Rubber phase dispersion in polypropylene

Impact properties of rubber-modified blends are significantly dependent on particle size and size distribution (dispersion). Past work has shown strong variations in these particle parameters with different processing conditions and these variations reflect, in part, different shear fields developed during melt extrusion and moulding. A major problem ensues involving property variability because of process variability. It is neither practical nor economical to place stringent controls on process variability in a plant. Instead, our current research has indicated that lightly crosslinking the rubber reduced drastically the sensitivity of dispersion to processing conditions, and, with the correct rheology between the rubber and the resin, the same dispersion could be maintained through both the extrusion and moulding stages resulting in finished parts with increased chance of dispersion and property consistency. Four rubbers of different degrees of crosslinking and three polypropylenes of different melt flow and structure were blended at six rubber levels. Mixing was carried out with two twin-screw configurations and the blends were cast or injection moulded using a ram or a screw moulder representing six different processing shear histories. Dispersion was quantitatively characterized by scanning electron microscopy (SEM). Spherical rubber particles revealed on the fracture surface were counted and measured to determine particle size and size distribution for the individual blends. Correlation of the results indicated how particle size and size distribution was influenced by crosslinking and the rubber/resin rheology. This provided some understanding of the mechanics of soft-phase dispersion in these blends.     

A simple low-cost approach for transport parameter determination in mountain rivers

A simplified low-cost approach to experimentally determine transport parameters in mountain rivers is described, with an emphasis on the longitudinal dispersion coefficient (D_L). The approach is based on a slug injection of table salt (NaCl) as a tracer and specific conductance readings at different locations downstream of the injection spot. Observed specific conductance readings are fit using the advection-dispersion equation with OTIS-P, yielding estimates of cross-sectional area and longitudinal dispersion coefficient for various stream reaches. Estimates of the D_L are used to assess the accuracy of several empirical equations reported in the literature. This allowed the determination of complementary transport parameters related to transient storage zones. The empirical equations yielded rather high D_L values, with some reaching up an order of magnitude higher to those obtained from tracer additions and OTIS-P. Overall, the proposed approach seems reliable and pertinent for river reaches of ca. 150 m in length.     

纳米TiO2的表面处理及聚丙烯／TiO2复合体系的研究

通过多种方法对纳米TiO2粒子进行了表面处理，深入探讨了纳米粒子的分散机理。制备了PP／TiO2复合材料，对此复合材料进行了力学性能测试和结构表征，讨论了分散度和复合材料性能的关系。结果表明：通过熔融共混法可以将经适当表面处理的纳米TiO2粒子均匀地分散在聚丙烯中，纳米TiO2粒子在4％用量时可以使聚丙烯的缺口冲击强度提高1倍，同时其拉伸强度也有很大提高。     

Axial distribution of solids holdup for both hydrophilic and hydrophobic particles in three‐phase fluidized beds

The axial concentration distribution of the hydrophilic and hydrophobic particles, corresponding to poor and good attachment to rising bubbles in water, was investigated in a gas‐liquid‐solid fluidized bed. The sedimentation‐dispersion model depicted satisfactorily the axial distribution of solids holdup by modifying only the terminal settling velocity, which considered the effect of an additional drag force resulting from the attached rising bubbles. This model explained correctly the different phenomena, i.e. solids holdup decreased with increasing the axial height in the non‐attached system, but increased in the attached system.     

纳米二氧化硅-乙二醇体系的凝胶现象及其应用

不同样品的纳米二氧化硅-乙二醇体系的凝胶现象可分为三种类型:转变十分尖锐而且可逆;转变尖锐但不可逆;及缓慢转变。指出选择凝胶转变十分尖锐而且可逆的纳米二氧化硅-乙二醇体系可适用于涤纶聚合工艺。     

抗甲胎蛋白聚苯乙烯磁珠的制备

在磁流体存在下,进行苯乙烯-丙烯酸-马来酸酐-二乙烯基苯的共聚合,合成出粒径介于500～625nm、表面光滑、单分散的球形聚苯乙烯磁珠;磁珠耐酸碱,在浓度为1mol/L盐酸或氢氧化钠及氯化钠溶液中不凝集;控制丙烯酸用量可使磁珠表面羧基量达4 5mg/g。物理吸附法致敏磁珠的最佳条件为:包被用甲胎蛋白(AFP)抗体最适稀释度为:V(AFP抗体)∶V(磷酸氢二钠-柠檬酸缓冲液)=1∶200,最适pH=7 0,温度37℃,作用时间1h。     

Elucidation of polyurethane dispersions in a batch rotor-stator mixer

In this study, the effect of high energy input from mechanical agitation, provided with a high shear rotor-stator, on the drop size and the drop size distribution (DSD) of aqueous polyurethane (PU) dispersions is investigated. The effect of the dispersed phase volume fraction (ϕ) on the DSD of aqueous PU dispersions is also examined to understand the fundamental characteristics that result from the high shear mixing. DSD is measured by using either a high magnification video probe or dynamic light scattering, depending on the range of drop sizes. For the PU without any ionic content, the distributions appear to be bimodal with rather large drop sizes. The mean sizes of the first and second modes are about 10 and 22 μm, respectively. For the PU with an ionic content, the mean drop sizes are approximately 80 nm. The distributions reveal that functional chemistry plays a more dominant role in the process of making PU dispersions than the mechanical agitation, and that ϕ has a weak effect on the mean drop sizes. The results further suggest that mechanical agitation can be used to control the breadth of the distributions.     

Channel effect ofnC6 aromatization on Pt/KL catalysts

Designed Pt/KL catalysts were prepared and characterized by CO chemisorption and XRD. Pulse catalytic tests usingn-hexane as the probe were performed. The results showed that Pt particles located in the L-zeolite channels were fundamental for aromatization, and the spatial effect of the channels was essential for dehydrocyclization. Obstruction of the channels, while having no influence on the high Pt dispersion, affects the product distribution ofnC₆ in addition to a sharp reduction in reactivity.     

Effects of Attraction Radius and Flight Paths on Catch of Scolytid Beetles Dispersing Outward Through Rings of Pheromone Traps

Results were analyzed from six previous studies in which marked bark and ambrosia beetles, Ips typographus, I. paraconfusus, and Trypodendron lineatum (Coleoptera: Scolytidae), were released at the center of concentric rings of pheromone traps. Assuming nearly straight flight paths, a filtering equation model predicts recapture percentages on several trap rings of specified radii, trap numbers, and effective attraction radius (EAR) of a pheromone trap. Equations were used to calculate recapture percentages on concentric trap rings as a function of increasing EAR and gave polynomial relationships for each ring with terms equal to the number of inner rings plus one. Results were confirmed by computer simulations. Filtering equations were iterated with increasing EAR values to find one that gave a recapture percentage for the innermost trap ring that matched the field results. The estimated EAR for a synthetic pheromone bait of I. typographus was similar in five tests (range 1.39–1.78 m), but in two other tests was larger (3.27 and 15.9 m). The EAR for pheromone of 75 male I. paraconfusus in ponderosa pine logs ranged from 0.35 to 34.5 m (mean of 4.7 m) and was generally larger for previously pheromone-responding beetles than for freshly emerged ones. For T. lineatum, the EAR of lineatin-baited traps at 100-m radius was 2.43 m. Recaptures of I. typographus were reasonably predicted by the estimated EARs in the filtering model. To obtain perfect fits, another model assumed the EAR could vary with ring radius (dispersal distance) and found that the EAR for I. typographus decreased with dispersal distance in four experiments, but increased or was variable in two others. However, in I. paraconfusus and T. lineatum, the EAR increased with dispersal distance. Simulations that varied combinations of the EAR and random angles of maximum turning (AMT) of beetles stepwise showed that a nearly straight flight path for I. typographus explained observed catches on trap rings best, while a higher AMT of 36° was better to explain catches of T. lineatum. Simulations show that catch per trap ring in relation to radial distance can be influenced by the beetle's AMT (still unobserved in the field). A conceptual model of dispersal and host selection in aggressive bark beetles with regard to pioneer and joiner colonization strategies is presented.     

Textural properties evolution of Ir and Ru supported on alumina catalysts during hydrazine decomposition in satellite thruster

Ir/Al₂O₃, Ru/Al₂O₃, and Ir-Ru/Al₂O₃ catalysts with total metallic contents of 30% in mass were prepared by an incipient wetness method. The characterization of these materials, before and after their use for hydrazine decomposition in a satellite thruster, was performed by measurement techniques of specific surface area, volume and pores size distribution, H₂ chemisorption, TEM and basic chemical analysis. An average decrease of 11% in the BET surface area was observed, independent of the catalyst composition. The total specific pore volume remained unchanged because the volume reduction in the size range diameters between 1.0 and 10 nm was compensated by the increase in the diameters size range between 10 and 100 nm. A reduction of the H₂ quantity adsorbed on the Ir/Al₂O₃ catalyst can be explained by the metal loss through erosion as well as by its partial occlusion within the pores of the alumina support. On the other hand, catalysts containing Ru showed an increase of H₂ chemisorbed amount, attributed to a more complete reduction of this material after hydrazine decomposition, in spite of the erosion and occlusion losses. Such observations were confirmed by TEM, which showed a great stability of the distributions of the metallic particle sizes in all catalysts.