Rosin sizes aluminium rosinate

For the period from around 1840 to the early 1970s paper was usually made in an acidic environment at pHs of around 4-5. This was because many grades required the use of rosin and aluminium sulfate for the control of water penetration (sizing), and solutions of aluminium sulfate exhibit a pH of around 4.5. Aluminium sulfate has also been popular with paper makers because it assists the flocculation of colloidal particles and therefore behaves as a mildly... 

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). 

Rosin is a non-reaclive prodnct and is retained on the anionic fibre by either attaching itself to a cationic source in the case of rosin soap, or anionic rosin emulsion or by having a cationic surface charge. The main requirement is that it requires a source of aluminium species to form the actual sizing agent, aluminium rosinate. Rosin is normally modified with maleic anhydride or fumaric acid to increase its reactivity with aluminium species and improve its efficiency at higher pH. The method by which this aluminium species is formed and retained in the wet-end of the paper/ board machine differs between anionic and cationic rosin sizes. 

Because of the lower levels of aluminium species required, the options for size addition with rosin emulsions are much greater, such that it is possible to add rosin emulsions and aluminium species close together, or premix in a controlled way, at pH up to 7.0. By doing this, the rosin emulsion can be essentially cationic at the point of mixing with the fibre and, if sufficient aluminium species is present, give effective sizing under what is normally considered unrealistic conditions for rosin sizing. 

This premix of rosin emulsions and aluminium species has led to the development of cationic rosin emulsions for sizing at pseudo-neutral pH (6.0-7.0). 

With the first type, an aluminium species will still have to be added for sizing, bnt considerably less than that required for the appropriate anionic rosin emulsion. However, the addition of the alumininm species needs to be close to, or with, the cationic rosin emulsion to avoid the problems of alnmininm chemistry at neutral/alkahne pH. 

The most critical chemical in rosin sizing is the source of aluminium ions to react with the rosin size, as unless the alnmininm species is contained in the product, as in type 3 of the cationic rosin sizes, there will be no sizing. It is possible to obtain sizing with other metal ions, but these are much less efficient, or more costly, than alnmininm. As previonsly stated, the two most commonly nsed chemicals for this pnrpose are alnmininm sulphate (papermaker s alum) and PAC. 

With ASA, good first pass retention of ASA is paramount to good sizing efficiency, as any ASA not retained in the first pass can be easily hydrolysed in the white-water system. This is because the ASA dispersion is not as stable in the wet-end as that of rosin, or AKD, as these products are designed to be stable for a period of months. This hydrolysis product can react with calcium and/or magnesium to form sticky salts, which can deposit and cause many problems. If aluminium is not added to the ASA dispersion, then it should be added to the white-water system to react with any unretained, hydrolysed, ASA to prevent the formation of these salts, by formation of the less/non-sticky aluminium salt. There are appUcations of ASA that do not use aluminium species, where first pass ASA retention is optimised, but these tend to be in the minority. 

For rosin sizing with traditional soap or dispersed anionic sizes, much depends on the alum or aluminium species used. Theoretically, the amount of Al ion required to neutralise and precipitate one part of rosin is 0.3. However, other factors control the level of Al required, and these have a bearing on lack of sizing with soap or dispersed rosin sizes. These factors are ... 

The mechanism is formation of a polymeric cationic aluminium species on the fibre and fines, followed by attraction of the dispersed rosin. As the polymeric species is only completely formed at pH 5.2-5.5, and at its most cationic, the efficiency of dispersed rosin sizes is reduced below pH 5.2. 

Conversely, for soap sizes, as they are dependent on neutralisation of the rosin soap by cationic aluminium species at pH 3.0-5.0, the neutralisation is not efficient, so rosin soaps lose efficiency above pH 5.2 as this polymeric species is formed. 

An alternative at high pH is to use a compound which maintains its cationicity above pH 6.0 and contains polymeric aluminium species, such as PAC (see Fig. 5.1). As the pH is increased, this can be used in preference to alum and, when used in a pre-mix system with dispersed rosin size, will give more efficient sizing, especially when added late to the wet-end system. 

The particles formed tend to be smaller than the aluminium floes, but grow to macro particle sizes. It would be possible to carry out sizing with these salts if retained, but they have very high melting points, so unless the dryer temperatures are 150°C (which is extremely unlikely) the rosin will not be able to spread adequately to give a sizing effect. 

As has been previously explained, this differs for soap and dispersed sizes (anionic, or cationic), as soap size precipitates are almost entirely aluminium rosinate, which must have the correct moisture and temperature before sintering takes place, whereas dispersed sizes contain high levels of free rosin, which can melt redistribute and react with aluminium species under normal drying conditions. 

Deposits can also occur at high pH due to a lack of AF species with alum. Alum may have reacted with rosin, but there is not sufficient charge on the particle to retain it. It then will be deposited in the stock approach system as basic aluminium rosinate. This is aluminium rosinate where the cationic part of the aluminium has been neutralised by the hydroxyl ion. This tends to occur more with soap sizes than with rosin sizes as the alum needs to react with the rosin soap and then be retained. With rosin dispersions this effect is less. 

Several chemicals are added to the fibre slurry in the stock-preparation phase to improve the properties of the final product. Acids or bases may be used for pH adjustment. Sizing agents control the penetration of liquids, and they are added either at the wet end of the paper machine or applied to the surface of the paper in the machine. Rosin is a typical sizing agent it is usually precipitated onto the fibres with the help of aluminium sulphate (alum). Wax or synthetic sizing agents, such as epoxides, can also be used. 

The introduction of compoimds for retention and drainage in the paper industry began with the invention of rosin sizing through Moritz Illig 1807 in Darmstadt/Germany. Rosin size is made of tall or tree resins, which are either soponified with caustic soda or dispersed with protective colloids. The rosin size was at first fixed to fibre with potash alum, a double salt of aluminium and potassium aluminium sulphate. Later on aluminium sulphate was... 

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