Preparation of Ni-Fe layered double hydroxides and its application in thermoplastic polyurethane with flame retardancy and smoke suppression

Colored Radiative Cooling and Flame-Retardant Polyurethane-Based Coatings: Selective Absorption/Reflection in Solar Waveband

The aesthetic demand has become an imperative challenge to advance the practical and commercial application of daytime radiative cooling technology toward mitigating climate change. Meanwhile, the application of radiative cooling materials usually focuses on the building surface, related tightly to fire safety. Herein, the absorption and reflection spectra of organic and inorganic colorants are first compared in solar waveband, finding that iron oxides have higher reflectivity in NIR region. Second, three kinds of iron oxides-based colorants are selected to combine porous structure and silicon-modified ammonium polyphosphate (Si-APP) to engineer colored polyurethane-based (PU) coating, thus enhancing the reflectivity and flame retardancy. Together with reflectivity of more than 90% in near-infrared waveband and infrared emissivity of ≈91%, average temperature drops of ≈5.7, ≈7.9, and ≈3.8 °C are achieved in porous PU/Fe2O3/Si-APP, porous PU/Fe2O3·H2O/Si-APP, and porous PU/Fe3O4·H2O/Si-APP, compared with dense control samples. The catalysis effect of iron oxides in the cross-linking reaction of pyrolysis products and dehydration mechanism of Si-APP enable PU coating to produce an intumescent and protective char residue. Consequently, PU composite coatings demonstrate desirable fire safety. The ingenious choice of colorants effectively minimizes the solar heating effect and trades off the daytime radiative cooling and aesthetic appearance requirement.

High-Value and Environmentally Friendly Recycling Method for Coal-Based Solid Waste Based on Polyurethane Composite Materials

This study aims to provide a high-value and environmentally friendly method for the application of coal-based solid waste. Modified fly ash/polyurethane (MFA/PU) and modified coal gangue powder/polyurethane (MCG/PU) composites were prepared by adding different contents of MFA and MCG (10%, 20%, 30%, 40%). At the filler content of 30%, the compressive strengths of MFA/PU and MCG/PU are 84.1 MPa and 46.3 MPa, respectively, likely due to an improvement in interface compatibility, as indicated by scanning electron microscopy (SEM). The MFA/PU and MCG/PU composites present their highest limiting oxygen index (LOI) values of 29% and 23.5%, respectively, when their filler content is 30%. MFA has advantages in improving the LOIs of composites. Cone calorimetry (CCT) and SEM demonstrate that the two composites exhibit similar condensed-phase flame-retardant behaviors during combustion, which releases CO2 in advance and accelerates the formation of a dense barrier layer. Compared with the MFA/PU composites, the MCG/PU composites could produce a more stable and dense barrier structure. Water quality tests show that heavy metals do not leak from FA and CG embedded in PU. This work provided a new strategy for the safe and high-value recycling of coal-based solid waste.

A universal eco-friendly flame retardant strategy for polylactic acid fabrics and other polymer substrates

Various polymer substrates have their particular combustion features, therefore, developing an effective universal flame retardant strategy for various polymer substrates is of great practical importance. Meanwhile, as substitutes for petroleum-based products, bio-based flame retardants and biodegradable polylactic acid (PLA) meet the requirements of sustainable development. In this work, a fully bio-based flame retardant coating (PAGS) was prepared using phytic acid (PA) and guanosine (GS). PAGS was used as a universal flame retardant coatings for polylactic acid (PLA) fabrics and other substrates, including cotton fabrics, polyethylene terephthalate (PET) fabrics, polyamide (PA) fabrics, polyurethane (PU) foams, polyethylene terephthalate (PET) films, and woods. The PAGS-treated substrates were able to self-extinguish and eliminate molten droplets. Similarly, the PAGS coating significantly suppressed the heat release of each substrate. The P-containing free radicals in the gas phase were able to interact with highly reactive H, HO and alkyl radicals, blocking the chain reaction during combustion. The flammable gas density was also diluted by nonflammable gases. The formed continuous porous and dense intumescent char layer hindered heat and oxygen. It is suggested that this work provides a simple and efficient flame retardant strategy for improving the fire safety of various polymer substrates.

Tunable construction of fire safe and mechanically strong hierarchical composites towards electromagnetic interference shielding

Cotton fabric composites were designed to be protected by fire safe thermoplastic polyurethane (TPU) composites for developing electromagnetic interference (EMI) shielding polymer composites with superior mechanical properties. Herein, the as-prepared MXene was coated onto the fiber surface of cotton and then thermally compressed with TPU composites, which were filled with the sodium dodecyl sulfate modified layered double hydroxides functionalized the short carbon fiber hybrids through melt blending method. Then, a series of highly fire safe cotton/TPU hierarchical composites were constructed by a designed thermal compression technique. For instance, the obtained cotton/TPU hierarchical sample showed greatly reduced peak of heat release rate, peak of carbon monoxide production rate and peak of carbon dioxide production rate of TPU by 50.1%, 52.1% and 55.4%, respectively. Furthermore, the cotton/TPU hierarchical composites possessed the EMI shielding effectiveness of 40.0 dB in the X band and 54.6 dB in the K band. The mechanical property of the cotton/TPU hierarchical composites was also reinforced, where the elongation at break and toughness values of the TPU/SCF/mLDH1/C2 hierarchical composite were 21.47 and 18.30 times higher than those of pure TPU, respectively. These mechanically strong hierarchical composites have brought a promising attempt to broaden their practical application, removing the fire hazards and electromagnetic waves radiation from the environment.

Construction of dopamine supported Mg(Ca)Al layered double hydroxides with enhanced adsorption properties for uranium

A novel dopamine-supported Mg(Ca)Al layered double hydroxide composite was synthesized by co-precipitation method. The existence of Ca²⁺ and dopamine could promote the capture of uranium on the layered double hydroxides. In batch experiments, the composite exhibited good uranium removal performance, including high adsorption capacity (687.3 mg/g), strong anti-interference and good reusability (the removal percentage was still higher than 90 % after five cycles). At low initial uranium concentration, the uranium removal percentage on the composite exceeded 99.7 % and the residual concentration of uranium in the solution was <0.03 mg/L, reaching the limited standard of the World Health Organization. The studies of adsorption kinetics and isotherm indicated that the uranium adsorption behavior on the composite conformed to the pseudo-second-order kinetic and Langmuir isotherm models, suggesting that the process was a monolayer adsorption dominated by chemical adsorption. Furthermore, the high-efficiency uranium adsorption on the Mg(Ca)Al layered double hydroxide was mainly attributed to the strong complexation between the active sites (-OH and -NH₂) and uranium, the precipitation of interlayer intercalation ions (CO₃^2- and OH^-) to uranium and the ion exchange of Ca²⁺ to uranium. Due to these advantages, the dopamine-supported Mg(Ca)Al layered double hydroxide composite is expected to be used as fine adsorbent to remove uranium from wastewater.

Improving the hygroscopicity and flame retardancy of polyamide 6 fabrics by surface coating with β-FeOOH and sulfamic acid

The combustion of polyamide 6 (PA6) fabrics releases toxic smoke, which will pollute the environment and threaten human life and health. Herein, a novel eco-friendly flame-retardant coating was constructed and applied to PA6 fabrics. Needle-like β-FeOOH with a high surface area was firstly constructed onto the surface of PA6 fabrics by the hydrolysis of Fe³⁺, sulfamic acid (SA) was then introduced by a facile dipping and nipping method. The growth of β-FeOOH also endowed the PA6 fabrics with certain hydrophilicity and moisture permeability, resulting in improved comfortability. The limiting oxygen index (LOI) of the prepared PA6/Fe/6SA sample was increased to 27.2% from 18.5% of control PA6 sample, and the damaged length was reduced to only 6.0 cm from 12.0 cm of control PA6 sample. Meanwhile, the melt dripping was also eliminated. The heat release rate and total heat release values of the PA6/Fe/6SA sample were decreased to 318.5 kW/m² and 17.0 MJ/m², respectively, compared with those of control PA6 (494.7 kW/m² and 21.4 MJ/m²). The analysis results indicated that nonflammable gases diluted flammable gases. The observation of char residues demonstrated that the stable char layer was formed, which effectively inhibited the transfer of heat and oxygen. The organic solvent-free coating does not contain any conventional halogens/phosphorus elements, which provides a useful methodology to produce environmentally friendly flame-retardant fabrics.

Architecting fire safe hierarchical polymer nanocomposite films with excellent electromagnetic interference shielding via interface engineering

Integrating high flame retardancy and excellent electromagnetic interference (EMI) shielding into polymetric materials is extremely necessary, and well dispersing conductive fillers into polymeric materials is still a great challenge because of incompatible interfacial polarity between polymer matrix and conductive fillers. Therefore, under the premise of maintaining integral conductive films in the process of hot compression, constructing a novel EMI shielding polymer nanocomposites where conductive films closely adhere to polymer nanocmposites layers should be a fascinating stratety. In this work, salicylaldehyde-modified chitosan decorated titanium carbide nanohybrid (Ti₃C₂T_x-SCS) was combined with piperazine-modified ammonium polyphosphate (PA-APP) to fabricate thermoplastic polyurethane (TPU) nanocomposites, which were used for construction of hierarchical nanocomposite films by inserting reduced graphene oxide (rGO) films into TPU/PA-APP/Ti₃C₂T_x-SCS nanocomposite layers through our self-developed air assisted hot pressing technique. The total heat release, total smoke release and total carbon monoxide yield for TPU nanocomposite containing 4.0 wt% Ti₃C₂T_x-SCS nanohybrid were 58.0%, 58.4% and 75.8% lower than those of pristine TPU, respectively. Besides, the hierarchical TPU nanocomposite film containing 1.0 wt% Ti₃C₂T_x-SCS presented an averaged EMI shielding effectiveness of 21.3 dB in X band. This work provides a promising strategy for fabricating fire safe and EMI shielding polymer nanocomposites.