Influence of new organic alkali activators on microstructure and strength of fly ash geopolymer

The fly ash geopolymer with improved mechanical properties was prepared by a new mixture alkali activator. In this paper, sodium tert-butanol, an organic strong alkali was used as an activator for preparing fly ash geopolymer to improve their mechanical properties. The effect of activator content and type on the macroscopic level of fly ash geopolymer was investigated experimentally by three types of activators: sodium tert-butanol, sodium silicate, and sodium tert-butoxide/sodium silicate mix activator. The microstructure of the fly ash geopolymer was characterized by ATR-FTIR, SEM-EDS, XRD, and Brunauer-Emmett-Teller (BET) physical adsorption method. The results showed that the new mixture alkali activator prepared by 5% sodium tert-butoxide and 10% sodium silicate improved the denseness and integrity of the microstructure of the fly ash geopolymer. Consequently, the mechanical properties of fly ash geopolymer are improved. The microscopic results demonstrated that the C–OH in tert-butanol after the hydrolysis of sodium tert-butoxide and Si–OH in the geopolymer can form C–O–Si bonds, forming a more complex three-dimensional network structure. This paper reveals the enhancement mechanism of organic alkali as activators for preparing fly ash geopolymer, and provides support for the subsequent development of organic strong alkali activators.     

Chemical modification of cellulose acetate by allylation and crosslinking with siloxane derivatives

A new pathway to cellulose–siloxane hybrid materials was investigated. Allylated cellulose was prepared by chemical modification of cellulose acetate using three different procedures and was crosslinked afterwards by hydrosilylation in the presence of Karstedt's catalyst. Poly[dimethyl(methyl‐H)siloxane] with 25 mol% Si? H side groups and 1,1,3,3‐tetramethyldisiloxane were used as crosslinking agents in different ratios as regards the unsaturated component. The occurrence of the reaction was verified using Fourier transform infrared spectrometry following the reduction until disappearance of bands corresponding to Si? H and C?C bonds with the formation of new Si? C bonds that led to the crosslinking of the cellulose derivative. The reaction products were processed as films that were insoluble in common solvents. Surface (static contact angle, water vapour sorption capacity and swelling in various solvents), mechanical and thermal properties of the networks processed as films were investigated and the results were correlated with the reactant ratios. The crosslinking density was determined based on differential scanning calorimetry data. Copyright © 2012 Society of Chemical Industry     

Preparation and properties of a salt‐resistant superabsorbent polymer

Crosslinked sodium polyacrylate was prepared by solution polymerization with N,N‐methylene‐bisacrylamide (bisAM) as crosslinking agent; it was subsequently surface‐crosslinked by ethylene glycol diglycidyl ether (EGDE) and then was modified with inorganic salt to obtain a superabsorbent with water absorbency in 0.9 wt % NaCl aqueous solution at atmosphere and applied pressure (P ≈ 2 × 10³ Pa) of 55 and 20 g.g^?1, respectively. Moreover, it also had excellent hydrogel strength. The effects of reaction temperature, reaction time, neutralization degree (ND) of acrylic acid, amount of initiator, crosslinking agent, and surface‐crosslinking agent, mass ratio of inorganic salt to initial superabsorbent, molar ratio of sodium aluminate (NaAlO₂) to potassium dihydrogen hyphosphate (KH₂PO₄) on water absorbency (WA) in 0.9 wt % NaCl aqueous, and the hydrogel modulus were investigated and optimized. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2532–2541, 2004     

Self‐crosslinkable epoxidized natural rubber–silica hybrids

Epoxidized natural rubber (ENR)–silica hybrids without any other additives were prepared by an open‐mill mixing method at room temperature. The curing characteristics, crosslinking density, mechanical properties, and dynamical mechanical properties were investigated. The results indicate that the ENR–silica hybrid materials could be cured with silica as a crosslinking and reinforcing agent. Attenuated total reflection–Fourier transform infrared spectroscopy and solid‐state ¹³C‐NMR spectroscopy exposed the characteristics of the interfacial interaction in the hybrids and confirmed the existence of chemical bonds and hydrogen bonds between the epoxy group and Si? OH. Scanning electron microscopy illustrated a good dispersion of silica in the ENR matrix. Meanwhile, the modulus at 100% elongation of the hybrid reached 9.64 MPa when 100‐phr silica was loaded; a similar trend was observed for the hardness. Finally, our findings might extend the concept of rubber curing and open a new space for making an environmentally friendly rubber composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44605.     

Properties of hybrid materials derived from hydroxy‐containing linear polyester and silica through sol–gel process. I. Effect of thermal treatment

The transparent hybrid material, HLP/SiO₂, was prepared by an in situ sol–gel process of tetraethoxysilane (TEOS) at 30°C in the presence of hydroxy‐containing linear polyester (HLP) obtained by ring‐opening reaction of diglycidyl ether of bisphenol A (DGEBA) with adipic acid under the catalyzation of triphenylphosphine (TPP). The hetero‐associated hydrogen bonds between the HLP and the residual silanol of silica in the hybrids were investigated by FTIR spectroscopy. Upon heating the hybrid, the interfacial force between the HLP matrix and the silica network changed from hydrogen bonds into covalent Si—O—C bonds through dehydration of hydroxy groups in HLP with residual silanol groups in the silica network. The existence of covalent Si—O—C bonds was proved by solid‐state ²⁹Si‐NMR spectra. Other properties such as tensile strength, glass transition temperature (T_g ), solubility, and thermal stability of the hybrids before and after heat treatment were studied in detail. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1179–1190, 2000     

Modification of polyethylene–octene elastomer by silica through a sol–gel process

In this study, tetraethoxysilane (TEOS) and a metallocene polyethylene–octene elastomer (POE) were chosen as the ceramic precursor and the continuous phase, respectively, for the preparation of new hybrids by an in situ sol–gel process. To obtain a better hybrid, a maleic anhydride‐grafted polyethylene–octene elastomer (POE‐g‐MAH), used as the continuous phase, was also investigated. Characterizations of POE‐g‐MAH/SiO₂ and POE/SiO₂ hybrids were performed by Fourier transform infrared (FTIR) and ²⁹Si solid‐state nuclear magnetic resonance (NMR) spectrometers, a differential scanning calorimeter (DSC), a thermogravimetry analyzer, and an Instron mechanical tester. The results showed that the POE‐g‐MAH/SiO₂ hybrid could improve the properties of the POE/SiO₂ hybrid because the interfacial force between the polymer matrix and the silica network was changed from hydrogen bonds into covalent Si? O? C bonds through dehydration of hydroxy groups in POE‐g‐MAH with residual silanol groups in the silica network. The existence of covalent Si? O? C bonds was proved by FTIR spectra. For the POE/SiO₂ and POE‐g‐MAH/SiO₂ hybrids, maximum values of the tensile strength and the glass transition temperature were found at 9 wt % SiO₂ since a limited content of silica might be linked with the polymer chains through the covalent bond. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 966–972, 2003     

The structure of sodium silicate glass from neutron diffraction and modeling of oxygen-oxygen correlations

It is shown that modeling the first oxygen-oxygen peak in the neutron correlation function of a glass enables structural information about other correlations to be obtained, and the method is illustrated by application to a sodium silicate glass. The first O–O coordination number can be calculated from network theory, and sodium silicate crystal structures show that the mean O–O distance can be calculated from the Si–O distance, despite the distortion of the SiO₄ tetrahedra. Modeling the O–O peak for a sodium silicate glass allows the Na-O bond length distribution to be determined. For a binary glass with 42.5 mol% Na₂O, it is found that the Na–O coordination number is 4.8(2) with an average bond length of 2.45 Å, and the Na–O bond lengths are more widely distributed than in sodium silicate crystal structures. Sodium ions are bonded mostly to non-bridging oxygens (NBOs), and the Na–NBO coordination number may be four as in crystals. Sodium ions are also bonded to a smaller number of bridging oxygens (BOs). Contrary to previous reports, it is not concluded that Na–NBO bonds are shorter than Na–BO bonds, but instead that the Na–BO distribution is relatively narrow, whilst the Na–NBO distribution extends to both shorter and longer distance. The broad distribution of Na–O bond lengths arises from a relatively broad distribution of Na–NBO bond valences, subject to the overall requirement of charge balance.     

Character and mechanism of surface micromachining for C/SiC composites by ultrashort plus laser

A new surface micromachining way of ultrashort plus laser for C/SiC composites with high quality and efficiency was demonstrated, including picosecond and femtosecond laser. Surface morphologies, element content and bonding states of C/SiC composites were analysed in detail after machined by picosecond and femtosecond laser power respectively. For femtosecond laser machining, the amount of nanoparticles increased with increasing laser power. At 20 and 50?mW, Si–C, C–C and Si–O bonds existed in nanoparticles, while Si–C bonds disappeared at 70?mW. For picosecond laser machining, cauliflower-like particles and periodic ripple with certain depth were formed distinctly. Furthermore, thermal ablation phenomenon occurred, and only Si–O bonds existed in particles due to the oxidation of the carbon fibres and SiC matrix. The results showed that femtosecond laser with low power was more suitable to the surface machining due to better machining quality and less machining damage compared with high power picosecond laser.     

Synthesis and characterization of poly(vinyl alcohol)/water glass (SiO2) nano‐hybrids via sol‐gel process

A new class of materials based on inorganic and organic species combined at a nanoscale level has received large attention recently. In this work the idea of producing hybrid materials with controllable properties is applied to obtain foams to be used as catalyst supporting. Hybrids were synthesized by reacting poly(vinyl alcohol) in acidic solution with water glass. The inorganic phase was also modified by incorporating a hexamethyldisiloxane as precursor. The hybrid aerogel powder was analyzed by scanning electron microscopy, TG‐DTA, Nitrogen adsorption–desorption, X‐ray diffraction and fourier transform infrared spectroscopy (FTIR) spectroscopy. The powder obtained had a higher porosity varying from 65 to 90% and the nanopore diameter ranged from 17 to 20 nm. The surface area and nanopore volume decreased as polymer content increased in the hybrids. The sharp decline in the weight observed at around 500°C accompanied an exothermic peak of the DTA curve. The sharp peak was observed around 211°C represents the DTA curve of Poly vinyl alcohol constituent in nano hybrids. The peak at 1638 cm^?1 in the FTIR indicated the formation of Si? O? PVA? O? Si bridge in aerogel powder. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The structure of organosilicon plasma-polymerized coatings on metal substrates

The structure of coatings formed by the low pressure plasma-polymerization of hexamethyldisiloxane has been studied by FTIR and XPS techniques. The coatings were performed in two pressure regions: 0.63–0.88 and 0.36–0.44 torr. At both pressures much of the structure of the monomer appeared to be maintained. Coatings deposited at the higher pressure showed the expected increase in abstraction of methyl groups and formation of Si ? O ? Si crosslinks with increasing discharge power. The lower pressure coatings showed a markedly more diverse pattern of peaks associated with Si ? O bonds. The spectra of the moncmer, hexamethyldisiloxane, and of a highly crosslinked silicone resin were examined in order to clarify the way in which FTIR spectra varied during the polymerization and crosslinking processes. The different structures observed emphasize a considerable potential for tailoring structure by varying deposition conditions.     

Novel biodegradable superabsorbent hydrogels derived from cotton cellulose and succinic anhydride: Synthesis and characterization

The synthesis of novel superabsorbent hydrogels was investigated with the reaction of cotton cellulose and succinic anhydride (SA) in the presence of 4‐dimethylaminopyridine as an esterification catalyst in a mixture of lithium chloride (LiCl) and N‐methyl‐2‐pyrrolidinone (NMP) or in a mixture of tetrabutylammonium fluoride (TBAF) and dimethyl sulfoxide (DMSO), followed by NaOH neutralization. Interestingly, a hydrogel was obtained without any crosslinking agent, and this indicated the partial formation of a diester between the cellulosic hydroxyl group and SA. The products obtained in LiCl/NMP exhibited superior absorbency to these obtained in TBAF/DMSO. The former absorbed an amount of water about 400 times its dry weight, and this was comparable to a conventional sodium polyacrylate superabsorbent hydrogel. Furthermore, in an aqueous NaCl solution, the absorbency of the product hydrogels was higher than that of the sodium polyacrylate superabsorbent hydrogel. The formed hydrogels biologically degraded almost completely after 25 days, and this showed their excellent biodegradability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3251–3256, 2006     

Synthesis and optical and thermal properties of poly[methyl(2,9‐diphenyl‐ 7,8‐benzophenanthryl)silylene‐co‐1,4‐bis(methylphenylsilyl)phenylene]

Poly[methyl(2,9‐diphenyl‐7,8‐benzophenanthryl)silylene‐co‐1,4‐bis(methylphenylsilyl)phenylene] (PMBS‐co‐BSP) was synthesized by the condensation reaction of dichloromethyl(2,9‐diphenyl‐7,8‐benzophenanthryl)silane and 1,4‐bis(chloromethylphenylsilyl)benzene with sodium in toluene. Optical and thermal behavior of the polymer was investigated. Because of the introduction of substituted benzophenanthryl groups into the Si atoms of the polymer, the UV absorption wavelength of the PMBS‐co‐BSP red‐shifted significantly in the UV region, and a strong photoluminescence band was observed in the visible region other than the near‐UV photoluminescence typical of normal polysilane. The photochemical behavior was examined both in solution and in thin film by fluorescence and UV spectroscopy. Irradiation of the PMBS‐co‐BSP with a low‐pressure mercury lamp in solution resulted in homolytic scission of silicone–silicone bonds; the fluorescence emission intensities decreased gradually with increasing UV irradiation time and the maximum emission wavelength blue‐shifted significantly. Irradiation of thin solid films of the PMBS‐co‐BSP in air led to the formation of photoproducts containing Si? OH and Si? O? Si groups. The PMBS‐co‐BSP began to weigh less at about 300 °C and the weight loss of the polymer at 700 °C was calculated to be 75% of the initial weight in N₂. Copyright © 2006 Society of Chemical Industry     

Inverse suspension polymerization of sodium acrylate

A superwater-absorbent sodium polyacrylate was synthesized by inverse suspension polymerization, using Span60 as the dispersant, cyclohexane as the organic phase, N,N′-methylene bisacrylamide as the crosslinking agent, and potassium persulfate as the initiator. The effect of reaction conditions such as reaction time, crosslinking agent, and dispersant on deionized-water and saline solution absorbability, average particle size, and distribution of the sol–gel of the resin is discussed. The deionized-water and saline solution absorbabilities of sodium polyacrylate prepared at proper conditions were 300–1200 and 50–120, respectively; the number-average particle size was 10–50 μm and the gel portion was 20–85% by weight. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 789-794, 1997     

Characteristics of nitrile–butadiene rubber layered silicate nanocomposites with silane coupling agent

Nanocomposites of organophilic montmorillonite (C18‐MMT), nitrile–butadiene rubber (NBR), and a coupling agent were produced during a melt compounding process at room temperature. During the process, it was clearly observed that organo‐MMT particles were exfoliated into nanoscale layers of approximately 1–30 nm thickness, in addition to their original 40 μm thickness. These MMT layers were uniformly dispersed in the NBR matrix. The effects of a coupling agent such as 3‐(mercaptopropyl)trimethoxy silane in C18‐MMT/NBR nanocomposites were studied. The C18‐MMT/NBR nanocomposites in the presence of the coupling agent were identified and characterized by X‐ray diffraction, transmission electron microscopy, a universal testing machine, thermogravimetric analysis, and IR spectroscopy. It was observed that an additional silane coupling agent, 3‐(mercaptopropyl)trimethoxy silane, enhanced the chemical interaction and was accompanied by the formation of Si? O? Si coupling bonds between C18‐MMT and the coupling agent and Si? C coupling bonds between NBR and the coupling agent. This work resulted in improved properties of organo‐MMT/NBR nanocomposites because of the nanoscale effects and strong interaction of the coupling bonds between NBR and organo‐MMT. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2633–2640, 2003     

碱溶解玉米淀粉制备高吸水性树脂

以玉米淀粉、丙烯酸为原料,过硫酸铵(APS)为引发剂,N,N'-亚甲基双丙烯酰胺(MBA)为交联剂,将中和丙烯酸的NaOH提前加入体系溶解淀粉,一步法制备出淀粉基高吸水性树脂(SSAP1)。通过单因素实验探究了丙烯酸与玉米淀粉质量比、丙烯酸中和度、引发剂APS用量、交联剂MBA用量对产物吸水倍率的影响,获得最优制备参数。通过FTIR、XRD、SEM分析了SSAP1微观结构,对比了SSAP1和高温糊化淀粉制备出淀粉基高吸水性树脂(SSAP)的接枝率和应用性能。结果表明,碱溶解玉米淀粉成功接枝聚丙烯酸分子链并发生交联反应形成高吸水性树脂,该方法能更有效地破坏淀粉分子内氢键并提高反应效率;SSAP1吸水速率与重复吸水性能优于SSAP;SSAP1在蒸馏水和盐水(0.1 mol/L NaCl溶液)中的吸收倍率分别为464和34 g/g,相比SSAP的吸水倍率(428 g/g)和吸盐水倍率(26 g/g)有明显提升。     

水稻秸秆/膨润土基高吸水树脂的制备及其对Cu2+的吸附

以丙烯酸、丙烯酰胺为单体,水稻秸秆为有机材料,膨润土为无机材料,过二硫酸钾为引发剂,N-羟甲基丙烯酰胺为交联剂,采用水溶液聚合法制备了水稻秸秆/膨润土基高吸水树脂,并对其结构进行了表征。研究了溶液pH值、溶液初始浓度、树脂用量、吸附时间和温度对吸附Cu^2+的影响。结果表明:树脂对Cu^2+的吸附符合Langmuir等温模型,伪二阶动力学模型更能描述树脂对Cu^2+的吸附行为;吸附主要为单分子层吸附,吸附速率取决于表面的空吸附位点;温度越高越有利于反应的进行,且吸附过程中存在化学反应。     

The effect of layered silicates on the crosslinking reaction of silanol‐terminated polysiloxane

The effect of incorporation of clay nanoparticles on the vulcanization reaction of silanol‐terminated polysiloxane was studied. Three different types of commercial clays were investigated as reinforcement, namely: Cloisite 20 A (organically modified with nonpolar aliphatic chains), Cloisite 30B (modified with aliphatic chains containing hydroxyl‐end groups) and Nanofil 116, an unmodified montmorillonite as a reference. Nanoclays were found to increase the rate of curing, assessed by viscosity measurements, in all the examined systems and the acceleration rate is proportional to the content of the additive. Moreover, an increase of the area of peaks corresponding to the formation of Si? O? Si bonds (900–1200 cm^?1) was recorded by FTIR spectroscopy for pure and reinforced poly(dimethylsiloxane) (PDMS). Temperature modulated differential scanning calorimetry was also used for accurately monitoring the curing reaction of organoclay/PDMS hybrids, through the heat capacity and the enthalpy of cold crystallization measurements. For pure PDMS low reaction rate was observed during the first 200 min, followed by fast acceleration. A linear increase of the reaction rate as a function of time was observed for the organoclay/PDMS hybrids. POLYM. ENG. SCI., 55:957–965, 2015. © 2014 Society of Plastics Engineers     

反相悬浮法合成高吸水性树脂的研究

采用反向悬浮法合成了聚丙烯酸钠高吸水性树脂，考察了原料配比（单体中和度、引发剂用量、交联剂用量、油水比等）对产物吸水性能的影响。探讨了无机盐离子和有机溶剂的存在对产物吸水性能的影响。     

pH sensitivity and swelling behavior of partially hydrolyzed formaldehyde-crosslinked poly(acrylamide) superabsorbent hydrogels

Poly(acrylamide) superabsorbent hydrogel was synthesized through crosslinking method. Formaldehyde was used as a crosslinking agent. To achieve a hydrogel with high swelling capacity, the resulted hydrogels were saponified using NaOH solution at high temperature. During saponification, ammonia gas is produced from hydrolysis reaction of amide groups. The arising of ammonia produces porous structure in hydrogels, which is confirmed using scanning electron microscopy. The conversion of amide groups to carboxylate groups was identified by FTIR spectroscopy. The reaction variables in both crosslinking and hydrolysis reactions that affect the swelling of hydrogels were optimized. The swelling of the hydrogels in various salt solutions with various valencies and radii was studied. Also, the absorbency under load was measured. The hydrogels exhibited pH-sensitivity characteristics. A sharp swelling change was observed in lieu of pH variations in a wide range (1–13). The swelling variations were explained according to the swelling theory based on the hydrogel chemical structure. The pH-reversibility and on–off switching behavior makes the intelligent hydrogels as good candidates for considering as potential drug carries. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

Recent development of reactive force fields have enabled molecular dynamics simulations of interactions between silicate glasses and water at the atomistic scale. While multicomponent silicate glasses encompass a wide variety of compositions and properties, one common structural feature in these glasses is the combination of the network structure that is made up of silica tetrahedra linked through corner sharing interspersed with network modifiers like alkali and alkaline-earth ions that break up the Si–O–Si linkages by forming nonbridging oxygen. In reactions with water, ion exchange between alkali ions in the glass and proton or hydronium in the solution, as well as hydrolysis reaction of the Si–O–Si linkages and subsequent silanol formation, is observed and well documented. We have used a set of recently developed reactive force field to investigate the reactions between water and the surfaces of silica and sodium silicate glasses of different compositions for reactions up to 8 nanoseconds. Our results indicate sodium leaching into water and diffusion of water molecules up to 25 Å into the glass surface. We examined the structural and compositional changes inside the glass and around the diffused ions and use these to explain the rates of silanol formation at the surface. We also observed proton transport in the glass which has an indirect influence on the silanol formation rates. While the surface of the glass was rough to start with, it undergoes further modification into a hydrated gel-like structure in the glass for up to 5 Å in the higher alkali containing glasses. It was found that the leached sodium ions remain close to the interface and that fragments of silicate network from the surface is capable of dislodging from the bulk glass and enter the aqueous solution. These simulations thus provide insights into the formation and structure of an alteration layers commonly observed in multicomponent silicate glasses corroded in aqueous solutions.