Research On The Emulsification Of Liquid AKD And Its Application In Surface Sizing

At present,Alkyl ketene dimer(AKD)wax powder was usually used as a sizing agent in the sizing process of papermaking,which was prepared with fatty acid by the modification reaction.The molecular morphology of AKD was the linear structure.As an efficient and inexpensive sizing agent,AKD has been widely used in paper mills,and the emulsification and application technology were also increasingly perfect.However,it still had some problems such as easy hydrolysis,sizing hysteresis,easy to slip with heavy sizing.The new AKD sizing agent was studied in the following aspects: polymer emulsifier was used to replace traditional cationic starch emulsifier to improve the reaction speed and sizing efficiency;the liquid AKD was used to replace AKD wax powder and the molecular structure was changed from linear chain to the space form of branched chain mesh.However,the emulsification and application of liquid AKD for a new paper sizing agent have not been studied at home and abroad.Firstly,special liquid AKD polymer emulsifier was prepared by aqueous solution free radical copolymerization with monomers including styrene(St),butyl acrylate(BA),tert butyl acrylate(t BA),acrylamide(AM)and dimethylaminoethyl methacrylate(DM).The effect of the monomers ratio on emulsifier appearance,property,the stability and the sizing performance on liquid AKD emulsion was studied.The influence of reaction condition on the synthesis rate,viscosity of polymer emulsifier,and the stability and the sizing performance of the liquid AKD emulsion was also investigated.The results showed that the monomers were copolymerized and reacted completely.Furthermore,the optimal monomer ratio was as follows: w(St)was 5%,w(BA)was 6%,w(t BA)was 4%,w(AM)was 40%,w(DM)was 45%.The optimal reaction conditions were: 75℃ as reaction temperature,2.5h as reaction time,0.3% as initiator dosage(relative to total monomers quality),4 as reaction pH,100r/min as reaction speed.The indexes of special liquid AKD polymer emulsifier were as follows: solid content was 20%,viscosity was 450mpa·s,pH was 4,the number average molecular weight was 13505,the weight average molecular weight was 45880,and the dispersion degree of molecular weight was uniform.Then,the effect of formulation and technology on viscosity,dispersion,stability and sizing performance of liquid AKD emulsion were optimized by the single factor experiment.Liquid AKD emulsion was characterized by particle size,Zeta potential,transmission and scanning electron microscope(TEM).The results indicated that the optimal formulation and technology were as follows: emulsifying temperature was 45℃,emulsifying time was 15 min,emulsifying speed was 11000r/min,emulsifier dosage(relative to liquid AKD quality)was 20%.The average particle size of liquid AKD emulsion was 500 nm and the particle size distribution was uniform.The Zeta potential was +29.16 mV and the emulsion had good stability.The latex particle was spherical,well dispersed and the system was stable.Moreover,the morphology of emulsion particles was spherical.After sizing,the surface of the paper was more uniform,the gap between the fibers was less,and the paper was smooth.Compared with the commercially available AKD surface sizing agent,the self-made liquid AKD emulsion had the advantages of fast curing speed,low curing temperature and good sizing effect.Finally,the application effect of compound surface sizing agent was studied.The mixture of liquid AKD emulsion and other surface sizing agent was applied to surface sizing.The result showed that the polymer emulsifier had faster curing speed and better sizing performance than traditional cationic starch emulsifier.When the ratio of the liquid AKD emulsion to the solid AKD emulsion was 3:7(g/g),the cost performance was the highest and the sizing effect was significantly improved.When the ratio of styrene acrylic emulsion to liquid AKD emulsion was 2:8(g/g),Cobb60(g/m2)of the corrugated paper dropped from 100 to 27.0;the longitudinal breaking length increased by 8.91% and the transverse ring crush index increased by 4.11%.When the ratio of styrene acrylic emulsion to solid AKD emulsion was 2:8(g/g),Cobb60(g/m2)of the corrugated paper dropped from 100 to 29.1;the longitudinal breaking length increased by 6.22% and the transverse ring crush index increased by 2.91%.