Preparation And Properties Of Poly(P-Phenylene Terephthalamide)Aerogel Fibers

As a new porous material with high porosity and low thermal conductivity,aerogel has become the focus of attention in the field of thermal insulation,and is expected to replace the traditional thermal insulation materials.However,most of the aerogel materials are blocky,and their high porosity leads to poor mechanical properties,so they are difficult to carry out secondary processing,which greatly limits the application of aerogel materials in the field of thermal insulation textiles and clothing.Forming aerogel materials into one-dimensional aerogel fibers not only have all the excellent properties of aerogel,but also have additional flexibility,weavability and so on.It well solves the problem that the blocky aerogel materials are difficult to be used in the field of human wearable thermal insulation and some special scenes.The emergence of aerogel fibers will open up a new way for the design and manufacture of new thermal insulation textiles.Poly(p-phenylene terephthalamide)(PPTA)has excellent thermal stability,good flame retardant and chemical resistance.The preparation of aerogel fibers with PPTA as raw material can give aerogel fibers more excellent properties and broaden the application scenes of aerogel fibers.However,the hydrogen bond between PPTA molecules is strong,which makes it easy to gel during the synthesis process of PPTA.The resulting PPTA polymer is no longer soluble in conventional solvents and its melting point is higher than the decomposition temperature.Strong corrosive solvents such as concentrated sulfuric acid are needed for its reprocessing,which increases the requirements for production equipment and increases the production cost.At present,most PPTA aerogel fibers are prepared by using the nanofibers dispersion solution of PPTA fibers(aramid)as the spinning solution.This method not only depends heavily on the finished aramid fibers,but also requires a long time for the preparation of nanofibers,which seriously limits the industrial production of PPTA aerogel fibers.Therefore,this paper proposed a method to synthesize low concentration PPTA solution in order to slow down its gel speed and timely prepare PPTA aerogel fibers through centrifugal defoaming,wet spinning,freeze-drying and other processes.This method not only avoids the use of concentrated sulfuric acid in the production process,but also makes the process simpler and requires less time.In this paper,the effects of PPTA solution concentration and coagulation bath conditions on the structure and properties of aerogel fibers were studied.On this basis,the hydrophobic modification and phase transition functionalization of the prepared aerogel fibers were carried out to broaden their application field.The specific research contents and results are as follows:(1)Different concentrations of PPTA solution were synthesized,and aerogel fibers were prepared by wet spinning.With the increase of the concentration of PPTA solution,the strength of the aerogel fibers increased,the porosity decreased,and the thermal conductivity of the corresponding aerogel fabrics increased.The lowest thermal conductivity of aerogel fibers fabric prepared in this study is 29.65m W/(m·K).The prepared PPTA aerogel fibers have excellent high temperature resistance.After aging at 300℃for 1 h,the breaking strength of the aerogel fibers only decreased by 14%,and its pore structure did not change significantly.When the temperature of coagulation bath was 45℃and the concentration of coagulation bath was 10%,the aerogel fibers had the best mechanical properties.Under this condition of coagulation bath,the breaking strength of the aerogel fibers prepared with 2%PPTA solution is 11.8 MPa,and the BET specific surface area is 316.80 m~2/g.(2)The prepared PPTA aerogel fibers cannot be directly dried after absorbing water,otherwise the pore structure will shrink and collapse,which seriously limits its practical application scenes,so the surface hydrophobic modification of aerogel fibers was carried out by chemical vapor deposition in this study.After hydrophobic modification,the water contact angle of the aerogel fibers has up to 151°,achieving the superhydrophobic effect.After hydrophobic modification,the initial decomposition temperature of the aerogel fibers is358℃,indicating that the aerogel fibers can be used at high temperature,and the hydrophobic function will not be invalid because of high temperature.(3)The prepared PPTA aerogel fibers have the advantages of high porosity and good adsorbability.In this paper,PPTA/eicosane composite phase change fibers were prepared by filling eicosane as phase change material.The phase change fibers have high phase change latent heat(505.9 J/g)and excellent washing resistance,after washing in warm water containing detergent at 60℃for 20 min,the residual mass is still 98.21%of the original mass,and the latent heat of phase transition still at 495.3 J/g.In addition,the phase change fibers also have excellent acid and alkali corrosion resistance and good cycle stability of rising and cooling.PPTA/eicosane composite phase change fibers have good flexibility even when eicosane is solid,and can be woven into fabrics for thermal management and thermal infrared shielding of the human body.