Abstract
To prepare flame-retardant epoxy resin, phosphorus compound containing di-hydroxyl group (10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phospha phenanthrene-10-oxide, DOPO-HQ) was reacted with uncured epoxy resin (diglycidyl ether of bisphenol A, YD-128) and then cured using a curing agent (dicyandiamide, DICY). This study focused on the effect of phosphorus compound/phosphorus content on physical properties and flame retardancy of cured epoxy resin. The thermal decomposition temperature of the cured epoxy resins (samples: P0, P1.5, P2.0, and P2.5, the number represents the wt% of phosphorus) increased with increasing the content of phosphorus compound/phosphorus (0/0, 19.8/1.5, 27.8/2.0, and 36.8/2.5 wt%) based on epoxy resin. The impact strength of the cured epoxy resin increased significantly with increasing phosphorus compound content. As the phosphorus compound/phosphorus content increased from 0/0 to 36.8/2.5 wt%, the glass transition temperature (the peak temperature of loss modulus curve) increased from 135.2°C to 142.0°C. In addition, as the content of phosphorous compound increased, the storage modulus remained almost constant up to higher temperature. The limiting oxygen index value of cured epoxy resin increased from 21.1% to 30.0% with increasing phosphorus compound/phosphorus content from 0/0 to 36.8/2.5 wt%. The UL 94 V test result showed that no rating for phosphorus compounds less than 19.8 wt% and V-1 for 27.8 wt%. However, when the phosphorus compound was 36.8 wt%, the V-0 level indicating complete flame retardancy was obtained. In conclusion, the incorporation of phosphorus compounds into the epoxy chain resulted in improved properties such as impact strength and heat resistance, as well as a significant increase in flame retardancy.
Highlights
Epoxy resins are most widely used as matrices in advanced composites because of their high tensile strength/modulus, low shrinkage on cure, high adhesive strength, good chemical/corrosion resistance, and excellent dimensional stability
The structure of DOPO-HQ was confirmed from characteristic peaks of 3650–3140 cm−1 (O–H), 1477 cm−1 (P–C), and 1184 cm−1 (P=O/P–O–C) (see Figure 1(b))
The structure of the reaction products of YD-128 and DOPO-HQ can be confirmed by the appearance of mixed characteristic peak of YD-128 and DOPO-HQ (see Figure 1(c))
Summary
Epoxy resins are most widely used as matrices in advanced composites because of their high tensile strength/modulus, low shrinkage on cure, high adhesive strength, good chemical/corrosion resistance, and excellent dimensional stability. Since conventional epoxy resins are flammable, they cannot be used for materials requiring high flame resistance.[1,2,3,4]. There are various methods of making the epoxy resin more flame retardant. Examples of the flame retardant include inorganic flame retardants, halogen flame retardants, organic phosphorus flame retardants, and combinations thereof. Considering avoiding the occurrence of environmental pollution a long time ago, the tendency was to use a halogen-free flame retardant.[5,6,7]
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