Dunlop and Talalay Latex Foam

Student: In the manufacturing of latex foam products such as the mattresses, what are the main differences between the so called Dunlop process and the Talalay process? What gelling mechanism is involved in each case?

JohnWoon: Very briefly, in the Dunlop process, the gelling system is done in a one-stage operation. For gelling, zinc oxide and sodium silicofluoride (SSF) are used. The compounded latex (with curatives, soap etc) is first frothed mechanically before the addition of the gelling agents (i.e zinc oxide and SSF) followed by moulding.

SSF would undergo hydrolysis resulting in a drop in the latex pH due to the formation of hydrofluoric acid. This, coupled with the formation of zinc ammines, would lead to the gelling of the latex in the foam.

In the case of the Talalay process, a measured quantity of slightly foamed latex is poured into the mould to only partially fill it. After the mould has been closed, the latex is expanded by vacuum to completely fill the mould. The foamed latex is prevented from collapsing by rapidly dropping the temperature to -30°C and freezing it solid.

At this point, carbon dioxide gas is passed through the latex leading to a drop in pH and hence gelling. The temperature is then increased to 115°C to set and vulcanise the latex.

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