ZIF-8@Co-doped Boronate Ester Polymer Core-shell Particles: Catalytically Enhancing the Nonflammability and Smoke Suppression of Epoxy Resin

"One for two" strategy to construct an organic-inorganic polymer colloid for flame-retardant modification of flax fabric and rigid polyurethane foam

Polymeric materials such as fabric and foam have high flammability which limits their application in the field of fire protection. To this end, an organic-inorganic polymer colloid constructed from carboxymethyl chitosan and ammonium polyphosphate was used to improve the flame retardancy of flax fabric (FF) and rigid polyurethane foam (RPUF) based on a "one for two" strategy. The modification processes of FF and RPUF relied on pad-dry-cure method and UV-curing technology, respectively, and the modified FF and RPUF were severally designated as CMC/APP-FF and RFR-RPUF. Flame retardancy studies showed that CMC/APP-FF and RFR-RPUF exhibited limiting oxygen index values as high as 39.4 % and 42.6 %, respectively, and both achieved self-extinguishing behavior when external ignition source was removed. Thermogravimetric analysis and cone calorimetry test confirmed that CMC/APP-FF and RFR-RPUF had good charring ability and demonstrated reduced peak heat release rate values of 90.1 % and 10.8 %, respectively, distinct from before they were modified. In addition, condensed phase analysis showed that after burning, CMC/APP-FF became an integration char structure, whereas RFR-RPUF turned into a sandwiched char structure. In summary, the "one for two" strategy reported in this work provides a new insight into the economical fabrication of flame-retardant polymeric materials.

A novel P/N/Si/Zn-containing hybrid flame retardant for enhancing flame retardancy and smoke suppression of epoxy resins

Currently, additively efficient flame retardants are being developed to enhance the smoke suppression, flame retardancy, and thermal properties of composite materials. To this end, the current study designed and prepared a novel P/N/Si/Zn-containing organic-inorganic hybrid denoted as APHZ. Its inorganic part was 2-methylimidazole zinc salt (ZIF-8), which improved its smoke suppression and catalytic carbonization. The organic part (P/N/Si-containing compound) promoted its flame retardancy and interfacial compatibility between APHZ and epoxy resin (EP). The test results revealed that EP/APHZ-3 composites achieved a V-0 rating and a notable LOI value of 30.7% when introducing 3 wt% APHZ into the EP matrix. Cone calorimetry tests (CCT) further demonstrated that the average heat release rate (av-HRR), total smoke production (TSP), and CO production (COP) of EP/APHZ-3 were reduced by 23.3%, 14.0%, and 21.1%, respectively. Meanwhile, the char residual was increased by 60.6%, as compared to pure EP. Furthermore, the flame-retardant mechanism of EP/APHZ composites was investigated by the XPS, TG-FTIR, and Raman spectroscopy techniques. The observed synergistic effect of the imidazole skeleton ZIF-8 and P/N/Si-containing compound in APHZ facilitated the generation of a dense multi-element char layer, with the condensed phase flame-retardant mechanism playing a dominant role. These findings contribute to developing and designing high-performance flame-retardant EP.

Recent advances in metal-family flame retardants: a review

The use of polymer materials is inextricably linked to our manufacturing life. However, most of them are easily combusted in the air and the combustion process generates a large amount of toxic fumes and dangerous smoke. This can result in injuries and property damage, as well as limiting their use. It is essential to enhance the flame-retardant properties and smoke suppression performance by using multiple flame retardants. Metal-based flame retardants have a unique chemical composition. They are environmentally friendly flame retardants, which can impart good smoke suppression, flame retardancy to polymers and further reduce the production of toxic gases. The differences in the compounds formed between the transition metals and the main group metals make them act differently as flame retardants for polymers. As a result, this study presents the research progress and flame-retardant mechanism of flame-retardant polymers for flame retardants from different groups of metals in the periodic table of elements in a systematic manner. In view of the differences between the main group metals and transition metals, the mechanism of their application in flame retardant polymer materials is carefully detailed, as are their distinct advantages and disadvantages. And ultimately, prospects for the development of transition metals and main group metals are outlined. It is hoped that this paper will provide valuable references and insights for scholars in the field.

Phenylboronic acid-functionalized magnetic metal-organic framework nanoparticles for magnetic solid phase extraction of five benzoylurea insecticides

This research involves the construction of a phenylboronic acid-functionalized magnetic UiO-66 metal-organic framework (MOF) nanoparticle (CPBA@UiO-66@Fe₃O₄). Its design is primarily for the magnetic solid phase extraction (MSPE) of benzoylurea insecticides. An organic ligand, 2-amino terephthalic acid (2-ATPA), facilitated the introduction of amino groups while keeping the original crystal structure of UiO-66 intact. The constructed UiO-66 MOF showcases a porous structure and extensive surface area, thereby providing an optimal platform for further functionalization. The employment of 4-carboxylphenylboronic acid as a modifier notably amplified the extraction efficiency for benzoylureas. This improvement was due to the formation of B-N coordination and other secondary interactions. By integrating this with high-performance liquid chromatography (HPLC), we established a quantitative analytical method for benzoylurea insecticides. This method achieved a wide linear range (2.5-500 μg L^-1 or 5-500 μg L^-1), satisfactory recoveries (83.3-95.1%), and acceptable limits of detection (LODs: 0.3-1.0 μg L^-1). The developed method proved successful when applied to six tea infusion samples, representing China's six major tea categories. Semi-fermented and light-fermented tea samples demonstrated relatively higher spiking recoveries.

Mechanical properties of epoxy resin toughened with cornstarch

We investigated the effect of starch modification on the mechanical properties of phenolic epoxy resin (EP). Corn starch admixture of 2.5, 5, 7.5, and 10 wt% were added into the EP. The tensile strength, elongation at break, and elastic modulus of different corn starch contents were compared. The containing of corn starch showed a positive effect on the toughness of the epoxy but showed little effect on strength when the additive content was less than 10 wt%. The strength and elastic modulus increased first and then decreased with the increase in starch content and reached their maximum values at a content of 2.5 wt%. The enhancement effect might be due to corn starch’s mechanical properties, dispersibility, and interfacial interaction. With the increase in starch content, starch granules quickly contact each other, causing self-aggregation sedimentation and a decrease in strength and elastic modulus. The scanning electron micrographs of the toughened EP specimens showed ductile failure because of the starch particles. The surface morphology of the blend resin specimens was full of staggered and stepped cracks caused by the shearing damage, which is shown by obvious plastic fracture characteristics with plastic deformation ability. The initiation of micro-cracks in the EP matrix was induced by the incorporation of starch particles, which caused localized stepped shear damage in the matrix. More energy would be absorbed during this process, and the toughness of the EP would be enhanced. It is recommended that the best corn starch content should be 2.5 wt% to obtain excellent strength and good toughness.