Investigation On Phytic Acid Modified Corn Stalk-grafted Superabsorbent

In this thesis, the paper firstly used phytic acid to modify cork stalks by way ofultrasonic wave and investigated the factors affecting grafting degree of phytic acidonto corn stalks. Morphologies and structure of the phytic acid modified-corn stalkswere characterized by XRD, SEM, FTIR and optical microscope. Secondly phyticacid modified-corn stalk composite superabsorbents were prepared by graftcopolymerization with itaconic acid, vinyl pyrrolidone and acrylamide. Factorsaffecting water absorbency, salt absorbency, water retention and gel strength of thephytic acid modified-corn stalk composite superabsorbents, such as amount of phyticacid modified-corn stalks, phytic acid grafting degree, initiator amount, crosslinkeramount, neutralization degree of itaconic acid, itaconic acid/acrylamide mas ratio,itaconic acid/vinyl pyrrolidone mas ratio were investigated. Morphologies, structureand thermal resistance of the phytic acid modified-corn stalk compositesuperabsorbents were characterized by XRD, SEM, FTIR, optical microscope andTGA. Phytic acid modified-corn stalks composite superabsorbents, having good waterabsorbency, salt absorbency, water retention, gel strength and heat-resistant properties,have been synthesized. The main findings are as follows.1. Effect of reaction time, temperature, phytic acid amount, etc. on the graftingdegree of phytic acid onto corn stalks were investigated and optimal phytic acidmodification process conditions were as follows:50%phytic acid (based on corn stalkmass, the reaction time of3h, ultrasonic treatment time of30min, the reactiontemperature of60℃and the urea content of6%. Under the optimal phytic acidmodification process conditions19.06%grafting degree of phytic acid onto corn stalks was obtained.2. After polymerization process optimization, optimized parameters for thepolymerization were as follows:0.4%crosslinker,1.6%initiator, phytic acid modifiedstraw with grafting degree of11.91%, IA and AM mass ratio of30:70, IA and NVPmass ratio of70:30and10%phytic acid modified corn stalks. Under the optimalphytic acid modification process conditions19.06%grafting degree of phytic acidonto corn stalks was obtained. Under the optimal components and improvedpolymerization process conditions, phytic acid modified-corn stalks compositesuperabsorbents can reached63%of the equilibrium water absorbency (430g/g) with15.1min, an indicative of fast water absorption.3. Optical microscopy and SEM data showed that the phytic acid modified cornstalks demonstrated better dispersion and larger gaps after phytic acid modification.Lamellar structure of the phytic acid modified corn stalk was damaged andtransformed into small irregularly shaped pieces with increased sheets distance andsurface area. Phytic acid modified-corn stalks composite superabsorbents hadirregular corrugated surfaces, accompanied by a large number of small pores and gully.Optical microscopy showed that the phytic acid modified-corn stalks compositesuperabsorbents got swollen and formed network-like voids after water swelling. Theswollen phytic acid modified-corn stalks composite superabsorbents were filled withwater and their color got lighter.4. XRD of phytic acid modified-corn stalks showed that the crystal structure ofphytic acid modified-corn stalks was partially damaged, with increased amorphousregion and slight decreased crystallinity. XRD of phytic acid modified-corn stalkcomposite superabsorbents showed that sharp diffraction peaks of corn stalksdisappeared and a larger and wider dispersion peak was formed, a preliminaryindicative of transformation of polycrystalline structure into amorphous structure.5. FTIR spectrum of the phytic acid modified-corn stalks appeared characteristicabsorption peaks of phytic acid and corn stalks, indicating that phytic acid has graftedonto corn stalks. FTIR spectrum of the phytic acid modified-corn stalk compositesuperabsorbents appeared characteristic absorption peaks of phytic acid modified cornstalk, NVP unit, IA unit and AM unit, a preliminary indicative of the target structureof the synthesized phytic acid modified-corn stalk composite superabsorbents.6. TGA and DTG data showed that phytic acid modified-corn stalk compositesuperabsorbents decomposed with three stages, with the decomposed temperature exceeding240℃, indicating good thermal stability of the phytic acid modified-cornstalk composite superabsorbents.