Abstract
Thermoplastic and thermosetting modifications on epoxy resins were investigated in this study. Thermoplastic Phenoxy and Polycarbonoate were utilized to toughen epoxy by hot melt method and thermosetting cyanate ester was used to modify epoxy by solvent method.The miscibilities of Nylon-6、Nylon- 66、PBT、PET、PC、PPS、PPO and Phenoxy are suitable to toughen epoxy by hot melt method. Thermal and mechanical properties of epoxy toughened by Phenoxy、PC and blocked PU were investigate. Tensile strength shows a maximum value at 10phr of plastics content. Flexural strength and flexural modulus depend on the plastics used，however，the variation of data is small when plastics content is below 15phr plastics content except blocked PU，both properties decrease obviously when blocked PU added to epoxy. The fracture toughness properties epoxy modified by Phenoxy，Polycarbonate and blocked PU were studied. The toughening mechanism of the systems was investigated. Different crack patterns were observed on the test specimens with different plastic contents. The toughness of a toughened material is affected by the amount of particles，the miscibility of particle and matrix material and the property of matrix material. Under dynamic condition，the epoxy resin containing 10 phr blocked PU or 10 phr Phenoxy showed good toughness. On the other hand，the effect of adding Polycarbonate on toughness of epoxy resin is insignificant.Under quasi-static condition (KIC's test)，the best toughening result of resin by adding blocked PU and Polycarbonate was obtained at 15 phr and 10 phr，respectively. The toughening effect is insignificant by adding Phenoxy in epoxy.The toughening mechanism was investigated by SEM photographs of the fracture surface morphology. The toughening mechanism of the systems was confirmed by the Tg measurement.The BPT/BPZ/BPF/BPA-phenoxy resins are synthesized by various aromatic dihydroxyl monomers and DER 332 with an arylphosphonium salt catalyst﹒The in-situ fusion reaction is performed at a temperature ranging between 225~230℃ for 30 minutes. From the DSC and TGA analyses results，BPT-phenoxy and BPZ-phenoxy possess higher thermal properties than BPF-phenoxy and BPA-phenoxy from the perspectives of the steric hindrance of the molecular structure﹒Comparing toughness of the blend systems，it shows that BPA-phenoxy and BPZ-phenoxy have higher toughness than that of BPF-phenoxy and BPT-phenoxy﹒The bond strength of the compositions shows that the BPF-phenoxy and BPT-phenoxy possess a higher lap adhesive strength than BPA-phenoxy and BPZ-phenoxy﹒The synthesized tetrafunctional aliphatic epoxy resin had an epoxy equivalent weight of 382，Mn of 1492 and Mw of 2296 and a viscosity of 4.2 poise at 25 ℃. The tetrafunctional aliphatic epoxy blended Epon 828(epoxy) with a hardener will cause a crosslinking reaction.The blended system exhibits a higher toughness，good mechanical properties and slightly depressed glass transition temperature.The blended system also exhibits good compatibility，consequently，the impact strength was improved significantly and it shows stress-whitening clearly，but no visible flexible deformation occurs.The curing behavior of blends of cyanate ester with the epoxy resin(195xl) was studied by means of differential scanning calorimetry(DSC). From the DSC analyses results，two exothermic peaks are observed and the content of epoxy resin is near 70 phr.Epoxy-cyanate blends have low mechanical properties compared to conventional cyanate ester. The mechanical properties decreased gradually with increasing epoxy concertration.Previous results obtained on blends of cyanate ester with the epoxy resin systems were confirmed that the same chemical groups(triazine，isocyanurate and oxazolidinone) are observed on FTIR spectra. It was found that more chain-extending reaction(oxazolidinone groups) for titanate-catalyzed networks.