Preparation Of Aramid Fiber Paper By Foam Forming And Its Interface Enhancement

Aramid fiber paper based functional material is widely used in the area of rail transit,aerospace and insulating materials due to its excellent strength,insulation and high temperature resistance properties.However,the hydrophobic nature and long fiber length of aramid fibers make it hard to disperse during the wet forming process.Ultra-low forming consistency is typically employed during aramid paper formation but it can leads to a large amount of water and energy consumption.Therefore,increasing forming consistency and improving fiber dispersion are always pursuing in paper industry.Foam forming is a new forming technology which uses foam as fiber carrier.It was applied to the formation of aramid fiber paper for its advantage in fiber dispersion.In this work,effect of the ratio of chopped fiber and fibrid on the properties of foam and paper was investigated.Then,surfactant dosages and types,mixing speed were optimized so as to improve the characteristics of foam and paper properties.At last,aramid nanofibers were in situ grown in foam-formed aramid paper to strengthen the tensile index and dielectric strength.The main conclusions are as follows:(1)The effect of chopped fiber and fibrid ratio on foam characteristics and paper properties were studied.It was found that foaming height,foam stability and formation index were decreased with increasing the content of fibrids.Besides,the tensile strength would reach a maximum at the ratio of 6:4(fibrid:chopped fiber).Compared with wet-laid paper,the dryness of foam-laid paper gave an increase of 3%-units.Meanwhile,the formation index of foam-laid paper could increase 11.4%when the forming consistency of foam-laid paper was 7 times higher than that of wet-laid paper.(2)The effect of surfactant type,dosage and mixing speed on the properties of foam and paper were studied.Results showed that the formability and foam stability were enhanced with the increase of surfactant concentration(up to critical micelle concentration)and mixing speed.Nonionic surfactant could create a more stable foam system,smaller average bubble size and narrower bubble size distribution compared with other types of surfactant.When tween was used as foaming agent,a narrower bubble size distribution and a higher viscosity were obtained,resulting in an increase of 86.7%in formation index compared with wet-laid paper at a forming consistency of 0.04%.This indicated that the formation consistency of foam forming could be 8 times higher than that of wet-forming.Physical testing showed that the optimization of foam properties could improve the tensile index of foam-laid paper,but it would not be helpful for dielectric strength,which would decrease 20%?30%compared with wet-laid paper.(3)Interface enhancement of foam-laid paper by in situ proton reduction of aramid nanofiber(ANF).Results showed that the optimal precipitation concentration for para-aramid and meta-aramid nanofiber dispersion was 1%and 2%,respectively.Both para-aramid nanofiber and meta-aramid nanofiber exhibited excellent enhancement performance in tensile index and dielectric strength.The tensile index was increased by 45 times while the dielectric strength was increased by 1 time at most.The dielectric strength and tensile index of modified paper were similar to that of hot pressed wet-laid paper,which would be beneficial to shorten papermaking process and reduce energy consumption.