Preparation and Swelling Kinetic Analysis of Poly (HPMC-co-AA-co-AM) Super Absorbent Resin

Super absorbent resin(SAR)is prepared by aqueous high temperature polymerization using hydroxypropyl methylcellulose(HPMC)as monomer backbone material,acrylic acid(AA)and acrylamide(AM)as the graft copolymer monomer,potassium persulfate(KPS)as the initiator to generate free radicals,and N,N`-methylenebisacrylamide(MBA)as cross-linking agent for cross-linking reaction.Simutaneously,the influence of individual factors on the water absorption is investigated,and these factors are mainly AA,AM,KPS,MBA,HPMC,and reaction temperature.The optimized conditions are obtained by the experiment repeating for several times.The water absorption multiplicity and salt absorption multiplicity under the conditions are 782.4 and 132.5 g/g,respectivity.Furthermore,the effects of different temperatures and salt concentrations on its water absorption,as well as the swelling kinetics of SAR are studied.It is indicated the water-absorbing swelling process is mainly caused by the difference in water osmotic pressure and Na+concentration inside and outside the cross-linked molecular structure of the resin,which is not only consistent with the quasi-secondary kinetic model,but also with the Fick diffusion model.

Preparation and characterization of supramolecular gel suitable for fractured formations

The excellent mechanical properties of supramolecular gel could adapt to the complex reservoir environment and had broad application prospects in the field of oil and gas drilling and production engineering.In this paper,a supramolecular gel based on hydrophobic association and hydrogen bonding was prepared by micellar copolymerization,which could be used to plug fractures and pores in formations.Supramolecular gel was a gel network system with high performance characteristics formed by self-assembly of non-covalent bond interaction.The rheological properties,mechanical mechanics,temperature resistance and swelling ability of supramolecular gel were studied.The results showed that the supramolecular gel had a dense three-dimensional network structure with open and interconnected pore structures,which could exhibit good rheological properties and strong viscoelastic recovery ability.The mechanical properties of the supramolecular gel were excellent,it had a tensile stress of 0.703 MPa and an elongation at break of 1803%.When the compressive strain was 96%,the compressive stress could reach 14.5 MPa.Supramolecular gel also showed good temperature resistance and swelling properties.At the aging temperature of 135℃,supramolecular gels still maintained good gel strength,and it only took 12 h to reach the equilibrium swelling ratio of 35.87 in 1%NaCl solution.It was also found that supramolecular gel in low concentration saline(1%NaCl solution)showed relatively faster swelling than high concentration saline(25%NaCl solution).The swelling process of the supramolecular gel was non-Fick diffusion(typeⅡ).This indicated that the organic/inorganic permeability network was well formed.Therefore,the diffusion rate of small molecules could be guaranteed to be equal to the relaxation rate of large molecules before and after the phase transition temperature.In addition to the diffusion of water molecules,the swelling process of the supramolecular gel was also affected by the relaxation of gel network and polymer chain segment,the interaction between water molecules and polymer network and the groups of polymer network and other factors.Supramolecular gel particles could be used as plugging materials for drilling fluids,which had excellent ability to plug formation fractures and pores.The plugging ability of the supramolecular gel was up to 6.7 MPa for 0.5 mm fracture width,and 9.6 MPa for porous media with 5 mD permeability.Compared with HT-PPG gel particles commonly used in oil fields,supramolecular gel particles had better plugging ability on fractures and porous media.The development and application of supramolecular gel had far-reaching significance for promoting the functional application of polymer materials in drilling and production engineering.

Synthesis and Characterization of Hydrogels Based on Potato Starch/Poly(vinyl Alcohol)/N,N′-Methylenebisacrylamide

Several hydrogels were synthesized by free-radical polymerization in an aqueous medium based on potato starch(PS),poly(vinyl alcohol)(PVA),and N,N′-Methylenebisacrylamide(MBAm),being possible to study these hydrogels as a function of the proportion of components incorporated.In this way,the products generated from the synthesis were characterized by swelling and deswelling kinetics,the first swelling being verified with Schott and statistical models,allowing to contrast the proximity between the experimental and theoretical behavior.Additionally,water retention in soil(R%),spectroscopy(FTIR),morphological(SEM),and thermal(TGA and DSC)analysis allowing to know the intrinsic characteristics of the material,increasing in general terms the knowledge of this type of material.In this context,it was possible to verify the characteristics and effectiveness of the synthesis and crosslinking of the main components.The experimental results obtained show that the synthesized hydrogels present representative swellings consistent with kinetic and statistical models,optimal thermal stability depending on the amount of crosslinker,and excellent water retention in environments such as soil,presenting it as an excellent alternative to be used in agro-industrial applications in an eco-friendly way.

Dynamic swelling performance of hydrophobic hydrogels

Conventional gels manifest monotonous swelling or shrinking performance upon immersing in solvents until reaching an equilibrium state. Recently, we discovered that the “hydrophobic hydrogels” prepared from hydrophobic polymer networks demonstrated dynamic swelling performance without equilibrium states. Upon water immersion, the gels expanded tremendously at the first stage until reaching a swelling peak;subsequently, the gels shrunk at an extremely slow rate. While this phenomenon endows the material with an unusual feature, more efforts are highly demanding for the full understanding of this performance. Herein, we systematically investigate the hydrophobic hydrogels’ swelling kinetics by screening the organic solvent dependence, polymer effect, and temperature impact. It is revealed that the chemical structure of gels greatly influences the swelling kinetics. The higher the networks’ hydrophobicity, the slower the swelling kinetics. Meanwhile, organic solvents demonstrate a limited effect on the dynamic swelling performance. Moreover, higher temperature significantly accelerates the whole volume change process. Based on the swelling performance, we further develop hydrogel-based soft devices with timeprogrammable two-dimensional and three-dimensional shape-shifting performances.