Monday, September 29, 2008
Waterproof breathable membranes are common in outdoor clothing and gear, but most still rely on expanded polytetrafluoroethylene (ePTFE) polymers, the most common polymer for microporous hydrophobic membranes, which is coated or laminated to an outer fabric layer. Xscape Membranes, made by ENTEK Membranes LLC, Lebanon, Ore., rely on a new material: ultra-high molecular weight polyethylene (UHMWPE). Already in use in ballistics protection garments, lightweight climbing ropes, and battery separators, UHMWPE is made using a gel processing method developed by ENTEK.
A molecular weight greater than 3,000,000 g/mol and a resultant high melt viscosity means that UHMPWE is difficult to process. The extruded web is plasticized with oil, fillers are added to improve textile qualities, and the final material is extruded to obtain a biaxially oriented membrane that is at least 65% microporous with an average diameter of about 250 nm. The volume of each pore is 8,000 times smaller than a drop of water. The membranes have a tensile strength of 5,000 psi and are lightweight, weighing only 6.0 g/m2.
ENTEK membranes have a melt temperature of just 130°C, well below the 325°C of ePTFEs. But Xscape Membranes also cost much less and rank near the top of each major moisture vapor transmission rate test.
ENTEK Membranes LLC, www.entek-international.com