Abstract
The flame retardancy of an engineering plastic, poly(butylene terephthalate) (PBT), with a biobased flame retardant (FR) made from phosphorylated linseed oil (PLO) and phosphorylated downstream corn oil (PCO) was studied. Different phosphorus moieties were incorporated into the vegetable oil backbone through a ring-opening reaction. The chemical structure of the phosphorylated oil was confirmed by Fourier-transform infrared (FTIR) and nuclear resonance magnetic (NMR) spectroscopy. It was found that the incorporation of only 7.5 wt% of PLO was sufficient to change the UL-94 fire class of PBT from non-rating to V-0. The flame-retardancy mechanism of the PBT/PLO blends was evaluated from TGA-FTIR analysis. The combined effects of the gas phase mechanism and the dripping tendency of the blends aided to retard the flame propagation effectively. As the synthesized PLO and PCO contained high free fatty acids, the acid-ester exchange reaction occurred in the blends to form oligomers during the ignition. As a result, the blend dripped immediately and the drips carried all the heat to prevent fire. This work suggests that this sustainable biobased FR could be a desirable alternative to halogen-based FRs for PBT and other engineering polymers to develop more environmentally friendly FR products for various future applications.
Highlights
The flame retardancy of an engineering plastic, poly(butylene terephthalate) (PBT), with a biobased flame retardant (FR) made from phosphorylated linseed oil (PLO) and phosphorylated downstream corn oil (PCO) was studied
This includes the use of hybrid metal and phosphinate salts[4,6,7], aluminium hypophosphites (AHP)[5,8], aryl phosphates/novolac[9], phosphorus-intumescent FR compounds10, 9,10-dihydro-9-ox a-10-phosphaphenanthrene-10-oxide (DOPO)-based FRs11, brominated-organic compound-antimony trioxide (Sb2O3)[12,13], and brominated compounds[14,15]
Properties Acid value Hydroxyl value Weight percentage of phosphorus calculated from 1H nuclear magnetic resonance (NMR) Weight percentage of phosphorus measured by Inductively coupled plasma optical emission spectroscopy (ICP-OES)
Summary
The flame retardancy of an engineering plastic, poly(butylene terephthalate) (PBT), with a biobased flame retardant (FR) made from phosphorylated linseed oil (PLO) and phosphorylated downstream corn oil (PCO) was studied. Poly(butylene terephthalate) (PBT) is an important engineering plastic which is widely used in many structural components, such as electronic housing, insulators and auto parts This is due to its high mechanical strength, good dimensional stability, rapid crystallization rate (desirable for injection molded parts) and high heat deflection temperature[1,2]. Most of the conventional FRs available in the market are still based on halogen-containing compounds These FRs are very effective to impart flame retardancy in plastic materials, they generate toxic gases (hydrogen halides, HCl, HBr) and smoke upon burning. Fox et al.[18] developed effective biobased FRs from phosphorylated modified cellulose fibers for poly(lactic acid) (PLA) composites They observed considerable enhancements in flame retardancy of PLA after the addition of modified cellulose. Other green FRs, such as protein, chitin, etc., have been highlighted and review by Sonnier et al.[20]
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