Solvent-Free Synthesis of Organic–Inorganic Polyphosphoramide-Halloysite Nanohybrids for Thermally Stable and Fire-Resistant Polylactide

Abstract

Biodegradable and renewable polylactide (PLA) exhibits excellent mechanical properties but is prone to high flammability, limiting its application to textiles, electronics, and packaging. In PLA, polyphosphoramides have shown their exceptional fire-retardant properties, but their existing synthesis methods often involve toxic solvents. Despite high efficiency, recently, polyphosphoramides prepared via green synthesis led to a reduced thermal stability of PLA. Herein, we report a series of organic−inorganic hybridized polyphosphoramides-halloysite nanotube nanohybrids (DM-OHn) via a one-pot solvent-free copolymerization. The results show that addition of only 1.5 wt % DM-OH16 leads to a 5 °C increase in the initial decomposition temperature of PLA and enables the latter to achieve a desired UL-94 V-0 rating and a high limiting oxygen index (ca. 32.6%), in addition to a well-preserved tensile strength. This work provides an eco-benign green strategy for the design of organic−inorganic polyphosphoramides nanohybrids for creating fire-retarding PLA with improved thermal stability and preserved mechanical strength, which are expected to be used as sustainable fireproof bioplastics for industrial applications.

Enhanced Flame Retardancy, Ultraviolet Shielding, and Preserved Mechanical Properties of Polylactic Acid with Fully Biobased Multifunctional Additives by a Green Method

“…23 Feng et al synthesized organic−inorganic hybridized polyphosphoramide-halloysite nanotube nanohybrids (DM−OH n ) and showed that the addition of only 1.5 wt % DM−OH 16 enabled PLA to achieve the UL-94 V-0 rating. 24 Xu et al designed a new phosphaphenanthrene-benzimidazole derivative (D-AB), which resulted in a satisfactory UL-94 V-0 rating and high limiting oxygen index (LOI) of 30.5% for PLA with 5 wt % content of D-AB, as well as improved its melt-dripping behavior. 25 These FRs can effectively improve the flame retardancy of PLA.…”

Rethinking the pathway to sustainable fire retardants

“…[64] More recently, Feng et al reported a one-step solvent-free approach for synthesizing polyphosphoramide fire retardants that endow PLA with excellent flame retardancy. [12][13][14] For this green yet facile synthesis strategy, no post-treatment is involved, including products purification and solvent waste disposal. For these eco-friendly advantages, a growing number of attempts focusing on green solvents or solvents-free methods for FRs synthesis should be encouraged, expediting the real-world application of these green approaches in industry.…”

“…Another example is methanol formed in the green synthesis of polyphosphoramides based on amine ester exchange reaction. [12][13][14] The only by-product methanol can be collected via vacuum pumping system and reused. Thus, it is advisable to make more efforts to convert the chemical waste to resources.…”

“…[11] In addition, researchers have reported green synthesis of FRs, for example, aqueous solution and solventless synthetic routes. [12][13][14] The elimination of toxic solvents greatly contributes to minimizing environmental hazards and potential worker exposure. Moreover, scientists have started to assess toxicological profiles of some organophosphorus FRs.…”

Functionalized Mesoporous Silica Fire Retardant via Hierarchical Assembly for Improved Fire Retardancy of Unsaturated Polyester

“…Unsaturated polyester (UP) is widely used in transportation, building materials, and electrical insulation and has become a valuable engineering resin because of its superior mechanical resistance, excellent electrical insulation, and ease of processing. − Since neat UP is flammable, its applications are greatly limited, thus leading to an increasing demand for flame-retardant UP. Incorporating flame-retardant additives into the UP matrix is a convenient way to obtain flame-retardant UP materials. − Traditionally, halogenated flame retardants were widely used; however, with an increasing awareness of environmental protection, halogen-free flame retardants have become increasingly popular for UP, including two-dimensional materials, − intumescent flame retardants, , and organophosphorus flame retardants. − Due to their high efficacy, low toxicity, and good compatibility with the polymer matrix, organophosphorus flame retardants have become viable flame retardants. − Zhao et al synthesized a poly­(hydroxyphenyl imino methyl phenol spirocyclic pentaerythritol diphosphonate), and its addition into UP led to a limiting oxygen index (LOI) value of 28.2% and a UL 94 V-0 rating in the resultant flame-retardant UP as well as a sharp decrease in the peak heat release rate (PHRR) by 60%, demonstrating a dramatic enhancement in flame retardancy. Liquid organophosphorus flame retardants have some shortcomings, even though previous studies have shown that they can enhance flame retardancy.…”