Flame-retardant Wrapped Ramie Fibers towards Suppressing "Candlewick Effect" of Polypropylene/Ramie Fiber Composites

In this work, a flame-retardant polypropylene (PP)/ramie fiber (RF) composite was prepared. The ramie fibers were wrapped chemically by a phosphorus-and nitrogen-containing flame retardant (FR) produced via in situ condensation reaction so as to suppress their candlewick effect. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) demonstrated that the ramie fibers wrapped chemically by FR (FR-RF) were obtained successfully. Thermogravimatric test showed that the PP/FR-RF composite had more residue and better thermal stability at high temperatures than the PP/RF composite. Cone calorimeter (CC) results indicated that the peak of heat release rate (PHRR) and total heat release (THR) correspondingly decreased by 23.4% and 12.5% compared with the values of neat PP/RF. The PP/FR-RF composite created a continuous and compact char layer after the combustion. Combining FTIR analysis of char residue after CC test with heat conduction coefficient results, it could be concluded that the charring of FR on RF greatly weakened the candlewick effect of RF, and more char residue in the RF domain facilitated the formation of more continuous and compact char layer in the whole combustion zone, consequently protected PP composites during combustion, resulting in the better flame retardancy of PP/FR-RF composite than that of PP/RF composite.