Manufacturing of LVL using cost-effective resin impregnation and layup technologies

Abstract

The purpose of this study was to develop a cost-effective method to manufacture high-performance laminated veneer lumber (LVL) from mountain pine beetle (MPB)-affected veneers through partial resin impregnation and optimum board layup. Dry MPB-affected veneer sheets were segregated into two stress grades based on dynamic modulus of elasticity (MOE). A new phenol formaldehyde resin with a 30% solids content was formulated for resin impregnation. To reduce resin consumption, only veneer sheets used as outer layers were dipped in the resin for 5 min and then dried to manufacture 13-ply LVL. The bending properties, shear strength and dimensional stability of these LVL billets were examined and compared to those from the controls made from entirely untreated veneers. The results demonstrated that high-grade (E1) MPB-affected veneers had lower resin solids uptake than low-grade (E2) counterparts based on a 5 min dipping. Compared with the controls, the LVL billets made from resin-impregnated veneers for outer layers yielded increased surface hardness, significantly improved dimensional stability, shear strength and modulus of rupture on both edgewise and flatwise as well as better appearance with no cosmetic concerns. However, the improvement in LVL bending MOE was dependent on initial veneer stress grade. For high-grade (or density) E1 veneers, the use of impregnated veneers resulted in insignificant improvement in bending MOE. The optimum product layup was to place one ply of impregnated E1 grade veneer each for product face and back. By contrast, for low-grade (or density) E2 veneers, the use of impregnated veneers yielded a significantly higher flatwise bending MOE compared to the controls. The recommended product layup was the placement of two plies of impregnated E2 grade veneer sheets each for product face and back.