Carbon dioxide foaming process

A gas foaming/particulate leaching process can be employed to fabricate interconnected open pore structures of PLGA for controlled release of DNA [113,199]. This process employs carbon dioxide to process a mixture of polymer and porogen, in order to fuse adjacent polymer particles into an interconnected structure. The DNA can be lyophilized with the microspheres [113] or encapsulated within the microspheres [200,201]. Lyophilization of DNA with the microspheres can provide large quantities of incorporated DNA, with relatively rapid release kinetics. Incorporation of DNA into the microspheres provides for a more sustained release relative to the lyophilization method [200], with the release kinetics dependent on the polymer molecular weight and microsphere size [201]. DNA can be incorporated into polymer microspheres using several approaches [201-205]. Subcutaneous implantation of scaffolds results in transfected cells observed within the scaffold... 

In standard foam production, a mixture of liquid materials is dispensed and the gas bubbles within the foam structure are only generated by a rather slow chemical reaction. In the case of liquid carbon dioxide foaming the mixture is already dispensed in a two-phase process. 

D. Miller, P. Chatchaisucha, V. Kumar, Microcellular and nanocellular solid-state poly-etherimide (PEI) foams using sub-critical carbon dioxide 1. Processing and structure. Polymer 50 (23) (2009) 5576-5584. 

Table 11.12. Extruder Design and Processing Conditions for Carbon Dioxide Foaming S ... 

Miller, D., P. Chatchaisucha, and V. Knmar. 2009. MicroceUnlar and nanocellnlar sohd-state polyetherimide (pei) foams nsing sub-critical carbon dioxide I. Processing and strnctnre. Polymer 50 (23) (November) 5576-5584. doi 10.1016/j.polymer.2009.09.020. http // linkinghnb.elsevier.eom/retrieve/pii/S0032386109007770. 

The elastomer process is very similar to the Dennis process. It involves a number of steps in which a gas, formerly carbon dioxide and now fluorocarbon, is mixed with a plastisol under pressure. When released to atmospheric pressure, the gas expands the vinyl compounds into a low density, open-ceUed foam which is then fused with heat. 

A method of manufacturing latex foam. Compounded latex is partially frothed and fully expanded by application of vacuum to the mould the gel is frozen, set by carbon dioxide and vulcanised by raising the temperature of the mould. See Dunlop Process. 

The foams can be obtained by the action of a diiscyanate on a polyol and water. The reaction with water forms carbon dioxide and the reaction with polyol forms a urethane polymer. Catalysts play a crucial role in the process. Tin octeate and dibutyl tin dilaurate are preferred catalysts along with tertiary amines. 

The other foaming process is referred to as the prepolymer method. The monomers are reacted to form a low molecular-weight prepolymer. Later the prepolymer is mixed with small amounts of water and is heated. The water reacts with the free isocyanate groups to liberate carbon dioxide, which foams the polyurethane as cross-linking starts. 

Most systems have more than one response. The wine-making process introduced in Section 1.1 is an example. Percent alcohol and bouquet are two responses, but there are many additional responses associated with this system. Examples are the amount of carbon dioxide evolved, the extent of foaming, the heat produced during fermentation, the turbidity of the new wine, and the concentration of ketones in the final product. Just as factors can be classified into many dichotomous sets, so too can responses. One natural division is into important responses and unimportant responses, although the classification is not always straightforward. 

Details are given of the development of an on-line sensor using near IR spectroscoy for monitoring carbon dioxide concentration in polymeric extrusion foaming processes. The calibration curve relating the absorbance spectrum at 2019 nm to the dissolved gas concentration was derived so as to infer dissolved carbon dioxide gas concentration... 

EFFECT OF TALC ON CELL NUCLEATION IN EXTRUSION FOAM PROCESSING OF POLYPROPYLENE WITH CARBON DIOXIDE AND ISOPENTANE... 

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