USING NEUTRAL ALKALINE-CURING RESINS TO PRODUCE WET-STRENGTH GRADES FROM RECYCLED PULP

The effects of neutral-curing wet-strength resins on the wet- and dry-strength properties of virgin and recycled pulps are compared. Results are presented for bleached pulps, unbleached pulps, and blends of chemithermomechanical and bleached pulps. While paper from recycled pulps is generally weaker than paper from virgin pulps, the results show that recycled pulps responded to wet-strength resins at least as well as virgin pulps. For both virgin and recycled pulps, the unbleached pulps and the pulp blends were more responsive than the bleached pulps. This was also true for recycled pulps treated with a combination of resin and carboxymethylcellulose, where dry strength increased more for the unbleached pulps and the pulp blends than for the bleached pulps. On average, epoxide-class wet-strength resins outperformed azetidinium-class resins in bleached grades. The study also shows that when wet-strength broke is repulped by hypochlorite, most of the strength loss is due to drying and redispersing the paper rather than to chemical degradation by the oxidant.