Spray drying powder characteristics

In precipitation reactions, powder characteristics depend on the speed of the nucleation of particles and their growth due to the mass flow to the surfaces. In freeze drying and spray drying, powder characteristics primarily depend on the size of droplets, which in turn is determined by the parameters of a nozzle and characteristics of the flow of a carrier gas. Both these methods enable one to obtain powders with very high surface area. 

The dispersed droplet size, referred to as emulsion or particle size, can be reduced in the spray drier infeed matrix by more vigorous mixing or homogenization. There is also a new technique for creating small emulsions termed microfluidization which will be discussed later. This research was designed to determine whether the size of emulsion in the infeed solution will affect the characteristics of the final spray dried powder. Materials and Methods... 

Spray-dried powders are formulated to give the best overall cleaning performance and flow characteristics at the lowest possible formulation costs. Typical spray-dried detergent formulations are shown in Table 36.6. Slurry preparation is considered to be the single most important factor in spray drying. Control of the raw material order of addition, slurry solids level, slurry temperature, viscosity, and aeration enable manufacturers to deliver the desired final product characteristics. The spray tower itself is simply a contained heat source that removes moisture at a uniform rate dependent upon the quality and the quantity of feed to the dryer. If feed variables are not controlled, variability in the... 

Confectionery is not made directly from the root but from a liquorice extract. These are obtained either in the form of a spray dried powder or the paradoxically named block juice . The spray dried extract is a free-flowing powder, yellowish brown in colour with a mild liquorice aroma and the characteristic bitter-sweet taste, whereas block juice is a solid block, resembling coal, but with the overpowering liquorice flavour and bitter-sweet taste. 

Kulvanich P, Leesawat P, Patomchaiviwat V. Release characteristics of the matrices prepared from co-spray-dried powders of theophylline and ethylcellulose. Drug Dev Ind Pharm 2002 28 727-739. 

Equation 1.2 has been originally proposed to express the relaxation phenomena in a polymer. The relaxation constant, p, represents the breadth of energy distribution in the polymer relaxation phenomena. P = 1 means a simple relaxation, and smaller values of P mean larger breadth of the energy distribntion. Since a spray-dried powder consists of various particles having different release characteristics, its total (or overall) release behavior might be the snm of the KWW relaxation equation of an individual particle i ... 

Shiga, H. Yoshii, H. Nishiyama, T. Furuta, T. Forssele, P. Poutanen, K. Linko, P. Flavor encapsnla-tion and release characteristics of spray-dried powder by the blended encapsulant of cyclodextrin and gum arable. Drying Technology 19(7), 1385-1395, 2001. 

The photos of Fig. 6.12 visualize in a non-destructive manner the distribution of emulsion flavor droplets (red color) over the cross-section of the spray-dried powder and the internal morphology of the product (i.e., the presence, or not, of a vacuole). Therefore, they show that the CLSM is a new valuable tool for studying and observing the encapsulated flavor. The technique can even be applied to study the release characteristics of flavor from the powder in real time (Yoshii et al., 2007). 

The powders resulting from spray drying experiments with PVP K30 solutions showed comparable characteristics to conventional pressure or pneumatic spray dried powders. 

Tile shapes are pressed on hydraulic presses, ranging from 500 to 2500 tons of capacity, using steel- or rubber-lined steel dies. Spray dried powder lends itself ideally to hydraulic, rapid, automatic pressing. The characteristic free flowing nature and uniform particle size of these powders are ideal for rapid, uniform filling of die cavities, even for somewhat complex trim shapes. 

Chemical engineers could also work to devise processes to improve the flow characteristics of powders after they are formed. Such research would help control agglomeration of particles in subsequent processing steps as well as facilitate the production of compacted ceramic preforms. For example, gas-solid chemical reactions might be used to tailor the chemical composition of powders. As another example, better methods of componnding powders with binders might be achieved by processes that mix powders with suitable binders in a liquid and then spray dry the resulting suspension. 

Table 7.7 Particle Size and Bulk Density Characteristics of Some Spray-Dried Ceramic Pressing Powders...

Gereg and Capolla developed process parameters determined by a model laboratory bench scale Carver press, model C (Carver Inc. Savannah, Georgia, U.S.A.), which were translated to production scale compactor parameters (6). Their study provided a method to predict whether a material is suitable for roller compaction. Their study objectives were to characterize properties of the material to identify process parameters suitable to achieve the necessary particle size and density using the dry granulation process and then translate laboratory information to a production scale roller compactor. Actually, information developed from a Carver press was correlated and scaled-up to a production scale Fitzpatrick roller compactor. Model IR 520 (Fitzpatrick Co., Elmhurst, Illinois, U.S.A.) The compactor produced very similar powder granule characteristics as the Carver press. Various lactose materials, available as lactose monohydrate or spray dried lactose monohydrate, were used as the model compounds. Results indicated that a parametric correlation could be made between the laboratory bench Carver press and the production scale compactor, and that many process parameters can be transferred directly. 

Controlled optimal particle size and size distribution ensures superior flow properties of coprocessed excipients and reduced reliance on addition of glidants. The volumetric flow properties of SMCC were studied in comparison with those of the physical mixture of its parent excipients (42). The particle size range of the two test samples was found to be similar, but the flow of coprocessed excipient was better than that of the physical mixture. A comparison of the flow properties of Cellactose with its parent excipients was also performed (5) by measuring the angle of repose and Hausner ratio, and Cellactose was found to have better flow characteristics than lactose or a physical mixture of cellulose and lactose. The spray-dried coprocessed product had a spherical shape and even surfaces, which resulted in improved flow properties. On similar terms, mechanically coating the 2% CSD over microfine cellulose powder resulted in improving its flow properties (43). 

The process itself is more art than science. There is hardly any information in the open scientific literature. Most publications have to do with spray drying of ceramic powders (ref. 15 and references therein, ref. 16). There are also some standard books about spray drying [17]. Important process parameters are the viscosity of the liquid, the solids content of the suspension, the film-forming characteristics, the type of atomizer, the temperature, the rotation speed of the wheel, gas velocity, etc. 

AIR particles are low-density lipid-based particles that are produced by spray drying lipid-albumin-drug solutions. These particles are characterized by their porous surface characteristics and large geometric diameter while having a low aerodynamic diameter [176,177], This technology has been used to produce porous particle powder formulations of L-dopa that have been investigated for the treatment of Parkinson s disease [178],... 

J. Kim, E.H., Chen, X.D., and Pearce, D. (2005). Melting characteristics of fat present on the surface of industrial spray-dried dairy powders. Colloids Sutf. B. 42, 1-8. 

---