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. 2020 Sep 28;12(10):2238.
doi: 10.3390/polym12102238.

Development of Biodegradable Flame-Retardant Bamboo Charcoal Composites, Part II: Thermal Degradation, Gas Phase, and Elemental Analyses

Shanshan Wang  1 , Liang Zhang  1 , Kate Semple  2 , Min Zhang  1 , Wenbiao Zhang  1 , Chunping Dai  2
Affiliations

Development of Biodegradable Flame-Retardant Bamboo Charcoal Composites, Part II: Thermal Degradation, Gas Phase, and Elemental Analyses

Shanshan Wang et al. Polymers (Basel). .

Abstract

Bamboo charcoal (BC) and aluminum hypophosphite (AHP) singly and in combination were investigated as flame-retardant fillers for polylactic acid (PLA). A set of BC/PLA/AHP composites were prepared by melt-blending and tested for thermal and flame-retardancy properties in Part I. Here, in Part II, the results for differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), X-ray diffraction (XRD), and X-ray photoelectron analysis (XPS) are presented. The fillers either singly or together promoted earlier initial thermal degradation of the surface of BC/PLA/AHP composites, with a carbon residue rate up to 40.3%, providing a protective layer of char. Additionally, BC promotes heterogeneous nucleation of PLA, while AHP improves the mechanical properties and machinability. Gaseous combustion products CO, aromatic compounds, and carbonyl groups were significantly suppressed in only the BC-PLA composite, but not pure PLA or the BC/PLA/AHP system. The flame-retardant effects of AHP and BC-AHP co-addition combine effective gas-phase and condensed-phase surface phenomena that provide a heat and oxygen barrier, protecting the inner matrix. While it generated much CO2 and smoke during combustion, it is not yet clear whether BC addition on its own contributes any significant gas phase protection for PLA.

Keywords: aluminum hypophosphite; bamboo charcoal; composites; flame retardancy; polylactic acid.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Heat flow curves of (a) PLA and BC/PLA, (b) BC/PLA/AHP with different amount of AHP added.
Figure 2
Figure 2
TG and DTG curves for (a,b) BC and AHP, (c,d) BC/PLA mixes, and (e,f) BC/PLA/AHP mixes.
Figure 3
Figure 3
(a) Fourier transform infrared (FT-IR) spectra of PLA, BC/PLA, and BC/PLA/AHP; (b) X-ray photoelectron analysis (XPS) spectra of BC/PLA/AHP (25/50/25); (c) XPS P2p spectra of BC/PLA/AHP (25/50/25); and (d) X-ray diffraction (XRD) patterns of BC/PLA/AHP after thermal decomposition.
Figure 4
Figure 4
Three-dimensional thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) spectra of gaseous products in the thermal decomposition of PLA and flame-retardant composites: (a) PLA, (b) BC/PLA, and (c) BC/PLA/AHP.
Figure 5
Figure 5
FTIR spectra of gas phase products of (a) PLA, (b) BC/PLA, and (c) BC/PLA/AHP at various temperatures.
Figure 6
Figure 6
FTIR spectra of gaseous products for the thermal decomposition of PLA, BC/PLA 25/75, and BC/PLA/AHP 25/50/25 composites at Tmax.
Figure 7
Figure 7
Absorbance spectra for pyrolysis products (a) PH3, (b) hydrocarbons, (c) CO, (d) CO2, (e) aromatic compounds, and (f) carbonyl groups for PLA, BC/PLA, and BC/AHP at various temperatures.
Figure 8
Figure 8
Schematic representation of the flame-retardant mechanism of BC/PLA/AHP during combustion.
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