A kind of novel silicon-, phosphorus-containing hybrid material and its use as the modifier of DGEBA epoxy resins

Abstract

As an important packaging material, much work has been done in an attempt to improve DGEBA epoxy resins to be used in electric industry. In order to improve heat resistance, the cross-linking density of epoxy resins has been attempted to increase, or rigid groups have been introduced to copolymerize with epoxy resin. However, these methods have been confirmed that they will induce friability. In addition, as Si-O-Si bonding is more flexible than C-C bonding, siloxane oligomer is introduced to the matrix to improve toughness of epoxy resins, but the glass transition temperature (Tg) becomes lower by reason of low compatibility between epoxy resin and siloxane. Moreover, the pure epoxy resins are flammable. It is worth notice that halogen-containing resins are considered to limit the use by reason that they will release toxic gases while heating. Phosphorus-containing epoxy resins could substitute for halogen-containing resins for the use of flam-retardant. The introductions of phosphoric ethers, DOPO or its derivatives to the matrix have been reported. Such methods are confirmed to improve flam-retardant with epoxy, but The decreasing of heat resistance and toughness can't be ignored when too much phosphorus is in the resins. From the above, it is known that present achievements can improve the property of epoxy resins at one side, but they can not improve or at least keep the other properties. In this study, a kind of novel silicon, phosphorus-containing hybrid material was prepared and it could be used as the modifier of DGEBA epoxy resins. The thermal stability, toughness and flam-retardant of the modified resins were all improved. For one thing, the hybrid material was mainly composed of polysiloxane, and the Si-O-Si chains in the matrix would improve toughness for the resins. For another, the hybrid material contained a lot of hydroxyl groups in the structure. The compatibility with epoxy resins and the modifier is good. The Si-OH groups in the hybrid material could react with the hydroxyl groups in DGEBA when the resins were cured. The heat resistance was improved on account of higher cross-linking density of the resins. What's more, phosphorus-containing groups were introduced in the hybrid material. P and Si could both act to exhibit the considerable synergistic effect on flam-retardant even though the weight of P was low. In this paper, the thermal, mechanical and flammable properties of the cured samples were investigated in detail by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), as well as tensile, impact and limited oxygen index (LOI) testing. The result showed that the hybrid modified epoxy resins exhibited good thermal stability, toughness and flam-retardant property. With the ratio m(DGEBA) : m(SPCH)=100 : 25, Tg of the modified sample was 49.35 °C higher than that of the pure sample, and LOI was raised from 21.5 to 29.8. The char yield of E-25 at 800°C reached to 37.8 %, which compared to 12.9 % of the pure sample. But the toughness of E-25 was not so prominent if compared with E-15. The impact stress of sample E-15 reached to 24.1 kJ·m-2. For all modified samples, the tensile strengths were all basically maintained. SEM micrographs of the fracture surfaces indicated that these modified resins were homogeneous and tough. In the practical application, the different ratios of the modifier in epoxy resin were chosen with actual demand.