based resins from highly hydrolyzed soy flour are not recommended at this time.
Unhydrolyzed soy flour was combined with a PF resin in the manufacturing of medium density fibreboard (MDF) product with ultra low formaldehyde emissions. The soy flour showed excellent compatibility with the PF resin, indicating that there is potential to partially replace PF resin with soy flour in the production of MDF to lower adhesive cost.
Copolymerized SoyM resins showed high bond strength and high curing speed in the lap shear test. Formic acid was found to be an effective catalyst to accelerate the curing speed for these resins. Quantification of the benefits of using these SoyM resins with a formic acid catalyst to replace urea-formaldehyde adhesives in MDF and particleboard products is recommended.