Cure behaviour and mechanical properties of Si3N4 ceramics with bimodal particle size distribution prepared using digital light processing

Digital light processing is a vital additive manufacturing technology used for manufacturing ceramic parts. The particle size distribution of ceramic suspensions significantly affects the cure behaviour and mechanical properties of ceramics. In this study, the cure behaviour and mechanical properties of Si₃N₄ ceramics with a bimodal particle size distribution were studied. The results indicated that the suspension with coarse particles had a higher cure depth for a lower absorbance but poor mechanical properties. The bending strength of the samples with the optimal ratio (coarse:fine particles = 3:7) reached a maximum of 728.7 ± 10.33 MPa, which is 16.5% higher than that of the samples prepared using only fine particles.     

Adhesion enhancement in waterborne acrylic latex binders synthesized with phosphate methacrylate monomers

The effect of the addition of a phosphoric acid group containing monomer on polymerization kinetics, copolymer microstructure and end-use properties of a latex prepared by seeded emulsion polymerization of MMA/BA/MAA/AAEMA/SIPOMER PAM100 was studied. It was found that despite of the surface activity of the phosphated monomer, the polymerization kinetics was not affected. Gel content increased with the concentration of phosphate monomer due mainly to the presence of divinyl ester phospate impurities. Gel improved the chemical resistance of the latex films. However, the most affected property was adhesion. Increasing amounts of the phosphated monomer led to a strong enhancement of the adhesion due to chemical interactions established with the metal surface. It was also found that the feeding strategy of the phosphated monomer played an important role in the adhesion enhancement. Latexes synthesized using a delayed addition of the phosphate monomer showed better performance than latexes prepared following a conventional addition strategy. The latexes synthesized during the investigation were evaluated as binders in a primer formulation. A primer with good adhesive and corrosion resistance properties was achieved using a 5 wt.% of the phosphated monomer.     

Measurement based modeling and control of bimodal particle size distribution in batch emulsion polymerization

In this article, a novel modeling approach is proposed for bimodal Particle Size Distribution (PSD) control in batch emulsion polymerization. The modeling approach is based on a behavioral model structure that captures the dynamics of PSD. The parameters of the resulting model can be easily identified using a limited number of experiments. The resulting model can then be incorporated in a simple learning scheme to produce a desired bimodal PSD while compensating for model mismatch and/or physical parameters variations using very simple updating rules. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

高转化率乳聚丁苯橡胶聚合过程中乳液相对分子质量分布与粒径分布考察

采用中石油吉化分公司乳聚丁苯橡胶高转化率大生产配方,考察了实验室聚合反应釜聚合反应单体转化率随反应时间的变化,采用激光粒度分析仪和凝胶渗透色谱仪测定了聚合反应不同单体转化率的胶乳的粒径分布与分子质量分布,结果表明：胶乳粒径呈正态分布,粒径主要集中分布在0.1μm附近,胶乳的平均粒径随反应时间的延长逐渐增大,但是增加的幅度越来越小;聚合反应时间在11 h前（即转化率小于72%）,胶乳的重均分子质量、Z均分子质量一直增大,而数均分子质量变化无明显规律;而分子质量分布宽度指数随反应的进行变小,表明调整的高转化率配方合成的丁苯橡胶可有效改善聚合生成的胶乳粒径分布。     

大粒径聚丙烯酸丁酯胶乳的制备

采用种子乳液聚合法制备了丙烯酸酯-苯乙烯-丙烯腈共聚物生产工艺中的基础胶乳聚丙烯酸丁酯(PBA),考察了配方和工艺条件对其粒径增大的影响。结果表明,在合成种子胶乳时可加入质量分数0.2%～0.8%的乳化剂十二烷基硫酸钠;在种子胶乳粒径放大试验时,加入质量分数0.3%的乳化剂十二烷基硫酸钠及补加的单体量为种子胶乳总固体物质量的33倍可以得到大粒径的PBA胶乳。采用种子乳液聚合法进行PBA胶乳粒径放大方法简便、效果明显。     

聚合条件对丁苯胶乳粒径的影响

通过乳液聚合方法合成了适用于聚氯乙烯(PVC)改性甲基丙烯酸甲酯-丁二烯-苯乙烯共聚物(MBS)的种子胶乳,利用一步法工艺获得一定粒径的丁苯胶乳,研究了乳化剂加入量、加入方式,聚合温度,聚合反应时间对粒径的影响,合成了粒径在200～300nm的丁苯胶乳。     

影响ABS树脂用EBR胶乳粒径的因素

考察了影响ABS树脂用乳液聚丁二烯橡胶（EBR）胶乳粒径的诸因素，包括初乳化剂用量、补加乳化剂用量、电解质用量、引发剂用量、初水配比及聚合温度等，得到了影响胶乳粒径各因素的线性关系。结果表明，影响EBR胶乳粒径的主要因素为初乳化剂、补加乳化剂及电解质用量，工业生产中应通过调节这些因素来实现不同EBR胶乳的生产。     

Control of particle size and carboxyl group distribution in soap‐free emulsion copolymerization of methyl methacrylate–ethyl acrylate–acrylic acid

Polymer microspheres with narrow size distribution and with carboxyl groups on their surfaces were synthesized by soap‐free emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA), and acrylic acid (AA), and the distribution of –COOH in the latex was determined by conductometric titration. Effects of ingredients on polymerization, latex particle size (D_p), and its distribution, and the distribution of –COOH were investigated. Results showed that monomer conversion and the amount of embedded –COOH (E_a) decreased, and D_p increased with increasing amounts of NH₄HCO₃. The amounts of surface –COOH (S_a) and water –COOH (F_a) and the number of –COOH on each square centimeter of the particles' surface (S_d) increased with increasing amounts of NH₄HCO₃ and AA. With the increase of initiator (APS) and AA, D_p deceased. E_a increased with the increase of AA. F_a increased and then remained constant, and S_d decreased with the increase of initiator. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 433–438, 2004     

Synthesis of monodisperse styrene/methyl methacrylate/acrylic acid latex using surfactant‐free emulsion copolymerization in air

Monodisperse styrene/methyl methacrylate/acrylic acid (St/MMA/AA) copolymer microspheres have been prepared with surfactant‐free emulsion polymerization in air. The presence of oxygen in the system not only caused an induction period but also decreased the average particle size (D_p). However increasing AA concentration ([AA]) gave a reduction in the induction period. The FTIR and NMR analysis of the latex copolymer confirmed that the correlation of the copolymer compositions with the feed compositions was much better at the lower [AA] than at the higher levels. The AA contents of the copolymers obtained in air were much lower than those of the copolymers obtained under N₂ protection. Decreasing [AA] led to decrease in the copolymer molecular weight and broadening of the molecular weight distribution, but the particle size distribution (δ/D_p) was unaffected. In addition, the average particle diameter (D_p) was proportional to [AA]^–0.255, and increasing comonomers feed content caused linear increase of D_p, and a monodisperse sample with final solids contents up to 34.2 wt % was obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Calculation of the particle size distribution in suspension polymerization using a compartment-mixing model

A modelling strategy for effective estimation of the particle size distribution (PSD) in suspension polymerization is presented. The strategy consists of coupling a population balance equation (PBE) and a compartment-mixing (CM) model to account for the non-homogeneous mixing in the tank reactor. The values for the rate of energy dissipation of each compartment are estimated from Computational Fluid Dynamics (CFD) calculations and experimental reports on systems with the same agitator and geometric characteristics. Model predictions using the CM model are compared with predictions that assume homogeneous mixing and experimental data on PSD from styrene and divinylbenzene pilot-plant suspension polymerization reactors of 1 and 5 L with Rushton and PBT impellers.     

Bimodal particle size distribution polymer/oligomer combinations for printing ink applications

This paper describes a study in which anionically stabilised acrylic latices with a bimodal particle size distribution, produced by blending polymer particles of 50 and 350 nm in different blend ratios, are blended with oligomers. Reversibility, rheology, drying behaviour, film formation and blocking resistance of these systems were studied Reversibility appears to show two regions of linear dependence on the total particle surface area. The lower the surface area, the lower the amount of oligomer needed for good reversibility. The rheological data was fitted by the Krieger–Dougherty equation and it appeared that both in the presence and absence of oligomer an 80/20 large/small blend exhibited the highest maximum packing fraction. Short drying times were obtained with bimodal blends at high solids content and the drying profiles could be explained by the Croll model. The presence of oligomer was shown to exhibit a positive effect on film formation and when the oligomer is hard, the blocking resistance is already very good at low oligomer content, resulting in a very good MFT/blocking resistance balance. The latter can also be obtained when as well the size as the T_g of the polymer particles is varied.     

Batch emulsion polymerization of vinyl chloride: Application of experimental design to investigate the effects of operating variables on particle size and particle size distribution

In this article, the influences of operating variables on the particle size (PS) and particle size distribution (PSD) of emulsion poly(vinyl chloride) in batch reactor were investigated using Taguchi experimental design approach. The variables were temperature (T), water to monomer weight ratio (R), concentrations of initiator ([I]) and emulsifier ([E]), and agitation speed (S). Scanning electron microscope was used together with image analysis software to determine the PS and PSD. Statistical analysis of results revealed that the PS of emulsion poly(vinyl chloride) strongly depends on emulsifier and initiator concentrations, respectively, whereas the other factors have no significant effects in the range of levels investigated in this study. Except initiator concentration, all factors have important influence on the PSD (significance sequence: S > R > T > [E]). It is implied from the greater influence of agitation speed relative to temperature on PSD that the shear coagulation predominates the Brownian coagulation in this system. The relative optimum condition for a typical paste application was also determined using overall evaluation criteria. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology and particle size of nanograde polyurethane/polyacrylate hybrid emulsions

Poly(urethane acrylate) (PUA) composite particles were prepared by seeded surfactant‐free emulsion polymerization. The aqueous polyurethane (PU) dispersions were used as seed particles. The diameters of the seed particles of the aqueous PU dispersions and PUA composite latexes were measured by dynamic light scattering. The microstructures of the PUA composite emulsion particles were observed by transmission electron microscopy. The influences of the amount of the hydrophilic chain extender, the types of initiators, and the PU/polyacrylate (PA) weight ratios on the diameters of the aqueous PU and composite emulsions were also studied. The results showed that the PUA composite emulsions formed a core–shell structure with PU as the shell and with PA as the core. The diameter of the PU seed particles and the particle size of the PUA composite emulsions greatly depended on the amounts of the hydrophilic chain extender used in the preparation of the PU seed; when the hydrophilic chain extender concentration was 7.4%, the average diameter of the PUA composite emulsion particles showed the minimum value. The types of initiators and PU/PA weight ratios did not have a significant influence on the diameter of the PUA composite latex particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Particle size distribution control in emulsion polymerization

Effects of the operating policies—the initial initiator amount; the initial emulsifier amount; the monomer addition mode: batch or semibatch; and the monomer addition rate under “monomer‐starved conditions” for the control of particle size distribution (PSD)—were studied through a model that simulates batch and semibatch reactor operations in conventional emulsion polymerization. The population balance model incorporates both the nucleation stage and the growth stage. The full PSDs were reported, which have normally been omitted in earlier studies. It was shown through simulations that the broadness of the distributions, both initial (obtained after the end of nucleation) and final (after complete conversion of monomer), can be controlled by the initial initiator amount and the emulsifier amount. The higher initiator amounts and the lower emulsifier amounts favor narrower initial and final distributions. The shape of the initial PSDs and the trends in the average size and range were preserved with subsequent addition of monomer in the batch or in the semibatch mode, although the final PSD was always considerably narrower than that of the initial PSD. The addition of monomer in the semibatch mode gave narrower distribution compared to that of the batch mode, and also, lower monomer addition rates gave narrower distributions (larger average sizes), which was a new result. It was further shown through simulations that, under monomer‐starved conditions, the reaction rate closely matched the monomer feed rate. These conclusions are explained (1) qualitatively—the shorter the length of the nucleation stage and the larger the length of the growth stage (provided the number of particles remains the same), the narrower is the distribution; and (2) mathematically—in terms of the “self‐sharpening” effect. Experimental evidence in favor of the self‐sharpening effect was given by analyzing the experimental particle size distributions in detail. The practical significance of this work was proposed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2884–2902, 2004     

影响苯丙乳液黏度与粒径的因素分析

采用种子乳液聚合法,以苯乙烯、丙烯酸丁酯、丙烯酸异辛酯、甲基丙烯酸甲酯等为主要原料合成了用于制备胶粘剂的苯丙乳液。重点研究了引发剂、乳化剂及种子单体的用量及硬软单体不同配比对苯丙乳波黏度和粒径的影响。实验结果表明,当引发剂用量为0.5％（占单体总质量,后同）、乳化剂用量为1％、种子单体用量为8％、硬软单体配比为30／46的条件下,合成的笨丙乳液黏度较高、粒径小、粒度分布宽,用该乳液制备的胶粘剂具有优良的施工性能.     

Preparation of poly(vinyl acetate) latex with ultrasonic and redox initiation

The high water solubility of vinyl acetate (VAc) monomer increases the need for a good initiator system to speed up the polymerization and remove unreacted monomers. Ultrasonic energy can be used to initiate VAc redox emulsion polymerization in the absence of an inert gas and with sodium dodecyl sulfate as a surfactant. Combining ultrasonic energy and a redox initiator at the ambient temperature leads to a higher conversion and higher rate of polymer production in comparison with just using a redox initiator. Ultrasonic energy plays an important role in synthesizing and controlling the polymer structure. The particle size distribution is an important variable in the formulation of latex paint. Ultrasonic energy has an effect on the particle size distribution and average molecular weight of VAc polymer. The particle size increases with an increase in the monomer conversion for ultrasonic polymerization, whereas the particle size stays constant with the monomer conversion for redox polymerization. An ultrasonic polymer has a broader particle size distribution than a redox polymer. The average molecular weight of poly(vinyl acetate) falls with an increase in the sonication time, whereas it increases with time for a redox polymer. Ultrasonic energy also produces a stable, milky white, opaque latex. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 812–817, 2005     

激光粒度仪测定PTA粒径分布

介绍了激光粒度仪测定PTA粒径分布的分析方法 ,通过试验确定了分析条件 ,并与筛分法分析结果进行了对比。该方法简捷、快速、重现性好 ,适用于PTA产品的粒度分析。     

Preparation of mesoporous NiO with a bimodal pore size distribution and application in electrochemical capacitors

Mesoporous nickel oxide with a porous structure exhibiting a bimodal pore size distribution (2.6 and 30.3 nm diameter pores) has been synthesized in this paper. Firstly, a mesoporous precursor of coordination complex Ni₃(btc)₂·12H₂O (btc = 1,3,5-benzenrtricarboxylic acid) is synthesized based on the metal-organic coordination mechanism by a hydrothermal method. Then mesoporous NiO with a bimodal size distribution is obtained by calcining the precursor in the air, and characterized by transmission electron microscopy and N₂ adsorption measurements. Such unique multiple porous structure indicates a promising application of the obtained NiO as electrode materials for supercapacitors. The electrochemical behavior has been investigated by cyclic voltammogram, electrochemical impedance spectra and chronopotentiometry in 3 wt.% KOH aqueous electrolyte. The results reveal that the prepared NiO has high-capacitance retention at high scan rate and exhibits excellent cycle-life stability due to its special mesoporous character with bimodal size distribution.     

二项式分布在种群平衡模型模拟粒度分布中的应用

提出了一种适用于几何网格的子粒子二项式分布函数,并应用于种群平衡模型模拟活性污泥絮凝后的粒度分布。结果表明：与二元分布相比,该二项式分布可以得到更准确的粒度分布和平均粒度模拟值;通过校核二项式分布参数C_p的取值,可以提高粒度分布和平均粒度的模拟精度。相比于二元分布或正态分布只能描述一种类型的子粒子分布,该二项式分布具有较强的适应性,调整参数C_p的取值,可以得到更多可能的子粒子分布;参数C_p还可以表征粒子的破碎方式--较小的C_p值表征粒子具有较强的稳定性,易破碎生成较大的子粒子;较大的C_p值表征粒子具有较弱的稳定性,易破碎生成较小的子粒子。     

Recalculation of the monomer reactivity and experimental differences in emulsion and microemulsion copolymerizations of partially water‐soluble monomers

On the basis of the copolymerization data for the emulsion and microemulsion polymerizations of ethyl acrylate and methyl methacrylate, the monomer concentrations at the copolymerization loci were calculated, with the assumption that the sum of their concentrations at the polymerization loci was equal to unity. The equivalency of the locus and feed concentrations, as for styrene, was invalid because of the partial water solubility of both the monomers. Consequently, the locus concentration rather than the initial feed concentration was used to recalculate the monomer reactivity at the actual site of polymerization, and this was called the true reactivity ratio. The apparent reactivity ratios for emulsion and bulk polymerizations were different, whereas those for microemulsion and bulk polymerizations were similar. This difference was attributed to the mode of polymerization in the emulsions and microemulsions, leading to different copolymer compositions for similar initial feed concentrations. This was verified experimentally from the thermal properties and particle size distribution measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2802–2810, 2002