A Gas-Steamed Route to Mesoporous Open Metal-Organic Framework Cages Enhancing Flame Retardancy and Smoke Suppression of Polyurea

Improving the Flame Retardancy and Mechanical Properties of Vinyl Ester Resins through Maleated Epoxidized Corn Oil/Epoxy Resin Additives for Sustainable Thermoset Composites

Thermoset polymers serve a significant role in modern industrial applications, and with a global annual output of over 65 million tons to meet this growing demand for sustainable materials, scientists and engineers need to go beyond what makes a material best for a certain use. Vinyl ester (VE) is a thermosetting polymer derived from polyester and epoxy resin. Its mixing properties distinguish it from its competitors, offering advantages in terms of curing efficiency, wettability, corrosion resistance, and low cost, which are crucial for modern industrial applications. Researchers have continuously explored the modifications of the intrinsic properties of VE using additives to enhance its flame retardancy and mechanical characteristics for more cost-effective and environmentally friendly materials applicable across various industries. In this study, we developed an easy-to-process eco-thermoset blend additive (50% v/v), known as maleated epoxidized corn oil/epoxy resin (MEPECO). Adding an optimal amount of MEPECO (5%) to the VE resin significantly improved its flame retardancy properties, as assessed by pyrolysis-combustion flow calorimetry, contact angle measurements, and thermogravimetric analysis. The mechanical properties, specifically strength, also showed substantial enhancement with the same optimal amount of MEPECO, as determined by flexural testing and spectral analysis. However, during the digestion of the eco-thermoset resin, the modulus and impact energy were notably lower owing to shear-yielding localization, as evidenced by the morphological analysis. This paper presents a novel in situ and straightforward technique for the easy and effective blending of eco-thermoset additives into petroleum-based epoxy resins, thereby facilitating their potential application in the development of sustainable green composite materials.

Joint Exfoliation of MXene by Dimensional Mismatched SiC/ZIF-67 Toward Multifunctional Flame Retardant Thermoplastic Polyurethane

The single-layer MXene fully demonstrates the advantages of 2D materials, especially catalytic, conductive, and mechanical properties. However, the high energy consumption and low efficiency faced by MXene in the divestiture process are still challenges that need to be solved urgently. In this article, dimension mismatch and collaborative stripping strategies are skillfully combined to easily realize the transformation from multi-layer MXene to single layer. In addition, the functionalized MXene@SiC@polyaniline (MXene@SiC@PANI) nano-hybrid materials are used as fillers to improve the thermal conductivity, flame retardant, and antibacterial properties of thermoplastic polyurethane (TPU). The surface temperature of TPU/MXene@SiC@PANI composites increased from 33.4 °C to 59.8 °C within 10 s. In addition, the antibacterial efficiency of TPU composites against Escherichia coli and Staphylococcus aureus is 69.6% and 88.9%, respectively. Compared with pure TPU, the peak heat release rate and total heat release are reduced by 71.4% and 34.6%, respectively. The flame-retardant mechanism of MXene hybrid materials is systematically discussed. It is worth noting that the introduction of PANI enhances the compatibility between the filler and the polymer, effectively maintaining the mechanical properties of the TPU itself. This work provides a convenient method for the multi-functional practical application of TPU.

Structure of Metal-Organic Frameworks Eco-Modulated by Acid-Base Balance toward Biobased Flame Retardant in Polyurea Composites

Biobased-functionalized metal-organic frameworks (Bio-FUN-MOFs) stand out from the crowd of candidates in the flame-retardant field due to their multipathway flame-retardant mechanisms and green synthesis processes. However, exploring and designing Bio-FUN-MOFs tend to counteract the problem of compromising the flame-retardant advantages of MOFs themselves, which inevitably results in a waste of resources. Herein, a strategy in which MOFs are ecologically regulated through acid-base balance is presented for controllable preparation of Bio-FUN-MOFs by two birds with one stone, i.e., higher flame-retardant element loading and retention of more MOF structures. Specifically, the buffer layer is created on the periphery of ZIF-67 by weak etching of biobased alkali arginine to resist the excessive etching of ZIF-67 by phytic acid when loading phosphorus source and to preserve the integrity of internal crystals as much as possible. As a proof of concept, ZIF-67 was almost completely etched out by phytic acid in the absence of arginine. The arginine and phytic acid-functionalized ZIF-67 with yolk@shell structure (ZIF@Arg-Co-PA) obtained by this strategy, as a biobased flame retardant, reduces fire hazards for polyurea composites. At only 5 wt % loading, ZIF@Arg-Co-PA imparted polyurea composites with a limiting oxygen index of 23.2%, and the peaks of heat release rate, total heat release, and total smoke production were reduced by 43.8, 32.3, and 34.3%, respectively, compared to neat polyurea. Additionally, the prepared polyurea composites have acceptable mechanical properties. This work will shed light on the advanced structural design of polymer composites with excellent fire safety, especially environmentally friendly and efficient biobased MOF flame retardants.