Microfluidic fabrication of polysiloxane/dimethyl methylphosphonate flame‐retardant microcapsule and its application in silicone foams

Abstract

A novel and versatile route for fabricating flame‐retardant microcapsules via microfluidics technology is reported. The flame‐retardant microcapsules were prepared with a dimethyl methylphosphonate (DMMP) core and an ultraviolet‐curable (UV‐curable) polysiloxane shell. Furthermore, a UV‐curable polysiloxane was synthesized. The synthesis mechanism of UV‐curable polysiloxane and the curing mechanism of flame‐retardant microcapsules were analyzed. To verify that DMMP was encapsulated in the microcapsules, X‐ray fluorescence was used before and after microencapsulation. The resulting microcapsules were well monodispersed and exhibited a good spherical shape with a smooth surface. In addition, the size of the microcapsules decreased dramatically with an increasing flow‐rate ratio of the middle‐/inner‐phase or outer‐phase flow rate. The thermal stability of the microcapsules was worse than shell materials but superior to DMMP. Silicone foams (SiFs) with microcapsules prepared using a dehydrogenation method achieved a relatively higher limiting oxygen‐index value than the pure SiF, which indicated that the microcapsules could enhance the flame retardation of SiFs effectively. Because of the polysiloxane shell, the microcapsules had good compatibility with SiFs, and the influence of microcapsules on the mechanical properties of SiFs was unremarkable.

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

“…To this end, an encapsulation approach was applied to address the above-mentioned challenges. , An encapsulated shell can improve the flame retardancy of organophosphorus flame retardants through synergistic effects. Kang et al used polysiloxane as a shell to encapsulate dimethyl methylphosphonate (DMMP) to achieve improved thermal stability after encapsulation within the microcapsules, compared to DMMP. Boonkongkaew and Sirisinha reported bisphenol-A bis­(diphenyl phosphate) (BDP) encapsulated within halloysite nanotubes (HNT) for polyamide 6 and were successful in retaining the thermal stability and the mechanical strength of polyamide 6 without reducing the elastic modulus.…”

Comparative Study of M(Ⅱ)Al (M=Co, Ni) Layered Double Hydroxides for Silicone Foam: Characterization, Flame Retardancy, and Smoke Suppression

“…Among them, adding flame-retardant fillers method is relatively simple and has a low cost. However, the high loadings and low flame-retardant efficiency limit its application [ 43 , 50 , 51 , 52 ]. In our previous work [ 53 ], the addition of transition-metal-containing NiTi-LDH was able to significantly improve the flame retardancy and smoke suppression of SiF.…”

Flame retardancy effects between expandable graphite and halloysite nanotubes in silicone rubber foam

“…The flame retardancy of SiF is mainly improved through flame retardant compounds, 20 microencapsulation 21 and layer-by-layer self-assembly. 22 Deng et al 23 studied the flame retardancy of SiF by compounding ultrafine aluminum hydroxide (ATH) with ultrafine calcium carbonate (CC).…”

“…Kang et al 24 applied superfine talc powder (SFT) hollow glass beads (HGBs) as flame retardants, and when 10 wt% SFT or 5 wt% HGBs was added, SiF was classified as The UL-94-V0. Kang et al 21 prepared a KH550-coated dimethyl methyl phosphonate (DMMP) microcapsule by means of microchannel UV curing using DMMP as the core and γ-methylacryloxy propyltrimethoxysilane (KH570) as the shell. When 15 wt% microcapsules were added, the SiF LOI reached 31.6%, and the material was classified as UL-94-V0.…”