Development of wet-strength

The development of wet-strength in a cellulose fiber matrix assisted by a chemical additive requires some or all of the following to occur [17]  

Wet-strength additives form covalent bonds with the cellulose fibers. Covalent bonds are much more resistant to water than hydrogen bonds are and, thus, can contribute to the improved strength of the cellulose network by the formation of polymer-fiber bridges. 

There are two theories regarding the mechanism of wetstrengthening. The first states that the wet-strength effect is due to a reaction between the resin and the cellulose, which leads to the 

Wet-strength resins in general also increase the dry-strength of paper. 

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When using PAE resins, two mechanisms explain the development of wet strength in paper (Fig. 8.3). The first is a preservation or restriction mechanism but is more often referred to as homo-CTOSslinking . After adsorption onto the fibre surface, the azetidnium functionality of resin reacts with amine sites elsewhere on the backbone of the resin, effectively forming a self-crosslinked network that physically... 

Neal CW. A Review of the Chemistry of Wet-Strength Development. In TAPPI Wet and Dry Strength Short Course Notes 1988 1-24. 

Neal, C.N. (1988), A review of the chemistry of wet strength development, Tappi Wet and Dry Strength Short Course Proceedings. 

Espy HH (1995) The mechanism of wet-strength development in paper a review. Tappi J... 

PAE resins require the application of heat for the chemical reactions to occur. Usually, the maximum level of wet-strength is not achieved on the paper machine. The paper requires ageing (resin curing) to fully impart the wet-strength to the fiber network. At higher dryer temperatures the wet-strength development of the paper is improved both "off-machine" and with ageing [23, 47]. 

The first industrial hardboard was developed by W. Mason in the mid-1920s he found that a mat of wet fiber pressed in a hot press would produce a self-bonded flat panel with good strength, durabiUty, and stabiUty. The product was patented in 1928, trademarked as Masonite, and commercial production began. Over time several other processes for producing hardboards have been developed from modifications of the original process. Brief descriptions of these processes foUow and a flow chart of the process is shown in Figure 5. 

During the next 15 years the urea resins were also developed for use as adhesives, as textile finishing agents and in the production of surface coatings and wet-strength paper. Since World War II the development of chipboard has resulted in a large new outlet for urea-based resins which have also found other uses, such as in firelighters and foams. 

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