Wet-strengthening in acid conditions

The UF resins are the least expensive ones. These resins are usually applied for the manufacture of sack paper (e.g., cement packaging]. The resin addition of 0.5 to 3%, calculated on dry fibers, produces a wet-strength level of up to 40% of the diy-strength initial value [23]. 

3 Wet-Strengthening in neutrai and aikaiine conditions Polyaminopolyamide-epichiorohydrin resins (PAE) 

The amount of PAE resin required in hygienic paper production is between 0.1% and 4% calculated on dry fibers. Depending on the addition level, the relative wet-strength can be increased to over 35% without significantly drop in paper absorbency. 

Two mechanisms explain the development of paper wet-strength by PAE homo-cross-linking and co-cross-linking [75]. 

Homo-cross-linking. After PAE adsorption onto the fiber surface, the azetidnium group of resin reacts with amine sites on the resin, which results in the formation of a self-cross-linked network that physically entangles fibers during paper drying. When the paper is re-wetted, this resin network restricts the re-hydration of the fibers and protects the hydrogen bonds formed between fibers. 

---