The Application of Hyperbranched Polymers in Plastic(PA & HDPE) Processing
|Course||Materials Science and Engineering|
|Keywords||Hyperbranched polyesters Blend Nylon 6 High density polyethylene Rheological behavior Mechanical properties|
Hyperbranched polymers have attracted considerable and increasing interests during recent years because of their unique properties. Unlike dendrimers prepared by stepwise synthesis, hyperbranched polymers need a simple preparation process. Owing to the highly functionalized globular structures, hyperbranched polymers exhibit different properties from those of linear polymers of the same molar mass, such as lower entanglement degree, a large number of functional end groups, low viscosity in solution and in the molten state, etc. Hyperbranched polymers are considered as a more rapidly prepared and more economical replacement for perfect dendrimers in some applications, such as processing aids for linear polymers, coating, and composites modification.In the paper, the hyperbranched polyesters with suitable meet point which we synthesized in our lab, were used as rheological modifier in injection molding process of plastics, including nylon 6 and high density polyethylene (HDPE) to improve the processability of these polymers.The synthesized aromatic hyperbranched polyesters with different contents were blended with nylon 6 in a twin-screw extruder. The effects of hyperbranched polyesters on the crystallization behavior of nylon 6 were investigated using non-isothermal DSC, polarizing microscopy (POM) and wide-angle X-ray diffraction (WAXD) method. The results showed that the hyperbranched polyesters had a little effect on the crystallization rate, but mainly acted as a nucleation agent, therefore small crystallites were observed by POM. Furthermore, WAXD results indicated the crystal forms of nylon 6/hyperbranched polyesters were changed compared to pure nylon 6. In the blends,γ-crystal form content was less than that in pure nylon 6, even the total crystallinity is increased due to the addition of hyperbranched polyesters. SEM micrographs of an etched blend film showed the homogeneous dispersion of hyperbranhced polyesters in scale of 100-250nm in the nylon 6 matrix. Owing to the increase of melt flow rate of blends according to the melt flow index (MFI) experiments, the injection molding temperatures of nylon 6/hyperbranched polymers blends could be decreased dramatically, therefore the thermal degradation of nylon 6 could be reduced. It is interesting that the mechanical properties of nylon 6/hyperbranched polyesters could be improved compared to pure nylon 6.Blends of HDPE as matrix and various hyperbranched polyesters were prepared in a twin-screw extruder. The melting and crystallization behavior of the blends were investigated by DSC and WAXD. It was shown that the blends exhibited a little higher crystallization temperature and crystallinity compared to the pure HDPE whereas the melting temperature of blends almost remained the same. SEM photos showed a homogeneous distribution of hyperbranched polyesters in the matrix HDPE. The surface appearance of HDPE/HBPs extrudates was superior to the pure HDPE extrudates, and the melt fracture was successfully limited. The influence of hyperbranched polyesters on the rheological behavior of the blends was studied. The complex viscosity of the blends was reduced at a small amount of the hyperbranched polyesters, this leads to the result that the temperatures of barrel for the blends were decreased obviously, whereas the tensile strength of the blends was increased compared to the pure HDPE.