| Polyimide(PI)fiber has some excellent properties of radialization-resistance,heat-resistance,high strength,insulation due to its rigid structure of molecular chain that is increasingly being used in aerospace,filtration and purification,electronic information and other fields.But its strength is always hard to improve in industry production.Take wet spun P86 fiber as an example,though it is heat-resistant,the mechanical property isn't ideal.At present,studies on characteristics of the molecular structure of PI and improving PI fiber's strength are advanced development and important research's trends.In practical production process,one-step method spinning fiber maintains a relatively high mechanical property however the toxic solvent not only does harm to both health and environment but also hard to be recycled,furthermore,this method may cost more;two-step method spinning has many controlled conditions and forms fiber smoothly,but the internal defects problem should be solved and the process of preparing a high strength polyimide fiber still needs to be improved.Polyamide acid(PAA)solution which was copolymerized with special modification third monomer was formed into fiber by wet spinning method,then the PI fiber was prepared by thermal imidization and hot-stretching from PAA fiber,at last,the PI fiber with good performace was obtained.In the PAA spinning process,this kind of solution with high concentration has a certain significance and improvement,and for industry production and practical application,it's also a breakthrough.The polyamic acid spinning solution of 20%polymer content was polymerized by ODA,TMmPDA,PMDA with the solvent of dimethylacetamide(DMAc),its viscosity decreased while the temperature increased,it shows a good fluidity and is able to be spun.After testing the basic properties of PI film,the results turn that no matter how long the storage time is,its film is hydrophobic,good insulator,low water absorption,a certain resistance to UV effects,and excellent mechanical property.According to the discussion,the PAA spinning solution has spinnablity.When preparing as-spun PAA fiber by wet spinning,the factors of process and conditions were studied.Coagulation values,ternary phase diagram and fiber morphology were analysized comprehensively,the most appropriate coagulation bath is DMAc/water(20:80)at room temperature.Besides the consideration of safety and cost,this DMAc/water bath doesn't congulate too fast to form skin-core structure and defects but fast enough to form and lead fiber into good perfomace.In addition,the washing condition of temperature and time were indentified as 60? and 10-30 seconds,the shiny drawable PAA fiber was obtained.After preparing the polyamic acid fiber,the dynamics of thermal imidization process was studied by thermogravimetry(TG)and the modified polyimide fiber was characterized by Fourier transform infrared spectrosocopy(FTIR),fiber strength test,etc.The PAA fiber was heated at 300? for 1 hour,then thermal drawed with load,the heavier the load carries,the higher the strength becomes.The experimental results showed that this kind of modified PAA solution contained a third monomer can be imidized and thermal drawed into a excellent heat-resistant PI fiber whose breaking strength is 4.02cN/dtex.Thermal drawing has a critical influence on the mechanical property of PI fiber. |
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