Multifunctional Chitosan Nanofiber-Based Sponge Materials Using Freeze-Thaw and Post-Cross-Linking Method

The fabrication of porous sponge materials with stable structures via cross-linking diverse polymers presents significant challenges due to the simultaneous requirements for phase separation as a pore-forming step and cross-linking reactions during the fabrication process. To address these challenges, we developed a sponge material solely from natural-based polymers, specifically chitosan nanofibers (CSNFs) and dialdehyde carboxymethyl cellulose (DACMC), employing a straightforward, eco-friendly technique. This technique integrates a facile freeze-thaw method with subsequent cross-linking between CSNFs and DACMC. This method effectively addresses the difficulties associated with pore formation in materials, which typically arise from the rapid formation and precipitation of polyionic complexes during the mixing of anionic and cationic polymers, using ice crystals as a rigid template. The resultant sponge materials exhibit remarkable shape recoverability in their wet state and maintain light, stable porosity in the dry state. Furthermore, in comparison to commonly used commercial foams, this composite porous material demonstrates superior fire retardancy and thermal insulation properties in its dry state. Additionally, it shows effective adsorption capacities for both cationic and anionic dyes and metal ions. This method of using biobased polymers to produce porous composites offers a promising avenue for creating multifunctional materials, with potential applications across various industries.

Improving the fire-retardant performance of industrial reactive coatings for steel building structures

The main aim of this study was to determine key factors that regulate fire-retardant effectiveness of intumescent coatings comprising of ammonium polyphosphate, melamine, pentaerythritol, polymer binder. Fulfillment of the research objectives resulted in the development of a coating with R120 fire resistance. The expected service life of the coating is at least 15 years when applied at Z2 type of environmental conditions (indoor use). It was established that in order to provide fire resistance of around R30 it is advisable to use the styrene-acrylic polymers as binders for both water-based and organic-based intumescent systems. The ratio of target components ammonium polyphosphate/melamine/pentaerythritol in such systems should be close to 2/1/1. The coating thickness is to be 0.4-0.5 mm. To achieve higher fire resistance (R60 or more) the coating should include a vinyl acetate derivative as a binder (copolymers with ethylene or vinylversatate). Target components ratio in this case is to be close to 3.5/1/1.5, while the coating thickness should be kept at 1.6-1.8 mm. If the required class of fire resistance is above R120, coating thickness is usually to be kept above 3.5 mm. In order to achieve higher fire resistance, it is advisable to use nano-clay additives and reinforcing fibers in intumescent compositions. The obtained results were used in the development of intumescent coating, which is produced industrially and provides over R120 fire resistance of steel, which was confirmed in standardized full-scale fire tests.

Preparation of a Polymeric Phosphoramide Flame-Retardant and Its Effect on the Flame-Retardant Properties of Epoxy Resin

The flammability of epoxy resins and knowing how to achieve curing are particularly important factors during use. A novel approach for enhancing the fire resistance and reducing the smoke emission of epoxy resin during the curing process is suggested, which involves the utilization of a three-source integrated polymerization intumescent flame-retardant. In this study, the synthesis of poly 4,4-diaminodiphenylsulfone spirocyclic pentaerythritol bisphosphonate (PCS) is achieved through using solution polymerization, utilizing 4,4'-diaminodiphenylsulfone (DDS) and spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride (SPDPC) as initial components. Following that, the EP underwent the inclusion of PCS to examine its resistance to heat, its ability to prevent flames, its effectiveness in reducing smoke and its curing effect. Compared to the unmodified epoxy resin, the addition of PCS can not only cure the epoxy resin, but also decompose before the epoxy resin and has a good carbonization effect. With the addition of 7 wt.% PCS, the LOI value can achieve 31.2% and successfully pass the UL-94 test with a V-0 rating. Moreover, the cone calorimeter experiment demonstrated a noteworthy decline of 59.7% in the maximum heat release rate (pHRR), 63.7% in overall heat release (THR), and 42.3% in total smoke generation (TSP). Based on the examination of TG-FTIR and SEM findings, there is ample evidence to suggest that PCS, functioning as a phosphorus-nitrogen intumescent flame-retardant that combines three origins, has the potential to exhibit a favorable flame-retardant impact in both its gas and condensed phases.

Preparation of phosphorus-doped chitosan derivative and its applications in polylactic acid: Crystallization, flame retardancy, anti-dripping and mechanical properties

The topic of biobased flame-retardant PLA has always been of great interest. In our study, we successfully synthesized a phosphorus-containing chitosan derivative (PCS) and combined it with aluminum hypophosphate (AP) to create an effective flame-retardant PLA system. PCS acted as an enhancer, enhancing the thermal performance, crystallinity, and toughness of PLA/AP. Compared to PLA modified with 12 wt% AP achieving UL-94 V-2 level and 24.3 % of limited oxygen index, PLA containing 3 wt% PCS and 9 wt% AP achieved UL-94 V-0 level and limited oxygen index of 28 %. The system testing studies such as CCT, Raman, XPS, and TG-IR results indicated that PLA/AP/PCS exhibited a dual flame-retardant mechanism of condensed and gas phases.

A scientometric analysis and recent advances of emerging chitosan-based biomaterials as potential catalyst for biodiesel production: A review

Chitosan is a widely available polymer with a reasonably high abundance, as well as a sustainable, biodegradable, and biocompatible material with different functional groups that are used in a wide range of operations. Chitosan is frequently employed in widespread applications such as environmental remediation, adsorption, catalysts, and drug formulation. The goal of this review is to discuss the potential applications of chitosan and its chemically modified solids as a catalyst in biodiesel production. The existing manuscripts are integrated based on the nature of materials used as chitosan and its modifications. A short overview of chitosan's structural characteristics, properties, and some ideal methods to be considered in catalysis activities are addressed. This article includes an analysis of a chitosan-based scientometric conducted between 1975 and 2023 using VOS viewer 1.6.19. To identify developments and technological advances in chitosan research, the significant scientometric features of yearly publication results, documents country network, co-authorship network, documents funding sponsor, documents institution network, and documents category in domain analysis were examined. This review covers a variety of organic transformations and their effects, including chitosan reactions against acids, bases, metals, metal oxides, organic compounds, lipases, and Knoevenagel condensation. The catalytic capabilities of chitosan and its modified structures for producing biodiesel through transesterification reactions are explored in depth.

Research Progress on the Improvement of Flame Retardancy, Hydrophobicity, and Antibacterial Properties of Wood Surfaces

Wood-based materials are multifunctional green and environmentally friendly natural construction materials, and are widely used in decorative building materials. For this reason, a lot of research has been carried out to develop new and innovative wood surface improvements and make wood more appealing through features such as fire-retardancy, hydrophobicity, and antibacterial properties. To improve the performance of wood, more and more attention is being paid to the functioning of the surface. Understanding and mastering technology to improve the surface functionality of wood opens up new possibilities for developing multifunctional and high-performance materials. Examples of these techniques are ion crosslinking modification and coating modification. Researchers have been trying to make wooden surfaces more practical for the past century. This study has gradually gained popularity in the field of wood material science over the last 10 years. This paper provides an experimental reference for research on wood surface functionalization and summarizes the most current advancements in hydrophobic, antibacterial, and flame-retardant research on wood surfaces.

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.

Fabrication of two multifunctional phosphorus–nitrogen flame retardants toward improving the fire safety of epoxy resin

To improve the fire safety of epoxy resin (EP), two novel phosphorus–nitrogen flame retardants, which named as diphenyl allylphosphoramidate (DPCA) and N-allyl-P, P-diphenylphosphinic amide (DCA), were synthesized by acyl chloride reaction and introduced into EP for fabricating EP composites. The combustion tests showed that incorporation of 5 wt% DPCA or 5 wt% DCA into EP led to the exceptional limited oxygen index (LOI) value (27.1% or 31.6%). Besides, the peak of heat release rate of EP-5 wt% DPCA and EP-5 wt% DCA was reduced by 40.69% and 36.69%, respectively, compared to pure EP. The enhanced fire resistance of EP was ascribed to the trapping effect of fillers in the gas phase and the charring effect in the condensed phase. Furthermore, ultraviolet-visible spectra revealed that both EP-5 wt% DPCA and EP-5 wt% DCA have considerable transparency. This study is expected to broaden the application of EP in the industrial area.

Simultaneously enhance the fire safety and mechanical properties of PLA by incorporating a cyclophosphazene-based flame retardant

The application of poly(lactic acid) (PLA) has been limited in flame-retardant field, and flame-retardant modification usually deteriorates its mechanical properties. In this study, a reactive flame-retardant hexa(ethylene oxide)-cyclotriphosphazene (HCCP-EP) was synthesized and used to improve the fire retardancy of PLA. As a result, the limiting oxygen index of PLA increased from 19.5% to 27.3% with an addition of 3 wt% HCCP-EP, and the PLA/HCCP-EP blend reached to underwriters laboratories (UL)-94 V-0 rating. The cone calorimeter test results showed that the peak heat release rate and total heat release of PLA decreased by 12.6% and 18.5%, respectively. Interestingly, the tensile strength of PLA increased slightly after the incorporation of HCCP-EP. The improved mechanical properties are ascribed to the fine dispersion of HCCP-EP and the coupling reaction between the epoxy groups of the HCCP-EP and the terminal groups of PLA during the melt processing.

Magnesium hydroxide coated hollow glass microspheres/chitosan composite aerogels with excellent thermal insulation and flame retardancy

The development of an environmental-friendly thermal insulation and flame retardant material has attracted widespread attention in modern architecture. In this work, a kind of novel aerogel composites were prepared by incorporation of Mg(OH)₂ coated hollow glass microspheres (HGM) into chitosan (CSA) matrix and then cross-linking by glutaraldehyde (abbreviated as CSA-HGM-Mg(OH)₂). The as-prepared composite aerogel exhibits vertical directional channel with high porosity and excellent thermal insulation with a low thermal conductivity of 0.035 W m^-1 k^-1. Besides, it shows excellent flame retardancy with a high limit oxygen index (LOI) value up to 50.8, which is one of the highest values among the most of flame retardants reported previously. Also, a very low peak heat release rate (pHRR) of 24.12 kW m^-2 was obtained which makes the aerogel composite reaching UL-94 V-0 rating. Such results may be attributed to a synergy effect by combination of its abundantly porous structure derived from HGM to give a better thermal insulation and excellent nonflammability of CSA and Mg(OH)₂ to offer a superior flame retardancy. Taking advantages of its high mechanical strength, low cost materials, simple and scalable preparation method, CSA-HGM-Mg(OH)₂ aerogel composites may hold great potential for future thermal insulation and flame retardant applications.

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.

Synergistic Flame Retardant Effect of Barium Phytate and Intumescent Flame Retardant for Epoxy Resin

Recently, widespread concern has been aroused on environmentally friendly materials. In this article, barium phytate (Pa-Ba) was prepared by the reaction of phytic acid with barium carbonate in deionized water, which was used to blend with intumescent flame retardant (IFR) as a flame retardant and was added to epoxy resin (EP). Afterward, the chemical structure and thermal stability of Pa-Ba were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA), respectively. On this basis, the flammability and flame retardancy of EP composites were researched. It is shown that EP/14IFR/2Ba composite has the highest limiting oxygen index (LOI) value of 30.7%. Moreover, the peak heat release rate (PHRR) of EP/14IFR/2Ba decreases by 69.13% compared with pure EP. SEM and Raman spectra reveal the carbonization quality of EP/14IFR/2Ba is better than that of other composites. The results prove that Pa-Ba can cooperate with IFR to improve the flame retardancy of EP, reducing the addition amount of IFR in EP, thus expanding the application range of EP. In conclusion, adding Pa-Ba to IFR is a more environmentally friendly and efficient method compared with others.

Phosphine oxide for reducing flammability of ethylene-vinyl-acetate copolymer

In this work, a phosphorous-containing flame retardant, phenylphosphonate-based compound (EHPP), is synthesized by alcoholysis and hydrazinolysis of phenylphosphonic dichloride, which is subsequently introduced to ethylene-vinyl-acetate (EVA) copolymer to improve its flame retardant performance. The resultant compound was characterized by Fourier transform infrared (FTIR), 1H NMR, 13C NMR, and 31P NMR. The influence of the EHPP on the combustion behaviors of EVA is studied by limiting oxygen index (LOI), UL-94, and cone calorimeter test. The results show that 1 wt% EHPP can reduce peak heat release rate (PHRR) by 40%. Moreover, 2 wt% EHPP can increase LOI from 20.5% to 25.5%. Thermogravimetric analysis/infrared spectrometry (TGA-FTIR) was used to detect the gaseous products of EVA/EHPP to study the gaseous-phase flame retardant mechanism. The EHPP released phosphorus-containing radicals to capture highly active free radicals to improve the flame retardancy of EVA.