机械活化固相醚化法制备羧甲基淀粉和羧甲基壳聚糖混合物及其溶解性能

Preparation of the compound of carboxymethyl starch and carboxymethyl chitosan by mechanical activation-strengthened solid phase etherification and its solubility

羧甲基木薯淀粉和羧甲基壳聚糖混合物不仅可有效改善淀粉物化性质,还可引入抑菌性能好的羧甲基壳聚糖。以木薯淀粉、壳聚糖为原料,氯乙酸钠为醚化剂,氢氧化钠为催化剂,采用机械活化固相醚法制备羧甲基木薯淀粉和羧甲基壳聚糖混合物。以黏度为评价指标,通过单因素和正交试验设计优化确定最佳制备工艺,采用红外光谱(Fourier transform infrared spectroscopy,FTIR)、X-射线衍射(X-ray diffraction,XRD)、扫描电镜(Scanning electron microscope,SEM)对羧甲基淀粉的结构进行表征,并考察混合物的取代度和溶解度。结果表明,机械活化破坏了淀粉、壳聚糖的结晶结构,降低结晶度,醚化试剂更容易渗透到内部使淀粉、壳聚糖发生羧甲基化反应。最佳工艺参数为:淀粉与壳聚糖质量比0.5:0.5、淀粉与氯乙酸钠的摩比1:0.9、氢氧化钠质量分数18.8%(占淀粉干基质量)、球磨温度50℃、球磨时间60 min、转速380 r/min、磨球体积500 m L。在该试验条件下制备得到的羧甲基木薯淀粉和羧甲基壳聚糖混合物的黏度为1025 m Pa·s,其中羧甲基木薯淀粉的取代度为0.79,羧甲基壳聚糖的总取代度为1.17,溶解度为90.87%,且随着壳聚糖比例增大,混合物溶解度不断减小。FTIR、XRD、SEM进一步证实木薯淀粉、壳聚糖均发生了羧甲基化反应。

The compound of carboxymethyl starch and carboxymethyl chitosan can not only improve the physiochemical properties of starch effectively but also introduce the antibacterial properties of chitosan, the compound of carboxymethyl starch and carboxymethyl chitosan was synthesized by mechanical activation-strengthened solid phase etherification, using cassava starch and chitosan as raw materials, monochloroacetate（MCA） as etherifying agent and sodium hydroxide（Na OH） as catalyst. Single factor experiments and orthogonal array design methods were used to optimize the preparation conditions based on viscosity. The structure of the compound of carboxymethyl starch and carboxymethyl chitosan were characterized by using fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD） and scanning electron microscope（SEM）, and the degree of substitution（DS） and viscosity of the compound of carboxymethyl starch and carboxymethyl chitosan were systematically investigated. The results indicated that mechanical activation destroyed the crystalline structure, decreased the degree of crystallinity of cassava starch and chitosan, which made etherification reagent more easily penetrate into the cassava starch and chitosan internal. The optimal processing conditions for the compound of carboxymethyl starch and carboxymethyl chitosan are that： the mass ratio of starch and chitosan is 0.5：0.5, the molar ratio of starch and sodium chloroacetic is 1：0.9, sodium hydroxide mass fraction is 18.8%（dry starch weight）, ball-milling time 90 min, ball-milling temperature 50 ℃, stiring speed 380 r/min, tack media 500 m L. Under the optimal conditions, the viscosity is 1025 m Pa·s and the degree of substitute（DS） of carboxymethyl cassava starch is 0.79, the carboxymethyl chitosan is 1.17 and solubility is 90.87% of products. With the increase in ratio of chitosan, the viscosity of the compound is reducing. The etherification reaction of cassava starch and chitosan have been confirmed further by FTIR, XRD, SEM. The research findings of this paper can provide references for production and applications of freshkeeping material.