Study On Recycled PET In-situ Fiberilizing To Modify Polyolefins

In-situ micro-fibrillar composites based on High Density Polyethylene(HDPE)/recycled poly(ethylene terephthalate)(r-PET) and Polypropylene(PP)/r-PET were prepared by reactive extruder through reactive extrusion, cold drawing and annealing. The choice of matrix, the temprature condition of reactive extrusion, cold drawing,content of r-PET and draw ratio on the impact of the in-situ fibrilizing was studied through experiment. By scanning electron microscopy (SEM),SEM sample preparation and etching methods of in-situ micro-fibrillar composites, impact of the r-PET content and draw ratio on the morphology of in-situ micro-fibrillar composites were studied. The crystallization and the mechanical properties of in-situ micro-fibrillar composites were studied respectively through DSC and mechanical testing. The impact of injection molding temperature on the mechanical properties of in-situ micro-fibrillar composites was explored.The results showed that the MFR of HDPE used for matrix should be between 7-20 g/10min; the optimum temprature of reactive extrusion for preparing in-situ micro-fibrillar composites based on HDPE/r-PET is 250℃; cold-drawing process is that the melt should anneal after the second stretching; the annealing temperature is 80～90℃; the temperature of cold water bathe is about 35℃; the content of r-PET for preparing in-situ micro-fibrillar composites should be between 5%～35% and the draw ratio should not be too small; the greater the content of r-PET and the draw ratio, the larger the MFR of in-situ micro-fibrillar composites.The SEM results showed that the samples for microscopic observation should be frozen firstly in liquid nitrogen, and then etched in hot xylene. The best etching temperature for HDPE/r-PET in-situ micro-fibrillar composites is the boiling point of xylene and the time is 10-minutes. with the draw ratio increases, the micro-fiber aspect ratio becomes larger, but it will not change up to a certain extent; with r-PET content increases, the micro-fiber content also increases.The DSC curves showed that, for HDPE/r-PET in-situ micro-fibrillar composites, r-PET micro-fibrils did not play a role in promoting the crystallization of PE; with cooling rate increases, the crystallization peak becomes broaden, both the peak position and the maximum crystallization temperature Shifts to lower temperature, which indicats that the crystallization process of HDPE/r-PET in-situ micro-fibrillar composites is controlled by nucleation; the crystallinity of in-situ micro-fibrillar composites is higher than pure HDPE.Mechanical test showed that the tensile strength, elongation at break and impact strength of in-situ micro-fibrillar composites increase with the increase of draw ratio; at the same stretch ratio, with r-PET content increases, the tensile strength and elongation at break first increases and then decreases; when the draw ratio is 15, r-PET content is 20%, the tensile strength of HDPE/r-PET in-situ micro-fibrillar composites reaches the maximum, is 30.7MPa, compared with the HDPE increased by 41.7%, compared to common blends increased by 21.8%; the maximum of un-notched impact strength for HDPE/r-PET in-situ micro-fibrillar composites is 64.8 KJ/m2, compared to HDPE increased by 26.8%. The suitable injection molding temperature for in-situ micro-fibrillar composites should be far below the melting point of r-PET.Besides, the choice of matrix, the temprature condition of reactive extrusion, the etching method, and the mechanical properties of PP/r-PET in-situ micro-fibrillar composites was studied through experiment. the optimum temprature of reactive extrusion is 240℃; For PP/ r-PET in-situ micro-fibrillar composites, the best etching temperature is also the the boiling point of xylene, and the time is 8-minutes; r-PET micro-fibers can play a eterogeneous nucleation role and promote crystallization.