Test Method for Relative Molecular Mass of UHMWPE

Test Method for Relative Molecular Mass of UHMWPE

UHMWPE (ultra-high molecular weight polyethylene) is a kind of polymer, its relative molecular mass will affect its performance. There are many methods to determine the relative molecular mass. Different methods are adopted because of the difference of the relative molecular mass and the types of polymers. UHMWPE is mostly determined by viscosity method in production and scientific research. Its measuring instrument is simple, easy to operate and has good accuracy.

The principle of measuring relative molecular mass by viscometry is simple. UHMWPE is dissolved by solvent at high temperature and its viscosity is measured by Ubbelohde viscometer. The higher the viscosity, the higher the relative molecular mass. The specific methods are as follows: UHMWPE 11-15mg is dissolved slowly at (135 +0.5) ℃ with 50 ml mixture of dekalin and p-xylene for about 60 minutes, and then the viscosity is measured in a Ubbelohde viscometer. The volume of Ubbelohde viscometer is 2 ml and the diameter of capillary is 0.55 mm. After measuring the viscosity, the relative molecular mass was calculated by certain conversion, and the measurement method was carried out according to GB 1841-80.

The relative molecular mass test can reflect whether the selection of parameters in UHMWPE forming process is reasonable. The main validation processes include the rationality of antioxidant selection, sintering temperature, sintering time, pressure and cooling rate.