Interfacial flame-retardant glass fiber synergistically reinforced polylactic acid with ammonium polyphosphate

GF-KH550 with amino-rich surface was firstly obtained from amination treatment of cut glass fiber (GF) by 3-aminopropyl triethoxysilane (KH550). Hyperbranched polyphosphamide interfacial flame-retardant glass fiber (GF@HBPN) was then synthesized by in-situ polymerization on the surface of GF-KH550 using triethylamine as acid binding agent as well as catalyst, POCl3 and 4, 4-diaminodiphenylmethane as monomers, and characterized by FTIR, XPS, SEM and TGA. Finally, polylactic acid (PLA) composites (GF-KH550/PLA, GF@HBPN/PLA and APP/GF@HBPN/PLA) were prepared from GF-KH550, GF@HBPN or mixture of GF@HBPN and ammonium polyphosphate (APP), and further tested for analyses on their thermal stability, mechanics and flame-retardant properties. The results showed that compared with that of PLA, GF-KH550/PLA displayed obviously improved tensile strength but worsened combustion performance due to the candle wick effect of GF, while GF@HBPN/PLA exhibited increment both in tensile strength as well as combustion performance (UL-94 V-2). The improvement in combustion performance of GF@HBPN/PLA was attributed to the inhibition of candle wick effect by the interfacial carbon residue formed on GF surface, however, this improvement was not enough to achieve the ideal flame-retardant effect. The 10%APP/30%GF@HBPN/PLA composites prepared with 10% (mass fraotion) APP and 30% (mass fraction) GF@HBPN exhibited excellent fire safety performance with the limit oxygen index of 26.8%±0.2% and the vertical combustion grade of UL-94 V-0. Moreover, the heat release rate peak value, total heat release rate and average effective heat of combustion rate decreased by 31.39%, 23.57% and 18.80%, respectively, compared with those of PLA. © 2024 Fine Chemicals. All rights reserved.