Resin Mixture Research Articles

ULTRASTRUCTURAL ORGANIZATION OF NEURONS OF THE LATERAL PREOPTIC NUCLEUS OF THE HYPOTHALAMUS OF OLD RATS UNDER VARIOUS LIGHT CONDITIONS

Purpose – to study the changes in the ultrastructure of neurons of the lateral preopticnucleus (LPON) of the hypothalamus of old rats under various light conditions.Material and methods. The experiments were carried out on 36 old white male rats.The material was fixed in a 2.5% solution of glutaraldehyde, prepared on the basisof phosphate buffer with a pH of 7.2–7.4. Then, postfixation was performed in a 1%solution of osmium tetraoxide and dehydrated in propylene oxide, after which it waspoured into a mixture of epoxy resins. Ultrathin sections made on an ultramicrotomeLKB-3 were contrasted with uranium acetate and lead citrate according to the Reynoldsmethod and studied under electron microscope TEM - 125 K.Results. Studies of LPON neurons under the standard light mode revealed nuclei withuneven contours. The nucleoli are quite large. The neuroplasm contains well-developedtubules of the rough endoplasmic reticulum (ER) and small cisternae of the Golgi complex(GC). Mitochondria are rounded, small, with moderately pronounced cristae. Underconditions of round-the-clock darkness, we have found that the cell nuclei are rounded,less often determined by the nucleoli. In the neuroplasm there are locally dilated tubulesof the ER and cisternae of the GC, mitochondria with enlightened matrix and fragmentedcristae. Under conditions of round-the-clock illumination, the nuclei of the rounded formwith uneven contours of a nuclear membrane forming deep intussusception are revealed.Nucleoli were rarely identified. In the hyaloplasm, locally dilated tubules of the ERare identified. Mitochondria are small in size with an enlightened matrix and reducedcristae.Conclusions. The obtained results of submicroscopic examination of LPON neuronsof the hypothalamus of old rats revealed their relatively increased functional activityin the dark period. Under conditions of round-the-clock lighting, more pronouncedhypertrophic and initial destructive changes of the nuclei and organelles of the neuronsof the LPON of the hypothalamic were revealed, compared with the animals that wereunder the conditions of round-the-clock darkness. This is confirmed by the change in theultrastructure of nerve cells at 2 am the appearance of "dark" cells.

Environmentally benign and durable superhydrophobic coatings based on short fluorocarbon chain siloxane modified halloysite nanotubes for oil/water separation

Fluorinated siloxane (F-Si(OCH 3 ) 3 ) was synthesized from perfluoro (2-methyl-3-oxyhexyl) fluorine and N- (β-aminoethyl) -γ-aminopropyltrimethoxy silane, and then was used for hydrophobic modification of halloysite nanotubes (F-HNTs). A mixture of epoxy resin and F-HNTs was sprayed onto the surface of the stainless steel mesh. F-HNTs enhanced the surface roughness and reduced the surface energy, giving the mesh superhydrophobic/superlipophilic properties. The static water contact angle of coated mesh can reach 155.4 ± 0.3°. A series of oil and water mixtures can be separated, and the separation efficiency was higher than 97.8 ± 0.3%. After 50 cycles, the separation efficiency was still higher than 96.2 ± 0.5%. The coating mesh also had high separation efficiency for oil-water mixtures with different volume ratios and pH values. More importantly, the coated mesh still showed good stability in the harsh test conditions, such as strong acid, strong alkali, sand-paper wear and so on. Since the preparation of the coated mesh has the advantages of simplicity, scalability, and economy, it is expected to be applied on a large scale in the field of oil-water separation in the future. • Fluorosiloxane modified HNTs was used for fabricating superhydrophobic coatings. • Modified HNTs/epoxy was sprayed on the stainless steel mesh for oil-water separation. • This coated mesh has excellent separation efficiency and separation flux. • The coated mesh exhibited excellent stability under harsh external conditions.

Electrothermally triggered selective shape memory capabilities of CNT doped nanocomposites by Digital Light Processing

The capabilities of Digital Light Processed CNT doped nanocomposites for electrothermally triggered selective shape memory have been explored. Here, selective shape memory enables fixing the temporary shape and recovering the original one of different regions of a specimen individually, without affecting the other regions. In this regard, the shape memory capabilities of different matrices based on mixtures of rigid and elastic resins, consisting in hard segments (HS) and soft segments (SS), respectively, doped with CNTs have been investigated. A decrease in the HS:SS ratio leads to a decrease in the glass transition temperature, which constitutes the transformation temperature needed for fixing the temporary shape and recovering the original one. However, the electrical conductivity experiences a sudden drop, reaching values below the percolation threshold at 0:100 samples. Therefore, only the 100:0 and 80:20 samples were valid for shape memory triggered by Joule's effect. Furthermore, selective shape memory tests were conducted by placing different electrodes throughout the material by dividing the specimen in one, two or three individual regions that could be activated selectively. Here, it has been observed that the shape recovery ratio was above 75% in every case, proving the potential of the proposed materials and technique for selective shape memory activation by Joule's heating.

Synthesis and microwave absorption performance of layered hard carbon embedded with ZnO nanoparticles

C-based microwave absorbers have attracted intensity research interesting for more than 80 years, and many of them appear to be strong candidates as advanced high-performance microwave absorbers. Hard carbon (HC) based composites, as an important type of C-based materials, however, have rarely been studied as microwave absorbers, and their microwave absorption properties are largely unknown still now. In this study, the composites composed of layered HC embedded with ZnO nanoparticles (LHC@ZnONP) are synthesized by pyrolyzing the mixture of phenolic resin and ZnO nanoparticles.The morphology and structure of the LHC@ZnONP composites are examined by scanning electron microscopy, x-ray diffractometer, Raman spectrometer, transmission electron microscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared spectrometer. The microwave absorption properties of the as-synthesized composites are characterized by a vector network analyzer in the frequency range of 2–18 GHz. The LHC@ZnONP composites are stacked by HC layers with thickness of ~100 nm and ZnO nanoparticles with diameters of 25 nm, and exhibit a low optimal reflection loss of −38 dB and broad effective absorption bandwidth of 5.7 GHz at an absorption thickness of 3.3 mm. Their high dielectric loss capacity is mainly attributed to the interfacial polarization from the ZnO/HC and LHC/LHC interfaces, as well as the enhanced dipolar polarization caused by the defects, nanopores, and residual organic functional groups in the HC layers. Our study for the first time confirms the excellent microwave absorption properties of HC-based composites, which may provide a new insight for the design of high-performance microwave absorbers.

Nickel Boride/Boron Carbide Particles Embedded in Boron-Doped Phenolic Resin-Derived Carbon Coating on Nickel Foam for Oxygen Evolution Catalysis in Water and Seawater Splitting.

Electrolysis of seawater can be a promising technology, but chloride ions in seawater can lead to adverse side reactions and the corrosion of electrodes. A new transition metal boride-based self-supported electrocatalyst was prepared for efficient seawater electrolysis by directly soaking nickel foam (NF) in a mixture of phenolic resin (PR) and boron carbide (B4 C), followed by an 800 °C annealing. During PR carbonization process, the reaction of B4 C and NF generated nickel boride (Nix B) with high catalytic activity, while PR-derived carbon coating was doped with boron atoms from B4 C (B-CPR ). The B-CPR coating fixed Nix B/B4 C particles in the frames and holes to improve the space utilization of NF. Meanwhile, the B-CPR coating effectively protected the catalyst from the corrosion by seawater and facilitates the transport of electrons. The optimal Nix B/B4 C/B-CPR /NF required 1.50 and 1.58 V to deliver 100 and 500 mA cm-2 , respectively, in alkaline natural seawater for the oxygen evolution reaction.

Tuning nanomechanical properties of microstructures made by 3D direct laser writing

3D Direct laser writing (3D DLW) based on two photon polymerization represents a powerful technique for the additive manufacturing of 3D micro- and nano-structures, which have a number of promising applications in areas including biology and cell cultures up to soft robotic. New applications often entail the contact and movement of nanoscale areas, therefore understanding of the mechanical properties involved in such systems is necessary for creating reliable micro and nanoscale applications. Notably, knowledge about nanomechanics of 3D printed structures and its dependence on its geometry and contact size remains essential. This study focuses on the investigation of the Young’s modulus of 3D printed microstructures by Atomic Force Microscopy. Using the PeakForce QNM AFM mode, it was possible to determine the influence of the laser power and the monomer and their mixture on the micromechanical properties, in particular the Young's modulus. The fabricated structures are 2D structures, consisting of successive lines forming a square. Three different resins have been used based on poly(ethyleneglycol)diacrylate (PEGDA), trimethylolpropane triacrylate (TMPTA) and pentaerythritol triacrylate (PETA). The results obtained show that the increase in laser power increases the Young's modulus of these raw materials, since it induces a stronger crosslinking density. Mixtures of resins have also been formulated inducing a Young's modulus structure increase when increasing the amount of PETA. By combining these two approaches, tuning of the nanomechanical properties of the final microstructures on an unprecedented range covering 3 orders of magnitude, from MPa up to GPa have been successfully achieved. This major result paves the way to in-depth reflection on future works in nanorobotics or biomedical devices, where complex mechanical behavior are highly desired.

A novel three-dimensional network-based stearic acid/graphitized carbon foam composite as high-performance shape-stabilized phase change material for thermal energy storage

Three-dimensional porous carbon materials have received extensive attention as supports for shape-stabilized phase change materials (PCMs). In order to improve the loading capacity, thermal conductivity and encapsulation performance for PCMs, a three-dimensional graphitized carbon foam (GCF) was developed with gradient hierarchical porous surface. The GCF was successfully prepared by pyrolysis of nano-magnesium oxide/epoxy resin mixture followed by surface treatment through a carbon-thermal reaction of Fe 2 O 3 . Using the GCF prepared at 1200 °C (GCF-1200) as a support for stearic acid (SA), a novel three-dimensional network-based SA/GCF composite was achieved as shape-stabilized PCM. The results show that the GCF-1200 has a large SA loading capacity of 84.66 wt% without any liquid leakage. The prepared SA/GCF-1200 composite exhibits a good interfacial bonding between the GCF-1200 and SA without obvious phase separation in its fracture surface. The composite possesses a high compressive strength of 9.45 MPa increasing by about 3.02-fold compared with the GCF-1200, and meanwhile has a significantly improved thermal conductivity of 1.012 W/m K by 4.36 times that of pristine SA. In addition, the melting and freezing enthalpy for the composite was measured as 181.8 and 182.7 J/g, respectively, which corresponds to a thermal storage efficiency of up to 99.9%. More importantly, it presents excellent thermal reliability and chemical stability without evident changes in enthalpy after 200 thermal cycles. Therefore, the composite has a great potential for thermal energy storage applications. • Graphitized carbon foam (GCF) is obtained with gradient hierarchical porous surface. • Large loading capacity and high thermal conductivity of the GCF is achieved. • A good interfacial bonding between the GCF and stearic acid (SA) is observed. • A three-dimensional network-based shape-stabilized SA/GCF composite is prepared. • The composite phase change material has a good thermal stability and reliability.

Waste eliminated by waste under COVID-19 pandemic: Mixed plastic waste derived N,O-rich porous carbon nano-coral reefs for chlorophenol pollutants efficient capture

Both increasing emission of chlorophenol chemicals and plastic waste pollution are severe global environmental challenges, which is worth being explored to respond with a "waste eliminated by waste" coupling treatment strategy. Herein, we propose a one-step recyclable nano-MgO template strategy to prepare in-situ N, O-doped novel porous carbon coral reefs (PCNCR) directly derived from the mixture of real waste PET and melamine formaldehyde resin. The template precursor can be conveniently recycled by facile acetic acid pickling, vacuum evaporation and drying, and the whole preparing process does not involve any toxic solvents, massive consumption of pore-forming agents, or discharge of salty wastewater. The obtained PCNCRs have hierarchical porous structures and abundant N, O-doped species, and the textural parameters can be modulation linearly by varying the mass ratio of magnesium acetate to mixed waste plastics. The optimized PCNCR-1.25 exhibited remarkable adsorption capacity for chlorophenol contaminants (777.5 mg/g for 4-Chloro-3,5-dimethylphenol, PCMX and 538.74 mg/g for 4-Chloro-3-methylphenol, PCMC) in aqueous solution. Adsorption isotherm fitting studies revealed chlorophenol contaminants tended to be rapidly adsorbed on the PCNCR surface in the form of monolayer. And the system reached adsorption equilibrium at about 15 min, which was described by linear driving force model. Reusability test verified that PCNCR-1.25 had excellent adsorption stability for chlorophenol in continuous adsorption-regeneration cycles. DFT calculation illustrated the enhancement of chlorophenol adsorption by heteroatom species, especially nitrogen dopants. This work highlighted a low-cost and sustainable approach to defuse the dual environmental threat of chlorophenol emissions and plastic waste pollution simultaneously.

Development of thermoplastic epoxy filaments with shape memory properties

In this paper, an epoxy resin mixture composed of epoxy and phenol monomers is used to prepare thermoplastic epoxy polymer (EP-TP) through a polymerization reaction and shape memory thermoplastic epoxy filament (SMEF-TP) was successfully developed for the first time through a melt-drawing process. Tensile tests showed that the yield stress of the developed SMEF-TP reached 63 MPa, which is an increase of 54% compared with EP-TP films. Shape memory experiments showed that the developed SMEF-TP has excellent shape memory performance, with a shape fixation rate of 97%, a shape recovery rate of over 97%, and good stability in cycling. Based on the shape memory performance analysis, the shape recovery stress of the SMEF-TP was characterized. Shape recovery stress responded to temperature stability and increased with the increase of strain, reaching 1.45 MPa at a strain of 35%. The SMEF-TP can reach an energy density of 0.066 J/cm3 during thermal actuation and shows greater application potential when processed into textiles. In addition, the chemical structure, thermal performance, and dynamic mechanical performance of SMEF-TPs are analyzed. The developed SMEF-TP shows excellent shape memory performance, and the output shape recovery stress is more than 5 times that of EP-TP film, which provides huge application potential in the fields of artificial muscles and smart textiles.

Preparation, Characterization, and Evaluation of the Anticorrosion Performance of Submicron/Nanocarbon from Jute Sticks.

Jute stick, one of the most commonly and abundantly available agricultural waste product, was converted to a value-added submicron/nano jute carbon by using pyrolysis and high-energy ball milling techniques. The submicron/nano jute carbon was characterized using FE-SEM, TEM, EDS, XRD, XPS and Raman spectroscopy. The anticorrosive performance of the submicron/nano jute carbon was investigated through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) and salt spray techniques, on mild steel plates coated with a mixture of epoxy resin and the submicron/nano jute carbon. The electrochemical impedance of the steel coated with the composite coating was two orders of magnitudes higher than that of the specimen coated with neat epoxy. Consequently, the corrosion rate of specimens coated with composite coating was 13-20 times higher than that of steel coated with neat epoxy coating. The salt spray results also indicate an improvement in the corrosion resistance performance of the composite coating compared to the neat epoxy. The uniform distribution of the submicron/nano jute carbon particles in the epoxy resin improved the denseness of the composite coating by acting as a barrier against the diffusion of chloride, moisture, and oxygen, thus, improving the corrosion resistance of the developed coating.

Microstructures and luminescent regulation of Ce‐doped silicate glasses with high transmittance and thermal stability

AbstractThe traditional model for wLEDs usually encapsulates the phosphor and resin mixture on the InGaN blue‐emitting chip. However, the poor thermal stability of silicone resin will lead to the reduction of the luminescent intensity of the wLED devices. Glass has excellent thermal stability and transparency, which is a promising alternative to resins. In this work, Ce‐doped silicate luminescent glasses have been developed by a high‐temperature melting quenching method in air atmosphere. The luminescent intensity can be enhanced by increasing the heat treatment temperature and extending the heat treatment time in 10%H2/Ar atmosphere because Ce4+ ions can be reduced to Ce3+ ions. However, when the heat treatment temperature reaches 850°C, the generation of precipitates in the glass can reduce the luminescent intensity. The transmittance of glass can reach 87%, and the highest luminous intensity obtained when heat treated at 800°C. The glass transition temperature is 740°C and the thermal conductivity of the glass is .95 W m−1K−1, which is about five times higher than that of resin. The results show that the emerging Ce‐doped silicate luminescent glass could be the potential material for wLED applications.

Investigation of Young’s Modulus and thermal conductivity of epoxy based composite fiberglass material

In this research work, an investigation was made on the Young’s Modulus and thermal conductivity of fiberglass material reinforced with epoxy resin and hardener gum. Composites are made up with epoxy resin: hardener gum mixture of 10:1 ratio. Dog bone type specimen with end tab samples were prepared in different layers to find the Young’s modulus by center-loaded method and thermal conductivity by Lee’s apparatus method. Experimental results show that the Young’s Modulus increases when increasing the number of layers and amount of epoxy resin and hardener gum mixture apply on it. However, the thermal conductivity depends on the thickness of fiberglass mat reinforced with hardener gum and epoxy resin mixture.

Micro-cavity perfect blackbody composite with good heat transfer towards a flat-plate reference radiation source for thermal imagers

One of the key measures to secure reliable fever screening is to calibrate a thermal imager with an accurate flat-plate blackbody device in real time. We provide durable perfect blackbody plates with both high emissivity of >0.998 and good heat transfer, ideal for a high-precision reference radiation source. Reflectance measurements and heat transfer simulation demonstrate that a micro-cavity composite of a thin resin double layer or resin mixture with thermally conductive filler is an important solution for improving the emissivity and thermal performance of blackbody plates.

INFLUENCE OF DILUENTS AND PLASTICIZERS ON THE PROPERTIES OF EPOXY-POLYSULFIDE COMPOSITES

It was found that to increase the adhesive and physicomechanical properties of compositions based on epoxy resin and polysulfide rubber (thiokol), cured without heat treatment, it is necessary to carry out a preliminary thioetherification reaction (PRTE) due to the interaction of rubber mercaptan groups and oxirane cycles of epoxy resin at elevated temperatures and then use the product of this reaction to cure at room temperature. Composite materials based on the products of the thioetherification reaction significantly surpass analogs based on mechanical mixtures of epoxy resin and thiokol in terms of cohesive and adhesive strength, deformation capacity, fracture work, and specific impact strength. It is shown that the introduction of both diluents and plasticizers into the products of the preliminary thioetherification reaction of epoxy resins and polysulfide rubbers leads to an increase in the parameters of tensile strength and deformation capacity. The greatest strengthening effect is achieved with the use of oligoesteracrylate MGF-9 and glycidyl ether of diethylene glycol DEG-1, the smallest - with the introduction of the plasticizer EDOS. It was found that the introduction of plasticizers promotes some increase in the adhesive strength, but much less in comparison with the cohesive strength. In this case, the adhesion and cohesive characteristics change antibatically. It has been shown by dynamic mechanical spectrometry that the presence of diluents and plasticizers in epoxy-polysulfide composites leads to a decrease in the temperatures of the maximum values of the tangent of the angle of mechanical losses, loss modulus, the initial and final sections of the transition of the material from the glassy to the highly elastic state, as well as the density of the chemical network in the epoxy matrix.

Optimized condition for eco-friendly wood composites manufactured from castor oil-based polyurethane

Castor oil is used as polyurethane (PU) polyol raw material with three kinds of isocyanate. In this study, polymeric diphenylmethane diisocyanate (PMDI), Desmodur L and Desmodur N were used to compare the structures of aromatic isocyanate oligomers, aromatic isocyanate trimers and aliphatic isocyanate trimers. Water, organosiloxane and dibutyltin dilaurate were used as the bubble agent, surfactant and catalyst to manufacture PU resin with molar ratios of NCO/OH of 1/1, 1.5/1 and 2/1, respectively. The results show that increasing the NCO/OH molar ratio increases the water absorption and hard segment content of PU resins. PMDI-based PU and Desmodur N-based PU resins have high thermal stability. The low-density composites of ca. 450 Kg/m3 were prepared successfully from a mixture of PU resin and China fir (Cunninghamia lanceolata) particles. The results demonstrated that increasing the NCO/OH molar ratio and using Desmodur L are optimal and beneficial to improving the composites’ dimensional stability and internal bonding strength. The composites prepared with bio-based PU resins have lower thickness swelling rates and higher internal bonding strengths than formaldehyde-based and commercial PU-based resins. Bio-based PU composites can be used as eco-friendly building materials and replace formaldehyde-based manufacturing composites.

Investigation on tensile behavior of glass-fiber reinforced polymer matrix composite with varying orientations of fibers

The main objective of this work is to develop a new polymer based composite material having different reinforcement angle orientations and studies its tensile behavior. For fiber reinforced polymer matrix composites E-2 glass fiber reinforcement and epoxy resin for matrix is used. E-2 g1ass fiber has high strength, chemical resistance and good insulating properties. Epoxy being less viscous allows good adhesion to fibers used in laminate preparation, without misalignment of fibers. Hand layup technique has been adopted for preparation of laminate. Glass fibers are laid, mixture of epoxy resin and hardener is smeared on it alternately, until laminate of desired thickness is achieved, and is left to atmosphere for curing. 2.5 mm laminate is prepared by placing glass fibers of 0.25 mm thickness one above the other. The prepared laminate is then taken for cutting according to ASTM standards (D3039) of 3 sets of rectangular specimens. For first set comprises of 90° angle-oriented specimen, second and third sets for 45° and 30° respectively. These specimens are subjected to tensile test in Lloyd UTM and load being applied gradually at the rate of 2 mm/min is continued until the material fails. The computer simulation plots the graph during the entire testing process and stops when the material fails.

Electrode for selective bromide removal in membrane capacitive deionisation

Due to the shortage of freshwater around the world, seawater is becoming an important water source. However, seawater contains a high concentration of bromide that can form harmful disinfection by-products during water disinfection. Therefore, the current seawater reverse osmosis (SWRO) has to adopt two-pass reverse osmosis (RO) configuration for effective bromide removal, increasing the overall desalination cost. In this study, a bromide selective composite electrode was developed for membrane capacitive deionisation (MCDI). The composite electrode was developed by coating a mixture of bromide selective resin and anion exchange polymer on the surface of the commercial activated carbon electrode, and its performance was compared to that of conventional carbon electrode. The results demonstrated that the composite electrode has ten times better bromide selectivity than the conventional carbon electrode. The study shows the potential application of MCDI for the selective removal of target ions from water sources and the potential for resource recovery through basic modification of commercial electrode.

Laboratory Research and Evaluation on Design and Application Performance of High-Performance Cold-Mix Resin.

To improve the safety of orthotropic steel bridge decks and the construction efficiency of bridge deck pavement by enhancing the performance of pavement materials, a new-generation, high-performance cold-mix resin was prepared by carrying out the combination of micro-characteristic analysis and performance test. Meanwhile, the pavement performance and fatigue performance of high-performance cold-mix resin mixtures and hot-mix epoxy saphalt mixtures as a control group were studied experimentally. The results show that different kinds of epoxy resins show bisphenol structure in essence. The curing exothermic peak temperature of the cold-mix resin increases with the heating rate. Both the specific heat capacity (△CP) of cold-mix resin and cold-mix resin asphalts exhibit a sudden change between −20 °C and 40 °C. In resin asphalt mixtures, cold-mix resin forms the network structure skeleton whereas the asphalt distributed in the form of tiny particles. The dosage of respective component has a significant effect on the tensile strength and elongation at break of cold-mix resin. Compared with hot-mix epoxy asphalt mixtures, cold-mix resin mixtures exhibit comparable water stability and high and low-temperature performance, as well as greater fatigue life.

Vibration Damping Behavior of Composite Laminates Interleaved with PZT- and SMA-Particle-Dispersed Resin Mixture Films

In this study, functional particles such as piezoelectric (PZT) ceramic and shape memory alloy (SMA) particles have been incorporated in composite laminates to accelerate the loss of vibration energy. PZT ceramic particles and SMA particles are mixed with epoxy resin and rolled into a film shape before they are interleaved between prepreg plies for better distribution of the particles. Loss factor (tan δ) was measured with various particle loadings to verify the effectiveness of interleaving in the vibration damping of laminate specimens. It was observed that there existed an optimal content for maximizing the damping ability avoiding an aggregation of the particles. In addition, when PZT and SMA particles are applied simultaneously, PZT could enhance the vibration damping capability of SMA because PZT particles could generate thermal energy, and it would accelerate the phase change of the SMA particles. In this research, the effective way for enhancing the particle dispersion was suggested, and the particle loading could be controlled by finding an optimal content. Flexural moduli of the specimens were also measured, and they exhibited no change as the content of the particles increases. Therefore, dispersed particles used in this study increased the vibration damping capacity without reducing the mechanical properties.

New Insights on Expandability of Pre-Cured Epoxy Using a Solid-State CO2-Foaming Technique.

Foaming an epoxy is challenging because the process involves the curing reaction of epoxy and hardener (from monomer to oligomer, to a gel and a final three-dimensional crosslinked network) and the loading of gas phase into the epoxy phase to develop the cellular structure. The latter process needs to be carried out at the optimum curing stage of epoxy to avoid cell coalescence and to allow expansion. The environmental concern regarding the usage of chemical blowing agent also limits the development of epoxy foams. To surmount these challenges, this study proposes a solid-state CO2 foaming of epoxy. Firstly, the resin mixture of diglycidylether of bisphenol-A (DGEBA) epoxy and polyamide hardener is pre-cured to achieve various solid-state sheets (preEs) of specific storage moduli. Secondly, these preEs undergo CO2 absorption using an autoclave. Thirdly, CO2 absorbed preEs are allowed to free-foam/expand in a conventional oven at various temperatures; lastly, the epoxy foams are post-cured. PreE has a distinctive behavior once being heated; the storage modulus is reduced and then increases due to further curing. Epoxy foams in a broad range of densities could be fabricated. PreE with a storage modulus of 4 × 104–1.5 × 105 Pa at 30 °C could be foamed to densities of 0.32–0.45 g/cm3. The cell morphologies were revealed to be star polygon shaped, spherical and irregularly shaped. The research proved that the solid-state CO2-foaming technique can be used to fabricate epoxy foams with controlled density.