High Shear Dispersion Research Articles

The performances of BMI nanocomposites filled with nanometer SiC

Nanocomposites of bismaleimide (BMI) with different proportions of nanometer SiC were prepared by a high shear dispersion process and casting method at elevated temperature. The mechanical and tribological properties of the nanocomposites were investigated. The bending strength and impact strength of the nanocomposite specimens were determined, and the sliding wear performance of the nanocomposites was investigated on an M-200 friction and wear tester. The dispersion of nanometre SiC was observed with a transmission electron microscope (TEM), while those of the worn surfaces and transfer films on the counterpart steel ring were observed with a scanning electron microscope (SEM). The experimental results indicate that the nanocomposites exhibited lower friction coefficient and wear loss as well as higher bending and impact strength than BMI resin under the same testing conditions. The lowest wear rate was obtained with the nanocomposite containing 6.0 wt % SiC, while the highest mechanical properties were obtained with the nanocomposite containing 2.0 wt % SiC. The wear mechanism of the nanocomposite is mainly adhesion wear, while that of pure BMI resin is mainly fatigue cracking with plastic deformation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1246–1250, 2005

Separation of titanoferrous impurities from kaolin by high shear pretreatment and froth flotation

Separation of colouring titanoferrous impurities from cryo-filtered kaolin was tried in the laboratory so as to achieve brightness improvement and maximum clay recovery. The process consists of high shear agitation with the dispersant (high shear dispersion—HSD) and with the collector (high shear conditioning—HSC) as pre-flotation steps followed by reverse flotation to float out the impurity. While HSD and HSC were carried out at 65% solids, the flotation was done with 20% solids. The flotation feed was prepared from a raw clay collected from the western part of India. The raw clay was processed by blunging, de-sanding followed by three-stage hydrocycloning for sizing and finally a two-pass cryo-filtration. The cryo-filtered clay forms the feed for flotation and consisted of 90% particles below 2 μm and about 70% below 1 μm. This material assayed 1.06% of TiO 2 and 0.29% Fe 2O 3 and measured a brightness of 83.4 % and a yellowness of 7.1% ISO. The flotation test results showed that the major players for the impurity removal are HSD, HSC, dosage of dispersant and collector and temperature of flotation. Even though as high as 35% of TiO 2 could be removed from the clay by flotation, the brightness increased only by 0.5%. However, when flotation product was bleached with sodium hydrosulphite (hydros), the brightness enhancement by the combined processing is 1.8 units. If only reductive bleaching of the feed clay is done without resorting to flotation, the brightness increase is merely 0.4%. Comparing these three results, it can be inferred that the low enhancement in brightness by flotation alone may be due to the fact that the liberated iron/titania particles during HSD and HSC may be getting ‘re-coated’ on the clay particles during flotation and/or drying. Reductive bleaching after flotation may be partially removed this ‘re-coated’ iron resulting in additional improvement in brightness. Further studies are planned to identify the type of ‘coating’ or ‘re-coating’, if any, so that methods can be adopted to prevent the same.

Advantages of Commercial Rutile Titanium Dioxide Slurry for Paper Applications

Paper mills have used titanium dioxide to generate opacity in high quality paper and paperboard for many years. Dry anatase pigments were used at first since this was the only technology available. Invention of the chloride rutile process created opportunities for new levels of performance in the paper industry. Commercial rutile slurry was introduced over 25 years ago to the North American marketand has been continually improved. Over 95% of the titanium dioxide used in this market is commercial slurry. More recently the use of stable paper slurries has been growing in both Europe and Japan.Commercial rutile slurry offers performance advantages over slurry produced by the paper mill. High shear dispersion equipment allows optimization of the particle size and increased light scattering. Opacity gains of 10-12% have been demonstrated in the lab. Mill trials have confirmed even higher performance gains.Anatase pigments have a lower refractive index and generally larger particle size. Both attributes will contribute to lower scattering performance than a rutile pigment. Mill trials have demonstrated over 20% reduction in pigment use when switching from an anatase pigment to rutile.Handling and storage of slurry products is not difficult. Proper design of the equipment will insure trouble free operation and high product quality. Correct addition to the paper process will maintain the high performance of the pigment.

Dry powder precursors of cubic liquid crystalline nanoparticles (cubosomes

Cubosomes are dispersed nanostructured particles of cubic phase liquid crystal that have stimulated significant research interest because of their potential for application in controlled-release and drug delivery. Despite the interest, cubosomes can be difficult to fabricate and stabilize with current methods. Most of the current work is limited to liquid phase processes involving high shear dispersion of bulk cubic liquid crystalline material into sub-micron particles, limiting application flexibility. In this work, two types of dry powder cubosome precursors are produced by spray-drying: (1) starch-encapsulated monoolein is produced by spray-drying a dispersion of cubic liquid crystalline particles in an aqueous starch solution and (2) dextran-encapsulated monoolein is produced by spray-drying an emulsion formed by the ethanol–dextran–monoolein–water system. The encapsulants are used to decrease powder cohesion during drying and to act as a soluble colloidal stabilizer upon hydration of the powders. Both powders are shown to form (on average) 0.6 μm colloidally-stable cubosomes upon addition to water. However, the starch powders have a broader particle size distribution than the dextran powders because of the relative ease of spraying emulsions versus dispersions. The developed processes enable the production of nanostructured cubosomes by end-users rather than just specialized researchers and allow tailoring of the surface state of the cubosomes for broader application.

Preparation of Polymer Particles in Nonaqueous Direct and Inverse Miniemulsions

Polymerizable miniemulsions were formulated in nonaqueous media, and it is shown that these systems exhibit characteristics similar to those of aqueous miniemulsions. Depending on the polarity of the continuous medium and the dispersed phase, the formulation of direct and inverse miniemulsions is possible. Direct miniemulsions in nonaqueous media are exemplified by dispersing styrene in formamide or glycol. Inverse miniemulsions were generated with the polar monomer hydroxyethyl methacrylate, acrylamide, or acrylic acid in cyclohexane or hexadecane as the unpolar continuous phase, and the miniemulsions were polymerized to latexes. For both the direct and inverse miniemulsions, it was shown that during high shear dispersion a steady state of droplet size is reached and that addition of a strong lipophobe (for inverse systems) or ultrahydrophobe (for regular systems) is required to stabilize the resulting miniemulsion for sufficient times. With surface tension measurements, the coverage of the particles with surfactant was determined to be incomplete. These facts are typical for the miniemulsion state; i.e., it is proven that organic miniemulsions indeed can be made and polymerized.

Geotechnical properties of fresh cement grout—pressure filtration and consolidation tests

This technical note examines the effects of removing water from a fresh cement suspension by pressure filtration, which turns the slurry into a material having significant effective stresses; it also clarifies some aspects of the consolidation behaviour of this filtered material. The test series covered: (1) a sulphate-resisting Portland cement (SRC); (2) an ordinary Portland cement (OPC); and (3) a super-fine Portland cement (MFC). They were all normal cements, obtained in 25kg batches. The experiments were like one-dimensional consolidometer tests with top drainage only, but used a slurry as starting material. The usual assumptions for one-dimensional consolidation analysis were made, and the filter cake was also treated as a stiff uniform layer. In the experimental procedure, the grout was mixed for a time in a high-shear disperser, then transferred to a consolidometer tube lubricated with mould release oil, with one layer of tissue and two layers of filter paper placed carefully on top of the grout. A displacement transducer measured the piston movement. Charts and tables are presented for the results of the filtration and consolidation tests. The analysis and data are required for quantitative assessment of construction effects, due to cement grouting or concrete placement in the ground.