Property enhancements due to the in situ formation of fine-scale extended structures by chaotic mixing of polymer melts

Chaotic mixing was employed in this study as a specially effective means to directly develop various fine-scale structures in polymer blends during melt processing. Three-dimensional chaotic advection was induced in melts within a cylindrical mixing cavity in response to the alternate motions of cavity surfaces. The emergent fine-scale extended structures in melts were subsequently captured upon solidification and mechanical properties were measured for different degrees of microstructure development.; The minor phase morphology developed during chaotic mixing was novel and distinctly different from those obtained by conventional processing techniques. In blends where interfacial tension was negligible, very thin sheets with numerous folds were generated. The thickness of the sheets decreased exponentially with processing time. In blends where interfacial tension was influential, lamellae were transformed to fibrils and later to droplets. The morphology development was documented by both optical and electron microscopy. Compared to the rapid breakdown of minor phase pellets into highly dispersed droplets which occurs in conventional batch mixing or extrusion, the structural development in melts during chaotic mixing was a gradual and progressive process and could be influenced by judicious manipulation of mixing conditions.; Impact tests were performed for 9 vol% LDPE/PS blends. Results demonstrated that very different impact properties in association with different microstructures were obtained for different mixing times. Lamellar structures were produced shortly after mixing began. These structures provided high impact toughness and long fracture times. When mixing was performed for considerably longer times, fine-scale fibrillar structures arose which provided greater strength and rigidity under impact. Tensile tests were carried out on blends consisting of a 10 vol% LCP minor phase and a PEN matrix. Electron microscopic examinations revealed that fibrils with diameters less than 10 {dollar}mu{dollar}m and aspect ratios up to 300 were produced after a short mixing time. Further mixing resulted in refinement of the fibrillar structures, and consequently significant enhancements in tensile properties.; The mechanisms of in-situ formation of fine-scale extended structures that this study has revealed may be useful in modifying or designing melt processing devices so that blends with favorable microstructures and improved properties can be produced.