| The high strength and high modulus performance of carbon fiber mainly depend on the kind and quality of precursor,technology of pre-oxidation and carbonization. High quality polyacrylonitrile is the main key factors to prepare perfect precursor fiber.There are some difference and shortage on domestic carbon fiber research, especially on high performance PAN polymer and precursor.The qulity of PAN precursor fibre has been the choke point of developing high performance carbon fiber in our country.PAN precursor polymers used for high performance polyacrylonitrile (PAN) precursors can be prepared by copolymerzation of acrylonitrile(AN) with appropriate comonomers.In this paper,we mainly investigated the effect of structure and feed ratio of comonomers on structure and properties of PAN copolymers.Free-radical solution polymerizations of AN with itaconic acid(IA), methacrylate(MA),monomethy itaconate(MMIA) were carried out.The effect of feed ratio,concentration of comonmer,temperature of reaction and concentration of initiator on coplymerization were studied.The conversion of the polymerization and the relative average molecular weight of products were determined by weighting and Ubbelondhe viscosimeter approaches,respectively.It was shown that the polymerization yeild increases with the increase of reaction temperature, concentration of monomer,concentration of initiator,but decreases with the increasement of comonomer content.The relative molecular weight of the copolymers decreases with the increase of reaction temperature,concentration of initiator and the content of comonomer,but increases with the increasement of monomer concentration.The composition and sequence distribution of Poly(acrylonitrile-co-itaconic acid) were simulated by Monte Carlo method.It was shown that the sequence distribution can be controlled by varying feed ratio,polymerization temperature and time.The structure and properties of PAN homopolymer and different copolymers were studied by DSC,TG and FTIR measurements.The component of copolymers were mesured by FTIR spectra method.The DSC spectra were used to investigate the thermal properties of PAN copolymers.It can been seen from the results of DSC patterns that incorporation of MMIA and IA results in the decrease of initiation temperature and broadened exothermic peak during cyclization reaction of precursors, but incorporation of MA into PAN retards the cyslization reaction of precursors. Incorporation of MMIA,IA,MA made the degradation temperature of polymer increase.The char residue increases with the increasement of MMIA and IA content.The acromatic index is defined and it changes with varying treatment time and termperature,which is calculated based on the change of FTIR charateristic peaks.It is found that the cyclization reaction of PAN homopolymer is slower than that of copolymer,and it is difficult to form ladder aromatic stucture for homopolymer, hinting that the incorporation of MMIA into PAN is very effective for increase of the cyclization reaction rate.For example,the acomatic index of P(AN-co-MMIA) is higher than that of PAN homopolymer after heat treatment for 4 h in air at 220℃.To study the spinability of spinning dope,rheological behavior of PAN/DMSO solutions was evaluated by Germanic HAAKE Company's RS1 type cone-and-plate rheometer.The results shows that,With the higher molecular weight of PAN,the change of apparent viscosity of PAN solution is more sensitive to shear rate.When the molecular of PAN copolymer is 10.83×10~4,the structural visvosity index is 2.98. Meanwhile,it was also found that the apparent viscosity decreased with the increase of spinning temperature.The spinability of P(AN-co-MA),P(AN-co-MMIA), P(AN-co-IA) spinning dope were studied.Under the condition of same relative average molecular weight and solution concentration,the spinability of P(AN-co-MA) spinning dope is best,and that of P(AN-co-MMIA) spinning dope is between the P(AN-co-MA) and P(AN-co-IA) spinning dope. |
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