MEMBER Wood Products;

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MEMBER Forest Operations; Pulp, Paper and Bioproducts;

N/A $ (CAD)


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The objective of this project was to evaluate the potential for waterglass to be used as an additive during OSB manufacture to enhance the fire resistance of the material commonly used as sheathing and webstock for wood I-joists. Although not yet developed in North America, commercial OSB products that have had the flakes treated with flame retardants during manufacture are available in Europe. Waterglass is simple, inexpensive and exhibits some adhesive capacity for wood and previous attempts have been made to apply it as a surface and impregnation treatment for solid and composite wood to reduce its flammability. The water soluble material was sprayed and blended with the flakes, followed by drying and blending with either PF or pMDI resins before mat forming and hot pressing. Work took place in two phases: Phase 1 low addition levels up to 10%, and Phase 2: High addition levels 15 and 20% of two grades of waterglass. Boards were made to the same target density of 38.5 pcf and so there was some weight substitution of wood for waterglass at the higher levels of addition. Boards were tested for standard physical and mechanical properties (density, IB, flexure, and 24 h water absorption/thickness swell, and combustion behavior using a small scale cone calorimeter test). Even high addition levels of waterglass did not affect the flexural properties of OSB, and significantly enhanced the internal bond strength of boards made using PF resin. The biggest drawback to its potential use as an additive is the high susceptibility to moisture absorption and thickness swell when exposed to wetting; some boards made with high waterglass addition were up to 85% in thickness swell. Contrary to expectations waterglass addition did not extend the time to ignition, and in some cases ignition occurred earlier. High addition levels (20%) of high-solids content waterglass produced a 30% decrease in mean heat release rate, 17% reduction in mass loss rate and 13% reduction in CO2 yield during combustion tests, likely associated with the decreased content of flammable wood substrate in the boards. Waterglass addition does not appear to have the same effect on flame retardancy of OSB as commercial fire-retardant formulations developed for treating wood. Previous research on treating wood flakes with commercial fire retardants found the method to be effective: a 10-fold increase in time to ignition and a 73% decrease in peak heat release rate HRRpeak during combustion to 66kW/m2. None of the boards produced using waterglass had HRRpeak less than 200 kw/m2. Based on the findings this avenue of investigation has been discontinued.


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  • Wood products member
  • Pulp, paper and bioproducts member
  • Forest operations member