Rosin sizes alkalinity

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). 

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. 

Calcium carbonate cannot be used in the same low pH papermaking process that contains alum and rosin size. The presence of carbonate in an acid papermaking process causes severe problems such as foam, excess alum demand, inefficient sizing conditions with rosin size, and troublesome deposits. The alkaline system, therefore, enables the paper-maker to use calcium carbonate as a primary filler as well as to use more recycled paper. 

A few of the alkaline sizes that are available today are supplied as prepared emulsions. Large investments in handling systems become unnecessary. With no alum required and given a fairly wide papermaking pH range within which they function, maintaining proper sizing conditions can be simpler for an alkaline size than for rosin size. An alkaline system requires fewer additives and is less complex. 

The effect of acidity caused by alum-rosin size has been obviated by the substitution of sizing agents which are effective slightly on the alkaline side of neutrality. It has been established that papers of satisfactory permanence can be manufactured with such sizes. It is possible to use rosin as a size and to avoid the conjunction with alum by a number of processes. There are insufficient data on the aging characteristics of paper sized with the available modified rosin sizes to judge the effect on permanence. Possible reactions of the rosin, such as oxidation and formation of peroxides, must be considered. 

However, the general trend is towards neutral and alkaline papermaking, so currently the predominance is with cationic rosin sizes for neutral and ASA/AKD sizes for alkaline. The difference in the three types can be described by ... 

The pH of the system and the acidity/alkalinity tend to decide the type of sizing agent reqnired. In general rosin size tends to be favonred in acidic conditions and ASA, or AKD, sizing in alkaline conditions. 

The presence of alkalinity for rosin size is normally an effect seen with increasing pH, as normally alkalinity increases with increasing pH. 

There are some components which may be regarded as anionic trash that are beneficial to rosin sizing such as saccharinic acids from alkaline pulping and hemicelluloses from unbleached pulps. These can form complexes with AP+ ions and produce rosin size precipitates of lower melting or sintering points. This promotes more efficient sizing. 

The main reason for deposits with rosin size is due to the presence of alkalinity or high pH. The Na and Mg + caused by the alkalinity react with rosin size, forming small floes which are no longer cationic in nature, as stated previously. They are thus less likely to be retained, but grow to form macroflocs which can be deposited in the stock approach system on the wire. These macroflocs being organic in nature are often associated with oil from defoamers and antifoams and, of course, with any fillers that are in the system. 

Wang F, Tanaka H., Mechanisms of neutral-alkaline paper sizing with usual rosin size using alum-polymer dual retention aid system, 7 Pulp Pap. Sci, 27(1), 2001, 8-13. 

The market for rosin sizes consumes over 30% of rosin production. However, competition from synthetic sizes has increased, with particular pressure being seen in alkaline papermaking applications. 

Internal Sizing. The most widely used internal sizes are alkyl ketene dimers (AKD), alkenylsuccinic anhydrides (ASA), and rosin-based sizes that are used with papermaker s alum (aluminum sulfate with 14 waters of hydration), polyaluminum chloride (PAG), or polyaluminum siUcosulfate (PAS) (61). The rosin-based sizes are used under acidic conditions. Since the mid 1980 s there has been a steady conversion from acid to alkaline paper production, resulting in static to declining demand for the rosin-based sizing systems. Rosin is a complex mixture of compounds and consists primarily of monocarboxyhc acids with alkylated hydrophenan threne stmctures (62). A main constituent of wood rosin, gum rosin and taH-oil rosin is abietic acid. 

No specific information on the possible effect of the synthetic sizes on permanence is available, and they are not mentioned in the standard 04), but it seems unlikely that they would be deleterious. Presumably they have been used in comnercial grades of neutral/alkaline paper subjected to accelerated ageing tests. In terms of general effects on paper, the synthetic sizes have a tendency to reduce the surface frictional properties of paper to a greater extent than rosin. For example, this makes it more difficult to stack piles of cut sheets without slippage. However, the effect is less noticeable when high proportions of chalk filler are used, because the blocky particles increase friction. 

The most commonly used sizing agents today are rosins, commonly used in acidic papermaking systems, and synthetic sizing agents such as alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA), as shown in Figure 7.18. The latter two components are suitable for papermaking processes under neutral and alkaline conditions. 

Zhuang J.F., Biermann C.I., Neutral to alkaline rosin soap sizing with metal-ions and polyethylenimine as mordants, Tappi 7,78(4), 1995, 155-162. 

Another group of effective sizes include alkyl ke-tene dimers (- fatty diketenes) and alkenylsucci-nic anhydrides. These products react with the OH-groups of the cellulose fiber. While rosin-based sizes can only by used in acid paper making processes, the cellulose-reactive sizes are used in neutral and alkaline paper making. The result is better sheet strength, reduced corrosion on the equipment, less salt in the effluent and better stability of the paper towards aging (archival paper). 

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