【作者】 柳建良；

【导师】 崔英德；

【作者基本信息】 广东工业大学 ， 应用化学， 2012， 博士

【摘要】 高吸水性树脂(Super absorbent polymers, SAP)是可以吸收自重数百倍至上千倍水的一类物质,且吸收的水不易用机械方法分离。目前世界上商业性最广泛的是聚丙烯酸盐类(包括淀粉接枝和丙烯酰胺共聚等)高吸水性树脂,该类树脂吸水性能好,但耐盐性和生物降解性差。聚天门冬氨酸(polyaspartic acid,简称PASP)属蛋白质结构,具有很强的吸水性和良好的生物降解性,但凝胶强度低和耐盐性差。因此,选用绿色天然物质L-天冬氨酸(LASP)为添加原料,采用合适的制备方法和工艺来提高传统丙烯酸-丙烯酰胺(AA-AM)高吸水树脂的吸水性能、耐盐性能、生物降解性能和蓄冷保鲜性能,对实现其工程应用具有重要的理论意义和现实意义。本文研究以绿色天然物质LASP为添加原料,采用过硫酸钾为引发剂,N’N-亚甲基双丙烯酰为交联剂,合成LASP/AA/AM高吸水性树脂。探索了聚合物合成中的单因子和多因子组合的最佳条件,测定了聚合反应过程中单体反应级数和聚合反应活化能。对LASP/AA/AM高吸水性树脂的吸水性能、生物降解性能、蓄冷性能、保鲜性能等进行了检测和分析,并用红外光谱仪(FT-IR)和扫描电子显微镜(SEM)对LASP/AA/AM高吸水性树脂的结构进行表征,得到如下结论：(1)以过硫酸钾为引发剂,N’N-亚甲基双丙烯酰为交联剂,以丙烯酰胺和适度中和丙烯酸为基本单体,加入适量的LASP为添加单体,采用水溶液法制备了高性能LASP/AA/AM高吸水性树脂。研究了LASP添加量、WAA:WAM比例等因子的最适量,且得出各因子对树脂吸水倍率的影响顺序为：LASP用量>WAA:WAM比例>引发剂用量>交联剂用量。正交试验确定了本共聚反应的最佳组合,即LASP用量为单体用量8%,引发剂用量为单体用量0.5%,交联剂用量为单体用量0.2%,WAA:WAM比为70：30,获得树脂的最高吸水倍率达到了1017g/g,最高吸盐水倍率达到98g/g。(2)采用水溶液引发LASP/AA/AM共聚,单体反应级数为1,共聚反应活化能为29.45KJ/mol。LASP含量为5%时,聚合反应速率最高,说明添加LASP单体有加速聚合反应的作用。通过FTIR和SEM对合成的高吸水树脂结构进行表征,在FTIR图谱上,1322cm-1处出现了C-N的伸缩,859cm-1出现表示分子顺反结构的谱带,某些基团发生位移,并出现相应的振动伸缩峰,都证明了LASP与AA、AM发生了聚合反应。树脂表面结构SEM图显示AA/AM树脂表面较光滑,而LASP/AA/AM树脂表面较粗糙,有不规则的棱和沟壑出现,印证了LASP/AA/AM树脂比AA/AM树脂有更加优良吸水倍率和吸水速率。(3)微生物生长培养实验表明,LASP/AA/AM树脂微生物生长级数达到最高级4级,而AA/AM树脂微生物生长级数只是1级,表明LASP/AA/AM树脂的碳源能有效被微生物所利用；通过树脂薄片被微生物降解后的表面结构SEM表征,AA/AM树脂表面只表现出轻微的侵蚀,而LASP/AA/AM树脂表面变得密集的粗糙蓬松,表明树脂已大量被微生物降解利用。基本说明了添加LASP后,LASP/AA/AM高吸水树脂具有良好的生物降解性能。(4)饱和的高吸水性树脂中绝大部分是水,而且水的物性参数基本上未变,其中水的蒸汽压、冰点、比热容、融潜热等基本物性与水相似,故高吸水性树脂一水体系具备固-固蓄冷材料特点,可以同时调节环境中的温度和湿度。高吸水树脂蓄冷系统有较大的潜热,LASP/AA/AM树脂-水体系、AA/AM树脂-水体系的熔融热分别为427.9、386.47,明显大于纯水-冰的335。与冰蓄冷系统比较,AA/AM树脂-水蓄冷系统降温速度最快,LASP/AA/AM树脂-水其次,冻结温度以LASP/AA/AM树脂最低,可能是在冰蓄冷系统中,蓄冷介质只有水,而在高吸水树脂复合蓄冷剂的蓄冷系统中,蓄冷介质除了水还有空气,有效提高了传热速率。而高吸水树脂复合纯水的蓄冷系统释冷较快,绝对温度较低,且持续时间较长,LASP/AA/AM树脂-水蓄冷系统释冷性能较优于AA/AM树脂-水的蓄冷系统。(5)贡柑果实水分活度介于0.986～1.0间,可以充分反映果实水分活性的变化,果实成熟度高,水分活性也较高。贡柑果实果汁红外光谱在1649.4(1654.6-1638.4cm-1)附近峰位差异性大,是可以直接用于可溶性糖组分定性分析的波数；在1055.6(1057.1～1053.5cm-1)附近峰位差异性小,可适用于定量分析蔗糖等可溶性糖总量的变化。贡柑不同采收期的果实可溶性糖红外光谱表现出差异,采收迟的果实呈现接近果糖的红外光谱特征。贡柑果实蔗糖、葡萄糖、果糖等可溶性糖含量变化呈“S”型变化模式,其峰位的变化与TSS含量增加呈逆向变化关系,但和甜味品质变甜变淡趋势相同。2,4-D处理贡柑后能明显延长果实风味品质保持期,但不能阻止果实甜味品质变淡,其蔗糖、葡萄糖、果糖等可溶性糖含量变化完全不同于对照的“S”型变化特征。(6)贡柑贮藏试验结果表明,常温贮藏出现异味,冰温贮藏出现冻害结冰沙的现象,唯有低温贮藏的果实仍有蜜味,但质地也不能保持。加冰去热可以显著改善贡柑果实好蒂率、好果率及果实外观色泽,也对果实内含物含量和风味的保持有所帮助,贡柑果实采后加冰处理无论好蒂率、好果率以及果实品质均以冰果比1比2处理为优。采用Aloe、2,4-D和LASP/AA/AM树脂-水蓄冷等保鲜处理的好蒂率和好果率均在96%以上,果实风味品质处理与对照有明显的区别,处理中以2,4-D处理为最好,LASP/AA/AM树脂-水蓄冷处理只是风味变淡,没有出现异味。更多还原

【Abstract】 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.更多还原