Microfibrous cyclodextrin boosts flame retardancy of poly(lactic acid) II - phosphorous silane treatment further enhances the effectivity

Abstract

Recently, the flame retardant effectiveness of a 2-hydroxypropyl-β-cyclodextrin (CD) type bio-based carbonising agent has been evinced to noticeably increase when used in a microfibrous form, as obtained by electrospinning method. In the present research, the flame retardant performance of the electrospun CD was further enhanced by reactive surface modification with a phosphorous silane (PSil) compound. Surface-treated and untreated CD-based carbonising agents were compared, both in powder and in microfibrous form, besides ammonium polyphosphate (APP) to form an intumescent flame retardant system for poly(lactic acid) (PLA). The Limiting Oxygen Index (LOI) of the flame-retarded PLA composites increased outstandingly, from 25.0% (corresponding to the 15 wt% APP containing PLA) to as high as 37.5%, as a result of adding only 3 wt% of PSil-treated microfibrous CD to the system. Also, the main combustion characteristics improved; compared to neat PLA, about 50% reduction in the peak heat release rate (pHRR) and 25% reduction in total heat release (THR) were achieved, accompanied by an increased amount of char residue after combustion. The beneficial effect of the PSil-treated CD microfibre relies mainly on its enhanced physical and chemical interaction with APP and its increased charring ability and thermal stability, which contribute to the formation of a fire protecting char of increased structural integrity.