Synthesis, Cure And Propetries Of Plant Oil Based Epoxy Thermosetting Monomers

The development of epoxy resin industry and business is growing rapidly in recent years,it is also a tendency that the renewable resources replace the fossil resources for the sustainableprogress of epoxy resins. However, there were indeed many disadvantages or drawbacks ofnatural plant oils derivatives such as tung oil, polymerized fatty acids, and cardanols whenthese agriculture and forest products were applied in epoxy resins for research anddevelopment. Therefore, the aim of this work is to develop light color, high modulus, hightoughness, dual crosslinked, and self-crosslinked epoxy resins or curing agents. By using thecarboxyl, double bonds, and phenol hydroxyl of these natural products, a series of classicchemical reactions such as epoxidization, Diels-Alder reaction, Williamson ether synthesis, andMannich reaction were used to design or modify the molecules of epoxy resins and curingagents. Some other curing method was also introduced into the epoxy curing process. Otherepoxy resin with different structures was also blended with oil based epoxy resins to get afomulation with the optimal properties. The relationships between the structures and propertieswere studied and disscussed in detail in this work as well. This work offered theoretical basisand references for the efficient utilization of natural plant oils and the sustainable progress ofepoxy industry. The specific contents are the following five parts:1. a light color cardanol-based epoxy curing agent (MBCBE) was synthesized fromcardanol butyl ether, formaldehyde and diethylenetriamine. In comparison, a phenalkamine(PKA) with a similar structure was also prepared. MBCBE has a much lighter color than thatof PKA. The chemical structures of MBCBE were confirmed by GC-MS and FT-IR. The curebehaviors of diglycidyl ether of bisphenol A (DGEBA) with these two curing agents wasstudied by differential scanning calorimetry (DSC). The morphology, mechanical properties,thermal properties of the cured epoxies were also investigated. The DSC results indicated thatMBCBE is less reactive than the phenalkamine. The morphology of the cured MBCBE/DGEBA consisted of cavities dispersed within a continuous epoxy matrix which wereobserved by scanning electron microscope (SEM). The infrared spectra (FT-IR), soxhletextraction and thermogravimetric analysis (TGA) results confirmed that the phase separationwas arised by the unreacted CBE separated out from the epoxy matrix during the cure. Thecavities markedly improved the lap shear strength and impact strength of the cured resin.Compared with PKA/DGEBA, MBCBE/DGEBA showed an obvious two-stage weight losscurve, the first stage was mainly resulted from the dispersed phase filled with the unreactedCBE separated out from the epoxy matrix.2. In this work, a21-carbon dicarboxylic acid (C21DA) and a22-carbon tricarboxylic acid(C22TA) were prepared by the Diels-Alder addition of tung oil fatty acids with acrylic acid andfumaric acid, respectively, and subsequently converted into corresponding di-and triglycidylesters. There were no solvents used in the addition and glycidylation reactions. The excessepichlorohydrin used in the latter reaction was reused. Furthermore, for the first time calciumoxide was introduced as a water scavenger in the gycidylation process to effectively avoid theside reactions. The chemical structures of the products were confirmed using1H nuclearmagnetic resonance (1H-NMR),13C nuclear magnetic resonance (13C-NMR)and electrospray ionization mass spectrometry (ESI-MS) analyses. The curing behaviors ofthe di-and triglycidyl esters were studied using DSC. Flexural, impact and dynamicmechanical properties of the cured resins were also determined. A commercial bisphenol Aepoxy DER332and an epoxidized soybean oil (ESO) were used as performance comparison inthe study. Results indicated that the diglycidyl and triglycidyl esters had overall superiorperformance to ESO for epoxy applications. Particularly, the triglycidyl ester of the C22TAdisplayed comparable strength, modulus and glass transition temperature to that of DER332.3. A novel bio-based epoxy monomer with conjugated double bonds, glycidyl ester ofeleostearic acid (GEEA) was synthesized from tung oil fatty acids and epichlorohydrin, andthen characterized by1H-NMR and13C-NMR. DSC and FT-IR were utilized to investigate thecuring process of GEEA with dienophiles and anhydrides. DSC indicated that GEEA could crosslink with both dienophiles and anhydrides through these two synergetic ways: Diels-Alderreaction and epoxy/anhydride ring-opening reaction. Furthermore, Diels-Alder reaction wasmuch more active than the ring-opening of epoxy and anhydride in the curing process. FT-IRalso revealed that GEEA successively reacted with dienophiles and anhydrides in bothcrosslinking methods. DMA and mechanical tensile testing were used to study the thermal andmechanical properties of GEEA cured by maleic anhydride, nadic methyl anhydride (NMA)and1,1’-(methylenedi-4,1-phenylene)bismaleimide. Due to the independence between thecuring agents, dienophile and anhydride, a series of thermosetting polymers with variousproperties could be obtained by adjusting the composition of these two curing agents.4. Based on part3, a self-crosslinking monomer with both epoxy and anhydride groups(GEMA) was synthesized from GEEA and maleic anhydride. The structure of GEMA wasconfirmed by1H-NMR,13C-NMR, and distortionless enhancement by polarization transfer(DEPT)13C-NMR. The feasibility of the synthesis and the chemical reaction during thesynthesis were investigated by DSC and FT-IR, respectively. The curing behavior of GEMA inthe presence of tertiary amine was also studied by DSC. The dynamic mechanical propertiesand tensile properties were measured by DMA and tensile test. The results showed that therewas no epoxy/annydride reaction but only Diels-Alder raction during the synthesis of GEMA.The cure mechanism of GEMA was similar to that of conventional glycidyl ester epoxy resinand anhydride. The glass transition temperature of cured GEMA is108°C. The tensile strength,strain, and the elastic modulus of cured GEMA are42.5MPa,3.2%, and1930.3MPa,respectively.5. In this work, a rosin-derived diacid and a dimerized fatty acid were converted todiglycidyl ester type epoxies through the synthesis method offered in part2, respectively, andthe chemical structures of the products were confirmed by1H-NMR, FT-IR and ESI-MS. NMAwas used as curing agent to cure these two biobased epoxies and their mixtures in differentweight ratios. The cure behavior of these two epoxies with NMA was studied using DSC.Flexural and dynamic mechanical properties of the cured resins were determined using three point bending test and DMA. Thermal degradation of the cured resins was examined usingthermogravimetric analysis (TGA). Results suggest that the rigid rosin-derived epoxy and theflexible dimer acid-derived are complementary between flexural strength and flexural modulus.The combination of DGEAPA:DGEDA (5:3) by weight could result in resins with the bestflexural strength.