# One-Pot Preparation of Easily Dispersible Hexagonal Mg(OH)2 Modified with THPS and Its Flame-Retardant EVA Copolymer

## TL;DR

This paper describes a new method to modify magnesium hydroxide with THPS to improve its flame-retardant properties in EVA polymer composites.

## Contribution

A one-pot hydrothermal method to modify Mg(OH)2 with THPS, enhancing flame retardancy and reducing smoke production in EVA.

## Key findings

- THPS-modified Mg(OH)2 achieved a V-0 rating and an LOI value of 31.3% in EVA composites.
- The composite showed a 62.2% reduction in total smoke production compared to unmodified Mg(OH)2.
- The modification improved dispersion and formed a protective layer during combustion.

## Abstract

As an eco-friendly flame-retardant additive, magnesium hydroxide (MH) is widely employed in low-smoking, halogen-free polymer materials due to its environmentally benign nature. In order to enhance flame retardancy performance, the modified MH was modified with tetrakis(hydroxymethyl)phosphonium sulfate (THPS) by a one-pot hydrothermal method. The resulting morphology was characterized using scanning electron microscopy (SEM), and it shows the dispersion of nanometer particles and almost no aggregation. The X-ray photoelectron spectroscopy (XPS) along with Raman spectroscopy show that the THPS is connected with the Mg(OH)2 by chemical bond. The sample was incorporated into ethylene–vinyl acetate (EVA) to evaluate the flame retardancy was assessed via limiting oxygen index (LOI) and vertical burning tests (UL-94). The results show that THPS modified MH effectively enhanced the flame retardancy, achieving a V-0 rating and an LOI value of 31.3%. In addition, the composites retain good mechanical integrity. The thermal analysis with TGA and DTG shows the formation of the MgO decomposition product, along with water vapor and phosphorus-containing radicals released by modified MH in the combustion process, forming a strong flame-retardant protective layer. In addition, the maximum smoke density of EVA/MHP-3 composite was 155.4, lower than 411.3 for EVA/MH, with a 62.2% reduction in total smoke production. The result shows that THPS is effective for improving the flame-retardant efficiency of inorganic metal hydroxide in polymer composites.