Thermal Curing Process Research Articles

Anomalously enhanced thermal performance of carbon-nanotubes coated micro heat pipes

We conduct experiments to study the effects of incorporation of carbon nanotubes (CNTs) coatings on the thermal performance of micro heat pipe (MHP) arrays. The microchannels of MHP are fully coated with CNTs which are functionalized through a thermal curing process. The cured CNTs coating manifests a superhydrophilic characteristic and fast water permeation property. The rapid water permeation through CNTs nanostructure enhances the evaporation at the evaporator section and the fluid circulation synergically in the MHP. For evaporation, the superhydrophilic highly permeable porous CNTs nanostructures increase the nucleation sites and promote film-wise evaporation which is more efficient than the bulk evaporation. For circulation of working fluid, an intricately interconnected CNTs networks facilitate the fluid transport with enhanced capillary pressure. The effective thermal conductivity, which denotes the overall performance of a micro heat pipe manifests a maximum enhancement of 202%; and the evaporator heat transfer coefficient which represents the evaporation strength is enhanced up to 61%. Computationally, molecular dynamics simulations are performed to investigate the fast water permeation property of CNTs nanostructure which leads to the anomalous thermal performance enhancement. This study provides interesting insight into the viability of incorporating CNTs nanostructures into an MHP for microscale cooling applications.

Extraordinarily enhanced evaporation of water droplets on graphene-nanostructured coated surfaces

Functionalized graphene coating possessing the unique property of ultrafast water permeation manifests itself in enhancing the evaporation heat transfer. The intermolecular interactions between the intercalated water molecules with the hydrophobic carbon atoms and the oxygenated functional groups in the graphene nanocapillaries facilitate the magnificent spreadability and permeability of water on a heated surface. The fast water permeation property of graphene can be controlled through a thermal curing process at different curing temperatures. Here we experimentally investigate the application of graphene nanoplatelets (GNPs) coatings for the enhancement of evaporation of small sessile water droplets at sub-boiling temperatures. The ultrafast water permeation within the functionalized nanostructured GNPs facilitates the fast absorption of latent heat of evaporation, leading to the anomalously effective filmwise evaporation. Ultimately, the cooling effectiveness of a water droplet on the GNPs-coated surface is extraordinarily enhanced by an unprecedented maximum of 4866% at a surface temperature of 75 °C compared against the bare surface. These results envision the great potential of graphene-based coatings to address the issues of increased heat generated from the high power density electronics, leading to enhanced performance and extended component lifespans.

3D Interconnected Boron Nitride Networks in Epoxy Composites via Coalescence Behavior of SAC305 Solder Alloy as a Bridging Material for Enhanced Thermal Conductivity.

In this study, hybrid fillers of spherically shaped aggregated boron nitride (a-BN) attached with SAC305, were fabricated via simple stirring and the vacuum filtration method. a-BN was used as the primary conductive filler incorporated with epoxy resin, and these fillers were interconnected each other via the coalescence behavior of SAC305 during the thermal curing process. Based on controlled a-BN content (1 g) on 3 g of epoxy, the thermal conductivity of the composite filled with hybrid filler (a-BN:SAC305 = 1:0.5) reached 0.95 W/mK (33 wt%) due to the construction of the 3D filler network, whereas that of composite filled with raw a-BN was only 0.60 W/mK (25 wt%). The thermal conductivity of unfilled epoxy was 0.19 W/mK.

Thermal kinetics of free volume in porous spin-on dielectrics: Exploring the network- and pore-properties

Comprehensive ex-situ and in-situ investigations of thermal curing processes in spin-on ultra-low-k thin films conducted by positron annihilation spectroscopy and Fourier transform infrared spectroscopies are presented. Positron annihilation lifetime spectroscopy of ex-situ cured samples reveals an onset of the curing process at about 200 °C, which advances with increasing curing temperature. Porogen agglomeration followed by diffusive migration to the surface during the curing process leads to the generation of narrow channels across the film thickness. The size of those channels is determined by a pore size distribution analysis of positron lifetime data. Defect kinetics during in-situ thermal curing has been investigated by means of Doppler broadening spectroscopy of the annihilation radiation, showing several distinct partially superposed and subsequent curing stages, i.e., moisture and residual organic solvents removal, SiOx network cross-linking, porogen decomposition, and finally creation of a stable porous structure containing micropore channels interconnecting larger mesopores formed likely due to micelle like interaction between porogen molecules, for curing temperatures not larger than 500 °C. Static (sequencing curing) states captured at specific temperature steps confirm the conclusions drawn during the dynamic (continuous curing) measurements. Moreover, the onset of pore inter-connectivity is precisely estimated as pore interconnectivity sets in at 380–400 °C.

Morphology, thermal, and mechanical properties of κ-aluminum oxide/CTBN/epoxy nanocomposites

In this study, novel κ-aluminum oxide (κ-Al2O3) nanosheets and carboxyl-terminated butadiene-acrylonitrile (CTBN) liquid rubber were homogeneously mixed in epoxy resin solution by a homogenizer with a high shear force. Then, κ-Al2O3/CTBN/epoxy nanocomposites were fabricated by a stepwise thermal curing process. The dispersion of κ-Al2O3 nanosheets in the CTBN/epoxy blend was examined by a transmission electron microscopy. The effects of κ-Al2O3 nanosheets on the thermal, tensile, and morphological properties of κ-Al2O3/CTBN/epoxy nanocomposites were systematically studied. Results indicated that κ-Al2O3 nanosheets can effectively increase both the tensile modulus and elongation at break of κ-Al2O3/CTBN/epoxy nanocomposites. Meanwhile, the optimized properties were observed when 5 phr of κ-Al2O3 nanosheets were added. The thermal stability (Td5%) and glass transition temperatures (Tg) of κ-Al2O3/CTBN/epoxy nanocomposites were also higher than those of CTBN/epoxy blend. According to experimental results, the κ-Al2O3 nanosheets can be considered as suitable and effective as a reinforcing material for epoxy resin or other polymers.

Vibration damping and dynamic mechanical attributes of core-shell particles modified glass epoxy prepregs cured using microwave irradiations

Microwave curing has a tremendous potential to be used as an alternative to other thermal curing processes due to its shorter curing time and lower consumption of energy. Current research investigates the damping and dynamic mechanical characteristics of core-shell polymer (C/SH) particle modified glass fibre prepreg (GFRP) manufactured using microwave irradiations. The addition of C/SH particles has shown a significant improvement in damping and dynamic mechanical properties. The optimal areal weight per interface (AWI) for C/SH particles was established as 40 gsm. With this optimal addition, the laminates showed a 21.5% increase in mechanical loss factor, tan δ, and 52.7% in the vibration damping capability as noticed from dynamic mechanical and the forced vibration tests respectively. The underlying reasons for the improvement in properties with the addition of C/SH particles are also deliberated in this paper.

The study on curing and weight-loss mechanisms of benzoxazine during thermal curing process

Based on the weight loss and small molecule volatiles released during the thermal curing process of three kinds of benzoxazines, bisphenol A/aniline type benzoxazine (BA-a), p-cresol/diamine type benzoxazine (MPH-mda) and 2,4-xylenol/4,4′-methylenebis-(2,6-diisopropyl) aniline type benzoxazine (DMPH-mdpa), their curing mechanisms and the weight-loss mechanisms were studied. The weight-loss ratios and structure changes of these benzoxazines during the curing process were studied by weighing method, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The volatiles released from these benzoxazines during different curing stages were collected by a self-made experimental device. The structures of these volatiles were characterized by FTIR and proton nuclear magnetic resonance spectroscopy (1H NMR). The results showed that the mixtures of imine, triazine, aniline and Schiff base were released from the cracking of the intermediate during the thermal curing of BA-a. Compared with BA-a, the weight loss of MPH-mda was smaller, and its volatile was a small amount of stable diamine type Schiff base. For DMPH-mdpa, because all active reaction points on benzene ring were occupied by alkyl groups, it cannot form effective polymer structures after ring-opening reactions, which led to that DMPH-mdpa had the most weight loss during the curing process, and mainly generated phenol type volatiles.

An in-situ crosslinking binder for binder jet additive manufacturing

Additive Manufacturing (AM) of metals is a potentially disruptive technology that could significantly change the industrial supply chain. There are a limited number of AM methods capable of creating metal parts, and one method showing significant potential is Binder Jet AM (Binder Jetting). Binder Jetting utilizes an inkjet print head to deposit a binder fluid onto a powder bed and bind together powder particles into a desired geometry. This study investigates a new binder system consisting of a difunctional monomer, triethylene glycol dimethacrylate (TEG-DMA). TEG-DMA exhibits excellent printability with an Ohnesorge’s number of .258 making the Z number 3.876. During the thermal curing process, the difunctional monomer polymerizes and crosslinks at the onset temperature of 138 °C, becoming a solid dimethacrylate network. When the binder is utilized within the stainless-steel powder bed at 200 °C, it forms a network incorporating the stainless-steel particles, binding the powder into any specified geometry. Crosslinking the monomer within the stainless-steel 420 powder bed imparts a flexural strength of 1.0–3.3 MPa to the green part depending on the volume of monomer in the part. After sintering, the final stainless-steel parts results in a void fraction close to 60 % and carbon content below 0.4 %.

Symmetrical Wrinkles in Single-Component Elastomers with Fingerprint-Inspired Robust Isotropic Dry Adhesive Capabilities.

Robust and inexpensive dry adhesives have a great potential in multitudinous industrial applications. However, to date, the fabrication of dry adhesives, prepared using high aspect ratio structures in general, requires specific equipment and time-consuming processes, which limit their practicable utilization. Inspired from human fingerprints, in this study, we created durable single-component elastomer surfaces with symmetric and multiple concentric-shaped wrinkled patterns that exhibit isotropic dry adhesion capabilities. The dynamic interfacial release-induced surface wrinkling property of a rigid degradable polymeric capping layer [i.e., poly(l-lactide) (PLLA)] was exploited on a soft elastomer substrate [i.e., polydimethylsiloxane (PDMS)] to spontaneously form wrinkled PLLA/PDMS bilayer composites. After conducting a two-step thermal curing process on the composite and hydrolysis of the PLLA capping layer, a single-component microwrinkled PDMS surface with a large area and symmetric patterns could be generated. The patterns show flexible, durable, and isotropic dry adhesion capabilities that could be controlled by tuning their geometrical parameters (wrinkle wavelengths and amplitudes) and elastic modulus. In particular, the formation of symmetrically wrinkled patterns without using expensive lithography for patterning and costly material precursors is an advantage and could be extended to other industrial applications, such as damage-free transportation, biomimetic climbing robots, and biocompatible medical patches.

Isoconversional cure kinetics of a novel thermosetting resin based on linseed oil

In the current work, the thermal curing process of maleinated acrylated epoxidized linseed oil (MaAELO) mixed with reactive diluent, initiator, and accelerator was studied by using isothermal differential scanning calorimetry (DSC) and dynamic rheology. The investigations encompassed (1) the determination of the whole set of apparent kinetic parameters, Ea(α), A(α), and f(α) by using two accurate isoconversional kinetic analysis methods and the compensation effect, (2) the prediction of cure conversion curves, α(t), at arbitrary processing temperatures with all three kinetic parameters in comparison with the prediction based on Ea(α) alone, and (3) the determination of molecular and macroscopic gelation during the thermal cure of MaAELO resin mixture. The thermal cure of MaAELO resin mixture did not start immediately but after a remarkable induction period. It was possible to determine the kinetic parameters and use them to predict the induction period for arbitrary process temperature. In addition, the glass transition temperature, Tg, of thermally cured MaAELO resin mixture was measured by thermomechanical analysis and dynamic DSC.

Engineered superhydrophilicity and superhydrophobicity of graphene-nanoplatelet coatings via thermal treatment

Superwettable materials are destined for a wide range of multifunctional applications. An ingenious, cost-effective yet simple method is proposed to control the superwettability of graphene through a thermal curing process at 300 °C under atmospheric pressure. By functionalizing graphene nanoplatelets (GNPs) with oxygenated groups, superhydrophilic surface with a water/air contact angle of 0° manifesting the ultrafast water permeation property is synthesized. Oppositely, superhydrophobic surface with antiadhesive property to water is obtained by functionalizing GNPs with siloxane groups under the same conditions. The superhydrophobicity is justified with a static contact angle of 163° ± 2.8° with a low contact angle hysteresis of 1.53° ± 0.86°. The chemical structures of the superwettable graphene are elucidated using various spectroscopy techniques. Theoretically, by using molecular dynamics simulations, we have further examined and testified the tunable superwettability phenomena of graphene. This study provides important insights into a facile approach in synthesizing advanced materials with superwettability for multifunctional high-performance applications.

Development and Characterization of Stable Polymer Formulations for Manufacturing Magnetic Composites

Polymer bonded permanent magnets find significant applications in a multitude of electrical and electronic devices. In this study, magnetic particle-loaded epoxy resin formulations were developed for in-situ polymerization and material jetting based additive manufacturing processes. Fundamental material and process issues like particle settling at room temperature and elevated temperature curing, rheology control and geometric stability of the magnetic polymer during the thermal curing process are addressed. Control of particle settling, modifications in rheological behavior and geometric stability were accomplished using an additive that enabled the modification of the formulation behavior at different process conditions. The magnetic particle size and additive loading were found to influence the rheological properties significantly. The synergistic effect of the additive enabled the developing of composites with engineered magnetic filler loading. Morphological characterization using scanning electron microscopy revealed a homogenous particle distribution in composites. It was observed that the influence of temperature was profound on the coercive field and remanent magnetization of the magnetic composites. The characterization of magnetic polymers and composites using rheometry, scanning electron microscopy, X-ray diffraction and superconducting quantum interference device (SQUID) magnetometry analysis enabled the correlating of the behavior observed in different stages of the manufacturing processes. Furthermore, this fundamental research facilitates a pathway to construct robust materials and processes to develop magnetic composites with engineered properties.

Deformation measurement within adhesive bonds of aluminium and CFRP using advanced fibre optic sensors

Monitoring the deformation within an adhesive joint during the curing cycle provides valuable information regarding the build-up of thermal strain and stress. Distributed fibre optic sensors are very useful for spatial continuous measurements of deformation or temperature. Integrated into a hybrid joint, the thermal curing process of the adhesive can be monitored. This detailed insight into the joint helps to understand the deformation and thereby also the resulting stress. Analysing the deformation process establishes the foundation to adapt techniques to reduce the thermally induced deformation and thereby the resulting stress.

Sustainable access to fully biobased epoxidized vegetable oil thermoset materials prepared by thermal or UV-cationic processes.

Beyond the need to find a non-toxic alternative to DiGlycidyl Ether of Bisphenol-A (DGEBA), the serious subject of non-epichlorohydrin epoxy resins production remains a crucial challenge that must be solved for the next epoxy resin generations. In this context, this study focuses on the valorization of vegetable oils (VOs) into thermoset materials by using (i) epoxidation of the VOs through the “double bonds to epoxy” synthetic route and (ii) synthesis of crosslinked homopolymers by UV or hardener-free thermal curing processes. A thorough identification, selection and physico-chemical characterization of non-edible or non-valuated natural vegetable oils were performed. Selected VOs, characterized by a large range of double bond contents, were then chemically modified into epoxides thanks to an optimized, robust and sustainable method based on the use of acetic acid, hydrogen peroxide and Amberlite® IR-120 at 55 °C in toluene or cyclopentyl methyl ether (CMPE) as a non-hazardous and green alternative solvent. The developed environmentally friendly epoxidation process allows reaching almost complete double bond conversion with an epoxy selectivity above 94% for the 12 studied VOs. Finally, obtained epoxidized vegetable oils (EVOs), characterized by an epoxy index from 2.77 to 6.77 meq. g−1 were cured using either UV or hardener-free thermal curing. Both methods enable the synthesis of 100% biobased EVO thermoset materials whose thermomechanical performances were proved to linearly increase with the EVOs' epoxy content. This paper highlights that tunable thermomechanical performances (Tα from −19 to 50 °C and Tg from −34 to 36 °C) of EVO based thermoset materials can be reached by well selecting the starting VO raw materials.

Large-Area Stable Superhydrophobic Poly(dimethylsiloxane) Films Fabricated by Thermal Curing via a Chemically Etched Template.

Inspired by nature, large-area stable superhydrophobic poly(dimethylsiloxane) (PDMS) films have generated extensive interest for various applications such as self-cleaning, corrosion protection, liquid transport, optical services, and flexible electronics. However, the current methods used to prepare such films are difficult to apply for efficient large-area fabrication. In this article, an effective technique for fabricating low adhesive superhydrophobic films based on the use of a chemically etched template followed by a thermal curing process is introduced. On the basis of this approach, the importance of chemical solution concentration as well as etching time is discussed to outline the specific rules required for forming different surface topographies of the templates. Then, PDMS films with varying wettabilities can be fabricated in which one can achieve CA > 160° and SA < 10°. Finally, for engineering needs and actual preparation, large-area PDMS films are obtained via a roll-to-roll (R2R) process, which show a superhydrophobic property even after high-intensity friction and have excellent acid and alkaline resistance, UV resistance, and optical transparency. The prepared large-area stable superhydrophobic PDMS films have the potential to be used in the aerospace field in the future because of their excellent anti-icing performance.

Amine-Functionalized TiO2 Nanoparticles Covalently Loaded into Epoxy Networks via Thermal and Microwave Curing Processes

TiO2 nanoparticles were surface modified by NH2-functionalized organic moieties, and then chemically loaded into diglycidyl ether of bisphenol A-derived epoxy networks. Amine functionalization of these organically modified nanoparticles allowed them to have an efficient participation in the curing processes. Alongside the main amine hardener, i.e., 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane, the aminated TiO2 played the role of a new inorganic co-hardener. Thermal and microwave-assisted curing processes resulted in epoxy-based composites incorporated by uniformly dispersed TiO2 nanoparticles. Diffuse reflectance ultraviolet-visible spectra showed that unlike the neat synthesized counterparts, TiO2-loaded epoxy composites have significant absorption in the visible range of 400–700 nm. According to the results obtained from atomic force microscopy technique, it was found that the microwave-assisted curing process results in a smoother surface in comparison with the thermal one. Transmission electron microscopy obviously demonstrated that the average size of the loaded particles is below 50 nm. Thermogravimetric analysis of the TiO2-containing epoxy networks revealed that the resulted composites are thermally decomposed through a simple one-step process at about 360 °C. Dynamic mechanical thermal analysis profiles indicated that no agglomeration of the nanoparticles occurs during the curing processes of the epoxy resin, and the incorporated nanoparticles somewhat limit the segmental motions of the polymer chains.

Influence of N‐vinyl‐2‐pyrrolidone and methacrylic acid on thermal curing process of 2‐hydroxyethyl methacrylate hydrogel

ABSTRACTThis study investigated the effects of N‐vinyl‐2‐pyrrolidone (NVP) and methacrylic acid (MA) comonomers on the curing characteristics and properties of poly(2‐hydroxyethyl methacrylate) (PHEMA) hydrogel for soft contact lenses. A real‐time temperature measurement system was devised and the exothermic behaviors of hydrogel contact lenses comprising PHEMA, P(HEMA/NVP), and P(HEMA/MA) during oven‐curing condition were analyzed. The results of the real‐time temperature measurement were compared with the experimental analysis by using differential scanning calorimetry at different heating rates. NVP and MA content changes affected the HEMA‐based hydrogel's equilibrium water content (EWC), contact lens diameter, and gel fraction. HEMA‐based hydrogel sheets with varying NVP and MA contents were fabricated and mechanically characterized. The temperature at which the exothermic reaction occurred varied depending on the type of added comonomer and the exothermic reaction of HEMA containing NVP was delayed. When NVP was added, the mechanical strength and EWC were lower than when MA was added. In order to maintain the mechanical properties while improving the equilibrium moisture content of the lens, it was found that the use of MA is more advantageous than the use of NVP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48622.

Optimized Synthesis of Biodegradable Elastomer PEGylated Poly(glycerol sebacate) and Their Biomedical Application.

Poly(glycerol sebacate) (PGS), a biodegradable elastomer, has been extensively explored in biomedical applications for its favorable mechanical properties and biocompatibility. Efforts have been made to fabricate multifunctional PGS copolymer in recent years, in particular PGS-co-PEG (poly(glycerol sebacate)-co-polyethylene glycol) polymers. However, rare research has been systematically conducted on the effect of reactant ratios on physicochemical properties and biocompatibility of PGS copolymer till now. In this study, a serial of PEGylated PGS (PEGS) with PEG content from 20% to 40% and carboxyl to hydroxyl from 0.67 to 2 were synthesized by thermal curing process. The effects of various PEGS on the mechanical strength and biological activity were further compared and optimized. The results showed that the PEGS elastomers around 20PEGS-1.0C/H and 40PEGS-1.5C/H exhibited the desirable hydrophilicity, degradation behaviors, mechanical properties and cell viability. Subsequently, the potential applications of the 20PEGS-1.0C/H and 40PEGS-1.5C/H in bone repair scaffold and vascular reconstruction were investigated and the results showed that 20PEGS-1.0C/H and 40PEGS-1.5C/H could significantly improve the mechanical strength for the calcium phosphate scaffolds and exhibited preferable molding capability for fabrication of the vascular substitute. These results confirmed that the optimized PEGS elastomers should be promising multifunctional substrates in biomedical applications.

Thermomechanical characterization and modeling of fast-curing polyurethane adhesives

In the context of lightweight design and modern hybrid technologies, the importance of structural and soft adhesives in industrial applications is increasing. Therefore, this paper examines a relatively soft polyurethane adhesive characterized by showing nonlinear viscoelastic behavior at room temperature and enduring large deformations. It is well suited for applications under dynamic loadings and can compensate gap changes generated by materials with different thermal expansion coefficients. Theoretically, the examined one-component polyurethane adhesive can be cured either thermally or through humidity, resulting in the same mechanical characteristics. Comparing both curing reactions, humidity curing is much slower than thermal curing. The latter can be controlled through the temperature, which may be applied through heating rates of up to $$150\,\hbox {K}\,\hbox {min}^{-1}$$. However, in comparison with metals polyurethane conducts the heat with a much smaller rate which results in high temperature gradients within the adhesive layer. This paper focuses on the modeling of a fast-curing polyurethane adhesive under consideration of the changes in density and thermomechanical material properties induced by thermal curing. Therefore, the material properties need to be observed throughout the thermal curing process, from the uncured fluid to the cured rubber material. In the long term, the accurate prediction of the materials behavior will ultimately facilitate the optimization of the curing process.

Corrosion Studies of 12-Aminododecanoate Modified Zn-Al LDH/Epoxy Coating

Addition of environmentally friendly layered double hydroxide (LDHs) to organic coatings can increase barrier properties within the coatings due to the platelet structure of the LDHs. A new approach combining silane coupling agents to enhance compatibility of the inorganic and organic matrix is used to form improved corrosion resistance coatings. For this work, Zn-Al-LDH are prepared via a co-precipitation method and modified by sodium 12-aminododecanoate through an anion exchange process. The organo-modified layered double hydroxide (LDH) is functionalized using 3-aminopropyltriethoxysilane (APTES) which is then incorporated into the epoxy matrix (EPON 828). The reaction between amine part of the amino dodecanoate as a strong nucleophilic group and epoxy ring part as an electrophilic group improves compatibility of LDHs layers and epoxy molecules in the composite. Differential scanning calorimetry is used to study this exothermic epoxy-amine ring opening reaction to determine the curing temperature of the coatings before and after modified LDH inclusion. The change in LDH structure, effect of incorporation of modified LDHs in the epoxy matrix, grafting of APTES on the LDH surface and elemental analysis are investigated respectively, by x-ray diffraction, thermogravimetric analysis, infrared spectroscopy and energy dispersive x-ray analysis. In the last step of preparation, Epikure 3571 as a curing agent, is added to the LDHs/epoxy system, then the coating is applied on steel substrates. After the thermal curing process, the anti-corrosion performance provided by this coating is assessed by multiple methods including, open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl aqueous solution. Further, scanning electron microscopy is used to study morphological changes on the coating before and after immersion test and to scan the localized corrosion spots. The results are compared with the coated steel samples with clear epoxy coating and none modified LDH/epoxy. Figure 1