Alkyl ketene dimer sizes

Figure 16 ToF-SIMS images of total ion current, AKD (alkyl ketene dimer) size, optical brightener and hexosan distribution on multipurpose paper surface after coating with Au-Pd. Reproduced from Fardim and Holmbom [70], with permission from Elsevier. 2005.

The wettability of various wood fibres was studied in [173], including bleached and unbleached, and alkyl ketene dimer sized and non-sized fibres. An improvement of the wettability with an increase of the surfactant concentration, except nonionics, was observed for all types of fibres. It has been noted in [174] that the electrokinetic potential of fibres determines considerably the efficiency of their washing and dying. Alkali mercerisation of cotton influences not only the fine structure, morphology and conformation of cellulose molecules, but also the negative electrokinetic potential of the cotton fibres. Based on this, the selection of mercerisation conditions due to changes in the NaOH concentration will allow to... 

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. 

The trend towards increased calcium carbonate usage and therefore neutral pH paper making has meant that there has been a steady decline in the use of rosin and alum and a concomitant increase in the use of sizes which are effective at higher pH. Commercially the most important in this group are the alkenyl succinic anhydrides (ASA) and the alkyl ketene dimers (AKD). These are able to esterify fibre surfaces directly and are more effective at neutral to high pH. 

Sometimes internal sizing agents such as alkyl ketene dimers and... 

Figure 1. Postulated sizing reactions of (a) alkyl ketene dimers and (b) alkyl succinic anhydrides. R. and R are short alkyl chains. Cell-OH represents cellulose.

With the advice of A. L. Rothschild and others, a series of experiments was begun in the Herty Foundation laboratories that culminated, in December 1959, in the production, on commercial equipment, of a paper meeting the tentative specifications. This was done at the Standard Paper Manufacturing Company in Richmond, Virginia. The pulps were all chemical wood the sizing was alkyl ketene dimer, which is compatible with mild alkalinity and calcium carbonate was added to maintain alkalinity (3). 

Traditionally papermaking is made at acid pH of about 4.5. Because of this the sizing of paper is carried out with resin acid salts in the presence of alum. Under these conditions, the resin acid anions complex with the aluminium cations and the complex formed is attracted to and deposited on the fibre surface. The purpose of sizing is to render the paper more resistant to water-based printer s ink. Today there is much interest in so-called alkaline sizing at about pH 7, which is preferred for specialist long-life papers. Here sizes such as alkyl ketene dimer replace alum. Alkaline papermaking has the further advantage that fillers such as calcium carbonate can be employed. 

Modern papers are often sized with an alkyl ketene dimer that reacts with hydroxyl groups on the cellulose, and the large alkyl group imparts water-repellency (see Figure 3). The product is a white solid that is emulsified with water for application onto the paper. 

Alternative types of size quickly filled the void, rosin was reformulated to enable sizing up to pH 6.5, whilst alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) provided non-rosin solutions. 

Alkyl ketene dimer (AKD)-based sizing agents... 

Since the beginning of papermaking in Western Europe, gelatin was used to reduce the sorption of water (paper sizing) by papers to improve the buffer effect and feathering of the inks [1], Nowadays, papers are sized with synthetic sizes such as alkyl ketene dimers (AKDs) and alkenyl succinic anhydrides (ASAs), which were developed for the paper industry in 1953 and 1974, respectively [2], but gelatin sizing continues to be used for artist quality papers. 

Fatty acids are raw materials for fatty amines, ethoxylated fatty amines, quaternary ammonium compounds (Quats), fatty acid-polyamine condensates, fabric softeners based on esterquats, fatty add amides, alkyl keten dimers for paper sizing and amphoteric surfactants. Binding of oleic add anhydride to cellulose fibre by chemical grafting is a recently introduced sustainable process to protect construction timber for outdoor use, such as pinewood shutters, from moisture and outside attack. Impregnation of the wood involves two stages firstly in an autoclave, where vacuum and pressure ensure its penetration, and then in a tank where the wood is soaked in a bath of anhydride, to encourage grafting of the anhydride on the wood. ... 

Lindstrom, T. and Soderberg, G., On the mechanism of sizing with alkyl ketene dimers. Part 3, The role of pH, electrolytes, retention aids, extractives, Ca-lignosulfonatos and mode of addition on alkylketene dimer retention, Nord. Pulp Paper Res. J., 1(2), pp. 31-38 (1986). 

Seppanen, R., Tiberg, F. and Valignat, M. P., Mechanism of internal sizing by alkyl ketene dimers (AKD). The role of the spreading monolayer precursor, Nordic Pulp Paper Res. J., 15, 452-458 (2000). 

Yu, L. P. and Gamier, G., Mechanism of internal sizing with alkyl ketene dimers the role of vapour deposition, in The Fundamentals of Papermaking Materials, Vol. 2, Baker, C. F., (Ed.), Pira International, Leatherhead, UK, 1997, pp. 1021-1046. 

Alkyl ketene dimers are typically utilized for sizing in the pulp and paper industry. The term sizing means to reduce the tendency of the dry material to absorb water. They are synthesized from fatty acids as shown in Figure 5.3. 

It is important to emphasize that even if a measurable is not simply related to underlying physical properties, the measurable may still represent a valuable practical analytical tool for industrial purposes(114). Kaplan, et al. used DWS to study structure formation in alkyl ketene dimer emulsions(l 15). These systems are used in paper manufacture as sizing agents, but lead to technical difficulties if they gel, which they sometimes do. Within a few days, spectra of systems that were going to gel could readily be distinguished from spectra of systems that would remain stable. 

An alternative to surface sizing is internal sizing, the addition of a sizing agent to the wet end before the formation of the paper sheet. In this process step, however, exclusively low molecular weight sizing agents like rosin acids or alkyl ketene dimers (AKD) are applied. 

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