Oriented strandboard (OSB) manufacturing technology has been advancing steadily during the past few years. Today, the industry can produce higher quality OSB at lower costs than ever before in the product's history. Research results have shown that drying costs can be reduced and strand quality can be improved through proper wood yard management, and that the production efficiency can be improved through various ways of optimizing the pressing and processing operations. OSB quality has been improved and board density has been reduced by using long and thin strands in panel face layers and relatively short and thick strands in the panel core. The press times have been reduced by using higher press temperatures and higher mat face-layer moisture contents. The degree of strand alignment has been improved by controlling the falling distance from the alignment heads to the top of mat being formed. Strands alignment has been further enhanced by arranging the alignment disc gaps in such a way so that narrower strands can be aligned through narrower gaps and directed towards core while wider strands can be aligned through wider gaps and directed towards the panel surfaces. Based on these technical advancements, OSB can be produced faster and at a lower density without sacrificing quality. Consequently, the OSB industry is in the position to improve panel quality without resorting to costly options such as increasing resin content and press time.
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.
Development of two-stage thermo-reforming technology for the manufacturing of cup-shape fibreboard. Part I. Investigation of effects of different resin systems and secondary hot pressing on panel properties
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.
Five fungal species were used to modify and activate natural binding agents from wood fibres for manufacturing MDF panels. Two different methods of the bio-treatment were carried out using these five different fungal species. In the first method, the fungi were inoculated to black spruce (Picea mariana) sawdust, incubated for 20 days at 25ºC, and then refined into wood fibres, with the UF resin loadings of 0% and 8%, respectively. The second method was carried out using normal fibres refined from fresh black spruce sawdust. The fibres were blended with the fungal filtrates in the rotary blender and incubated for 12 hours. MDF panels were made from these different fibres. The mechanical and physical properties were evaluated and compared with the normal MDF panels made of UF resin. Preliminary test results indicate that:
To some extent, the experimental work showed that the self-bonding ability existed after the bio-treatment of wood fibres using the fungal species studied in the project;
All the fungal treated fibres showed the improved bond quality in MDF. The fibres treated with Type-4 fungus yielded the highest bonding strength in the panels with the first treatment method while that with Type-3 had the best result using the second method;
The internal bond strength of all trialed panels without urea-formaldehyde (UF) resin was lower than that of the normal MDF with 8% or 12% UF resin and below the requirement of ANSI standard;
The results suggest that the fungal species studied behave different and no obvious correlation between IB and thickness swell or water absorption can be established;
No obvious consistent trend in MOR and MOE of the panels made with five bio-treatments between two different methods was observed;
Similar MOE and MOR were obtained in the second method among different treatments except T1. The MOE and MOR of T1 panels were lower than those of the rest panels and all of them were significantly lower than those of the control MDF;
This preliminary experiment showed that it is possible to produce MDF using bio-treated fibres with reduced UF resin content in the fibres and it was feasible to use crude extracts of fungi to replace high pure laccase. However, the experimental work was preliminary and further work is required to identify more suitable fungal species and better treatment and process conditions to substantially reduce the time of incubation and process cost to be compatible with the current resin systems used in the manufacture of MDF.