Spray drying humidity

The second step is to disperse the core material being encapsulated in the solution of shell material. The core material usually is a hydrophobic or water-knmiscible oil, although soHd powders have been encapsulated. A suitable emulsifier is used to aid formation of the dispersion or emulsion. In the case of oil core materials, the oil phase is typically reduced to a drop size of 1—3 p.m. Once a suitable dispersion or emulsion has been prepared, it is sprayed into a heated chamber. The small droplets produced have a high surface area and are rapidly converted by desolvation in the chamber to a fine powder. Residence time in the spray-drying chamber is 30 s or less. Inlet and outlet air temperatures are important process parameters as is relative humidity of the inlet air stream. 

The range of application of shear cell testing methodology is seen in Tables 2-6. Table 3 relates the flow properties of mixtures of spray-dried lactose and bolted lactose. These mixtures, in combination with the excipients tested, cover a broad range of flow. Tables 4 and 5, for example, show lot to lot variations in the flow properties of several materials, and Table 6 shows the variation in flow properties of bolted starch, sucrose, and phenacetin at different relative humidities (RH). Figure 8 presents the yield loci of sucrose at four different consolidation loads. Also shown in the figure are the shear indices determined at each consolidation load. 

For example, amorphous clarithromycin was prepared by grind and spray-drying processes, and XRPD was used to follow changes in crystallinity upon exposure to elevated temperature and relative humidity [59]. Exposure of either substance to a 40°C/82% RH environment for seven days led to the formation of the crystalline form, but the spray-dried material yielded more crystalline product than did the ground material. This finding, when supported with thermal analysis studies, led to the conclusion that the amorphous substances produced by the different processing methods were not equivalent. 

Spray drying is the most widely used, least expensive and favored route among the methods available for encapsulation (2) Various theories of volatile retention in spray drying have been proposed and reviewed (3). In addition to the nature of flavor compounds, flavor retention is governed by type of carriers, infeed composition, solids concentration (4), dryer inlet/exit air temperature, air velocity and humidity, feeding rate and atomization characteristics. In addition to flavor retention,the stability of the encapsulated product, as mentioned earlier, is also of importance and is governed by nearly the same parameters. However,the effect and mechanics of each individual factor are much less understood. 

A remarkable advantage of cyclodextrin complexed flavor fonnulations over spray-dried and micro-encapsulated ones is their negligable hygroscopicity under high humidity conditions. 

Labrude and Rasolomana [1.80] reported an atomizer-spray-drying system for oxyhemoglobin in a 0.25 M sucrose solution at temperatures between +80 and +100 °C, which resulted in an unchanged dry product if the relative humidity was kept below 3%. When this dry product was compared with a freeze-dried product, in both cases a met-oxyhemoglobin (met-HBO) content of-3% was found. By ERP and spectro-... 

An aqueous gel (1 liter per min) is spray dried at 25°C in a counter-current spray dryer. The droplets produced by atomization are 50 pm in diameter and remain that size throughout drying. If the drying rate is limited by mass transfer in the boimdary layer, what height of the spray dryer of cross-sectional area 1 m is required if the drying air (100 liter per min) enters at 150°C and = 0% relative humidity. See problem 3 for the data. 

FIGURE 12.40 Compaction of spray dried alumina at 92% relative humidity. Data from Reed [23, p. 337]. 

FIGURE 13.29 (a) Compaction of spray-dried alumina at 92% relative humidity, (b) Cumulative pore size distributions by Hg porosimetry for spray dried AI2O3 (Alcoa A-17-1) for different pressing pressures. Data taken from Reed [6, p. 337]. 

Vidgren P, Vidgren M, Paronen P. Physical stability and inhalation behavior of mechanically micronized and spray dried disodium cromoglcate in different humidities. Acta Pharmaceutica Fennica 1989 98 71-8. 

Naini V, Byron P, Phillips EM. niysicochemical stability of crystalline sugars and their spray-dried forms dependence upon relative humidity and suitability for use in powder inhalers. Drug Dev Ind Pharm 1998 24 895-909. 

Example 17 Drying a Pure Water Drop (Marshall, Atomization h- Spray Drying, 1986.) C culate the time to dry a drop of water, given the air temperature and relative humidity as a function of drop size. 

Figure 2 The dynamic vapor sorption chart for lactose. A humidity-induced recrystallization event of spray-dried lactose is marked. Steps refer to relative humidity changes. Source Courtesy of Surface Measurement Systems (1).

Saltmarch, M. and Labuza, T.P. Influence of relative humidity on the physicochemical state of lactose in spray-dried sweet whey powders, /. Food Sci., 45,1231,1980. 

FIGURE 1.12 Schematic illustration of a spray-dried particle in humid air environment. 

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