| Recently,in-situ fibrillation of polymer blend,which converts the dispersed particles into micro-or nano-fibrillar structure,has attracted much attention.Owing to the flexibility and high aspect ratio,the fibrils can deform adequately in response to interfibrillar interactions during flow.When the fibrils concentration exceeds a certain value,the deformed fibrils can form a physical network structure which renders the blends excellent properties.The presence of such an entangled fibrillar network has greatly enhanced microfibrillar composites’(MFCs’)crystallization kinetics,mechanical properties and rheological properties.Currently,most of the microfibrillar composites are prepared by“melt extrusion-hot drawing-quenching" or"melt extrusion-solid phase stretching-annealing".Although these two processing methods have been widely used for preparation of MFCs,it is undeniable that it is complicated and involves multiple stages.Triangle arrayed triple-screw extruder(TTSE)is a novel type of polymer processing equipment with special mixing characteristics and high productivity.It consists of three meshing zones and a central region and generates greater shearing and extensional flow field for polymer compounding.In this work,we demonstrated that a single extrusion process with TTSE was effective to prepare microfirbils in PP polymer matrix without post-extrusion drawing.By adjusting the processing conditions,MFCs with well-dispersed high aspect ratio fibrils were prepared.The impact of screw configuration,processing parameters,type of dispersed phase on the fibrillar morphology were thoroughly studied.In addition,the microfibrils formation mechanism of different blends system and the rheological properties,mechanical and thermal properties of the blends were investigated.The main conclusions are as follows:1.The effect of twin-screw extruder and screw configuration on the fibril formation was investigated.The polybutylene terephthalate(PBT)fibrils were also found in the PP/PBT blends prepared by direct extrusion via twin-screw extruder(TSE),while the microfibrillar morphology was significantly inferior to that of the samples prepared by TTSE.It was found that the combination 1#was more suitable for the fiberization of the PP/PBT system.2.The polypropylene/polybutylene terephthalate(PP/PBT)and polypropylene/polyamide 6,6(PP/PA66)MFCs were prepared by direct extrusion.The response surface design and orthogonal experimental method were designed to assess the effects of the dispersed phase content and processing parameters(temperature,screw speed and feed rate)on the morphology of fibrils.It can be found that the most important influence factor on the fibril formation is the dispersed phase content and temperature,followed by screw speed and feed rate.The largest aspect ratio(220)of PA66 fibril was achieved,while the maximum aspect ratio(954)of PBT fibril was obtained.3.In order to investigate the the formation mechanism of in-situ microfibrils obtained by TTSE direct extrusion,the phase morphology of the dispersed phase was analyzed by collecting samples at three different sites along the extruder.The morphological evolution procedures of PBT particles started from spherical pellets to ellipsoids or ribbons,forming short fibrils,and consequently high-aspect-ratio fibrils appeared under the alternating shear-extensional flow field.However,the morphology development of PA66 dispersed phase involved the formation of sheet structures,and finally the sheets were torn to form the fibrils.Furthermore,the effect of different kinds of fibrils on the rheological properties of the same matrix were studied and it showed that the PA66 fibril with small aspect ratio showed a better elastic enhancement on the PP matrix.4.The effects of PA66 fibrillar morphology on the dynamic shear rheological properties,extensional behavior,mechanical and thermal properties of PP matrix were studied.The gel points of PP/PA66 blends with different aspect ratios of PA66 fibrils were systematically analyzed according to the Winter-Chambon criteria.The obtained results showed that the storage modulus,complex viscosity and the radius of Cole-Cole plot circle of PP/PA66 MFCs were improved with an increasing fibrillar aspect ratio.Meanwhile,the loss tangent tanδ value decreased and the PP/PA66 MFCs exhibited a pseudo-solid or gel-like behavior.The gel point concentration,which was determined by the Winter-Chambon criterion,decreased with the increasing fibrillar aspect ratio.Additionally,high-aspect-ratio PA66 fibrils have dramatically improved PP’s melting temperature,crystallization kinetics,and mechanical properties. |
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