Our 2008 study of cellulose sponge production methods compared the technology with viscose fibre production and a non-confidential version was presented at the EDANA symposium in Baveno Italy in June 2010.
While using the same basic xanthate dissolution technology as fibres, sponges are made on a small scale and as a result are expensive niche products restricted mainly to higher value semi-durable household cleaning applications. Are they small scale because the market is inherently small or is the market size restricted by the high price? The technology for producing sheet sponges by more economical processes on a much larger scale appears to exist already, and sheet sponges produced on such a scale would be bulky highly absorbent “nonwovens” with many potential uses in disposable hygienic products.
Because sponge sheets have to be reinforced with fibres to get adequate strength, the use of viscose technology may be unnecessary. Pulp may dissolve well enough in caustic soda alone, especially at sub-zero temperatures to yield a dope with sufficient undissolved fibres to act as reinforcement. Forming pores by air dispersion or creation of ice crystals may obviate the need for the traditional glaubers salt pore-former and the resulting dope preparation process could take place in a single large pulper. The dope could be extruded through a wide die onto a conveyor for regeneration prior to washing. The whole process would be more analogous to pulp manufacturing technology than the current sponge routes and could operate on a larger scale.
Carried out at a pulp mill with infrastructure for recovering the caustic soda, costs of the resulting “spongy nonwoven” would be significantly less than the current sponge sheets and could be usable in the wider hygienic disposables market.