Rosin sizing

Paste rosin sizes are supplied as viscous pastes containing 60—80% solids. These sizes may contain unmodified or fortified rosin that has reacted (ie, been fortified) with either maleic anhydride [108-31-6] or fumaric acid [110-17-8] (see Fig. 3). In either case, the unmodified or fortified rosin is treated with aqueous alkaH so that the degree of neutralization, ie, saponification, varies from 75—100% depending on the physical state desired for the commercial product. Before use, the paste size must be converted to a stable, dilute rosin size emulsion by careful sequential dilution with warm water foUowed by cold water, with good agitation. 

Fig. 3. Resin acids in rosin sizes, R = CH(CH2)2- The rosin acids are represented here as abietic acid [514-10-3] (1) and levopimaric acid [79-54-9] (2). In rosin there are other isomers and disproportionation products. The product of reaction with fumaric acid (3) is levopimaric acid— fumaric acid adduct...

Rosin sizing usually involves the addition of dilute aqueous solutions or dispersions of rosin soap size and alum to a pulp slurry (44—46). Although beater addition of either coreactant is permissable, addition of both before final pulp refining is unwise because subsequently exposed ceUulose surfaces may not be properly sized. The size and alum should be added sufficiendy eady to provide uniform distribution in the slurry, and adequate time for the formation and retention of aluminum resinates, commonly referred to as size precipitate. Free rosin emulsion sizes, however, do not react to a significant degree with alum in the pulp slurry, and addition of a cationic starch or resin is recommended to maximize retention of size to fiber. Subsequent reaction with aluminum occurs principally in the machine drier sections (47). 

The higher efficiency of fortified rosin sizes is beHeved to result from the semihydrophilic nature of the rosin adduct molecules, which results in a more dispersed system of particles during size precipitation by alum. Consequendy, there is a more uniform distribution of somewhat smaller particles on the sized fibers. This dispersing effect may result from the strong tendency of aluminum to coordinate with organic anions. 

The pulp and paper industry and potable and wastewater treatment industry are the principal markets for aluminum sulfate. Over half of the U.S. aluminum sulfate produced is employed by the pulp and paper industry. About 37% is used to precipitate and fix rosin size on paper fibers, set dyes, and control slurry pH. Another 16% is utilized to clarify process waters. The alum sold for these purposes is usually Hquid alum. It is frequendy acidic as a result of a slight excess of H2SO4. Aluminum sulfate consumption by the pulp and paper industry is projected to remain constant or decline slightly in the near term because of more efficient use of the alum and an increased use of alkaline sizing processes (13). 

Rosin is commonly modified with maleic or fumaric acid to improve efficiency. Since the 1970s, dispersions of unsaponifted rosin have become more popular as a result of their improved sizing efficiency, lower alum requirements, and reduced pH sensitivity vs saponified rosins. Cationic dispersed rosin size, which can be effective at near-neutral and neutral papermaking conditions, is also available (63—65). Commercially available rosin sizes include Pexol, Neuphor, and Hi-pHase (Hercules Inc.), Plasmine and NeuRos (Plasmine), Stafor (Westvaco), Novaplus, and Novasize (Georgia Pacific), and NeuRos and Roscol (Akzo Nobel). 

The normal sequence of addition ia the dyeiag process is pulps, filler, dyestuffs, rosia size, and alum. The dyestuffs are either taken up by the fiber because of their affinity or they must be fixed on the fiber in a finely divided form by suitable fixing agents. Alum, which is required to precipitate the rosin size, has a strong precipitating and fixing effect on dyestuffs. 

In the manufacture of colored papers, it is best to add the dyestuffs before addition of rosin size and alum. This is not always possible in continuous dyeing procedures where dyestuffs must be added to stock containing size and/or alum, and this may cause premature laking of the dyestuffs and subsequent loss of tinctorial strength and/or dullness of shade. The proper selection of dyestuffs can help to reduce these disadvantages. 

Haxz-karboUdsung, /. (Paper) solution of rosin in carbolic acid, -keraselfe, /. rosin curd soap, rosin soap, -kiefer,/. pitch pine, -kitt, m. resinous cement, -kocher, m. (Paper) rosin boiler, -kohle, /. bituminous coal, -kdrper, m. resin(ous) substance, -lack, m. resin lake resin varnish, -leim, m. (Paper) rosin size, -leimung, /. (Paper) sizing with rosin, -leimverseifung, /. rosin-size cutting. ... 

Harz-masse, /. resinous mass or composition (Paper) rosin size, -milch, /. a suspension of resin or rosin, -naphta, /. resin oil. -31, n. resin oil rosin oil. -pech, n. resinous pitch, rosin. 

As in the case of rosin sizing, the first step is to retain the emulsified size particle in the wet web. The mechanism of retention is probably by heterocoagulation of the cationic size particles to the negatively charged fibre surface. The charge characteristics of the stabilising polymer become important as demonstrated by the effect of pH on the retention of AKD emulsion particles stabilised with a tertiary cationic starch (Figure 7.17). 

Since the early days of machine made paper in the first half of the nineteenth century, the most widely applied method of Internal sizing has been the use of naturally occurring resinous materials ("rosins") in conjunction with an aluminium salt, usually aluminium sulphate (called "alum" by paper-makers). Various forms of rosin sizes (rosin soaps, rosin emulsions, fortified rosins) have been developed over the years to improve the process, but these variants still involve the use of alum as a means of ensuring that fibres retain a layer of size. 

The important point is that the cellulose in these alum/rosin sized papers is susceptible to acid hydrolysis, which results in a lowering of the degree of polymerisation and, eventually, to a serious reduction in the strength of fibres and to complete embrittlement of the paper. Some recent work in the writer s laboratory suggests that when alum/rosin papers are made, the hydroxonium ions which lead to the degradation are adsorbed independently of aluminium ionic species (4). 

One of the most industrially important characteristics of papers is their chemical stability, which enables them to withstand degradation with its consequential loss of tensile and tear strength and fold endurance under normal conditions of use. However, this stability is not absolute. Cellulose is susceptible to oxidation and the glycosidic linkage is susceptible to hydrolysis. In order to protect book papers from acid degradation, they must not be exposed to acid. Acids are generated from the alum-rosin size as well as from such... 

Materials. All paper samples were cut from a continuous length of machine-made rolls. Two different papers have been studied. One is a bleached Kraft wood pulp waterleaf (50-lb basis weight) made by Neenah Paper Mills from a stock that comprised northern softwoods (60Z) and Lake States hard woods (40J), and contained no additives. The second paper, Foldur Kraft, is a bleached Kraft paper (70-lb basis weight) made by Champion Paper Company from a stock of 90Z softwoods and 10Z hardwoods, with alum-rosin size and 8Z titanium dioxide filler. This paper was obtained 15 years ago. Since then it has been stored indoors in areas which have not enjoyed a carefully regulated environmental control. 

Paper in particular is a problem today much of it is still being made on the acid side from the use of alum rosin sizes, and this limits its life. There are 150 years of similar bad paper on the shelves. Librarians are the custodians of millions of books which are too brittle to use. Often there is nothing to be done but to cut the books apart, microfilm the information, and discard them. Textiles too have been subjected to the exigencies of rapid machine production and mishandled so that their permanence has dropped. The artifacts of our present civilization are fragile, and much of our cultural heritage is slipping silently away. 

The most commonly used sizing agent for paper has been rosin size. Rosin size requires alum and an acidic environment in the papermaking process. This results in acidity in the paper itself. 

The neutral or alkaline pH of the paper machine system necessary for a high extract pH in the paper is not compatible with the rosin size-alum sizing system. To set rosin size properly on fiber, alum is required. Since total acidity is an approximate measure of the amount of alum in solution, it is often used as a control in connection with rosin sizing. The most effective size-alum precipitate forms at a papermaking pH between 4.2 and 4.8 and a total acidity between 90 and 150 ppm. The low pH of the process water, high total acidity, excess alum, and the size-alum precipitate all place a severe limit on the permanency properties of paper. 

---