Hydrophobically Modified Fillers Used To Size Papers

Sizing provides suitable water resistance for paper while filling provides suitable appearance, printability, optical properties and lowers papermaking cost. However, both sizing and filling can damage paper strength. This research tried to prepare hydrophobically-modified fillers that combined fillers with sizing agents to lower their adverse effects on paper strength. Styrene-acrylic latex shows good film-forming and hydrophobic property, it was first used to modifiy talc powder and sericite. It is discovered that talc powder adsorbs more styrene-acrylic latex than sericite and the modified talc powder shows higher sizing effect than the modified sericite. However, both of them can not provide adequate water resistance for paper. Accordingly talc powder and sericite were modified by paraffin wax and used to size paper. The results indicate that paraffin wax modified talc and sericite fillers can be used as efficient sizing agents at an addition level of 30% based on oven-dry pulp. The talc powder adsorbs more paraffin wax and shows higher sizing efficiency when it is modified by paraffin wax than sericite powder. The adsorption efficiency of paraffin wax on fillers is improved with increasing temperature, reaction time and stirring speed. The incorporation of paraffin wax with talc powder reduces the paper strength losses caused by the interruption of talc filler and paraffin wax on fiber bonding while does not decrease the water resistance of paper.Seeing that paraffin wax modified fillers could provide adequate sizing effect, talc powder was further modified by AKD and used to size paper. The results show that the AKD modified talc powder displays higher sizing effect at the same addition levels when higher mass ratio of AKD is used on the modification process. The adsorption of AKD on talc powder does not hurt the sizing efficiency of AKD, but improve the tensile strength of the sized paper. When AKD modified talc powder is used to size paper, the optimal pH value of pulp is 8.0, which is just same as conventional AKD emulsions. Paper sized by AKD modified talc powder loses some of its water resistance along with time. The optimal modification parameters including modification temperature, stirring speed, stirring time and modification pH value are 60℃, 8000rpm, 5min and 6, respectively. At the same time, the modification process and sizing application of AKD modified sericite was also studied. The optimal modification conditions are same as that of AKD modified talc powder. The largest mass ratio of AKD to sericite is 1:15 while that AKD to talc powder is 1:5 when all of the AKD are adsorbed. The papesr sized by AKD modified sericite hardly find any sizing reverse phenomena when the sericite is modified under weak acidic conditions. The stability of AKD adsorbed on sericite is higher than that on talc powder.The modification and sizing mechanisms of AKD modified fillers were analyzed by means of FTIR, XPS and contact angle measurement. The results indicate that AKD is deposited on talc powder and sericite mainly as an amorphous form by physical adsorption. The hydrolysis of the AKD deposited on sericite is slower than that on talc powder when the modified fillers stand for a long time as their water suspension. The AKD on sericite reacts with the active groups of sericite surface through its functional group of lactone ring resulting in a chemical combination. The AKD modified fillers show high hydrophobicity and provide appropriate hydrophobic properties for paper by uniform distribuation in their sized paper. Some of AKD may react with cellulose hydroxyl groups during the drying process of paper. After the paper is finished, small amount of AKD desorbed from the filler surface with the extension of time resulting in the loss of paper sizing degree. However, with further postpone of storing time, the desorbed AKD may slowly migrate to fiber surface and react with fiber. Therefore, the sizing degree of paper shows a slight increase. When the migration of AKD from filler surface is balanced by the reaction of AKD with fiber, the sizing degree of paper tends to sustain at a stable value.The surface sizing performance of the AKD modified filler when used together with oxidized starch and styrene-acrylic latex was investigated since more and more internal sizing was replaced by surface sizing for paperboard. The results show that the best mass ratio of the AKD modified filler to oxidized starch as well as styrene-acrylic latex is 1:4:1. The paper sizing degree can reach 60s when the paper was sized on both sides. The tensile strength of paper can be significantly improved. Tearing resistance and folding endurance can also be improved when the paper was surface-sized on both sides by the mixture of AKD modified filler, oxidized starch and styrene-acrylic latex.