Synergetic Effect of α-ZrP Nanosheets and Nitrogen-Based Flame Retardants on Thermoplastic Polyurethane

Abstract

A supramolecular self-assembly method was used to prepare melamine cyanurate/α-ZrP nanosheets (MCA@α-ZrP) as a novel hybrid flame retardant for thermoplastic polyurethane (TPU). Microstructure characterization showed a uniform dispersion with strong interfacial strength of the MCA@α-ZrP hybrid within the TPU matrix, leading to simultaneous enhancements in both mechanical and fire-safety properties. The TPU/MCA@α-ZrP nanocomposite exhibited 43.1 and 47.0% increments in tensile strength and fracture energy, respectively. Thanks to the platelike structure of α-ZrP coupled with the dilution effect of MCA (releasing nonflammable gases), the hybrid MCA@α-ZrP reduced the peak heat release rate of TPU by 49.7% in comparison with 15.8 and 35.4% for TPU/MCA and TPU/ α-ZrP composites, respectively. The fire performance index of TPU is significantly promoted by 90% upon adding the MCA@α-ZrP hybrid. Additionally, LOI and UL-94 tests showed high flame-retarding characteristics for the MCA@α-ZrP hybrid. For example, LOI increased from 20.0% for neat TPU to 25.5% for the MCA@α-ZrP hybrid system, and it was rated V-1 from the UL-94 test. Furthermore, the smoke production and pyrolysis products were significantly suppressed by adding the MCA@α-ZrP hybrid into TPU. Interfacial hydrogen bonding, the dilution effect of MCA, forming a "labyrinth" layer, and catalytic action of α-ZrP nanosheets synergistically improved both the mechanical performance and flame retardancy of TPU nanocomposites. This work provides a new example of integrating traditional flame retardants with functional nanosheets to develop polymeric nanocomposites with high mechanical and fire-safety properties.

Supramolecular-Wrapped α-Zirconium Phosphate Nanohybrid for Fire Safety and Reduced Toxic Emissions of Thermoplastic Polyurethane

“…The well-ordered lamellar structure usually improves the carbonization degree of char residues; this forms impermeable char layer which can stop/slow down the flow of volatile gases and mass heat to fortify the flames. 19 The flame-retarding mechanism will be elucidated in the following sections.…”

“…It is noteworthy to mention that the tensile strength of the ABS/La@PN-RGO composite increased by 16% without compromising its strain at break. Zirconium phosphate (α-ZrP) nanosheets were also studied as reinforcing filler and a FR additive; 19 α-ZrP nanosheets have high thermal stability and ion-exchange feature and are able to intercalate and/or exfoliate within the host matrix. Recent research showed that α-ZrP can act as an active solid acid catalyst to improve the flame retardancy of polymers due to its Lewis acid sites on its surface.…”

“…Therefore, modifying α-ZrP's surface by chemical surfactants before adding into a polymer was the focus of many studies. Han et al 19 self-assembled melamine cyanurate on the surface of α-ZrP sheets to form a nanohybrid MCA@α-ZrP; this nanohybrid was used as a reinforcing and flame-retarding filler for TPU matrix. Tensile strength and fracture energy of the TPU/MCA@α-ZrP composite increased by 43.1 and 47.0%, respectively.…”

“…Zirconium phosphate (α-ZrP) nanosheets were also studied as reinforcing filler and a FR additive; α-ZrP nanosheets have high thermal stability and ion-exchange feature and are able to intercalate and/or exfoliate within the host matrix. Recent research showed that α-ZrP can act as an active solid acid catalyst to improve the flame retardancy of polymers due to its Lewis acid sites on its surface. , However, the solid acid sites on α-ZrP sheets can facilitate polymer degradation at the beginning of fire, leading to fast weight loss.…”

Peelable Microwave Absorption Coating with Reusable and Anticorrosion Merits

“…Apart from the effect of the polymer matrix of peelable coatings on the tunable adhesion and cohesion, the performance (i.e., type, content, or structure) of the microwave absorber also affects the trade-off in adhesion and cohesion . The presence of microwave absorber can increase the cohesive strength and stiffness of coatings, which are associated with the control of adhesion. , The filler contents will inevitably affect the structural integrality and energy dissipation under the external force of the coating, − which is vital for the desirable peelability. Therefore, in view of the complex and diverse chemical/physical bonds and surface-interface interactions between the microwave absorber and polymer matrix of coating, developing a simple and novel peelable MA coating system is highly desired.…”