CO2碳化法制备微米级球霰石型食品碳酸钙的研究

采用CO2碳化法制备了微米级球霰石型食品级碳酸钙,探讨了碳化温度、Ca2+浓度、混合气中CO2浓度等制备工艺参数对碳酸钙晶型和形貌的影响,探讨了氨水用量、碳化时间对碳酸钙产率的影响,并采用FT-IR、XRD和SEM对制备的碳酸钙进行了表征。结果表明,碳化温度升高、混合气中CO2浓度降低,制备的碳酸钙晶型由球霰石型转变为方解石型;Ca2+浓度增加,制备的碳酸钙颗粒尺寸增大,碳化时间增加,产率先增加后减小。最佳制备条件为碳化温度20℃,Ca2+浓度0.3 mol/L,混合气中CO2浓度30%,[氨水]/2[Ca2+]摩尔比为1.1,碳化时间为24 min,制备的微米级球霰石型碳酸钙颗粒分布均匀,平均粒径为3.79μm,产率>99%,重金属含量低于国家标准《食品添加剂GB1898-2007轻质碳酸钙》的要求。     

无皂乳液聚合制备亚微米级单分散聚苯乙烯微球

采用无皂乳液聚合法制备了具有单分散性的亚微米级聚苯乙烯微球,考察了聚合体系pH值、单体及引发剂用量对聚合转化率、微球粒径及其分布的影响。结果表明,采用NaOH和NaHCO,复合溶液调节聚合体系pH值是控制聚合动力学、微球粒径及单分散性的有效手段,当其质量比为1：1时效果较好。随碱性复合溶液加入量的增加,最终转化率下降,微球粒径则由于复合溶液同时起到电解质的作用而存在极大值。随过硫酸钾(KPS)质量分数的增加,反应前期聚合转化率增大,但其用量过大,会导致体系pH值偏低,KPS过早消耗完毕,故反应后期最终转化率偏低;其用量过低,会影响粒径的单分散性。当KPS质量分数为单体的2％～3％时,聚合体系稳定性增加并改善了微球的单分散性,粒径趋小。单体用量的变化对聚合速率影响不大,随单体质量分数的提高,微球最终粒径增大,当单体质量分数过高,会影响微球的单分散性乃至体系失稳,一般以不超过10％为宜。     

Production of micron-size monodisperse polymer particles by seeded polymerization utilizing dynamic swelling method with cooling process

Monodisperse polystyrene particles (6.6 μm diameter) were produced by seeded polymerization utilizing the dynamic swelling method with cooling process as follows. Monodisperse polystyrene seed particles (1.8 μm diameter) were dispersed in ethanol/water (3/4 w/w) medium containing styrene monomer, benzoyl peroxide as initiator and poly(vinyl alcohol) as stabilizer at 65d?C. By lowering the temperature to ?5d?C at a speed of ?1d?C/min the polystyrene seed particles were swollen from 1.8 to 7.7 μm by the absorption of styrene monomer, keeping the high monodispersity. An appropriate amount of water was then added to the dispersion at ?5d?C to depress the redissolution of styrene from the swollen particles into the medium. By elevating the temperature the seeded polymerization was carried out at 70d?C. The production of submicron-size polystyrene new particles as a by-product was depressed by the addition of NaNO₂ to the medium.     

分散聚合法制备微米级聚苯乙烯微球

简要评述了微米级聚苯乙烯 ( PS)微球的制备方法 ,并着重介绍了用分散聚合法制备 PS微球时单体浓度、介质、稳定剂、引发剂与温度、反应时间、搅拌速度、气氛等影响因素及微米级 PS微球的应用与发展。     

交联型三维有序聚苯乙烯胶体晶体的制备及表征

采用无皂乳液聚合法制备了单分散亚微米级聚苯乙烯微球.考查了过硫酸铵的浓度和交联剂的用量对聚苯乙烯微球粒径、粒径分布及聚苯乙烯转化率的影响.结果表明：随着硫酸铵浓度的增加,聚苯乙烯粒径增大,单分散指数有增大的趋势;增加交联剂的用量,聚苯乙烯微球的粒径减小;转化率增加、单分散指数变大,当引发剂的浓度为12 mg/mL,交联剂含量为10.03%时,粒子粒径为0.523μm,制得的聚苯乙烯微球仍然呈现单分散性,聚苯乙烯表面和断面SEM图表明合成的胶体晶体材料三维高度有序.     

单分散微米级聚醋酸乙烯酯微球的合成与表征

研究了醋酸乙烯酯在醇/水介质中以过硫酸钾-亚硫酸氢钠为氧化-还原引发剂的分散聚合.考察了分散介质的醇水比、聚合温度及搅拌速率等因素对聚合体系的稳定性、微球粒径及其分布的影响,用扫描电镜对聚合物粒子形态进行表征.研究结果表明,在异丙醇/水介质中,聚醋酸乙烯酯微球的粒径随着醇水比、聚合温度和搅拌速率的提高而增大,粒径分布变宽.在标准配方条件下,制得了单分散,粒径分别为2.0 μm、4.0 μm和5.0 μm的聚醋酸乙烯酯微球.     

水热法制备TiO2片晶及光催化性能

以稳定的金红石相TiO₂为原料,水热法制备出微米级TiO₂片晶。采用扫描电镜（SEM）、X射线粉末衍射（XRD）、N₂吸附-脱附等分析手段对样品进行了分析。将不同温度下煅烧后样品进行甲基橙降解实验。实验结果表明,反应48 h可获得长60～80μm、宽30～60μm、厚4～9 μm的介孔片晶。经450℃煅烧可得到锐钛矿相占83.6%的混晶,比表面和孔径分别为68 m²·g^-1、21.6 nm,对甲基橙降解率最高,在30 min内降解了92.4%,60 min几乎全部降解,其催化活性优于商用P25,且微米级的颗粒更容易回收再利用。     

石墨/石蜡复合相变储热材料的热性能研究

膨胀石墨(EG)在超声作用下解离成微米级石墨片层(MSGF),并加入到石蜡基体中制备得到石墨/石蜡复合相变储热材料,并对复合相变材料的结构和热性能进行表征。实验结果表明,该石墨/石蜡复合相变储热材料储热速率加快,化学性质稳定。随MSGF质量分数的增加,固态及液态复合材料的导热系数均呈非线性显著增长,相变温度及相变潜热略有降低。     

Novel extensional device to efficiently form fine oil-in-water food emulsions

Two immiscible liquids are commonly mixed by mechanically dispersing one into the other to form emulsions. Surfactants or emulsifiers confer stability. Mechanical mixing, in practice, is an energy-intensive shear flow that is ineffective when the ratio of the dispersed-phase viscosity to the continuous-phase viscosity exceeds about four. Extensional flows are not subject to this viscosity ratio limit. This superiority of extensional flow was exploited to fabricate a novel, continuous-flow, cone-shaped device with an extensional strain of eight to make fine soybean oil-in-water emulsions. A spherical insert having a wall clearance of 25 μm was an effective design factor. Starting with ‘coarse’ 50 wt.% oil emulsions, two stretching episodes were needed for size reduction. The temperature rise was negligible, and the results were independent of the emulsifier type employed. Increasing flow rate and stretching episodes, reducing wall clearance, enhancing emulsifier concentration, and multiple passes through the device gave progressively smaller drops; the volume-averaged diameter became less than 2 μm, and the number-averaged diameter reached 0.5 μm, narrowing the size distribution. The emulsions that formed had a high viscosity and were stable. The performance of a scaled-up device was compared with other mixers. At equivalent energy density and 50 wt.% oil, drop sizes were similar for a valve homogenizer but larger for a rotor-stator mixer. At 80 wt.% oil, the rotor stator-mixer again required more energy for the same drop size, but emulsions prepared with the valve homogenizer broke. The findings of this study can help to design industrial-scale energy-efficient extensional-flow dominant devices for the formation of food emulsions.