Preparation of Porous Polyolefin Films or Membranes through Stretching Method

Membranes are thin layers that act as selective barriers to separate the components of materials and control the mass transfer between different phases. Therefore, their two main functions include: component selectivity and the permeability characteristics. Membranes according to their material sources are classified into four categories referred as polymeric, ceramic, metal and liquid types. Among these, polymeric membranes are the most favorable materials because of their availability in various chemical structures, their optimum physical properties and lower prices. Polymeric membranes are produced by four main methods known as solution casting, stretching, template leaching and track etching. Among them, stretching technique is inexpensive and because no solvent is used in this process, stretching method has lower environmental impacts. Among different polymers, polyolefines such as polyethylene (PE) and polypropylene (PP), due to their lower price, semi-crystallinity, good mechanical properties, chemical stability and easy process ability, are more appropriate for manufacturing of polymeric membranes by stretching method. Porous membranes are used in applications such as battery separators and drug delivery devices for controlling the permeation rate of chemical components. In this paper, we present some useful information on the above subject by reviewing the related published works in this area.