This report compares international standards for particleboard, waferboard, OSB, MDF, hardboard as well as cement bonded wood composite panels. Property requirements are discussed and comparisons are made between countries. Formaldehyde emission regulations were surveyed in eighteen countries.
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.
The impact of formaldehyde on human health causes great concerns nowadays. As it was one of the cheapest cross linking agents and a by-product of bio-process, finding an adhesive or resin product or material without formaldehyde and its derivatives is very challenging. Thus, one has to use a systematic method to work out the issue of reducing formaldehyde emission. However, as more people understand the challenge of reducing formaldehyde emission and endorsing the cost increase in developing new products with no or low formaldehyde emission, it provides a great opportunity to upgrade product line and develop new products.
In this project, bio-polymer, epoxy, polyvinyl acetate (PVA), urea formaldehyde (UF), phenol formaldehyde (PF), melamine urea formaldehyde (MUF), diphenylmethane diisocyanate (pMDI) resins and a new resin formulation developed at Mississippi State University (MSU) together with bio-based resins derived from bark, soy bean protein, lignin and wood have been tested. Epoxy, MSU, MUF, PF, pMDI, PVA, UF resins and soy bean protein and bark based PF resins were used for panel performance evaluation.
PVA and epoxy resins did not show any advantages in panel performance. MSU resin has potential in reducing panel free formaldehyde emission. PF resin will help improve panel modulus of elasticity (MOE) and modulus of rupture (MOR), thickness swelling (TS), water absorption (WA) and linear expansion (LE). It was found that MSU, MUF, PF and MDI resins offer great possibilities for medium density fiberboard (MDF) and particleboard applications.
A commercially available MUF resin was found especially suitable for particleboard application, in terms of low free formaldehyde emission and panel strength.
Mixing MDI with UF resin in particleboard application has potentially in improving panel internal bond strength (IB), MOE, and MOR performances and reducing panel TS and LE. It also has the potential to improve panel productivity.
A new three-layer with high surface or face moisture content (MC) concept was developed in this project. This concept was evaluated using different types of panel, especially high density fiberboard (HDF), MDF, and particleboard. The following variables were evaluated: UF face resin contents, panel face layer MC contents, MDI resin contents in panel core layer, hot press times, hot press temperatures, panel face and core ratio and types of face resins. At 11.1 mm (7/16 inch) panel thickness, the concept can mainly be applied successfully in making particleboard panels at a face:core ratio of 40:60, at 6% resin in face and 9% resin in core layers, with UF, PF, MDI, a combination of UF and MDI and a combination of UF, MDI and PF resins, with face MC up to 20% and core MC 6%, hot pressed at 180°C and 130 seconds. The particleboard panels made had improved panel performance, especially in terms of surface quality, when compared with panels made using conventional processing. To better use the concept, resins with hydrolysis resistance may be required.
Further, the three-layer with high face MC process concept was used to make HDF without resin in face layers. The same concept has also been applied to MDF panel manufacturing. It was found that the concept can be more easily adopted with MDI resin in MDF operation. With high MC in the face and with a small amount of resin in the core layer, one should be able to make HDF to meet the performance requirement. Generally, the experiment has shown that the new process concept has big potential in reducing panel operation cost with improved performance.
It was recommended that FPInnovations should do further work with the panel industry to allow the research results to be transferred to industry as soon as possible. Any resin with a renewable feature has great potential. Bark and wood should be considered first throughout the process to convert soy bean protein, wood and bark into resin or parts of resin.