Pelletization encapsulation

A final category of encapsulating materials consists of reaction products of the nucleus material and a reagent. For example, pellets of nitronium perchlorate have been encapsulated in shells of the less reactive amm perchlorate (AP) by exposing the pellets to ammonia gas. The fragile AP shells were usually further protected by a top-coating of A1 or a polymer film (Ref 2). The most familiar example of this process is the natural one wherein A1 powders (or articles) become coated with a protective coating of A1 oxide thru exposure to atmospheric air... 

Insulin (molecular weight 7000) has been formulated in controlled release microbeads and pellets (135,136). A solvent evaporation micro-encapsulation procedure was used to produce microspheres with up to 20% by weight insulin. Solvent-casting techniques were used to prepare pellets. The investigations demonstrated that the PLA... 

Reactor fuel consists of uranium that has been formed into a usable metal alloy and provided as small pellets, rods, or plates. The fuel is encapsulated with a metal cladding, such as zircaloy, which adds mechanical strength and also prevents radioactive contamination. Nuclear reactor waste or spent nuclear fuel consists of the fuel pellets that have been used... 

Boron nitride capsules containing 10-20 nm particles of magnetite were produced by forming pellets of boron nitride magnetite in a ratio of 8 2 and arc melting the pellets in an Ar/N2 atmosphere for a few minutes. HRTEM confirmed that the magnetite particles were encapsulated in the boron nitride (Hirano et al., 1999). 

The consolidated titanate waste pellets are similar in appearance to their glass counterparts, i.e., both are dense, black and apparently homogeneous. Microscopic analyses, however, reveal important differences between these two waste forms. While little definitive work has been done with glassy waste forms, it is apparent that several readily soluble oxide particulates of various nuclides are simply encapsulated in the glass matrix. The titanate waste form has undergone extensive analyses which includes optical microscopy, x-ray, scanning electron microscopy, microprobe, and transmission electron microscopy (l ) The samples of titanate examined were prepared by pressure sintering and consisted of material from a fully loaded titanate column. Zeolite and silicon additions were also present in the samples. 

Figure 5.7. Mineralization profiles of fluoranthene by non-immobilized and polyurethane-immobilized cells (PU pellet) of strain EPA505. Results of studies with (a) inorganic nutrients in incubation medium and (b) inorganic co-encapsulated nutrients.

Carbon and Phosphorus Burial Efficiencies. The estimate of diatom carbon demand (12-15 g/m2 per year) is consistent with the flux of carbon to the sediment surface. With sediment-trap fluxes corrected for resuspension, we measured a total annual deposition flux of 12.5 g of C/m2. In comparison, Eadie et al. (24) obtained 23 g of C/m2 for a 100-m station, based on three midsummer metalimnion deployments. Of our total, 83% of the carbon was associated with diatoms, and the primary diatom carbon flux was 10.3 g of C/m2. Thus, about 15-30% of the diatom carbon was regenerated in the water column during sedimentation. Approximately 10% of the diatom flux reached the sediment surface encapsulated in copepod fecal pellets the remaining 90% was unpackaged. 

In an effort to develop an effective bioadhesive system for buccal administration, insulin was encapsulated into polyacrylamide nanoparticles by the emulsion solvent evaporation method [98]. Though nanoparticle formation ensures even distribution of the drug, pelleting of the nanoparticles was performed to obtain three-dimensional structural conformity. In addition, it was hypothetized that the pelletized particles will remain adhered to the mucosa, leading to good absorption. While studying bioadhesion and drug release profiles, it was found that the... 

To increase thermal conductivity of powder layer metal powders of copper, aluminium are added. Composites are compacted in pellets, which can be sintered in addition. Their main characteristics are coefficient of effective thermal conductivity and coefficient of gas-permeability. The weight fraction of powder in such compacts serves as the controlled parameter, and it has the optimum, when gas-permeability does not worsen sharply at acceptable thermal conductivity. Encapsulation of hydride powder by material with high thermal conductivity followed by compaction of pellets and their sintering is also used. 

Example 1 Encapsulation of Lithium Aluminum Hydride with Poly(chloro-p-xylylene). In the distillation zone were placed 5.0 grams of dichloro-di-p-xylylene. In a 4-oz. polyethylene bottle were placed 10.0 grams (400 pellets) of lithium aluminum hydride (LAH). LAH was obtained from Metal Hydrides, Inc., as 1/8-inch diameter pellets. The bottle was positioned in the coating chamber, the system was... 

Example 2 Encapsulation of 3/16-inch Sodium Hydroxide Pellets with Poly( chloro-p-xylylene ). Fifty grams of sodium hydroxide pellets were encapsulated with polymerizing chloro-p-xylylene generated by pyrolysis of 5.0 grams of dichloro-di-p-xylylene over a 15-minute period. The bottle was rotated at 60 r.p.m. during the run. A pyrolysis temperature of 660°C. and system pressure of 50 //, were employed. A total of 51.97 grams of encapsulated pellets was recovered at the end of the run. 

To evaluate the perfection of encapsulation, the coated pellets were immersed in pure methanol. Evolution of hydrogen from one or more points indicates the presence of a pinhole or other imperfection in the coating. Since the encapsulated pellets are denser than methanol, pinholes in individual pellets are detected easily by evolution of a stream of hydrogen bubbles rising from the pellet to the surface. Such pellets are removed. The test is continued for 15 minutes, and the percent of pinhole-free pellets is calculated. Typical data are presented in Table I. 

J Cf is encapsulated and shipped in eight standard Special Form capsules and packages to meet the needs of the different medical, industrial, and research applications used. The isotope is available as californium oxide, californium-palladium cermet wire or pellets, and, in the case of medical therapy sources, californium-palladium cermet sheathed in platinum-iridium alloy. Capsules are available in a variety of metals and alloys (Table 1, Figures 1 through 8). 

For all shipments of 252cf purchased by encapsulators and users (may be in the form of oxide, cermet wire, or cermet pellets)... 

Companies will custom formulate colorant and additive products designed to be used by plastic molders, who will, in turn, produce the final consumer products. The raw materials for colorant and additive products may be in powder, liquid, or solid form. The products formulated from them may also be in powder, liquid, or solid form. Dry color formulations (powder form) currently comprise less than 5% of the total colorant and additive products being produced today. Liquid formulations account for another 5% however, this form of product is increasing in popularity and is expected to capture a larger share of the colorant and additives market in the near future. The solid form, known as concentrates or masterbatch products, are concentrated ingredients encapsulated in a carrier resin that is usually in pellet form. This type of product comprises the overwhelming majority of the formulated products used by molders and compounders today. A discussion of the basic production processes associated with the production of the various colorant and additive product types is presented below. 

When the encapsulated resin exits the thermal process, it no longer represents a significant potential for generating dust emissions. At the pelletizer, commonly called a chopper, the resin is still relatively pliant and is actually cut or sliced rather than chopped. This operation does not create dust emissions. 

---