Blowing agents and foaming processes described

The recent Rapra conference on blowing agents and foaming processes drew a record number of delegates from across the world.

Foaming plastics is a developing art, with new types of biodegradable materials to work with and increasing regulations on the gases used to blow the foam.

Researchers gave expert presentations on the latest technology at the 8th Rapra conference on blowing agents and foaming processes 2006, which had a record number of delegates from across the world.

Clariant described new masterbatch chemical blowing agent technology incorporating a new melt stabilising additive, Cesa Extend.

Lehmann and Voss presented data on foam extrusion and ways of controlling foam structure and the thickness of outer foam layers.

Expancel has expandable microsphere technology.

There were several papers on polyurethane blowing agents such as the physical, liquid blowing agent Ecomate from Foam Supplies, methylal from Lambiotte and Cie, and HFC from Solvay Fluor.

Cracow University of Technology has been working on blowing PU foams using microwave irradiation.

Polylactic acid can be difficult to foam.

The National Research Council of Canada has investigated the continuous extrusion foaming of PLA using a carbon dioxide blowing agent.

There was a very narrow processing window: lower than 7% by weight did not give low density foams and above 8.3% by weight lead to severe shrinking on ageing.

Salvatore Innace presented a very interesting paper on foaming polycaprolactone, trying different nucleating agents from talc to nanocomposites.

Noreen Thomas gave an excellent overview of cellular PVC-U and the use of formulation technology such as acrylic processing aids, to improve melt extensibility and strength.

Sekisui Alveo described work on non-PO foams, such as Peek, PA6, PVDF, PSU, SEBS, TPU and polyetheramides.

The company has experimented with a three-step process: sheet extrusion, crosslinking and foaming as compared with conventional extrusion and injection moulding.

The new process was most suitable for less stiff materials such as TPE.

The polyetheramide foams (Pebaxfoam) gave good breathability, high energy recovery, flexibility at low temperatures and compression set.

RWTH Aachen University has looked at the effect of varying the diameter of talcum particles (a passive nucleating agent) on PE foam.

Researchers examined the four parameters affecting foam structure in extrusion: varying the physical blowing agent content; increasing the content of nucleating agent; the pressure gradient at the die exit; and the shear rate in the die.

Professor Michaeli spoke about analysing foam structures.

Dr Lee of Sealed Air discussed the analysis of extruded PP/PS interpolymer.

The University of Manchester has developed technology to overcome the poor heat transfer properties of polyolefins.

A combination of conventional heating to expand the surface of the material is combined with microwave heating to expand the interior.

The University of Valladolid has examined thermal conductivity, acoustic absorption and creep properties of polyolefin foams to create customised materials.

Professor Chul Park spoke about extending the foamability of polypropylene, by tailoring the melt strength and crystallisation kinetics.

Laval University covered studies of LDPE recycling with azodicarbonamide as the foaming agent.

Sulzer Chemtec has a new physical blowing agent technology, Optifoam, that can be retrofitted to existing equipment.

The system comprises a special nozzle, which is mounted at the downstream end of an injection moulding machine or extruder.

Trexel covered microcellular foaming technology.

Berstorff has looked at twin screw technology where up to three different blowing agents and polymers with different melt flow indices and additives can be mixed in one stage.

Professor Lindt of the University of Pittsburgh described foaming polystyrene using carbon dioxide and HFC and an HCFC.

BASF presented information on ways to improve the thermal insulation properties of polystyrene foam including Styropor and Styrodur.

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