Synergistic flame retardant effects of nano-kaolin and nano-HAO on LDPE/EPDM composites

A novel flame retardant system composed of nano-kaolin and nano-HAO (nano-sized hydroxyl aluminum oxalate) was used for flame retarding the low density polyethylene (LDPE)/ethylene propylene diene rubber (EPDM) blends. Results of fire testing showed that nano-kaolin and nano-HAO exhibited excellent synergistic effects on the flame retardancy of the LDPE/EPDM composites. When 12 wt% nano-kaolin took the place of 12 wt% nano-HAO in the composites, the LOI of the composites increased from 31.0% to 35.5% and the composites could meet the UL94V-0 standard. Through thermogravimetric and differential thermal analysis (TG-DTA) it was found that nano-HAO mainly affected the degradation of the experimental composites chemically. Meanwhile, results of scanning electronic microscope (SEM) and Fourier transformation infrared spectra (FTIR) of the composites on the char layer revealed that nano-kaolin mainly affected the transfer process physically by aggregating with nano-HAO and thus the synergistic effect on flame retardancy appeared.