Mechanical properties of ultra high molecular weight polyethylene obtained with different cocatalyst systems

Three types of semicrystalline ultra high molecular weight polyethylene, obtained with amorphous SiO2-supported Ziegler-Natta catalyst systems modified by vanadium and titanium, have been studied by wide angle X-Ray scattering, dynamic mechanical thermal analysis and microhardness methods. In all the cases a significant amount of monoclinic modification is observed, which is estimated to be of the order of 10%. With increasing the degree of crystallinity and quantity of entanglements, storage modulus and alpha relaxation increase and gamma relaxation decreases. A weak beta relaxation occurs only in the sample obtained with vanadium catalytic systems. Microhardness measurements give the possibility of distinguishing the effect of crystallinity from the effect of entanglements: Vickers microhardness is sensitive predominately to crystalline phase, while total microhardness is sensitive also to the structural peculiarities in the amorphous phase.