Flame-Retardant Wood Composites Based on Immobilizing with Chitosan/Sodium Phytate/Nano-TiO2-ZnO Coatings via Layer-by-Layer Self-Assembly

Research and Application of Biomass-Based Wood Flame Retardants: A Review

Wood is widely used as a construction material due to its many advantages, such as good mechanical properties, low production costs, and renewability. However, its flammability limits its use in construction. To solve the problem of wood flammability, the most common method to improve the fire safety of wood is to modify the wood by deep impregnation or surface coating with flame retardants. Therefore, many researchers have found that environmentally friendly and low-cost biomass materials can be used as a source of green flame retardants. Two aspects of biomass-based intumescent flame retardants are summarized in this paper. On the one hand, biomass is used as one of the three sources or as a flame-retardant synergist in combination with other flame retardants, which are called composite biomass intumescent flame retardants. On the other hand, biomass is used alone as a feedstock to produce all-biomass intumescent flame retardants. In addition, the potential of biomass-based materials as an environmentally friendly and low-cost FR source to produce high-performance biomass-based flame retardants with improved technology was also discussed in detail. The development of biomass-based intumescent flame retardants represents a viable and promising approach for the efficient and environmentally friendly production of biomass-based flame retardants.

Facile fabrication of a novel self-healing and flame-retardant hydrogel/MXene coating for wood

To improve flame retardancy of wood, a novel high-water-retention and self-healing polyvinyl alcohol/phytic acid/MXene hydrogel coating was developed through facile one-pot heating and freeze-thaw cycle methods, and then painted on wood surface. The coating exhibit excellent self-healing property and significantly enhanced water-retention property (water content ≥ 90 wt%), due to the increased hydrogen bonds within the coating system with the presence of MXene nanosheets. Compared to pristine wood, the flame retardancy of coated wood is greatly improved, such as passed V0 rating in UL-94 test, increasing time to ignition (TTI, from 32 to 69 s), and decreased heat release rate and total heat release by 41.6% and 36.14%. The cooling effect and large thermal capacity of high-water-retention hydrogel, and physical barrier effects for flammable gas products, heat and oxygen by MXene nanosheets and the compact char layer formed during combustion play key roles in the flame retardancy enhancements of the wood. High thermal stability of MXene nanosheets is another beneficial factor. The detailed flame-retardant and self-healing mechanisms were proposed.

Efficient and Durable Flame-Retardant Coatings on Wood Fabricated by Chitosan, Graphene Oxide, and Ammonium Polyphosphate Ternary Complexes via a Layer-by-Layer Self-Assembly Approach

An efficient and durable flame-retardant coating was constructed on wood via a layer-by-layer (LBL) self-assembly approach by using a chitosan (CS), graphene oxide (GO), and ammonium polyphosphate (APP) ternary flame-retardant system. Both scanning electron microscopy (SEM) characterization and Fourier transform infrared spectroscopy (FT-IR) analysis indicated that CS-GO and APP polyelectrolytes were successfully deposited on wood, and the deposition amount was increased with the numbers of the LBLs. Thermogravimetric analysis revealed that the CS-GO-APP coating could decrease the initial and maximum thermal decomposition temperature of the coated wood while increase the char residue significantly, which may be attributed to the earlier degradation of CS and APP and effective heat barrier of the incorporated GO, thus increasing the thermal stability of the modified wood. The limited oxygen index (LOI) and cone calorimeter analysis results of the pristine and coated wood indicated that the fire resistance was significantly improved after CS-GO-APP modification; when 15 BLs were deposited on the wood, the LOI was increased from pristine 22 to 42, while the heat release rate and total heat release decreased from pristine 105.50 kW/m² and 62.43 MJ/m² to 57.51 kW/m² and 34.31 MJ/m², respectively. What is more, the 24 h immersion experiments and abrasion tests proved the excellent durability of the deposited coating. Furthermore, the SEM images of the char residues after flaming test proved that the CS-GO-APP assembly coating could promote the char layer formation on the wood surface and block the heat and flame spread, thus protecting the wood from fire attacking.

Qualitative and quantitative investigation on adsorption mechanisms of Cd(II) on modified biochar derived from co-pyrolysis of straw and sodium phytate

Developing effective modification methods and obtaining a comprehensive understanding of adsorption mechanisms are essential for the practical application of biochars for the removal of heavy metals from solutions. In this study, rice straw was impregnated with sodium phytate and pyrolyzed at 350 °C, 450 °C, and 550 °C to synthesize modified biochars (i.e., MBC350, MBC450, and MBC550). The Cd(II) adsorption capacities and contributions of different mechanisms, including the effects of biochar-derived dissolved organic matter (BDOM), were investigated using batch sorption experiments and characterization analyses. The modification of sodium phytate promoted the pyrolysis of biomass, thereby increasing the BDOM content and aromatic structures at low and high pyrolysis temperatures, respectively. Moreover, the modification also increased the exchangeable Na⁺ and carbonate contents in the modified biochars. Compared with the raw biochars, the Cd(II) adsorption capacities of modified biochars increased by 3.3-4.3 times, and MBC550 had the highest Cd(II) adsorption capacity (126.5 mg/g), of which precipitation with minerals and interaction with π-electrons contributed 41.7% and 45.8%, respectively. However, at a lower pyrolysis temperature, the Cd(II) adsorption attributed to ion exchange and co-deposition with BDOM significantly increased, especially on MBC350 (33.9 and 12.6 mg/g, respectively). These results indicate that modification by sodium phytate effectively enhanced various adsorption mechanisms, thereby increasing the Cd(II) adsorption capacity. In addition, the contribution of co-deposition with BDOM to adsorption was unneglectable for the biochars pyrolyzed at low temperatures.

Preparation and Characterization of Insulating Panels from Recycled Polylaminate (Tetra Pak) Materials

Eco-sustainability and the reuse of materials are highly topical issues. In fact, in recent years, much study and research has been developed on this aspect, making the eco-sustainability of materials a real need. Polylaminate containers, more commonly called Tetra Pak containers, represent the most used packaging in the world. This work proposes a new strategy for the reuse of discarded polylaminate containers in order to create panels that can be used in construction and in particular as insulating panels. The proposed thermal method has been optimized in terms of operating variables such as time, temperature, pressure, number of polylaminate sheets. The results obtained show that the proposed thermal method is suitable for obtaining panels with characteristics suitable for use in green building. The advantage of the thermal method is that it does not use chemical or other binders and moreover uses only and exclusively sheets of recycled polylaminate.

Research Progress of Wood Cell Wall Modification and Functional Improvement: A Review

The modification of wood cell walls is based on the characteristics of the chemical composition and structure of the cell wall. Various physical and chemical modifications to these characteristics enhance the original properties of the cell wall and give additional functionality. Through complex modification, wood has also obtained the opportunity to become a multifunctional material. Scholars have paid more attention to the microscopic properties of the cell wall with continuous enrichment of modification methods and improvement of modification mechanisms. This article summarizes the methods of cell wall modification in recent years and proposes prospects for future development: (1) innovation of modifiers and combination with modification mechanism, as well as improvement of cell wall permeability; (2) the application directions of cell wall structures; and (3) the application of nano-technologies in cell wall modification. This review provides further ideas and technologies for wood modifications.

Enhancing the thermostability, UV shielding and antimicrobial activity of transparent chitosan film by carbon quantum dots containing N/P

The chitosan (CS) transparent film has attracted much attention in food and medicine packaging areas due to their biodegradability and good availability. A novel carbon quantum dots compound containing nitrogen and phosphorus (NP-CQDs) was obtained by reacting citric acids, with urea and phytic acids. The density of the film was increased, and the water vapor permeation was reduced by the presence of NP-CQDs. The introduction of 4 wt% NP-CQDs increased the water contact angle of the CS film from 79.2° to 105.8°. The shielding on UV-A and UV-B transmittance was increased with the NP-CQDs loading. The film containing 4 wt% NP-CQDs blocked more than 90.2% UV-A and 96.5% UV-B; however, it only blocked 26.8% visible light. It also exhibited better antibacterial activity to both E. coli and S. aureus than the control CS film. This work provided a feasible way to prepare multifunctional bio-safe film.

Nanocellulose Based Filtration Membrane in Industrial Waste Water Treatment: A Review

In the field of industrial wastewater treatment, membrane separation technology, as an emerging separation technology, compared with traditional separation technology such as precipitation, adsorption, and ion exchange, has advantages in separation efficiency, low energy consumption, low cost, simple operation, and no secondary pollution. The application has been expanding in recent years, but membrane fouling and other problems have seriously restricted the development of membrane technology. Natural cellulose is one of the most abundant resources in nature. In addition, nanocellulose has characteristics of high strength and specific surface area, surface activity groups, as well as being pollution-free and renewable, giving it a very wide development prospect in many fields, including membrane separation technology. This paper reviews the current status of nanocellulose filtration membrane, combs the widespread types of nanocellulose and its derivatives, and summarizes the current application of cellulose in membrane separation. In addition, for the purpose of nanocellulose filtration membrane in wastewater treatment, nanocellulose membranes are divided into two categories according to the role in filtration membrane: the application of nanocellulose as membrane matrix material and as a modified additive in composite membrane in wastewater treatment. Finally, the advantages and disadvantages of inorganic ceramic filtrations and nanocellulose filtrations are compared, and the application trend of nanocellulose in the filtration membrane direction is summarized and discussed.

Innovative Polyelectrolyte Treatment to Flame-Retard Wood

Fire protection has been a major challenge in wood construction for many years, mainly due to the high flame spread risk associated with wood flooring. Wood fire-retardancy is framed by two main axes: coating and bulk impregnation. There is a growing need for economically and environmentally friendly alternatives. The study of polyelectrolyte complexes (PECs) for wood substrates is in its infancy, but PECs’ versatility and eco-friendly character are already recognized for fabric fire-retardancy fabrics. In this study, a new approach to PEC characterization is proposed. First, PECs, which consist of polyethyleneimine and sodium phytate, were chemically and thermally characterized to select the most promising systems. Then, yellow birch (Betula alleghaniensis Britt.) was surface-impregnated under reduced pressure with the two PECs identified as the best options. Overall, wood fire-retardancy was improved with a low weight gain of 2 wt.% without increasing water uptake.

Clays as Inhibitors of Polyurethane Foams' Flammability

Polyurethanes are a very important group of polymers with an extensive range of applications in different branches of industry. In the form of foams, they are mainly used in bedding, furniture, building, construction, and automotive sectors. Due to human safety reasons, these applications require an appropriate level of flame retardance, often required by various law regulations. Nevertheless, without the proper modifications, polyurethane foams are easily ignitable, highly flammable, and generate an enormous amount of smoke during combustion. Therefore, proper modifications or additives should be introduced to reduce their flammability. Except for the most popular phosphorus-, halogen-, or nitrogen-containing flame retardants, promising results were noted for the application of clays. Due to their small particle size and flake-like shape, they induce a "labyrinth effect" inside the foam, resulting in the delay of decomposition onset, reduction of smoke generation, and inhibition of heat, gas, and mass transfer. Moreover, clays can be easily modified with different organic compounds or used along with conventional flame retardants. Such an approach may often result in the synergy effect, which provides the exceptional reduction of foams' flammability. This paper summarizes the literature reports related to the applications of clays in the reduction of polyurethane foams' flammability, either by their incorporation as a nanofiller or by preparation of coatings.

Green and Efficient Processing of Wood with Supercritical CO2: A Review

Wood processing is a crucial step of wood utilization, but the adding of environmentally hazardous feedstocks and the use of unreasonable technology allow it to harm the environment and human health. Supercritical CO2 (scCO2) is a non-toxic, odorless, and safe solvent, which is widely used in studies and industrial production, but there is no review summarizing wood processing with scCO2. The unique structure and chemical properties of wood combined with scCO2 technology produce positive results. In this paper, wood processing with scCO2 is summarized, including wood impregnation, wood drying, wood thermochemical conversion, and wood extraction. The green and efficient characteristics of wood processing with scCO2 are explained in detail for researchers, engineers, and investors to provide a clean wood processing method. Further study is needed to reduce its energy consumption and commercialize it eventually.

Progress in Biodegradable Flame Retardant Nano-Biocomposites

This paper summarizes the results obtained in the course of the development of a specific group of biocomposites with high functionality of flame retardancy, which are environmentally acceptable at the same time. Conventional biocomposites have to be altered through different modifications, to be able to respond to the stringent standards and environmental requests of the circular economy. The most commonly produced types of biocomposites are those composed of a biodegradable PLA matrix and plant bast fibres. Despite of numerous positive properties of natural fibres, flammability of plant fibres is one of the most pronounced drawbacks for their wider usage in biocomposites production. Most recent novelties regarding the flame retardancy of nanocomposites are presented, with the accent on the agents of nanosize (nanofillers), which have been chosen as they have low or non-toxic environmental impact, but still offer enhanced flame retardant (FR) properties. The importance of a nanofiller’s geometry and shape (e.g., nanodispersion of nanoclay) and increase in polymer viscosity, on flame retardancy has been stressed. Although metal oxydes are considered the most commonly used nanofillers there are numerous other possibilities presented within the paper. Combinations of clay based nanofillers with other nanosized or microsized FR agents can significantly improve the thermal stability and FR properties of nanocomposite materials. Further research is still needed on optimizing the parameters of FR compounds to meet numerous requirements, from the improvement of thermal and mechanical properties to the biodegradability of the composite products. Presented research initiatives provide genuine new opportunities for manufacturers, consumers and society as a whole to create a new class of bionanocomposite materials with added benefits of environmental improvement.

Surface Properties of Spray-Assisted Layer-By-Layer ElectroStatic Self-Assembly Treated Wooden Take-Off Board

Wooden take-off board is easy to crack, deform, discolor, and decay when it is used outdoors, which not only increases maintenance costs but also reduces its service life. Multifunctional coatings with UV-resistant, water-repellent, and flame-retardant properties were successfully obtained on the surface of a wooden take-off board substrate by spray-assisted layer-by-layer self-assembly. The coatings consisted of positively-charged chitosan, Al (OH)3, and negatively-charged sodium phytate through electrostatic adsorption several times. The treated wood exhibited high UV resistance, and the color remained constant after 720 hours of ultraviolet irradiation. The wettability of the wood surface after treatment became superhydrophobic, with initial static contact angles as high as 140°. In addition, limiting oxygen index and air exposure combustion tests were used to verify that chitosan, sodium phytate, and aluminum hydroxide could synergistically confer significant fire resistance to modified wood.

Flame-Retardant Systems Based on Chitosan and Its Derivatives: State of the Art and Perspectives

During the last decade, the utilization of chitin, and in par0ticular its deacetylated form, i.e., chitosan, for flame retardant purposes, has represented quite a novel and interesting application, very far from the established uses of this bio-sourced material. In this context, chitosan is a carbon source that can be successfully exploited, often in combination with intumescent products, in order to provide different polymer systems (namely, bulky materials, fabrics and foams) with high flame retardant (FR) features. Besides, this specific use of chitosan in flame retardance is well suited to a green and sustainable approach. This review aims to summarize the recent advances concerning the utilization of chitosan as a key component in the design of efficient flame retardant systems for different polymeric materials.

Preparation and Synergistic Effect of Chitosan/Sodium Phytate/MgO Nanoparticle Fire-Retardant Coatings on Wood Substrate through Layer-By-Layer Self-Assembly

Fire-retardant chitosan/sodium phytate/MgO nanoparticle (CH/SP/nano-MgO) coatings were loaded on a wood substrate via electrostatic layer-by-layer self-assembly and characterized by scanning electron microscopy and energy-dispersive spectrometry. The flammability and thermal degradation of the original wood and wood samples treated with chitosan, chitosan/sodium phytate, chitosan/sodium phytate/MgO nanoparticles were studied by limiting oxygen index (LOI), exposure combustion experiments and thermogravimetric analysis (TGA), respectively. The CH/SP/nano-MgO coating served as an intumescent fire-retardant system that created a physical protection cover and exhibited the best fire retardant performance. The LOI value was 30.2% and required approximately 16–17 s to self-extinguish when exposed to air. The TGA curves also showed that char formation protected the wood from combustion.

Effect of MF-Coated Epoxy Resin Microcapsules on Properties of Waterborne Wood Coating on Basswood

In this paper, melamine–formaldehyde (MF) was used as the wall material, and epoxy resin was used as the core material to prepare microcapsules. The optical properties, mechanical properties and ageing resistance of waterborne topcoat were investigated by adding different mass fractions of microcapsules into the waterborne topcoat. Through scanning electron microscopy and infrared spectroscopy analysis, the prepared microcapsules of core-wall ratio of 0.50 were more uniform. It was found that when the mass fraction of microcapsules is less than 10.0% and the core–wall ratio is 0.50, the original color difference of the coating can be maintained. With the increase in microcapsule mass fraction, the gloss of the topcoat film gradually decreases. The mass fraction of the microcapsule of 4.0% with the core–wall ratio of 0.50 can maintain the original gloss of 30.0 GU. The topcoat film with the MF-coated epoxy resin microcapsules of the core–wall ratio of 0.50 has high impact resistance, adhesion and hardness. The results showed that the gloss loss and color difference of the coating with the MF-coated epoxy microcapsules were the lowest when the mass fraction of microcapsules was 4.0%, indicating that microcapsules can improve the stability of coating. These results lay a technical foundation for the development and application of high-performance wood coatings.

Potential Use of Wollastonite as a Filler in UF Resin Based Medium-Density Fiberboard (MDF)

Urea-formaldehyde (UF) resins are primary petroleum-based, increasing their potential environmental footprint. Identifying additives to reduce the total amount of resin needed without adversely affecting the panel properties could reduce these impacts. Wollastonite is a mineral containing calcium and silica that has been used as an additive in a variety of materials and may be useful as a resin extender. Nanoscale wollastonite has been shown to enhance the panel properties but is costly. Micron-scale wollastonite may be a less costly alternative. Medium-density fiberboards were produced by blending a hardwood furnish with UF alone, micron-sized wollastonite alone, or a 9:1 ratio of UF to wollastonite. Panels containing of only wollastonite had poor properties, but the properties of panels with 9:1 UF/wollastonite were similar to the UF-alone panels, except for the internal bond strength. The results suggest that small amounts of micron-sized wollastonite could serve as a resin extender. Further studies are suggested to determine if the micron-sized material has similar positive effects on the resin curing rate.