The Synthesis And Characterization Of Modified PPTA And The Research Of Spinning Process

Poly-p-phenylene diamine terephthalamide(referred to as PPTA)fibers,also known as aramid 1414 in China,are often called high-performance organic material due to their excellent thermal and mechanical properties,which are mainly determined by the amide bond and the aromatic structure of macromolecular backbone.As a result,their existence makes the molecule chain rigid-rods and can bind each other by the hydrogen bond.However,the high melting point and the high glass transition temperature(Tg)along with their bad solubility in various organic solvents,limit their widespread usage only to liquid crystal spun in concentrated sulfuric acid.While low temperature polycondensation solution method is a mature way for industrial production,by introducing ether bond,methylene or the third or fourth monomer with large side chain group into the aromatic polyamide,we can increase the solubility and moldability of the aromatic polyamide,so that the solution can be directly spun in organic solvent,which is a way to expand its application field.In this paper,the 4,4'-diaminodiphenyl ether(4,4'-ODA)is chosen for the third monmer and is conducted co-condensation reaction with p-phenylenediamine(PDA)and terephthaloyl chloride(TPC)at the low temperature NMP-LiCl/CaCl2 solution system.And then the impacts of different monmer ratio on the polymers forms and viscosity have been discussed along with the effects of the molar concentration of monmer,reaction time,TPC feeding times,reaction temperature,the amount of pyridine,the amount of co-solvent,chloride/diamine ratio and other factors on the relative molecular weight of the polymers.Through a lot of cross-comparison experiments,this paper found the optimal reaction conditions for wet spinning:a monomer ratio of 25%ODA,25%PDA,50%TPC,a monomer molar concentration of 0.3mol/L,reaction time of 40-50min by feeding TPC by three times,temperature at 5?,LiCl(1.6g/100ml),amount of pyridine(2.5ml/100ml),chloride/diamine molar ratio of 1.02.With these conditions,the spinning dope with a viscosity up to 3.81 can be prepared.The structure and properties of polymers were characterized and analyzed by infrared spectroscopy,elemental analysis,thermal analysis,X-ray diffraction and solubility tests.From the FI-IR,we learn that the peak of-O-bond will enhance with the increasing amount of 4,4'-ODA,illustrating the fact that the 4,4'-ODA is involved in the copolymerization reaction.The elemental analysis showed the difference of C,H,N between the self-made modified PPTA,PPTA and Technora.Thermal gravimetric analysis showed the PPTA with ODA structure still has superior thermal performance both in the air and nitrogen atmosphere.The 5%weight loss,10%weight loss and the maximum weight loss temperature are only slightly lower than original PPTA,but they decrease with the increasing amount of ODA.X-ray diffraction results indicated that the crystallinity of polymer decreased with the introduction of ODA structure,but the surface of the amorphous region increased.On the other hand,the solubility tests in many organic solvents showed the solubility of copolymers gets better with the increasing amount of ODA structure,and can even be dissolved in NMP/LiCl solvent system at room temperature when with a molratio of 25%ODA.Through the rheological test for modified PPTA in the NMP system,the copolymer solution with 4,4'-ODA is a kind of typical shear thinning fluid.The apparent viscosity of the slurry decreases with increasing temperature but increases with the rising level of concentration.The solution stability test results showed that the copolymer solution has a very good stability both at room temperature and at the temperature of 60? almost without degradation and can be in long-term storage without deterioration.By taking coagulation bath with NMP/LiCl/H2O,we can get the newborn fiber which has good mechanical properties and stability through wet spinning of liquid containing 25%ODA.The experiment shows that while the strength of as-spun fibers increased with the liquid's increasing inherent viscosity and also with the increase of tensile strength,it decreased with the increasing coagulation bath temperature.But the elongation at break had no significant links with the above factors.We can get the optimum strength fibers in the coagulation bath with 10%NMP.By scanning electron microscopy,the original fibers through wet spun have no obvious holes and defects,but the only regret is that fibers' surface made from higher inherent viscosity are rougher.The original liquid with lower viscosity shows good fluidity at 60?,so the fibers' surface is relatively smooth.Because the mechanical properties of homemade fibers are weaker than the foreign products,so the study of improving the mechanical properties by hot tensile will continue by others in our group.