| Paper industry is one of the most important components of national economy system in China.Recently,paper industry has been rapidly developed,and related raw materials,product properties,production cost and environment requirement also changed,such as increase use of recycled paper,upgrading of paper surface properties,raising of production cost,and so on.In order to solve the problems mentioned above,application of paper chemicals had been one of the important methods.Due to the advangtages of suiting paper various species, improving paper surface obviously,decreasing paper product cost and reduce the environment pollution from paper process,surface sizing agent had been used to sovle these problems as one of the most efficient chemicals in papermaking.In order to develop environment friendly soap-free surface sizing agent with excellent performance and low cost,styrene-acrylate copolymer based styrene(St),butyl acrylate(BA),acrylic acid(AA) and so on was prepared by introducing sodium vinyl sulfonate(HS-1) into emulsion polymerization.The core-shell type soap-free latex was obtained by charging comonomers continuously and designing the component of core and shell layer.The optimum conditions were chosen as m(St):m(BA)=42:47,w(MMA)=4%,w(AA)=3%, w(HS-1)=3%,w(B130)=5%,w(MA)=1%,m(core):m(shell)=2:8,temperature at 78℃,w(APS)=0.5%,charging time of 2.5h,total reaction time of 6h.The predesigned molecular structure and shape of the optimum product was obtained by analyzing its IR spectrum,DSC graph and TEM photo.Its particle average size by volume,surface tension and average molecular weight was respectively 280nm,50.588mN/m and 229338.Good effect was obtained as using pilot product SSTOP in laboratory and paper mill.The result charged with 0.78kg/t of SSTOP in art coated base paper showed that Cobb value of face and back side of the paper decreased by 28.6%and 40.8%respectively,and surface strength,tensile index and tear strength increased by 14.2%,7.4%and 16.7%in turn,compared to that of application of single surface sizing starch.The result in white paperboard showed that Cobb value of face and back side of paperboard with 0.15kg/t of SSTOP were respectively decreased to 26.5g/m2 and 31.5g/m2.At the same condition,the sizing effect of SSTOP was equal to that of foreign product BK-350,better than that of domestic product BJ-25 and DZ-10.The result with 0.75kg/t of SSTOP in offset printing paper showed that Cobb value and surface strength of face and back side of paper were 22g/m2,24g/m2,2.9m/s and 2.3m/s respectively.At the same application condition,Cobb value of face and back side of paper sized with SSTOP decreased by 10.2%and 14.2%,and surface strength increased by 20.8%and 21.0%,compared to that of paper sized with DZ-10.Cationic surface sizing agent was prepared on the basis of St,BA and methacryloxyethyltrimethyl ammonium chloride(CM) by introducing a macromolecule surfactant(EM) made in our lab into the soap-free emulsion copolymerization.Critical micelle concentration of EM was set up at 12g/L.The reaction dynamics equation of cationic soap-free emulsion polymerization was obtained as Rpâˆ[EM]0.34[APS]0.45[CM]0.77,and the apparent activation energy was 64.3kJ.mo1-1.The optimum conditions were given as m(St):m(BA)=117:100, w(CM)=3.4%,w(EM)=8%,w(APS)=0.5%,reaction time of 4h.The predesigned molecular structure and morphology of the optimum sample was obtained by analyzing its IR spectrum,ATR-IR spectrum,DSC graph and TEM photo.Its particle average size by volume,surface tension and Zeta potential was 77.4nm, 46.866mN/m and+30mv respectively.Good mathematic model based on preparation of cationic soap-free surface sizing agent was built by using the software of MODDE 7.Good effect was obtained as using pilot product CPSS-1 in laboratory and paper mill.The result in white paperboard showed that Cobb value of back side of paperboard without any internal sizing agent was decreased to 44g/m2 as charging CPSS-1 with 0.6kg/t,which was better than that of foreign product. The result in corrugated paper showed that Cobb value of face side of paper was 42g/m2,ring crush index of CD was 7.8m/s,breaking length of MD was 4.3km, burst index was 2.2kPa.m2/g and fold of CD was 14.The water absorbency(y) of styrene-acrylate based copolymer film was proportion to the Cobb value(x) of sized paper with the equation abbreviated as y=3.49561n(x)+10.504 at the experimental conditions.A simple way to evaluate the sizing effect of styrene-acrylate based copolymer was obtained as follows: better sizing effect was obtained as the water absorbency of copolymer film was less.As glass transition temperature(Tg) of copolymer was varied from 7.95℃to 33.91℃,relationship between Cobb value of sized paper and Tg of copolymer film was concluded as y(Cobb value)=-1.16521n(Tg)+18.878,and relationship between surface strength of sized paper and Tg of copolymer film was deducted as y(surface strength)=-0.32881n(Tg)+4.31.Relationship between product surface tension and foam volume in surface sizing liquid was given as y(foam volume)=1.1389(surface tension)2-114.01x+2878.6.For paper unsized or sized by surface sizing agent,the analysis of contact angle showed that application of surface sizing agent made initial contact angle of water in paper surface larger,and limited water drop penetrate into fibers of paper,which resulted in the improvement of water resistance of paper;The analysis of DSC-TGA showed that hydrogen bond or covalent bond among CPSS-1,oxidized starch(OS) and paper fibers were formed,leading to the improvement of the stability of paper in hot atmosphere and transition temperature of CPSS-1 in paper;The analysis of XPS showed that there existed the uniform film composed of CPSS-1 and OS,its hydrophilic group bonded to paper fibers but its hydrophobic group moved to the top paper surface,and new covalent bond and hydrogen bond were also formed by charging CPSS-1,all of which contributed to the improvement of water resistance and surface strength of paper;The analysis of AFM showed that good compatibility between soft phase and hard phase of OS and CPSS-1 was obtained,the hydrogen bond was formed and uniform distribution of CPSS-1 and OS in paper surface was observed,as a result,smoothness of paper surface increased obviously;The analysis of SEM and CLSM showed that network structure was formed by absorbing CPSS-1 and OS into paper fibers,bond among paper fibers became tighter,number of cavity in paper surface was less and uniformity of paper surface was enhanced,all of which improved the properties of paper surface.
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