No abstract

A novel way of preparing an intumescent flame retardant (IFR) and its master batch by the reactive extrusion of melamine phosphate and pentaerythritol, together with a polypropylene (PP) carrier, in a twin-screw extruder has been established. The effect of the PP carrier resin on the flame retardancy and water resistance of the intumescent-flame-retarding PP materials was investigated by using the limited oxygen index (LOI), UL94 test, elemental analysis (EA), thermogravimetric analysis (TGA) and water solubility testing, respectively. In addition, the mechanism of the carrier effect was analysed by melt flow index (MFI), scanning electron microscopy (SEM), and TGA. The experimental results show that with increasing content of carrier resin (PP) in the IFR master batch from 0 to 15 wt%, the flame retardancy LOI of the PP/IFR (25 wt% loading) blend increased from 29.5 to 32, and the UL94 level at 1.6 mm thickness was improved from failure to a V-0 rating. In addition, the water resistance of a flame-retarded composite at 25 wt% IFR loading was greatly improved, i.e. after treatment with hot water at 70 • C for 168 h, the reducing rate of element N in the IFR/PP blend decreased from 18.3% with 5 wt% carrier resin to 12.9% with 15 wt% carrier resin, and the LOI reduction rate decreased from 15.3% without any carrier resin to 10.9% with 15 wt% carrier resin, while the flame-retarded PP with an IFR master batch containing 10-15 wt% carrier resin maintained its UL94 V-0 rating at 3.2 mm thickness. The improvement in flame retardancy was attributed to the improved flame-retardant (FR) dispersion due to the carrier resin, while the improved water resistance was explained by the lowered water solubility of the IFR, the improved FR dispersion and the improved compatibility of the FR with the matrix resin due to the carrier resin. Reactive extrusion is a novel way to obtain pelletissed IFRs without powder pollution and their corresponding flame-retarding materials with a number of desired properties.

We investigate the conformation of poly(2,6-diphenyl- p -phenylene oxide) (PPPO) in good and mixed solvents by small-angle neutron scattering (SANS) across its ternary phase diagram. Dichloromethane was selected as a “good” solvent and heptane as a “poor” solvent whose addition eventually induces demixing and polymer precipitation. Below the overlap concentration c *, the polymer conformation is found to be well described by the polymer-excluded volume model and above by the Ornstein–Zernike expression with a correlation length ξ which depends on the concentration and solvent/nonsolvent ratio. We quantify the decrease in polymer radius of gyration R g , increase in ξ, and effective χ parameter approaching the phase boundary. Upon flash nanoprecipitation, the characteristic particle radius (estimated by scanning electron microscopy, SEM) is found to scale with polymer concentration as well as with nonsolvent content. Significantly, the solution volume per precipitated particle remains nearly constant at all polymer concentrations. Overall, our findings correlate ternary solution structure with the fabrication of polymer nanoparticles by nonsolvent-induced phase separation and precipitation.