Novel variations in the microstructure of auxetic ultra-high molecular weight polyethylene. Part 2: Mechanical properties

A highly fibrillar auxetic form of ultra-high molecular weight polyethylene (UHMWPE) has been fabricated by using a powder processing route comprising two stages-sintering and extrusion. The resulting material has a low density (720 kg/m(3)) and low flexural strength and modulus (up to 6 MPa and 62 MPa, respectively) but much larger negative Poisson's ratio when compared with auxetic UHMWPE fabricated using an additional preliminary compaction stage followed by sintering and extrusion. The effects of die geometry on the mechanical properties of this material are examined. The indentation resistance and ultrasonic attenuation of the novel, highly fibrillar auxetic material were measured, and it was found that the indentation resistance was enhanced only at very low loads (i.e. 5 N and 10 N) when compared with conventionally processed UHMWPE. After this, the lack of structural integrity of the material outweighed the benefits of its being auxetic. However the ultrasonic attenuation was found to be extremely good, and much enhanced over conventionally processed UHMWPE, with the attenuation coefficient being at least 47 dB/cm, compared with 8 dB/cm.