Study On The Synthesis And Inhibition Of Modified Polyaspartic-acid/salt(PASP) Using Ethanediamine And Maleic Anhydride

Polyaspartic acid saltis a kind of multi-functional polymer materials with good biodegradable and non-toxic properties,as a green scale inhibitor,the sales volume of which is growing rapidly in recent years through all of the world.PASP can be used widly in water treatment,daily chemicals,agriculture and medical field owing to its polar group of-COOH and-NHCO-in the molecular structure.There are two main routes for the synthesis of PASP,one is L-aspartic as the raw material,which can be used to synthesize PSI by direct thermal polymerization;and the other route is maleic anhydride as the raw material,which can react with NH3 to produce intermediate and then to prepare PSI by direct thermal polymerization.PASP can be obtained by the hydrolysis of PSI under alkaline condition.In this paper,the synthesis mechanism and process of PASP-Na using maleic anhydride and ammonia water as the raw materials were investigated firstly.In particularly,the effects of molar ratio of maleic anhydride and ammonia,reaction time,reaction temperature and the amount of alkali on the molecular weight were discussed in detail.On the molecular weight of the factorssuch as the polymeriztion time of PSI,and optimize the technological conditions.Structures of the maleic anhydride,intermediate,polysuccinimide and PASP-Na were characterized with FT-IR,1HNMR and 13 CNMR.However,low molecular weight of PASP-Na limits its wider application range.In order toincrease the molecular weight of PASP-Na,the modifier was prepared by the grinding method of maleic anhydride and ethanediamine under room temperature,and then reacted with PSI to produce M-PASP-Na.The result shows that higher molecular weight of M-PASP-Na(MW=13 554.92)was obtained when the grinding time is 2.0 h with the molar ratio of maleic anhydride and ethanediamine 1.0:1.0.Structures of the maleic anhydride,ethanediamine and M-PASP-Na were also characterized by FT-IR and 1H NMR as well.However,this kind of M-PASP-Na can only be synthesized with minor amount.So as to produce bulk M-PASP-Na,another optimized process was investigated in detail as follow:PSI reacted with ethanediaminedirectly to produce the intermediate and then maleic anhydride was added to produce M-PASP,followed with the addition of NaOH to prepare M-PASP-Na with high molecular weight.The reaction conditions were investigated in detail on the molar ratio of PSI and ethanediamine,the reaction temperature and the reaction time.High molecular weight of M-PASP-Na(12 879.86)was obtained with the molar ratio of PSI and ethanediamine 1.0:1.0 at 70 ℃ for 1.5 h and then followed with the addition of the equal molar maleic anhydride to ethanediamine at 70 ℃ for 2.5 h.In order to testify the good performance of M-PASP-Na,the scale inhibition of which was investigated and result shows that the calcium carbonate inhibition rate reach up to 94.77 %withthe dosage of 20 mg·L-1when themolecular weight of M-PASP-Na 11 090.41 compare with that of 57.71 % withthe dosage of 20 mg·L-1when themolecular weight of unmodified PASP-Na 5 752.13.