High-performance Epoxy Thermosets Research Articles

Recyclable fully biobased high-performance epoxy thermosets

Thermosetting polymeric materials play a pivotal role in numerous sectors due to their versatility in tailoring physicochemical and mechanical properties and their exceptional performances. The aim of this study is to design 100 % bio-based high performant and recyclable thermosets. To achieve this goal, a natural and renewable-based epoxy monomer, triglycidyl ether of phloroglucinol (TGPh), was crosslinked with biobased anhydrides to create novel polymeric resins. Through detailed investigations, it was found that the designed materials have storage moduli values at room temperature ranging from 2.1 to 3.4 GPa, with damping factors spanning from 86 °C to 163 °C depending on the nature of the anhydride. Tensile tests corroborated the performant mechanical properties of the designed bio-resins, showing Young's modulus values ranging from 1.2 to 1.5 GPa. Furthermore, the water absorption values are very low, ranging from 0.25 % to 0.35 %. Besides, the designed bio-resins exhibited rapid dissolution in TBD/EG solution, as well as thermo-mechanical reprocessability.

High fire-safety epoxy thermosets with a macromolecular phosphorus-nitrogen containing flame retardant at a low loading

In this article, a macromolecular phosphorus-nitrogen containing flame retardant defined as PDPSB was incorporated into epoxy resins (EP). The fire safety, flame-retardant mechanism and mechanical properties of EP/PDPSB thermosets were systematically investigated. The EP-5 sheets containing 5 wt% PDPSB passed V-0 level in the vertical burning tests (UL-94) with a high limiting oxygen index (LOI) value of 30.9%. The results of cone calorimeter tests (CCT) revealed that both the emission of heat and smoke for EP/PDPSB thermosets was substantially suppressed. Compared to pure EP, the values for peak of heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) of EP-5 were dropped by 19.4%, 31.5% and 33.0%, respectively. Remarkably, the char residue mass of EP-5 was enhanced by 87.7%. The maximum smoke density (Ds, max) was slashed by 18.9%. Furthermore, the tensile, flexural and charpy impact strength of EP-5 were maintained to 97.3%, 95.1% and 86.9%, respectively. The investigation of flame-retardant mechanism demonstrated PDPSB exerted flame retardant effect both in condensed and gaseous phase by the scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectra (XPS), laser Raman spectra (LRS) and thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR). As PDPSB was a one-component multifunctional additive renowned for its exceptional efficiency, it was anticipated to facilitate the advancement of high-performance epoxy thermosets via researching on EP/PDPSB thermosets.

Dynamic reversible mechanism of phenol-carbamate bonds and their potential for the development of thermo-healing, recyclable and high-performance epoxy thermosets

In this paper, a series of small monomers were synthesized to explore the dynamic reversible properties of phenol-carbamate bonds (PCBs), and the bimolecular exchange mechanism of PCBs was verified. Based on this mechanism, a novel thermo-healing recyclable epoxy resin with high mechanical performance and shape memory function was successfully developed. Meanwhile, the number of reversible phenol-carbamate bonds in this system was increased by molecular structure design, which increased the chance of reversible cleavage and recombination of the dynamic covalent bonds. Compared with our previous work, the thermo-healing efficiency of the epoxy thermosets was greatly increased, and the target polymer achieved an excellent balance between high thermo-healing efficiency and good mechanical performance. Further post-treatment experiments show that the cured epoxy resin can also be well recycled by solvent degradation or hot-pressing process. What's more, a novel carbon fiber (CF) reinforced polymer composite material was synthesized by taking that prepared epoxy thermoset as a matrix, which greatly improve the mechanical properties of epoxy resin, and the CF cloths can be recycled when the epoxy resin is removed by chemical degradation. In addition, due to the existence of reversible crystallizable switching segments in the epoxy resin system, when the temperature is above its Tg, it can be triggered by thermal energy, so that the film can rapidly recover from the temporary shape to the permanent shape. This study also provides a new direction for the development of novel multifunctional intelligent polymers.

Design and synthesis of epoxy prepolymer containing aromatic imide structures for thermoset with excellent thermal, mechanical and dielectric properties

Recently, the development of epoxy thermosets with imide rings has received extensive attention due to their superior integrated properties, especially for thermal, mechanical and dielectric properties, compared to those of commercialized bisphenol A epoxy thermosets, yet remains substantial challenges, such as the high epoxy equivalent weight (EEW) of the epoxy prepolymers and the poor processibility of the epoxy systems. In this work, an imide-containing epoxy prepolymer (BAPT-EP) was facilely synthesized. It had a relatively low EEW of 340 g/equiv. and could be dissolved in hardener methylhexahydrophthalic anhydride (MHHPA) to give a homogeneous BAPT-EP/MHHPA system with good processibility. Thanks to the aromatic imide structures, the cured BAPT-EP/MHHPA showed improved overall properties. In particular, it had a 47.9 °C, 24.7 °C, 29.4%, 77.3% and 10.0% increase in the glass transition temperature, temperature at 5% mass loss, tensile strength, Young’s modulus and tensile toughness, respectively, compared to those of bisphenol A epoxy prepolymer (DGEBA)/MHHPA thermoset. Meanwhile, BAPT-EP/MHHPA thermoset featured good charring ability with a high char yield of 26.4% (800 °C/N2), remarkable dimensional stability with a low coefficient of thermal expansion of 52.5 ppm/°C and good dielectric properties with a low dielectric constant of 3.24 at 100 MHz. This work provides an elegant strategy to prepare high-performance epoxy thermosets with imide structures, which have promising applications in electronics.

Design and synthesis of polyetherimides as a flame-retarded thermolatent hardener for high-performance epoxy thermosets

To simultaneously improve the storage stability of epoxy/imidazole systems and flame retardancy without sacrificing the thermal, mechanical and dielectric properties of thermosets, a novel multifunctional polyetherimide containing benzimidazole and phosphorus (mPI) was synthesized and used as a hardener for diglycidyl ether of bisphenol A (DGEBA). In addition to retaining the effective curing behavior of imidazole, mPI, a macromolecular hardener and flame retardant, could endow the mixture of DGEBA and mPI (EP/mPI) with the long latent period and thermosets with the high performance. The results showed that mPI was unreactive at ambient temperature and underwent the rapid curing reaction at 170 °C that is a little higher than its glass transition temperature (Tg) of 164.7 °C, and EP/mPI showed the long thermal latent period of 70 days or more. Meanwhile, the cured EP/mPI attained the UL-94 V-0 rating with the LOI value of 31.2%. Besides, EP/mPI thermoset showed a 42.9 °C, 47.6 °C, 18.2 °C, 135.4% and 60.6% increase in the Tg, heat deflection temperature, temperature at 5% mass loss, storage modulus and Young's modulus, respectively, as well as a 3.6% decrease in the dielectric constant at 100 MHz, in comparison with those of the traditional cured DGEBA/benzimidazole (EP/BIM). This work provides a facile strategy to prepare one-pot epoxy/imidazole formulations and flame-retarded epoxy thermosets with high performance by using the well-designed multifunctional polyetherimides as a hardener and flame retardant, which has good application prospects in electronics.

Development of Sustainable High Performance Epoxy Thermosets for Aerospace and Space Applications.

There is an imperative need to find sustainable ways to produce bisphenol A free, high performance thermosets for specific applications such as the space or aerospace areas. In this study, an aromatic tris epoxide, the tris(4-hydroxyphenyl)methane triglycidyl ether (THPMTGE), was selected to generate high crosslinked networks by its copolymerization with anhydrides. Indeed, the prepared thermosets show a gel content (GC) ~99.9% and glass transition values ranged between 167-196 °C. The thermo-mechanical properties examined by DMA analyses reveal the development of very hard materials with E' ~3-3.5 GPa. The thermosets' rigidity was confirmed by Young's moduli values which ranged between 1.25-1.31 GPa, an elongation at break of about 4-5%, and a tensile stress of ~35-45 MPa. The TGA analyses highlight a very good thermal stability, superior to 340 °C. The Limit Oxygen Index (LOI) parameter was also evaluated, showing the development of new materials with good flame retardancy properties.

In-situ constructing ultra-high-aspect-ratio core–shell nanostructures to achieve high-performance epoxy thermosets and their carbon fiber reinforced epoxy composites

Using block copolymers to improve the mechanical properties of materials was a promising method, and the effect was positively correlated with the aspect ratio of the nanostructures. However, except for worm-like and branched worm-like nanostructures, nanostructures with higher aspect ratios have not been reported so far and its forming methods was unknown. In this paper, a feasible approach was provided to in-situ construct ultra-high-aspect-ratio core–shell nanostructures in epoxy, and the morphology evolution during the epoxy preparation process was clarified. It was shown that the tensile strength, elongation at break, fracture toughness and tensile modulus of the nanostructured epoxy were simultaneously improved when the content of block copolymer was as low as 1.75 wt%, achieving 93.6 MPa (31.3% improved), 7.9% (79.5% improved), 133.5 N/mm3/2 (184%) and 2693 MPa (5.6% improved), respectively. The interlaminar shear strength (ILSS) of the corresponding carbon fiber reinforced polymer (CFRP) composites was 32.5% higher than that of the control CFRP composites. Meanwhile, it was worth pointing out that the glass transformation temperatures (Tg) of the modified epoxy matrices and their corresponding CFRPs were similar to those of the unmodified materials. The improvement mechanisms on tensile strength, toughness and ILSS were also systemically investigated. It was expected that this work could provide a feasible routine for in-situ constructing complex morphological nanostructures in epoxy resins and some new ideas for the design of next-generation advanced composites.

Complete Degradation of a High-Performance Epoxy Thermoset Enabled by γ-ray-Sensitive Motifs Based on the Cascaded Synergetic Strategy

γ-Radiation derived from clean energy has emerged as a promising technology for disposal of waste plastics. However, due to radical-mediated uncontrolled recombination, a foremost challenge remains in radiation-triggered complete degradation for thermoset plastics. Herein, the radiation-sensitive epoxy thermoset (EP-DESN) containing phenyl imine-conjugated N–N bonds (PINN bonds) and S–S bonds was designed to initiate rapid degradation at a dose of 10 kGy. The phenyl imine-conjugated linkages can stabilize the radiation-induced broken N–N bonds, overcoming radical-mediated uncontrolled recombination and cross-linking. Moreover, the phenyl-iminyl-conjugated radicals generated by PINN bond scission can cleave the active S–S bonds to promote subsequent spontaneous degradation for maximum degradation efficiency. Meanwhile, EP-DESN exhibited superior thermal robustness and chemical resistance comparable to some conventional high-performance epoxy thermosets. Using EP-DESN as a binder, we prepared recyclable carbon fiber-reinforced composites, and nondestructive recycling of value-added carbon fiber (CF) is achieved, thus facilitating the concept of a circular CF economy.

Fluorinated anhydride-terminated imide oligomers toward high-performance epoxy thermosets enabled by hydroxyl elimination and low dielectric polarizability strategy

In this paper, for the first time, a novel fluorinated anhydride-terminated imide oligomer 6FDA-ODA was prepared with a facile and one-step route, and used as the multifunctional co-curing agent of methylhexahydrophthalic anhydride (MHHPA) for commercial bisphenol A epoxy resin (DGEBA). For the epoxy thermoset containing 30 phr of 6FDA-ODA, 6FDA-ODA-30 exhibited a high glass transition temperature (Tg) of 151.6 ℃ and an initial degradation temperature of 382.5 ℃, and also showed a 211%, 134% and 11.8% increase in impact strength (20.5 kJ/m2 vs. 6.6 kJ/m2), char yield (in N2) (15.2% vs. 6.5%) and tensile strength (71.3 MPa vs. 63.8 MPa), respectively, compared with the pure epoxy thermoset (6FDA-ODA-0). Moreover, 6FDA-ODA-30 possessed a low dielectric constant of 3.23 at 1 MHz and high water resistance (water absorption = 0.52%) due to the introduction of bulky trifluoromethyl (-CF3) and imide moieties. This paper provides a facile design strategy and new opportunity for synthesizing anhydride-terminated imide oligomer, possessing high potential for the utilization in advanced matrix materials for microelectronic and aerospace industries.

A Vanillin-Derived, DOPO-Contained Bisphenol as a Reactive Flame Retardant for High-Performance Epoxy Thermosets

Quest for bio-based halogen-free green flame retardant has attracted many concerns in recent years. Herein a reactive functional flame retardant containing phosphorus VDP is synthesized from vanillin, 9,10-dihydro-9-oxa-10-phosphophene-10-oxide (DOPO) and phenol via a facile way. VDP is characterized with 1H NMR, 31P NMR, FTIR and Time of Flight Mass Spectrometry, and used as a new reactive flame retardant for bisphenol epoxy thermosets. Thermogravimetry analysis shows that when the VDP loading is only 0.5P% (based on phosphorus content), the residue increases from 14.2% to 21.1% at 750°C in N2 compare with neat DGEBA. Correspondingly, the limit oxygen index increased to 29.6%, and flame retardancy reaches UL-94 V0 grade. Micro combustion calorimetry (MCC) and cone calorimetry analyses demonstrate that VDP can significantly lower flammability of the epoxy thermoset. With only 0.5P% of VDP, the heat release rate, total heat release rate and smoke production are reduced markedly. At the same time, the mechanical properties of the modified epoxy thermosets are also improved. The impact strength increases by 34% and the flexural strength increased by 23%, with 1.5P% of VDP. In short, VDP not only improves the flame retardancy, but also improves the mechanical properties of the epoxy thermosets.

Preparation and properties of novel bio-based epoxy resin thermosets from lignin oligomers and cardanol

A series of lignin-based epoxy resins (LEPs) were prepared by the reaction of epichlorohydrin with lignin oligomers derived from partial reductive depolymerization of lignin. To overcome the high viscosity and brittleness defects in practical applications, the LEPs were blended with renewable epoxied cardanol glycidyl ether (ECGE) and then cured with methyltetrahydrophthalic anhydride (MeTHPA) to form high-performance epoxy thermosets. The effects of degree of lignin depolymerization, chemical composition of lignin oligomers and dosage of ECGE on thermal and mechanical properties of the cured products were investigated. The LEP/MeTHPA thermosets exhibited good thermal and mechanical properties. Especially, by separating monomer-rich fractions from lignin oligomers, the thermal and mechanical properties of the cured product were improved obviously. Notably, the incorporation of ECGE also possessed a positive effect on reinforcing and toughening the cured products. With 20 wt% ECGE loadings, the tensile, flexural and impact strength of the cured product reached the maximum value of 77 MPa, 115 MPa and 14 kJ/m2, respectively, which were equivalent to the commercial bisphenol A epoxy resins thermosets. These findings indicated that the novel bio-based epoxy resins from lignin oligomers and cardanol could be utilized as renewable alternatives for BPA epoxy resins.

Hyperbranched flame retardant to simultaneously improve the fire-safety, toughness and glass transition temperature of epoxy resin

It is highly desired yet very challenging to overcome the flammability and brittleness of epoxy resin without compromising its glass transition temperature (Tg). Herein, an epoxy-terminated hyperbranched flame retardant (EHBFR) was designed and synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and renewable protocatechualdehyde as well as guaiacol. When the synthesized EHBFR was taken to modify diglycidyl ether of bisphenol A (DGEBA), it is found that the incorporation of EHBFR remarkably improved its fire safety, endowing it with a UL-94 V-0 rating and a limiting oxygen index (LOI) of 33.0 vol%. Meanwhile, the notched impact strength of modified DGEBA at 25 and −196 °C (quenched by liquid nitrogen) exhibited significant increment by 135% (from 3.39 to 7.97 KJ/m2) and 114% (from 2.34 to 5.01 KJ/m2), respectively. Moreover, the Tg of modified epoxy resin did not show any decrease, and even increased from 172 to 194 °C when the content of EHBFR was 10 wt%, due to the synergistic effect of rigid DOPO-containing groups and high crosslink density. This work offers an efficient strategy for constructing high-performance epoxy thermosets with excellent flame retardancy, superior toughness and strength, as well as elevated Tg.

Cure kinetics and properties of high-performance epoxy thermosets cured with active ester-terminated poly (aryl ether ketone)

Benzene-1,3,5-triyl tribenzoate (TBB), both 3,5-bis(benzoyloxy)benzoate-terminated poly (aryl ether ketone) oligomers (BPAPK and TMPK), containing active ester (Ph−O−(C=O)− structure), were prepared and served as curing agents for dicyclopentadiene novoalc epoxy (DCPD). The curing kinetics and properties of three epoxy thermosets were systematically investigated. The model reaction of TBB and glycidyl phenyl ether was designed to understand the curing mechanism of oxirane ring with active ester. TMPK/DCPD displays the lowest reaction activation energy, which is the result of the combined influence of free volume and diffusion. In addition, TMPK/DCPD has the highest Tg value (218°C), which enhances 34.6% and 42.5% compared with BPAPK/DCPD and TBB/DCPD, respectively. Meanwhile, TMPK/DCPD also shows superior dielectric and water resistance properties due to no secondary alcohol generated after curing and hydrophobic tetramethyl-substituted biphenyl structure. Herein, TMPK/DCPD as high-performance epoxy thermosets has potential applications in electronic packaging fields.

Phosphorylated cardanol-formaldehyde oligomers as flame-retardant and toughening agents for epoxy thermosets

Presently, flammability and brittleness are two major problems for EP which has restricted its development and application in industrial. Under the global advocacy of green and sustainable development, developing bio-based flame-retardant and toughening agents which can endow epoxy resins with high fire resistance and satisfactory mechanical properties is of significant demand for its industrial applications. Herein, three kinds of phosphorylated cardanol-formaldehyde oligomers (CF-PO(OPh)2, CF-POPh2, and CF-PPh2) were synthesized and introduced into epoxy thermosets. The incorporation of CF-PO(OPh)2, CF-POPh2, and CF-PPh2 can remarkably improve the mechanical performance of EP composites, especially the tensile strength and elongation at break. With 10 wt% of CF-PO(OPh)2, CF-POPh2, and CF-PPh2, the tensile strength of epoxy thermosets reached 67.1, 74.5, and 70.3 MPa, respectively; the elongation at break of epoxy thermosets was raised by 133.3%, 162.5%, and 150.0%, respectively, as compared to neat EP. EP composites containing CF-PO(OPh)2, CF-POPh2, and CF-PPh2 also exhibited remarkably enhanced flame retardancy simultaneously. Besides, CF-PO(OPh)2 exhibited the best flame-retardant efficiency by comparison with CF-POPh2 and CF-PPh2, and the results manifested that epoxy composite with only 2.5 wt% CF-PO(OPh)2 could pass the UL-94 V-0 rating as well as a high LOI value of 28%, and the LOI value of EP/CF-PO(OPh)2–10 reached up to 32%. Moreover, CF-PO(OPh)2 also displayed an excellent catalytic charring effect and great suppression effect on heat and smoke release. The cone calorimeter test results showed that EP composite containing 10 wt% CF-PO(OPh)2 exhibited the most significant PHRR reduction which was 53.8% lower than pure EP, and the char yield of EP/CF-PO(OPh)2–10 after the cone calorimeter test was 14.0% which was much higher than that of pure EP (5.7%). This work opens a new vision for the synthesis of bio-based flame-retardant and toughening agents with a special oligomeric structure combining rigidity with flexibility, and contributes to the production of high-performance epoxy thermosets.

Phosphorus-based triazine compound endowing epoxy thermosets with excellent flame retardancy and enhanced mechanical stiffness

Searching highly-efficient flame retardants for flame-resistance and smoke-suppressed epoxy thermosets with enhanced mechanical performance has aroused considerable interest in the field of flame-retardant materials. Herein, a phosphorus-based flame retardant, 6,6′,6''-(1,3,5-triazine-2,4,6-triyl)tris(oxy))tris(3-methoxybenzene-4,1-diyl))tris(hydroxymethylene))tris(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (Trif-D), was synthesized using a two-step method and served as the flame-retardant additive for commercial epoxy thermoset. The epoxy thermoset with the low loading of 5.0 wt% Trif-D (Trif-D-5, phosphorus content = 0.39 wt %) possessed a UL-94 V-0 rating (with a limiting oxygen index of 33.1%). According to the cone calorimeter test, compared with epoxy thermoset without Trif-D addition (Trif-D-0), the reductions of peak heat release rate and total smoke production in Trif-D-5 were 66.3% and 51.3%, respectively. The mechanism analysis confirmed that the phosphorus-based structure from Trif-D contributed both the gaseous-phase and condensed-phase flame retardance of epoxy network. Moreover, Trif-D-5 possessed the high mechanical stiffness due to the introduction of rigid structures (phosphaphenanthrene, triazine and benzene) from Trif-D, showing 5.2%, 3.6% and 5.9% increase in storage modulus (at 30 °C) (3.03 GPa vs. 2.88 GPa), tensile modulus (3.47 GPa vs. 3.35 GPa) and flexural modulus (2.89 GPa vs. 2.73 GPa) as compared to Trif-D-0, respectively. The present paper investigates a facile method for the fabrication of high-performance epoxy thermosets with excellent flame retardance and enhanced mechanical stiffness.

In-situ construction of “octopus”-like nanostructure to achieve high performance epoxy thermosets

Inspired by the octopus, a typical nanostructure consisting of a spherical “body” and worm-like “tentacles with suckers” was constructed through incorporating polydimethylsiloxane-block-poly(ε-caprolactone)-block-polystyrene (BXLS) in epoxy thermosets. The novel nanostructure of BXLS copolymer and its morphology evolution during the epoxy curing process were investigated by transmission electron microscopy, field emission scanning electron microcopy and small-angle X-ray scattering. The mechanical properties of epoxy composites were significantly enhanced with a very low BXLS loading fraction. A 1.75 wt% of BXLS block copolymer could increase the tensile strength and fracture toughness up to 93.57 MPa and 137.43 N/mm3/2, which were 1.31 times and 2.92 times that of the neat epoxy, respectively. Meanwhile, the toughening mechanism and the relationship between the high-performance properties of the epoxy composites and the nanostructure of the BXLS block copolymer were thoroughly studied. It is expected that our work can provide some new ideas and approaches for fabricating high-performance thermosets.

Toughening Effect and Flame-Retardant Behaviors of Phosphaphenanthrene/Phenylsiloxane Bigroup Macromolecules in Epoxy Thermoset

A series of novel phosphaphenanthrene/phenylsiloxane bigroup macromolecules (DDSi-n) were synthesized and applied to obtain high-performance epoxy thermosets. DDSi-n macromolecules simultaneously enhanced the anti-impact and flame-retardant performance of epoxy thermosets. The impact strength of the DDSi-n-containing thermoset (DDSi-n/EP) was maximally increased by nearly 140% in 8% DDSi-1/EP because of the flexible phenylsiloxane block and the polar phosphaphenanthrene group interacting with matrix in DDSi-n macromolecules. Meanwhile, the evidently elevated anti-ignition and self-extinguishing performance, the suppressed combustion heat, and the enhanced charring capability of DDSi-n/EP were all caused by the flame-retardant group synergistic effect of phosphaphenanthrene and phenylsiloxane groups of DDSi-n macromolecules in thermosets. Compared with the individual phosphaphenanthrene or phenylsiloxane group in monogroup contrasts, the phosphaphenanthrene and phenylsiloxane groups in bigroup DDSi-n macro...

Fully biobased and high performance epoxy thermosets from epoxidized soybean oil and diamino terminated polyamide 1010 oligomers

Fully biobased and high performance epoxy thermosets were synthesized through curing of epoxidized soybean oil (ESO) with crystalline diamino terminated polyamide 1010 oligomers (OPAs). Four OPAs with different molecular weights were prepared to cure ESO. The results of isothermal curing investigation indicated that the curing rate decreased with increasing molecular weight of the OPA. The effects of chain length of OPAs on the thermal transition, crystallization behavior mechanical properties, heat resistance and thermal stability of the ESO thermosets were investigated in detail. The results showed that the crystallization was significantly enhanced, the glass transition temperature and the melting temperature increased to a higher temperature range with increasing OPA chain length. The tensile strength, Young's modulus, storage modulus and elongation at break increased considerably with increasing OPA chain length, due to the gradually enhanced network stiffness through crystallization and reduced crosslink density through increasing chain length between crosslinking sites. The heat resistance of the thermosets was also enhanced with increasing OPA chain length due to the increased melting temperature of the thermoset. In addition, the biobased epoxy thermosets showed excellent thermal stability with onset decomposition temperature of higher than 330 °C.

Divanillin-Based Epoxy Precursors as DGEBA Substitutes for Biobased Epoxy Thermosets

Biobased epoxy monomers from divanillyl alcohol were successfully synthesized and characterized. These monomers, that is, diglycidylether of divanillyl alcohol (DiGEDVA), triglycidylether of divanillyl alcohol (TriGEDVA), and tetraglycidyl of divanillyl alcohol (TetraGEDVA), were then cured with cyclo-aliphatic diamine (IPDA), employed as hardener. The vanillin-based epoxy thermosets so-formed were then characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analyzer (DMA), and tensile tests and were compared to a DGEBA-based reference. These biobased thermosets display phase transition Tα from 140 to 200 °C and have thermal degradation comparable to the DGEBA-based network. This divanillin platform thus appears to be a promising substitute to bisphenol A with the aim at designing high-performance epoxy thermosets for structural composite and adhesive applications.

High-Speed 3D Printing of High-Performance Thermosetting Polymers via Two-Stage Curing.

Design and direct fabrication of high-performance thermosets and composites via 3D printing are highly desirable in engineering applications. Most 3D printed thermosetting polymers to date suffer from poor mechanical properties and low printing speed. Here, a novel ink for high-speed 3D printing of high-performance epoxy thermosets via a two-stage curing approach is presented. The ink containing photocurable resin and thermally curable epoxy resin is used for the digital light processing (DLP) 3D printing. After printing, the part is thermally cured at elevated temperature to yield an interpenetrating polymer network epoxy composite, whose mechanical properties are comparable to engineering epoxy. The printing speed is accelerated by the continuous liquid interface production assisted DLP 3D printing method, achieving a printing speed as high as 216 mm h-1 . It is also demonstrated that 3D printing structural electronics can be achieved by combining the 3D printed epoxy composites with infilled silver ink in the hollow channels. The new 3D printing method via two-stage curing combines the attributes of outstanding printing speed, high resolution, low volume shrinkage, and excellent mechanical properties, and provides a new avenue to fabricate 3D thermosetting composites with excellent mechanical properties and high efficiency toward high-performance and functional applications.