Micro-Macro Scale Relationship in Creep Deformation of Ultra High Molecular Weight Polyethylene

Macroscopic and microscale creep deformations of UHMWPE were investigated by using in situ SAXS. A methodology for the measurement of the local creep deformation of inter-lamellar amorphous phase has been proposed. The local strain of inter-lamellar amorphous phase (epsilon(a)) and macroscopic strain (epsilon(macro)) were evaluated and they were compared to study the relationship between macroscopic and microscale creep deformation of UHMWPE. Both of them exhibit two deformation regions against creep time. The entanglements show a strong impact on both the macroscopic and local inter-lamellar amorphous phase creep behavior and they can be well correlated to the molecular weight between two entanglements estimated from strain-hardening modulus. Compared to the macroscopic creep deformation, local inter-lamellar amorphous layers have a smaller creep deformation. From the local creep measurement, the apparent modulus of inter-lamellar amorphous phase can also be estimated (200 < Ma < 500 MPa). These values are much higher than the Young's modulus of bulk amorphous PE, which can be well explained by the confinement of the lamellar stacks and the enhancement of the amorphous phase with the relatively high concentration of entanglements. This study provides a useful means and quantitative data for achieving the scale transition between the micro and the macro structural levels for the study of viscos-elastic deformation.

Automated summary

Macroscopic and microscale creep deformations of UHMWPE were studied using in situ SAXS. A methodology for measuring the local creep deformation of inter-lamellar amorphous phase was proposed, showing that entanglements play a significant role in both macroscopic and local creep behavior.