Preparation And Application Of ASA Neutral Sizing Agent Based On Microparticle Emulsification Technology

According to the stabilizing theory of Pickering emulsions, ASA emulsions stabilized by solid-based emulisiying systems including NaF modified bentonite, NaF modified bentonite together with magnesium aluminum hydroxides and NaF modified bentonite together with chitosan and ammonia, were prepared. The effects of the solid-based emulisiying systems on the emulsification of ASA/water system as well as on the centrigiation stability of the obtained ASA emulsion was investigated while the sizing performance, droplet size and droplet size distribution, hydrolyzing stability of the ASA emulsion as well as the function of alum in ASA sizing were studied by means of conventional analysis, optical microscopy, contact angle measurement, field emission scanning electron microscopy and x-ray photoelectron spectroscopy.The modified bentonite with a permanent negative charge has excellent stabilizing effect on the ASA/water emulsion system. The larger the amount of the bentonite, the smaller the emulsion droplet size, and the the better of stability of the emulsion. ASA/water system can be emulsified into W/O type emulsion by magnesium aluminum hydroxides with poor stability. Water phase will be separated from the magnesium aluminum hydroxides stabilized emulsions. The separated water phase is reduced by increasing the amount of magnesium aluminum hydroxides. The joint application of the magnesium aluminum hydroxides with the bentonite can significantly improve the stability of the ASA emulsion. However, with the increase of magnesium aluminum hydroxides, the emulsion stability will deteriorate. When the mass ratio of magnesium aluminum hydroxides to bentionite is 0.07 and the total charge level of the two solid emulsifiers is 7% based on the mass of ASA while the initial oil volume fraction is 33.3%, ASA/water can be well emulsified into a homogeneous and stable O/W emulsion.Chitosan and ammonia can significantly improve the stability and sizing performance of ASA emulsion when they are used as co-emulsifiers of the modified bentionite. Chitosan precipitated from its acidified aqueous solution by ammonia participate the emulsification of ASA together with the modified bentonite. The precipitated chitosan may promote the adsorption of the bentonite onto the oil/water interface forming a more compact and stable protective layer. However, the addition of ammonia enhances the alkalinity of the ASA emulsion, which reduces the hydrolyzing resistance and the sizing performance of the ASA emulsion. Stable ASA emulsion with good performance can be obtained when the bentonite, chitosan and ammonia have a charge level of 7%, 0.125% and 2.25%, respectively. However, the emulsion should be used within 30min, after which the hydrolization of ASA will be lead to a heavy loss of the sizing efficiency of the ASA emulsion.Appropriate shearing intensity is required to prepare a uniform and stable ASA emulsion. Low shearing intensity can not provide sufficient energy for breaking ASA into small droplets while too high a shearing intensity will cause the coalacence of ASA droplets. The appropriate shearing rate and shearing time should be 10000r/min and 5min; respectively. Salts would cause the demulsification of ASA emulsion. The salts with high valence metal ions show higher negative effects on the stability of the ASA emulsions.At the same addition amount, the ASA emulsion stabilized by the bentonite alone shows the lowest sizing performance while the ASA emulsion stabilized by bentonite together with chitosan and ammonia has the highest sizing performance. The sizing performance of ASA emulsion stabilized by bentonite and magnesium aluminum hydroxides lies between that of the above two ASA emulsions. The sizing performances of all of the above ASA emulsions will decline significantly after being prepared for one hour. The introduction of aluminum sulfate remarkably enhances the sizing efficiency of the ASA emulsions by inducing the hydrophobic orientation of the hydrolysis products of ASA. Therefore, adding aluminum sulfate in ASA sizing will reduce the cost of sizing via lowering the addition level of ASA since ASA is more expensive than aluminum sulfate. The addition level of aluminum sulfate may be as high as 2%. For the internal sizing of the solid stabilized ASA emulsions, oven dried papers show higher sizing degrees while air dried papers show lower sizing degrees since high temperature promotes the spreading of ASA. Under the laboratory experiment conditions, 0.2% of ASA based on oven-dry pulp can give an adequate sizing degree. Softwood pulp is easierly sized by the ASA emulsion than the other pulps such as hardwood pulp and mixed pulp of hard wood and wheat straw pulp.