Preparation And Properties Of Organic/Halloysite Nanotubes Superabsorbent Composites Materials

In recent years, the organic/inorganic superabsorbent composites that are used asa new type of water absorbent have attracted a lot of interest in the world. Due to theadvantages of organic and inorganic substances, such as desirable gel strength, highthermal stability and good water absorbency in salts solution, the studies on thecomposites are becoming more and more significant. Halloysite nanotube is a naturalaluminosilicate clay mineral that has a hollow tubular structure. The properties whichinclude large aspect ratio, high thermal stability, non poisonous and harmless and lowcost, provide many opportunities for advanced applications in many composites.In this study, three kinds of superabsorbent composites were synthesized by freeradical polymerization of various organic monomers with HNTs using APS as aninitiator and MBA as a crosslinker in aqueous solution. The as-preparedsuperabsorbent composites were characterized by Fourier transform infrared (FTIR)spectroscopy, scanning electron microscope (SEM) and thermogravimetric analysis(TG) and the comprehensive properties of the composites have also been investigated.We obtain the following results:(1) Study on the preparation and water absorbency property of PAA-AM/HNTssuperabsorbent compositePAA-AM/HNTs superabsorbent composite was synthesized using AA and AMand HNTs. The influences of contents of HNTs and APS, molar ratio of AM to AAand neutralization degree of AA on water absorbency were investigated. The highestwater absorbency of PAA-AM/HNTs was1276g/g in deionized water under themost favorable preparation parameters: a HNTs content of10%, an APS content of1.0%, a molar ratio of AM to AA of3:5, a neutralization degree of AA of70%. TheSEM results revealed that HNTs and PAA-AM were combined well together to forma porous structure with a pore size of about10μm, and HNTs were uniformlydistributed in the composite. Not only the water absorbency in solutions with different pH, salts and organic solvents, but also the swelling rate, water retentionability and reswelling capability of PAA-AM/HNTs were invstigated. The resultsshowed that compared with PAA-AM, the swelling rate of PAA-AM/HNTs wasobviously improved, which reached1255g/g. The water retention ability ofPAA-AM/HNTs was better than PAA-AM during the5hours at60°C and100°C.Moreover, PAA-AM/HNTs had an excellent reswelling ability of78.0%afterrepeating the reswelling capability test five times.(2) Study on the preparation and water absorbency property ofPAMPS-AM/HNTs superabsorbent compositePAMPS-AM/HNTs superabsorbent composite was prepareded by free radicalpolymerization using2-acrylamido-2-methyl propane sulfonic acid, AM and HNTs.The influences of contents of HNTs and MBA, molar ratio of AMPS to AM andhydrolysis time on water absorbency were investigated. The highest waterabsorbency of PAMPS-AM/HNTs was1080g/g in deionized water under the mostfavorable preparation parameters: a HNTs content of5%, a MBA content of0.1%, amolar ratio of AMPS to AM of1:5, a hydrolysis time of1h. The superabsorbentcomposite showed a loose structure and rough surface from the SEM images and abetter thermal stability than PAMPS-AM. Not only the water absorbency insolutions with different pH, salts and organic solvents, but also the swelling rate,water retention ability and reswelling capability of PAMPS-AM/HNTs wereinvstigated. The results showed that compared with PAMPS-AM, the swelling rateof PAMPS-AM/HNTs was higher for0-30min in deionized water, which reached1050g/g. The water retention ability of PAMPS-AM/HNTs was better thanPAMPS-AM during the3.5hours at60°C and100°C. PAMPS-AM/HNTscomposite had a reswelling ability of83.3%after repeating the reswelling capabilitytest five times.(3) Study on the preparation and adsoption of copper ions onCTS-PAA-AM/HNTs superabsorbent compositeA novel superabsorbent composite CTS-PAA-AM/HNTs composed of CTS, AA,AM and HNTs was prepared by solution polymerization and the research on the adsorption of copper ions onto CTS-PAA-AM/HNTs has been carried out. Thecharacterization results indacated that CTS, AA, AM and HNTs were combined welltogether. The thermal stability was improved by adding HNTs in the composite. Thesurface was coarse and the structure was loose. The effects of adsorbent dose,contact time, initial copper concentration, temperature and pH on adsorptioncapacity were investigated. The results showed that when the adsorbent dose was0.1g, the removal efficiency reached77.8%. The adsorption capacity of copper ionsincreased with the temperature and initial concentration until the equilibrium wasreached, when the temperature was298K and the initial concentration was600mg/L, the adsorption capacity of copper ions was132mg/g, which was higher thansome other adsorbents. As the initial concentration became higher, it need more timeto reach equilibrium, when the initial concentration was200mg/L, the time was50mins. When the pH was4-7, the adsorption capacity of copper ions was above95mg/g. Moreover, the composite showed a regeneration ability of86.5%after theadsorption/desorption cycles was carried out five times.To sum up, the natural HNTs were used as an inorganic additive to preparedifferent superabsorbent composites in this study. The results indicated thecomposites had good adsorbability, thermal stability and reusability. The substantialenhancement of these properties enables the composites suitable for numerouspractical applications.