Gluing Hardboard with Protein Adhesives

Thirteen adhesives for gluing hardboard were evaluated. Among the types of protein adhesives were soya, blood, soya-blood blend, casein, and soya-casein blend glues. The cold press, no clamp feature of soya and soya-casein blend glues make it possible to produce interior grade flush doors and other products without the necessity for expensive hot pressing equipment, complicated clamping procedures, or a heated plant in the winter time. On the other hand, soya-blood and blood glues make it possible to hot press hardboard using protein adhesives. If a cold press operation requires clamping, soya and soya-casein blend glues can be used, but it is also possible to use a casein glue which offers the advantages of greater water resistance and more simplified mixing procedures. The properties of low or high temperature curing, good gap filling characteristics, glue line alkalinity, fairly low cost, relatively low sensitivity to operating variables and good adhesion to all grades and types of hardboard results in the favored use of protein adhesives for gluing hardboard in many applications. Hot press soya-blood blends and straight blood glues have the greatest water resistance of the protein glues, with casein next in order. Protein glues are susceptible to fungus attacks under conditions conducive to the growth of mold; however, if these conditions are present, mold-inhibiting materials are available and are satisfactory. A proportion of phenolic resin added to hot press protein glue will also give good mold-inhibiting properties. Protein glues will stain wood or wood-based products such as hardboard and care must be taken to remove glue from visible surfaces. Deep screening marks on the back of hardboard panels must be removed prior to gluing to assure a satisfactory bond.

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