| Bisphenol A epoxy resin is widely used in adhesives,coatings and other fields due to their good adhesion properties,excellent mechanical properties and high chemical stability.However,there are series of high-density three-dimensional network structures between the molecules of epoxy resins after they are cured by curing agent due to the inherent rigid structure of bisphenol A epoxy resin.And the materials become brittle and have poor impact resistance,fatigue resistance and toughness so that their application in national production and life are severely restricted.In order to overcome these defects,the aim of this work is to develop some kind of epoxy resins or curing agents with excellent toughness,high strength,high modulus and good thermal stability.By using the conjugated double bond,ester bond,and allyl hydrogen of a specialty oil in China-tung oil,a series of chemical reactions such as Diels-Alder reaction,saponification reaction,and epoxidization were used to design or modify the molecules of epoxy resins and curing agents.Other nano-fillers such as carbon nanotubes was also blended with tung oil-based epoxy resins to acquire a system with the optimal properties.And the relationship between structures and properties were analysed in this study,the curing kinetics of some of the curing systems were discussed as well.1.The tri-functional glycidyl ester was synthesized from tung oil,and the product structure was confirmed by 1H NMR,13 C NMR and FTIR.The tung-oil-based triglycidyl ester(TOTGE)was blended with epoxy resin E51 and cured by latent curing agent 594.The properties of the cured product were studied by mechanical propety test and thermogravimetric analysis(TGA).The results showed that the elongation at break of the cured product was increased with the increasing of TOTGE content,indicating that the synthesized tung-oil-based epoxy resin had good flexibility.At the same time,the hardness,tensile strength and transform ation temperature of the cured product showed a downward trend.The initial decomposition temperature of the cured material was up to 400oC or more,with excellent thermal stability.2.A robust and tough MWCNTs-TEPA/TOTGE nanocomposites from the TOTGE,and functionalized multi-walled carbon nanotubes(MWCNTs)were made as reinforcing phases by grafting of tetraethylenepentamine(TEPA)on MWCNTs(MWCNTs-TEPA).The prepared MWCNTs-TEPA were characterized using TGA and X-ray photoelectron spectroscopy(XPS).The analyses results showed that TEPA molecules were successfully grafted on MWCNTs.As a consequence of the covalent interactions between MWCNTs and TOTGE,the MWCNTs-TEPA uniformly dispersed in TOTGE,and the MWCNTs-TEPA/TOTGE composites showed significantly improved mechanical properties as compared to neat tung-oil-based epoxy resin.With the addition of 1.5 wt% MWCNTs-TEPA,the tensile strength,elongation at break,Young's modulus and toughness of the composites were improved by 18.14%,209.54%,8.49% and 465.71%,respectively.The dynamic mechanical properties and thermal stabilities of composites were also demonstrated.A commercial bisphenol A epoxy resin E51 was used as control in this study.Results indicate that the MWCNTs-TEPA/TOTGE composite with 1.5% content had overall superior performances to that of E51.It is worth noting that the pure tung-oil-based epoxy resin exhibited the same tensile strength,elongation at break,Young's modulus and toughness as E51.3.The two kinds of anhydride curing agents made by our laboratory which named N,N-m-phenylene dimaleimide tung oil polyimide anhydride(HVAT anhydride)and N,N-4,4-diphenylmethane bimaleimide tung oil polyimide anhydride(BMIT anhydride)were prepared from tung oil.They were used as heat resistant curing agent,and the curing reaction behavior of two kinds of tung oil polyimide anhydride-epoxy curing systems were discussed.The curing kinetics and curing process of tung oil polyimide anhydride-epoxy curing systems and tung oil anhydride-epoxy curing system were all comparative studied by non-isothermal differential scanning calorimetry(DSC)technique at different heating rates,the results indicated that the Kissinger's methods for calculating the apparent activation energy value gave the results of 89.54,85.42 and 84.78 k J/mol,respectively.The reaction orders were calculated with the Crane equation,which were all 0.92.Finally the extrapolation method was introduced to determine the most optimal curing process conditions of these three curing systems,which were all 100oC/2 h+120oC/2 h+150oC/1 h.At the same time,mechanical performance analysis showed that the tensile strength of tung oil polyimide anhydride-epoxy curing systems were 36.42 and 38.60 MPa,respectively;the bending strength were 57.19 and 46.68 MPa,respectively;and the compressive strength were 108.15 and 116.97 MPa,respectively.So the comprehensive mechanical properties of tung oil polyimide anhydride-epoxy curing systems significantly stronger than tung oil anhydride-epoxy curing system whose tensile strength,bending strength,compressive strength and compressive strength were 10.65 MPa,5.51 MPa,53.22 MPa and 6.61 MPa,respectively;the Tg of HVAT anhydride-epoxy curing system(99.60oC)and the Tg of BMIT anhydride-epoxy curing system(91.96oC)are significantly higher than the tung oil anhydride-epoxy curing system(57.63oC).And the shapes of thermogravimetric curves of HVAT anhydride and BMIT anhydride curing systems are both consistent,the heating initial decomposition temperatures were 395.3oC and 396.9oC,respectively.The slope of thermogravimetric curves of the first two are significantly smaller than the TOA curing system with the increase of temperature,which all shows that tung oil polyimide anhydride-epoxy curing systems possess better heat resistance than tung oil anhydride-epoxy curing system does. |
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