Dispersion Effect Of Elongation Flow Field On Polyolefin/nano-CaCO₃ Filled System

Elongation flow field is one kind of high effective disperse blending. The dispersion blending effect of nano-CaCO₃ particles in polyolefin under elongation flow field was investigated in this paper. The mechanical performance, microscopic construction and morphology of filled system were characterized; the reinforcement and toughening mechanism of the dispersed nano-particles were discussed in this paper. The microscopic morphology and construction of original nano-particles were observed and analyzed; the difference of dispersion blending between shear flow field and elongation flow field was compared; the various dispersions related different elongation flow field strength, matrix resin (HDPE and PP) and nano-CaCO₃ fraction were investigated. The tensile strength and rupture elongation rate were measured and analyzed; microscopic morphology and construction of original nano-particle aggregates in the filled system were also described and discussed; the crystallinity, crystalline modification and microcrystallite size of filled system were discussed on the basis of DSC and WAXD.The results of the experiments were: under elongation flow field, the nano-CaCO₃ particles could be dispersed uniformly in the matrix during the melt mixing. In the original nano-particle aggregates, the particles joint were sticking, heaping and overlapping, the associative strength was different, single particle surface was smooth. The dispersion of elongation flow field was better than shear flow field's. With the strength improved of elongation flow field, nano-CaCO₃ aggregates would be more dispersed, the tensile strength and rupture elongation rate of filled system were increasing, the performance of filled system were more stability. Low fraction of filled system was better than high fraction's in the dispersion blending effect, mechanical performance and crystallinity, although both of their microcrystallite size were nearly same. In HDPE filled system, the performance was increasing with the strength of elongation flow field, but in PP filled system there was some differences- the dispersion effect was best under middle strength elongation flow field, it was proved that the action time is important in dispersion blending, in PP filled system there was some fraction ofβcrystalline modification under elongation flow field. During the dispersion blending, resin entered agglomerated particle of nano-CaCO3 and non-crystalline area occurred network construction, there were some particles inside the branches of network, the interface between particles and matrix firstly appeared cracks, energy was consumed by network construction during brittle failure process, and energy was consumed by network construction and cracks enlarging during tensile break process. The dispersion was better in elongation flow filed, so area of network construction was larger, the branches were refined, more cracks came out to consume energy and microfibers were more dramatic. These factors would reinforce and tough filled system.The research of this paper provided some reference for the melting dispersion blending of polyolefin filled system, and it also helped to more appropriately design with processing and equipment (machine and mold).