Fig.3-9 showed the effect of rosin and wet strength agent on wet tensile strength when other factors were held at 0 level. When rosin was lover than 0 level, wet tensile strength increased with the increase of wet strength agent; When rosin was higher than 0 level, the increase of wet tensile strength became flat with wet strength agent increased, the maximum occurred when wet strength agent was held at 3%, and rosin was held at 0.4%. The reason was that the increase of rosin, affected the adsorption of the fibre to wet strength agent, to a certain extent, reduced the effect of wet strength agent, wet tensile strength would not increase or decrease.

3.4.3 Effect of bauxite and wet strength agent on wet tensile strength

Fig.3-10 showed the effect of bauxite and wet strength agent on wet tensile strength when other factors were held at 0 level. When bauxite was at any level, wet tensile strength gradually increased with the increase of wet strength agent ;When bauxite was lower than 0 level, wet tensile strength increased, When bauxite was higher than 0 level, wet tensile strength decreased, the maximum occurred when wet strength agent was held at 3%, and bauxite was held at 4.5%.The reason was that the increased amount of added bauxite in the slurry system, leaded to adsorption of anionic trash in fibre system, affected the adsorption to the wet strength agent, resulted in decrease of wet tensile strength.