Performance of intumescent flame retardant master batch synthesized through twin-screw reactively extruding technology: effect of component ratio

A novel technology, i.e., reactive extrusion, was used to synthesize intumescent flame retardants (IFRs) and their master batches by reacting melamine phosphate (NIP) and pentaerythritol (PER). Limiting oxygen index (LOI), UL94 test, melt flow index (MFI), thermogravimetric analysis (TGA), Fourier transfer infrared (FT-IR) and scanning electron microscopy (SEM) were used to investigate the effect of carbon source (char former/blowing agent ratio) of IFR on the flame retardancy and the water resistance of IFR/Polypropylene (PP) blend. The experimental results show that the char former/blowing agent ratio has a great effect on the flame retardancy and the water resistance of the composite. The flame retardant system, optimally at MP/PER = 1.6 (molar ratio) or additional carbonization agent content = 17.0 wt.% in intumescent system, shows excellent flame retardancy, i.e. UL94 V-0 ratings at both 3.2 and 1.6 mm thickness at 25 wt.% flame retardant (FR) loading, and UL94 V-0 rating at 3.2 mm thickness at 20 wt.% FR loading in IFR/PP formulation. Also, the water resistance of flame-retarded material was improved greatly by selecting a reasonable char former/blowing agent ratio, i.e. at MP/PER = 1.6 (molar ratio) or additional carbonization agent content = 17.0 wt.% in intumescent system, IFR/PP blend at 25 wt.% flame retardant loading can still reach UL94 V-0 rating after treatment with water at 70 degreesC for 168 h. The polarity of IFRs, dispersion of IFRs in PP matrix and compatibility of IFRs with PP matrix were also found to influence the water resistance of 1FR/PP blend based on IR, water solubility test and SEM. The thermal stability of IFR/PP blend, affected by char former/blowing agent ratio, was proved to be well correlated with its flame retardancy whether before or after water treatment. (C) 2003 Elsevier Science Ltd. All rights reserved.