Flame Retardancy And Thermal Decomposition Studies Of Polyacrylonitrile

Polyacrylonitrile(PAN) is a vinyl polymer, and a derivative of the acrylate family of polymers. In the domain of textile, mainly the polymer is dissolved in special solvents and produced as acrylic fiber, a kind of copolymers containing vinyl comonomer, which provide the similar properties as wool. Thus the most common use of acrylics is as fibers to make knitted clothing, like socks and sweaters, as a replacement of wool.Owing to very high heat of combustion and vigorous burning behavior in air, Polyacrylonitrile is associated with high levels of fire hazard. As mentioned in previous part, PAN fibers are widely used for home textiles as well as knitwear and clothing. Because of the increased requirement of flame retatdance in these fields, there is an urgent need for improving flame retardancy performance of PAN fiber. It has been well known that Flame-retardance for acrylic containing fiber can be achieved by using brominated flame retardant and copolymers like Modacrylics. However, recent perception that halogen-containing materials are an ecological hazard, limit their wide use in industry, moreover the corrosivity of halogen is known as being harmful to equipment and lead to reduced life cycle of machine. Consequently, there is a major interest in replacing halogenated flame retardants by environmentally sustainable alternatives.At present the studies focus on environmentally friendly Phosphorus-containing compounds which can act both in gas-phase and condensed phase. Recent findings reported that phosphate based flame retardants, especially ammonium polyphosphate, as flame proofing agents for PAN, obtained encouraging results. APP is effective not only because it has high phosphorus content but also because it yields phosphorus acid which is a potential catalyst for char formation. Despite of its advantage, APP suffers from its high water solubility, which prevents their industrial use. In our study, we selected a new melamine coated Ammonium polyphosphate, aiming at solving above problems.It is well established that Nitrogen compounds such as urea, melamine and allantoin, when used in cellulosic flame-retardant finishing with phosphorus compound, promote a great enhancement of the flame retardant effect. However, there have been very few studies of phosphorus- nitrogen synergism in PAN; therefore, we carried out the study to investigate phosphorus - nitrogen synergistic action in the flame retardancy of PAN polymer.In order to realize the rapid assessment of flammability of PAN polymer in the presence of a wide range of flame retardants, we have developed a new method for producing film sample used for the LOT and other thermal analysis tests in my diploma work. This film-making method is designed for preparing very thin film samples (from 20 to 80 um), which are well representative of textile fiber. This procedure is very similar to wet-spinning process of PAN fiber and briefly outlined as follows. The flame retardant was firstly dispersed in DMF under stirring, then PAN powder was added to the dispersion and thoroughly mixed, the mixture was then heated at 80℃for 5minutes to obtain a homogeneous paste. The film was prepared (20 - 80 um thickness), in Erichsen film machine on an aluminum plate. The aluminum plate was dried in oven at 40℃for 12 hours in order to remove DMF.Four different kinds of APPs: ammonium polyphosphate: 8um (APP), ammonium polyphosphate small size: 4um (APPSS), melamine coated ammonium polyphosphate: 18um (APPCM), melamine coated ammonium polyphosphate small size: 7.5um (APPCMSS), were used as flame retardant for PAN and films were prepared using above film-making method. The effectiveness of these compounds was studied using LOI, small flame test under Bunsen burner, TGA and PCFC thermal analysis. LOI and the results of small flame test of treated PAN films showed that all APPs treated pan films exhibited good flame retardant properties; with 25% FR content, PAN films achieved self extinguishing behavior. Test performed on TGA and PCFC for treated PAN films indicated that APPs significantly increased thermo-stability of PAN at the first pyrolysis stage by promoting the formation of cyclized structure. The latter study for thermal decomposition kinetic also confirmed this result. LOI value, TGA response and total heat combustion suggested that water treatment had only small impact on the flame retardancy of APPs treated PAN films. The Phosphorus-nitrogen synergism in PAN films was investigated in this work. The LOI of treated PAN films revealedthe remarkable synergistic effect of the combination of urea with APP in PAN.