Resins dry strength

Dry strength resins are used to impart strength to the sheet much like cationic starch. They are used to increase the bonding area between the fibres and augment the hydrogen bonding which holds the sheet together in its dry state. 

Dry strength resins have existed since the 1950s and were predominantly in use in Korea and Japan where starch was mostly regarded as a food source. In addition, low molecular weight polyacrylamides were readily available to the extent that they could be manufactured nearby and pumped to the paper machine. 

Wet strength resins unlike dry strength resins are added predominantly to impart strength to paper when it becomes wet. The chemistry, development and application of the predominant products are reviewed in Chapter 8 in some detail. 

Since the original introduction of polyacrylamides, considerable development has taken place, and their use is now regarded as standard in most mills. Three major applications have become established retention, water treatment (from save-all to effluent plant) and as a dry strength resin. 

Table 7.1 General effects of refining and dry strength resins...

Dry strength resins are generally supplied either as a powder or as a water-based solution or emulsion. In all cases, they can be readily dispersed in water. 

Opinions vary as to the optimnm point to add a dry strength resin, and indeed this can differ from one paper machine to another. It will also to some extent depend upon the specific objectives for nse. The most commonly nsed point of addition is to the thick stock, after the last refining has been carried ont. Strazdins [13] reported a laboratory study on a European secondary fibre fnmish, where the benefits of resin addition to the long fibre fraction were demonstrated. Good mixing is essential to obtain the best performance from the product, so addition to a weU-stirred chest or the down leg of the thick stock level box is ideal. If the dilnte resin is added to a pipeline, optimum mixing will be achieved if a mnltipoint injection system is nsed. 

The use of such cationic promoters is not restricted to use with anionic resins. Benefits such as reduced resin usage or higher dry strength values have also been seen when used with cationic resins. An example of this occurred in a European tissue mill, which was using a dry strength resin to improve the sofmess of its toilet tissue. The addition of 1 kg/t of a cationic polyamine reduced resin usage by 40%, for the same physical results. Collateral benefits were increased drainage, improved runnability and increased felt life. 

Interference by other additives will also prevent a dry strength resin from performing well. This is usually accompanied by changes in performance of the interfering agent. 

Some dry strength resins offer a collateral benefit of increased drainage. This can also occur when the charge balance in a system changes. Increases in drainage can have an adverse effect on sheet formation due to the rapid consolidation of the fibre stock on the wire. This may be overcome by reducing the consistency of the flow box stock. 

Farley, C.E. (1988), Polyacrylamide Dry Strength Resins Applications, Tappi wet emd dry... 

ACCOSOFT 808-90. See Quaternium-27 Accosperse 20. See Polysorbate 20 Accosperse 60. See Polysorbate 60 Accosperse 80. See Polysorbate 80 Accostrength 1000 Dry Strength Resin. See Acrylates/acrylamide copolymer Acetuf 3045, Accurel EG 100. See Polypropylene... 

Polyvinylamines are a relatively new group of wet-strength resins. These products are en-vironmentally friendly, their use does not result in any negative ecological impact (see also Section 3.6.5 on Dry Strength Resins). Their cost-performance ratio is at present less favorable than the conventional WSR in most cases. 

Fig. 3.28 Flowsheet of paper production process with integrated metering points and addition sequences of various chemical additives. (DSR = dry strength resin, DSR-PAM = dry strength resin - poiacryiamide, OBA = opticai brightening agent, PAC = polyaiuminum chioride, RDA = retention drainage aid, WSR = wet strength resin.)...

Dry-strength resins are based on polyacrylamide or on natural gums. Again, ->guar and locust bean gums, which are capable of forming hydrogen bonds with the cellulose fiber, are used. 

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