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Introduction Many paper products requiring longer term exposure to water are made with PAE wet-strength resin. The backbone of PAE is the polyamide derived from the condensation of adipic acid with diethylenetriamine (Crisp and Riehle 2018 ). Some of the secondary amines are subsequently converted to azetidinium groups by reaction with epichlorohydrin. A simplified structure of PAE is shown in Figure 1 . The cationic azetidinium groups and protonated secondary amine groups promote PAE adsorption onto pulp fiber surfaces; a study of PAE adsorption on regenerated

References Chen , S.-L., Wang, S., Lucia, L.A. ( 2004 ) New insights into the fundamental nature of lignocellulosic fiber surface charge. J. Colloid Interface Sci. 275 : 392 –397. Chiang , W.G.J., Tichenor, G.J.W. ( 1986 ) Novel graft polyacryreflamide copolymers and processes for their preparation and use. EP Patent 18 : 7275 . Dunlop-Jones, N. (1996) Wet strength chemistry. In: Paper Chemistry. Ed. Roberts, J.C. Blackie Academic & Professional, New York. pp. 98–119. Espy , H.H. ( 1995 ) The mechanism of wet-strength development in paper: A review. Tappi J

Introduction Wet strength is one the most difficult paper properties to improve. Whereas polyethylene films have the same strength wet or dry, paper products undergo a catastrophic loss of strength when exposed to water. Individual wood pulp fibers are somewhat weaker wet than dry; unbleached pulp fibers have about the same strength wet or dry, whereas bleached fibers can be up to 30 % weaker (Gurnagul and Page 1989 ). However, fiber weakening does not explain the low strength of wet paper. Instead, water swelling of fiber-fiber joints severs hydrogen bonds and

Introduction Papers and paperboards requiring wet strength include, for example, papers for sacks and bags, wallpapers, label, tissue, filter and laminating papers, and liners and paperboards for special packaging applications (Dunlop-Jones 1996 ; Crisp and Riehle 2009 ). Breaking of such substrates when rewetted in the course of converting or intended use has to be prevented. Wet strength paper retains at least 10 % of its original dry tensile strength after being fully soaked in water (Crisp and Riehle 2009 ). The relative wet strength can exceed 35

On the mechanism behind wet strength development in papers containing wet strength resins Lars Wiigberg and Mirjam Bjorklund, SCA Research AB, Sundsvall, Sweden Keywords: Adsorption, Wet strength agents, Bonding strength. Infrared spectra, Mechanical properties, Chemical pulps. Car- boxymethylation. Electrostatic charge, Swelling. Bonded area, Polyelectrolytes. SUMMARY: The improvement in strength when a polyamide- amine epichlorohydrine (PAE) polymer is added to a number of carboxymethylated pulps has been investigated in order to see whether or not

material formation mixing them with oppositely charged fibers is developed in this work. An application of this material as filler for pharmacological tablets is proposed. Layer-by-layer nanocoating of mill broken fibers for improved paper Yuri M. Lvov, George A. Grozdits, Sandeep Eadula, Zhiguo Zheng and Zonghuan Lu, Louisiana Tech University, USA Dry and wet strength of paper 26 PCCS06 06-12-18 15.29 Sida 552 Nordic Pulp and Paper Research Journal Vol 21 no. 5/2006 553 Materials and Methods The polyelectrolytes used are linear poly(allylamine hydrochloride) (PAH

The influence of two wet strength agents on pore size and swelling of pulp fibres and on tensile strength properties Mats Haggkvist, STFl and Stora Corporate Research AB, Daniel Solberg and Lars Wsgberg, SCA Research AB and Lars ~dbe rg , STFl and AssiDoman AB. Sweden Keywords: Butanetetracarboxylic acid, (BTCA), Polyamide- amine epichlorohydrin resin, (PAE), NMR, Relaxation, Pore size distribution, Swelling, Wet strength. SUMMARY: The effect of two wet strength agents, butanetetra- carboxylic acid (BTCA) and polyamide-amine epichlorohydrin resin (PAE

185 T==lå=íÜÉ=jÉÅÜ~åáëãë=_ÉÜáåÇ=íÜÉ=^Åíáçå=çÑ=tÉí=píêÉåÖíÜ ====~åÇ=tÉí=píêÉåÖíÜ=^ÖÉåíë Bo Andreasson SCA Graphic Research, Sundsvall Lars Wågberg Department of Fibre and Polymer Technology, KTH, Stockholm 7.1 Introduction 185 7.2 Wet-Strength Mechanisms 186 7.3 The Chemistry of Commercial Wet-Strength Resins 189 7.3.1 Urea-Formaldehyde 189 7.3.2 Melamine-Formaldehyde 190 7.3.3 Alkaline-Curing Resins 192 7.3.4 Glyoxalated Polyacrylamide Resin (G-PAM) 196 7.3.5 Starch 200 7.4 Functional Groups in Fibres 203 7.5 Future 204 7

laboratory cylinder press available at MoRe Research in Örnsköldsvik (Pettersson et al. 2017 , Norgren et al. 2018 ). The results indicated a possibility of reaching the same level of tensile strength with HYP as with bleached kraft pulp, as well as somewhat better compression strength. Another very important result is that sheets based on lignin-rich pulp show much higher wet strength than sheets from bleached kraft pulps when pressed at a high temperature well above the softening point of lignin. The main objective of the research presented here is to contribute to the

conditions, with the greatest strength reduction found for f-strength tested dry. After delig- nifi cation, only f-strength under wet conditions was substan- tially reduced; dry f-strength and both dry and wet z-strength hardly changed. A combined treatment of prehydrolysis and delignifi cation resulted in disintegration of the veneers, which made strength determination impossible. It was concluded that, in addition to cellulose, the hemicelluloses determine the f-strength under dry conditions, while lignin confers wet strength but appears not to contribute to