Synthesis Of Acrylic Acid-iconic Acid Copolymers And Its Application In Hemihydrate Gypsum

It is an important measure to build ecological civilization in the new era to adhere to the development concept that clean water and green mountains are invaluable assets,implement the national policy of energy conservation and emission reduction,and vigorously develop green building materials.Gypsum belongs to green building materials,the comprehensive utilization of industrial by-product gypsum can realize energy saving and emission reduction,land resource conservation and environmental governance.However,the hardening speed of hemihydrate gypsum is too fast to meet the actual construction needs.Therefore,in the actual operation,it is necessary to add retarder to prolong the setting time of gypsum so as to meet the construction requirements.Although retarding agents on the market have a long setting time for gypsum,they have a greater loss of strength.Therefore,it is an important task to study retarding agents with good retarding properties and little influence on the strength of gypsum.The organic acid containing carboxyl group has a better retarding effect on gypsum,and the water-soluble polymer can improve the bonding property between gypsum and matrix.The mechanical properties of gypsum tend to be enhanced at lower dosage.Therefore,the linear polymer,acrylate-iconic acid copolymer containing many carboxyl groups was synthesized by free radical polymerization of aqueous solution.The synthesis method is mature and easy to operate.The main contents are as follows:（1）The copolymer[P（AA-IA）]of acrylic acid（AA）and iconic acid（IA）was prepared by free radical polymerization of aqueous solution using acrylic acid（AA）and iconic acid（IA）as monomers.The copolymer was successfully prepared by Fourier transform infrared absorption spectroscopy（FT-IR）.The retarding properties of P（AA-IA）s in hemihydrate gypsum were systematically discussed by studying the effects of monomer proportion and the amount of chain transfer agent on the setting time,hydration heat flow and electrical conductivity.The results showed that when m（AA）:m（IA）=1:1.86 and m（APS）:m（MPA）=0.4:1.8,P（AA-IA）-3-3 showed the best retarding performance.The carboxyl group in P（AA-IA）-3-3 can be complexed with Ca²⁺and adsorbed on the surface of hemihydrate gypsum,which inhibits the crystal growth of hemihydrate gypsum and prolongates the setting time of hemihydrate gypsum.The initial setting time and final setting time ofα-hemihydrate gypsum mixed with 0.1%P（AA-IA）-3-3 were 84 min and 96 min,respectively.The initial and final setting time ofβ-hemihydrate gypsum mixed with 0.3%P（AA-IA）-3-3 were 40 min and 55 min,respectively.Compared with blank gypsum,when the curing time of gypsum is 28 d,the compressive strength and flexural strength ofα-hemihydrate gypsum system mixed with 0.1%P（AA-IA）-3-3 increased by 57.54%and25.48%,respectively.However,the compressive strength and bending strength ofβ-hemihydrate gypsum system doped with 0.3%P（AA-IA）-3-3 decreased by 38.07%and37.80%,respectively.Through the characterization of the porosity and the morphology of the products,the results show that the crystal density ofα-hemihydrate gypsum system is tight,and the porosity decreases.In theβ-hemihydrate gypsum system,the crystal becomes short and coarse,increasing the porosity,which is consistent with the strength data.（2）Using AA,IA and acrylamide（AM）as monomers,acrylic-acrylamide-iconic acid copolymer[P（AA-AM-IA）s]was synthesized by free radical polymerization.FT-IR was used to determine the successful preparation of polymer.By studying the effect of the ratio of carboxyl group to amide group on the setting time,heat flow and conductivity of hemihydrate gypsum,the retarding property of P（AA-AM-IA）s in gypsum was systematically discussed.The results showed that P（AA-AM-IA）showed the best retarding performance when the molar ratio of carboxyl group to amide group was 60:1.With 0.1%P（AA-AM-IA）-1,the initial setting time and final setting time ofα-hemihydrate gypsum were 41 min and 72 min,respectively.But the initial setting time and final setting time ofβ-hemihydrate gypsum doped with 0.3%P（AA-AM-IA）-1 were 28 min and 40 min,respectively.Compared with blank gypsum,when the curing time of gypsum was 28 days,the compressive strength and the flexural strength ofα-hemihydrate gypsum system was increased by 6.53%and 13.86%,respectively,when 0.1%P（AA-AM-IA）-1 was added.The compressive strength and bending strength of specimens doped with 0.3%P（AA-AM-IA）-1 andβ-hemihydrate gypsum system decreased by 22.36%and 17.07%,respectively.（3）AA,IA,and 2-acrylamide-2-methylpropyl sulfonic acid（AMPS）as monomers were synthesized by free radical polymerization of acrylic acid-（2-acrylamide-2-methylpropyl sulfonic acid）-iconic acid copolymers[P（AA-AMPS-IA）s].Using FT-IR to determine the successful preparation of polymer.The effect of the ratio of carboxyl and sulfonic acid groups on the setting time,hydration heat flow and conductivity of gypsum was investigated.The retarding property of P（AA-AMPS-IA）s in gypsum was systematically discussed.The results indicated that P（AA-AMPS-IA）-1 showed the best retarding performance when the molar ratio of carboxyl group to sulfonic group was 1.5:1.Compared with blank gypsum,the initial setting time and final setting time ofα-hemihydrate gypsum doped with 0.05%P（AA-AMPS-IA）-1 were 125 min and 194 min,respectively.The initial and final setting time ofβ-hemihydrate gypsum doped with 0.3%P（AA-AMPS-IA）-1 were 69 min and 87 min,respectively.When the curing time of gypsum was 28 days,the compressive strength and flexural strength of specimens doped with 0.05%P（AA-AMPS-IA）-1 andα-hemihydrate gypsum system increased by 75.82%and 41.81%,respectively.Adding 0.3%P（AA-AMPS-IA）-1,the compressive strength and bending strength ofβ-hemihydrate gypsum system increased by 65.50%and 34.92%,respectively.Through the characterization of the porosity and the morphology of the products,the results showed that the crystal accumulation inα-hemihydrate gypsum system is more dense.In theβ-hemihydrate gypsum system,the crystals are more robust and the porosity is reduced,which is consistent with the strength data.