Pyrolysis products and thermal degradation mechanism of intrinsically flame-retardant calcium alginate fibre

Nanocellulose-based porous lightweight materials with flame retardant properties: A review

This review discusses the development and application of nanocellulose (NC)-aerogels, a sustainable and biodegradable biomaterial, with enhanced flame retardant (FR) properties. NC-aerogels combine the excellent physical and mechanical properties of NC with the low density and thermal conductivity of aerogels, making them promising for thermal insulation and other fields. However, the flammability of NC-aerogels limits their use in some applications, such as electromagnetic interference shielding, oil/water separation, and flame-resistant textiles. The review covers the design, fabrication, modification, and working mechanism of NC porous materials, focusing on how advanced technologies can impart FR properties into them. The review also evaluates the FR performance of NC-aerogels by employing widely recognized tests, such as the limited oxygen index, cone calorimeter, and UL-94. The review also explores the integration of innovative and eco-friendly materials, such as MXene, metal-organic frameworks, dopamine, lignin, and alginate, into NC-aerogels, to improve their FR performance and functionality. The review concludes by outlining the potential, challenges, and limitations of future research on FR NC-aerogels, identifying the obstacles and potential solutions, and understanding the current progress and gaps in the field.

Flexible Aluminum-Air Battery Based on High-Performance Three-Dimensional Dual-Network PVA/KC/KOH Composite Gel Polymer Electrolyte

With a large theoretical capacity and high energy density, aluminum-air batteries are a promising energy storage device. However, the rigid structure and liquid electrolyte of a traditional aluminum-air battery limit its application potential in the field of flexible electronics, and the irreversible corrosion of its anode greatly reduces the battery life. To solve the above problems, a PVA/KC/KOH (2 M) composite gel polymer electrolyte (GPE) with a three-dimensional dual-network structure consisting of polyvinyl alcohol (PVA), kappa-carrageenan (KC), and potassium hydroxide was prepared in this paper by a simple two-step method and applied in aluminum-air batteries. At room temperature, the ionic conductivity of the PVA/KC/KOH (2 M) composite GPE was found to be up to 6.50 × 10-3 S cm-1. By utilizing this composite GPE, a single flexible aluminum-air battery was assembled and achieved a maximum discharge voltage of 1.2 V at 5 mA cm-2, with discharge time exceeding 3 h. Moreover, the single flexible aluminum-air battery maintains good electrochemical performance under various deformation modes, and the output voltage of the battery remains at about 99% after 300 cycles. The construction of flexible aluminum-air batteries based on a three-dimensional dual-network PVA/KC/KOH composite GPE provides excellent safety and high-multiplication capabilities for aluminum-air batteries, making them potential candidates for various flexible device applications.

Anisotropic composite aerogel with thermal insulation and flame retardancy from cellulose nanofibers, calcium alginate and boric acid

With the increasing severity of energy shortages and environmental pollution, there is an urgent need for advanced thermal insulation materials with excellent comprehensive performance, including low thermal conductivity, high flame resistance, and strong compressive strength. Herein, an anisotropic composite aerogel based on cellulose nanofibers (CNF), calcium alginate (CA), and boric acid (BA) is fabricated using a directional freeze-drying strategy. The CA and BA, as double cross-linking agents, associated with oriented porous structure provide the resultant aerogel with good mechanical strength. Additionally, self-flame retardant CA and BA act as synergistic flame retardants that endow the aerogel with excellent flame retardance properties such as a limiting oxygen index value of 44.2 %, UL-94 V-0 rating, and low heat release. Furthermore, this composite aerogel exhibits outstanding thermal insulation performance with a low thermal conductivity of approximately 30 mW m-1 K-1. Therefore, the composite aerogel is expected to have a wide potential application in areas such as construction, automotive industry, batteries, petrochemical pipelines, and high-temperature reaction devices.

Rethinking the pathway to sustainable fire retardants

Flame retardants are currently used in a wide range of industry sectors for saving lives and property by mitigating fire hazards. The growing fire safety requirements for materials boost an escalating demand for consumption of fire retardants. This has significantly driven both the industry and scientific community to pursue sustainable fire retardants, but what makes a sustainable flame retardant? Here an overview of recent advances in sustainable flame retardants is offered, and their renewable raw materials, green synthesis and life cycle assessments are highlighted. A discussion on key challenges that hinder the innovation of fire retardants and design principles for creating truly sustainable yet cost-effective fire retardants are also presented. This short work is expected to help drive the development of sustainable, cost-effective fire retardants, and expedite the creation of a more sustainable and safer society.

Natural Pyranosyl Materials: Potential Applications in Solid-State Batteries

Solid-state batteries have become one of the hottest research areas today, due to the use of solid-state electrolytes enabling the high safety and energy density. Because of the interaction with electrolyte salts and the abundant ion transport sites, natural polysaccharide polymers with rich functional groups such as -OH, -OR or -COO^- etc. have been applied in solid-state electrolytes and have the merits of possibly high ionic conductivity and sustainability. This review summarizes the recent progress of natural polysaccharides and derivatives for polymer electrolytes, which will stimulate further interest in the application of polysaccharides for solid-state batteries.

Leaf decomposition and flammability are largely decoupled across species in a tropical swamp forest despite sharing some predictive leaf functional traits

Decomposition and fire are major carbon pathways in many ecosystems, yet potential linkages between these processes are poorly understood. We test whether variability in decomposability and flammability across species are related to each other and to key plant functional traits in tropical swamp forests, where habitat degradation is elevating decomposition and fire regimes. Using senesced and fresh leaves of 22 swamp tree species in Singapore, we conducted an in situ decomposition experiment and a laboratory flammability experiment. We analysed 16 leaf physical and biochemical traits as predictors of decomposability and components of flammability: combustibility, ignitability and sustainability. Decomposability and flammability were largely decoupled across species, despite some shared predictive traits such as specific leaf area (SLA). Physical traits predicted that thicker leaves with a smaller SLA and volume decomposed faster, while various cation concentrations predicted flammability components, particularly ignitability. We show that flammability and decomposability of swamp forest leaves are decoupled because flammability is mostly driven by biochemical traits, while decomposition is driven by physical traits. Our approach identifies species that are slow to decompose and burn (e.g. Calophyllum tetrapterum and Xanthophyllum flavescens), which could be planted to mitigate carbon losses in tropical swamp reforestation.

Sheath-core structured Ca-alginate/PVA aerogel fibers via directed freezing wet-spinning

Biomass-based aerogel fibers have attracted increasing attention due to their renewable nature. However, their disadvantages, such as low mechanical strength, poor long-range order, and easy combustion, are still significant challenges. Herein, a directed freezing-assisted forced stretching strategy is developed to fabricate sheath-core structured Ca-alginate/polyvinyl alcohol (Ca-A/PVA) aerogel fibers with Long-range-ordered pores. The Ca-A/PVA aerogel fibers (3:2 m/m) exhibit the best comprehensive mechanical properties in terms of low thermal conductivity of 0.0524 W·m^-1·K^-1, a density of 0.1614 g·cm^-3, a porosity of 89.9 %, a tensile strength of 8.72 MPa, a tensile modulus of 249.7 MPa, a toughness of 1.98 MJ∙m^-3, and a self-extinguishing time from the fire of <1.2 s. The Ca-A/PVA fabrics showed a maximum absolute temperature difference of 11.4 °C at -20 °C and 14.0 °C at 60 °C compared to the plate temperature. The presented strategy is generalizable to other alginate-based aerogel fibers (e.g., alginate/guar gum).

Facile construction of agar-based fire-resistant aerogels: A synergistic strategy via in situ generations of magnesium hydroxide and cross-linked Ca-alginate

Biomass-based aerogel materials have many advantages, such as low thermal conductivity and non-toxicity. These materials are environmentally friendly and have broad development potential in the fields of packaging, cushioning and green building insulation. However, defects, such as low mechanical strength and poor fire safety, greatly limit the application of these materials. In this work, the agar/polyvinyl alcohol composite aerogel modified by the magnesium hydroxide (MH)/sodium alginate (SA) composite flame retardant system was developed by using a freeze-dried technology and the strategy of in-situ generation of MH and crosslinking of SA. The results showed that the MH/SA dramatically enhanced the mechanical and thermal stability of the composites. The compression modulus of AP-M35S15 was 2.37 MPa, which was 152.13 % higher than that of AP-M50. The limiting oxygen index value of AP-M35S15 was 34.1 % and reached V-0 level in the vertical burning test, which was better than those of the samples with a single MH effect. The cone calorimetric test showed that the MH/SA composite flame retardant system performed better in extending the ignition time, slowing down the heat release rate and reducing the total heat release and had a more complete dense carbon structure after burning.

Structurally Tailoring Clay Nanosheets to Design Emerging Macrofibers with Tunable Mechanical Properties and Thermal Behavior

Bio-derived nanomaterials are promising candidates for spinning high-performance sustainable textiles, but the inherent flammability of biomass-based fibers seriously limits their applications. There is still an urgent need to improve fiber flame retardancy while maintaining excellent mechanical performance. Here, inspired by the structural properties of layered nanoclay, we report a novel and efficient strategy to synthesize the strong, super tough, and flame-retardant nanocellulose/clay/sodium alginate (CRS) macrofibers via wet-spinning and directional drying. Benefiting from the precise modulation of arrangement and orientation of nanoclay in macrofibers, the new inorganic structure exhibits excellent mechanical and thermal functional properties. The anisotropic structure contributes to high toughness: the tensile strength was 373.3 MPa and the toughness was 26.92 MJ·m^-3. Remarkably, rectorite nanosheets as a thermal and qualitative insulator significantly improve the flame retardancy of the CRS fibers with a heat release rate as low as 6.07 W/g, thermal conductivity of 90.5 mW/(m·K), and good temperature tolerance (ranging from -196 to 100 °C). This facile and high-efficiency strategy may have great scalability in manufacturing high-strength, super tough, and flame-retardant fibers for emerging biodegradable next-generation artificial fibers.

Cellulose-based composite thermal-insulating foams toward eco-friendly, flexible and flame-retardant

Cellulose nanofibrils (CNFs) have been developed as building blocks for highly porous foams which are superior in thermal insulation. Unfortunately, the flammability and poor mechanical performance of CNF foams limited their practical applications. In this strategy, biopolymer sodium alginate, together with nontoxic boric acid and borate, were explored to play the roles of flame retardants for methyltrimethoxysilane cross-linked CNF foams. Their co-effects on preventing CNF foams from being ignited were revealed. The composite foams were self-extinguish and showed a considerably increased limited oxygen index (up to 39.5%). Additionally, the foams were flexible with good resilience and bendability. The eco-friendly foams with low thermal conductivity (0.028 W m^-1 K^-1 at 25 °C), flexibility, and non-ignitability can meet the satisfactory in energy-conservation, wide applicability, and use safety.

Seaweed-Derived Alginate-Cellulose Nanofiber Aerogel for Insulation Applications

The next generation of green insulation materials is being developed to provide safer and more sustainable alternatives to conventional materials. Bio-based cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties; however, their high flammability restricts their application. In this study, the design concept for the development of a multifunctional and non-toxic insulation material is inspired by the natural composition of seaweed, comprising both alginate and cellulose. The approach includes three steps: first, CNFs were separated from alginate-rich seaweed to obtain a resource-efficient, fully bio-based, and inherently flame-retardant material; second, ice-templating, followed by freeze-drying, was employed to form an anisotropic aerogel for effective insulation; and finally, a simple crosslinking approach was applied to improve the flame-retardant behavior and stability. At a density of 0.015 g cm-3, the lightweight anisotropic aerogels displayed favorable mechanical properties, including a compressive modulus of 370 kPa, high thermal stability, low thermal conductivity (31.5 mW m-1 K-1), considerable flame retardancy (0.053 mm s-1), and self-extinguishing behavior, where the inherent characteristics were considerably improved by crosslinking. Different concentrations of the crosslinker altered the mechanical properties, while the anisotropic structure influenced the mechanical properties, combustion velocity, and to some extent thermal conductivity. Seaweed-derived aerogels possess intrinsic characteristics that could serve as a template for the future development of sustainable high-performance insulation materials.

Suppression of Smoldering of Calcium Alginate Flame-Retardant Paper by Flame-Retardant Polyamide-66

Calcium alginate (Ca-Alg) fibers are renewable fibers obtained from the ocean with essential flame retardancy, which have recently been applied as components of flame-retardant paper. However, the application of Ca-Alg fibers is limited because of their tendency to smolder. Therefore, composites papers were fabricated by blending using flame-retardant polyamide-66 (FR-PA), with a 5 wt% content of phosphorous flame retardant, which will form molten carbon during combustion. When the FR-PA content is 30% of the composite paper, FR-PA forms a compact carbon layer on the surface of the Ca-Alg fibers during combustion, which isolates the mass/heat transfer and effectively suppresses the smoldering of Ca-Alg. This consists of a condensed flame retardant mechanism. Furthermore, the combustion and thermal degradation behavior of paper were analyzed by cone calorimetry (CONE), TG and TG-IR. Ca-Alg in the composite paper decomposed and released CO₂ before ignition, which delayed the ignition time. Simultaneously, the FR-PA contained in the composite paper effectively inhibited the combustion of volatile combustibles in the gas phase. Overall, FR-PA and Ca-Alg improve the thermal stability of the composite paper in different temperature regions under air atmosphere. Ca-Alg reduces the formation of aromatic products and NH₃ in the composite paper under N₂ atmosphere. Ca-Alg-based paper with excellent flame retardancy was successfully prepared.

Fire behavior of innovative alginate foams

A new biosourced composite foam (AF, associating foamed alginate matrix and orange peel filler) is successfully tested for fire-retardant properties. This material having similar thermal insulating properties and density than fire-retardant polyurethane foam (FR-PUF, a commercial product) shows promising enhanced properties for flame retardancy, as assessed by different methods such as thermogravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC) and a newly designed apparatus called RAPACES for investigating large-scale samples. All these methods confirm the promising properties of this alternative material in terms of fire protection (pHRR, THR, EHC, time-to-ignition, flame duration or production of residue), especially for heat flux not exceeding 50 kW m^-2. At higher heat flux (i.e., 75 kW m^-2), flame retardant properties tend to decrease but maintain at a higher level than FR-PUF. The investigation of the effect of AF thickness shows that the critical thickness (CT) is close to 1.5-1.7 cm: heat diffusion and material combustion are limited to the CT layer that protects the underlying layers from combustion. A multiplicity of factors can explain this behavior, such as: (a) negligible heat conduction, (b) low heat of combustion, (c) charring formation, and (d) water release. Water being released from underlying layers, dilutes the gases emitted during the combustion of superficial layers and promotes the flame extinction.

Three-Dimensional Porous Alginate Fiber Membrane Reinforced PEO-Based Solid Polymer Electrolyte for Safe and High-Performance Lithium Ion Batteries

The rational design and optimization of solid polymer electrolytes (SPEs) are critical for the application of safety and high efficiency lithium ion batteries (LIBs). Herein, we synthesized a novel poly(ethylene oxide) (PEO)-based SPE (PEO@AF SPE) with a cross-linking network by the introduction of alginate fiber (AF) membranes. Depending on the high-strength supporting AF skeleton and the cross-linking network formed by hydrogen bonds between the PEO matrix and AF skeleton, the obtained PEO@AF SPE exhibits an excellent tensile strength of 3.71 MPa, favorable heat resistance (close to 120 °C), and wide electrochemical stability window (5.2 V vs Li/Li⁺). Meanwhile, the abundant oxygen-containing groups in alginate macromolecular and the three-dimensional (3D) porous structure of the AF membrane can greatly increase Li⁺ anchor points and provide more Li⁺ migration pathways, leading to the enhancement of Li⁺ conduction and interfacial stability between the SPE and Li anode. Furthermore, the assembled LiFePO₄/PEO@AF SPE/Li cells also exhibit satisfactory electrochemical performance. These results reveal that PEO incorporating with AFs can boost the mechanical strength, thermostability, and electrochemical properties of the SPE simultaneously. Furthermore, one will expect that the newly designed PEO@AF SPE with cross-linked networks thus provides the possibility for future applications of safety and high-performance LIBs.

Preparation and Properties of an Alginate-Based Fiber Separator for Lithium-Ion Batteries

The membrane is one of the key inner parts of lithium-ion batteries, which determines the interfacial structure and internal resistance, ultimately affecting the capacity, cycling, and safety performance of the cell. In this article, an alginate-based fiber composite membrane was successfully fabricated from cellulose and calcium alginate with flame-retardant properties via a traditional papermaking process. In the membrane, the calcium alginate plays a bridging role and the cellulose acts as a filler. After 100 cycles, lithium-ion batteries by the alginate-based fiber separator exhibited better capacity retention ratios (approximately 90%) compared with those of commercial PP separators. Furthermore, the alginate-based fiber separator demonstrated fine thermal stability and electrochemical properties, showing a stable charge-discharge capability and no hot melt shrinkage at higher temperatures, which is a breakthrough in improving the safety of the cell. This research affords a new way for the large-scale fabrication of safe lithium-ion battery separators.

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.

An Alginate Hybrid Sponge with High Thermal Stability: Its Flame Retardant Properties and Mechanism

The worldwide applications of polyurethane (PU) and polystyrene (PS) sponge materials have been causing massive non-renewable resource consumption and huge loss of property and life due to its high flammability. Finding a biodegradable and regenerative sponge material with desirable thermal and flame retardant properties remains challenging to date. In this study, bio-based, renewable calcium alginate hybrid sponge materials (CAS) with high thermal stability and flame retardancy were fabricated through a simple, eco-friendly, in situ, chemical-foaming process at room temperature, followed by a facile and economical post-cross-linking method to obtain the organic-inorganic (CaCO₃) hybrid materials. The microstructure of CAS showed desirable porous networks with a porosity rate of 70.3%, indicating that a great amount of raw materials can be saved to achieve remarkable cost control. The sponge materials reached a limiting oxygen index (LOI) of 39, which was greatly improved compared with common sponge. Moreover, with only 5% calcium carbonate content, the initial thermal degradation temperature of CAS was increased by 70 °C (from 150 to 220 °C), compared to that of calcium alginate, which met the requirements of high-temperature resistant and nonflammable materials. The thermal degradation mechanism of CAS was supposed based on the experimental data. The combined results suggest promising prospects for the application of CAS in a range of fields and the sponge materials provide an alternative for the commonly used PU and PS sponge materials.

Effective Adsorption of Methylene Blue dye onto Magnetic Nanocomposites. Modeling and Reuse Studies

In the present study, new adsorbent beads of alginate (A)/maghemite nanoparticles (γ-Fe2O3)/functionalized multiwalled carbon nanotubes (f-CNT) were prepared and characterized by several techniques, e.g., N2 adsorption-desorption isotherms, Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM) and further tested for the adsorption of the dye methylene blue (MB) from water. The beads (A/γ-Fe2O3/f-CNT) presented a relatively low BET specific surface area value of 59 m2g−1. The magnetization saturation values of A/γ-Fe2O3/f-CNT beads determined at 295 K was equal to 27.16 emu g−1, indicating a magnetic character. The time needed to attain the equilibrium of MB adsorption onto the beads was estimated within 48 h. Thus, several kinetic and isotherm equation models were used to fit the kinetic and equilibrium experimental results. The number of adsorbed MB molecules per active site, the anchorage number, the receptor sites density, the adsorbed quantity at saturation, the concentration at half saturation and the molar adsorption energy were quantified using the monolayer model. The calculated negative ΔG0 and positive ΔH0 values suggested the spontaneous and endothermic nature of the adsorption process. In addition, A/γ-Fe2O3/f-CNT composites can be used at least for six times maintaining their significant adsorptive performance and could be easily separated by using a magnet from water after treatment.

A Novel Inherently Flame-Retardant Composite Based on Zinc Alginate/Nano-Cu2O

A novel flame-retardant composite material based on zinc alginate (ZnAlg) and nano-cuprous oxide (Cu₂O) was prepared through a simple, eco-friendly freeze-drying process and a sol-gel method. The composites were characterized and their combustion and flammability behavior were tested. The composites had high thermal stability and achieved nearly non-flammability with a limiting oxygen index (LOI) of 58. The results show remarkable improvement of flame-retardant properties in the ZnAlg/Cu₂O composites, compared to ZnAlg. Furthermore, the pyrolysis behavior was determined by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and the flame-retardant mechanism was proposed based on the combined experimental results. The prepared composites show promising application prospects in building materials and the textile industry.

Highly efficient flame-retardant and low-smoke-toxicity poly(vinyl alcohol)/alginate/ montmorillonite composite aerogels by two-step crosslinking strategy

A highly efficient flame-retardant and ultra-low-smoke-toxicity biodegradable material, poly(vinyl alcohol) (PVA)/alginate/montmorillonite (MMT) composite aerogel, was fabricated by a new environment-friendly two-step crosslinking strategy using borate and calcium ions. Compressive and specific moduli of the crosslinked PVA/alginate/MMT (P4A4M4/BA/Ca) aerogel increased to 7.2- and 1.9-folds those of the non-crosslinked aerogel, respectively, and the limited oxygen index value increased to 40.0%. Cone calorimeter tests revealed that the total heat release and peak heat release rate values of the P4A4M4/BA/Ca composite aerogel distinctly decreased. Remarkably, the total smoke release value of the P4A4M4/BA/Ca aerogel was considerably lower than those of non-crosslinked PVA composite aerogels, indicating its superior smoke suppression ability and high fire hazardous safety. The flame-retardancy mechanism of the crosslinked P4A4M4/BA/Ca composite aerogels involved a combination of the gaseous phase and condensed phase flame retardancy. The high-performance PVA/alginate/MMT biodegradable composite aerogels with good sustainability is a promising alternative to conventional flame-retardant foams.

Preparation of Ion-Exchanged TEMPO-Oxidized Celluloses as Flame Retardant Products

Cellulose, as one of the most abundant natural biopolymers, has been widely used in textile industry. However, owing to its drawbacks of flammability and ignitability, the large-scale commercial application of neat cellulose is limited. This study investigated some TEMPO-oxidized cellulose (TOC) which was prepared by selective TEMPO-mediated oxidation and ion exchange. The prepared TOC was characterized by Fourier transform infrared (FT-IR) spectroscopy and solid-state ¹³C-nuclear magnetic resonance (¹³C-NMR) spectroscopy. The thermal stability and combustion performance of TOC were investigated by thermogravimetry analysis (TG), microscale combustion calorimetry (MCC) and limiting oxygen index (LOI). The results demonstrated that the thermal stability of TOC was less than that of the pristine material cellulose, but the peak of heat release rate (pHHR) and the total heat release (THR) of all TOC were significantly reduced. Additionally, the LOI values of all TOC products were much higher 25%. In summary, the above results indicated that the modified cellulose with carboxyl groups and metal ions by selective oxidation and ion exchange endows efficient flame retardancy.

Preparation of CdTe/Alginate Textile Fibres with Controllable Fluorescence Emission through a Wet-Spinning Process and Application in the Trace Detection of Hg2+ Ions

Fluorescent textile fibres (FTFs) are widely used in many industrial fields. However, in addition to fibres with good fluorescence, fibres with excellent colour controllability, structural stability and appropriate mechanical strength still need to be developed. In this work, CdTe/alginate composite FTFs are prepared by taking advantage of the interactions between CdTe nanocrystals (NCs) and alginate macromolecules via a wet-spinning machine with a CaCl₂ aqueous solution as the coagulation bath. CdTe NCs were chemically fixed in the fibre due to the interactions among surface ligands, macromolecules and coagulators (calcium ions), which ensured the excellent dispersity and good stability of the fibres. Förster resonance energy transfer (FRET) between NCs in the fibre was found to be restricted, which means that the emission colour of the fibres was totally controllable and could be predicted. Other properties of alginate fibres, such as flame retardance and mechanical strength, were also well preserved in the fluorescent fibres. Finally, FTFs showed good selectivity toward trace Hg²⁺ ions over other metallic ions, and the detection could be identified by the naked eye.

A simple technique for development of fibres with programmable microsphere concentration gradients for local protein delivery

Alginate has been a biologically viable option for controlled local delivery of bioactive molecules in vitro and in vivo. Specific bioactive molecule release profiles are achieved often by controlling polymer composition/concentration, which also determines the modulus of hydrogels. This largely limits alginate-mediated bioactive molecule delivery to single-factors of uniform concentration applications, rather than applications that may require (multiple) bioactive molecules delivered at a concentration gradient for chemotactic purposes. Here we report a two-phase PLGA/alginate delivery system composed of protein-laden poly-d,l-lactic-co-glycolic acid (PLGA) microspheres wet-spun into alginate fibres. Fluorescein isothiocyanate-conjugated bovine serum albumin (FITC-BSA) was used as a model protein and the developed structures were characterized. The fabrication system devised was shown to produce wet-spun fibres with a protein concentration gradient (G-Alg/PLGA fibre). The two-phase delivery matrices display retarded FITC-BSA release in both initial and late stages compared to release from the PLGA microspheres or alginate fibre alone. In addition, incorporation of higher concentrations of protein-loaded PLGA microspheres increased protein release compared to the fibres with lower concentrations of BSA-loaded microspheres. The "programmable" microsphere concentration gradient fibre methodology presented here may enable development of novel alginate scaffolds with the ability to guide tissue regeneration through tightly-controlled release of one or more proteins in highly defined spatio-temporal configurations.

Highly Efficient Flame Retardant Hybrid Composites Based on Calcium Alginate/Nano-Calcium Borate

Hybrid composites with low flammability based on renewable calcium alginate and nano-calcium borate were fabricated using an in situ method through a simple, eco-friendly vacuum drying process. The composites were characterized by X-ray diffractometry (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The combustion behavior and flammability of the composites were assessed by using the limiting oxygen index (LOI) and cone calorimetry (CONE) tests. The composites showed excellent thermal stability and achieved nonflammability with an LOI higher than 60. Pyrolysis was investigated using pyrolysis⁻gas chromatography⁻mass spectrometry (Py-GC-MS) and the results showed that fewer sorts of cracking products were produced from the hybrid composites compared with the calcium alginate. A possible thermal degradation mechanism of composites was proposed based on the experimental data. The combined results indicate that the calcium borate had a nano-effect, accumulating more freely in the hybrid composites and contributing significantly to both the solid phase and gas phase, resulting in an efficient improvement in the flame retardancy of the composites. Our study provides a novel material with promising potentiality for flame retardant applications.

Stabilization of Ca-deficient hydroxyapatite in biphasic calcium phosphate ceramics by adding alginate to enhance their biological performances

It is of significance to further improve the bioactivity of existing calcium phosphate (Ca–P) biomaterials to satisfy the needs of regenerative medicine.