A Novel Intumescent MCA-Modified Sodium Silicate/Acrylic Flame-Retardant Coating to Improve the Flame Retardancy of Wood.

The incompatibility between inorganic flame retardants and organic acrylic coatings represents a significant challenge that requires resolution. This work selected environmentally friendly organic aqueous acrylic coatings as the substrate, sodium silicate hydrate as the inorganic flame retardant, and melamine cyanurate (MCA) as the flame-retardant modifier and the flame-retardant co-modifier, with the objective of improving the dispersion and flame-retardant properties of sodium silicate hydrate in the aqueous acrylic coatings. Subsequently, the sodium silicate/MCA/waterborne acrylic acid flame-retardant coating was prepared. The flame-retardant treatment was then applied to poplar veneer in order to create a flame-retardant poplar veneer. The dispersion of the flame-retardant coating was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), and X-ray diffractometry (XRD). Furthermore, the flame-retardant properties of the flame-retardant poplar veneer were analyzed by thermogravimetry (TG), limiting oxygen index (LOI), and cone calorimeter. The results demonstrated that the MCA-modified sodium silicate flame retardant was well dispersed in aqueous acrylic coatings. The results of the flame-retardant properties of the poplar veneer indicated that the ignition time of the 9% flame retardant-treated poplar veneer was increased by 122.7%, the limiting oxygen index value was increased by 43.0%, and the peak heat release rate (pHRR), the peak total heat release rate (pTHR), and the peak mass loss rate were decreased by 19.9%, 10.8%, and 27.2%, respectively, in comparison to the non-flame retardant-treated poplar veneer. Furthermore, the residual char mass increased by 14.4%, and the residual char exhibited enhanced thickness, density, and regularity. The results demonstrated that MCA was an effective promoter of sodium silicate dispersion in acrylic coatings. Furthermore, the sodium silicate/MCA/waterborne acrylic flame-retardant coating significantly enhance the flame retardancy of wood, and its flame retardant mechanism was consistent with the synergistic silicone-nitrogen expansion flame-retardant mechanism. This work presents a novel approach to enhancing the dispersion of inorganic flame retardants in organic coatings, offering a valuable contribution to the advancement of research and application in the domains of innovative flame retardant coatings and flame retardant wood.

Sodium Silicate/Urea/Melamine Ternary Synergistic Waterborne Acrylic Acid Flame-Retardant Coating and Its Flame-Retardant Mechanism.

Waterborne acrylic coatings, the largest market share of predominant environmentally friendly coatings, face limitations in their extensive application due to their flammability. The flame-retardant properties of the coatings could be significantly enhanced by incorporate inorganic flame retardants. However, inorganic flame retardants tend to aggregate and unevenly disperse in waterborne acrylic coatings, causing a substantial decrease in flame retardancy. In this work, sodium silicate was utilized as a flame retardant, with urea and melamine serving as modifiers and synergistic agents. This combination resulted in the preparation of a sodium silicate/urea/melamine ternary synergistic waterborne acrylic flame-retardant coating. This coating was applied to the surface of poplar veneer to create flame-retardant poplar veneer. Subsequently, various instruments, including a scanning electron microscope (SEM), a limiting oxygen index meter (LOI), a thermogravimetric analyzer (TG), and a cone calorimeter (CONE), were employed to investigate the relevant properties and mechanisms of both the flame-retardant coating and poplar veneer. The results demonstrated that the sodium silicate/urea/melamine ternary synergistic flame retardant did not exhibit aggregation and could be uniformly dispersed in waterborne acrylic coatings. The physical and mechanical properties of the ternary synergistic flame-retardant poplar veneer coating were satisfactory. Melamine and urea, acting as modifiers, not only greatly enhanced the dispersibility of sodium silicate in waterborne acrylic coatings, but also assisted in the formation of a silicon-containing char layer through the generation of nitrogen, achieving ternary synergistic flame retardancy. In conclusion, this work explores a novel method to efficiently and uniformly disperse inorganic flame retardants in organic coatings. It significantly improves the dispersibility and uniformity of inorganic flame retardants in organic polymers, thereby substantially enhancing the flame-retardant performance of coatings. This work provides a theoretical basis for the research and application of new flame-retardant coatings in the field of chemistry and materials.

Antimildew Effect of Three Phenolic Compounds and the Efficacy of Antimildew Sliced Bamboo Veneer.

The development of the bamboo industry has been hindered by environmental issues caused by the application of bamboo preservatives. Chinese herbal phenolic compounds have been shown to possess broad-spectrum, potent antimildew properties, making them promising candidates for the development of new bamboo mildew inhibitors. In this study, we investigated the antimildew properties of three phenolic compounds, eugenol, carvacrol, and paeonol, against common mildews in bamboo materials using the Oxford cup method and the double-dilution method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the antimildew mechanism and its effects on mildew cell morphology. Our results showed that carvacrol exhibited the strongest antimildew activity, with minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values of 1.56 mg/mL and 1.76 mg/mL, respectively, followed by eugenol and paeonol. At a concentration of 25 mg/mL, eugenol and carvacrol had an inhibitory rate of over 50% against various mildews. Different concentrations of the three compounds significantly disrupted the morphology and structural integrity of mildew hyphae, with the extent of damage increasing with concentration and treatment duration. In the sliced bamboo mildew prevention experiment, carvacrol at a concentration of 29.25 mg/mL was found to be highly effective against all tested mildews. Our study provides new insights and a theoretical basis for the development of eco-friendly bamboo mildew inhibitors based on plant phenolic compounds.

Preeminent Flame-Retardant and Smoke Suppression Properties of PCaAl-LDHs Nanostructures on Bamboo Scrimber.

Bamboo scrimber is widely used in interior decoration, architecture, and many other fields. However, it has caused huge security risks due to its inherent flammability and easy-to-produce toxic volatiles after combustion. In this work, the bamboo scrimber with superior flame retardant and smoke suppression properties was produced via the coupling of phosphocalcium-aluminum hydrotalcite (PCaAl-LDHs) with bamboo bundles. The results demonstrated that the flame-retardant bamboo scrimber (FRBS) heat release rate (HRR) and total heat release (THR) were, respectively, reduced by 34.46% and 15.86% compared with that of untreated bamboo scrimber. At the same time, the unique multi-layer structure of PCaAl-LDHs effectively slowed down the release rate of flue gas by extending its escape path. Cone calorimetry showed that the total smoke emissions (TSR) and specific extinction area (SEA) of FRBS were, respectively, reduced by 65.97% and 85.96% when the concentration of the flame retardant was 2%, which greatly developed the fire safety of the bamboo scrimber. This method not only improves the fire safety of bamboo scrimber but can also be expected to broaden its use scenarios.

Preparation of PO43--Intercalated Calcium-Aluminum Hydrotalcites via Coprecipitation Method and Its Flame-Retardant Effect on Bamboo Scrimber.

To improve the flame retardancy of bamboo scrimber, flame-retardant CaAl-PO4-LDHs were synthesized via the coprecipitation method using PO43- as the anion of an intercalated calcium-aluminum hydrotalcite in this work. The fine CaAl-PO4-LDHs were characterized via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), cold field scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and thermogravimetry (TG). Different concentrations (1% and 2%) of CaAl-PO4-LDHs were used as flame retardants for the bamboo scrimber, and the flame retardancy of the bamboo scrimber was characterized via cone calorimetry. The results showed that CaAl-PO4-LDHs with excellent structures were successfully synthesized via the coprecipitation method in 6 h and at 120 °C. Compared with the bamboo scrimber without the flame retardant treatment, the peak heat release rate (HRR) of the bamboo scrimber treated with 1% and 2% concentrations of flame-retardant CaAl-PO4-LDHs decreased by 16.62% and 34.46%, the time taken to reach the exothermic peak was delayed by 103 s and 204 s and the Time to Ignition (TTI) was increased by 30% and 40%, respectively. Furthermore, the residual carbon of the bamboo scrimber did not change significantly, increasing by 0.8% and 2.08%, respectively. CO production decreased by 18.87% and 26.42%, respectively, and CO2 production decreased by 11.11% and 14.46%, respectively. The combined results show that the CaAl-PO4-LDHs synthesized in this work significantly improved the flame retardancy of bamboo scrimber. This work exhibited the great potential of the CaAl-PO4-LDHs, which were successfully synthesized via the coprecipitation method and applied as a flame retardant to improve the fire safety of bamboo scrimber.

Screening of Ionic Liquids against Bamboo Mildew and Its Inhibition Mechanism.

Ionic liquids are a class of organic molten salts that consist entirely of cations and anions. They are characterized by their low vapor pressure, low viscosity, low toxicity, high thermal stability, and strong antifungal potential. In this study, the inhibitory performance of ionic liquid cations against Penicillium citrinum, Trichoderma viride, and Aspergillus niger was investigated, along with the mechanism of cell membrane disruption. The Oxford cup method, SEM, and TEM were employed to examine the extent of damage and the specific site of action of ionic liquids on the mycelium and cell structure of these fungi. The results showed that 1-decyl-3-methylimidazole had a strong inhibitory effect on TV; benzyldimethyldodecylammonium chloride had a weak inhibitory effect on PC, TV, AN, and a mixed culture; while dodecylpyridinium chloride exhibited significant inhibitory effects on PC, TV, AN, and Mix, with more prominent effects observed on AN and Mix, exhibiting MIC values of 5.37 mg/mL, 5.05 mg/mL, 5.10 mg/mL, and 5.23 mg/mL, respectively. The mycelium of the mildews showed drying, partial loss, distortion, and uneven thickness. The cell structure showed separation of the plasma wall. The absorbance of the extracellular fluid of PC and TV reached the maximum after 30 min, while that of AN reached the maximum after 60 min. The pH of the extracellular fluid decreased initially and then increased within 60 min, followed by a continuous decrease. These findings provide important insights for the application of ionic liquid antifungal agents in bamboo, medicine, and food.

Process and Anti-Mildew Properties of Tea Polyphenol-Modified Citral-Treated Bamboo.

In order to reduce the oxidative degradation of citral, our research group modified citral with the natural antioxidant from tea polyphenols and applied it to bamboo processing to enhance the anti-mold effect of bamboo, but its application to the bamboo treatment process and the anti-mold effect is still not clear. For this reason, in this paper, the tea polyphenol-modified citral anti-mildew treatment of bamboo as well as the anti-mildew properties of bamboo were explored using the orthogonal testing method and a UV-vis spectrophotometer. The results showed that when the concentration of tea polyphenol-modified citral reached 175 mg mL-1 and above, the efficacy of the anti-mildew treated bamboo against common molds reached 100%; the improved anti-mildew treatment process parameters for bamboo were as follows: impregnation pressure 0.6 MPa, impregnation time 150 min, and tea polyphenol-modified citral concentration 200 mg mL-1. Following the tea polyphenol-modified citral anti-mildew treatment of bamboo, not only did it improve the anti-mildew properties of the bamboo materials, but it also added a fresh lemon fragrance without altering the original colour, microstructure, and chemical properties of the bamboo materials.

Antioxidant-Mediated Modification of Citral and Its Control Effect on Mildewy Bamboo.

To reduce the oxidative degradation of citral and improve its antimildew performance, citral was modified with natural antioxidants such as tea polyphenols, ascorbic acid, and theaflavin in the present study. Additionally, the effects of these natural antioxidants on the citral degradation rate and DPPH radical-scavenging rate, as well as the effectiveness of antioxidant-modified citral in the antimildew treatment of bamboo were investigated. Ascorbic acid, theaflavin, and tea polyphenols improved the antioxidant performance of citral to some extent, and the tea polyphenols exhibited the best antioxidant performance. When the amount of tea polyphenols added to citral reached 1.0%, the oxidative degradation of citral was effectively prevented. Compared with citral, tea-polyphenol-modified citral could reduce the efficacy of the bamboo antimildew treatment against all four mildews and the effectiveness of the antimildew treatment reached 100%. Citral modification with antioxidants reduced the amount of citral required in the treatment, thereby reducing the treatment cost for bamboo mildew.

Preparation of Citral Compound and Its Bamboo Antimildew Properties.

To reduce the amount of citral used without reducing the antimildew performance of bamboo, the citral compound preparation process, the distribution of the compound in bamboo, and its antimildew performance were investigated using the Oxford cup method, Fourier-transform infrared spectroscopy, and ultraviolet spectrophotometry. The results revealed that the combination of citral with cinnamaldehyde or thymol may lead to partial chemical reactions, which may change the chemical structure of citral and affect its bacteriostatic properties. The bacteriostatic properties of the citraldehyde thymol compound against common molds of bamboo were considerably superior to those of the citral cinnamaldehyde compound. The limonaldehyde thymol compound showed a low distribution trend outside and vice versa inside in the treated bamboo. The citral thymol compound exhibited good antimildew performance at a concentration of 200 mg/mL. The citral thymol compound could reduce the amount of citral by approximately 67 mg/mL without reducing the antimildew performance of bamboo.