Preparation of UHMWPE membranes via thermally induced phase separation: effect of solvent removal conditions on structure and properties

Due to its high mechanical strength and other outstanding properties the ultra-high molecular weight polyethylene (UHMWPE) is a promising material for membrane preparation. In this work, it was shown that thermally induced phase separation (TIPS) method can be used for preparation of UHMWPE membranes from a mixture of this polymer with decalin even without subsequent drawing of the films. Two ways of decalin removal from the membrane precursor were used: drying from solvent at ambient conditions and extraction into iso-propanol with subsequent drying in air. It was shown that the former way leads to significant shrinkage and thus to membranes with a thickness of ~14 μm, porosity of ~24%, permeance of ~150 l/m² h bar, bubble point of ~1.7 bar and tensile strength of ~8.6 MPa. The structure and properties of the samples prepared using the latter way of decalin removal depend on the duration of the extraction stage. It was established that the decrease of extraction time from 24 to 1 hour results in a decrease of membrane porosity (from ~86 to ~81%) and permeance (from ~1700 to ~1550 l/m² h bar), and an increase of tensile strength (from ~0.73 to ~0.92 MPa), while elongation at break (~280%), melting temperature (~136.5°C) and crystallinity degree (~82%) remain almost unchanged. The main reasons for the observed tendencies are discussed. The obtained data showed that changing the conditions of solvent removal may be used as an effective method of controlling the structure, physico-mechanical and transport properties of the membranes.