Synthesis and characterization of bio-based epoxy blends from renewable resource based epoxidized soybean oil as reactive diluent

Bio-based hyperbranched epoxy resins: synthesis and recycling

Epoxy resins (EPs), accounting for about 70% of the thermosetting resin market, have been recognized as the most widely used thermosetting resins in the world. Nowadays, 90% of the world's EPs are obtained from the bisphenol A (BPA)-based epoxide prepolymer. However, certain limitations severely impede further applications of this advanced material, such as limited fossil-based resources, skyrocketing oil prices, nondegradability, and a "seesaw" between toughness and strength. In recent years, more and more research has been devoted to the preparation of novel epoxy materials to overcome the compromise between toughness and strength and solve plastic waste problems. Among them, the development of bio-based hyperbranched epoxy resins (HERs) is unique and attractive. Bio-based HERs synthesized from bio-derived monomers can be used as a matrix resin or a toughener resulting in partially or fully bio-based epoxy thermosets. The introduction of a hyperbranched structure can balance the strength and toughness of epoxy thermosets. Here, we especially focused on the recent progress in the development of bio-based HERs, including the monomer design, synthesis approaches, mechanical properties, degradation, and recycling strategies. In addition, we advance the challenges and perspectives to engineering application of bio-based HERs in the future. Overall, this review presents an up-to-date overview of bio-based HERs and guidance for emerging research on the sustainable development of EPs in versatile high-tech fields.

Role of Bio-Based and Fossil-Based Reactive Diluents in Epoxy Coatings with Amine and Phenalkamine Crosslinker

The properties of epoxy can be adapted depending on the selection of bio-based diluents and crosslinkers to balance the appropriate viscosity for processing and the resulting mechanical properties for coating applications. This work presents a comprehensive study on the structure-property relationships for epoxy coatings with various diluents of mono-, di-, and bio-based trifunctional glycidyl ethers or bio-based epoxidized soybean oil added in appropriate concentration ranges, in combination with a traditional fossil-based amine or bio-based phenalkamine crosslinker. The viscosity of epoxy resins was already reduced for diluents with simple linear molecular configurations at low concentrations, while higher concentrations of more complex multifunctional diluents were needed for a similar viscosity reduction. The curing kinetics were evaluated through the fitting of data from differential scanning calorimetry to an Arrhenius equation, yielding the lowest activation energies for difunctional diluents in parallel with a balance between viscosity and reactivity. While the variations in curing kinetics with a change in diluent were minor, the phenalkamine crosslinkers resulted in a stronger decrease in activation energy. For cured epoxy resins, the glass transition temperature was determined as an intrinsic parameter that was further related to the mechanical coating performance. Considerable effects of the diluents on coating properties were investigated, mostly showing a reduction in abrasive wear for trifunctional diluents in parallel with the variations in hardness and ductility. The high hydrophobicity for coatings with diluents remained after wear and provided good protection. In conclusion, the coating performance could be related to the intrinsic mechanical properties independently of the fossil- or bio-based origin of diluents and crosslinkers, while additional lubricating properties are presented for vegetable oil diluents.

Robust Vanillin-Derived Poly(thioether imidazoles) as Both a Latent Curing and Toughening Agent for One-Component Epoxy Resins

One-component epoxy resins based on latent curing agents have garnered research attention owing to their outstanding storage stability and excellent processability, while their development considerably depends on the design and preparation of sustainable latent curing agents. Herein, taking structural advantage of lignin-derived vanillin, a biobased polymerizable aromatic imidazole monomer with α,ω-diene functionality was designed and prepared, which was applicable in subsequent thiol-ene polymerization, yielding a series of robust poly(thioether imidazoles) with excellent tunability of the structure and properties. The findings indicated that the precursors comprising poly(thioether imidazole) and commercially available epoxy resins could keep their fluidity at 25 °C for over 90 days and rapidly cured into resins under elevated temperature, demonstrating that the poly(thioether imidazole) can serve as both a latent curing and toughening agent for one-component epoxy resins because of homopolymerization initiated by imidazole groups and the introduction of an aliphatic chain in the as-prepared poly(thioether imidazole) matrix.

The chemistry insight: epoxy sealant as an alternative remedial operation for well integrity

Epoxy resin is commonly used in the oil and gas industry due to its excellent toughness, low shrinkage, good adhesive strength, and relatively good thermal resistance. It is used for water shutoff, zonal isolation, cementing, enhanced oil recovery, and preventing leakage in wells. This paper reviews the chemistry aspect of using an epoxy resin system as a sealant to prevent well leakage and it offers insights into the chemistry of the epoxy resin system, as applied in previous studies. The paper also unveils the reasons for the application of this system from the chemistry perspective, allowing this aspect to be better understood. Success in the investigated cases depended on the formulation design. The epoxide and hydroxyl functional groups have been found to contribute substantially to the excellent performance of the sealant system. Furthermore, the amine curing agent triggers the abrupt reaction of the oxirane ring to stabilise when the cured sealant is perfectly applied. Based on the findings, it is suggested that other types of epoxies, namely epoxidised oils, require further study. Finally, in terms of safety and sustainable energy, it is suggested that more curing agent and diluent studies are undertaken.

Cardanol-Derived Epoxy Resins as Biobased Gel Polymer Electrolytes for Potassium-Ion Conduction

In this study, biobased gel polymer electrolyte (GPE) membranes were developed via the esterification reaction of a cardanol-based epoxy resin with glutaric anhydride, succinic anhydride, and hexahydro-4-methylphthalic anhydride. Nonisothermal differential scanning calorimetry was used to assess the optimal curing time and temperature of the formulations, evidencing a process activation energy of ∼65-70 kJ mol-1. A rubbery plateau modulus of 0.65-0.78 MPa and a crosslinking density of 2 × 10-4 mol cm-3 were found through dynamic mechanical analysis. Based on these characteristics, such biobased membranes were tested for applicability as GPEs for potassium-ion batteries (KIBs), showing an excellent electrochemical stability toward potassium metal in the -0.2-5 V voltage range and suitable ionic conductivity (10-3 S cm-1) at room temperature. This study demonstrates the practical viability of these biobased materials as efficient GPEs for the fabrication of KIBs, paving the path to increased sustainability in the field of next-generation battery technologies.

Structural Features and Properties' Characterization of Polylactic Acid/Natural Rubber Blends with Epoxidized Soybean Oil

Because of the effort to preserve petroleum resources and promote the development of eco-friendly materials, bio-based polymers produced from sustainable resources have attracted great attention. Among them, polylactide (PLA) and natural rubber (NR) present prominent polymers with unique barrier and mechanical features. A series of samples with improved phase compatibility were obtained by blending PLA and NR using a double-rotor mixer. A plasticizing and enhancing effect on the polymers' compatibility was achieved by using epoxidized soybean oil (ESO) as a natural plasticizer and compatibilizer. ESO compounding in the PLA-NR blends increased the mobility of the biopolymer's molecular chains and improved the thermal stability of the novel material. The size of the NR domains embedded in the continuous PLA matrix decreased with the ESO content increment. The combination of thermal analysis and scanning electron microscopy enabled the authors to determine the features of potential packaging material and the optimal content of PLA-NR-ESO for the best mechanical properties.

Vegetable Oil-Based Thiol-Ene/Thiol-Epoxy Resins for Laser Direct Writing 3D Micro-/Nano-Lithography

The use of renewable sources for optical 3D printing instead of petroleum-based materials is increasingly growing. Combinations of photo- and thermal polymerization in dual curing processes can enhance the thermal and mechanical properties of the synthesized thermosets. Consequently, thiol-ene/thiol-epoxy polymers were obtained by combining UV and thermal curing of acrylated epoxidized soybean oil and epoxidized linseed oil with thiols, benzene-1,3-dithiol and pentaerythritol tetra(3-mercaptopropionate). Thiol-epoxy reaction was studied by calorimetry. The changes of rheological properties were examined during UV, thermal and dual curing to select the most suitable formulations for laser direct writing (LDW). The obtained polymers were characterized by dynamic-mechanical thermal analysis, thermogravimetry, and mechanical testing. The selected dual curable mixture was tested in LDW 3D lithography for validating its potential in optical micro- and nano-additive manufacturing. The obtained results demonstrated the suitability of epoxidized linseed oil as a biobased alternative to bisphenol A diglycidyl ether in thiol-epoxy thermal curing reactions. Dual cured thermosets showed higher rigidity, tensile strength, and Young’s modulus values compared with UV-cured thiol-ene polymers and the highest thermal stability from all prepared polymers. LDW results proved their suitability for high resolution 3D printing—individual features reaching an unprecedented 100 nm for plant-based materials. Finally, the biobased resin was tested for thermal post-treatment and 50% feature downscaling was achieved.

Epoxidation of Fatty Acid Methyl Esters Derived from Algae Biomass to Develop Sustainable Bio-Based Epoxy Resins

The objective of this research was to investigate the development of epoxides from Chlorella vulgaris lipids to obtain a novel bio-based resin. The process involved the production of fatty acid methyl esters (FAMEs) by in situ transesterification of microalgal biomass, followed by epoxidation of the FAMEs to obtain bioresin. During the FAME production process, an assessment was made of the main factors affecting the production of unsaturated fatty acid methyl esters (UFAMEs), such as catalyst dosage and methanol:hexane volume ratio. For step epoxidation, an evaluation of the catalyst concentration, temperature and formic acid:hydrogen peroxide ratio was made. From the results obtained, UFAME production was maximized using 20 wt% of catalyst dosage and a volume ratio of 1:2 (v/v, methanol:hexane). Then, in the epoxidation stage, a higher yield was obtained using 1 wt% of catalyst with a volume ratio of 1:1 and maintaining a temperature of 70 °C. The bioresin was blended with neat epoxy resin (DGEBA) and cured with tetraethylenepentamine (TEPA). Bio-based resin was characterized via Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) to evaluate this material as an alternative source for oleochemistry.

Bio-Based Epoxy Shape-Memory Thermosets from Triglycidyl Phloroglucinol

A series of bio-based epoxy shape-memory thermosetting polymers were synthesized starting from a triglycidyl phloroglucinol (3EPOPh) and trimethylolpropane triglycidyl ether (TPTE) as epoxy monomers and a polyetheramine (JEF) as crosslinking agent. The evolution of the curing process was studied by differential scanning calorimetry (DSC) and the materials obtained were characterized by means of DSC, thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), stress-strain tests, and microindentation. Shape-memory properties were evaluated under free and totally constrained conditions. All results were compared with an industrial epoxy thermoset prepared from standard diglycidyl ether of Bisphenol A (DGEBA). Results revealed that materials prepared from 3EPOPh were more reactive and showed a tighter network with higher crosslinking density and glass transition temperatures than the prepared from DGEBA. The partial substitution of 3EPOPh by TPTE as epoxy comonomer caused an increase in the molecular mobility of the materials but without worsening the thermal stability. The shape-memory polymers (SMPs) prepared from 3EPOPh showed good mechanical properties as well as an excellent shape-memory performance. They showed almost complete shape-recovery and shape-fixation, fast shape-recovery rates, and recovery stress up to 7 MPa. The results obtained in this study allow us to conclude that the triglycidyl phloroglucinol derivative of eugenol is a safe and environmentally friendly alternative to DGEBA for preparing thermosetting shape-memory polymers.

A hyperbranched polymer from tung oil for the modification of epoxy thermoset with simultaneous improvement in toughness and strength

In order to increase the toughness of epoxy resin and make full use of biological resources, a tung oil-based hyperbranched polymer (TOHBP) was synthesized.

New Epoxy Thermosets Derived from Clove Oil Prepared by Epoxy-Amine Curing

New thermosets from a triglycidyl eugenol derivative (3EPOEU) as a renewable epoxy monomer were obtained by an epoxy-amine curing process. A commercially-available Jeffamine^® and isophorone diamine, both obtained from renewable resources, were used as crosslinking agents, and the materials obtained were compared with those obtained from a standard diglycidylether of bisphenol A (DGEBA). The evolution of the curing process was studied by differential scanning calorimetry and the materials obtained were characterized by means of calorimetry, thermogravimetry, thermodynamomechanical analysis, stress–strain tests and microindentation. 3EPOEU formulations were slightly less reactive, and the thermosets obtained showed higher T_gs than those prepared from DGEBA, since they had higher crosslinking density than formulations with DGEBA because of the more compact structure and higher functionality of the eugenol derivative. 3EPOEU thermosets showed good thermal stability and mechanical properties. The results obtained in this study allow us to conclude that the triglycidyl derivative of eugenol, 3EPOEU, is a safe and environmentally friendly alternative to DGEBA.

A renewable tung oil-derived nitrile rubber and its potential use in epoxy-toughening modifiers

The renewable tung oil-derived nitrile rubber, toughening epoxy resin dramatically, may take the place of traditional petroleum-based epoxy-toughening modifiers.

Development of hyperbranched crosslinkers from bio-derived platform molecules for the synthesis of epoxidised soybean oil based thermosets

Bio-based carboxyl-terminated hyperbranched crosslinkers have been synthesised by the facile esterification reaction of glycerol with succinic anhydride (Gly-SA). The Gly-SA crosslinking molecules have a large number of terminal carboxyl groups, which can crosslink through the epoxide of epoxidised soybean oil (ESO), making a highly flexible transparent film with excellent oxidative resistance. The effect of different molecular weights of Gly-SA cured ESO on the thermal and mechanical properties of the resulting films was also investigated. This study demonstrated that an increase in the molecular weights of Gly-SA, led to a decrease in the curing rate of mixtures, whilst the glass transition temperature (T _g) of Gly-SA cured ESO increased due to the incorporation of the bulky crosslinker. The use of a Gly-SA crosslinker prepared at 150 °C, resulted in a film (EGS150) with a tensile strength 13 times greater than of the control film, exhibited more than a 220% increase in elongation at break and the Young's modulus quadrupled compared to the value obtained for the control sample. It is noteworthy that the tensile strength and elongation at break improved with increasing Gly-SA chain length, suggesting the pre-polymerised crosslinkers contribute to the enhanced mechanical properties of the materials.