by Duncan Geddes
Polyether polyols having molecular weights between 2000 and 7000 are used for the production of polyether polyurethane foams. They are produced by adding propylene oxide and ethylene oxide to triols and/or diols. By varying the functionality of the starter alcoholic mixture it is possible to optimise the desired properties of the foams manufactured.
One class of polyether polyols used for flexible polyurethane foam production is high ethylene oxide (EO) containing polyols. These polyols are normally triols of between 3000 to 5000 molecular weight and contain approximately 75% of ethylene oxide units. The small quantity of propylene oxide units is important in ensuring that the polyol remains liquid under normal working conditions. Polyols of this type are used typically in blends with conventional polyols as “cell openers”, and in the manufacture of either very soft foam (for baby sponges) or hydrophilic foams. Foams of high water absorbency can be achieved using ratios of up to 75% of high EO polyols in combination with conventional type polyols.
Hydrophilic foams can also be manufactured using low isocyanate (NCO) pre-polymers (Hypol, Dow trademark) made from all ethylene oxide polyols. The pre-polymers are reacted with a large surplus of water to produce foams.
The wicking/absorbency properties of hydrophilic foams can also be enhanced by heat compression of the foam which improves the overall porosity of the foam.
Application areas for hydrophilic foams:-
- Medical: Wound management.
- Cosmetic: Applicators and removers.
- Consumer goods: Sponges, antibacterial wipes, foam mops.