Study On Morphology And Properties Of LDPE/CaCO₃Nanocomposites Prepared By Vane Extruder

Filling modification is one of the effective methods to improve the properties andexpand the applications of polymer materials. Due to its simpleness and convenience,melt preparation of polymer nanocomposites have been used and investigated wildlyin recent years. The dispersion of the filler is a key for the nanocomposites, which isalso the biggest difficulty in the melt preparation of the nanocomposites. It is foundthat the dispersion of the filler in the polymer matrix is not only related to its structure,modification, compatibilizer, but also depends on the flow filed and strength of themixing methods.Compared with shear flow field, extensional flow field is more effective andenergy-efficient for particles dispersion, however, it is difficult to realize with thepre-exiting equipment. A continuous volumetric extensional flow field is formed witha series of vane groups in the vane extruder, which can be also used for polymerprocessing as the screw extruder.In this work, low density polyethylene （LDPE）/nano-calcium carbonate（nano-CaCO₃） composites was prepared by the vane extruder, then with analyzing themicro structure, the thermal behaviors and the mechanical properties, the effect of thevolumetric extensional flow field on the LDPE/nano-CaCO₃composites wasinvestigated. The key works and conclusions were as follows:（1） SEM and DSC results showed that compared with the simple shear flow filedin screw extruder, the nanoparticles were evenly and finely dispersed with the effectof the continuous volume extensional flow field in the vane extruder, and theaggregation size of the filler particles was much less. Composites with improvedmechanical properties were prepared.（2） The structure and properties of the composites was sensitive to the vane speed.Restricted by both the dispersion efficiency and time, the dispersion state of thenano-CaCO₃particles was improved firstly and then became poor as the vane speedincreasing, performing the best when the vane speed is90rpm. （3） Compared with vane speed, the microstructure of the nanocomposites is notso sensitive to the processing temperature. The elongation at break keeps the samewith processing temperature increasing from175to190centigrade, only a slightdecreasing at195centigrade.`（4） The nanoparticles dispersed the most uniformly in the LDPE matrix afterprocessed secondly, and the tensile properties performed the best at the same time.（5） The results showed that lower die pressure was better for the dispersion of thenano-CaCO₃in the LDPE matrix, and the corresponding tensile properties performedbetter.