Thermoplastic polyurethane (TPU), block copolymer bearing hard and soft segments, is synthesized mainly from polyether and/or polyester based long chain diols and diisocyanates. With altering the kind and amount of hard and soft segments, the final properties of TPU can be adjusted with outstanding characteristics of mechanical strength, flexibility, good abrasion resistance, excellent chemical resistance, and processability diversity. With these special properties, it finds numerous applications in many engineering fields [1, 2]. However, its flammable character with dense smoke and heat genereation limits its use. Intense effort is seen in the literature to enhance the fire retardant performance of TPU [3, 4].
Animal-based fibers such as wool, silk and feathers are the most important second class natural reinforcement elements used in thermoplastic polymer-based composite materials. 15 million tons of chicken feather (CF) are approximately released each year as waste material to the environment. To find novel applications to CF has growing interest with increasing enviromental concisious. CF is used as reinforcing material in biocomposite applications due to its low cost, light weight, and reasonable mechanical characteristics [5–7].
CF mainly composed of protein (90 wt%) reffered to as keratin. Keratin, containing heteroatoms of nitrogen, oxygen, and sulfur, leaves remarkable ash when it burns. Accordingly, feather and/or modified keratin-based materials are considered as promising additives in flame retardant applications [8–10]. In the literature, the mechanical and thermal properties of feather containing composites are investigated with various matrix materials including TPU [11–14]. However, the fire retardant performance of CF containing TPU composites is not studied.
In the current study, commercially avaliable phosphorus-based flame retardant additives are selected for producing environmentally friendly and light weight biocomposites due to their remarkably low toxic nature, low densities, and potential effectiviness. It is well known fact that phosphorus based additives are higly effective in heteroatom containing polymers like CF, and TPU [15, 16]. The flame retardant performances of ammonium polyphosphate (APP) [17, 18], aluminum diethylphosphinate (AlPi) [19–21], and aluminium hypophosphite (AHP) [22–26] in TPU take into consideration for selecting these additives in TPU/CF based composites, as well.
Chen et al. observed that the addition of 10 wt% APP increased limiting oxygen index (LOI) value from 23.5 to 31.3% . Chen et al. found that the inclusion of 20 wt% APP in TPU cause increament from 21.5 to 31.3% in LOI value . Sut et al. used AlPi with different synergistic additives. They observed that the highest vertical UL 94 (UL 94 V) rating of V0 was obtained with flame retardant mixture containing AlPi [19, 20]. Li et al. found that 30 wt% AlPi was required to get V0 rating and the LOI value was about 23%. Chen et al. made two different studies with the use of AHP. In these studies, it was detected that 10 wt% AHP was required to get V1 rating and LOI value increased from 24 to 32.5% with the inclusion of 20 wt% AHP [23, 24]. Xiao found that 30 wt% AHP was needed to get V0 rating and the LOI value of 30.2%  Savas et al. observed that the addition of 20 wt% AHP was required to get V0 rating and the LOI value of 29% . In all these studies, enhanced flame retardant performance was observed with reduced peak heat release rate (pHRR), and total heat evolved (THE).
In the current study, the effect APP, AlPi, and AHP amount on the thermal and flame retardant characteristics of CF containing TPU composites are investigated. The properties of the biocomposites are examined using thermal gravimetric analysis (TGA), UL 94 V, LOI, and mass loss calorimeter studies.