PP Particles Research Articles

Thermo-oxidative stability of PP waste films studied by imaging chemiluminescence

Imaging chemiluminescence (ICL) was used to study the oxidative stability of PP waste films and of unstabilised PP particles for comparison. It was found that the unstabilised particles oxidised homogeneously with no induction period, whereas stabilised PP waste films showed a considerable distribution of induction times sometimes affected by the presence of threadlike defects. Individual specimens of a population of PP films all showed a sigmoidal increase of the CL intensity after the induction period. A sequence of chemiluminescence images showed a propagating oxidation front and a perfect match of the fraction of oxidising material covered by the front and the increase in chemiluminescence intensity. The role of physical spreading in the oxidation of stabilised PP material was clearly demonstrated. On artificial recycling of these films ICL showed a significant change in the oxidative stability (residual lifetime) much earlier than FTIR (carbonyl index) and DSC (oxidation induction temperature).

Morphology, conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).

Effect of discontinuous phase size on physical properties of LLDPE/PP blends obtained in the presence of peroxide

Linear low-density polyethylene and polypropylene (LLDPE/PP) blends were compatibilized with peroxide using two distinct blending techniques and the blend properties were compared. One was the concurrent blending method in a polymerization reactor (reactor blend), and the other was the conventional melt blending in a twin-screw extruder (extruder blend). Scanning electron microscopy revealed that the reactor blend resulted in dispersed PP particles less than 1 μm in diameter, whereas the particles were 3 to 4 μm in diameter for the extruder blend. The rheological properties judged from Rheometrics mechanical spectrometry, capillary rheometry, melt index, complex viscosity, and melt strength also suggested different natures for the two types of blends. The extruder blend showed a sharp change in flow properties as a function of peroxide and coagent concentration, whereas this was only gradual for the reactor blends. For mechanical properties, the reactor blends were superior in elongation at break to the extruder blends. These observations suggest that the level of interfacial tension was lower for the reactor blends than for extruder blends. This could be interpreted as taking LLDPE/PP copolymer formation at the interface into account. ©1999 John Wiley & Sons, Inc. Adv Polym Techn 18: 43–51, 1999

Preparation and characterization of electrically conductive polypropylene/polypyrrole composites

Polypropylene particles 35 μm in diameter were chemically coated with polypyrrole. The content of polypyrrole varied from 1.1 to 10.4 wt%. Polypropylene/polypyrrole (PP/PPy) composite films about 0.2 mm thick were prepared by compression moulding of modified powders. The electrical conductivity of compression moulded samples depends on the concentration of polypyrrole, and reached values from 4 × 10 −10 to 5 × 10 −3 S cm −1, which is about seven orders of magnitude higher than the conductivity in the blends prepared by mechanical mixing of PP and PPy in the same PPy concentration range. The PP/PPy composites were characterized by elemental analysis, infrared spectroscopy, light microscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). SEM pictures showed significant different in coverage of the surface of the PP particles, while the concentration change was within the range from 1.1 wt% to 8.9 wt% PPy.