Study On The Preparation And Structure&Performance Of BTDA-TDI/MDI Ternary Co-polyimide Fibers

Aromatic polyimide fiber with good mechanical properties and excellent thermostability is widely used in atomic energy industry,space industry,environment industry and other important fields.BTDA-TDI/MDI ternary co-polyimide fiber was polycondensated from 3,3'4,4'-benzophenone tetracarboxylic dianhydride(BTDA)and methylphenylene diamine(TDI)/methylene diamine(MDI).Now,the only commercialized product is the P84(?)from the Lenzing Co.Itd.In this article,BTDA-TDI/MDI ternary co-polyimide fiber was prepared by wet-spinning method with the N,N-dimethylacetamide(DMAc)as solvent.The influence of the relative molecular mass of polymer,concentration of the solution and the temperature on the rheological properties of the BTDA-TDI/MDI ternary co-polyimide/DMAc were studied,as the reference for the choice of spinning conditions.This article also studied the effect of coagulation bath concentration and temperature,jet stretch ralio on the structure and properties of as-spun fiber with the DMAc/H2O as the coagulant.Lastly,the impact of the temperature,gas medium and the draw ratio in the heat-treatment process on the structure and properties of the fiber,as well as the chemical resistance and the loss of the mechanical properties were studied.The static rheological and dynamic rheological properties of BTDA-TDI/MDI ternary co-polyimide/DMAc spinning solution showed that the system mentioned above was typical pseudoplastic fluid.With the increase of concentration of solution and the relative molecular mass of polymer,the apparent viscosity,activation energy for viscous-fluid,complex viscosity,the loss modulus G" and storage modulus G' all increased,however,non-Newtonian viscous index,critical shear rate and loss angle tan ? decreased.With the increase of temperature,the apparent viscosity,structural viscosity index,complex viscosity,the loss modulus G" and storage modulus G" decreased,while non-Newtonian viscous index and loss angle tan ? increased.With the increase of shear rate(or frequency),the apparent viscosity,complex viscosity,activation energy for viscous-fluid and loss angle tan ? decreased,while the loss modulus G" and storage modulus G' increased.BTDA-TDI/MDI ternary co-polyimide fiber was prepared by wet-spinning method with the DMAc/H2O as the coagulation bath.The results showed that with increasing the concentration of coagulation bath,the cross-section shape of as-spun fibers changed from elliptical shape to circular shape while the thickness of cortex of as-spun fibers decreased along with the intensity and mechanical properties of as-spun fibers increasing.With increasing of the temperature of coagulation bath,the cross-section shape of as-spun fibers changed from elliptical shape to circular shape however the intensity decreased.With increasing of jet stretch ratio,the diameter of as-spun fibers decreased while the intensity and mechanical properties of as-spun fibers increased.The structure of as-spun fibers was imperfect,so the heat-treatment process had a profound effect on the final structure and performance of polyimide fibers.The results of DSC and DMA showed that the glass transition temperature of BTDA-TDI/MDI ternary co-polyimide as-spun fiber was between 320?350?.The results of the heat-treatment process gave follow conclusions:the best heat treatment gas medium was nitrogen atmosphere and the best heat treatment temperature was 350?,the maximum of draw ratio 4 times,the highest break strength reaching to 1.79 cN/dtex.The results also showed that the heat treatment had no change on the chain structure of fibers.The crystallinity,the orientation and the thermostability of fibers increased after the heat treatment.The holes on the surtface of the fibers closed with the escape of the solvent.In dilute acid fibers showed a certain stability,hile the fiber's break strength decreased quickly in alkaline environment.Under high temperature,along wiith the extension of time,the break strength of the fibers gradually reduced and the higher the temperature was,the more obvious the decline was.