Development And Application Of A Mixer Dominated By Normal Stress In Synergy With Ultrasonic Vibration For UHMWPE Composites Melt Blending

Melt blending is one of the most common methods for preparing polymer nanocomposites in industrial production,to obtain the better performance of composites,the key of this method is to solve the dispersion problem of nano particles in composites.Ultra high molecular weight polyethylene(UHMWPE)is a kind of engineering plastics with excellent comprehensive properties and extremely processing conditions,resulting in conventional processing equipment based on shear deformation is hardly able to process UHMWPE,which to certain extent limited the applications of UHMWPE and its composites in industry.In this thesis,we have developed a novel mixer dominated by normal stress in synergy with ultrasonic vibration with the aid of vane extruder which based on volume elongation deformation.The melt blending process of the new mixer was analyzed in detail,the physical mathematical model of mixing unit was established and solved,the results showed that the material in the mixer has a periodic convergent/divergent flow under the effect of volume elongation deformation,the melt blending of volume elongation deformation in synergy with ultrasonic vibration shear deformation was realized eventually.By means of the novel mixer,CNTs were well dispersed in UHMWPE matrix,thus the homogeneous UHMWPE/CNTs composites were prepared.The mechanism of the effect of the normal stress field,the normal stress field in synergy with ultrasonic vibration on the melt blending of polymer nanocomposites were investigated separately.We have successfully developed the vane mixer and melt blended the UHMWPE with high melt viscosity and CNTs,the effects of rotor speed(30-60rpm),mixing time(3-6min)and CNTs loadings(1,3,5,10wt%)on the structure and properties of UHMWPE/CNTs composites were studied.The results showed that CNTs well dispersed in UHMWPE matrix in the range of given rotor speed and mixing time.The addition of CNTs to UHMWPE can obviously improve the thermal stability,crystallization and mechanical properties of the composites.Rheological tests showed that low content(1,3wt%)and high content(10wt%)CNTs have the opposite effect on storage modulus and complex viscosity of UHMWPE.High efficiency dispersive mixing of UHMWPE and CNTs can be achieved under the synergies of ultrasonic vibration and normal stress.The effects of ultrasonic time(20,30,40s)and ultrasonic power(500,1000W)on the structure and properties of UHMWPE/CNTs composites were studied.The results showed that the synergistic effect of two kinds of force fields can improve the dispersion of CNTs in the matrix,thus enhance the thermal stability,crystallization and mechanical properties of UHMWPE composites.With ultrasonic vibration introduced in melt blend dominated by normal stress,the storage modulus and complex viscosity of the composites with 1wt%,3wt% and 5wt% CNTs were decreased,however,the storage modulus and complex viscosity of the composites with 10wt% CNTs were increased.