Preparation of Polylactide Composite with Excellent Flame Retardance and Improved Mechanical Properties

Synthesis of a phosphorus-containing L-lactic acid-based flame-retardant plasticizer for simultaneously enhancing flexibility and flame retardancy of poly(lactic acid)

This work provides a straightforward strategy for synthesizing efficient bio-based flame-retardant plasticizers, offering promising prospects for flame-retardant flexible materials. Poly(lactic acid) (PLA) has garnered significant attention as an environmentally friendly polymer among numerous biodegradable materials. However, its high flammability and brittleness severely hinder its application in the field of electronics and electrical devices. To address these challenges, a bio-based flame-retardant plasticizer (EPDL) was designed and synthesized using renewable L-lactic acid, which significantly enhances the flexibility and flame retardancy of PLA. Incorporating 40 phr EPDL resulted in PLA achieving UL94 V-0 grade and a limiting oxygen index of 34.3 %, demonstrating excellent flame-retardant properties. Meanwhile, the peak of heat release rate and total heat release of PLA/EPDL blends exhibited a marked reduction by 23.1 % and 34.1 % compared to that of pristine PLA, respectively. The flame-retardant action mode of EPDL is the combination of gas phase and condensed phase action. Additionally, the introduction of 40 phr EPDL significantly enhanced the ductility of PLA, resulting in a substantial rise in the elongation at break of the PLA/EPDL to 181.8 %, which is approximately 52 times higher than neat PLA. Intriguingly, the crystallization performance of PLA was enhanced by the presence of EPDL.

Flame-Retardant Properties and Mechanism of Polylactic Acid-Conjugated Flame-Retardant Composites

The DOPO derivative-conjugated flame retardant 4, 4'-{1'', 4'' - phenylene - bis [amino - (10‴ - oxy -10‴-hydro-9‴-hydrogen-10‴ λ⁵ -phosphaphenanthrene-10''-yl)-methyl]}-diphenol (P-PPD-Ph) with two hydroxyl groups was synthesized. Polylactic acid conjugated flame-retardant composites with P-PPD-Ph were papered by using a twin-screw extruder. The flame-retardant properties of polylactic acid-conjugated flame-retardant composites were investigated. The flame-retardant properties of PLA-conjugated flame-retardant composites were characterized by the limiting oxygen index (LOI) and the vertical burning test (UL94). The results showed that the PLA-conjugated flame-retardant composites achieved a V-0 rating (UL-94, 3.2 mm) when the conjugated flame retardant was added at 5 wt%, and increase in LOI value from 22.5% to 31.4% relative to composites without added conjugated flame retardant. The flame-retardant mechanism of PLA-conjugated flame-retardant composites were further studied by TG-FTIR, the results showed that the P-PPD-Ph promoted the PLA-conjugated flame-retardant composites to decompose and also released fragments with quenching and dilution, which suggests that P-PPD-Ph for PLA-conjugated flame-retardant composites mainly play a role of the gas-phase flame retardant.

Mechanically Robust and Flame-Retardant Polylactide Composites Based on In Situ Formation of Crosslinked Network Structure by DCP and TAIC

The addition of intumescent flame retardant to PLA can greatly improve the flame retardancy of the material and inhibit the dripping, but the major drawback is the adverse impact of the mechanical properties of the material. In this study, we found that the flame retardant and mechanical properties of the materials can be improved simultaneously by constructing a cross-linked structure. Firstly, a cross-linking flame-retardant PLA structure was designed by adding 0.9 wt% DCP and 0.3 wt% TAIC. After that, different characterization methods including torque, melt flow rate, molecular weight and gel content were used to clarify the formation of crosslinking structures. Results showed that the torque of 0.9DCP/0.3TAIC/FRPLA increased by 307% and the melt flow rate decreased by 77.8%. The gel content of 0.9DCP/0.3TAIC/FRPLA was 30.8%, indicating the formation of cross-linked structures. Then, the mechanical properties and flame retardant performance were studied. Results showed that, compared with FRPLA, the tensile strength, elongation at break and impact strength of 0.9DCP/0.3TAIC/FRPLA increased by 34.8%, 82.6% and 42.9%, respectively. The flame retardancy test results showed that 0.9DCP/0.3TAIC/FRPLA had a very high LOI (the limiting oxygen index) value of 39.2% and passed the UL94 V-0 level without dripping. Finally, the crosslinking reaction mechanism, flame retardant mechanism and the reasons for the improvement of mechanical properties were studied and described.

A Novel Self-Assembled Graphene-Based Flame Retardant: Synthesis and Flame Retardant Performance in PLA

In this study, a novel flame retardant (PMrG) was developed by self-assembling melamine and phytic acid (PA) onto rGO, and then applying it to the improvement of the flame resistance of PLA. PMrG simultaneously decreases the peak heat release rate (pHRR) and the total heat release (THR) of the composite during combustion, and enhances the LOI value and the time to ignition (TTI), thus significantly improving the flame retardancy of the composite. The flame retardant mechanism of the PMrG is also investigated. On one hand, the dehydration of PA and the decomposition of melamine in PMrG generate non-flammable volatiles, such as H₂O and NH₃, which dilute the oxygen concentration around the combustion front of the composite. On the other hand, the rGO, melamine, and PA components in PMrG create a synergistic effect in promoting the formation of a compact char layer during the combustion, which plays a barrier role and effectively suppresses the release of heat and smoke. In addition, the PMrGs in PLA exert a positive effect on the crystallization of the PLA matrix, thus playing the role of nucleation agent.