Study On The Effect And Mechanism Of Pre-flocculation Of Alkyl Ketene Dimer On Paper Water Resistance

With the development of neutral sizing in the papermaking industry,alkyl ketene dimers（AKD）have been widely used in a variety of neutral and alkaline sizing papermaking technologies.Precipitated calcium carbonate（PCC）has become the most widely used raw material in the paper industry besides fiber due to its ability to reduce costs and improve paper performance.However,PCC particles have a large specific surface area,which is easier to adsorb AKD and reduce the retention of AKD on the fiber,and PCC is easy to promote AKD hydrolysis and make it invalid,which reduces the sizing efficiency.Therefore,how to maintain the sizing efficiency of AKD is a difficult problem to be solved urgently in the current paper industry.This subject uses papermaking wet end multi-agents to co-preflocculate and modify AKD and PCC on-line,study the formation rules and characteristics of AKD agglomerates,and demonstrate the essence of co-preflocculation to improve the sizing efficiency of AKD.The influence of pre-flocculation system on mechanical properties and optical properties of paper.Firstly,Cationic polyacrylamide（CPAM）and bentonite dual retention systems were used for pre-flocculation and filling,and the effects of the four PCC flocculation processes on paper properties and filler retention were compared.The results show that the larger flocs reduce the bonding resistance between the fibers and reduce the light scattering area,so the mechanical properties of the paper are improved and the optical properties are reduced.At the same time,the uniformity index and air permeability of the paper also decrease.AKD is added to the slurry in advance,and a better sizing degree and filler retention rate can be obtained when the pre-flocculation process of[PCC-CPAM-Cationic starch（CS）-bentonite]is used.Secondly,the effects of three AKD pre-flocculation processes on the Cobb₆₀value and filler retention were compared.The changes of AKD floc particle size,AKD floc particle strength and other indicators during the flocculation process were analyzed.The results show that after AKD flocculation and blending with PCC,processes A-f P{fiber+[AKD-bentonite-CS-CPAM-PCC]}and B-f P{fiber+[AKD-CS-bentonite-CPAM-PCC]}ensure the retention of filler while further improving the sizing effect of paper,while the sizing effect of process C-f P{fiber+[AKD-bentonite-CPAM-CS-PCC]}is poor.The analysis found that process A and B had better flocculation effect,the size distribution of the formed flocs was more concentrated,the particle uniformity was better,and the floc strength was higher.Moreover,AKD adsorbed by fibers in process A and B was more than that in C,the sizing effect of the hand-made sheet was better.Finally,a new multi-component co-flocculation method was explored,in which AKD and PCC were first flocculated separately and then blended.The results show that,compared with the non-flocculation process L{fiber+AKD+bentonite+CPAM+CS+PCC},the retention rate of fillers in the two processes M{fiber+[AKD-bentonite-CPAM]+[PCC-CS]}and N{fiber+[（AKD-Bentonite-CPAM）+（PCC-CS）]}is greatly improved,but the sizing effect is worse.Furthermore,by increasing the amount of CS added,increasing the particle size of PCC flocs,reducing the specific surface area,and reducing the amount of PCC adsorbed to AKD,the Cobb₆₀values of processes M and N were continuously reduced,and the sizing effect was continuously improved.At the same time,the mechanical properties of the three processes had all been improved,and the filler adhesion coefficient had gradually increased.