Emulsification And Microencalpsulation Of Cellulose-reactive Sizing Agent With Microparticles

Employing solid particles in stead of conventional emulsifiers to stabilize emulsions show many advantages such as enhancing emulsion stability to coalescence, preparing emulsion high discontinuous phase volume fraction and eliminating or decreasing the adverse effects of surfactants. In this paper, solid particles including Laponite, aluminum polysulfate (PAS) and cationic soap-free polystyrene-acrylate microsphere were employed to serve as stabilizers for alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA) emulsions, and their emulsification effectiveness were investigated. To protect ASA from hydrolysis, some exploratory researches were conducted to fabricate ASA capsules via such technique as locking colloid particles that adsorbed on ASA droplets by sintering or sintering agent, coating sodium alginate stabilized ASA droplet by gelation or polyelectrolyte deposition at the interface.It was found in the research that AKD can not be stabilized by Laponite solely and the performance of the particle in AKD emulsification can be improved by chitosan and n-propylamine. Modification of Laponite with n-propylamine favored the preparation of AKD dispersions with higher creaming stability and smaller particle size when Laponite was used as the stabilizer of the AKD dispersion. By adsorbing onto the particle surface through electrostatic interactions, the n-propylamine reduced the interface tension and contact angle between AKD wax and n-propylamine modified Laponite aqueous dispersion. The highest stabilization performance of the n-propylamine modified Laponite on AKD dispersion can be achieved at 10% of n-propylamine based on the mass of Laponite. The close-packed layer of Laponite particles on the surface of AKD droplet can be proved by Laser Scanning Confocal Microscope. Laponite-stabilized AKD sizing emulsions featuring average particle sizes between 3-6μm and AKD contents of 20~25% were obtained by optimizing the composition of the initial colloidal suspension, such as particle concentration, the pH of the aqueous dispersion of the modified Laponite, the temperature of melted AKD and the aqueous phase, stirring speed and time to 3~4%, 6~7, 65℃/ 75℃, 8000 ~11000 r/min and 3~5 min, respectively. Furthermore, the n-propylamine modified Laponite stabilized AKD dispersion provides more controllable sizing response and higher sizing efficiency than cationic starch stabilized AKD dispersions.ASA could be well emulsified into a stable O/W emulsion with PAS at the charge level of 0.25% and the mass ratio of ASA to water in the range of 3:2 to 1:3. The creaming stability of ASA emulsion did not improved significantly with the increase of agitation intensity such as stirring speed and stirring time. Moreover, the increase of PAS to ASA mass fraction resulted in a decrease in emulsion volume fraction. Cationic soap-free copolymer microsphere was synthesized at the condition of St/BA/MBA ratio, DMC and AM were 10/5/3, 15% and 3% separately, and the obtained particle was smaller than 200 nm in diameter. This microparticle can stabilize a N-dodecenyl succinic anhydride, a model ASA, emulsion with droplet less than 4μm while can not give a stable ASA emulsion.As refer to polystyrene-acrylate microsphere stabilized ASA emulsion, the way of lightly sintering the particles by heating or by urea-formaldehyde bindering were proved too violent to encapsulate ASA. Chitosan can be used as a sintering agent of negatively charged montmorillonite particles that adsorbed on ASA droplet surface to prepare ASA emulsions with high sizing performance, especially at charge level of 0.125%. However, the precipitation of chitosan by ammonia greatly worsened the sizing performance of the ASA emulsion. Moreover, PAS and low molecular weight chitosan can perform as efficient film-forming agents by adsorbing on the surface of ASA droplet stabilized by alginate. ASA emulsion can keep stable when the dosage of PAS or chitosan is less than 30%, and ASA hydrolysis rate appeared slow down. However, the sizing efficiency decreases rapidly, indicating that the hydrolysis of ASA is difficult to control by conventional microencapsulation.