Improving the flame retardancy and accelerating the degradation of poly (lactic acid) in soil by introducing fully bio-based additives

Highly flame retardancy, barrier, mechanical and persistent antibacterial polylactic acid film with high-parallel interconnected thousand layered cake architecture

In this work, a bio-based material (CGP) is obtained by combing chitosan, gelatin and polyvinyl alcohol through a simple solution mixing to simultaneously address polylactic acid film (PLA)' flammability and poor barrier, toughness and antibacterial properties by soaking. The results of open fire testing show that modified PLA films can effectively prolong the combustion time, improve the thermal stability and reduce the release of heat in the cone calorimeter test. For the PLA sample after soaking for 5 times (PLA-5) in particular, it can reduce the peak heat release rate (pHRR) and total heat release (THR) values to 85.8 kW/m2 and 1.3 MJ/m2 from the values of 129.5 kW/m2 and 1.8 MJ/m2 for PLA, respectively. Structural analysis suggests that CGP primarily operates in the condensed phase by forming physical barriers. Meanwhile, the modified PLA films can exhibit superior barrier effects, which indicate the oxygen transmission rate value of PLA-5 decreases to 0.9 cm3/(m2·day) from the 392.5 cm3/(m2·day) of raw PLA film. Moreover, the PLA-5 also have excellent toughness (the value increased to 200.5 % from 31.0 %) and persistent antibacterial effects (it still has 100 % sterilization after 500 days).

Fully bio-based intumescent flame retardant hybrid: A green strategy towards reducing fire hazard and improving degradation of polylactic acid

Polylactic acid (PLA) is a promising renewable polymer material with excellent biodegradability and good mechanical properties. However, the easy flammability and slow natural degradation limited its further applications, especially in high-security fields. In this work, a fully bio-based intumescent flame-retardant system was designed to reduce the fire hazard of PLA. Firstly, arginine (Arg) and phytic acid (PA) were combined through electrostatic ionic interaction, followed by the introduction of starch as a carbon source, namely APS. The UL-94 grade of PLA/APS composites reached V-0 grade by adding 3 wt% of APS and exhibited excellent anti-dripping performance. With APS addition increasing to 7 wt%, LOI value increased to 26 % and total heat release decreased from 58.4 (neat PLA) to 51.1 MJ/m2. Moreover, the addition of APS increased its crystallinity up to 83.5 % and maintained the mechanical strength of pristine PLA. Noteworthy, APS accelerated the degradation rate of PLA under submerged conditions. Compared with pristine PLA, PLA/APS showed more apparent destructive network morphology and higher mass and Mn loss, suggesting effective degradation promotion. This work provides a full biomass modification strategy to construct renewable plastic with both good flame retardancy and high degradation efficiency.

Recent advances in flame retardant and mechanical properties of polylactic acid: A review

The large-scale application of ecofriendly polymeric materials has become a key focus of scientific research with the trend toward sustainable development. Mechanical properties and fire safety are two critical considerations of biopolymers for large-scale applications. Polylactic acid (PLA) is a flammable, melt-drop carrying, and strong but brittle polymer. Hence, it is essential to achieve both flame retardancy and mechanical enhancement to improve safety and broaden its application. This study reviews the recent research on the flame retardant functionalization and mechanical reinforcement of PLA. It classifies PLA according to the type of the flame retardant strategy employed, such as surface-modified fibers, modified nano/micro fillers, small-molecule and macromolecular flame retardants, flame retardants with fibers or polymers, and chain extension or crosslinking with other flame retardants. The functionalization strategies and main parameters of the modified PLA systems are summarized and analyzed. This study summarizes the latest advances in the fields of flame retardancy and mechanical reinforcement of PLA.

Self-assembled biobased chitosan hybrid carrying N/P/B elements for polylactide with enhanced fire safety and mechanical properties

The inherent shortcomings such as flammability, brittleness, and low crystallinity limit the broad applications of poly(lactic acid) (PLA). To improve the fire resistance and mechanical properties of PLA, a chitosan-based core-shell flame retardant additive (APBA@PA@CS) was prepared for PLA via the self-assembly of interionic interactions among chitosan (CS), phytic acid (PA), and 3-aminophenyl boronic acid (APBA). The peak heat release rate (pHRR) and total heat release rate (THR) of PLA composite containing 3 wt% APBA@PA@CS decreased from 460.1 kW/m² and 75.8 MJ/m² to 419.0 kW/m² and 53.1 MJ/m², respectively. The presence of APBA@PA@CS contributed to the formation of a high-quality char layer rich in phosphorus and boron in the condensed phase and released non-flammable gases in the gas phase to hinder the exchange of heat and O₂, thereby having a synergistic flame retardant effect. Meanwhile, the tensile strength, elongation at break, impact strength, and crystallinity of PLA/APBA@PA@CS were increased by 3.7 %, 17.4 %, 5.3 %, and 55.2 %, respectively. This study provides a feasible route to construct a chitosan-based N/B/P tri-element hybrid to improve the fire safety performance and mechanical properties of PLA biocomposites.

Biodegradable thermoset poly(lactic acid) resin containing phosphorus: Flame retardancy, mechanical properties and its soil degradation behavior

With the growing environmental awareness, poly(lactic acid) (PLA) is regarded as one of the most promising varieties of bio-based polyesters owing to its environment-friendly and biodegradable advantages. However, poor thermal stability and flammability disadvantages limit the applications of PLA. Herein, a series of biodegradable intrinsic flame-retardant thermoset PLA resins (DMMP-M4sPLA) were designed. DMMP-M4sPLA resins exhibit excellent flame retardancy, achieving UL 94 V-0 rating and limiting oxygen index (LOI) of 28.1 %-31.7 %. Meanwhile, the cured DMMP-M4sPLA resins show a high glass transition temperature and tensile strength. In addition, the resins demonstrate full degradation with no harmful degradation products. This work provides an advanced design strategy to create bio-based and biodegraded resins with superior flame retardant and mechanical performance, holding great potentials in the fields of aviation interior, automotive, etc.

Synergistic effect of poly(ionic liquid) and phosphoramide on flame retardancy and crystallization of poly(lactic acid)

Crystallinity and flame retardancy are two key properties for poly(lactic acid)(PLA) in applications. In this paper, a quaternary phosphonium salt poly(ionic liquid) (PIL) and a phosphamide (POFA) were prepared. The PIL, POFA and their blend were used to regulate the flame retardancy and crystallization behaviors of PLA using the limiting oxygen index, UL-94 vertical burning, and thermogravimetric analysis, and differential scanning calorimetry etc. The results showed that a synergistic effect exists between PIL and POFA on flame retardancy. When 6 wt% PIL/POFA (2/1) was added into PLA, its LOI value is 28.0 vol%, and achieves the UL-94 V-0 rating while the PLA composites containing 6 wt% PIL or POFA just achieve the UL-94 V2. The PIL/POFA improves the flame retardancy of PLA by melting-away mode. In addition, the crystallization rate of PLA containing PIL/POFA is faster than that of PLA/PIL and PLA/POFA. The degradation of PLA induced by PIL/POFA produces some small molecular oligomers, which enhances the molecular chain mobility and rearrangement, thus contributes to better flame retardancy and faster crystallization.

A Facile Immobilization Strategy for Soluble Phosphazene to Actualize Stable and Safe Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) have attracted extensive attention owing to their high energy density and abundant sulfur resources. However, LSBs are still restricted by the unsatisfactory electrochemical performance resulting from the shuttle effect of lithium polysulfide (LiPSs), and the potential fire hazard caused by inflammable ether electrolytes and polyolefin separators. Herein, a facile immobilization strategy for hexachlorocyclotriphosphazene (HCCP) is creatively applied to address the above issues simultaneously. Insoluble HCCP cross-linked microspheres (H-CMP) are firstly obtained at ambient temperature using tannic acid (TA) as a cross-linking agent and then a multifunctional separator coating is constructed based on H-CMP. The released phosphorus-related radicals from H-CMP in wide temperatures effectively prevent the combustion of electrolytes and separators, and hence improve the fire safety of the Li-S pouch cell. Furthermore, H-CMP availably chemisorbs LiPSs to interdict the shuttle effect, thereby dramatically improving the electrochemical performance of LSBs. The effectiveness of this strategy is also verified in high sulfur loading (6.38 mg cm^-2 ), high temperature (50 °C), and Li-S pouch cells. More importantly, H-CMP exhibits sufficient stability for Li metal and suppression of Li dendrites. This facile immobilization strategy for multifunctional phosphazenes provides a competitive option for the large-scale fabrication of high-safety and high-performance LSBs.

Roles of phosphoramide derivatives in flame retardancy, thermal degradation and crystallization behaviors of polylactic acid

Two kinds of phosphoramide derivatives containing one (POFA) or two (BPOFA) phosphoramide bonds were synthesized using diphenylphosphinic chloride, phenylphosphonic dichloride and furfurylamine, respectively. The flame retardancy, thermal degradation and crystallization behaviors of polylactic acid (PLA)/POFA and PLA/BPOFA blends were investigated using the limiting oxygen index (LOI), UL-94 vertical burning tests, cone calorimeter tests, thermogravimetric analysis and differential scanning calorimetry. A small amount of 1.0 wt% BPOFA increases the LOI of PLA from 20.4 vol% to 28.0 vol% and achieves the UL-94 V0 rating, while 7.0 wt% POFA is needed to achieve the UL-94 V0 rating indicating that the PLA/BPOFA has better flame retardancy than that of PLA/POFA. Both POFA and BPOFA decrease the amount of flammable gaseous compounds and play positive roles in transesterification of PLA. More importantly, BPOFA is easier to catalyze the degradation of PLA and improve UL-94 rating by melting-away mode. Moreover, the BPOFA accelerates the crystallization rate and thus improves the crystallinity of PLA, while POFA does not show a positive effect on crystallization behaviors of PLA.

Development of multifunctional highly-efficient bio-based fire-retardant poly(lactic acid) composites for simultaneously improving thermal, crystallization and fire safety properties

Currently, it is still a huge challenge to prepare high performance eco-friendly poly(lactic acid) (PLA) with high thermal stability, good processability, excellent crystallization behavior, good transparency and highly-efficient fire safety. In this paper, a novel bio-based nucleation agent N-(furan-2-ylmethyl)-P,P-diphenylphosphinic amide (FPPA) was prepared and used for the fabrication of fire safety PLA/FPPA composites. The chemical structure of FPPA was measured by FTIR, NMR and MS. Further, the crystallization behavior, thermal stability, fire safety and mechanical properties of PLA/FPPA composites were performed by TGA, DSC, polarization microscope, LOI, UL94, cone calorimeter, DMA and, SEM, Raman, GC-MS, and TGA-FTIR. The results showed that the multifunctional FPPA not only had a high thermal stability and was a good nucleation agent for PLA. Moreover, only loading of 3 wt% FPPA increased the LOI of PLA from 19.0 to 33.8 % with UL-94 V-0 classification. Furthermore, the heat release rate and total heat release values of PLA/3%FPPA composite reduced by 6.3 % and 15.3 % in cone-calorimeter test. Such high fire safety was mainly attributed to specific fire safety radicals due to thermal degradation of FPPA to interrupt composites burning in gas phase. Besides, transparency and mechanical properties were almost not changed because of low loading of FPPA in PLA. This multifunctional bio-based fire-retardant for PLA with good comprehensive performance promises broad application in engineering electronics, automobiles, 3D printing and construction materials.