Influence of Reaction Parameters on Water Absorbency of Starch Grafted Superabsorbents

Superabsorbents starch grafted sodium polyacrylate was synthesized by inverse suspension polymerization, using toluene as the continuous phase, potassium persulfate as the initiator. The effect of reaction parameters, such as starch pretreatment temperature, neutralization degree of monomer, reaction time and temperature, concentration of initiator, molar ratio of monomer and starch, on water absorbency of the starch grafted polymer was studied. The effects of the last two parameters were investigated by uniform design method, and the prediction equation was obtained.

An Investigation into the Performances of Cement Mortar Incorporating Superabsorbent Polymer Synthesized with Kaolin

Cement-based materials are fundamental in the construction industry,and enhancing their properties is an ongoing challenge.The use of superabsorbent polymers(SAP)has gained significant attention as a possible way to improve the performance of cement-based materials due to their unique water-absorption and retention properties.This study investigates the multifaceted impact of kaolin intercalation-modified superabsorbent polymers(K-SAP)on the properties of cement mortar.The results show that K-SAP significantly affects the cement mortar’s rheological behavior,with distinct phases of water absorption and release,leading to changes in workability over time.Furthermore,K-SAP alters the hydration kinetics,delaying the exothermic peak of hydration and subsequently modifying the heat release kinetics.Notably,K-SAP effectively maintains a higher internal relative humidity within the mortar,reducing the autogenous shrinkage behavior.Moreover,K-SAP can have a beneficial effect on pore structure and this can be ascribed to the internal curing effect of released water from K-SAP.

THERMOSENSITIVE SUPERABSORBENTS BASED ON POLY(N,N-DIETHYLACRYL AMIDE-co-SODIUM ACRYLATE)

A series of poly（N,N-diethylacrylamide-co-sodium acrylate） with a degree of crosslinking of 1 mol% have been prepared as therrnosensitive superabsorbents for water. The critical swelling temperatures or the volume phase transition temperature （VPTT） and the water absorption capacity of the polymers can be modulated by varying the amount of sodium acrylate （0-60 tool%） in the copolymers. The water absorption and swelling properties of the different hydrogels have been studied as function of temperature. The crosslinked copolymers can absorb large amounts of water at ambient temperatures and dehydrate at higher temperatures with relative ease, making the absorbent materials thermally responsive and thus reusable. The water absorption capacity of the copolymers depends on the pH of the media as the acrylate monomer has a higher water absorption in its deprotonated state. Added urea in the media raises and sharpens the VPTT values of the copolymers containing sodium acrylate.

Preparation, characterization and salt-resistance of a coal based super absorbent composite

Potassium humate was extracted from brown coal. A novel super absorbent composite, poly （acrylic acid-co-acryla- mide）/potassium humate （PAA-AM/KHA）, was prepared by graft polymerization of acrylic acid, acrylamide and coal based potassium humate using N, N＇-methylenebisacrylamide as a crosslinker and potassium peroxydisulfate as an initiator. The effects of reaction temperature, degree of neutralization of the poly （acrylic acid） and the amounts of crosslinker, initiator and potassium humate were investigated. Salt resistance tests were also carded out. The composite prepared under optimal conditions had a potassium bumate content of 10% and exhibited a water absorption of 770 g/g in distilled water, and 349, 286 and 41 gig in 0.5 mol/L KC1, MgC12 and A1CI3 solutions respectively. The results indicate that the salt resistance of PAA-AM/KHA was superior to that of poly （acrylic acid-co-acrylamide） because of the collaborative effect of functional groups of the coal based potassium humate. The PAA-AM/KHA micro powder was characterized by IR spectroscopy and the micrographic surface was characterized by scanning electron microscopy. Introduction of potassium humate into the poly （acrylic acid-co-acrylamide） structure creates a composite more suitable for use as a water-managing material in the renewal of arid and desert environments. The salt resisting property of the composite is improved, production costs are reduced and the growth stimulant effect is still present.

Super-absorbent swellable polymer as grouting material for treatment of karst water inrush

Grouting is the most commonly used method to control water inrush in underground engineering.Traditional cement-based materials are easy to dilute and hard to coagulate under the influence of large flow and high-velocity water inrush.To address these deficiencies,a new type of polymer grouting material with an excellent expansion ratio was synthesised.The material quickly absorbs water and has an expansion ratio of 1:300.The material is composed of a superabsorbent polymer(SAP),glycerol,and ethanol.The effects of water quality on the expansion ratio and expansion rate of the material were examined,and the best solid–liquid ratio for the slurry was determined by fluidity measurements.A karst specially designed pipeline water inrush test device showed that 800 g of SAP can achieve 0.6 m/s water flow blockage in the smooth pipeline,demonstrating that the ability of the SAP slurry to block water inrush is superior to those of other materials.This study provides a reference for water inrush plugging,and has important implications for the reduction and control of karst pipeline-type water inrush disasters,ensuring the safety of construction sites and preventing loss of life and damage to property.

Effect of SAP on Properties of High Performance Concrete under Marine Wetting and Drying Cycles

The internal curing effect of superabsorbent polymer(SAP) on the properties of high performance concrete(HPC) under marine wetting and drying cycles(WD cycles) was investigated. Compressive strength, hydration and chloride migration were experimentally investigated and the results were evaluated by compasison with those under fresh water curing(FW). Water absorption and porosity were also evaluated only under WD cycles. The results showed the important influence of wetting and drying cycles on the properties of SAP modified HPC properties. Carefully designed, SAP minimized the long-term compressive strength of HPC under marine WD cycles. The hydration rate was faster in the initial curing, but became lower as compared with that cured in FW. In addition, SAP improved the long-term water absorption resistance and chloride migration resistance of HPC under marine WD cycles. The examination of the porosity showed a lower increase of the volume of capillary pores in SAP modified HPC under long term WD cycles compared with that without SAP. Therefore, internal curing by SAP could improve the durability properties of HPC under marine WD cycles.

Effects of superabsorbent polymer particles on flexural properties and self-healing behavior of ECC

In order to improve the self-healing behavior and the recovery of mechanical properties of engineered cementitious composites(ECC),the approach of incorporating superabsorbent polymer(SAP)in mixtures is investigated.The rapid water penetration test and four-point bending test were conducted to evaluate the effects of self-healing on the water permeability and mechanical properties of pre-damaged ECC.The self-healing process and self-healing products were observed by the environment scanning electron microscope(ESEM)and energy dispersive X-ray spectroscopy(EDS).The experimental results show that all ECC mixtures exhibit excellent flexural capacity,meanwhile maintaining a crack width below 50μm.The incorporation of SAP particles in ECC can apparently improve the mechanical recovery of ECC mixtures after 10 healing curing cycles,such as flexural deformation and flexural stiffness.The flexural stiffness of ECC containing 4%SAP particles after self-healing can be recovered to 80%.The self-healing test results show that when the water permeability of ECC mixtures incorporating SAP particles is close to zero,only three healing cycles are needed.When ECC incorpora ting more SAP particles,the accelerated self-healing process can be finished in the first three cycles,and self-healing product is mixed Ca(OH)2/CaCO 3 with CaCO 3 being a major component in the later stage.It is,therefore,feasible to produce ECC materials incorporating SAP particles,while simultaneously maintaining higher material ductility and self-healing behavior.

Mechanical property of strain-hardening cementitious composites modified with superabsorbent polymers

In order to improve the tensile property, flexuralproperty and drying shrinkage of strain-hardening cementitiouscomposites （SHCC）, mixtures quantitatively modified withsuperabsorbent polymer （SAP） were investigated. Theuniaxial tensile test, the four-point bending test, thecompressive test, the drying shrinkage test and theenvironmental scanning electron microscope （ESEM） wereemployed to investigate the tensile strain capacity, flexuraldeformation capacity, compressive strength, drying shrinkage,crack width and self-healing of SHCC. The experimentalresults show that SHCC modified with SAP particles exhibitsexcellent ductility and deformability, and the tensile strain isup to about 4.5% and the average crack width is controlledaround 40 μm. Meanwhile, the drying shrinkage of SHCCmodified with SAP particles can reduce by about 60%.Furthermore, the self-healing behavior is observed in thecracks of specimen after three cycles of high-low relativehumidity curing, and the self-healing products can completelyfill the cracks of SHCC specimens modified with SAPparticles. It is, therefore, feasible to produce SHCC materialmodified with SAP particles, while simultaneously retaininghigher material ductility.

Preparation and Charcterization of Konjac Superabsorbent Polymer

A superabsorbent polymer was prepared by grafting sodium acrylate （ SA ） onto Konjac flour using potassium persulfate （KPS） and N, N＇-methylene bis acrylamide （ MBA ） as an initiator and crosslinker , respectively. The effect of various preparation conditions on its water absorbency was investigated. When the Konjac Flour content was 3.0g, the acrylic acid （AA） content was 30.0 g, the amount of initiator was 0. 150 g, the neutralization degree of monomer was 85% , the reaction temperature was 60 ℃ and the amount of crosslinker was 0.025 g, the polymer＇s absorbency was 750 times in pure water and 279 times in tap water at ambient temperature. It had also high water retention. The graft efficiency reached 67% . The analyses of FT-IR and SEM indicate that sodium acrylate is grafted on the polysaccharides of Konjac flour.

Superabsorbent Capability and High Retention Ability of China Clay(Kaolinite)/Polyacrylic Acid Composites for Aqueous Solution

Majority of superabsorbent polymers (SAPs) yet reported either have low gel strength or high production cost. Therefore, we synthesized a novel polyacrylic acid-grafted China clay (Kaolinite) super-absorbent polymer composite (SAPC) with high thermal stability, low cost of production and superior sorption and retention capability for water and salt solution. The resulting SAPCs were extensively characterized and analysed by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results suggested that the composites were thermally stable. Water absorbency increased with increase of clay content up to 45%, while further increase in clay content decreased the water absorbency. Percentage of acrylic acid (AA) and clay by weight shows the optimum absorbency in 35% and 40% respectively. Crosslinker and initiator contents were optimized to be 0.5% and 0.3% by weight respectively. The resulting polymer composite showed high water absorbency of about 785 g/g and 103 g/g of 1% NaCl solution with above 90% retention ability at 50 oC.

Superabsorbent polymer for water management in forestry

The effectiveness of a superabsorbent polymer of sodium polyacrylate was studied, with emphasis on water management, i.e., absorption, retention and desorption in the soil. The polymer was applied in plots with a sandy soil near Grandola (southern Portugal). Characterization of the most relevant physical and chemical properties of the polymer was made, namely, its specific gravity, particle diameter, capacity of water absorption and desorption. In the plots with and without the polymer, soil moisture was continuously monitored, and grassland biomass samples were collected and weighed. The results reflected the effective role of the polymer both in the improvement of the water regime in the soil and in the substantial increment of grassland productivity.

Preparation of Superabsorbent Polymers with Increased Saline Absorbency

Superabsorbent having enhanced absorbency of 0.9%NaCl solution was synthesized on one basis of incorporating zwitterionic (sulfobetaine) monomer into the previous monomer mixture, which comprises ionic (AA) and nonionic monomers, and another basis of introducing inorganic salt B. As far as saline absorbency is concerned, introduction of inorganic salt B is more useful than the sulfobetaine monomer.

Properties and Structure of Microcrystal Muscovite Composite Superabsorbent

Microcrystal muscovite composite superabsorbents（MMCSA） were prepared by water solution polymerization using acrylic acid, acrylamide and itaconic acid as comonomers and microcrystal muscovite as an inorganic additive. Properties, such as water absorbency, salt absorbency, gel strength, water retention capacity and structure of MMCSA characterized by SEM and XRD, were investigated. Water absorbency, salt absorbency, gel strength, water retention capacity and thermostability were enhanced by incorporation of suitable amount of microcrystal muscovite. Water absorption of MMCSA was rapid, requiring 24.55 min to reach 63% of equilibrium absorbency（1218 g/g）. Microcrystal muscovite was physically combined into the polymeric network without destroying its polycrystalline structure and microcrystal muscovite composite superabsorbent had some irregular, undulant, and small microporous holes with sheet-like microcrystal muscovite distributed in the polymeric matrix.

A Novel Method for Studying the Re-Swelling Capacity of Superabsorbent Polymers in An Artificial Crack

Re-swelling capacity is a key factor influencing the self-sealing efficiency of superabsorbent polymers (SAPs) in concrete.In this paper,a new parameter (re-swelling ratio,η),the volume ratio of the crack which was filled with the expansive SAPs and the dry SAPs,was given to quantify the re-swelling capacity of a single SAPs particle.An innovative immersion test was used to study the η value of SAPs in the hardened cement paste with an artificial crack.Moreover,the influence of the crack width and particle size on the sealing efficiency of SAPs in the cracked paste was investigated by a water permeability test.The results showed that the mass ratios of the expansive SAPs in an artificial crack were less than those in a free state.The η value of SAPs in the hardened paste with an artificial crack increased with the increase of the crack width due to the restricting effects of the crack.The expansive SAPs in the cracked paste could totally seal or partly seal the crack within the original void.Moreover,the sealing efficiency of SAPs slightly increased with the rise of the crack width (0.25 to 0.5 mm) and the reduction of the particle size.This research demonstrates that the crack width in concrete and the particle size of SAPs are the key factors influencing the re-swelling behavior of SAPs which should be taken into consideration when designing the self-sealing concrete containing SAPs.

Synthesis of Acrylic Acid/Kaoline Powder Superabsorbent Composite by Inverse-suspending Polymerization

An acrylic acid/kaoline powder superabsorbent composite with a water absorbency of the superabsorbent composite about 1/800 was synthesized by inverse\|suspending polymerization reaction between acrylic acid monomer and kaoline ultrafine powder. The influence of the dispersant agent on the configuration of the products in the inverse suspension polymerization is investigated. The influences of the kaoline powder,cross\|linker,initiator,neutralization degree and the volume ratio of oil to water phase on the water absorbency of the superabsorbent composites are discussed in the paper.

Influence of CaO-based expansive agent,superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The macroscopic properties of concrete are highly determined by the microstructure.In this study,the influence of CEA and SAP addition on the pore structure evolution of cement paste under different curing temperatures was evaluated via low-field nuclear magnetic resonance spectroscopy.Test results indicated that,in cement paste,a higher CEA content led to a higher porosity and a larger most probable pore diameter(MPPD).Meanwhile,SAP addition increased the porosity and MPPD of CEA cement paste at early age but decreased them after 7 d,and a higher SAP content always brought a higher porosity and MPPD.Furthermore,the addition of SAP led to a lower porosity and MPPD of CEA cement paste than that of plain cement paste after 14 d.Moreover,the porosity and MPPD of CEA cement paste decreased first and subsequently increased as the curing temperature raised.

Preparation of superabsorbent by graft copolymerization of acrylic acid onto corn starch using K_2S_2O_8 and rare earths as initiators

K2 S2 O8 and rare earths （RE） were used as initiators to prepare superabsorbents by graft copolymerization of acrylic acid （ AA ） onto corn starch. The effects of monomer concentration, initiator K2 S2 O8 concentration, cross-linker concentration, reaction temperature and the concentration ratio of RE and K2 S2O8 on the graft copolymerization were studied in terms of the water absorption capacity of superabsorbents. Results indicate that the optimum conditions obtained for the grafting of AA onto 5g starch are as follows： AA of 75. 773 g/L, K2S20s of 0. 437 g/L, RE of 0. 874 g/L, cross-linker of 0. 381 g/L and temperature of 70 ℃. The maximum water absorption capacity obtained is 740 g/g. The new method of graft polymerization is easily proceeded and controlled. The graft copolymers were characterized by infra-red spectroscopy, scanning electron microscopy and TG. Results characterized by IR and SEM give strong evidence for grafting of AA onto corn starch, and those characterized by TG reveal that the grafting of AA improves the theimostability of corn starch.

Influence of Suspension Parameters on Water Absorbency of Starch-g-poly( sodium acrylate) Synthesized by Inverse Suspension Polymerization

Superabsorbents starch grafted sodium polyacrylate was prepared by inverse suspension polymerization, using toluene as the continuous phase, potassium persulfate as the initiator. The effect of suspension parameters, such as volume ratio of continuous phase and dispersed phase, type and dosage of suspending agents, on water absorbency of the starch grafted polymer was studied. Different starch derivatives were also investigated. Superabsorbents made of cationic starch has higher water absorbency than that made of native corn starch.

Experimental Synthesis of Polyacrylic-Type Superabsorbent Polymer and Analysis of Its Internal Curing Performances

A solution polymerization method has been used to synthesize a polyacrylic-type superabsorbent polymer(SAP).The influence of various influential factors,such as the temperature,neutralization degree,cross-linking agent,and initiator,on the water absorption capacity of SAP has been investigated.The results show that the absorption can display a non-monotonic behavior depending on the synthesis conditions.The absorption can also change according to the pH,ion types and ion concentration.As the pH value increases,the water absorption capacity decreases significantly.It also decreases if the N^(a+)concentration becomes higher and becomes particularly low in solutions containing Mg^(2+).With the addition of SAP,the compressive strength of cement mortar decreases;the internal relative humidity can be maintained at 96%within 200 hours;and autogenous shrinkage can be reduced by nearly 69%.