基于醋酸乙烯酯的大分子添加剂对模具石膏机械性能的影响

发布时间：2018-07-31 08:24

【摘要】：在保持模具石膏试件吸水性能的基础上,提高试件的机械强度是石膏模具行业亟待解决的难题之一。文中以含有醋酸乙烯酯单元的大分子(不同水解度的聚乙烯醇PVA和聚醚聚酯型磺酸基大分子PES)为添加剂,考察了其对模具石膏的抗折、抗压强度和吸水率的影响,以获得能够在不降低石膏吸水率的前提下提高其机械强度的理想外加剂。另外研究了外加无机盐、拌合水p H和养护时间对大分子改性β-半水石膏(β-H)的影响,最后研究了大分子添加剂对β-H的水化进程及晶体形貌的影响。具体研究内容及主要结论如下:1.通过控制聚醋酸乙烯酯(PVAc)的水解反应条件,得到了不同水解度(65%~99%)的PVA,并研究了不同水解度PVA对α、β-H试件的机械强度和吸水率的影响。结果表明,水解度为65%~99%的PVA均能在不同程度上提高石膏试件的机械强度,但其吸水率有所降低。其中,水解度为78%的PVA(PVA78)可使得α、β-H试件在吸水率少量降低的同时,最大幅度地提高其抗折强度和抗压强度。当PVA78掺量为0.05wt.%时,可使得β-H试件的抗折、抗压强度较未添加大分子的石膏试件分别提高了26%和4%,吸水率仅降低了1%。0.1 wt.%的PVA78可使得α-H试件的抗折、抗压强度分别较未添加大分子的石膏试件提高了21%和5%,吸水率提高了1%。最后,测定了PVA78改性β-H的水化度、凝结时间、水化温度和体系的电导率,发现PVA78可以加速β-H的水化进程。2.研究了养护时间、拌合水p H、外加无机盐对PVA78改性β-H试件的影响。结果表明,PVA78的加入使β-H的p H使用范围由7~9扩大至5~9。而外加盐的存在则会降低PVA78改性的β-H试件的机械强度,其降低的程度与无机盐的种类有关。具有较强促凝作用的Na2SO4和具有较强缓凝作用的CH3COONa和Na2CO3对PVA78改性的β-H试件的机械强度降低程度较大,而Na NO3和Na Cl对PVA78改性β-H试件的强度降低程度较小。另外,外加盐对β-H试件机械强度的降低作用是通过改变其晶体形貌来实现的:外加盐使得二水硫酸钙的晶体变短,晶体之间的连接点减少,使强度降低。3.以醋酸乙烯酯(VAc)、甲基丙烯磺酸钠(SMS)和大分子单体甲基烯基聚氧乙烯聚氧丙烯嵌段共聚醚(608)为原料,采用水相自由基共聚法合成了聚醚聚酯型磺酸基大分子(PES)。通过单因素实验和正交试验筛选出PES性能最优的配方为:nSMS:n608:nVAc=1:5:14,WAPS=1.5 wt.%,温度为80 oC。PES的最佳掺量为0.1wt.%时,PES改性β-H试件的抗折强度较空白提高5%,抗压强度降低2%,吸水率较空白提高2%。4.通过测定PES改性β-H的水化度、水化温度和体系的电导率,发现PES对β-H的水化进程并无明显影响;而通过电镜分析其晶体形貌发现,PES的掺入使得石膏的晶体形貌由大片状变为柱状或小片状,增加了晶体结构的紧密程度,改善了β-H试件的机械强度。
[Abstract]:On the basis of maintaining the water absorbency of gypsum test piece, improving the mechanical strength of the specimen is one of the problems to be solved urgently in gypsum mould industry. In this paper, the effects of macromolecules containing vinyl acetate units (polyvinyl alcohol PVA and polyether polyester sulfonic acid macromolecule PES) on the bending, compressive strength and water absorption of gypsum were investigated. In order to obtain the ideal admixture which can improve the mechanical strength of gypsum without reducing its water absorption. In addition, the effects of inorganic salts, mixing water pH and curing time on the modification of 尾 -hemihydrate gypsum (尾 -H) were studied. Finally, the effects of macromolecular additives on the hydration process and crystal morphology of 尾 -H were studied. The specific research contents and main conclusions are as follows: 1. By controlling the hydrolysis conditions of polyvinyl acetate (PVAc), different degree of hydrolysis (65%) was obtained, and the effects of different degree of hydrolysis (PVA) on mechanical strength and water absorption of 伪, 尾 -H specimens were studied. The results show that the mechanical strength of gypsum specimens can be improved by PVA with hydrolysis degree of 65% and 99%, but the water absorption is decreased. Among them, PVA (PVA78) with a hydrolysis degree of 78% can increase the flexural strength and compressive strength of 伪, 尾 -H specimens at the same time that the water absorption rate decreases slightly. When the content of PVA78 is 0.05wt.%, the bending resistance of 尾 -H specimen can be increased by 26% and 4% than that of gypsum specimen without macromolecular addition, respectively, and the water absorption of 伪 -H specimen can be reduced by only 1.0.1 wt.% PVA78, and the bending strength of 伪 -H specimen can be increased by 26% and 4%, respectively, when the addition of PVA78 is 0.05wt.%, the bending resistance of 伪 -H specimen can be improved. The compressive strength was increased by 21% and 5%, respectively, and the water absorption was increased by 1% compared with the gypsum specimen without macromolecular addition. Finally, the hydration degree, setting time, hydration temperature and conductivity of 尾 -H modified by PVA78 were measured. It was found that PVA78 could accelerate the hydration process of 尾 -H. The effects of curing time, mixing water pH and inorganic salt on PVA78 modified 尾 -H specimens were studied. The results showed that the pH range of 尾 -H was expanded from 7- 9 to 5g 9 with the addition of PVA78. The mechanical strength of 尾 -H specimens modified by PVA78 was decreased by the presence of added salt, and the degree of reduction was related to the type of inorganic salts. The mechanical strength of 尾 -H specimens modified by PVA78 was decreased greatly by Na2SO4 with stronger coagulation-promoting effect and by CH3COONa and Na2CO3 with stronger retarding effect, while the strength of 尾 -H specimens modified by PVA78 was reduced by Na NO3 and NaCl to a lesser extent. In addition, the effect of added salt on the mechanical strength of 尾 -H specimen is achieved by changing the crystal morphology: the addition of salt makes the crystal of calcium sulfate dihydrate shorter, the connection point between crystals decreases, and the strength decreases by 0.3. Polyether polyester sulfonic group macromolecule (PES). Was synthesized by water phase free radical copolymerization of vinyl acetate (VAc),) sodium methpropylene sulfonate (SMS) and macromolecular monomer methylenyl polyoxyethylene polyoxypropylene block copolymer (608). Through single factor experiment and orthogonal test, the optimum formula of PES performance is: 1: 608: n VAc1: 5: 14 WAPSX 1.5 wt. and the optimum temperature of 80 oC.PES is 0.1 wt.%. The bending strength of 尾 -H modified by PES is increased by 5%, the compressive strength is reduced by 2%, and the water absorption is increased by 2. 4% compared with the blank. By measuring the hydration degree, hydration temperature and conductivity of 尾 -H modified by PES, it was found that PES had no obvious effect on the hydration process of 尾 -H. By electron microscope analysis, it was found that the crystal morphology of gypsum was changed from large sheet to columnar or small sheet with the addition of PES, which increased the compactness of crystal structure and improved the mechanical strength of 尾 -H specimen.
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ174.62;TQ177.37

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