Microencapsulation and Surface Functionalization of Ammonium Polyphosphate via In-Situ Polymerization and Thiol–Ene Photograted Reaction for Application in Flame-Retardant Natural Rubber

Abstract

A novel type of microencapsulated ammonium polyphosphate (MAPP) with a triallyl cyanurate (TAC)/SiO2 double-layered shell was synthesized through in-situ polymerization, followed by the thiol–ene photograted reaction. With a double bond in the TAC outer shell, MAPP could be utilized as a highly efficient flame retardant for intumescent flame-retarded natural rubber (NR). The chemical structure, morphology, and performance of MAPP were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, water contact angle (WCA), scanning electron microscopy, and thermogravimetric analysis. MAPP exhibited a hydrophobic feature with a WCA of 101° because of its organic outer shell, which made MAPP well dispersed in the NR matrix as well as enhanced the compatibility between the MAPP and NR matrix. The resulting intumescent flame-retardant NR compounds not only achieved excellent flame-retardant performance but also obtain improved mechanical properties because of the presence of 3D-cross-linking networks between the MAPP and NR matrix. The NR/MAPP compounds also presented good water resistance because of the microencapsulation of APP with an SiO2 inner shell, which provided a waterproof barrier for APP. Based on the cone calorimetric results, the NR/MAPP compounds also presented a decline in total heat release and heat release rate but an improvement in ignition time due to the fact that both the SiO2 inner layer and TAC outer shell could enhance the formation of a high-strength thermally stable char layer during combustion, thus preventing heat transmission and diffusion. The significant enhancement in flame-retardant performance was principally ascribed to the synergistic char-forming effect derived from the APP core and TAC/SiO2 shell. This work provides a new idea for development of APP-based flame-retardant additives and also explores their potential applications in intumescent flame-retardant polymeric systems.

Synthesis and Characterization of Aluminum 2-Carboxyethyl-Phenyl-Phosphinate and Its Flame-Retardant Application in Polyester

“…With an increasing CPA-Al ratio in polyester textile, the contact angle gradually decreased from 123.6 • to 75.6 • . Due to the carboxyl functional group of CPA-Al being a hydrophilic group, the contact angle of polyester textile will be reduced, indicating that the polyester textile changed their surficial property from hydrophobic to hydrophilic [42][43][44]. That is why the amounts of water vapor permeation gradually increased [45].…”

Enzymatic and Chemical Approaches for Post‐Polymerization Modifications of Diene Rubbers: Current state and Perspectives

“…Moreover, the thiol-ene reactions are frequently employed to introduce "clickable" functional groups in the polymer backbone. Rubber functionalization through thiol-ene click reactions also include modulation of the polymer hydrophobicity by introduction of polar groups, [142][143][144] introduction of inorganic materials, [63,145] improvement of the dispersion of nanomaterials, [137,146,147] polymer coating, [148] introduction of biomolecules, [149][150][151][152] synthesis of patterned microstructures, [153,154] linking of ionic liquids, [155] and introduction of dynamic hydrogen bonds for self-healing properties. [143,[156][157][158] Some biological applications include preparation of antibacterial materials, [159,160] surface preparation to protein adsorption [161] and synthesis of chiral materials by introduction of chiral amino acids.…”

Rigid Polyurethane Foams Containing Modified Ammonium Polyphosphate Having Outstanding Charring Ability and Increased Flame Retardancy

“…They have been widely used in many polymer-based materials. As a typical phosphorusand nitrogen-containing halogen-free flame retardant, APP has been widely used in many polymers including RPUF (Deodhar et al, 2011;Hazer et al, 2019;Wu et al, 2019). The degree of polymerization is an important factor affecting the flame retardancy of APP and also affects the compatibility between APP and the polymer matrix.…”