Influência da qualidade das lâminas no desempenho físico-mecânico de painéis compensados de Hevea brasiliensis

Abstract

The cultivation of rubber tree has been settled in as a profitable and sustainable activity, with a significant growth in planted areas in Brazil. Established with the main objective of production of latex, rubber tree plantations have, at the end of this cycle, good prospects as suppliers of raw material for the segment of solid wood products. Previous studies have shown the technical viability for log lamination (hot and cold processes) of Hevea brasiliensis, for plywood production, as an option of higher added value product. This study evaluated physical and mechanical performance of plywood of Hevea brasiliensis (clone RRIM 600) made with graded veneers (stress wave method) in stiffness classes (low, medium and high dynamic modulus of elasticity). Mechanical evaluations were conducted on plywood made with nine 2.3mm thick veneers, produced in the Indústria de Compensados Caribea Ltda, in São Manuel, São Paulo - Brazil. Plywood were made using the same equipment and general variables of the manufacturing process adopted by this industry, considering five arrangements: T1 – homogeneous low (plywood produced with only low dynamic modulus of elasticity veneers); T2 – combined low (plywood produced with high dynamic modulus of elasticity veneers in the face and back and low dynamic modulus of elasticity veneers in the inner); T3 – alternate (plywood produced with alternated quality veneers - high and low modulus of elasticity); T4 – homogeneous medium (plywood produced with only medium dynamic modulus of elasticity veneers); T5 – combined medium (plywood produced with high dynamic modulus of elasticity veneers in the face and back and medium dynamic modulus of elasticity veneers in the inner). Physical and mechanical performance of plywood was evaluated by static bending, bond strength in shear (by tension load), moisture content, water absorption, thickness swelling and density tests, performed using the ABNT – Associação Brasileira de Normas Técnicas – standards for plywood. Considering that all arrangements studied showed very good physical and mechanical performance, major conclusion is that the equipment and variables used were appropriate for rubber wood plywood manufacture. The average lamination yield was 39.9%, when considering the volume of green veneers in relation to the logs with bark, and 44.9% when considering logs without bark; losses in the lamination process were compatible with those routinely observed in the plywood industry. It was possible to grade veneers in distinct modulus of elasticity classes using non-destructive stress wave method, resulting modulus of elasticity ranging from 4,887 MPa to 13,010 MPa. The use of mechanically graded veneers significantly influenced the longitudinal bending strength of plywood. The density of plywood panels ranged from 723 kg/ m3 to 815 kg/ m3. The bond strength to the shear stress reached values greater than 2.0 MPa, qualifying plywood panels for indoor use – IR, intermediate use – IM, and external use – EX, according to the standard project 31:000.05-001/1 (ABNT, 2004). Results also indicated that rubber wood has great potential for industrial production of plywood for general use – GER, industrial use – IND, and to form concrete – FOR.