Synchronous modification of ZIF-67 with cyclomatrix polyphosphazene coating for efficient flame retardancy and mechanical reinforcement of epoxy resin.

Cyclomatrix polyphosphazenes have attracted widespread attention in the field of polymer flame retardancy. Nevertheless, the optimal manifestation of their distinctive structural attributes and flame-retardant properties necessitates a judicious selection of condensation monomers and synergistic templates during the fabrication of polyphosphazene flame retardants. In our previous studies, it was discovered that when ZIF-67 is functionalized with polyphosphazene, the by-product HCl from phosphazene polycondensation causes etching on ZIF-67. Based on this "synchronous etching" effect, a series of hybrid materials comprising cyclomatrix polyphosphazene and ZIF-67, denoted as ZIF-67@PDS (PDS, poly-(cyclotriphosphazene-co-4,4'-diaminodiphenyl sulfone)), ZIF-67@PBS (PBS, poly-(cyclotriphosphazene-co-Bisphenol A)), and ZIF-67@PZS (PZS, poly-(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)), was synthesized utilizing DDS (4,4'-diaminodiphenyl sulfone), BPA (Bisphenol A), and BPS (4,4'-sulfonyldiphenol) monomers as precursors, respectively. Upon the incorporation of 2.0 wt.% of ZIF-67@PDS, ZIF-67@PBS, and ZIF-67@PZS, the flame retardant and mechanical characteristics of EP composites exhibited marked enhancement. The unique structural characteristics of hybrid and the synergistic effects of Co-P-N contribute to the improvement of comprehensive properties. Compared with pure EP, EP/ZIF-67@PZS has the best enhancement effect, and its pHRR, THR, and TSP decreased by 34.0%, 30.0%, and 40.5%, respectively. In terms of mechanical strength, ZIF-67@PZS also increases the flexural strength of EP by 37.42%. Relying on the "synchronous etching" effect, this study explores and verifies the effective combination of ZIF-67 and different types of polyphosphazenes, and obtains a series of ZIF-67-derived cyclomatrix polyphosphazene hybrids with different morphologies and properties in one step. It provides a new idea and strategy for the simultaneous modification of polyphosphazene materials and the preparation of multifunctional flame retardants in the future.

Study on Properties and Degradation Behavior of Poly (Adipic Acid/Butylene Terephthalate-Co-Glycolic Acid) Copolyester Synthesized by Quaternary Copolymerization.

At present, the development and usage of degradable plastics instead of traditional plastics is an effective way to solve the pollution of marine microplastics. Poly (butylene adipate-co-terephthalate) (PBAT) is known as one of the most promising biodegradable materials. Nevertheless, the degradation rate of PBAT in water environment is slow. In this work, we successfully prepared four kinds of high molecular weight polyester copolyesters (PBATGA) via quaternary copolymerization. The results showed that the intrinsic viscosity of PBATGA copolymers ranged from 0.74 to 1.01 dL/g with a glycolic acid content of 0-40%. PBATGA copolymers had excellent flexibility and thermal stability. The tensile strength was 5~40 MPa, the elongation at break was greater than 460%, especially the elongation at break of PBATGA10 at 1235%, and the thermal decomposition temperature of PBATGA copolyesters was higher than 375 °C. It was found that PBATGA copolyester had a faster hydrolysis rate than PBAT, and the weight loss of PBATGA copolymers showed a tendency of pH = 12 > Lipase ≈ pH = 7 > pH = 2. The quaternary polymerization of PBAT will have the advantage of achieving industrialization, unlike the previous polymerization process. In addition, the polymerization of PBATGA copolyesters not only utilizes the by-products of the coal chemical industry, but also it can be promising in the production of biodegradable packaging to reduce marine plastic pollution.

Influence of the Crystal Structure of Melamine Trimetaphosphate 2D Supramolecules on the Properties of Polyamide 6.

To explore the influence of the crystal structure difference of melamine trimetaphosphate (MAP) on the application performance of its polymer composites, an intumescent flame retardant with the optimal crystal type was designed and synthesized to improve the mechanical properties and flame retardancy of polyamide 6 (PA6). I-MAP and II-MAP were obtained using different concentrations of MA and sodium trimetaphosphate (STMP) in an acidic aqueous solution. The morphology, chemical composition, and thermal stability were comprehensively characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The dispersion, mechanical properties, and flame retardancy of PA6/I-MAP and PA6/II-MAP were evaluated by SEM, stress and strain, limiting oxygen index test (LOI), vertical burning test (UL-94), cone calorimetry (CONE) test, and char residue analysis. The conclusion is as follows: I-MAP and II-MAP have a greater influence on the physical properties of PA6 but less influence on the chemical properties. Compared with PA6/I-MAP, the tensile strength of PA6/II-MAP is 104.7% higher, the flame rating reaches V-0, and PHRR is reduced by 11.2%.

Multielement Flame-Retardant System Constructed with Metal POSS-Organic Frameworks for Epoxy Resin.

The direct coordination between polyhedral oligomeric silsesquioxane (POSS) and Co forms an assembly of nanoparticles with low specific surface area and leads to a poor dispersion state in the epoxy resin matrix, resulting in unsatisfactory flame-retardant efficiency. Metal-organic frameworks (MOFs), for instance, ZIF-67, provide not only the cobalt element but also the porous framework that endows the nanocomposite of MOFs and POSS with high specific surface area and abundant Co sites in the silica skeleton. Herein, ZIF-67 is hybridized with octacarboxyl POSS, resulting in the removal of the alkaline ligand to form novel metal POSS-organic frameworks (MPOFs). The size differences for organic groups and silica nanocages of POSS vs. micropores of ZIF-67 gave rise to a reverse click reaction, reforming octavinyl POSS isolated on the outer surface of the Co complex, which could be further modified by a phosphorous flame retardant using an addition reaction. The obtained MPOFs-P with 2 wt % loading in epoxy resin could improve the limiting oxygen index value of the composites to 27.0% and pass the V-0 rating in the UL-94 test. Meanwhile, the peaks of the heat release rate and especially the total smoke production were reduced by 46.6 and 25.2%, respectively. The robust char layer reduces the emission of toxic gas CO by 39.8%. The above epoxy product with promising flame retardancy also improved mechanical properties, thanks to the filler with a unique nanostructure. The ingenious work offers enlightenment for the hybridization method of MOFs and POSS to fabricate a multielement flame-retardant system for epoxy resin with high efficacy.

Precise Control of a Yolk-Double Shell Metal-Organic Framework-Based Nanostructure Provides Enhanced Fire Safety for Epoxy Nanocomposites.

Nanomaterials derived from metal-organic frameworks (MOFs) are highly promising as future flame retardants for polymeric materials. The precise control of the interface for polymer nanocomposites is taking scientific research by storm, whereas such investigations for MOF-based nanofillers are rare. Herein, a novel yolk-double shell nanostructure (ZIF-67@layered double hydroxides@polyphophazenes, ZIF@LDH@PZS) was subtly designed and introduced into epoxy resin (EP) as a flame retardant to fill the vacancy of yolk/shell construction in the field. Meanwhile, the interface of the polymer nanocomposites can be further accurately tailored by the outermost layer of the nanofillers from PZS to Ni(OH)2 (NH), by which hollow nanocages with treble shells (LDH@PZS@NH) were obtained. It is remarkably interesting that LDH@PZS@NH endows the EP with the lowest peak of heat release rate in the cone calorimeter test, but the total heat and smoke releases (THR and TSP) of the nanocomposites are even higher than those of the neat polymer. In contrast, EP blended with ZIF@LDH@PZS shows outstanding comprehensive performance: with 2 wt.%, the limiting oxygen index is increased to 29.5%, and the peak heat release rate is reduced by 26.0%. The impact and flexural strengths are slightly lowered, while the storage modulus is enhanced remarkably compared with that for neat EP. The flame retardant mechanism is systematically explored focusing on the interfacial interactions of different hybrids within the epoxy matrix, ushering in a new stage of study of nanostructural design-guided interface manipulation in MOF-based polymer nanocomposites.