Rigid polyurethane-clay nanocomposite foams considered in this work are made with different clay types and for different clay concentrations. The densities of the foams are in the range of 140-160 kg/m 3 with possible application as structural materials and for underwater buoyancyrelated uses. Wide-angle X-ray diffraction and transmission electron microscopy studies confirm the formation of nanocomposites. The compressive modulus and the storage modulus of the foams increase and the mean cell size decreases with addition of clay. However, the hydraulic resistance of the nanocomposite foams, a measure of the strength of the foam lamellae, is lower than that of the foams without clay.
Rigid polyurethane foams are generally “closed celled” with a gas entrapped in each cell. The properties of such foams are significantly affected by the cell size distribution and morphology of the cells. For example, in thermal insulation foams, small cells lead to lower thermal conductivity and in foams for buoyancy applications, stronger cell windows are resistant to ingress of water until higher hydraulic pressures. The effect of formulation parameters on the size and structure of rigid polyurethane foams was investigated. Foams were made with different surfactants, with variation of surfactant concentration at different blowing agent concentration, with variation of nucleating agent concentration and with variation of catalyst concentration. Micron sized silica particles were used as nucleating agent. The densities of the foams were in the range of 140 to 165 kg/m3. The cell window areas of different foams have been measured. The bubble size in the polyol depends on the surface tension lowering ability of a surfactant, and the entrainment of a large number of small bubbles during mixing leads to a foam with a small cell size and a narrow cell size distribution. Increasing the concentration of the surfactant reduces the cell size and narrows the distribution. Increasing the proportion of organometallic catalyst in the amount of total catalyst used, results in smaller cell sizes, which are narrowly distributed. Hydraulic resistance of the foams was monitored by measuring buoyancy losses at different hydraulic pressures. Hydraulic resistance of the foams can be improved by decreasing the area and increasing the thickness of the cell windows.
Foams used in buoyancy applications must resist penetration by water at significant depths of immersion. The behavior of water blown rigid polyurethane foam at different water pressures from 0 to 3 MPa are studied in this work. The effects of different surfactants on the cell structure and hydraulic resistance of the foams are examined. The foams have densities in the range of 145 to 160 kg/m 3 . With increasing applied hydraulic pressure, it is found that the foams have very small buoyancy losses at low pressures but beyond a threshold pressure, buoyancy losses increase rapidly. The threshold pressures of the foams increase with decrease in cell window area. A cell window is the lamella of the foam material that separates two adjacent cells. The cell sizes of the foam are found to correlate with the size of the air bubbles entrained during initial mixing. Surfactants, which reduce the surface tension of the polyol to the greatest extent, are found to give the finest initial bubbles, smaller cells, and foams with the highest hydraulic resistance.
Stabilizing or reducing periodontal pocket depth can have a positive influence on the retention of teeth in dogs. A topical 2% clindamycin hydrochloride gel (CHgel) was evaluated for the treatment of periodontal disease in dogs. The CHgel formulation provides for the sustained erosion of the matrix, but also flows into the periodontal pocket as a viscous liquid, and then rapidly forms a gel that has mucoadhesive properties and also may function as a physical barrier to the introduction of bacteria. A professional teeth cleaning procedure including scaling and root planing was done in dogs with one group receiving CHgel following treatment. Periodontal health was determined before and after the procedure including measurement of periodontal pocket depth, gingival index, gingival bleeding sites, and number of suppurating sites. There was a statistically significant decrease in periodontal pocket depth (19%), gingival index (16%), and the number of bleeding sites (64%) at 90-days in dogs receiving CHgel. Additionally, the number of suppurating sites was lower (93%) at 90-days for the group receiving CHgel. The addition of CHgel effectively controlled the bacterial burden (e.g, Fusobacterium nucleatum) at both day 14 and 90. Gingival cells in culture were shown to rapidly incorporate clindamycin and attain saturation in approximately 20-minutes. In summary, a professional teeth cleaning procedure including root planning and the addition of CHgel improves the gingival index and reduces periodontal pocket depth.
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