Preparation And Application Of Cross-linked Hydroxypropyl Carboxymethyl Modified Starch As Wallpaper Adhesives

Cross-linked hydroxypropyl carboxymethyl corn starch was synthesized throughcross-linked, hydroxypropylation and carboxymethylation modification. Thepreparation process of hydroxypropyl, cross-linked hydroxypropyl and hydroxypropylcarboxymethyl starches were studied respectively. The physicochemical properties, thegranule structure, as well as application in wallpaper adhesive of prepared modifiedstarches were investigated.Effects of reaction time and temperature, ethanol, sodium hydroxide andpropylene oxide dosage on hydroxypropylation were studied. From the perspective ofincreasing hydroxypropyl molar substitution, the optimal conditions for preparinghydroxypropyl starch were obtained by single factor experiments as follows: reactiontime was20h, reaction temperature was65°C, the ratio of ethanol and corn starch was3:1(m/m), sodium hydroxide was3.0%based on dry weight of starch, the ratio ofpropylene oxide and corn starch was3:1(m/m). The molar substitution ofhydroxypropyl starch was0.3914.The cross-linked process of hydroxypropyl starch was studied. From theperspective of increasing degree of cross-linking, the optimal conditions for preparingcross-linked hydroxypropyl starch were obtained by single factor experiments asfollows: reaction time was4h, reaction temperature was50°C, sodium hydroxide was0.9%based on dry weight of starch, cross-linking agent was0.05%based on dry weightof starch, the degree of cross-linking was2.53mL. In addition, hydroxypropylcarboxymethyl starch was synthesized through hydroxypropylationcarboxymethylation based on corn starch with one-step method. From the perspectiveof increasing viscosity, the optimal conditions for preparing hydroxypropylcarboxymethyl starch were obtained by single factor experiments as follows: reactiontime was10h, reaction temperature was60°C, chloroacetic acid dosage was25%basedon dry weight of starch, sodium hydroxide was21%based on dry weight of starch, theratio of propylene oxide and corn starch was1.5:1(m/m). The hydroxypropyl molar substitution was0.0595, the carboxymethyl substitution was0.3069, the viscosity was6527mPa.s.The microstructure of corn starch, hydroxypropyl starch, cross-linkedhydroxypropyl starch, hydroxypropyl carboxymethyl starch, cross-linkedhydroxypropyl carboxymethyl starch were investigated by Fourier transform infraredspectrometer (FT-IR), X-ray diffraction (XRD), Scanning electron microscop (SEM).Modified starch showed stretching vibration absorption peaks of–OH strengthened andnew absorption peaks at1328-1603cm-1appeared. The crystalline type was notchanged, the relative crystallinity decreased when the levels of hydroxypropylation andcarboxymethylation modification were higher. The surface transformation changes ofstarch granules before and after modification were observed. Results indicated that thereaction occurred both inside and outside starch granules. Physical and chemicalcharacteristics of modified starch were discussed, cross-linked hydroxypropylcarboxymethyl starch had good properties of viscidity, resistance to freezing, rheology.Compound modified starch as adhesive in wallpaper was studied, including wetviscosity, dry viscosity and sliding property. Results showed that, the application valueof this compound modified starch, especially hydroxypropyl carboxymethyl starch andcross-linked hydroxypropyl carboxymethyl starch, had been greatly improved, thepreparation of compound modified starch could help to improve the value of corn starchin the industry.