PSA分析技术应用于非堆核设施的研究及建议

PSA方法为明确说明复杂系统的功能因果联系提供一个规范的结构程序,用来评估失效的后果并推定工厂运行危险的数字估计。从原则上说,核动力厂PSA研究所使用的方法学与化工厂所使用的是相同的。但是,核化工厂的非反应堆核设施PSA存在着一些特点,使得相关研究非常必要。     

1,3,5-苯三甲酸衍生物类新型成核剂的合成及应用研究

合成了新型成核剂1,3,5-苯三甲酸三（环己胺）（BTCA-TCHA）,研究了该成核剂对等规聚丙烯力学性能、结晶行为和熔融行为的影响。结果表明,成核剂BTCA-TCHA可明显改善等规聚丙烯的力学性能和光学性能,并可以大幅度提高结晶峰温度。当BTCA-TCHA添加量为0.2 %时,等规聚丙烯的拉伸强度和弯曲模量可分别提高9.72 %和12.4 %,雾度降低53.5 %。当降温速率为20 ℃/min时,添加BTCA-TCHA的等规聚丙烯的结晶峰温度可从空白样的114.6 ℃提高到126.8 ℃。BTCA-TCHA的性能与传统的山梨醇类成核剂Millad 3988基本接近。     

新一代聚丙烯成核剂的合成及应用

介绍了二(3,4-二甲基二苄叉)山梨糖醇(DMDBS)的合成路线和作用机理,并以山梨糖醇和3,4-甲基苯甲醛为原料,在固体酸的作用下,不用分离水就能直接合成出新一代聚丙烯透明成核剂DMDBS.结果表明,在醇醛物质的量比2.1、催化剂加量4.5％(质量分数,以醇醛质量总和为基准,下同)、反应温度25℃、反应时间5h、溶剂...     

Study on lactose attrition inside the mixing cell of a laser diffraction particle sizer using a novel attrition index

Attrition is the general term that describes the breakdown of crystals due to collisions with each other or some other body, or by a shearing fluid. These interactions produce new crystals from the parent crystals and are likely to be a major source of secondary nucleation in industrial crystallizers. However, these collision interactions are difficult to devolve because they occur simultaneously.This work studies lactose monohydrate attrition within the small sample presentation unit of a laser diffraction particle sizer (Malvern Mastersizer, 2000, UK). Stirrer speed, particle concentration and initial crystal size were varied and particle size distributions (PSDs) were recorded every 2 min for 1 h. From these, three basic attrition mechanisms were recognizable: shattering, chipping and abrasion. The degree of attrition was quantified using indices: the shattering index (SI) and attrition index (AI), which are both typical of literature indices; and the differential attrition index (DAI) proposed here. All indices show similar trends although the DAI is more sensitive to subtle changes in PSDs.Of the three variables studied, particle concentration least affects attrition. Experiments with low initial crystal size and low impeller speed produce fines in the < 10-μm range, indicating that abrasion is the dominant attrition mechanism. In contrast, when the initial crystal size is large and impeller speed is high, crystal fragments are produced across all size ranges indicating that all three attrition mechanisms occur. This variation across the results indicates that the three mechanisms are differentiated by the collision energy intensity, which is a function of both crystal size and impact velocity. These experimental observations were found to closely follow theoretical predictions for crystal-impeller impacts (Synowiec et al. Chem. Eng. Sci. 48 (1993) 3485-3495 and Mersmann et al. Chem Eng & Technol. 11 (1988) 80-88). When applied to industrial crystallizers, this work demonstrates that careful selection of pumps and impellers is needed to control secondary nucleation.     

Effect of surface nucleation on isothermal crystallization kinetics: Theory, simulation and experiment

Surface nucleation of poly(l/d-lactide) at the interface with aluminum was studied by performing isothermal DSC analysis of amorphous samples of varying thickness between 100 °C and 130 °C. To ensure complete wetting of the aluminum surface, a hot melt laminating process was used to prepare the samples. Theoretical aspects of surface crystallization kinetics were explored and the resulting model was compared with the results of Monte-Carlo simulations. Three stages of surface crystallization were identified depending on the growth geometry: (1) impingement-free growth, (2) increasingly laterally-constrained transverse growth, and (3) interstitial growth. By fitting the Monte-Carlo simulation to the experimental half-times of crystallization the surface nucleation concentration and the bulk nucleation rate was estimated at 4 different temperatures. It was found that both surface nucleation concentration and the bulk nucleation concentration decrease with increasing crystallization temperature.     

Mechanism of seeded dispersion polymerization of methyl methacrylate using submicron polystyrene seed particles

Submicron polystyrene (PS) latex particles were used as seed in seeded dispersion polymerization of methyl methacrylate (MMA) to investigate the particle nucleation and aggregation behavior in this type of polymerization. The PS seed particles were located and tracked during the reaction using a refractive index matching technique. The number of PS seed particles present in the poly(methyl methacrylate) (PMMA) particles was investigated in detail throughout the reaction. The change in the distribution of PMMA particle populations containing different numbers of seed particles indicated that intensive nucleation and aggregation occurred during the early stage of the reaction until a transition point of 8.7% conversion was attained under the reaction conditions studied. The size of the large particles at this point was around 1 μm. These particles were regarded as mature particles that did not aggregate with other mature particles. Meanwhile, immature particle were still generated continuously from the continuous phase. These immature particles could not survive the aggregation process to grow to become mature particle, but instead, were captured by the mature particles. Therefore, the total number of the mature particles remained constant from this point until the end of the reaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymorphism in a metallocenic isotactic polypropylene as revealed by means of FTIR spectroscopy: Influence of the processing conditions

The polymorphic structure in specimens of a metallocenic isotactic polypropylene, processed under different conditions, has been studied by means of wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The proportions of the different polymorphs have been evaluated, and the influence of the processing parameters (nucleating agents, cooling rate, and nature of the surface of the molds) has been analyzed. The combination of WAXS, DSC, and FTIR results confirms the adequacy of this last technique to obtain quantitative information about the competition between the crystalline phases of polypropylene. It has also been proved that the nature of the mold can enhance considerably the activity of beta‐nucleating agents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and properties of poly(butylene succinate) filled with lignin: A case of lignosulfonate

A new kind of blend material was prepared by the incorporation of lignosulfonate calcium (LS), as the filler, into biodegradable poly(butylene succinate) (PBS), as the polymeric matrix, with the process of melt mixing and subsequent compression molding. The nucleation of LS improved the crystalline properties of the PBS component in the blends. Combined with the rigidity nature of the LS filler, the Young's modulus values of the blends were enhanced. Furthermore, the introduction of LS in this biodegradable polyester slightly increased the hydrophilicity of the blends, shown as higher values of water uptake at equilibrium; this might facilitate the biodegradation of hydrophobic polyesters. Consequently, this study opened one way of enhancing the rigidity and decreasing the cost of biodegradable PBS‐based polymeric plastics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Modeling evidence in support of coagulative nucleation theory

An extensive lumped model was developed for emulsion polymerization. It incorporated all of the complex processes: aqueous‐phase radical balances for all radical species arising from initiator decomposition and from exit; determination of radical number inside the particles by balance among rates of radical entry into, exit from, and termination inside the particles; determination of the monomer concentration inside the particles and in the aqueous phase by a thermodynamic equation; and particle formation by micellar, homogeneous, and coagulative nucleation. Model validation was done for the system with styrene (monomer), potassium persulfate (initiator), and sodium dodeceyl sulfate (emulsifier) and for the variables, which included the duration of nucleation, conversion at the end of nucleation, and total number of particles formed. The validation process revealed that coagulation during nucleation needed to be included in the model, even for emulsifier concentrations above the critical micelle concentration. The model predictions were in good quantitative agreement with the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Thermal and mechanical properties of polypropylene/wood‐flour composites

In this research, polypropylene/wood‐flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T_c), crystallinity, and melting temperature (T_m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T_m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T_m and T_c were also examined. T_c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood‐flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood‐flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011