Tensile and thickness swelling properties of strands from Southern hardwoods and Southern pine: Effect of hot-pressing and resin application

Tensile and the moisture-induced thickness swelling properties of wood strands are among the most fundamental parameters in modeling and predicting engineering constants of strand-based composites such as oriented strandboard (OSB). The effects of hot-pressing and resin-curing on individual strand properties were investigated in this study. Strands from four Louisiana-grown species—willow (Salix spp.), yellow-poplar (Liriodendron tulipifera L), red oak (Quercus spp.) and southern yellow pine (Pinus taeda L.)—were tested. It was found that the properties of strands were different from the various wood species and that hot pressing and resin-curing significantly modified the strand properties. This indicated that an adjustment of strand mechanical and swelling properties from the solid wood values is necessary for better prediction of engineering constants of strand composites. Among the four species tested, yellow-poplar strands demonstrated the best initial and postprocessing tensile and thickness swelling properties. The willow strands were initially inferior but showed significant improvements in their properties after hot pressing and resin-curing. This indicated that willow, a low-density and low-strength species, could be used as a good supple­ ment material for OSB furnish. Strands are the basic elements for composing strandbased composites such as oriented strandboard (OSB). Their mechanical and dimensional properties and even the storage time have significant influence on the overall composite per­ formance (Carll 1998). For simplicity, several studies as­ sumed that the properties of strands derived from solid wood carried over to the panel (Suchsland 1972, Suchsland et al. 1995, Xu and Suchsland 1997). Nevertheless, this might not be an accurate assumption for estimating engineering con­ stants of strand composites. Tensile modulus and strength of sweet-gum strands, for example, were much lower than these of solid wood of the same species (Price 1975); similar obser­ vations were made for Douglas-fir strands (Geimer et al. 1985, 1997). Furthermore, during the OSB manufacturing processes (flaking, drying, blending, mat forming, and hotpressing), strands inevitably suffer from moderate to severe mechanical modifications that could alter the strand perfor­ mance significantly. Thus, understanding strand behavior during OSB manufacturing processes is one of the most im­ portant steps for predicting engineering constants of OSB panels. However, it is almost impossible to quantify the extent of physical damage imposed on strands during the entire manufacturing process (Geimer et al. 1985). Stepwise invesThe authors are, respectively, Materials Research Engineer, USDA Forest Serv., Forest Prod. Lab., Madison, Wisconsin ([email protected]); Professor, School of Renewable Natural Re­ sources, Louisiana State Univ. Agri. Center, Baton Rouge, Louisiana ([email protected]); Associate Professor, College of Material Sci. and Engineering, Northeast Forestry Univ., Harbin, China ([email protected]); and Former Research Associate, School of Renewable Natural Resources, Louisiana State Univ. Agri. Cen­ ter, Baton Rouge, Louisiana ([email protected]). This study was sup­ ported in part by the USDA National Research Initiative Competitive Grant Program (99-35103-8298 and 2003-02341). The financial contribution to the project is gratefully acknowledged. This paper was received for publication in July 2005. Article No. 10089. ✳Forest Products Society Member. ©Forest Products Society 2007. Forest Prod. J. 57(5):36-40.