Wood laminated structure

Developments in glued laminated structures and panel products such as plywood and chipboard raises the question of the durability of adhesives as well as wood. Urea-formaldehyde adhesives are most commonly used for indoor components. For exterior use, resorcinol adhesives are used for assembly work, whilst phenolic, tannin and melamine/urea adhesives are used for manufactured wood products. Urea and casein adhesives can give good outdoor service if protected with well-maintained surface finishes. Assembly failures of adhesives caused by exudates from some timber species can be avoided by freshly sanding the surfaces before glue application. 

Cellulose, which is more fibrous than wood flour, is used as a filler for urea and melamine plastics. Melamine dishware is a laminated structure consisting of molded resin-impregnated paper. Starch and soybean derivatives are biodegradable, and the rate of disintegration of resin composites containing these fillers may be controlled by the amount of these fillers present in polymers. 

Wood (qv) is aiguably the oldest building material used by humans to construct their dwellings. It is a natural product obtained from trees, used in both structural and decorative applications. The chemical composition of wood is largely cellulose (qv) and lignin (qv). Today there are a variety of composite or reconstituted wood products, such as plywood, particle board, wood fiber boards, and laminated structural beams, where small pieces of wood or wood fiber are combined with adhesives to make laiger sheets or boards (see Laminates). 

Structural Wood Laminating Adhesives Used Under Exterior (Wet Use) Exposure Conditions... 

Wood is essentially a good fire endurance material because it forms a carbonized layer on the surface during combustion which prevent flame development. The fire endurance is proportional to the cross section dimension of it A glued laminated wood for structural members called gluelam for building purposes make good use of this characteristics. It is difficult to make a door, especially a panel- stile constructed one which has a large thickness dimension. Such a door is usually made thin with a nice profile. Therefore fire retardant wood has been tried for such style wooden fire door. 

The combination of an adhesive and adherend is a laminate. Commercial laminates are produced on a large scale with wood as the adherend and phenolic, urea, epoxy, resorcinol, or polyester resins as the adhesives. Many wood laminates are called plywood. Laminates of paper or textile include items under the trade names of Formica and Micarta. Laminates of phenolic, nylon, or silicone resins with cotton, asbestos, paper, or glass textile are used as mechanical, electrical, and general purpose structural materials. Composites of fibrous glass, mat or sheet, and epoxy or polyester resins are widely employed as reinforced plastic (FRP) structures. 

Boron has been included as a neutron absorber in various materials in addition to concrete. For example, borated graphite, a mixture of elemental boron and graphite, has been used in fast-reactor shields. Boral, consisting of boron carbide (B4C) and aluminum, and epoxy resins and resin-impregnated wood laminates incorporating boron have been used for local shielding purposes. Boron has also been added to steel for shield structures to reduce secondary gamma-ray production. In special situations, where a shield has consisted of a heavy metal and water, it has been beneficial to add a soluble boron compound to the water. 

Glued Laminated Beam (Glulam)- A structural beam composed of wood laminations or lams. The lams are pressure bonded with adhesives to attain a typical thickness of 1 V2. (It looks like 5 or more 2 X 4 s are glued together). 

MUF resin can be used as a cold-setting wood laminating adhesive for glulam and fingerjointing by the use of adequate acid hardeners. In all semiexterior and protected exterior structural applications where a clear/invisible glue line is preferred for aesthetic reasons then a MUF adhesive is preferred to the classical PRF adhesives used for this purpose. It is then more a question of fashion cycles, but notwithstanding this MUF resins have taken a considerable hold today in Europe (contrary to North America where PRFs are by far preferred) and confidence in them for this application has been steadily growing. 

To obtain wooden beams, with large sections (side >0.3 m), without splits or cracks, caused by shrinkage during drying, it is necessary to use laminated structures, while massive beams with smaller sections can be obtained by dividing the freshly cut wood along the axial direction then the... 

Nowadays, plastics are frequently combined with metals, glass, wood, or other materials. For example polyester and epoxy resins may be reinforced with glass fibre, or phenolic resins built up with asbestos to form laminated structures giving extra toughness and... 

In this paper, the thermal and mechanical characteristics of balsa wood and balsa wood laminates are reviewed, and it is shown that "composite" mechanics that have been developed for the class of synthetic fiber-reinforced plastic (SFRP) materials may be useful for describing the density and direction—dependent mechanical properties of balsa wood in bulk or laminated form. It may be asked whether such advanced analytical methods, perhaps combined with specially developed methods of test, could be used effectively towards developing more applicable QA/QC procedures that will clearly qualify balsa wood as a structural material in applications where strictest code compliance is a necessity. This question has prompted the following review and discussion. 

Structural composites and the principles of their construction have been known and used for literally thousands of years. Adobe brick, concrete, and laminated wood are the earliest known examples. The Assyrians and Babylonians are known to have used a type of concrete based on clay. A more robust type of concrete made from heated powdered clam and oyster shells that used lime (calcium oxide) as the binding agent was developed in ancient Egypt. Laminated structures such as wood pieces that have been mechanically fastened together or bonded together with an adhesive material of some kind have a similarly long history. 

Because of the widespread use of aluminum/wood laminates in architectural applications, literally thousands of durability-type water-resistance tests have been conducted. Such testing was routinely conducted for more than 25 years at the Alcoa Laboratories to establish the data which could give confidence to manufacturers of such bonded structures. While some of this... 

ASTM D 3535-79, Std. Spec, for Evaluating Resistance to Deformation Under Static Loading for Structural Wood Laminating Adhesives Used Under Exterior (wet use) Exposure Conditions. 

Many artificial composites, especially those reinforced with fibers, are anisotropic, which means their properties vary with direction (the properties of isotropic materials are the same in every direction). This is a characteristic they share with a widely used natural fibrous composite, wood. As for wood, when structures made from artificial fibrous composites are required to carry load in more than one direction, they are typically used in laminated form. It is worth noting that the strength properties of some metals also vary with direction. This is typically related to the manufacturing process, such as rolling. 

D-0905. Test Method for Strength Properties of Adhesive Bonds in shear by Compression Loading (Fig. 8). A basic compression shear test which is widely used in screening wood glues. It is also used in specifications D-3110 (on nonstructural wood laminating ad hesives), D-2559 and D-3024 (on exterior and interior structural wood laminating adhesives respectively) and D-4317 (on polyvinyl acetate based wood adhesives). 

The term laminated wood refers to glued wood laminates for bearing structures in construction. In this technique, known board sections (plates) are glued to tie segments, wherein the joints, for example, can be bridged by a comb-like structure (Deppe and Gersonde 1985). 

The joining of wood by adhesives is widely used in many fields of application. This comprises structural joints, glued-laminated timber, and coatings. In industrial processes, wood is structurally connected by formaldehyde-containing melamine or phenol resorcin resins which cure by polycondensation. Due to the very thin adhesive layers and the minimized formaldehyde content, the expected incorporation into the surrounding air is considerably less than the specified thresholds. In manually operated applications, dispersions of acrylates and polyvinyl acetate as well as urethanes are usually used to bond wood (Richter and Steiger 2005). 

---