Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Two or more non-extruded coatings or impregnations
Reexamination Certificate
1998-01-27
2001-08-28
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Two or more non-extruded coatings or impregnations
C428S537100
Reexamination Certificate
active
06281148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to fiber-reinforced plastic panels, wood composites and to methods of manufacturing such panels, and in particular to fiber-reinforced plastic panels that are bonded using industry recognized wood adhesives.
2. Description of the Related Art
FRP-wood hybrids offer considerable potential for widespread use in construction and infrastructure applications. In addition to increasing the strength, stiffness and ductility of engineered wood composites, the hybrids allow for the utilization of low-grade lumber in construction. The hybrids also offer flexibility in design allowing for longer spans, lower depths, and lighter structures. One important factor in developing this hybrid technology is to provide adequate bond strength between the FRP reinforcement and the wood.
Pilot studies in the past five years by the inventors and others have shown the significant promise of combining wood and FRP. The inventor's studies have revealed, for example, that FRP reinforcement in the order of 2% can increase the bending strength of wood beams by over 50%.
The idea of reinforcing wood is not new. Many studies on wood reinforcement have been performed in the past 40 years. Often metallic reinforcement was used including steel bars, prestressed stranded cables, and stressed or unstressed bonded steel and aluminum plates. While significant increases in strength and stiffness have been achieved, the problems encountered were generally related to incompatibilities between the wood and the reinforcing material. Wood beams reinforced with bonded aluminum sheets experienced metal-wood bond delamination with changes in moisture content of only a few percent. The differences in hygro-expansion and stiffness between the wood and reinforcing materials can lead to separation at the glue-line, or tension failure in the wood near the glue-line.
To improve durability, fiberglass has been used in a number of ways, such as for beam reinforcement, as face material of wood-core sandwich panels, as external reinforcement for plywood, and in the form of prestressed strands. Unlike traditional steel and aluminum reinforcement, FRP reinforcement of wood composites can be successful because the physical/mechanical/chemical properties of the FRP are very versatile. The FRP may be engineered to match and complement the orthotropic properties of wood; consequently, incompatibility problems between the wood and the reinforcing FRP are minimized.
FRP materials (fibers/matrix) can be readily incorporated into many of the manufacturing processes currently used to produce structural wood composites.
In recent years, the bond strength of the FRP-wood interface has been investigated by a number of researchers and some related patents have been issued. U.S. Pat. No. 5,498,460, issued to Tingley, discloses a method of bonding FRP to wood using surface sanding to “hair up” fibers. In U.S. Pat. No. 5,362,545, also issued to Tingley, the inventor discloses a method to produce surface recesses on the FRP to enhance the bond strength.
In Forest Products Journal, Vol. 44, No. (5), pp. 62-66, 1994, Gardner et el. examined several different adhesive systems for use in glue-laminated wood structures. These included resorcinol formaldehyde (RF), an emulsion polymer isocyanate (EPI), and an epoxy resin. For composite joints fabricated from glass-reinforced vinylester or polyester FRPs and yellow poplar, the highest shear strengths were obtained using the RF adhesives, followed by the epoxy and EPI systems. The RF adhesive was also found to produce the greatest percentage of dry test failures within the wood matrix for wood-vinylester FRP matrix systems with values exceeding 90%. However, polyester-wood joints were found to produce almost 100% cohesive failures within the FRP matrix under dry conditions. Wet tests produced only 20 to 40% wood failures for vinylester-wood joints and 80% FRP matrix failures for polyester/wood joints.
Dailey et al. disclose in the Proceedings of Composites Institute's 50th Annual Conference & Expo '95, Composites Institute of the Society of the Plastics Industry, Inc., Cincinnati, Ohio, pp. 1-4, Session 5-C, the bonding of pultruded glass/phenolic composites to Douglas-fir. Both resorcinol formaldehyde (RF) and resorcinol-modified phenolic (PRF) adhesives were studied. Initial shear testing showed the PRF to outperform the RF. The authors varied such parameters as open and closed times, clamping pressure, and cure periods. They concluded that a long curing period increased the bond strength and emphasized the need for additional research to completely quantity the mechanical properties of the FRP-wood hybrids.
There is not found in the prior art a simple, inexpensive, commercially viable method of bonding FRP panels together or to other surfaces, such as wood, that uses common, proven wood adhesives, yet meets or exceeds shear bond strength requirements as specified under ANSI/AITC 190.1 and cyclic-delamination requirements under AITC 200.
SUMMARY OF THE INVENTION
The present invention is a resin-starved pultruded-impregnated panel, wood composites utilizing said panel, and a method of making the same. In its most basic form, the panel of the present invention comprises a pultruded center portion made from a plurality of fibers bound together by a resin such that the surfaces of the center portion contain significantly less resin than the core, and a layer of an impregnating adhesive, having similar chemical a bonding adhesive used to laminate the surfaces of the panel to immediately adjacent layers of wood, applied to each surface to form the surfaces of the panel. In the preferred embodiment of the panel of the present invention, a plurality of sacrificial edges are bonded to at least two of the outside edges, and the center portion comprises a pultruded glass fiber reinforced plastic sheet impregnated with a phenol-resorcinal formaldehyde adhesive.
In its most basic form, the wood composite of the present invention comprises a single wood member and at least one resin starved pultruded panel disposed at a predetermined location against the wood member, and a bonding adhesive disposed between the surfaces of the member and the panel to bond them together. In the preferred embodiment of the invention, a plurality of wooden members are disposed in substantially parallel relation to one another, at least one resin starved pultruded panel is disposed at a predetermined location between two of the members, and the bonding adhesive is disposed between the surfaces of the members and the panel to bond them together. In this preferred embodiment, the resin starved pultruded panel has at least two planable sacrificial edges formed with, or bonded to, edges of the panel, such that the panel may be easily aligned with the members, and the shear strengths of bonds between surfaces of the panel and the wooden members exceed the shear strength of the immediately adjacent wood members. In some embodiments, the wooden members and the panel are bonded together to form glulam beams, LVL beams. PSL beams, LSL beans, I-joists, or flat composite panels such as plywood.
In its most basic form, the method of the present invention comprises the steps of forming a resin starved pultruded impregnated panel by forming a pultruded center portion having a pair of resin starved surfaces, impregnating the surfaces with an impregnating adhesive, removing a portion of the impregnating adhesive to form a substantially smooth flat surface, and partially curing of the remaining adhesive, disposing the panel against a wooden member, and bonding the panel and wooden member together to form a wood composite. In the preferred embodiment of the method, at least a second wooden member is disposed adjacent an opposite surface of the panel and bonded to the panel, a pair of sacrificial edges are bonded to the panel, and the composite structure is planed to size.
Therefore, it is an aspect of the invention to provide a method for reinforcing a wood composite that
Abdel-Magid Beckry
Dagher Habib
Shaler Stephen M.
Lawson, Philpot & Persson P.C.
Morris Terrel
Persson Michael J.
Torres Norca L.
University of Maine
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