Master of Science (MS)
Renewable Natural Resources
Random strandboards from mixed southern wood species were manufactured using calcium borate (CB) and zinc borate (ZB) as chemical additives and polymeric methylene diphenylmethane disocyanate (pMDI) as resin. There were four target levels of borate loading and two levels of resin content. Panel properties, including modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB) strength, linear expansion (LE), thickness swelling (TS), leachability, and swelling and strength retention properties under cyclic relative humidity, were measured. The influence of borate content, borate type, and resin content on various properties was analyzed. It was found that the addition of borate negatively impacted the mechanical and physical properties of the boards. The influence of ZB and CB on both mechanical and physical properties was similar. The increase of resin content improved the properties significantly, especially TS. A certain portion of borate leached out from test samples under the water-soaking conditions. There was a higher initial leaching rate and the leaching rate decreased with the lapse of leaching time. Panels with higher initial borate loading level had higher leaching rate for all panel types. The leaching rates of ZB and CB treated samples were similar. The increase of resin content helped reduce TS and boron leaching. Compared with PF-bonded boards, leaching rate was significantly reduced for the pMDI-bonded panels. Under cyclic humidity exposure condition, the addition of borate negatively influenced the maximum TS, residual TS, and mechanical properties. The effects of ZB and CB on the maximum TS, residual TS, and mechanical properties were similar. The increase of resin content significantly reduced residual TS, but had no influence on maximum TS and mechanical properties. The addition of borate did not have significant influence on the strength retention of the boards under long term cyclic humidity exposure condition.
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Zhou, Yiqiang, "Properties of borate-treated strandboard bonded with pMDI resin" (2004). LSU Master's Theses. 2566.