Poly(ethylene-co-chlorotrifluoroethylene), known as Halar~(~R) ECTFE, has been broadly used as high performance coatings and extrusion materials in CPI and semiconductor industries. ECTFE possesses very smooth surface attributed to its very fine crystallites. It also provides excellent resistance to chemical attack, high mechanical strength to resist mechanical damage, and good dielectric properties for insulation. In addition, ECTFE has superior adhesion to metal substrate and flame resistance to other partially fluorinated polymers such as polyvinylidene fluoride (PVDF) and poly(ethylene-co-tetrafluoroethylene) (ETFE). Limiting oxygen indices (LOI) are 64, 44 and 30 for ECTFE, PVDF and ETFE, respectively. In this study, thermogravimetry (TGA) provides clues to illustrate this superior flame resistance of ECTFE. TGA shows that ETFE is thermally pyrolyzed, possibly by chain scissions, to produce no char in both nitrogen and air atmospheres. This chain pyrolysis produces fast flowing low molecular weight species to induce dripping during burning above a flame. Along with flammable pyrolytic gas, this dripping phenomenon causes flame-spread concern. ECTFE and PVDF undergo dehydrohalogenation to produce polyene chars, which are further degraded at much slower rates than the first stage decompositions. The chars serve as oxygen and heat transfer barriers to give higher LOI. ECTFE has a slightly lower decomposition temperature than ETFE and PVDF, and generates HCI, which is a much better free radical scavenger to inhibit flame reactions in gas phase than HF. Thus, ECTFE has a significantly higher LOI than PVDF. In addition, char formation speed of ECTFE is faster than PVDF. Char also serves as barrier for polymer melt and pyrolyzed liquid to flow. Therefore ECTFE has a much higher dripping resistance then PVDF. In conclusion, ECTFE has the best flame resistance among those of partially fluorinated polymers from both flammability and flame spread viewpoints.
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