Preparation And Characterization Of Disulfide-containing Bio-based Epoxy Resins

Epoxy resins are widely used in coating,adhesive and composite materials due to considerable advantages including dimensional stability,chemical resistance and improved thermomechanical property,compared with traditional thermoplastics caused by their covalently cross-linked network.However,the traditional epoxy resins contain three main disadvantages: firstly,the raw material of epoxy resins root in fossil oil,which results in many environmental questions;secondly,the highly cross-linked structure also leads to the difficulties in reprocessing aspect(for example reshaping or recycling)once discarding making a lot of waste;thirdly,the cross-linked epoxy resins also results in the brittle property after full curing.As a result,once the thermoset epoxy resins were suffered from damage,they always been treated as wastes and dumped as landfill or incinerated,which significantly increased the overall material cost and brought in serious environmental concerns.Thus providing cured epoxy resins with self-healing property,reprocess ability and flexibility is of great importance from practical point of view.In this thesis,firstly,the bio-mass epoxy resins(IS-EPO)was synthesized by the reaction of isosorbide with ECH in the presence of sodium hydroxide and test its all kinds of properties.Secondly,IS-EPO was cured by two types of aromatic curing agents,which were MDA(without disulfide bonds)and MDS(with disulfide bonds)to obtain the MDA-EPO and MDS-EPO resins.After this,their properties were characterized.Thirdly,different content of ionic liquid MDS-EPO were prepared by adding different mass ionic liquid into MDS-EPO and their properties were characterized.IS-EPO was synthesized by the reaction of isosorbide with ECH in the presence of 50wt% sodium hydroxide.Fourier transform infrared spectroscopy(FT-IR)spectra and Nuclear Magnetic Resonance spectrometer(NMR)were used to identify the chemical structure of IS-EPO.The molar mass and molar mass distribution of IS-EPO were determined using Electro-spray ionization mass spectra(ESI-MS)and Gel Permeation Chromatograph-Laser Light Scattering Spectrometer.Epoxide number was tested by HCl-dioxane titration.The results showed that there were more than one component were present in IS-EPO and the monomeric and dimeric isosorbide diglycidyl ether were the main products of IS-EPO.The epoxy value were 0.32 g/mol and 0.56 g/mol,respectively.The suitable curing temperature was probed by Differential scanning calorimetry(DSC).MDS-EPO and MDA-EPO were prepared by curing equivalent amounts of IS-EPO and MDS or MDA with suitable temperature process,respectively.FT-IR spectra and DSC were used to decide whether the MDS-EPO and MDA-EPO were cured completely.The DSC,Thermogravimetric analysis(TGA)and Dynamic mechanical analysis(DMA)were used to characterize thermal and creep properties of the resin.Stress relaxation was tested by a rheometer.Then MDS-EPO and MDA-EPO were reprocessed by hot pressing using Flat vulcanizing machine and later tensile testing was done on a tensile tester.The thermal properties of reprocessed MDS-EPO were tested by DSC and TGA.Shape-memory and degradability of MDS-EPO and MDA-EPO were compared.The results showed that MDS-EPO and MDA-EPO were cured completely.The epoxy resins cured by MDS showed slightly lower modulus and thermal stability than MDA-EPO.The fast stress relaxation in MDS-EPO at temperature higher than Tg permitted the recycling and reprocessing of the fragmented samples for several times by hot press.Creep recovery of MDS-EPO was lower than MDA-EPO as increasing temperature.The MDS-EPO also exhibited good controlled shape-memory effect while MDA-EPO did not.MDS-EPO demonstrated decent degrading rate in 5 wt% Na OH solution.The model metathesis reaction in deuterated DMSO were detected by NMR to prove the effect of ionic liquid IL on disulfide exchange reaction.Then the MDS-EPO with different ionic liquid content were prepared.The cross section morphology was observed by scanning electron microscope(SEM).Then curing degree,thermal properties,reprocessibility and mechanical propertied were tested by the same method as described above.The results showed that IL can promote the disulfide bonds exchanging reaction.SEM images showed that the ionic liquid dispersed into MDS-EPO.With ionic liquid content increasing,both the Tg and the onset decomposition temperature of MDS-EPO decreased.After adding ionic liquid into MD-EPO,its stress relaxation process became slow and relaxation modulus cannot drop to zero.On the contrary,the relaxation modulus increased after a slight decrease.All the MDS-EPO with different ionic liquid content can be reprocessed and the tensile strength of reprocessed MDS-EPO exceed to its virgin MDS-EPO with increased ionic liquid amount.At the same temperature and press,increasing hot press time can improve reprocessed MDS-EPO mechanical properties.