August 2016 Spray 17 and dispersing agent would be required. The first item to be used was a refined form of Montmorllonite Clay (Bentonite) with the surface modified to give it a positive charge by brief exposure to a quaternary ammonium salt solution. The charged particles repelled each other and this allowed mixtures such as 90% ACH and 10% Bentonite 38 to be fully dispersed with a quick shake or two. A trace of Propylene Carbonate acted as a facilitating agent. These dispersing agents are typically 10% to 16% of the percentage of the active ingredient. Other bulking and dispersing agents are also useful in preventing hard settling. Chemically USP Bentonite is an absorbent form of hydrous colloidal aluminum silicate clay, having the general formula Al2O3•4SiO2•H2O. Talc has essentially the same composition, except for a different macro-structure, less than 0.2% H2O and treatments that include rendering it white and asbestos-free. The best talcs usually come from France and Italy. When very finely divided, talc can act as a bulking and dispersing ingredient. Various silyl compounds, such as extremely finely divided amorphous silicas (typically fumed silicas) can also add viscosity, bulking and dispersing characteristics. ACH and REACH powders have a tendency to partly plug or fully plug valves. The best powder valves are those with vapor-tap features. By dispensing mixtures of liquid, solids and gas, these valves can significantly lower delivery rates. In turn, this allows formulators to enlarge the valve stem and actuator orifices (making them less liable to plug) while still maintaining a satisfactorily moderate delivery rate. During the development program it is not uncommon for laboratory workers to prepare 100 or more samples of aerosols with a promising composition and valve, letting the units age both overnight and for a few days with their protective covers off and then checking each one for spray characteristics. Ideally, every aerosol should spray normally, without undue Isopropyl myristate is a clear, odorless and skin compatible ingredient found in aerosol formulas that can produce an unsightly, slightly yellow oil film on the underarm areas of shirts and blouses, often mistaken for sweat.
Spray August 2016
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