Supercritical fluid flame-retardant processing of polyethylene terephthalate (PET) fiber treated with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO): Changes in physical properties and flame-retardant performance

An eco-friendly flame-retardant process was employed to impart flame-retardant characteristics to polyethylene terephthalate (PET) fibers by treating these with a phosphorus-based flame retardant, 910-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), using supercritical CO2 as a solvent. DOPO was applied to the PET fibers without any other additives. The concentration of DOPO was changed from 1% o.w.f. to 9% o.w.f., and it was applied for 60 min at 120 degrees C and 25 MPa. As the DOPO concentration increased, many particles attached to the surface, creating a non-smooth surface. The phosphorous component increased with an increase in the amount of DOPO applied to the PET fiber, without the deterioration of physical properties such as tensile strength and elongation at break. When the sample was treated with 5% o.w.f DOPO, the char length decreased significantly, and the after-flame time was not observed. The limiting oxygen index (LOI) of >= 29 indicated excellent flame-retardant performance. Washing up to 50 times did not deteriorate the flame-retardant performance, as indicated by the retention of the LOI value of >= 29. Therefore, the PET fibers treated with DOPO using supercritical CO2 showed excellent washing durability and flame retardancy.