The work described in this report involved examination of the development of IB strength in OSB panels as a function of pressing parameters and mat moisture content. Response surface methodology (RSM) was used in the design the experimental work employing a Box-Behnken design with four (4) variables (platen temperature, pressing time, moisture content (MC) of the face layers of the mat and face/core ratio).
Results showed that the relationships between the study parameters and IB strength fit very well the form of quadratic polynomials. Within the limits studied, it was found that increasing the pressing time and/or temperature could significantly improve the IB strength in OSB panels. Also, the study showed that bonding strength is improved by reducing mat moisture content.
It recommended that the study proceed as planned, using a thermal analysis technique (DSC) to compare the chemical reactions and curing behaviour of some commercial PF resins. Also, lap-shear tests, will be employed to evaluate strength development of the adhesives as function of time, temperature and furnish moisture content. It also recommended that a bench-making will be proceeded at laboratory and mill scale to verify the model.
Strand drying is a necessary step in OSB production, as a means to reduce furnish moisture content to an acceptable level, which in part depends on the resin used. It has been mentioned that beside wood degradation which causes fines generation and fibre surface oxidation, other problems such as VOC emissions, excess energy consumption and variability in moisture content of strands may occur as a result of strand drying. This work involved the characterisation of strands from six commercial OSB mills. The methodology adopted in this study was to characterize strands collected before and after drying, as well as information on operation conditions in order to relate the effects of drying on the overall strand degradation. Strand quality was evaluated before and after drying in terms of the following characteristics:
Strand size distribution;
Strand surface oxidation;
Strand tensile strength.
Results on classification of wet strands showed very large variability in width distribution ranging from very narrow to very wide. Results on size distribution of dry strands revealed that strand degradation characteristics appear dependent on individual mill strategy that can vary considerably from mill to mill. The study showed that conveyer dryers caused the least strand size reduction of the three dryer types included in the study. Triple and single pass dryers caused similar amounts of strand size reduction. Test results also showed that drying conditions e.g. drying temperature, drying time and final moisture content played a key role in strand size degradation. Overall strand size classification results showed no clear pattern suggesting that the drying process is not the only factor responsible for post-strander fines generation. Other factors such as strand damage incurred during strand manufacturing and mechanical damage during strand handling may also play substantial roles in the reduction of strand size observed in this study.
The drying operation had little effect on tensile strength of the strands. However, measurement of strand surface contact angles revealed that surface oxidation is taking place during strand drying. For all strand samples, the contact angles measured on strands sampled before drying were lower than the contact angles measured after drying. The study clearly indicated that thermal degradation is not related to dryer type but to other drying conditions, namely the combination of temperature and residence time. Thus it is possible that strands dried for a relatively long time at lower temperatures can incur more surface oxidation that strands dried at higher temperatures, but for a much shorter time.
Composite panels were manufactured from waste wood and recycled, mixed plastics. The effects of key processing parameters including wood fibre content on the mechanical and physical properties of panels produced were evaluated. Chemical treatments of the recycled wood fibre were conducted to improve the dispersion and adhesion of fibres within the matrix. The morphology of the plastic/wood interface was examined critically using a scanning electron microscope (SEM). Experimental work on the hot processing of panels showed that a commercial high speed mixer, (K-mixer) failed to produce a uniform dispersion of the composite materials. The wet process studied presented a good option fro making composites from recycled wood and plastics. A significant improvement in bending strength and stiffness was observed for panels containing up to 60% wood fibre. However, because of the large amount of water required for the wet process, this technique was considered a less desirable approach. Dry processing appears to be the most environmentally sound method and produced panels with mechanical properties similar to those produced by the wet process. The SEM study on fracture interfaces elucidated the relationships between wood fibre/plastic matrix and mechanical properties of panels. Chemical treatments of recycled wood fibres were found to relieve the compatibility problem between wood and plastic, improving the adhesion between these components. Experimental work has also revealed that a commercial microwave generator can be employed to preheat mats prior to hot pressing.
The work described in this report involved examination of the development of IB strength in OSB panels as a function of pressing parameters and mat moisture content. Response surface methodology (RSM) was used in the design the experimental work employing a Box-Behnken design with four (4) variables (platen temperature, pressing time, moisture content (MC) of the face layers of the mat and face/core ratio). Results showed that the relationship between the study parameters and IB strength fits very well the form of quadratic polynomials. Within the limits studied, it was found that increasing the pressing time and/or temperature could significantly improve the IB strength in OSB panels. Also, the study showed that bonding strength is improved by reducing mat moisture content.
The work is also involved with the effect of resin kinetic on the bonding strength development. Several commercial phenol formaldehyde core resin were selected and characterised with a thermal analysis technique (DSC) to compare the chemical reactions and curing behaviour. The automated bonding evaluation apparatus or slap-shear test was employed to evaluate strength development of the selected adhesives as function of time, temperature and furnish moisture content. Test results showed that within the limits studied, increasing the pressing time and/or temperature could significantly improve the bonding shear. Also, the study showed that furnish moisture content and energy activity of the resin have limited effect on the bonding strength.
The study on the development IB strength as a function of resin energy activity, pressing temperature, pressing time and mat moisture content at the face layers, showed a significant effect of pressing time and temperature on the IB strength of the panel. Also resin with high activity energy was found to provide panel with low IB.