| Super-absorbent polymer (SAP), a functional macromolecular material, possesses excellent properties such as water-absorption, water-retention, etc. SAP has been widely used in many fields. Many studies have been carried out about the synthetic method and reaction mechanism. For the purpose of environmental protection and economic continuous development, this project focuses on the biodegradability of SAP based on acrylic acid (AA), because AA is the common monomer for the synthesis of SAP, and SAP based on AA is weakly biodegradable and will pollute underground water and soil.In this paper, a cyclic ketene acetal of 2-methylene-1,3-dioxepane (MDO) was prepared. And then biodegradable SAP with C-O-C in the backbone was synthesized by Ring-Opening copolymerization of MDO with acrylic acid (or acrylate). To improve the strength and anti-saline property, PEG was introduced into the SAP to give interpenetrated networks. During the study, structures of the intermediates, namely 2-Chloromethyl-1,3-Dioxepane(Cl-MDO), MDO, and biodegradable SAP were characterized with FT-IR, 1H-NMR, 13C-NMR, SEM, and DSC. The swelling property of the biodegradable SAP was studied as well. The detailed contents of this paper are as follows:2-Methylene-l,3-dioxepane can be synthesized by a two-step reaction. At first, an intermediate C1-MD0 was synthesized by condensation reaction of chloroacetaldehyde dimethyl acetal with 1,4-Butanediol (BDO) over D001 Ion Exchange Resin. Secondly, MDO was synthesized by reaction of C1-MD0 with potassium t-butoxode by using t-butyl alcohol as solvent. The optimized technological conditions were investigated, and the results are as follows:Cl-MDO was synthesized with: nCDA: NBDO as 1: 1.15, the mass content of D001 Ion Exchange Resin was 1%, the reaction temperature was 115℃. When the calculated amount of methanol has been collected, the crude product is fractionally distilled to produce Cl-MDO. The yield was over 95%.MDO was synthesized with: n(BuOK):n(Cl-MDO)= 1.20:1.0 and n(BuOH):n(BuOK)= 1.20:1.0. The reaction temperature was 105℃. After 5h the crude product was fractionally distilled to produce MDO. The yield was over 70%.Biodegradable SAP with C-O-C in the backbone was synthesized by the Ring-Opening copolymerization of MDO with acrylic acid (or acrylate) by solution polymerization and suspension polymerization. The two methods are as follows:Biodegradable SAP was synthesized by Ring-Opening copolymerization of MDO with acrylic acid (or acrylate) by means of solution polymerization. The reaction was initiated by potassium persulfate and crosslinked by N,N'-methylenebisacrylamide with tetrabutylammonium bromide (TBAB) as catalyst. The optimized technological conditions were the mass content of MDO 8%, the mass content of initiator 0.15%, the mass content of catalyst 2%, the neutralization degree of acrylic acid 85%, the monomer concentration 30%, the reaction temperature 75℃, the time of reaction 2h. The best absorbability of in salt free water was 350g/g and 82g/g in 0.9% NaCl solution.Biodegradable SAP was also synthesized by Ring-Opening copolymerization of MDO with acrylic acid (or acrylate) by means of suspension polymerization. The reaction was initiated by AIBN and crosslinked by N,N'-methylenebisacrylamide with cyclohexane as solvent, SP-60 as dispersant and TBAB as catalyst. The optimized technological conditions were the mass content of MDO 8%, the mass ratio of cyclohexane, asdispersed phase, to water was 5.5:1, the mass content of initiator and crosslinking agent were 0.3% and 0.2% respectively, the neutralization degree of acrylic acid 85%, the mass content of dispersant 5.5%, the mass content of catalyst 3%, the reaction temperature 75℃and the reaction time 2h.The best absorbability of the SAP in salt free water was 520g/g and 85g/g in 0.9% NaCl solution.To improve the properties of strength and anti-saline, the biodegradable SAP of polyethylene (PEG)-Semi-IPN-P(AA/MDO) was synthesized by means of suspension polymerization. The effect of the molecular weight and mass content of PEG on the absorbability of PEG-Semi-IPN-P(AA/MDO) was studied. The results showed that PEG can improve the properties of strength and anti-saline of the biodegradable SAP effectively. The best absorbability of the SAP in salt free water was 510g/g, and the absorbability in 0.9% NaCl solution was improved from 85g/g to 98g/g when the mass of PEG4000 was 4%.The effect of MDO and PEG on the swelling property of the SAP was studied. The absorbability and the swelling rate of P(AA/MDO) increased because of MDO, while the dehydration rate decreased. The strength was suitable, the swelling property and anti-saline of PEG-SIPN-P(AA/MDO) were the best when the mass of PEG4000 was 4%. In this paper, the effect of MDO and PEG on the response of the SAP to swelling temperature was studied.At last, the effect of MDO on the biodegradability of P(AA/MDO) was studied by the method of agar flat analysis and the amount of CO2 released by the SAP. The results showed that bacillus subtilis and aspergillus nigers can grow on the biodegradability SAP of P(AA/MDO); P(AA/MDO) with C-O-C in the backbone and they were biodegradable. The biodegradation behaviors of P(AA/MDO) were related to its backbone structure. The biodegradability can be improved as the mass of MDO increase with more C-O-C on the backbone. The biodegradability will become worse as the mass of MDO decreased. The sample prepared with the inverse suspension polymerization is easier to degrade than that prepared with the solution polymerization.
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