Effect of Adhesive on the Performance of Laminated Veneer Lumber
摘要
Wood peeled in the form of thin sheets are known as wood veneers which when laminated by a suitable synthetic resin a Laminated veneer lumber (LVL) is obtained which is extensively used in applications where strength of the composite is of prime concern such as in structural members namely beams, windows and door frames etc. Timbers harvested at lesser age contains juvenile wood which when sawn and subsequently seasoned not only results in defects but also in poor yield for a given volume of timber hindering it to be used for structural applications. Laminated veneer lumber addresses these problems by peeling short rotation timbers into veneers, eliminate the inherent defects like knots, pin holes, decay etc. and then laminate into lumber suitable for high end applications such as furniture frame work, window and door frame and structural members such as beams and columns. Existing Indian standard IS:14616 mandates the usage of boiling water proof (BWP) grade resin for laminating veneers into lumber. For interior applications BWP grade resin bonded LVL not only becomes uneconomical but also results in injudicious usage of resources. BWP grade resin requires higher process parameters such as high pressing temperature and specific pressure (hot press pressure) for lamination which again adds cost to the product. Hence it was intended to study the feasibility of laminating veneers from short rotation plantation timber species Melia dubia using an interior grade resin such as urea formaldehyde (UMF). From the study it is revealed that though UMF is an interior grade resin LVL bonded with the same satisfies most of the requirements as per IS:14616. It is also found from the study that though UMF resin bonded LVL performs satisfactorily for resistance to water (MR grade), preservative treatment of veneers as per IS:401 is affecting the bond between the veneers. Veneers without preservative treatment is found to have superior bond with the same resin than preservative treated veneers. Since for interior applications, LVLs would be given a coat of paint or pasted with a laminate preservative treatment may be treated as optional which supports judicious usage of raw material and also helps in reducing the product cost.