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Polymer foams | additives feature


Blowing up: advances in additives for foaming


Foaming offers several benefi ts to polymer processors and is used in a wide variety of applications, including automotive and packaging products. Primarily, foaming is used to reduce weight, which saves material costs. Less weight can also lead to fuel savings, for example in light-weight vehicles or in lighter packaging to trans- port. Foamed plastics can also provide insulation to increase energy effi ciency. So it is no surprise that foam- ing is gaining interest as a sustainable technology because of its ability to bring fuel and materials savings. Polymers can be foamed by injecting gas directly into the melt using a physical blowing agent, or by creating a gas in the melt using a chemical foaming or blowing agent (CFA). Blowing agents can also act as processing aids in the melt to improve throughput, as viscosity reducers to improve fl ow and reduce moulded-in stress, and to improve mould fi lling and reduce warping. Processes for direct gas injection, such as Trexel’s MuCell microcellular process, have been growing in use. Several new process technologies for physical foaming were discussed in Compounding World’s August 2012 article on ‘Expanding interest in light- weight parts’ (see http://bit.ly/CWfoam). These new technologies include Wittmann Batten-


feld’s direct nitrogen injection technology, R&D Factory’s water injection system, and Trexel’s and Mazda’s core-back expansion moulding technology. In addition to these process improvements, developments


www.compoundingworld.com Jennifer Markarian examines the


latest developments in additive and masterbatch technologies for foamed plastics applications


in additives for both chemical and physical foaming are also progressing.


Chemical foaming agents The most commonly used CFA is azodicarbonamide (ADCA or AZO), an exothermic CFA that produces nitrogen on decomposition. There are also other exothermic CFAs and endothermic CFAs, such as carbonates that release carbon dioxide. Exothermic CFAs have a high gas yield, which maximizes density reduction. Endothermic CFAs typically produce a smaller cell structure, which can improve physical properties and surface appearance. Blends of both types are also used. CFAs are added during extrusion or moulding of the


fi nal part either as a powdered additive or as a master- batch. Although CFA technology is well-established, customers and suppliers continue to look for further improvements in density reduction, physical properties,


January 2013 | COMPOUNDING WORLD 37


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