Physical and mechanical properties of hybrid poplar laminated veneer lumber produced with polyol added pMDI adhesive

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Abstract

Improving the performance of laminated veneer lumber can be a key to expanding the value-added use of renewable, fast-growing, low-density poplar raw material. This study evaluated the impact of a commercial neat pMDI (polymeric methylene diphenyl diisocyanate) and a pMDI formulation containing 5% polyol (pMDI +5%P) on the physical, mechanical, and bonding properties of laminated veneer lumber (LVL) prepared from poplar (Populus × euramericana I-214) veneers. Physical properties including the moisture content (9.03% and 8.75%), air-dry density (0.54 g/cm³ and 0.56 g/cm³), thickness (11.1% and 11.3%), and volumetric swelling (after 72 h) (19.9% and 18.9%), were found to be similar to 15-layered LVLs produced from pMDI and pMDI +5%P, respectively. However, mechanical test results showed that bonding quality (4.44 to 5.92 N/mm²) and correspondingly modulus of elasticity (MOE, 7880 to 9410 N/mm²), bending strength (MOR, 73.4 to 90.5 N/mm²), and screw withdrawal capacity (22.6 to 30.6 N/mm²) significantly (at 95% confidence level) increased on the LVLs produced from pMDI +5%P. Additionally, hardness on the surface (3460 to 4000 N), longitudinal (2950 to 3600 N), and parallel hardness (4570 to 5600 N) values of LVLs were increased. However, impact strength decreased from 4.50 to 3.80 kJ/m² with polyol addition. It can be said that this situation stems from an increase in adhesion brittleness upon the addition of polyol.

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