Study On Synthesis And Properties Of LASP/AA/AM Super Absorbent Polymer And Applied To Cool Storage Fresh-keeping

Super absorbent polymers(SAP) are a type of superabsorbent materials up to thousands and hundreds times of its deadweight and the absorbing water can not be separated by mechanical method. The most commercial type of SAP is polyacrylates which have superior absorb-water performance and poor salt-resistance performance and biodegradability. Polyaspartic acid(PASP) is a type of protein which has superior absorb-water performance and biodegradability, but poor salt-resistance performance and gel strength Therefore, L-aspartic acid(LASP) as natural material by adding into acrylic acid-co-acrylamide(AA-AM) is to improve the absorb-water performance, salt-resistance performance, cool storage performance and biodegradability of AA-AM SAP, which has important scientific value to promote the engineering applications of SAP.The copolymerization processes of LASP/AA/AM polymers with initiator (potassium supersulphate), crosslinking agent(N'N-methylene bis (acrylamide)) were studied. The results of synthesis conditions, polymerization kinetics, structure properties and performances of the copolymer by separate factors tests and orthogonal experiments are as follows:(1) LASP/AA/AM polymer was prepared by aqueous solution polymerization using proper amount of LASP/AA/AM as monomers, potassium supersulphate as initiator, N'N-methylene bis (acrylamide) as crosslinking agent, and proper neutralization degree of acrylic acid. The influence order of factors on polymerization was LASP content> WAA:WAM ratio> initiator content> crosslinking agent content. The results of orthogonal test showed that the best polymerization conditions were LASP8%wt of AA/AM, potassium supersulphate0.5%wt of AA/AM, N'N-methylene bis (acrylamide)0.2%wt of AA/AM, and WAA:WAM ratio70:30. According to these conditions, the absorbency of LASP/AA/AM polymer could get1017g/g, and the absorbency of0.9%NaCl solution could get98g/g. (2) The monomers reaction order, and activation energies of LASP/AA/AM copolymerization in aqueous solution were1and29.45KJ/mol, respectively. When LASP content was at5%wt of AA/AM, LASP/AA/AM copolymerization rate reached the highest, showing accelerated the polymerization by LASP. IR spectra of LASP/AA/AM SAP exhibits characteristic band of C-N around1322cm-1and molecular cis/trans-structure band of the copolymer around859cm-1. SEM photograph of LASP/AA/AM gel resin exhibits having irregular edge and gully and being rougher in the surface of gel, and showing more excellent water absorption ratio and water absorption rate than that of AA/AM gel resin.(3) Carbon sources of LASP/AA/AM SAP could be utilized by Penicillium sp.and Aspergillus niger through microbe incubation. SEM photograph of LASP/AA/AM SAP through degradation of fungi exhibits that the surface of LASP/AA/AM gel resin became rough and showed more excellent biodegradability than AA-AM gel resin.(4) The property of absorbing water by SAP is the same as free water, such as vapor pressure, freezing point, specific heat capacity, latent heat. So, SAP-water as a solid-solid cool storage material can regulate environmental temperature and humidity. Melting heats of LASP/AA/AM SAP-water, AA/AM SAP-water and water were in order of427.9,386.47,335. LASP/AA/AM SAP-water and AA/AM SAP-water cool storage systems had higher melting heat, faster cool-discharge, longer lower-temperature period than ice cool storage system. The cool-discharge performance of LASP/AA/AM SAP-water cool storage system was better than that of AA/AM SAP-water cool storage system.(5) The water activity of Gonggan fruits was0.986～1.0, which affected by water-loss and maturity of fruits. IR spectra of Gonggan fruit juice showed diversity around1649.4(1654.6～1638.4cm-1) which is suitable for qualitative analysis of soluble sugars, and similarity around1055.6(1057.1～1053.5cm-1) which is suitable for quantitative analysis of soluble sugars. IR spectra of Gonggan fruit juice at late harvest was similar with that of fructose. The changes of sucrose, glucose, fructose and soluble sugars of Gonggan fruit in control were "S" model, but showed no relationship with the increase of TSS content and closely relationship with the change of flavor quality during fruit storage6-12d. The flavor quality level and period of Gonggan fruit treated by2,4-D was better and longer, no peaks different from "S" model of control in the changes of sucrose, glucose, fructose and soluble sugars, that the lower level of soluble sugars was closely related with the change of flavor quality of Gonggan fruit.(6) The quality of'Deqing Gonggan'fruits after harvest showed light flavor and off-crisp texture:off-flavour under room temperature, light flavour and ice taste under ice temperature and light flavour and honey-sweet taste under low temperature. Good pedicle percent and good fruit percent of fruits were significantly increased with the increases of ice addition(p<0.01); and the best fruit quality was the1:2treatment. Good pedicle percent and good fruit percent of fruits treated by Aloe,2,4-D and LASP/AA/AM SAP-water cool storage system were more than96%, and fruit quality of treatments was in order of2,4-D,Aloe,LASP/AA/AM SAP-water cool storage system and CK.