Corrugating starch adhesive formulation

The carrier portion of the corrugator adhesive provides the viscosity needed to hold the raw starch in suspension and to retain water during application. Heating and stirring of the carrier and of the final product need to be carefully controlled in order to maintain the correct viscosity. In the majority of corrugator formulations, starch solids range from 18% to 21%, but may increase to 30% for specialty applications. About 15-17% of the total starch is used as carrier. 

The adhesives developed for the manufacture of damp-ply-resistant corrugated cardboard are based on the addition of spray-dried wattle extract, urea-formaldehyde resin, and formaldehyde to a typical Stein-Hall starch formula with 18-22 per cent starch content [75, 76]. The wattle tannin-urea-formaldehyde copolymer formed in situ and any free formaldehyde left in the glue line are absorbed by the wattle tannin extract. The wattle extract powder should be added at level of 4—5 per cent of the total starch content of the mix (i.e. carrier plus slurry). Successful results can be achieved in the range of 2-12 per cent of the total starch content, but 4 per cent is the recommended starting level. The final level is determined by the degree of water hardness and desired bond quality. This wattle extract UF-fortifier system is highly flexible and can be adapted to damp-proof a multitude of basic starch formulations. 

Likewise, many of the adhesive properties can be explained by reference to the amylose and amylopectin properties of the starch used. Jelly gums are usually made from waxy starches (100% amylopectin) and are stable at room temperature for many months, as would be expected from the slow retrogradation rate of this starch. A corrugating formulation must set to form a bond and become water resistant in a short period of time. The low molecular weight portion of the amylose would be expected to come out of solution fairly rapidly to make a temporary bond, and the high molecular weight portion would more slowly tend to create water resistance. 

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