Blowing agents impregnation

Bead Processes. These processes have generally replaced the above techniques. The styrene is polymerised by bead (suspension) polymerisation techniques. The blowing agent, typically 6% of low boiling petroleum ether fraction such as n-pentane, may be incorporated before polymerisation or used to impregnate the bead under heat and pressure in a post-polymerisation operation. 

Addition of Blowing Agents to Styrene Solutions of Polystyrene. If the pentane is added to a suspension polymerization of styrene after the bead identity point has been reached, the formation of blisters is avoided and the diffusion of pentane into the bead is rapid. Thus, the two objections to the pentane-in-monomer process and the post-polymerization impregnation processes are avoided (31, 119). The same system has also been used to introduce normally gaseous blowing agents, such as butane, propane, st/m-dichlorotetrafluoroethane, propylene, butene, and butadiene (51, 91,115). 

The impregnation during the polymerization at a conversion of about 65-85 % is currently the one technological process of practical importance. Procedures with addition of blowing agent at the point where the density of PS particles overcomes the density of the water phase (at about 66 % conversion) are preferred [24]. 

Insecticides, and particnlarly termiticides, may be dissolved in monomers polymerised to form foamable polymers, snch as polystyrene. The resulting monomer and insecticide may then be polymerised in a conventional manner and either impregnated with a blowing agent or expanded using an extrasion process to produce polymeric foam having insecticidal properties. The polymer may also contain a flame retardant. Such polymers and the foam made therefrom may be used in the constraction industry, particularly where insect infestation is a concern. 

Polymeric Beads, Expandable. Semi-processed products used to manufacture polymeric articles, and which have been impregnated with a flammable gas or liquid as a blowing agent. They may evolve small quantities of flammable gas during transport. ICAO A2... 

The test that law enforcement agencies use to approximate a person s blood alcohol level is based on the oxidation of breath ethanol. An oxidizing agent impregnated onto an inert material is enclosed within a sealed glass tube. When the test is to be administered, the ends of the tube are broken off and replaced with a mouthpiece at one end and a balloon-type bag at the other. The person being tested blows into the mouthpiece until the bag is filled with air. 

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