【作者】 麻秀星；

【导师】 钱觉时；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2010， 博士

【摘要】 高性能减水剂是配制高性能混凝土的关键技术之一。聚羧酸系减水剂具有高减水率、良好的保坍性和环境友好性等优点,是配制高性能混凝土的首选减水剂,也是当前减水剂技术领域的主要研究热点。本研究以马来酸酐的“无水酯化”工艺为基础,利用低温高效催化手段,得到具有较高双键活性的不饱和酯化大单体,并采用特殊的氧化还原引发体系在40℃下合成了固含量高达75%的聚羧酸系高性能减水剂(文中用“改进型PC”表示)。在酯化大单体合成中,利用固体酸催化剂,将马来酸酐(MAn)与不同分子量的甲氧基聚乙二醇(MPEG)按一定比例在低温、无氮气保护的条件下完成无溶剂酯化反应。通过正交设计实验,在分析核磁共振谱图的基础上,确定了最佳的酯化反应条件为:n(MPEG)∶n(MAn)=1∶2.5,催化剂用量为MPEG质量的1.6%,阻聚剂为MAn质量的0.3%,在75℃下反应5 h,可以得到酯化率为95%的大单体PMAn,同时控制双键剩余率为95%。在共聚合成中,结合红外光谱和核磁共振谱图,从引发体系的作用机理入手,比较了过硫酸铵和氧化还原两种不同引发体系下的共聚工艺,系统研究了引发剂投加方式及用量、反应温度、反应时间及体系浓度等对共聚工艺的影响。在所采用的次硫酸氢钠甲醛-过氧化氢氧化还原引发共聚工艺下,更多的酯化大单体参与了聚合,共聚进行得比较彻底,未聚合的单体残留很少,所合成的改进型PC减水剂的固含量可达到75%。对采用过硫酸铵引发体系在90℃～95℃下合成的聚羧酸系高性能减水剂(文中用“传统型PC”表示)和改进型PC在泵送混凝土中的应用进行了系统试验,并重点对改进型PC减水剂在混凝土中应用所存在的相容性难题进行了探讨。试验结果显示,改进型PC减水剂在新拌混凝土和易性、硬化混凝土强度等方面相比较传统PC有较强的优势,能有效减少水泥用量,降低混凝土材料成本,提高混凝土的综合性能。改进型PC与不同品牌膨胀剂、水泥的相容性均较好。随着集料中泥(或石粉)含量的增大,掺改进型PC混凝土的单方用水量增大,混凝土经时损失加大,抗压强度逐步降低。紫外-可见分光光谱分析显示,对改进型PC的吸附,泥>水泥>石粉,与宏观试验的结果相符。采用离心喷雾干燥工艺对改进型PC减水剂进行粉体制备研究,得到的减水剂粉体固含量达到99%。通过单因素试验研究了干燥室进口风温、进料液温度、进料液固含量对喷雾干燥工艺及粉体性能的影响,确定了喷雾干燥工艺适宜的参数范围为干燥室进口风温180℃~220℃,进料液温度20℃~40℃,进料液固含量20%~60%。采用2%碳酸钙作为抗结剂,喷雾干燥后的粉体分散性和稳定性较好。通过红外光谱分析发现聚羧酸减水剂分子结构中的羰基在干燥过程中发生了部分分解,但减水剂宏观性能仅受有限影响,粉体减水剂的性能与液剂减水剂基本相当。更多还原

【Abstract】 High-performance water-reducing agent is one of the key technologies to the preparation of HPC. Polycarboxylate Superplasticizer with a high water reducing ratio, good concrete-slump-lost controlling ability (good dispersibility and holding dispersibility) and environmental friendliness, etc., is the preferred water-reducing agent, and its synthesis technology is the current major research focus. Starting from“anhydrous esterification”of maleic anhydride,obtained high activity of unsaturated open-chain hydrocarbons esterifiable big monomer,based on low efficient catalyst method , and synthetize solid content up to 75% of polycarboxylate superplasticizer ("improved PC") using special redox initiator at 40℃.In the esterification of maleic macromonomer synthesis, reacting the maleic anhydride (MAn) with different molecular weight polyethylene glycol monomethyl ether by using the self-made solid catalysts according to a certain percentage under the condition of low-temperature and non-nitrogen. By orthogonal design experiments, analyzing the nuclear magnetic resonance spectroscopy based on the diagram to determine the best conditions for the esterification: n(MPEG)∶n(MAn)= 1:2.5, catalyst dosage is 1.6%(MPEG Wt%), inhibitor dosage is 0.3%(MAn Wt%), reaction at 75℃under 5 hours. Under the best conditions the esterification rate can get 95%, while controlling the rate of double bond for the remaining 95%.In the radical polymerization reactions, combine with IR and NMR spectra, from the trigger mechanism of the system to start, and then compare with ammonium persulfate and redox initiator system, the initiator dosing methods, dosage, and discuss the reaction temperature, reaction time and the system of concentration on the copolymerization reaction were systematic investigated. For sodium formaldehyde sulfoxylate- hydrogen peroxide redox system, the copolymerization of polymerization monomer residual rarely, solid content is as high as 75%.The application of traditional PC(ammonium persulfate initiator system at reaction temperature 90℃~95℃) and modified PC in the pumping concrete was explored,focus on compatibility problems of water-reducing agent in concrete application. In the same concrete mix, compared to traditional PC, the modified PC has a stronger advantage on workability of fresh concrete and mechanical properties of hardened concrete, while able to effectively reduce the amount of cement, reduces costs and improves overall performance of concrete. Besides, the compatibility of modified PC with expansion agents and different kinds of cement is good. As clay / powder dosage increases, water requirement increases,slump losses increase, but early compressive strength gradually reduces. Through infrared spectroscopy it is discovered that adsorption of powders on modified PC, mud>cement> stone powder, which is consistent with macro test results.Finally, the Preparing of powder polycarboxylate superplasticizer by centrifugal spray drying process are discussed in this paper and the powder solid content can reach 99%. Based on single factor experiments, the major parameters affecting the drying process are discussed and the appropriate process conditions were obtained such as the import air temperature of drying chamber must be controlled at 180℃~220℃;the spray-drying feed temperature controlled at 20℃~40℃, and the concentrations of liquid polycarboxylate superplasticizer are in the range of 20% to 60%. With calcium carbonate and dosage of 2% as resistance agent, powder has good dispersion and good stability. Through infrared spectroscopy it is discovered that the carbonyl group were partly decomposed during the drying process, but the obtained powder’s performance were limited impacted thus its performance is at the same level compared to the liquid superplasticizer.更多还原