Sizing agents

Locust bean gum and its derivatives are exceUent film formers and can be used either alone or in combination with starch as textile sizing agents and dye thickeners in textile printing, and as fiber bonding and beater additives in the papermaking industry. However, in most of these appHcations it has been replaced by guar. 

Tamarind kernel powder is insoluble in cold water, but upon heating forms thick viscous coUoidal dispersions at relatively low concentrations (2—3%). Upon drying, elastic films are formed. Tamarind seed polysaccharide is used as a low cost textile sizing agent in India. 

Other Uses. A small but growing oudet for C and higher linear olefins is the production of alkenylsuccinic anhydride (ASA) for the paper iadustry. ASA is an effective alkaline sizing agent and competes with alkylketene dimer (AKD) ia this appHcatioa. 

Papermaking additives can be categorized either as process additives or as functional additives. Process additives are materials that improve the operation of the paper machine, such as retention and drainage aids, biocides, dispersants, and defoamers they are primarily added at the wet end of the paper machine. Functional additives are materials that enhance or alter specific properties of the paper product, such as fillers (qv), sizing agents, dyes, optical brighteners, and wet- and dry-strength additives they may be added internally or to the surface of the sheet. 

Alkaline sizing agents are especially effective in milk-carton board and printing and writing grades that utilize calcium carbonate fillers. 

Mechanism. The general mechanism of effective sizing involves the foUowing sequential steps. (/) Efficient retention of the sizing agent in the... 

Alkylketene—dimer emulsion sizes can be appHed to the surface of paper and provide very efficient sizing. Used by themselves, these sizing agents can provide a sHppery surface consequendy, they often are used in conjunction with starch or some filler which reduces sHppetiness without detracting from sizing efficiency. 

Aluminum sulfate has largely replaced alums for the major appHcations as a sizing agent in the paper industry and as a coagulant to clarify municipal and industrial water suppHes. In terms of worldwide production, it ranks third behind alumina and aluminum hydroxide, with markets in excess of 3 x 10 t/yr (19). 

Fillers e.g. calcium carbonate, kaolin, titanium dioxide Sizing agents, starches Natural dyes, brighteners Retention aids... 

By control and substitution of chemicals used in the paper mills, manufacturers of packaging papers and board can contribute themselves directly to a small mineral oil reduction in their products. Some additives contain mineral oil as solvent such as flocculation or retention aids based on polyacrylamide (PAA), resin sizing agents or defoamers. A change of such products to mineral oil-free additives removes their own mineral oil input and reduces the contamination of packaging material. In the area of retention aids based on PAA, this conversion has already mostly taken place. 

Figure 10.16 Dissolution rates of films of water-soluble sizing agents in water at 20 °C [169]...

Table 10.11 Specific COD and BOD values found for important sizing agents [203]...

Sizing agent Specific COD value (mg 02/g) Specific BOD value (mg 02/g)... 

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