Spray and foam application of chemical binders to pulp fiber airlaids

Pulp fiber airlaid nonwovens were bonded with three binder formulations in a spray and foam process. The binders were: a commercial acrylic dispersion binder, a commercial bio-containing acrylic binder; and a citric acid-carboxymethyl cellulose mixture (CACMC) (1:1 by-weight). The binder solutions were applied at same concentrations onto A4-size airlaid sheets (80 gsm) under a vacuum with 2-sided spraying and 1-sided foam coating. The sheet structure, dry and wet tensile properties, and total absorption capacity were compared. The foam application densified and bulk bonded the sheets, whereas the spray application induced surface bonding. These factors fundamentally influenced the measured sheet properties. The dry tensile strength was linearly correlated with the relatively low binder dosages. The CACMC binder exposed the differences in the binder application processes well, and lead to strong sheets with small elongation and highly application method-dependent absorption capacity compared to acrylic binders.