A research project was carried out in collaboration with researchers from both University of British Columbia and University of Toronto to develop and test a range of hollow core composite sandwich panels based on lignocellulosic materials that can extend the current applications of wood composite products such as high density particleboard and fibreboard (hardboard and MDF). With proper engineering design and unique light weight structural features, wood fibre resources will be more effectively used and the performance of each component can be maximized in these types of novel composite panels. The outcome of this project is the development of Canadian-made light weight panels containing various low density cores, including honeycomb, low density wood wool composites and cup-shaped thin fibreboard, and high density surface panels, including plywood, hardboard and high density fibreboard (HDF) for the applications in ready to assemble (RTA) modular furniture, home and commercial cabinetry and door panels.
The work completed at Forintek included:
Development of low density wood wool panels (LCD) as the core material for the sandwich panels.
Development of cup-shaped high density fibreboard (CHDF) as the core material
Evaluation of edgewise and flat compression strength and creep behaviour of honeycomb sandwich panels fabricated by UBC.
Development of book shelf panels using four different core materials.
Performance evaluation of the book shelves developed.
The results of the experimental work suggest that:
Low density composite core materials can be made by the technology developed at Forintek laboratory using low density poplar wood wool and high viscosity phenol and formaldehyde resin with steam injection hot pressing technology. However, the strength of the panels was relatively low comparing to conventional low density particleboard, OSB or fibreboard.
The experimental work carried out on the cup-shaped high density fibreboard (CHDF) show the potential for developing various light weight core materials using current MDF process technology. The internal bond strength (IB) and water absorption (WA) of the cup-shaped panels were strongly correlated with panel density. IB increased and WA reduced when increasing the panel density. The flexibility of the technology could optimize the properties and performance of CHDF through manipulating the fibre refining process, profile design, resin system and hot pressing strategy. It shows that CHDF is a good alternative material to Kraft paper honeycombs for the manufacture of sandwich panels for higher strength and performance applications.
Test results from sandwich panels made of cup-shaped fibreboard core and HDF surface show that the nominal density of the cup-shaped core was one of the most important process parameters to adjust for the improvement of the sandwich panel properties. The flat compressive modulus, flat tensile strength and short-beam strength increased when increasing the nominal density of the core panels. Furthermore, the overall density of the sandwich panels were only fractionally increased by increasing the nominal density of the core panels due to the cup-shaped shape of the core panels. It suggests that higher nominal core density should be used when higher mechanical strength of the panels is required.
To a lesser extent, fibre type in the core panels also affects the sandwich panel properties. Longer wood fibres are recommended for use in the manufacture of the core panels.
The results of the experiment also show that increasing the thickness of the surface HDF panels increased the bending strength of the sandwich panels substantially. However, the overall density also increased.
Comparing shear properties of the four different sandwich panels developed by Forintek, we can identify that the ultimate shear strengths were different for different core materials. The sandwich panel made from polycarbonate core had the highest shear strength (0.744 MPa) followed by the panel made with CHDF (0.497 MPa). The sandwich panel made from low density wood wool core had much lower shear strength (0.012 MPa) which is lower than the paper honeycomb sandwich panels previously made by UBC with the same surface and core thickness (0.024 MPa).
The sandwich panels made with high density cup-shaped fibreboard had significantly higher core shear modulus (92.0 MPa) than any other sandwich panel studied in this project.
This report summarizes the experimental works that was carried out for a one-year research project developed as the continuation of previous research projects on the subject of light weight hollow core sandwich panels. The experiment focused on the investigation of creep behavior of light weight hollow core panel under long term static loading and high humidity conditions and its correlation with short term properties. Five types of surface panels were used, namely, 3.2 mm thick high density fibreboard with birch veneer on both sides, two thicknesses of M2 grade particleboard (6.3 mm and 9.5 mm) and two thicknesses of medium density fibreboard (6.3 mm and 9.5 mm). All panels were fabricated to the same final sandwich thickness of 45 mm using cell size of 12.7 mm Kraft paper honeycomb.
The results of the experiment show that the strongest facing material used to make the sandwich panels was the 3.2 mm hardboard with wood veneer lamination on both sides running along the long axis of the panel and test specimen, followed by the 6.3 mm MDF and the 9.5 mm MDF. The experiment demonstrated that exposing the panels to high humidity could cause strength loss of up to half of the original strength. However, the result of the experiment also suggested that it would be difficult to accurately predict the long term creep behavior of the sandwich panels using their corresponding short term flexural properties as the correlation between creep deformation and flexural properties was rather weak under the testing procedure and condition used.
The goal of this project, carried out at Forintek’s Quebec MDF Pilot Plant, was to develop an enhanced fibreboard product for exterior applications. The experimental work consisted of three different phases. Phase I consisted of selecting a suitable resin system from among five types of resin exposed to the same process conditions. Panels produced with the MUPF resin (resin R03) had the best overall moisture resistance and dimensional stability properties. Phase II defined optimal refining and hot pressing process conditions. Based on the experiment results and statistical analysis, a numerical optimization was carried out using Design Expert® computer software. Phase III examined the chemical modification of wood fibre by acetylation. The following conclusions can be reached from this research project:
Among the five different resin systems, resin R03 (an MUPF resin) produced the best overall panel properties for moisture resistance and dimensional stability and was most cost effective.
For resins R03 and R04 (MUF), post-press heat treatment showed marginal improvements in panel bonding strength, moisture resistance, and dimensional stability.
Panels made with MDI resin were comparable to R03 panels in terms of dry IB, but resulted in lower water resistance (lower one-hour boiling IB).
With resin R03, panel series S7 had the best overall panel properties among the 8 different types of panels made under the different process conditions.
Resin content of R03 in the panel had the greatest effect on IB, water resistance, and dimensional stability.
Higher steam temperature in the preheater improved panel moisture resistance and dimensional stability.
All properties tested in S7 produced results higher than those typical of wood plastic.
The cost to produce S7 is about 40% of the cost of wood plastic panels for similar applications.
Acetylated wood fibre demonstrated a great improvement in water resistance and dimensional stability. However, further research is required in order to find better adhesives and application methods to optimize MDF panel processes with acetylated fibre.
Wood fibre-based panel can replace wood plastic for exterior applications at a significant cost advantage.
Further work is required to optimize the process and to fully evaluate panel properties under long term outdoor conditions.
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.
Experimental work was carried out to investigate the effect of chemical pre-treatment of wood strands for the manufacture of OSB. The chemicals used for the pre-treatment included low molecular weight liquid PF, low molecular weight poly(ethylene glycol) and hydrogen peroxide. These chemicals were tested at two dosage levels. The untreated strands and chemically pre-treated strands were characterized for their pH, acid buffer capacity, base buffer capacity and PF resin gel time. Eighteen OSB panels were made with different chemically pre-treated wood strands and compared with the untreated OSB panels as a control using PF or MDI resins. A total of 27 OSB panels were made in this study.
The results suggested that the moisture resistance and dimensional stability of the OSB made from chemically pre-treated wood strands were generally better than the control panels made from untreated wood strands and 3.5% PF resin (C1). However, no obvious improvement was made when comparing to the control OSB panels using untreated wood strands bonded with 7% PF resin (C2) or 3.5% MDI resin (C3). The three different chemicals studied performed differently. The low molecular weight liquid PF performed better than hydrogen peroxide, followed by the low molecular weight poly(ethylene glycol). It was found that the wood pH and acid and base buffer capacities were changed after the chemical treatments. However, there was no obvious correlation between these changes and the corresponding PF gel times.
Experimental work was carried out to investigate the effect of chemical pre-treatments and refining process conditions on the panel properties of high density fibreboard (HDF) using typical mountain pine beetle (MPB) infested lodgepole pine sawdust and shavings from a Western Canadian MDF mill as raw materials. The characterisation of the raw materials was conducted in terms of pH, acid buffer capacity, UF resin gel time, and peak temperature and reaction heat tested by the differential scanning calorimetry (DSC). Three different combinations of chemical pre-treatment and refining process condition were studied. HDF panels were made from these three differently treated fibres with 20% urea-formaldehyde resin content on oven dry wood.
The results of the experiment indicated that wood shavings and the wood sawdust present different acid buffer capacities. While the sawdust has the lowest acid buffer capacity and close to both the fresh lodgepole pine and 100% beetle-killed wood studied previously, the acid buffer capacity of the shavings was the highest. Both edge thickness swell and thickness swell of the HDF panels reduced with increasing fibre refining temperature. However, internal bond strength, MOR and MOE of the panels were reduced. The chemical pre-treatment of wood furnish using 0.5% hydrogen peroxide did not improve the dimensional stability of the panel.