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. 2023 Jan 6;15(2):300.
doi: 10.3390/polym15020300.

Preparation and Mechanism of Toughened and Flame-Retardant Bio-Based Polylactic Acid Composites

Kai Xu  1   2 , Chentao Yan  1   2 , Chunlin Du  1   2 , Yue Xu  1   2   3 , Bin Li  1   2 , Lubin Liu  1   2
Affiliations

Preparation and Mechanism of Toughened and Flame-Retardant Bio-Based Polylactic Acid Composites

Kai Xu et al. Polymers (Basel). .

Abstract

As a biodegradable thermoplastic, polylactic acid (PLA) shows great potential to replace petroleum-based plastics. Nevertheless, the flammability and brittleness of PLA seriously limits its use in emerging applications. This work is focused on simultaneously improving the flame-retardancy and toughness of PLA at a low additive load via a simple strategy. The PLA/MKF/NTPA biocomposites were prepared by incorporating alkali-treated, lightweight, renewable kapok fiber (MKF) and high-efficiency, phosphorus-nitrogenous flame retardant (NTPA) into the PLA matrix based on the extrusion-injection molding method. When the additive loads of MKF and NTPA were 0.5 and 3.0 wt%, respectively, the PLA/MKF/NTPA biocomposites (PLA3.0) achieved a rating of UL-94 V-0 with an LOI value of 28.3%, and its impact strength (4.43 kJ·m-2) was improved by 18.8% compared to that of pure PLA. Moreover, the cone calorimetry results confirmed a 9.7% reduction in the average effective heat of combustion (av-EHC) and a 0.5-fold increase in the flame retardancy index (FRI) compared to the neat PLA. NTPA not only exerted a gas-phase flame-retardant role, but also a condensed-phase barrier effect during the combustion process of the PLA/MKF/NTPA biocomposites. Moreover, MKF acted as an energy absorber to enhance the toughness of the PLA/MKF/NTPA biocomposites. This work provides a simple way to prepare PLA biocomposites with excellent flame-retardancy and toughness at a low additive load, which is of great importance for expanding the application range of PLA biocomposites.

Keywords: high-effective flame retardant; mechanism; polylactic acid; toughening.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
The chemical structure of NTPA.
Figure 1
Figure 1
Mechanical properties of PLA/MKF biocomposites. (a) Tensile strength and flexural strength, (b) elongation at break, and (c) notched Izod impact strength.
Figure 2
Figure 2
(a) HRR and (b) THR curves of PLA/MKF/NTPA biocomposites.
Figure 3
Figure 3
(a) TG and (b) DTG curves of PLA/MKF/NTPA biocomposites under N2.
Figure 4
Figure 4
Digital images of the residual char of (a) PLA0, (b) PLA2.5, (c) PLA3.0, and (d) PLA3.5 after CCT; SEM images (200× and 2000×) of the residual char of (e) PLA2.5, (f) PLA3.0, and (g) PLA3.5 after CCT; (h) XPS analysis of char residues of PLA3.0 after CCT.
Figure 5
Figure 5
Three-dimensional TG-FTIR spectra of pyrolysis products of (a) PLA0, (b) PLA2.5, and (c) PLA3.0; (d) FTIR spectra at Tmax of PLA/MKF/NTPA biocomposites.
Figure 6
Figure 6
Mechanical properties of PLA/MKF/NTPA biocomposites. (a) Tensile strength and flexural strength, (b) notched Izod impact strength. (c) Energy absorption effect of MKF in impact tests. SEM images (200× and 2000×) of the fracture surfaces of (d) PLA0, (e) PLA2.5, and (f) PLA3.0.
Figure 7
Figure 7
Comparisons of variation in impact strength and loading of PLA3.0 with previously reported flame-retardant and toughened PLA materials containing biofiber which achieved a UL-94 V-0 rating.
See this image and copyright information in PMC

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