Research On The Retention Behaviors Of Latex In Non-asbestos Sheets

With the rapid development of synthetic latex and the increasing requirements of paper-based material, latex has gained a large application in paper industry. The addition of latex to the pulp could render the paper many properties, such as solvent resistance, heat resistance and abrasion resistance and so on.Non-asbestos sheets are usually prepared with latex acting as the binder and fibers as the skeleton. The retention of latex in the sheets determines the reinforcing effect of fibers, which is greatly related to the strength and density of non-asbestos sheets. In addition, latex render the sheets flexible and improve the solvent resistance, oil resistance and abrasion resistance of non-asbestos sheets greatly. However, because of the limits of preparation process, it is difficult to reach high density when preparing the non-asbestos sheets. In this sense, the retention of latex in non-asbestos sheets becomes very crucial. In this work, plant fibers, mineral fibers, organic fibers were used as the fiber skeleton, particles of different sizes were introduced into the sheets as the fillers, nitrile latex was applied as the binder to prepare the non-asbestos fiber sheets. The retention behaviors of latex were then studied in this paper.UV-visible absorption spectrum was selected to detect the latex content of white water. The influence of residual fillers and fibers on the accuracy of detection was tested in this work. By standing or centrifugation, the suspended particles in the white water could be eliminated in the experiments, thus declining greatly the positive deviation of Lambert-Beer law. The accuracy to detect the latex content of white water was therefore improved and the relationship between the content of nitrile latex and the absorbance was established in this work.The effects of different retention aids were compared in the work. The results showed that CPAM1200 could enhance the retention of nitrile latex most effectively and the flocculation was small but even stronger, which leaded to faster filtration speed. Moreover, when CPAM1200 was used as the retention aid, the tensile strength of non-asbestos was higher than that of the sheets with the other 2 agents.The retention model was established through the relationship between the content of nitrile latex in white water and the retention amount of nitrile latex. According to the equation, the adsorption rate of nitrile latex under the influence of retention aids and the maximum retention amount in the material could be quantified. The model showed that when CPAM1200 was used, the absorbency rate of nitrile latex was fastest. From the model, the value of N_max（based on the dry pulp） was 0.4664. Comparing the value of Ns and N_max, we found that when the Ns got closer to N_max, the tensile strength of fibers sheets were higher. When the addition of nitrile latex was set as 17.15%, Ns was a little bit higher than N_max and the tensile strength was highest in the present formulation, which showed that fibers and the fillers all provided “potential binding site” to facilitate the bonding of the components within the pulp system.Using bromine-labeled method and spectrum analysis, the distribution of nitrile latex in the non-asbestos sheets was analyzed, which helped to compare and then explore why the non-asbestos sheets showed different tensile strength when different methods were used to applied nitrile latex. The distribution of bromine was dense and uniform in both the surface and Z direction of impregnated sheets, which showed that nitrile latex distributed uniformly both in the surface and in the Z direction of impregnated sheets. However, the nitrile latex only distributed in the Z direction of the sheets when it was added in the wet end.