Starch as antiblocking agent in breathable polyurethane membranes

A breathable polyurethane membrane was manufactured by using a multilayer film extrusion technique. In this process, the monolithic membrane is blown as the inner layer of a three‐layer film in which the outer support layers are polyethylene‐based. The neat membrane surface was unacceptably sticky. It was found that starch was a suitable antiblocking agent outperforming mineral fillers. However, starch incorporation decreased the membrane permeability towards moisture. The experimental permeability results are consistent with the predictions of the Maxwell model for a randomly dispersed, impermeable spherical filler. Fitting the Wagner‐Sillar model indicated a near‐spherical particle shape and confirmed the impermeable nature of the starch particles. This unexpected result can be rationalized by assuming a highly crystalline or glassy nature for the starch domains. J. VINYL ADDIT. TECHNOL., 13:215–220, 2007. © 2007 Society of Plastics Engineers