The patented dry stretch method is comprised of extrusion/stretching process in which the resulting membrane can have specific porosity and gas permeation values. The stretching step produces the final microporous structure.
Initially, the polymer of choice is heated and extruded into a non-porous film or fibre. By controlling the extrusion process under which the film or fibre is formed, we create a crystalline structure that allows the formation of microvoids in a subsequent stretching step.
Extruded material is stretched under various temperatures to generate pore population and respective pore size to provide specific porosity (open area). This stretch process includes a reasonable relaxing of material stretch to minimize shrinkage of final product.
The basic principle is similar for both the production of flat sheet and capillary membranes: After extrusion, our membrane can be immediately processed on annealing and stretching lines that create the final porous form.
Microporous membranes produced via dry stretch have substantially elliptic shaped pores elongated in machine direction of membrane.
Typical applications for dry stretch capillary membranes are blood oxygenation and gas transfer.