The Use of Bark Extracts in Cold-Setting Waterproof Adhesives

HT-120 is a spray-dried sodium salt of an ammonia extract of Tsuga heterophylla bark with a phenolic hydroxyl content of about 10 percent. It is very reactive with formaldehyde. Since bark extracts such as HT-120 can be produced at low cost if done on a large scale and since HT-120 improves the cross-linking of resorcinol resin and phenol-modified resorcinol adhesives, various combinations of these were tested. Tests included pH, pot life, block shear (hard maple and Douglas-fir) and plywood weathering (Douglas-fir) more or less as required by specification MIL-A.-379B. HT-120 modified resins had excellent bonding strength and weathering behavior. Short pot life was overcome by reducing pH with maleic anhydride which also improved bonding. Small laminated timbers were adequately bonded by the adhesives. Solids content can be reduced considerably by combining bark extracts with resorcinol adhesives.

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