The Study Of Compatibility On Polypropylene/intumescent Flame Retardant Composites

Intumescent flame retardant(IFR) as fire-retardant is very popular by virtue of appending, flame-retardant, restraining smoke, innocuity and so on. But in the preparation of fire-retardant polypropylene, there are poor compatibility between polypropylene (PP) and IFR which make the mechanical properties of PP decrease. So improving the compatibility is very important. Pentaerythritol phosphate melamine salt (KDIFR) was prepared by pentaerythritol, phosphorus pentoxide and melamine, which was used in PP, achieved good flame-retardant effect. In this paper, KDIFR as the fire-retardant, silane coupling agent, a macromolecule compatibilizer--carboxyled polypropylene (EPP) and isocyanate(N75) are chosen as the compatibilizers to study the effect of compatibility and coupling, further investigate the crystal morphology in PP/KDIFR composites.1. KDIFR has a high surface energy because of its polarity and PP has a low surface energy because of its non-polarity. So there are poor compatibility between PP and KDIFR. Two kinds of silane coupling agents were chosen as the compatibilizers of PP/KDIFR. X-ray diffraction (XRD) indicated that KDIFR promoted the formation ofβ-form PP, KH-550 strengthen the P-nucleation of KDIFR, but the promotion was weakened by the addition of KH-560. SEM showed the adhension between KDIFR and PP was enhanced by silane. POM showed that the size of the spherulites of PP and the dispersed KDIFR particles became more uniform with the increase of silane. The mechanical properties of the composites were also improved. A recipe of PP/KDIFR /KH-560=70/30/5 was found to be optimal and compared with neat PP/KDIFR composites, the impact strength and tensile strength were improved by 24.2% and 9.6%, respectively.2. The EPP was chosen as the compatibilizer of PP/KDIFR. The results showed that EPP enhanced the matrix-filler surface adhesion. Compared with the PP/KDIFR, the impact strength and tensile strength of the PP/KDIFR/silane (64/30/6) was increased by 36.9% and 14.6%, respectively. SEM, POM and XRD showed that EPP activated the heterogeneous nucleation centers on flame retardant and made the distribution of the spherulite diameter became narrow and uniform, improving the interfacial dispersibility of flame retardant in the matrix.3.The isocyanate (N75) was chosen to modify the KDIFR surface. The N75 has N=C=O groups which can react with polar fire-retardants and alkyls which have good compatibility and coupling effect with PP. Because the N75 contains Carbon and Nitrogen, it has fire-retardant property itself. The application of N75 increased the mechanism properities in different degree. Especially, when the content of N75 was 5%, the tensile strength and impact strength of PP/KDIFR/N75 composite increased 8.1% and 14.1% respectively, comparing with PP/KDIFR. The flame retardancy of the composites was also improved when N75 was added.Comparing these results, EPP has the best effect, which indicates polymer compatibilizer has the advantage over small molecule compatibilizer.