Preparation And Characterization Of Molecular Sieve/Poly(Aspartic Acid) Composite Hydrogel

Poly(aspartic acid)(PAsp) hydrogel is a novel low cross-linked functionalpolymer material with strongly hydrophilic functional groups, such as carboxylgroup and amino et al. PAsp hydrogel is a functional polymer material, whichcan absorb a lot of water without being dissolved. However, the applicationfields of pure PAsp are limited due to its various defects, such as poor saltresistance, simple uni-structure and using poisonous cross-linkers etc. In orderto avoid such defects, in this paper a novel composite hydrogels weresynthesized in a aqueous system from poly(aspartic acid) grafted withaminpropyltriethoxysilane (KH550)(KPAsp) and the mesoporous molecularsieve MCM-41(mobile composition of matters). Factors influencing the waterabsorbing abilities of KPAsp/MCM-41composite hydrogels were investigated.In addition, characterizations for hydrogels’ structure and properties were alsoaccomplished. Firstly，mesoporous molecular sieve MCM-41was synthesized with TEOSand CTAB as the silica source and surfactant, respectively, using a hydrothermalmethod under alkaline conditions. Different diameter particle size of MCM-41was successfully prepared by adjusting the molar ratio of water and TEOS. Forfurther identification of microstructures of MCM-41, transform infraredspectroscopy (FTIR), scanning electron microscopy (SEM), thermo-gravimetricanalyses (TGA) and dynamic light scattering (DLS) had been used. The resultsshow that MCM-41has been successfully synthesized and it owns narrowdiameter distribution, high degree of order, a large amount of silicon hydroxyl onthe its surface. The diameter of the prepared particle range is from462nm to1064.0nm and in-stiu method prepared particle range is from127.8nm to597.2nm.Secondly, KPAsp/MCM-41composite hydrogel was synthesised in anaqueous system from poly(aspartic acid) grafted with aminpropyltriethoxysilane(KH550)(KPAsp) and the mesoporous molecular sieve MCM-41(mobilecomposition of matters); here, inorganic MCM-41particles were utilised as adirect cross-linker. The effects of different amount, average particle size ofMCM-41, various salt solutions on the composite hydrogel swelling ratio wereinvestigated. The composition and structure of the KPAsp/MCM-41compositehydrogels were determined byFTIR andSEM. The results indicated thatMCM-41addition could improve the physicochemical properties of the synthesised composites. At the amount of10wt%of MCM-41(particle size,462nm) the swelling ratios of composite hydrogels prepared in distilled waterand physiological saline reached284and87g/g (enhanced by1.56-and1.35-fold, respectively, compared with hydrogels without MCM-41). In chloridesalt solution of0.9wt%concentration, the water absorbency of the hydrogelswas increased in the following order Na+> Ca2+> Fe3+. The recorded FTIRspectra showed that MCM-41nanoparticles are effectively introduced into theKPAsp network structure and form KPAsp/MCM-41composite hydrogels. SEMimages confirmed that introduction of MCM-41inorganic particles into theorganic network structure can optimize the pore morphology of the compositehydrogels. Thermo-gravimetric analysis showed that the thermal stability of theKPAsp/MCM-41composite hydrogels significantly improves at27°C, which isan indication of successful introduction of MCM-41into the hydrogels.Though the introduction of MCM-41can enhanced the swelling ratio andcomposite hydrogels’ salt tolerance to a some extent, the swelling ratio of thecomposite hydrogel is still too low and MCM-41agglomerates may benegatively affect the hydrogel three-dimensional network structure. In order toavoid those defects, KPAsp/MCM-41composite hydrogels were synthesized byin-situ polymerization that can simplify prepared processes and reduce costs.KPAsp/MCM-41composite hydrogels were synthesized based on KPAspand MCM-41in-situ in aqueous solution. The dosage of MCM-41was determined by the calculation of solid content. Using FTIR, SEM and TGA forcharacterizing the structure of the hydrogel, the results show that theKPAsp/MCM-41composite hydrogel in-situ can successfully synthesized byin-situ polymerization and from the SEM images, the MCM-41particles as acrosslinking agent dispersed evenly in the network structure of the hydrogel,changing the amount or particle size of MCM-41has little impact on thethermal stability of composite hydrogel. KPAsp/MCM-41composite hydrogelswelling kinetics and sensitivity are studied, this new type of compositehydrogel swelling type belongs to Fickian diffusion and its has better salt,temperature and pH sensitivity which can enlarge the applying fields.