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.