Achieving high flame retardancy, crystallization and biodegradability PLA based on 1 wt% addition of novel fully bio-based flame retardant

Tuning polylactic acid performance using green citrate plasticizers of varying chain lengths

The addition of these plasticizers increases the chain mobility of PLA, enhancing its deformability while reducing both tensile strength and elastic modulus. Mechanical testing identified TEC at 20 wt% as the most effective formulation, achieving an elongation of 307 % and a reduction in tensile strength from 70.6 MPa (PLA) to 25.2 MPa. Formulations containing 10 wt% exhibited anti-plasticization effects, with a slight reduction in elongation from 3.4 % to 3.2 %. Thermal and thermomechanical analyses corroborated the plasticizing effect, demonstrating a decrease in glass transition temperature from 59.6 °C to 19.3 °C, which indicates sufficient chain mobility to attain a rubber-like state at room temperature. Enhanced mobility also promoted crystallization by modifying nucleation behavior, altering crystal growth dimensionality, and reducing the activation energy required. Shape memory characterization revealed a rapid initial recovery in plasticized samples; however, total recovery diminished at higher plasticizer contents near 20 %, while lower concentrations exhibited recovery rates close to 90 %. Due to their low molecular weight of the plasticizers, migration is anticipated, resulting in measurable weight loss when exposed to food simulants. This migration phenomenon is associated with an increase in free volume, which also contributes to the improved ductile properties observed in plasticized PLA.

P/N Zinc salt containing biological groups for synchronously enhanced the fire safety, anti-dripping and mechanical properties of polylactic acid

As a promising biodegradable alternative to petroleum-based plastics, Polylactic acid (PLA) faces significant challenges in industrial applications due to its inherent flammability and brittleness, necessitating material modifications for expanded utilization. This study addresses the critical challenges of flammability and brittleness in PLA through the development of a novel bio-based anti-dripping flame retardant system. A phosphorus‑nitrogen containing flame retardant (AAPZ), was successfully synthesized and incorporated with ammonium polyphosphate (APP) to create high-performance PLA composites. The optimized PLA/4.5APP/4.5AAPZ composite demonstrated exceptional flame retardancy, passing a UL-94 V-0 rating with complete suppression of melt dripping. Cone calorimetry analysis revealed significant improvements in fire safety, with peak heat release rate (PHRR) and total smoke release (TSR) reduced by 60.2 % and 28.3 %, respectively, compared to neat PLA. Remarkably, the composite maintained excellent mechanical properties, exhibiting a 185 % increase in elongation at break while preserving tensile strength. The synergistic flame-retardant mechanism was systematically investigated, demonstrating effective gas-phase and condensed-phase actions. This bio-based flame-retardant system not only overcomes the inherent limitations of PLA but also provides a sustainable solution for expanding its applications in demanding sectors.

Optimization of the ductile properties of poly(lactic acid) (PLA) using green citrate-based plasticizers and itaconic anhydride grafted PLA (PLA-g-IA)

This study investigates the production of poly(lactic acid) (PLA) formulations enhanced with natural plasticizers such as triethyl citrate (TEC) and trihexyl o-butyrate citrate (BTHC). Itaconic anhydride (IA) grafted with PLA (PLA-g-IA) was obtained via reactive extrusion to serve as a compatibilizer. The incorporation of plasticizers notably enhanced the ductility of PLA while simultaneously decreasing its ultimate tensile strength and elastic modulus. Among the plasticizers tested, TEC was more effective in enhancing ductility and energy absorption, as evidenced by increased impact resistance in Charpy tests. The addition of PLA-g-IA further improved the mechanical strength of the plasticized samples without sacrificing ductility. This enhancement is attributed to the higher reactivity of BTHC with itaconic anhydride (IA) groups. The addition of plasticizers lowered the glass transition temperature from 59.6 ºC to as low as 26.6 ºC, increasing chain mobility even at room temperature. Changes in chain mobility were also observed in the thermomechanical properties, resulting in a rubbery state under ambient conditions. Higher plasticizer content improved the speed of recovery immediately after activation. Morphological analyses supported these findings, confirming that combining PLA with natural plasticizers and utilizing PLA-g-IA can effectively tailor material properties. This approach offers a simplified processing method while enhancing performance.

Synthesis of a phenylmaleimide bridged phosphaphenanthrene derivative for enhancing the flame retardancy of poly(lactic acid)

To develop poly(lactic acid) (PLA) composites with high flame retardancy and excellent transparency is still a challenge. In this work, a phenylmaleimide bridged phosphaphenanthrene derivative (DHD) containing bisphosphaphenanthrene and phenylmaleimide groups was synthesized, and PLA composites based on DHD with excellent flame retardancy and transparency were prepared. The results showed that with the addition of just 2.5 wt% DHD, the PLA composites had a limiting oxygen index (LOI) of 28.6% and achieved UL-94 V-0 rating. Meanwhile, the peak heat release rate of the PLA/DHD-2.5 was reduced by 7.70% compared to pure PLA. It is worth mentioning that the PLA composites have good transparency properties. The flame retardant mechanism study indicated that the high flame retardant efficiency of DHD was attributed to the molecular synergistic effect between bisphosphophenanthrene and phenylmaleimide groups.

Facile synthesis of phosphoramide salts as flame retardants for Poly(lactic acid) with enhanced crystallization and retained tensile properties

The improvement of both the inherent combustibility and crystallization characteristics of PLA has long posed a significant challenge. In this study, this issue was effectively addressed through the facile synthesis of a series of phosphoramide salts containing phosphoryl groups, termed PPA-X (where X represents the corresponding diamine), using phenylphosphoric acid instead of phenylphosphonic dichloride. This approach avoided the typical problems associated with traditional flame retardants containing phosphoryl groups, including highly vigorous reactions, the need for acid-binding agents, and the generation of corrosive hydrogen chloride gas. A 3 wt% loading of PPA-P-phenylenediamine (PPA-PPD) enabled PLA to self-extinguish within 1 s, achieve V-0 rating in vertical burning tests, and attain a limiting oxygen index (LOI) of 27.1 %. Moreover, the crystallization half-time (t1/2) at 115 °C for PLA was significantly reduced from 22.9 min to 12.5 min, while its crystallinity increased from 13.8 % to 41.2 %. Importantly, the tensile strength and elongation at break of PLA were well-preserved. Overall, this study presents a simple and low-toxicity strategy for developing highly effective flame retardants and nucleating agents for PLA, with promising potential for industrial applications.

Different wetting states in riparian sediment ecosystems: Response to microplastics exposure

Climate change alters the wetting state of riparian sediments, impacting microbial community response and biogeochemical processes. Microplastics (MPs) invade nearly all ecosystems on earth, posing a significant environmental risk. However, little is known about the response mechanism of MP exposure in sediment ecosystems with different wetting states under alternating seasonal rain and drought conditions. In this study, sediments with three different wetting states were selected to explore the differential response of ecosystems to PLA MP exposure. We observed that PLA MP exposure directly affected biogeochemical processes in sediment ecosystems and induced significant changes in microbial communities. PLA MP exposure was found to alter the composition of key species and microbial functional groups in the ecosystem, resulting in a more complex, interconnected, but less stable microbial network. Our findings showed that PLA MP exposure enhances the contribution of stochastic processes, for example the dispersal limitation increasing from 7.41 % to 54.32 %, indicating that sediment ecosystems strive to buffer disturbances from PLA MP exposure. In addition, 87 pathogenic species were detected in our samples, with PLA MPs acting as vectors for their transmission, potentially amplifying ecosystem disturbance. Importantly, we revealed that submerged sediments may present a greater environmental risk, while alternating wet and dry sediments demonstrate greater resistance and resilience to PLA MPs pollution. Overall, this study sheds light on how sediment ecosystems respond to MP exposure, and highlights differences in sediment response mechanisms across wetting states.

A novel bio-based ferric flame retardant effectively improving the flame retardancy and mechanical properties of polylactic acid

PTDF is prepared by a convenient ionic reaction of phytic acid, terephthalic dihydrazide and iron salts in water. It is a new type of high efficiency flame retardant. PTDF has high phosphorus and nitrogen content and good thermal stability, which can effectively improve the flame retardancy of PLA. PTFE is an anti-drip agent and is often used to improve the flame retardancy of PLA together with flame retardants. The addition of 4 wt% PTDF and 0.1 wt% PTFE made PLA reach V-0 flame retardant grade from non-flame retardant, and the oxygen index increased from 19.5 % to 24.5 %. With the increase of PTDF content, the performance of PLA improved significantly. The peak heat release rate (PHRR) and THR of PLA/6PTDF composites decrease by 27.4 % and 16.2 %, respectively, and the flame retardant index FRI increase by 232 %, showing excellent flame retardant efficiency. 6 wt% PTDF can increase the crystallinity of PLA by 25.9 %, tensile strength, maximum force required for impact fracture and notch impact strength by 12 %, 37 % and 129 %, respectively, and effectively improve the mechanical properties and toughness of the composite. The bio-based flame-retardant PLA/PTDF composites reported in this paper can be applied to office equipment.

Nanoconfinement-Enhanced Fire Safety and Mechanical Properties of Polylactic Acid with Nanocerium Metal-Organic Frameworks

Ce-based metal-organic frameworks (Ce-MOFs) were successfully synthesized by coordinating binary acid and amino structures with cerium oxides. The quantum dot scale endows Ce-MOFs with enhanced modifiability. Additionally, the phosphorus-rich biomass phytic acid, with its numerous hydroxyl groups, strengthens the H-bond network within the system. Ce-MOFs-centered nanoconfinement can form through the multiple H-bond interactions between Ce-MOFs and polylactic acid (PLA) molecules, thereby improving the mechanical and flame-retardant properties of PLA. The PLA/CeCxOy-P-3 composite exhibited excellent fire retardancy and toxic gas suppression, with a 27.8% decrease in the peak heat release rate and a 50% reduction in the peak smoke production rate. Notably, PLA/CeCxOy-P-3 showed an 80% lower peak CO release compared with the pure PLA sample. Moreover, the incorporation of Ce-MOFs positively influenced the tensile properties of PLA, transforming it from brittle to tough. This work designed and synthesized Ce-MOFs on the quantum scale. The resulting Ce-MOFs with the anticipated structure offer a novel direction for preparing MOFs for flame retardant applications.

Cellulose Nanofiber-Based Nanocomposite Films with Efficient Electromagnetic Interference Shielding and Fire-Resistant Performance

Cellulose nanofiber (CNF) has been widely used as a flexible and lightweight polymer matrix for electromagnetic shielding and thermally conductive composite films because of its excellent mechanical strength, environmental performance, and low cost. However, the lack of flame retardancy seriously hinders its further application. Herein, renewable and biomass-sourced l-arginine (AR) was used to surface-modify ammonium polyphosphate (APP) and an environmentally friendly biobased flame retardant was synthesized by the coordination of zinc sulfate heptahydrate (ZnSO4·7H2O), which was named AAZ. AAZ was deposited on the surface of CNF by electrostatic adsorption and Zn2+ complexation. The biobased compatibilizer Triton X-100 was employed to assist the exfoliation of graphene nanoplatelets (GNPs) and their dispersion in the CNF matrix. Due to the formation of a dense lamellar layer resembling a shell structure, the CNF/GNPs composite films with a tensile strength of 52 MPa were obtained via vacuum-assisted filtration. Because the phosphorus-containing group produces a protective layer of PxOy compound and promotes the formation of a carbon layer by CNF and the combustion releases ammonia gas, the fire-resistant performance of the composite films was greatly improved. Compared with the pure CNF film, the composite film exhibits 33% reduction in PHRR value and 40% reduction in THR. In addition, the CNF/GNPs composite film with 20 wt % GNPs possessed high conductivity (2079.2 S/m) and electromagnetic interference (EMI) shielding effectiveness (37 dB). The ultrathin CNF/GNPs composite films have excellent potential for use as efficient flame retardant and EMI shielding materials.

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.

How the chemical structure of phosphoramides affect the fire retardancy and mechanical properties of polylactide?

Phosphoramides, as a kind of high-efficient fire retardants, have been designed in many structures and endowed exceptional fire retardancy to polylactide (PLA). However, due to ignorance of the structure-property correlation, the effect of phosphoramides' structure on the fire retardancy and mechanical properties of PLA is still unclear. Herein, a series of biobased phosphoramides (phosphoramide (V1), linear polyphosphoramide (V2) and hyperbranched polyphosphamide (V3)) were designed and incorporated into PLA, and the structural effect of phosphoramides on the fire-retardant and mechanical properties of PLA was deeply researched. Among three kinds of phosphoramides, the hyperbranched polyphosphoramide is more effective than the corresponding linear polyphosphoramide and phosphoramide in improving the fire-retardant and anti-dripping properties of PLA, and only linear polyphosphoramide shows a positive effect in the mechanical strength of PLA. This work provides a feasible strategy for creating mechanically robust and fire-retardant polymer composites by molecularly tailoring the structure of fire retardants and uncovering their structure-property relationship.

Effects of microplastics on carbon release and microbial community in mangrove soil systems

Mangrove ecosystems are major carbon sink biomes and also a sink of microplastics (MPs). The final enrichment of MPs in sediments may have a significant impact on the microbial community and carbon turnover in the soil. However, the effects of MP pollution on the mangrove soil microbial communities and carbon release remain unknown. Here, we conducted a manipulative incubation experiment by adding MPs to soil at different soil depths to examine the effect of enriched MPs on soil microorganisms and its function (i.e., decomposition of soil carbon). The results showed that the addition of MPs had no significant effect on the microbial diversity and CO2 cumulative emission in the topsoil but significantly increased CO2 release from the subsoil. The promoting effect of polylactide (PLA) on the release of CO2 from the subsoil was stronger than that of polyethylene (PE) and aging PE. In the subsoil, the activity of soil extracellular enzymes related to N acquisition increased with the MP addition, indicating an increase in microbial N deficiency. The subsoil was more sensitive to MPs because of the exacerbated nitrogen limitation. MP addition reduced the microbial diversity of the subsoil and altered soil microbial interactions. The increasing abundance of some microbial taxa, especially bacteria related to the sulfur cycle, indicated more active electron transfer and organic carbon mineralization in the subsoil. Our findings suggest that MP contamination has potential effects on microbial communities, nutrient cycling, and carbon release in mangrove soils that vary depending on soil depth.

Enhanced flame retardancy and toughness of eco-friendly polyhydroxyalkanoate/bentonite composites based on in situ intercalation of P-N-containing hyperbranched macromolecules

Polyhydroxyalkanoates (PHA) is a biodegradable polyester, and its application range is limited by the poor flame retardancy and low modulus. Bentonite (BNT) as a green inorganic filler can improve the modulus and flame retardancy of PHA to a certain extent. An in situ polymerization method was designed to intercalate P-N-containing hyperbranched macromolecules (HBM) among BNT layers (HBM-B) and to improve the flame retardancy while improving the dispersion of BNT in the PHA matrix. The layer spacing of BNT was increased from 1.2 nm to 4.5 nm. The effect law of the joint action of in situ intercalation of BNT and the HBM on flame retardancy and mechanical properties of PHA was systematically studied. The HBM-B showed stronger flame retardancy when the mass ratio of HBM to BNT was 75/25. The limiting oxygen index (LOI) of the PHA/HBM-B composite was increased to 27.6 % while maintaining good toughness. Compared to the physical blend of HBM and BNT (HBM/B), the elongation at break of PHA/HBM-B₂₅ composites can be increased by up to 10 times. When the content of HBM-B is up to 15 wt%, the LOI of PHA-Based composites can reach 29.6 % and the UL-94 rating reaches V-0, which meets the standard of flame-retardant material. Therefore, the present work is expected to expand the application of PHA-based composites in the field of flame retardancy.

Fabrication of Phytic Acid/Urea Co-Modified Bamboo Biochar and Its Application as Green Flame Retardant for Polylactic Acid Resins

It is of great significance to develop green, sustainable additives to improve the thermal stability and flame retardancy of biopolymers. In this work, a synergistic modification of P/N elements to bamboo biochar (mBC) was successfully achieved by grafting a reaction of phytic acid and urea with preoxidized bamboo biochar. Fourier transform infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance and scanning electron microscope determinations of the mBC demonstrated a successive grafting of phytic acid and urea to the originally porous surface. The ground mBC was blended with polylactic acid (PLA) to prepare mBC/PLA composites by extrusion and hot pressing. Mechanical strength studies showed a compromise in rigidity, which might originate from the mBC overdose and its limited miscibility with the resin. The thermogravimetric results supported the fact that the enhancement of thermal stability and flame retardancy of the composites with the mBC dosage, which showed that the mBC dosage in the PLA composites was not only lower than that of the conventional flame retardants, but also outperformed the counterparts using BC modified by inorganic phosphoric acid and urea. The mBC was prone to accelerate the earlier decomposition of the composites (30 °C lower in decomposition) and generate a continuous, dense residual carbon layer, which provides an effective shield resisting the mass and heat transfer between the combustion area and the underlying composite matrix. Only 10 wt% of mBC dosage could achieve a V-0 rating (UL94) for the composite, with a higher limiting oxygen index up to 28.3% compared to 20.7% for that of the virgin PLA; the cone colorimetric results also suggested that the flame retardancy had been greatly improved for all composites. In this work, biobased P-/N-containing bamboo biochar would be expected as a nontoxic biochar-based flame retardant that serves as green filler in polymer composites.

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.