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.
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.
It is a normal practice in oriented strandboard (OSB) production to store logs outdoors for a period of time prior to the flaking process. The duration of yard storage depends on harvest season and sources of log supply. Outdoor log storage without protection could change the mechanical and chemical properties of wood due to attack by various fungi. To understand how outdoor log storage affects the wood and subsequently the strandboard quality, two piles of aspen logs were set up outside and stored for a period of four months (July 9 to November 14, 2001). One of the piles was treated with a biological solution to prevent fungal growth. The other one was stored without such treatment. Both piles contained non-debarked and partially debarked logs. Evaluation of sap stain development indicated that all logs had been colonized by staining fungi with an average stain coverage of 9.37 to 57.18% and maximum stain penetration of 3.58 to 7.27 cm over the log cross-section. The variation of fungal colonization depended on log treatment and bark condition. The most effective way to prevent stain growth was with the combination of biological treatment and partial debarking. This was followed in effectiveness by biological treatment and no debarking, no treatment and partial debarking, and, finally, no treatment and no debarking. A series of strandboard was prepared from fresh and aged aspen logs. It was observed that all boards made from stored logs were statistically comparable to or superior to the control boards made from fresh aspen logs. The boards made from treated/partially debarked and untreated/non-debarked logs were statistically comparable to each other except for the higher wet MOR for the former. In addition, both board types were stronger than other boards in terms of IB and water resistance. Compared to control boards, the stronger boards in terms of water resistance were also made from biologically treated/non-debarked and untreated/partially debarked logs. Some individual stained strands were observed on the finished board surface, which could affect board appearance if the wood had been highly attacked by fungi. Less staining was found in the boards prepared from biologically treated and partially debarked logs, as compared to other stored logs.
Reinforced particleboards were made at several panel densities and with several resin treatments of the fibreglass reinforcing scrims. It was the inclusion of fibreglass scrims that dramatically increased the strength and stiffness of particleboards especially when the overall panel density was above 0.7 gm/cc. Of the various locations tested, reinforcement at the extreme surfaces was found to be the best. Treatment of the fibreglass with phenolic resins produced some improvement in wood-fibreglass bonding, however the addition of a coupling agent significantly improved the fibreglass fixation.