Synthesis and characterization of glass-containing superabsorbent polymers

By embedding hollow glass spheres of different sizes and densities into a matrix of crosslinked sodium polyacrylate, superabsorbent polymers were synthesized using a water-in-oil suspension polymerization. These glass-containing superabsorbents were capable of taking up water not only in form of a swollen polyacrylate gel, but also in form of additional free water between the glass spheres and the surrounding polyacrylate matrix. According to swelling measurements the maximum volume swelling degree of the glass-containing superabsorbents is in certain cases nearly double as large as the value of a superabsorbent without embedded glass spheres.     

微波作用下的细粉煤脱水研究

在煤炭开采和加工工业中 ,泥煤的脱水问题变得越来越重要。改进细粉煤脱水效果的方法主要有物理方法和化学方法两类。现有的物理方法主要是提高过滤压力 ,使滤饼的结构变得致密 ,从而挤出其中的水分 ;微波加热脱水是指煤饼中的极性分子水在微波场的作用下快速摆动 ,产生类似于摩擦的作用 ,而以热的形式表现出来 ,使水分蒸发[1] 。本文是在微波加热条件下 ,探讨了微波对脱水效果的影响以及微波脱水的最佳工艺条件。1　实验部分1 1　原料　实验样品为朱仙庄气煤、山家林肥煤、西曲焦煤、青龙山瘦煤。其工业分析见表 1,其中空气干燥基水分为块…     

高吸水性树脂研究进展

介绍了高吸水性树脂的结构、性能及其表征,结合经典理论与最新研究从热力学和动力学角度阐述其吸水机理,着重分析合成条件,组份和方法对高吸水性树脂性能的影响机制,简略地介绍了高吸水性树脂三十年来的发展及广阔的应用领域,并预测其研究与开发前景     

Theoretical analysis of centrifugal dewatering of superabsorbent hydrogels using Terzaghi-Voigt combined model

This paper presents results of experimental work carried out to study the centrifugal dewatering behaviors of superabsorbent hydrogels. Taking the creep deformation of the hydrogels into consideration and assuming that the mechanical properties of gel network can be represented by Terzaghi-Voigt combined model, the basic differential equation expressing the centrifugal dewatering of superabsorbent hydrogels is solved. The progress of centrifugal dewatering is represented by an average consolidation ratio U_c as in mechanical expression. The agreement between calculated and experimental U_c is satisfactory when the creep deformation of the material is considered. Consistent with mechanical expression and electro-osmotic dewatering, as the driving force for centrifugal dewatering increases, the modified consolidation coefficient of the hydrogel network C_e also increases. Effectiveness of centrifugal dewatering, expressed as a relative difference between the initial void ratio and final void ratio, increases with the rotational speed. For a given rotational speed, the final void ratio remains constant regardless of the initial weight of the gel. On the other hand, as the rotational speed of the centrifuge gets higher, the final void ratio decreases for all initial weights of the gel investigated in the current study. The magnitude of creep deformation B depends upon the amount of initial weight of the hydrogel. For a given rotational speed of the centrifuge, the magnitude of creep deformation becomes larger as the initial amount of hydrogel is increased.     

Determination of the swelling behavior of superabsorbent polymers by a tracer-assisted on-line spectroscopic measurement

This work reports on a method for the accurate determination of kinetic swelling behavior and properties of superabsorbent polymers by a tracer-assisted on-line spectroscopic measurement. Based on monitoring the spectral absorption of a tracer compound (blue dextran 2000) at 610 nm in a superabsorbent polymer containing solution, the swelling (water absorption) of the polymer during the process can be followed, from which the parameters in a kinetic equation can be obtained. The results showed that the data obtained by the present method has a good measurement precision and accuracy, in which the relative differences were less than 4.0% when comparing the data measured by a reference method (i.e., the tea bag method). Since the present method can perform an on-line measurement, it is much superior to the current tea bag method and therefore is very suitable to be used in the process related study for the swelling behavior of superabsorbent polymers in many applications.     

Fine tuning of SAP properties via epoxy‐silane surface modification

Using 3‐[(2,3‐epoxypropoxy)‐propyl]‐trimethoxysilane as a surface modifier, superabsorbent polymers with improved gel strength in their swollen state and saline absorbency under load are synthesized. The products are characterized using attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR), rheometry, scanning electron microscopy–energy dispersive X‐ray analysis, contact angle, thermogravimetric analysis, water absorbency and gel content. The temperature and the duration effect of the surface‐treatment process on residual monomer content are also investigated by high performance liquid chromatography. The gel strength (as shown by storage modulus) and absorbency under load are improved up to 3500–4000 Pa, and 30–40 g/g, respectively. It is suggested that the surface of the superabsorbent polymer particles has been modified by two mechanisms: i.e. interpenetrating polymer network and cross‐linking. Moreover, the surface modification has enhanced thermo‐stability and prohibited undesirable gel blockage. Depending on the post‐treatment method used, the wetting behavior of particles is also altered. Copyright © 2017 John Wiley & Sons, Ltd.     

SYNTHESIS AND PROPERTIES OF ACRYLIC-BASED SUPERABSORBENTS WITH ENHANCED CROSSLINKING ON PARTICLE SURFACE

A series of acrylic-based superabsorbent resins were synthesized by inverse suspension polymerization, using potassium persulfate as the initiator, N, N＇-methylene bisacrylamide （BIS） and divinylbenzene （DVB） as the multiple crosslinking agents. The morphology of the resulting superabsorbent resins revealed by SEM demonstrated that a hard shell layer was indeed formed due to surface crosslinking. The swelling and deswelling properties, and the mechanical strength of superabsorbents were investigated. The results indicated that the adding time of DVB and the amount of DVB participated in the crosslinking show a significant influence on the properties of superabsorbents. When DVB was added in polymerization later, the amount of DVB participated in reaction decreases and the surface crosslinked shell becomes thinner. It is suitable for DVB to be introduced in the later stage of the polymerization process, because the absorption rate of resin is efficiently improved in conjunction with higher water absorption. Furthermore, it was found that the mechanical strength of swollen superabsorbent with surface crosslinking was indeed enhanced in comparison with that of the conventional one.     

Dewatering Green Sapwood Using Carbon Dioxide Undergoing Cyclical Phase Change between Supercritical Fluid and Gas

Conventional kiln drying of wood operates by the evaporation of water at elevated temperature. In the initial stage of drying, mobile water in the wood cell lumen evaporates. More slowly, water bound in the wood cell walls evaporates, requiring the breaking of hydrogen bonds between water molecules and cellulose and hemicellulose polymers in the cell wall. An alternative for wood kiln drying is a patented process for green wood dewatering through the molecular interaction of supercritical carbon dioxide with water of wood cell sap. When the system pressure is reduced to below the critical point, phase change from supercritical fluid to gas occurs with a consequent large change in CO₂ volume. This results in the efficient, rapid, mechanical expulsion of liquid sap from wood. The end-point of this cyclical phase-change process is wood dewatered to the cell wall fibre saturation point. This paper describes dewatering over a range of green wood specimen sizes, from laboratory physical chemistry studies to pilot-plant trials. Magnetic resonance imaging and nuclear magnetic resonance spectroscopy were applied to study the fundamental mechanisms of the process, which were contrasted with similar studies of conventional thermal wood drying. In conclusion, opportunities and impediments towards the commercialisation of the green wood dewatering process are discussed.     

Preparation and Properties of Novel Slow-release PK Agrochemical Formulations Based on Carboxymethylcellulose-Graft-Poly(acrylic acid-co-itaconic acid) Superabsorbents

To improve the utilization of fertilizer and water resources at the same time, a new slow-release PK compound fertilizer (SRCF) with the function of water retention was prepared. Element analysis results showed that the product contained 20.46% potassium (shown by K₂O) and 15.45% phosphorus (shown by P₂O₅), which were trapped in the matrix of carboxymethylcellulose-graft-poly(acrylic acid-co-itaconic acid) superabsorbent polymer. Major factors affecting the water absorbency of SRCF such as weight ratio of itaconic acid (IA) to acrylic acid (AA), contents of crosslinker, K₂HPO₄, and carboxymethylcellulose (CMC) were investigated and optimized. The water absorbency of the product was 130 times its own weight if it was allowed to swell in tap water at room temperature for 1 h. Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric/Differential thermal analysis (TG/DTA) confirmed that AA and IA monomers were graft-copolymerized onto CMC backbone and presented the improved thermal stability. The water evaporation of the fertilizer-containing superabsorbents, as well as their nutrients release in sandy soil was carried out, and a possible slow-release mechanism was proposed. Additionally, compressive modulus measurements revealed that the introduction of CMC could improve the mechanical properties of the superabsorbents. These studies showed that the product with good slow-release and water retention properties, being economical and environment-friendly, could be expected to have wide potential applications in modern agriculture and horticulture.     

Investigation of Water Uptake Behavior of Superabsorbent Polymers Composed of N‐Vinyl‐2‐pyrrolidone and Partially Neutralized Acrylic Acid

Fast‐swelling micrometer sized superabsorbents were synthesized through a rapid solution polymerization of n‐vinyl‐2‐pyrrolidone (NVP) and partially neutralized acrylic acid (PNAAc) under normal atmospheric conditions using N,N'‐methylene bisacrylamide (MB) as crosslinker and sodium bicarbonate as porogen. The effect of various parameters such as crosslinker concentration, degree of neutralization of monomer acid, concentration of initiator have been evaluated. Water retention capacity of superabsorbents under varying loads was also examined. The drying behavior of polymers at 37°C was also studied. The gels showed sharp volume transition in solutions of divalent metal ions. The superabsorbents were also characterized by FTIR and TGA.     

Frontal copolymerization synthesis and property characterization of starch-graft-poly(acrylic acid) hydrogels

Recently, a considerable amount of research has centered on uniquely structured polymers synthesized through self-propagating frontal polymerization. The obtained polymer materials have better features than those obtained by using the classical batch route. The additional advantages are short reaction times and low cost. This work describes the first frontal polymerization synthesis of a graft copolymer superabsorbent hydrogel of acrylic acid onto starch at high monomer and initiator concentration. The effects of varying the relative amounts of the reaction components on the most relevant parameters relating to frontal polymerization were explored. The front velocity dependence on initiator concentration could be fit to a power function. The temperature profiles were found to be very sharp with a maximum temperature below 150 degrees C, which was responsible for high monomer conversion. The ultimate properties of the product appear to depend on the polymerization front velocity and the temperature. The high-temperature and rapid temperature increase at the polymerization front led to products with interconnected porous structures caused by the evaporation of water. So, a fast-swelling, highly absorbing hydrogel with respect to batch polymerization was obtained.     

Temperature Sensitive Superabsorbent Hydrogels from Poly(N-t-butyl acrylamide-co-acrylamide) Grafted on Sodium Alginate

Temperature-sensitive hydrogels based on N-t-butylacrylamide (TBA), acrylamide (AAm), and sodium alginate were prepared by free radical polymerization method. Methylenebisacrylamide (MBA) and amonium persulfate (APS) were applied as water soluble crosslinker and initiator, respectively. The chemical structure of the hydrogels was confirmed by FT-IR spectroscopy and thermogravimetric analysis (TGA) methods. Morphology of the samples was examined by scanning electron microscopy (SEM). By changing the initial TBA/AAm mole ratios, hydrogels with different swelling properties were obtained. The rate parameters were found to be 2.0, 2.4, and 3.5 min for the superabsorbents with AAm/TBA weight ratio of 1.0, 1.3 and 2.0 respectively. The swelling behavior in distilled water and different pH solutions was investigated. A preliminary swelling kinetics and the absorbency under load (AUL) were also studied. At the applied pressure (2.07 kPa), maximum swelling was found to be 17, 19, and 21 (g/g) for the superabsorbent hydrogels with AAm/TBA weight ratios of 1.0, 1.5 and 2.0, respectively.     

工业废碱催化剂MA与煤混合浸渍干燥的研究

以转筒干燥方式考察了福建无烟粉煤与工业废碱催化剂MA同时进行混合浸渍与干燥脱水的过程，讨论了煤的粒径，干燥温度，时间、气速、转筒转速、催化剂含量和转筒处理量等因素对煤与催化剂混合浸渍与干燥过程的影响。研究表明采用转筒干燥的方式,进口干燥空气温度在80 ℃～160 ℃、转筒处理量为214 kg/m3·h～1834 kg/m3·h、干燥气速0.12 m/s～0.30 m/s、干燥时间20 min内，混合物料的湿含量可降至<5%，且催化剂与煤浸渍充分均匀，满足流化床操作的要求，实现了最佳的催化气化效果。基于实验数据拟合了煤和废碱催化剂转筒干燥的传热系数方程，通过物料与能量衡算，模拟了混合物料连续干燥时沿转筒的湿含量的变化。     

Evaluation of the degree of cross-linking of cellulose-based superabsorbent hydrogels: a comparison between different techniques

Three different techniques have been applied to the evaluation of the degree of cross-linking of superabsorbent cellulose-based hydrogels obtained from water solutions of carboxymethylcellulose sodium salt (CMCNa) and hydroxyethylcellulose (HEC), chemically cross-linked with divinyl sulfone. These polyelectrolyte hydrogels are biodegradable and have the same sorption capacity as acrylate-based superabsorbents on the market. A ¹³C solid state NMR analysis was carried out on dry samples of hydrogel to obtain the degree of cross-linking, an important parameter that affects the swelling and mechanical properties of a hydrogel. Dynamic mechanical analysis was performed during the hydrogel cross-linking using a parallel plate rheometer under oscillatory deformations in order to monitor the evolution of the hydrogel viscoelastic properties during the synthesis. The value of |G*| and the slope of the stress-deformation ratio plots from uniaxial compression tests were used to evaluate the elastically effective degree of cross-linking according to classical rubber elasticity theory. Moreover, a dynamic mechanical analysis was carried out on cross-linked hydrogels at different degrees of swelling in order to investigate the influence of the swelling on the mechanical properties and the application of rubber elasticity theory to swollen hydrogels.     

Synthesis of a slow‐release and superabsorbent nitrogen fertilizer and its properties

A slow‐release and superabsorbent nitrogen fertilizer (SSNF) was synthesized by aqueous solution copolymerization of acrylic acid and maleic anhydride using N,N′‐methylene bisacrylamide as a crosslinker, ammonium persulfate and sodium sulfite as an initiator in the presence of urea. The effects on water absorbency such as amount of crosslinker, initiator, urea and maleic acid, degree of neutralization, etc. were investigated. To improve slow release and water retention properties, the product was surface‐crosslinked with trihydroxymethyl propane glycidol ether (6360). The nitrogen content of the SSNF synthesized under optimal conditions was 28.5%, and the water absorbencies were about 900 (g/g) in distilled water and 180 (g/g) in tap water. The nitrogen slow release behavior of the SSNF in water and water retention capacity of the soil with SSNF were also investigated. The results showed that the surface‐crosslinked product not only had good slow release property but also excellent soil moisture preservation capacity, which could effectively improve the utilization of fertilizer and water resources simultaneously. The results of the present work indicated that the SSNF could be found an application in agriculture and horticulture, especially in drought‐prone areas where the availability of water is insufficient. Copyright © 2006 John Wiley & Sons, Ltd.     

Study on superabsorbent of maleic anhydride/acrylamide semi‐interpenetrated with poly(vinyl alcohol)

A series of superabsorbents of maleic anhydride (MAH)/acrylamide (AM) interpenetrated with poly(vinyl alcohol) (PVA) were prepared by aqueous polymerization, using N,N‐methylenebiacrylamide (NNMBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The samples were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscope (SEM). The effects of reaction variables on the water absorbency of the superabsorbents in distilled water and in 0.9 wt% NaCl solution were investigated. In addition, the effect of the PVA content on the swelling rate and sensitivity to saline of the superabsorbents were also investigated. The results showed that the absorbency, both in 0.9 wt% NaCl solution and in distilled water, first decreased and then increased with increasing PVA content. Moreover, the resultant superabsorbent had a higher absorption rate and it became less sensitive to saline by incorporating certain amount of PVA into the network of the hydrogel. Copyright © 2009 John Wiley & Sons, Ltd.     

快速、高强超吸水凝胶的研究

概括介绍了一些在高吸水凝胶基础上提高凝胶吸水速率和膨胀凝胶强度的方法以及近年来的相关研究状况,展望了制备吸液量大、吸液快且强度高的水凝胶的研究发展前景.     

Energy-saving drying technology for porous media using liquefied DME gas

Process design and energy requirement for a practical plant are investigated for an energy-saving drying (dewatering) process invented by the authors in 2002 for high-moisture porous materials. The basic concept of the process involves the extraction of water from a high-moisture porous material by bringing it in physical contact with liquefied dimethyl ether (DME) at room temperature. Water content of DME asymptotically increases to the saturation value and the high-moisture porous material is dried almost perfectly. DME from the DME-water mixture is vaporized by decompression. DME and water are separated by flash distillation. DME vapor is compressed and cooled in a heat exchanger, and the latent heat of condensation is reused to vaporize the DME in the heat exchanger. Multistage compression and multistage flash distillation are employed. After compression, the temperature of DME is less than 50?°C. Because specific heat ratio of DME is only 1.11, the energy consumption of the compressor is reduced. Considering the adiabatic efficiency of the compressor and the net thermal efficiency, the total energy for dewatering is about 1100 kJ per 1-kg-water-content of the material being dewatered This process has significant potential and is compact than the existing dewatering processes.     

Autothermal biodrying of municipal solid waste with high moisture content

To carry out autothermal drying processes during the composting of biomass, a horizontal tubular reactor was designed and tested. A biodrying tunnel of the total capacity of 240 dm³ was made of plastic material and insulated with polyurethane foam to prevent heat losses. Municipal solid waste and structural plant material were used as the input substrate. As a result of autothermal drying processes, moisture content decreased by 50 % of the initial moisture content of organic waste of about 800 g kg⁻¹. In the tested cycles, high temperatures of biodried waste mass were achieved (54–56°C). An appropriate quantity of air was supplied to maintain a satisfactory level of temperature and moisture removal in the biodried mass and high energy content in the final product. The heat of combustion of dried waste and its calorific value were determined in a calorimeter. Examinations of pyrolysis and gasification of dried waste confirmed their usefulness as biofuel of satisfactory energy content.     

Novel sulfobetaine‐sulfonic acid‐contained superswelling hydrogels

Novel hydrogels based on zwitterionic monomer [3‐(methacrylamido)propyl] dimethyl (3‐sulfopropyl) ammonium hydroxide (MPDSAH) and a strong acid monomer (2‐acrylamido‐2‐methylpropane sulfonic acid, AMPS) were synthesized through solution polymerization under normal conditions to achieve nearly quantitative gel yield. The structure of the gels was confirmed using infrared spectroscopy. Thermal properties were simultaneously studied by differential scanning calorimetry and thermogravimetric analysis (DSC/TGA). The effects of the polymerization variables on the swelling capacity of the products were investigated. It was found that, in a certain range of the monomers mol ratio, increase of AMPS content was surprisingly accompanied with swelling reduction. The swelling exhibited lower sensitivity to the crosslinker concentration (range 0.6–1.2 wt%) compared with the conventional superabsorbents. However, in contrast with the conventional acrylic acid‐based superabsorbents, the neutralization degree of AMPS part of the new gels had only a small enhancing effect on their swelling capacity. The effect of total monomer concentration on the hydrogel absorbency was also studied. The fully ionic hydrogels showed an unusual pH‐independency behavior, so that their absorbency was nearly unchanged in a wide range of pH. Such unexpected behavior was also observed for the swelling in the ionic environments with various ionic strengths. Copyright © 2005 John Wiley & Sons, Ltd.