Crystallization, flame-retardant, and mechanical behaviors of poly(lactic acid)\9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-calcium montmorillonite nanocomposite

Poly(lactic acid) (PLA) nanocomposite with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) intercalated calcium montmorillonite (Ca-MMT) nanocompound was prepared, and the properties were compared with those of PLA/Ca-MMT, PLA/DOPO, and PLA/DOPO+Ca-MMT nanocomposites (where DOPO+Ca-MMT indicates a physical mixture of DOPO and Ca-MMT). The structures and properties of the four PLA nanocomposites were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry, thermogravimetric analysis, limiting oxygen index (LOI) testing, UL-94 vertical testing, and cone calorimetry measurements. The XRD and TEM tests showed that the DOPO-Ca-MMT nanocompound existed in both intercalated and exfoliated montmorillonite morphologies in the PLA matrix, a better dispersion state than the Ca-MMT added alone and DOPO+Ca-MMT in PLA; this benefited improvements in the crystallinity, thermal stability, and flame retardancy for the PLA/DOPO-Ca-MMT nanocomposite, as seen in the higher degree of crystallinity, higher LOI values, and lower peak heat-release rate. A loading of only 5 wt % DOPO-Ca-MMT increased the LOI value of PLA from 20.0 to 28.3% and made the PLA pass the UL-94 vertical test V-0 rating at a 3.2 mm thickness. The nanocomposites based on DOPO-Ca-MMT could be used as very efficient systems for flame-retardant PLA. The PLA/DOPO-Ca-MMT also had better tensile mechanical properties than the pure PLA and PLA/DOPO+Ca-MMT. The annealing specimens of the four nanocomposites were also characterized to study the relationship between the PLA crystallization and flame retardancy or mechanical properties. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46982.