Effect of a phosphorus-containing oligomer on flame-retardant, rheological and mechanical properties of poly (lactic acid)

All-in-one bio-derived poly(L-lactic acid)-based composite with fire-resistance and smoke-suppression performance

The flammability of bio-derived poly(L-lactic acid) (PLA) greatly limits its application and eco-friendly multifunctional fire-fighting PLA-based composites are highly desired. In this work, a fully bio-based modified CS (C-CS) and commercially available eco-friendly ammonium polyphosphate (APP) were used as a synergistic flame retardant agent (C-CS/APP) to investigate its effects on fire-proofing performance and diverse properties of the PLA. The PLA/5%C-CS/5%APP composite exhibited excellent fire-resistant performance with anti-droplet, smoke-suppression and self-extinguishing property, and its limited oxygen index enhanced by 37 % (compared with neat PLA). This composite reached the highest V-0 fire safety rating, and its peak of heat release rate and total smoke production reduced by 26.5 % and 68.3 %, respectively. In addition, the char residue yield after the cone calorimeter test increased by 46 times in the composite, indicating an outstanding char-forming capacity. The condensed phase flame retardancy played a crucial role on the fire-fighting of this composite, that is, significantly enhanced char residue (as a physical barrier) blocked the heat exchange and O2 entry, and further suppressed the combustion reaction. Additionally, the PLA-based composite showed outstanding UV-absorption property, good anti-bacterial effect, and increased hydrophilicity and crystallizability.

Synthesis of cerium-based flame retardant containing phosphorus and its impact on the flammability of polylactic acid

The synthesis and characterization of [Ce2(PPPA)4(OH)2]·4H2O, wherein PPPA denotes 3-(hydroxy(phenyl)phosphoryl)propanoate, were conducted. Its potential as a flame-retardant additive for poly(L-lactic acid) (PLA) in conjunction with ammonium polyphosphate (APP) was investigated. Remarkably, with just incorporation of the 1 % Ce-complex and 4 % APP, the resulting PLA composite (PLA-8) meets the V-0 standard, exhibiting an impressive limiting oxygen index (LOI) of 29.4 %. Moreover, the introduction of the Ce-complex leads to a significant extension of ignition time (TTI), a significant 24.1 % decrease in total heat release (THR) compared to pure PLA, and a notable increase in residual carbon rate from 0.3 % to 3.51 %. Although PLA-8 exhibits a minor decline of 8.7 % in tensile strength and 3.4 % in elongation at break, respectively, compared to pure PLA, there is a substantial improvement of 32.2 % in Young's modulus and 29.9 % in impact resistance. These results emphasise the potential of cerium-based phosphorus-containing flame retardants, with cerium playing a key role in enhancing the flammability characteristics of PLA. This study contributes to the development of sustainable and fire-resistant materials in polymer chemistry.

Highly impact toughened and excellent flame-retardant polylactide/poly(butylene adipate-co-terephthalate) blend foams with phosphorus-containing and food waste-derived flame retardants

Green polymeric foams are an important research topic for sustainable development. In this study, a natural multifunctional flame-retardant additive based on food waste was developed and evaluated for its ability to replace the commercial additives tricresyl phosphate (TCP) and trioctyl phosphate (TOP) in a polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) foam. A series of blend foams with additives were prepared by melt extrusion. According to the results, the blend foam with 20 phr of TCP showed the best combination of impact toughness and flame retardancy. TCP, however, poses health and environmental risks. Therefore, natural flame retardants (NFRs) were used to partially replace the commercial flame retardant (CFR). A combination of TCP and soybean residue (SB) produced an impact toughened and flame-retardant blend foam. When compared to the neat PLA/PBAT foam, the impact toughness of the best sample was increased by about 256 %. The optimal foam showed excellent flame resistance with a V-0 UL-94 rating and a high LOI value (31.8 %). SB has the potential to partially replace TCP as flame retardant and could be used in a broad range of PLA/PBAT foam applications.

Synthesis of DOPO-Based Phosphorus-Nitrogen Containing Hyperbranched Flame Retardant and Its Effective Application for Poly(ethylene terephthalate) via Synergistic Effect

To obtain industrialized poly(ethylene terephthalate) (PET) composites with highly efficient flame retardancy, a phosphorus-nitrogen (P-N) containing hyperbranched flame retardant additive was synthesized by 9,10-dihydro-9-oxa-10-phospho-phenanthrene-butyric acid (DDP) and tris(2-hydroxyethyl) isocyanurate (THEIC) through high temperature esterification known as hyperbranched DDP-THEIC (hbDT). The chemical structure of the synthesized hbDT was determined by FTIR, 1H NMR, 13C NMR, and GPC, etc. Subsequently, hbDT/PET composites were prepared by co-blending, and the effects of hbDT on the thermal stability, flame retardancy, combustion performance, and thermal degradation behavior of PET were explored to deeply analyze its flame retardant mechanism. The test results showed that hbDT was successfully synthesized, and that hbDT maintained thermal stability well with the required processing conditions of PET as retardant additives. The flame retardant efficiency of PET was clearly improved by the addition of hbDT via the synergistic flame-retardant effect of P and N elements. When the mass fraction of flame retardant was 5%, the LOI of the hbDT/PET composite increased to 30.2%, and the vertical combustion grade reached UL-94 V-0. Compared with pure PET, great decreased total heat release (decreased by 16.3%) and peak heat release rate (decreased by 54.9%) were exhibited. Finally, the flame retardant mechanism of hbDT/PET was supposed, and it was confirmed that retardant effect happened in both the gas phase and condensed phase. This study is expected to provide a new idea for the development of low toxic, environment-friendly and highly efficient flame retardant additive for polyesters in an industry scale.

Flame Retardancy Behaviors of Flexible Polyurethane Foam Based on Reactive Dihydroxy P-N-containing Flame Retardants

Green and environment-friendly high-efficiency flame retardants (FRs) are crucial to polymer FR modification. Here, a green FR 2-((bis(2-hydroxyethyl)amino)methyl)-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (HAMPP) was synthesized. The HAMPP was incorporated with a cyclic phosphorus structure, which will readily carbonize to inhibit or prevent further combustion. Moreover, the HAMPP contains dihydroxy reactive groups that can be used as a monomer in the polymerization reaction to obtain the main chain containing phosphorus polymer. Research studies on FRs were based on flexible polyurethane foam (PU-HAMPPs). The limiting oxygen index value of PU foam with 10% HAMPP could reach 23.7%, passing a UL-94 V-0 rating together. With the addition of HAMPP, the peak heat release rate of PU foam decreased significantly, the decomposition temperature increased, the heat release capacity reduced by 31%, and the char yield increased by 42%. The chemical composition and morphology of the char residual have been studied and analyzed thoroughly. We find that HAMPP forms a molten viscous protective layer uniformly on the material surface and releases some incombustible gases. These indicated that the FR exploited both condensed-phase and gas-phase flame retardancy mechanisms. Besides, the addition of FRs improved the mechanical properties.

Biodegradable Flame Retardants for Biodegradable Polymer

To improve sustainability of polymers and to reduce carbon footprint, polymers from renewable resources are given significant attention due to the developing concern over environmental protection. The renewable materials are progressively used in many technical applications instead of short-term-use products. However, among other applications, the flame retardancy of such polymers needs to be improved for technical applications due to potential fire risk and their involvement in our daily life. To overcome this potential risk, various flame retardants (FRs) compounds based on conventional and non-conventional approaches such as inorganic FRs, nitrogen-based FRs, halogenated FRs and nanofillers were synthesized. However, most of the conventional FRs are non-biodegradable and if disposed in the landfill, microorganisms in the soil or water cannot degrade them. Hence, they remain in the environment for long time and may find their way not only in the food chain but can also easily attach to any airborne particle and can travel distances and may end up in freshwater, food products, ecosystems, or even can be inhaled if they are present in the air. Furthermore, it is not a good choice to use non-biodegradable FRs in biodegradable polymers such as polylactic acid (PLA). Therefore, the goal of this review paper is to promote the use of biodegradable and bio-based compounds for flame retardants used in polymeric materials.

Fire-extinguishing characteristics and flame retardant mechanism of polylactide foams: Influence of tricresyl phosphate combined with natural flame retardant

Extrusion and compression molding techniques were used to process polylactide (PLA) foams using a mixture blowing agent. Tricresyl phosphate (TCP) and natural flame retardants (NFR) from pumpkin (PK) and soybean (SB) were added to rigid PLA foams and the flame retardant properties of the foams were investigated. The effects of TCP content, types and amounts of NFR, and the ratio of TCP to NFR were determined on the physical, thermal and morphological characteristics of the foams. The fire-extinguishing characteristics and flame retardant mechanism of PLA foams with TCP were studied by thermogravimetric analysis-Fourier transform infrared (TGA-FTIR), scanning electron microscope (SEM), limiting oxygen index (LOI), and UL-94 techniques. The results revealed the efficiency of TCP as a flame retardant for PLA foams. Increased TCP levels contributed to a significant enhancement in fire-extinguishing characteristics. Phosphoric acid from thermal decomposition of TCP was a key factor in the proposed mechanism of flame retardation. Flame inhibition and retarded ignition of the PLA foams were achieved at all compositions of TCP and NFR. Due to the presence of compounds such as cellulose, phosphate, and silica, both PK and SB could be used as effective NFRs for PLA foams. All these characteristics promise extended applications for PLA foam in bio, circular, and green economies.

Improved Thermal Processing of Polylactic Acid/Oxidized Starch Composites and Flame-Retardant Behavior of Intumescent Non-Wovens

Thermoplastic processing and spinning of native starch is very challenging due to (a) the linear and branched polymers (amylose and amylopectin) present in its structure and (b) the presence of inter-and-intramolecular hydrogen bond linkages in its macromolecules that restrict the molecular chain mobility. Therefore, in this study, oxidized starch (OS) (obtained after oxidation of native starch with sodium perborate) was melt-blended with polylactic acid (PLA) polymer to prepare PLA/OS blends that were then mixed together with ammonium polyphosphate (APP), a halogen-free flame retardant (FR) used as acid donor in intumescent formulations on twin-screw extruder to prepare PLA/OS/APP composites. OS with different concentrations also served as bio-based carbonic source in intumescent formulations. PLA/OS/APP composites were melt spun to multifilament fibers on pilot scale melt-spinning machine and their crystallinity and mechanical properties were optimized by varying spinning parameters. The crystallinity of the fibers was studied by differential scanning calorimetry and thermal stabilities were analyzed by thermogravimetric analysis. Scanning electron microscopy was used to investigate the surface morphology and dispersion of the additives in the fibers. Needle-punched non-woven fabrics from as prepared melt-spun PLA/OS/APP fibers were developed and their fire properties such as heat release rate, total heat release, time to ignition, residual mass % etc. by cone calorimetry test were measured. It was found that PLA/OS/APP composites can be melt spun to multifilament fibers and non-woven flame-retardant fabrics produced thereof can be used in industrial FR applications.

Phosphorus-Containing Flame Retardants from Biobased Chemicals and Their Application in Polyesters and Epoxy Resins

Phosphorus-containing flame retardants synthesized from renewable resources have had a lot of impact in recent years. This article outlines the synthesis, characterization and evaluation of these compounds in polyesters and epoxy resins. The different approaches used in producing biobased flame retardant polyesters and epoxy resins are reported. While for the polyesters biomass derived compounds usually are phosphorylated and melt blended with the polymer, biobased flame retardants for epoxy resins are directly incorporated into the polymer structure by a using a phosphorylated biobased monomer or curing agent. Evaluating the efficiency of the flame retardant composites is done by discussing results obtained from UL94 vertical burning, limiting oxygen index (LOI) and cone calorimetry tests. The review ends with an outlook on future development trends of biobased flame retardant systems for polyesters and epoxy resins.

Flame Retardancy and Mechanism of Novel Phosphorus-Silicon Flame Retardant Based on Polysilsesquioxane

A novel phosphorus-silicon flame retardant (P₅PSQ) was prepared by bonding phosphate to silicon-based polysilsesquioxane (PSQ) and used as flame retardant of poly (lactic acid) (PLA). The results show that PLA with 10 wt % P₅PSQ has a limiting oxygen index (LOI) 24.1%, the peak heat release rate (PHRR) and total heat release (THR) of PLA decrease 21.8% and 25.2% compared to neat PLA in cone calorimetric test, indicating that P₅PSQ shows better flame retardancy in comparison to PSQ. Furthermore, the study for the morphology and composition of carbon residue after the combustion of PLA and the gas release of PLA during combustion illustrate that P₅PSQ has flame retardancy in condensed phase and gas phase simultaneously. In condensed phase, phosphorus from phosphate promotes the formation of more stable and better carbon layer containing Si and P, which inhibits the transfer of heat and oxygen in the combustion. In gas phase, the phosphate in P₅PSQ emits phosphorus-containing compound that can restrain the release of C–O containing products, which may have effective flame retardancy for PLA in gas phase to a certain extent. In one word, P₅PSQ is denoted as a good phosphorus-silicon synergistic flame-retardant.

The Efficiency of Biobased Carbonization Agent and Intumescent Flame Retardant on Flame Retardancy of Biopolymer Composites and Investigation of their Melt-Spinnability

The objective of this study is to assess the efficiency of biobased carbonization agent in intumescent formulations (IFRs) to examine the flame retardant properties of polylactic acid (PLA) composites and to investigate their melt-spinnability. We used phosphorous-based halogen free flame retardant (FR) and kraft lignin (KL) as bio-based carbonization agent. After melt compounding and molding into sheets by hot pressing various fire related characteristics of IFR composites were inspected and were characterized by different characterization methods. It was fascinating to discover that the introduction of 5–20 wt% FR increased the limiting oxygen index (LOI) of PLA composites from 20.1% to 23.2–33.5%. The addition of KL with content of 3–5 wt% further increased the LOI up to 36.6–37.8% and also endowed PLA/FR/KL composites with improved anti-dripping properties. Cone calorimetry revealed a 50% reduction in the peak heat release rate of the IFR composites in comparison to 100% PLA and confirmed the development of an intumescent char structure containing residue up to 40%. For comparative study, IFR composites containing pentaerythritol (PER) as a carbonization agent were also prepared and their FR properties were compared. IFR composites were melt spun and mechanical properties of multifilament yarns were tested. The analysis of char residues by energy dispersive X-ray spectrometry (EDS) and SEM images confirmed that PLA/FR/KL composites developed a thicker and more homogeneous char layer with better flame retardant properties confirming that the fire properties of PLA can be enhanced by using KL as a carbonization agent.

Improving the stability and ductility of polylactic acid via phosphite functional polysilsesquioxane

To improve the stability and ductility of polylactic acid (PLA), chain extender or crosslinking agent of phosphite functional polysilsesquioxane (PPSQ) was synthesized by the reaction of phosphite group with the amino group of poly(amino-epoxy)silsesquioxane (PSQ). First, the reaction of PPSQ with PLA was characterized by molecular weight (M_w) and melt mass flow rate (MFR) of PLA after melting reaction. The results showed a 6.6% increase in the M_w of PLA and a 24.5% decrease in MFR value at the PPSQ loading content of 2 wt% in PLA, indicating that PPSQ takes chain extension or crosslinking in PLA. Then, this result was further supported by the thermal stability improvement of PLA, which was testified by the increase of oxidative activation energy and the oxygen onset temperature (OOT) value. PPSQ improved the water resistance and mechanical properties of PLA. The hydrolysis rate decreased by 46.8%, and the tensile strength and impact strength increased by 17.2% and 89.4%. Taken together, these results indicate that the addition of PPSQ can produce the PLA with excellent thermal stability, hydrolytic stability and mechanical properties.

Improving the stability and ductility of polylactic acid via phosphite functional polysilsesquioxane.

Investigation of the Flammability and Thermal Stability of Halogen-Free Intumescent System in Biopolymer Composites Containing Biobased Carbonization Agent and Mechanism of Their Char Formation

Starch, being a polyhydric compound with its natural charring ability, is an ideal candidate to serve as a carbonization agent in an intumescent system. This charring ability of starch, if accompanied by an acidic source, can generate an effective intumescent flame retardant (IFR) system, but the performance of starch-based composites in an IFR system has not been tested in detail. Here, we describe a PLA-based IFR system consisting of ammonium polyphosphate (APP) as acidic source and cornstarch as carbon source. We prepared different formulations by melt compounding followed by molding into sheets by hot pressing. The thermal behavior and surface morphology of the composites was investigated by thermogravimetric analysis and scanning electron microscopy respectively. We also conducted limiting oxygen index (LOI), UL-94, and cone calorimetry tests to characterize the flame-retardant properties. Cone calorimetry revealed a 66% reduction in the peak heat release rate of the IFR composites compared to pure PLA and indicated the development of an intumescent structure by leaving a residual mass of 43% relative to the initial mass of the sample. A mechanism of char formation has also been discussed in detail.

Renewable vanillin based flame retardant for poly(lactic acid): a way to enhance flame retardancy and toughness simultaneously

A bio-based PLA composite with excellent fire performance, improved toughness and good processability.

Improving the flame retardancy and mechanical properties of poly(lactic acid) with a novel nanorod-shaped hybrid flame retardant

A novel nanorod-shaped hybrid flame retardant (NRH-FR) was synthesized by the reaction of benzenephosphinic acid with powdery aluminium hydroxide and the PLA/NRH-FR nanocomposites with good flame retardancy and mechanical property were prepared.

Synthesis and characterization of hyperbranched polyether imides based on 1,3,5-tris[4-(4′-aminophenoxy)phenoxy]benzene

A new triamine monomer 1,3,5-tris[4-(4′-aminophenoxy)phenoxy]benzene, was synthesized by a three step process using hydroquinone, 1-chloro-4-nitrobenzene and 1,3,5-trichlorobenzene.

Review on flammability of biofibres and biocomposites

The subject on flammability properties of natural fibre-reinforced biopolymer composites has not been broadly researched. This is not only evidenced by the minimal use of biopolymer composites and/or blends in different engineering areas where fire risk and hazard to both human and structures is of critical concern, but also the limited amount of published scientific work on the subject. Therefore, it is necessary to expand knowledge on the flammability properties of biopolymers and add value in widening the range of their application. This paper reviews the literature on the recent developments on flammability studies of bio-fibres, biopolymers and natural fibre-reinforced biocomposites. It also covers the different types of flame retardants (FRs) used and their mechanisms, and discusses the principles and methodology of various flammability testing techniques.