Foaming of polymers

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

Journal of Applied Polymer Science 88, No. 12, 20th June 2003, p.2842-50 MICROCELLULAR FOAM OF POLYMER BLENDS OF HDPE/PP AND THEIR COMPOSITES WITH WOOD FIBER Rachtanapun P SeUce S E M Matuana L M Michigan,State University... 

Rachtanapun P, Selke SEM, Matuana LM (2003) Microcellular foam of polymer blends of HDPE/PP and their composites with wood fiber. J Appl Polym Sci 88 2842-2850... 

Ruckdaschel H, Altstadt V, Muller AHE (2007) Foaming of polymer blends - chance and challenge. Cell Polym 26 367-380... 

Finally, in the preparation of gas-filled materials on the basis of polymer-oligomer compositions, oligomers which are plasticizers or lubricants of the corresponding high polymers are used. Such compositions ensure miscibility of components with blowing agents, fillers, stabilizers, etc. and subsequent foaming of polymers is usually... 

Supercritical modification of polymers was studied by several scientists to improve or change the properties of polymers. Polymers can either be chemically or physically modified. Examples of chemical modifications are the functionalization of polymers (grafting) or a chemical reaction of the functional groups of polymers to obtain new materials [38, 39]. Examples of physical modifications are the preparation of polymer blends, impregnation of polymers with additives [46], or foaming of polymers [59-61]. Another studied topic of polymer modification and impregnation is the supercritical dyeing of polymer fibers [40, 41). 

I. Tsivintzelis, A.G. Angelopoulou, C. Panayiotou, Foaming of polymers with supercritical CO2 an experimental and theoretical study. Polymer 48 (20) (2007) 5928—5939. 

S. Siripurapu, et al, Controlled foaming of polymer films through restricted surface diffusion and the addition of nanosilica particles or C02-phihc surfactants. Macromolecules 38 (6) (2005) 2271-2280. 

M. Diunon, et al.. Block copolymer-assisted microcellular supercritical CO2 foaming of polymer and blends. Cellular Polymers 31 (4) (2012) 207-222. 

Sulfonylhydrazide blowing agents are used for the low temperature foaming of polymers like LDPE and EVA. 

Chen Z., Kynard K., Zeng C., Zhang, C., and Wang B., Foaming of polymer carhon nanotube nanocomposite from the retrograde phase. SPEANTEC 2011, 69, 2678-2682. 

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