Studies On The Dynamic Rheological Properties Of LLDPE/UHMWPE Composites

Study of the polymer dynamic rheological behavior not only can give guide topolymerization in polymer synthesis and obtain polymers of excellent processingproperties, but also plays a key role on assessing the polymer processing performance,analyzing processing process, choosing proper processing condition and conductingformula design.Through different mixed refine methods, such as using two step melting method,or changing the order of the staff, blending of ultra high molecular weightpolyethylene and other polyolefin with a amount of fillers to obtain compositematerials with special state of aggregation and improve the comprehensive propertiesof composite materials. These have been hot spots in recent years for researchers athome and abroad. As to blending system filled with rigid particles, researchers arefocus on the influence of rigid particles on mechanical properties, crystallizationproperties etc. Reports that dynamic rheological behavior appears difference due tochanging of melt microstructure and phase structure with as a result of differentprocessing conditions is less.This paper regards the composite system of LLDPE/UHMWPE andLLDPE/UHMWPE/sepiolite as models and explains some problems from the aspectof rheology. It mainly investigates the influence of mixed refine temperature, sepiolitewith or without modification, content of UHMWPE and sepiolite on dynamicrheological behavior and crystallization behavior. Moreover, the reason for changes ofdynamic rheological behavior has been analyzed, it is hope that it can provide somescientific basis and theoretical guidance to practical production processing ofpolyethylene system.The results of the study shows that: in system of LLDPE/UHMWPE, the storagemodulus in strain scanning increases with the improvement of the mixed refinetemperature, but linear visco-elastic region becomes shorter and the storage modulusdrift to high modulus at low frequency. Curves are superposed basically at highfrequency and the Viscoelastic change point is not appeared. The time that internalstress value of the system damping from initial value to zero increases. The initialcrystallization temperature of the system increases with enhancing of mixed refinetemperature. The crystallinity rise firstly and then decrease. When increasing thecontent of UHMWPE, linear visco-elastic region remains unchanged basically and the storage modulus drift to high modulus at low frequency. Curves are not superposedbasically at high frequency. Change point of storage modulus advances, inducedcrystallization time shortened and crystallinity increased obviously.In system of LLDPE/UHMWPE/sepiolite, storage modulus of system containingmodified sepiolite is lower than that system not containing modified sepiolite in strainscanning. It appears a tan δ peak in the low frequency. Change point of storagemodulus advances obviously, induced crystallization time gets shortened,crystallization speed and the crystallinity increases. It appears a tan δ peak in the lowfrequency with the proper mixed refine temperature in curve of frequency scanning.Change point of storage modulus in complex system shortens and induced time ofisothermal crystallization reduces. While, crystallinity increases slightly. Modulusincreases with enhancing the content of sepiolite at the low frequency. When thecontent of sepiolite reaches5%-20%, there is a tan δ peak curve in the curve at thelow frequency. When content of sepiolite reaches25%, storage modulus improvessignificantly at the low frequency. In addition,"the second platform" emerged.It is conclude that changes of the mixed refine temperature, UHMWPE contentsand the nature of filler have significant influence on the state of aggregation of thesystem,and so as to dynamic rheological behavior.