ASA Emulsion Stabilized By Alanine Modified Laponite

During China’s12th Five-Year-Plan Period, one of the mandates in papermaking industry isto enhance the innovation capability of paper industry, upgrade industrial technology, focus ondevelopment of low consumption, low pollution, high quality and high efficiency technology ofpulping and papermaking, paper chemicals and application techniques. Alkenyl succinicanhydrides (ASA) is one of the most promising paper sizing agent. ASA has many merits, suchas high sizing efficiency, wide adaptability to pH value and pulp and quick development of sizingdegree. However, ASA is normally emulsified with a large amount of cationic starch and a smallamount of surfactant. The massive amount of emulsifier enhances ASAsizing cost, and the use ofsurfactant decreases ASA sizing efficiency. The residual surfactant in white water could cause aseries of problems, which are harmful to the formation of paper sheet and the runnability of papermachine, such as, enhancing the complexity of water circulation system of papermaking,inducing foam, etc.In the dissertation, Laponite, an inorganic nanoparticle, was used to stabilize ASAemulsionsafter being modified by alanine. The modification of Laponite by alanine alters the surfaceproperties of Laponite and promotes the adsorption of Laponite at ASA-water interface. TheLaponite particles that adsorbed at the ASA-water interface construct a strong and dense filmaround ASA droplets, which separates the ASA droplets from direct contacting with water, thusthe ASA hydrolysis was significantly prevented. As a consequence, an environmentally friendlystable ASA Pickering emulsion with high sizing efficiency was developed. The main researchcontents, methods and conclusions of the dissertation can be summarized as follows:(1) By analyzing the variations of surface charge properties of alanine modified Laponite,which were detected by a particle charge detector (Mütek PCD-03) and a Zeta potential analyzer(Malvern Zetasizer Nano ZS90), the aggregation of Laponite particles, which were studied bymeans of particle size and turbidity measurements, and the pH value of Laponite aqueousdispersion with alanine charge level, it is reasonable to presume that the alanine molecules atthe Laponite particle surfaces constitute a multi-layer adsorption.(2) The interfacial tension between ASA and aqueous dispersions of Laponite oralanine-modified Laponite was determined by the du Noüy ring method using an automaticinterfacial tensiometer. The results show that the interfacial tension decreases with theconcentrations of Laponite and alanine. By the strong adsorption of alanine modified Laponite atthe ASA-water interface, and the gelling properties of Laponite dispersion with the increase ofalanine concentration, it can be speculated that the adsorbed alanine-modified Laponite particlelayer at the ASA-water interface construct a particle surface-surface binding structure or Laponite gel structure. All of the two structures could separate ASA from water, and thus the hydrolysisreaction ofASAwas prevented.(3) The effect of emulsification conditions on emulsion properties, such as, emulsionviscosity, conductivity, mean droplet diameter and droplet distribution, were investigated. Whenthe ASA volume fraction was less than50%, stable ASA-in-water Pickering emulsion wasobtained at emulsification speed of12000rpm, and emulsification time of3min. The emulsionstabilized by0.6%Laponite which was modified with1mmol/g of alanine has medium viscosity,narrow droplet distribution, small mean droplet diameter, and good stability against coalescencewithin24h.(4) Because ASA is prone to hydrolysis, the properties of ASA Pickering emulsion arechanged with storage time. The viscosity, conductivity and mean droplet diameter are increased,while the droplet size distribution becomes wider with increasing the storage time. The emulsionstabilized by Laponite modified with1mmol/g of alanine has good emulsion stability againstcoalescence and high hydrolysis resistance. Combining Laponite adsorption feature atASA-water planar interface and characteristics of Laponite aqueous dispersion, we speculatedthat the Laponite layer around ASA droplet constructed a strong compacted Laponite gelstructure. ASA is preferably encapsulated in the Laponite gel structure, the coalescence betweenASAdroplets decrease andASAhydrolysis is hindered.(5) The surface charge of ASA droplet in ASA Pickering emulsion stabilized by Laponite isquite opposite to that of ASA emulsion stabilized by cationic starch and surfactant, thus, theretention and spreading of ASA droplet on fibers have discrepancy. The effects of papermakingconditions, such as stock pH value, aluminum sulfate, retention system, on sizing efficiency wereinvestigated, and the results could be used to direct the application of ASAPickering emulsion inpapermaking sizing. The sizing degree of paper were tested by penetration method. Results showthat ASA emulsion has high sizing-efficiency when the pH value of the stock is ranged in5-10,the addition of aluminum sulfate favors sizing, and suitable retention system contributes to thesizing degree development. The effect of Laponite concentration and alanine concentration usedin ASA Pickering emulsion on sizing efficiency were also investigated in the dissertation. Theresults show that the sizing degree of handsheets increases with increasing Laponiteconcentration in ASAPickering emulsion, and the presence of alanine enhances the sizing degreeof handsheets. ASA emulsion stabilized by alanine-modified Laponite with an alanine chargelevel of1mmol/g has the highest sizing efficiency, and the sizing efficiency is less affected bystorage time even after the emulsion is stored for3h. The sizing degree of handsheets sized byalanine-modified Laponite stabilized ASA emulsion is hardly affected by the ASA volumefraction unless it is higher than50%. When the ASA volume fraction reaches60%, the sizingdegree decreases significantly.