Enhancement Of Pre-stretching Bamboo Slivers Or Spiral Bamboo Bundle On Poplar Parallel Strand Lumber

The prestress technology was used in this paper, aiming to improve mechanical propertiesof PSL made from waste veneer residues. The creep characteristics of bamboo sliver underconstant tensile stress was studied, as well as tensile properties of spiral bamboo bundle. Onthis basis, pre-stretching bamboo slivers or spiral bamboo bundle reinforced poplar PSL wereproduced according to the formation mechanism of prestress in the pre-stretching bamboo sliveror spiral bamboo bundle, the results showed that:At constant temperature and moisture content conditions, creep and creep recovery ofbamboo sliver measured by digital speckle correlation method was closely related to the leveland holding time of constant stress in the creep process. A large viscoelastic deformation can beget under stress of15%of tensile strength for4h, and this viscoelastic deformation recoverywas quite small in a short time after stress releasing.The tensile strength of spiral bamboo bundle, which was prepared based on the spiralmicrostructure of bamboo fiber, had significant improvement compared to non-twisted bamboobundle. Real elastic deformation of bamboo bundle can be get using cyclic loading andunloading at a small loading range, the elastic modulus of single-helix bamboo bundle wasbetter than that of double-helix types. The fracture mainly happened in the central of outerfibers along the spiral bamboo bundle, while fiber slipped and being pulled out fromnon-twisted bamboo bundle.The residual viscoelastic deformation induced by bamboo slivers with pre-stretchingtreatment can form compressive stresses in PSL, which will affect mechanical properties ofPSL. Due to the compressive stresses, the modulus of rupture (MOR), modulus of elasticity(MOE) and impact toughness of pre-stretching bamboo slivers reinforced PSL weresignificantly improved compared to unstressed bamboo slivers reinforced PSL and poplar PSL.The prestress had inhibition effects on the loss of horizontal shear strength of unstressedbamboo slivers reinforced PSL while it had no significant effect on the compressive strengthparallel to grain of poplar PSL.Prestress induced by single-helix bamboo bundle can significantly improved MOR, MOEand impact toughness of bamboo-wood composite PSL. The prestress also has some inhibitionon the loss of horizontal shear strength due to bamboo bundle. Single-helix bamboo bundlereinforced PSL has better comprehensive mechanical properties compared to other kinds ofbamboo bundle reinforced PSL or poplar PSL.