Effects of crosslinked polycarboxylate superplasticizers with crosslinking agent containing ester and amide groups on the properties of cementitious systems

Herein, crosslinked polycarboxylate superplasticizers were synthesized using acrylic acid, sodium methylallyl sulfonate and methyl polyethylene glycol acrylate as monomers, and monomers that contain either ester or amide groups as crosslinking agents. The superplasticizers that were synthesized from the ester- and amide-based crosslinking agents were respectively denoted as SP-E and SP-N. In addition, a series of performance characterizations were carried out to explore the influence of different functional groups in crosslinking agents on the performance of superplasticizers. Fluidity test results showed that the dispersibility and fluidity retention of cement pastes treated with the SP-E were better than those of cement pastes treated with SP-N. Meanwhile, the viscosity of the sample containing SP-E was lower than that containing SP-N. In addition, the amount of the two superplasticizers that had become adsorbed onto the surfaces of cement particles also differed, and in this case the adsorption capacity of SP-E was greater than that of SP-N. X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy tests showed that the ester-group based SP-E superplasticizers promoted cement hydration to a greater degree than that was achieved with their amide-bearing SP-N counterparts. This study would provide valuable insight for the development of crosslinked polycarboxylate superplasticizers.     

醚型聚羧酸系减水剂的合成及性能研究

烯丙基聚氧乙烯醚、顺酐、丙烯酸、丙烯酰胺为共聚单体,过硫酸铵为引发剂,通过自由基溶液聚合制得四元醚型聚羧酸减水剂。实验表明,最佳工艺条件为n（APEG）：n（MA）：n（AM）：nn（AA）=1：2：1：1．5,引发剂用量为4％．该减水剂在折固掺量为0．14％,水灰比为0129时,水泥的净浆流动度达到336mm,1h后为308mm。放置数月后减水剂稳定性不变。对不同厂家的四种水泥进行了净浆流动度试验,水泥适应性不佳但可调整掺量得到合适流动度。通过FTIR分析,表明MA、AM、AA均接入主链中,APEG接在AM上形成侧链。并依此得出了自制减水剂的分子式。     

蒸养条件下两性聚羧酸减水剂对胶砂及混凝土强度的影响

合成了阴离子型和两性型聚羧酸减水剂,研究了两类聚羧酸减水剂对水泥水化热、蒸养胶砂和蒸养混凝土强度的影响.结果表明:在蒸养条件下,与阴离子型聚羧酸减水剂相比,掺两性型聚羧酸减水剂的水泥水化温峰更高;在相同水灰比时,掺两性聚羧酸减水剂的蒸养胶砂和蒸养混凝土的强度也更高.XRD分析可知,掺入两性聚羧酸减水剂在蒸养条件下生成更多的AFm和氢氧化钙,促进了C3S和C2S的水化.     

Fluidizing efficiency of comb-like superplasticizers: The effect of the anionic function,the side chain length and the grafting degree

Superplasticizers and especially polycarboxylate grafted polyethylene oxide (PCE) demonstrated their efficiency to fluidify concrete. The aim of this work is to investigate the evolution of the fluidity as a function of adsorption in a sulfated solution with a wide variety of comb-like superplasticizers and at incomplete adsorption rate. Polymers with various side chain lengths, grafting ratios and also with modified anionic functions (carboxylate, dicarboxylate and phosphate) were synthesized. Inert calcite suspensions were used to mimic early age cementitious materials avoiding the cement hydration. Models of polymer conformation and yield stress prediction have been tested. But the most appropriate parameter which captures the fluidity/adsorption relationship is the mass of adsorbed polymer. A unique relationship “log(yield stress) vs. adsorbed mass of PCE” has been highlighted whatever the classical carboxylate PCE structure. The modification of the anionic function does not enhance the fluidizing efficiency. Each PCE has roughly the same fluidizing efficiency when it manages to adsorb in these ionic conditions.     

聚醚型聚羧酸减水剂的合成和表征及对水泥的微观作用机制

本文以聚醚、丙烯酸、丙烯酸羟乙酯为原料,通过自由基聚合法合成了聚羧酸减水剂JS-PCE和BT-PCE。通过正交优化所得的JS-PCE合成条件为:聚合温度25 ℃,抗坏血酸-巯基丙酸混液、丙烯酸滴加时间分别为3 h、2.5 h,酸醚物质的量比为4.25∶1,引发剂加量为聚醚质量的1.10%。添加JS-PCE的水泥净浆流动度达230 mm,表现出较好的流动性。采用界面化学及电化学等方法探究了减水剂对水泥的微观作用机制,结果表明聚羧酸减水剂在水泥颗粒表面存在饱和吸附量,其与水泥颗粒存在强吸附作用,因此产生分散和减水作用。流变行为分析得出JS-PCE和BT-PCE的最佳折固掺量分别为0.3%、0.4%。     

端羟基双子季铵盐对聚羧酸盐减水剂抗泥性能的影响

以1,4-对二氯苄为连接基团，分别以三乙胺和N,N-二甲基乙醇胺为头基，合成了具有不同端基的双子季铵盐（分别标记为KNJ-1和KNJ-2）。将其作为抗泥剂与聚羧酸盐减水剂复配以改善粘土对减水剂的负面效应，探究端羟基的引入对抗泥效果的影响。通过FT-IR和1H NMR对其进行结构表征。净浆流动实验考察抗泥剂的对流动度的影响，并结合XRD、XPS和 Zeta电位分析其与蒙脱土的作用机理。实验结果表明：与KNJ-1相比，加入0.3‰KNJ-2使水泥净浆初始流动度提高了35mm, 2h后流动度提高了165mm,表现出更好的抗泥效果。XRD和 XPS结果表明KNJ-2在蒙脱土的表面和层间吸附均优于KNJ-1，Zeta电位结果显示KNJ-2的加入使表面电位从初始的-15.67mV上升到-0.15mV。表明羟基可通过氢键作用优先吸附在蒙脱土的表面和层间，占据大量活性位点，减少了对聚羧酸盐减水剂的吸附，保障减水剂的高效分散能力，从而达到对粘土抑制的效果。     

Research on the performances of VPEG macromonomer grafted different functional groups to prepare polycarboxylate superplasticizers

The advent of novel polyether macromonomer has garnered significant attention within the industrial domain. In this study, a range of polycarboxylate superplasticizers (PCEs) was produced via free radical polymerization, employing a new polyether monomer, 4-hydroxybutyl vinyl polyethylene glycol ether (VPEG). This monomer served as the predominant component and was grafted with various functional monomers on its main chain. The molecular configuration of the resultant PCEs was discerned through Fourier infrared spectroscopy and gel permeation chromatography, while the surface tension underwent assessment via a surface tension meter. Both the initial and subsequent fluidity of cement paste and mortar were leveraged to ascertain the dispersion and retention efficacy of the synthetic PCEs. The ramifications of diverse functional group grafts of the new polyether monomer on the cement hydration procedure and strength attributes were elucidated via setting time, hydration heat assays of cement paste, SEM analysis, and compressive strength evaluations of mortar. Observations reveal that the carboxylic acid group significantly reduces surface tension, whereas the sulfonic acid group's effect remains minimal. The incorporation of both the amide and sulfonic acid groups marginally impacts the preliminary dispersion efficacy of PCEs but notably affects dispersion retention. Furthermore, these functional groups facilitate cement hydration, expedite the primary setting time of the cement paste, and bolster the initial compressive strength of the mortar. Specifically, the grafted of sodium methacrylsulfonate (SMAS) yields the most noticeable results. Finally, the working mechanism of PCEs with varying molecular structures has been explained in light both theoretical and experimental results. This research offers valuable insights for subsequent investigations into the fabrication of polycarboxylate superplasticizers using the VPEG macromonomer.     

Regulating the arm structure of star‐shaped polycarboxylate superplasticizers as a means to enhance cement paste workability

Star‐shaped superplasticizers, which incorporated polyol ester with unsaturated bond at their cores and bore comb‐type structures as their arms were synthesized via esterification‐copolymerization in aqueous phase from pentaerythritol, acrylic acid (AA), and isopentenyl oxy poly(ethylene glycol ether) (TPEG). The monomer ratios of AA and TPEG were varied and comonomer sodium methallyl sulfonate (SMAS) bearing short side chains was added to regulate the arm structure of star‐shaped polycarboxylate superplasticizers (SPCEs). The effects of the SPCEs on cement paste were investigated and the cement dispersion as well as early hydration mechanism were explored. As a main result, SPCEs with SMAS and certain molar ratios for anchoring groups and PEO side‐chains in their arm structure exhibited good paste dispersion and fluidity retention, which also delayed the early hydration process and prolonged both the initial and the final setting time. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46312.     

Investigation of the clay sensitivity and cement hydration process of modified HPEG‐type polycarboxylate superplasticizers

In this work, three kinds of HPEG‐type polycarboxylate superplasticizers (PCs) were synthesized with three kinds of typical functional monomers: [diallyl dimethyl ammonium chloride (DMDAAC), 2‐hydroxyethyl methacrylate (HEMA), and 2‐(dimethylamino) ethyl methacrylate (DMAM), respectively. The effects of montmorillonite clay on the fluidity of cement/PC pastes were investigated. It was found that the fluidity was negatively affected by the clays in the order: DMAM‐PC < HEMA‐PC < conventional PC (CPC) < DMDAAC‐PC. The DMAM‐PC was found to disperse cement well even in presence of montmorillonite clay. The dispersion performance of DMDAAC‐PC was much more effectively affected by clay due to the reaction between ammonium and montmorillonite. More study including mortar fluidity, adsorption behavior and morphology of the cement samples were investigated in details. Thermogravimetric analysis and X‐ray diffraction experiments allowed us to observe the influence of PCs on the hydrated products. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46572.     

Working mechanism of post‐acting polycarboxylate superplasticizers containing acrylate segments

Acrylate‐containing polycarboxylate superplasticizers were synthesized by copolymerizing acrylic acid, α‐methallyl‐ω‐methoxy poly(ethylene glycol) ether, and acrylic esters [hydroxyethyl acrylate (HEA) or hydroxypropyl acrylate (HPA)]. Their dispersing effects and fluidity‐retaining capabilities were evaluated by spread tests of cement pastes. The temperature sensitivity of the performance was especially focused upon. It was found by Fourier transform infrared spectroscopy and specific anionic charge density measurements that the ester groups in the acrylate‐containing copolymers hydrolyze in alkaline conditions, and thus additional R? COO^? groups are continuously produced. The gradual production of R? COO^? leads to increasing charge density and hence increasing adsorption of the polymer on the cement surface. The hydrolysis of HEA units is slightly faster than of HPA units in the corresponding copolymers. By this mechanism, a post‐acting, or delayed, dispersing effect is realized. Such post‐acting polymers alone or formulated with normal polycarboxylate superplasticizer can be used achieve a long fluidity retention of fresh concrete, especially under elevated temperatures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45753.     

侧链结构对聚羧酸盐减水剂性能的影响

以丙烯酸、甲氧基聚乙二醇丙烯酸酯、烯丙基磺酸钠为原料,分别制备引入羧基侧链、引入聚氧乙烯侧链以及同时引入羧基与聚氧乙烯侧链的聚羧酸减水剂.加入水泥净浆性能测试结果表明,羧基侧链对减水剂的分散性能影响较大,聚氧乙烯侧链对减水剂的保塑性能影响较大,同时具有两种侧链的减水剂的分散性能和保塑性能都得到提高.     

Influence of superplasticizers on the hydration of cement and the pore structure of hardened cement

This paper describes the influence of various types of superplasticizers such as naphthalene type (β-NS), refined lignin sulfonate type (LS) and polycarboxylate types (P34, S34) on the hydration of cement and the pore structure of hardened cement. Other superplasticizers except β-NS delayed the initial hydration of cement. In any case, it hardly influences the hydration reaction at late stage of cement. The retardation by the addition of superplasticizers is not observed after 28 days of curing. Large pores of 0.1 μm or more for hardened cement with LS or β-NS are larger than those of hardened samples with P34 or S34 cured for 28, 56 and 91 days. This is related to the coagulated structures of fresh cement pastes with various types of superplasticizers. It was presumed that the size of the cluster of aggregated particles became small when S34 or P34 that has a high dispersing ability was added compared to LS or β-NS that has a lower dispersing ability.     

Preparation of amphoteric polycarboxylate superplasticizers and their performances in cementitious system

A series of amphoteric polycarboxylate (PC) polymers were synthesized by radical copolymerization of acrylic acid (AA), [3‐(methacryloylamino) propyl] trimethylammonium chloride (MAPTAC) and ω‐methoxypolyoxyethylene methacrylate ester (MPEGMA). Cationic groups were introduced in to PC molecules with expectation of less retardation effect on cement hydration compared to the traditional anionic PC superplasticizers. The content of cationic groups in polymer was varied by changing the monomer ratio of MAPTAC to AA in the synthesis recipes. The structure of the synthesized amphoteric PCs was verified by gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The performances of the amphoteric PCs were evaluated by measurement of flowability and zeta‐potential of cement pastes and adsorption amount of PC in cement pastes. Impacts of the PCs on cement hydration were studied by isothermal calorimetry. It is concluded that both anionic and cationic PC polymers can be effectively adsorbed onto the surface of cement particles and thus change the zeta potential of cement pastes. The adsorption amounts of the amphoteric PCs decrease with increasing content of cationic units. A proper incorporation of cationic units into PC polymers may lead to a higher fluidizing performance in fresh cement pastes. The amphoteric PC polymers with higher content of cationic units show less retardation effect on cement hydration and hence higher early strength of cementitious materials may be achieved by using amphoteric PCs with appropriated content of cationic units without losing their plasticizing efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41348.     

抗泥型聚羧酸减水剂的制备及性能

以甲基丙烯酸（MAA）、甲基丙烯酸羟乙酯（HEMA）为单体,过氧化氢（H₂O₂）/抗坏血酸（Vc）为引发剂,甲基烯丙基磺酸钠（SMAS）为链转移剂,合成了一种抗泥型聚羧酸减水剂,通过红外光谱（FTIR）、凝胶渗透色谱（GPC）对聚合物进行结构表征,通过水泥净浆流动度、蒙脱土层间官能团、X射线衍射和吸附量测试,对其分散性能及抑制蒙脱土机理进行了探究。结果显示：合成的抗泥型聚羧酸减水剂在摩尔比为2.5：1时分散性能最佳,当减水剂折固掺量为0.25%时,水泥初始净浆流动度为268mm;与普通聚羧酸减水剂相比,合成的抗泥型减水剂对蒙脱土敏感性较低,与蒙脱土作用后的层间未出现抗泥型减水剂的特征官能团,层间距为1.40nm,抗泥型减水剂在蒙脱土上的吸附量远小于普通减水剂的吸附量。     

聚羧酸系减水剂的常温合成及性能

以异丁烯醇聚氧乙烯醚(HPEG)、丙烯酸(AA)、甲基丙烯磺酸钠(SMAS)为单体,通过芬顿试剂引发反应,在常温下制备了三元聚羧酸型减水剂(PC),探讨了不同反应条件对减水剂分散性能的影响,并通过傅里叶红外(FTIR)和凝胶渗透色谱(GPC)等手段对共聚物进行了表征。得到最佳合成条件为:引发剂滴加时间3h,引发剂过氧化氢/硫酸亚铁质量比1.2:1,反应温度30℃,酸醚摩尔比4:1,磺酸盐用量为单体总质量的1.6%,链转移剂用量为总单体质量的1.5% 。当减水剂折固掺量为0.3%时,水泥初始净浆流动度为290 mm,1h后提升到302mm。此常温下合成的减水剂具有良好的分散性和保持性,该方法是一种有应用前景的常温合成方法。     

Effect of cross‐linked polycarboxylate‐type superplasticizers on the properties in cementitious system

Fluidity and slump loss are main technical indicators for the quality of concrete. They are related to the dispersion of cement and hydration process, and are greatly affected by the structure of superplasticizers (SPs). For the purpose of obtaining SPs with excellent fluidity and slump retention, water‐soluble cross‐linked polycarboxylate ether copolymers (CLPCs) of acrylic acid and alkenyl alcohol type polyoxyethylene ether were synthesized. In order to gain full understanding of the effect of cross‐linked SPs on the properties in cementitious system, properties of the new SPs in cement paste were compared to those of traditional ones without cross‐linking agents. Mortar tests showed that CLPC performed obvious slow‐release function and kept about 10 mm higher than its initial paste flow after 150 min, while PC incurred loss of 15 mm after 150 min. Adsorption of CLPC on cement resulted in zeta potential being roughly the same as that in the case of PC, and enabled more effective slump retention to cement suspensions by rheological property tests. Ettringite peaks disappeared for CLPC on 1‐day curve and reappeared after 35 days, and the intensity of CH peaks for CLPC appeared weaker than Blank and PC after 1 day. The microstructure of CLPC after 1 day showed a very dense structure of smaller and thinner crystallites, which indicated that the early hydration was greatly delayed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40856.     

Effect of chain transfer agents in polycarboxylate superplasticizer on slump-retention of concrete

Two types of slump-retention polycarboxylate superplasticizers (PC-M and PC-S) were synthesized by using 3-mercaptopropionic acid or sodium hypophosphite as chain transfer agents, the effects of polycarboxylate superplasticizers on slump-retention of cement and concrete were investigated, and the mechanism of action and the structure of polycarboxylate superplasticizers were investigated by using conductivity, complexing Ca²⁺ concentration, gel permeation chromatography (GPC), nuclear magnetic resonance hydrogen spectroscopy (¹H-NMR), and nuclear magnetic resonance phosphorus spectroscopy (³¹P-NMR). The results indicated that the slump flow of cement paste mixed with PC-M was increased quickly within 60 min and then lost gradually, while PC-S increased slowly and evenly within 240 min. The slump flow of concrete mixed with PC-S reached 405 mm after 150 min, but the concrete mixed with PC-M was almost no fluidity after 150 min. The conductivity of the PC-M aqueous solution decreased quickly within 45 min, then slowly decreased, while the conductivity of the PC-S aqueous solution decreased slowly within 180 min. PC-M had a much greater complexation ability of Ca²⁺ than PC-S. The composition and structure of the two slump-retention polycarboxylate superplasticizers were altered by different chain transfer agents, and the hydrolysis-adsorption capacity of each component was different. The rate of hydrolyzation-adsorption of each component was PC-M₃ ≈ PC-S₃>PC-M₁>PC-M₂ ≈ PC-S₁>PC-S₂. The faster the adsorption rate, the faster the slump flow loss of concrete.     

Physicochemical studies of crosslinked thiolated polyvinyl alcohol hydrogels

This study is related to the post-crosslinking of thiolated polyvinyl alcohol (TPVA) hydrogels using three crosslinkers, sodium trimetaphosphate (STMP), boric acid (BA) and glyoxal (GLY) under alkaline conditions. The crosslinking reaction was carried out under different conditions: crosslinker nature, crosslinker content and crosslinking time. The influence of different crosslinkers on the physicochemical and structural characteristics of TPVA was evaluated. The three reagents used for crosslinking presented different action mode on hydrogels. The optimized crosslinking conditions were the crosslinker content is 0.1 % (w/v) at crosslinking time of 30 min. The results showed that the STMP-crosslinked TPVA had the maximum thiol content and swelling ability. All crosslinked TPVA samples were stable in different pH media. The involvement of thiol and other relevant groups after crosslinking in the different crosslinked TPVA samples was confirmed by attenuated total reflectance-infrared spectra. The microanalysis of elements present in the crosslinked samples were analyzed by energy-dispersive X-ray microanalysis.     

Treatment of gray wastewater and heavy metal removal from aqueous medium using hydrogels based on novel crosslinkers

Water contamination by heavy metals is a serious environmental problem. Several adsorbents with high adsorption capacity have been reported by researchers. In this paper we report the application of a new crosslinker allyl sorbitol (AS), and two other crosslinkers viz. allyl mannitol (AM) and allyl pentaerythritol (AP), toward the synthesis of polymer hydrogels. These hydrogels have been utilized for the removal of heavy metal ions from water. Chemically crosslinked polyacrylic acid hydrogels have been prepared using these crosslinkers viz. AS or AM or AP. The synthesized crosslinked hydrogels have been utilized for the removal of heavy metal ions from water. The maximum copper (Cu) metal ion removal of 81.8, 81.6, 86.8% and adsorption capacity of 409, 408, 434 mg/g were found with AS, AM and AP crosslinker based hydrogels respectively. While the maximum nickel (Ni) metal ion removal of 96.8, 96.6, 99.0% and adsorption capacity of 484, 483, 495 mg/g were found with AS, AM and AP crosslinkers based hydrogels respectively. The maximum chemical oxygen demand (COD) reduction of 72, 74, 78% and total dissolved solids reduction of 86%, 83%, 95% were found with AS, AM, AP based polymer gel respectively. Approximately, 439.2, 451.4, and 475.8 (mg COD removed/g polymer gel) of pollutants reduction capacity was achieved during their treatment.     

Poly(N-isopropylacrylamide) Hydrogels Crosslinked by Small-Molecular Crosslinkers Through Click Chemistry

A well-defined azido-poly(N-isopropylacrylamide) (PNIPA) was prepared by reversible addition-fragmentation chain transfer polymerization of NIPA and glycidyl methacrylate followed by the azidization of pendant epoxyl groups. Then the polymer was crosslinked via Click chemistry by bis- or tetra-alkynyl terminated compounds, which were synthesized through esterification of 1,3-propanediol and pentaerythritol with propiolic acid and 6-heptynoic acid, to fabricate PNIPA hydrogels. And the swelling properties of obtained hydrogels were studied as functions of crosslinker dosage and species. The results showed that the decrease of crosslinker dosage or increase of chain length thereof could enhance swelling capacities of hydrogels due to bigger free volumes within networks; the functionality of crosslinkers almost had no influence on swelling properties of hydrogels. In addition, no obvious distinction was found for lower critical solution temperature and swelling response to a temperature jump during reswelling and deswelling course, no matter what and how much crosslinker was used.