Hydrophobic polyethylene membrane for use in venting, degassing, and membrane distillation processes

Described is a polyethylene membrane and in particular an ultra-high molecular weight polyethylene member that provides a high air permeability and is hydrophobic. The membranes have small pores and are suitable for sterilization by exposure to gamma radiation. The membranes can be made by methods that involve one or more of stretching the membrane and grafting hydrophobic monomers onto the membrane surface. A perfluorinated monomer, such as perfluoro-n-octyl acrylate, can be grafted to one or more surfaces of the membrane. The membrane have a high flow rate compared to unstretched or ungrafted membranes.