Wood laminating adhesives

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

Applications for cold-setting, wood-laminating adhesives initially followed the same approach (47) used for laminating resins from western hemlock (38) (i.e., reaction of tannin with phenol-resorcinol-formaldehyde prepolymers). Improvements resulted through the application of Kreibich s Honeymoon technique (48) wherein one side of the material to be bonded is treated with resin and the other with catalyst. One of the preferred systems (49) was phenol-resorcinol-formaldehyde or tannin-resorcinol-formaldehyde at pH 8 with extra paraformaldehyde on the A-side and tannin at 53% solids or tannin-resorcinol-formaldehyde at pH 12 on the B-side. Such resin systems are currently used to laminate eucalyptus or pine in most South African timber-laminating plants. 

The reactivity of resorcinol with formaldehyde is essential for developing the cohesive strength of the interlayer and its bonding characteristics. Condensed tannins are known to be very reactive with formaldehyde (7-0), so these renewable phenolic polymers are good candidates as resorcinol replacements. Indeed, condensed tannins from wattle and pine bark extracts have been successfully used in cold-setting, wood-laminating adhesives, and the former are used extensively in the commercial production of laminated timbers in South Africa (Pizzi, A., National Timber Research Institute, Pretoria, South Africa, personal communication, 1982) (10-13). 

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. 

Uses Urethane-acrylic in clear coatings for paper and wood laminates, adhesives, metal decorating, plastics Features Exc. flexibility, toughness, abrasion resist. 

The n-butanol is used as a latent solvent and coupling aid in nitrocellulose lacquer formulations to improve blush resistance, flow and leveling properties of the lacquers. The alcohol is also used for urea-formaldehyde and melamine-formaldehyde resins in surface coatings and in wood laminating adhesives. n-Butanol serves as an extraction solvent in the pharmaceutical industry. 

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. 

Hemingway R W, Kreibich R E 1984 Condensed tannin-resorcinol adducts and their use in wood-laminating adhesives An exploratory study. J Appl Polym Sci 40 79-90... 

Kreibich R E, Hemingway R W 1987 Condensed tannin-sulfonates in cold-setting wood-laminating adhesives. For Prod J 37 (2) 43-46... 

With the exception of the early work by Herrick and Conca (95) there has, until recently, been surprisingly little research directed to the use of conifer bark tannins in cold-setting wood-laminating adhesives. Current prices for the resorcinol that generally makes up about 25% of the weight of cold-setting phenolic resins are about 1.80 to 1.85/lb. Therefore, comparatively expensive reactions and processing costs can be economically feasible in the development of these types of... 

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). 

---