Fast Curing Research Articles

Tin-Containing Crystalline Copolymers as Latent Catalysts for Polyurethanes

For many applications, polyurethanes (PU) need to have a fast curing speed but long pot life. Latent catalysts are seen to be one of the approaches that can fulfill the need. In this article, we ha...

Electrohydrodynamic Jet Printing of 1D Photonic Crystals: Part II—Optical Design and Reflectance Characteristics

AbstractAdditive manufacturing systems that can arbitrarily deposit multiple materials into precise, 3D spaces spanning the micro‐ to nanoscale are enabling novel structures with useful thermal, electrical, and optical properties. In this companion paper set, electrohydrodynamic jet (e‐jet) printing is investigated for its ability in depositing multimaterial, multilayer films with microscale spatial resolution and nanoscale thickness control, with a demonstration of this capability in creating 1D photonic crystals (1DPCs) with response near the visible regime. Transfer matrix simulations are used to evaluate different material classes for use in a printed 1DPC, and commercially available photopolymers with varying refractive indices (n = 1.35 to 1.70) are selected based on their relative high index contrast and fast curing times. E‐jet printing is then used to experimentally demonstrate pixelated 1DPCs with individual layer thicknesses between 80 and 200 nm, square pixels smaller than 40 µm across, with surface roughness less than 20 nm. The reflectance characteristics of the printed 1DPCs are measured using spatially selective microspectroscopy and correlated to the transfer matrix simulations. These results are an important step toward enabling cost‐effective, custom‐fabrication of advanced imaging devices or photonic crystal sensing platforms.

Visible light-induced cationic photopolymerization by diphenyliodonium hexafluorophosphate and benzothiadiazole dyes

New benzothiadiazole-based long-wavelength organic dyes (Y-1 and Y-2) were prepared for effectively sensitizing diphenyliodonium hexafluorophosphate (IOPF) to initiate the fast curing of bisphenol-A epoxy resin (E51) under visible light, avoiding traditional UV light sources that have high energy and high radiation. Y-1 and Y-2 have absorption spectra extended to more than 550 nm. By using Y-1 and Y-2 as photosensitizers for IOPF, E51 reach high epoxy conversions of 95% under light wavelength of 470-nm irradiation. IOPF and benzothiadiazole dyes present at the same time show good visible-light initiating activity. The high curing conversions are attributed to the photoelectron transfer reaction between diphenyliodonium hexafluorophosphate and benzothiadiazole dyes, based on our photochemical and electrochemical experiments. In addition, the terminated groups or of Y-1 (–F) and Y-2 (–OCH3) have a great influence on the photopolymerization rate of the curing systems and thermal properties of E51 after cured. In addition, E51 was even polymerized about 70% in the presence of 510-nm light filter.

Synthesis and photo-curing properties of polyurethane acrylates with difunctional acrylate

Although a photo curing is more efficient in terms of time, solvent, and cost than a thermal one, photo-curable coatings require low viscosity and fast curing speed due to workability and time saving, respectively. A high viscous oligomer with multi-acryl groups is one of main components to determine its physical property after curing and then viscosity of coatings is controlled by adding a diluent. The polyurethane acrylates were newly synthesized by using ethylene diamine as a chain extender in poly(ε-caprolactone) polyol, dicyclohexylmethane 4,4′-diisocyanate, and isocyanato acrylate (ICA) containing diacrylate and diisocyanate groups. IR spectra were used to identify the synthesis and photo curing process. The mechanical properties of the cured films were analyzed by UTM. The results showed that the tensile strength of the UV-cured films was depended on the ICA content in the polyurethane acrylates.

Recoverable room temperature curable reversible material

Repetitive use and effective recycling of the materials are vital to overcome the current environmental challenges. In case of polymeric materials, the high curing temperatures significantly limit their application. In this study, a series of polymers with thermal reversibility at room temperature were synthesized. The main chain of the polymer systems was composed of polyethylene glycol diglycidyl ether (PEGDGE) and polypropylene glycol diglycidyl ether (PPGDGE). The polymers were obtained by initial chain-extension of furfurylamine (FA) and subsequent Diels-Alder (DA) reaction with bismaleimide (BMI). Fourier transform infrared spectroscopy analysis revealed that the material exhibited fast curing rate and high conversion rate, with the conversion rate reaching 98 %. DSC and DMA characterization demonstrated that the reverse reaction occurred at about 100℃. The tensile analysis confirmed that the mechanical properties of the developed materials remain largely unchanged after recycling, as compared with the existing materials.

Development of a soft UV-NIL step&repeat and lift-off process chain for high speed metal nanomesh fabrication

In this work, we present a fabrication procedure of metal nanomesh arrays with the newly developed nanoimprint resist mr-NIL212FC used in a bi-layer resist system for a lift-off process. We comparatively analyzed and evaluated nanomeshes fabricated with a freshly prepared h-PDMS/PDMS stamp and a stamp used 501 times. Therefore, we first performed a step&repeat imprint test run in a self-built low cost step&repeat UV-NIL setup. We inspected the imprint behavior of the stamp, the UV-transmission through the stamp as well as stamp lifetime and stamp degradation with regard to the possible changes of its surface roughness.The nanomesh fabrication process is characterized by a good lift-off performance, leading to a low defect density of <1.26 defects 100 µm−2. Even after 501 imprints, only a negligible stamp degradation occurred without effecting the imprint performance. Likewise, the same holds true for the nanomeshes, which showed comparable low defect densities and feature sheet resistances of 3.54 ± 0.14 Ω/□ for the first and 3.48 ± 0.23 Ω/□ for the 501st nanomesh, respectively. AFM analyses further revealed that the maximum height of the roughness Rt changed over the course of the 501 imprints from 6.3 nm to 13.3 nm, representing <5% of the overall imprint height.In general, the mr-NIL212FC resist shows a good wettability and compatibility with standard h-PDMS/PDMS stamps, a fast curing behavior, a high replication fidelity, easy separation characteristics, and a very low diffusion of resist components into the stamp. The mr-NIL212FC resist allows exposure times as short as 2 s in the applied tool setup, enabling high throughput production. Moreover, all performed measurements indicate that a much higher number of imprints with one stamp seem possible.

Hexahydrotriazine derivative containing imidazole for fast curing, improved mechanical strength, and flame retardancy of epoxy

AbstractWe synthesized a hexahydrotriazine derivative containing imidazole, 1,3,5‐tris[4′‐(1H‐imidazol‐1‐yl)‐(1,1′‐biphenyl)‐4‐yl]‐1,3,5‐triazinane (HIM) and adapted it as a co‐curing agent for epoxy resin (EP). The curing kinetics of HIM were evaluated using elevated differential scanning calorimetry (DSC) analysis, and the curing speed was determined to be accelerated with HIM. Moreover, when 5 phr of HIM was applied to the epoxy system, the tensile strength of cured EP increased to 50.9 MPa. Because of the high nitrogen content of HIM, when the candidate amount of HIM was increased, the char yield increased. HIM (20 phr) showed a char yield of 36.1%, which is about 74% higher than that of the HIM (0 phr) reference (20.7%). The char layer acts as a barrier between oxygen and polymeric decomposition gases, inducing a high flame‐retardant property.

Post-peak mechanical characteristics of the high-water material for backfilling the gob-side entry retaining: from experiment to field application

The gob-side entry retaining (GER) technique enables pillarless coal mining by using roadside backfilling body (RBB). Due to the advantages of fast curing and high bearing capability after a large post-peak deformation, high-water material is commonly used to construct the RBB. The post-peak properties of the high-water material sample and the concrete sample were compared through uniaxial compression test (UCT) and acoustic emission (AE) test. It is found that the uniaxial compressive strength (UCS) of the high-water material sample is 10.29 MPa with a relatively high post-peak strength. When the strain of the high-water material sample is 12.7 times that of the concrete sample, the loading capacity of the high-water material sample remains 59% of UCS. It is shown that the internal damage of the high-water material sample is very slow in the post-peak stage and remains much less undamaged than the concrete sample. The procedures of GER were studied by numerical simulation. The numerical results suggested that the high-water material roadside backfilling body (HMRBB) underwent elastic deformation, followed by plastic deformation as the panel advanced. The loading stress in RBB increased first and decreased to 74% of its peak strength. The final deformation of the backfilling side was 9% of its width. In the field, the post-peak bearing capacity of HWRBB was pronouncedly enhanced after the bolt reinforcement, leading to a 56% decrease of the deformation of the backfilling body side. The deformation and loading capacity of the backfilling body satisfied the safe operation requirements.

Comparison between Catechol- and Thiol-Based Adhesion Using Elastin-like Polypeptides.

Different chemistries have been utilized for adhesive materials to achieve adhesion in a humidified environment. l-3,4-dihydroxyphenylalanine (DOPA) found in marine mussel adhesive proteins has generated great interest because DOPA participates in multiple reaction mechanisms that confer the ability to adhere in wet conditions. However, the mussel adhesive complex also contains proteins with a relatively high thiol content, and these proteins can contribute to adhesion through the formation of disulfide bonds or interactions with DOPA. This work probes the individual contributions and interactions of DOPA and thiol chemistries to adhesion. To do so, we took advantage of the sequence flexibility in elastin-like polypeptides (ELPs) to create model proteins with highly similar sequences that are rich in either DOPA or thiol residues. The sequence similarity between the two ELP adhesives allowed us to focus on the differences between DOPA- and thiol-based adhesion. Curing kinetics in a wet setting, capability to recover from disturbance in the curing process, and cytocompatibility of the two adhesives were compared. Both chemistries resulted in cytocompatible materials. However, thiol chemistry had faster curing kinetics and higher adhesion strengths, whereas DOPA chemistry showed better recovery from disturbances during the curing process. By utilizing both DOPA- and thiol-based chemistry simultaneously and adding iron ions, we achieved fast curing kinetics, strong adhesion strengths, and good recovery from disturbances to curing. These insights into the contribution of these chemistries to adhesion provide important lessons for researchers designing adhesives that work in a humid environment.

Can Homeopathy, a Particularly Mild Therapeutic Approach, Survive and Grow in a World of Violence?

This short treatise addresses a philosophical question concerning the place of homeopathy in our modern world. The question raised is whether a therapeutic system as peaceful, mild, and non-violent as homeopathy can survive and grow within a society that often displays the opposite characteristics.Much of contemporary society is more interested in fast and impressive cures, even if these may also bring side effects; whereas homeopathy can offer solutions with a personalized approach that requires long hours of case study by the homeopath to find the correct personal remedy that aims to bring about positive results, which the therapy can produce in deep chronic diseases.The conclusion drawn is that homeopathy does not readily fit within a modern and violent society that prefers quick and invasive solutions to its clinical problems.

Curing Kinetic Analysis of Acrylate Photopolymer for Additive Manufacturing by Photo-DSC.

In this research, the curing degree of an acrylate-based monomer using direct UV-assisted writing technology was characterized by differential photo calorimetry (Photo-DSC) to investigate the curing behavior. Triggered by the UV light, the duo function group monomer 1,6-Hexamethylene diacrylate (HDDA), photoinitiator 1173 and photoinhibitor exhibit a fast curing process. The exothermal photopolymerization reaction was performed in the isothermal mode in order to evaluate the different thermal effects that occurred during the photopolymerization process. The influences of both UV light intensity and exposure time were studied with single-factor analysis. The results obtained by photo-DSC also allow us to perform the kinetic study of the polymerization process: The results show that, for the reaction, the higher the UV intensity, the higher the curing degree together with faster curing speed. At the same time, the effect of the heat released during the exothermic reaction is negligible for the polymerization process. When increasing the exposure time, limited improvement of curing degree was shown, and the distribution is between 65–75%. The reaction enthalpy and related curing degree work as a function of time. The Avrami theory of phase change was introduced to describe the experimental data. The functions of a curing degree with light intensity and exposure time were achieved, respectively.

Gamma radiation shielding properties of poly (methyl methacrylate) / Bi2O3 composites

This work investigated the gamma-ray shielding performance, and the physical and mechanical properties of poly (methyl methacrylate) (PMMA) composites embedded with 0–44.0 wt% bismuth trioxide (Bi2O3) fabricated by the fast ultraviolet (UV) curing method. The results showed that the addition of Bi2O3 had significantly improved the gamma shielding ability of PMMA composites. Mass attenuation coefficient and half-value layer were examined using five gamma sources (Cs-137, Ba-133, Cd-109, Co-57, and Co-60). The high loading of Bi2O3 in the PMMA samples improved the micro-hardness to nearly seven times that of the pure PMMA. With these enhancements, it was demonstrated that PMMA/Bi2O3 composites are promising gamma shielding materials. Furthermore, the fast UV curing exerts its great potential in significantly shortening the production cycle of shielding material to enable rapid manufacturing.

Visible light cure packages for improved drying kinetics in alkyd coatings

A solventborne linseed oil alkyd was formulated with two different free radical photo-initiators and a photosensitizer to enhance autoxidative crosslinking. Irgacure 784 and Irgacure 819 significantly decreased the dry-to-touch and through-cure times of alkyd systems at ambient conditions using indoor lighting. Real-time Fourier transform infrared spectroscopy, and solid state 13C NMR were used to monitor the curing process and two mechanisms are proposed to explain the increase in crosslinking. Films were evaluated for tensile, viscoelastic, and thermal properties, indicating an increase in crosslink density. Coating performance was evaluated, significantly increasing film hardness, while maintaining appearance. However, the adhesion and chemical resistance decreased. Visible-light curable alkyds offer excellent appearance and fast curing rates, without the use of cobalt driers.

Bacteria encapsulation using synthesized polyurea for self-healing of cement paste

Cracks in concrete increase permeability and exacerbate the detrimental effects of weathering and potential chemical attacks. Common repair techniques involve the use of sealant agents or utilization of biotechnology methods that can self-heal the cracks. In this study, a polyurea polymer because of its adaptable mechanical properties needed for encapsulation (e.g. moisture barrier and spore immobilisation) and its fast curing reaction is proposed as a potential suitable shield and carrier for Bacillus pseudofirmus to produce calcium carbonate (CaCO3) crystal.Synthesis and encapsulation of the bacteria in the polyurea were performed using in-situ polymerization. Chemical characterization and microstructural analysis of the produced polyurea capsules show that the Bacillus pseudofirmus bacterial spores and nutrition were successfully encapsulated without affecting its chemical structure. The bacterial growth further was confirmed by integration of several morphological analyses. The polyurea microcapsules carrying the bacteria were well-mixed in a cement paste. The hardened specimens were cracked using a three-point bending apparatus to artificially trigger the healing effect of the bacteria capsules. The morphology and chemical characterization confirmed precipitation of calcium carbonate around the cracked zone. Polyurea encapsulation was found to be a practical approach to protect bacteria included in cementitious material for the purpose of self-healing.

Converting crystalline thermosetting urea–formaldehyde resins to amorphous polymer using modified nanoclay

Thermosetting urea–formaldehyde (UF) resins as the most common adhesives for wood-based composites emit formaldehyde, which forces producers to lower formaldehyde/urea (F/U) molar ratio for the UF resins synthesis. However, low-molar-ratio (below 1.0) UF resins have low formaldehyde emission at the expense of poor adhesion, which is responsible for the formation of crystalline domains as a result of hydrogen bonds between linear molecules. For the first time, this study reports the conversion of crystalline UF resins to amorphous polymers by blocking the hydrogen bonds, using transition metal ion-modified bentonite (TMI-BNT) nanoclay through in situ intercalation. The modified UF resins with 5% TMI-BNT showed an almost amorphous structure, faster curing and higher cross-linking density compared with those of neat resins, and resulted in 56.4% increase in the adhesion strength and 48.3% reduction in the formaldehyde emission. Thus, blocking hydrogen bonds in low F/U molar ratio UF resins with TMI-BNT converted crystalline UF resins to almost amorphous ones, resulting in a significant improvement in their adhesion with a low crystallinity.

Thermo-stamping co-curing process for CFRP/steel hybrid sheets and its interface strength improvement

The co-curing interface between CFRP and metal has a significant influence on the comprehensive mechanical properties of the composite structure. In this paper, a series of single lap specimens were fabricated by a thermo-stamping process with fast curing prepreg and dual phase steel DP980. The thermo-stamping co-curing experiments were conducted under different forming conditions based on a grit-blasted metal surface to study the effect of process parameters on the interface strength. In addition, two types of interface strength improvement methods were tested: cutting mechanical grooves on the metal surface and smearing different carbon nanotube or graphene coatings on the metal and prepreg surfaces. The interface strength improvement mechanism was further explained by microscopic characterization. Finally, a finite element model combining cohesive element damage and three-dimensional Hashin failure was established to predict the failure mode of the co-curing joint. The results show that the initial pressure, heating curve and laying up methods have a certain degree of influence on the interface strength, and the best interface enhancement effect could be obtained by coating a carbon nanotube/epoxy resin and a curing agent on the metal and prepreg surfaces, respectively.

Inception U-Net Architecture for Semantic Segmentation to Identify Nuclei in Microscopy Cell Images

With the increasing applications of deep learning in biomedical image analysis, in this article we introduce an inception U-Net architecture for automating nuclei detection in microscopy cell images of varying size and modality to help unlock faster cures, inspired from Kaggle Data Science Bowl Challenge 2018 (KDSB18). This study follows from the fact that most of the analysis requires nuclei detection as the starting phase for getting an insight into the underlying biological process and further diagnosis. The proposed architecture consists of a switch normalization layer, convolution layers, and inception layers (concatenated 1x1, 3x3, and 5x5 convolution and the hybrid of a max and Hartley spectral pooling layer) connected in the U-Net fashion for generating the image masks. This article also illustrates the model perception of image masks using activation maximization and filter map visualization techniques. A novel objective function segmentation loss is proposed based on the binary cross entropy, dice coefficient, and intersection over union loss functions. The intersection over union score, loss value, and pixel accuracy metrics evaluate the model over the KDSB18 dataset. The proposed inception U-Net architecture exhibits quite significant results as compared to the original U-Net and recent U-Net++ architecture.

Low‐temperature fast curable behavior and properties of bio‐based carbon fiber composites based on resveratrol

AbstractEnvironmentally friendly materials are an integral part of sustainable chemistry, and bio‐based polymer composites are an important class of materials. The manufacture of composites is expected to reduce or even eliminate the use of adjuvants, considering the importance of reducing energy consumption and avoiding health and environmental risks. In this study, a phenyl‐containing, polyfunctional, bio‐based epoxy resin (TGER) was synthesized, and carbon fiber‐reinforced, bio‐based epoxy resin composites were fabricated by vacuum‐assisted resin infusion using two aromatic amine curing agents, 4,4′‐diaminodiphenylmethane (DDM) and 3,3′‐diethyl‐4,4′‐diaminodiphenylmethane (DEDDM). Curing reactions and rheological behavior studies showed that TGER had higher curing reactivity toward DDM and DEDDM than to diglycidyl ether of bisphenol A (DGEBA) and possessed good processability. The results indicated that the resveratrol‐based epoxy resin displayed low‐temperature fast curing properties. The evaluation of the mechanical properties of the carbon fiber composites showed that the flexural strengths of CF/TGER/DDM and CF/TGER/DEDDM were 520 and 628 MPa, respectively. The initial decomposition temperature of CF/TGER composites is above 200°C. Furthermore, the carbon fiber–reinforced biopolymers possess excellent heat resistance. Therefore, carbon fiber‐reinforced, resveratrol‐based epoxy resin composites are promising candidates as alternatives to petroleum‐based high‐performance carbon fiber composites.

Improving the water resistance and adhesion strength of a mixed alkali silicate adhesive by optimizing the molar ratio and curing conditions

It is important to eliminate the use of organic adhesives that are harmful to humans and cause environmental pollution. Environmentally friendly, harmless inorganic adhesives are being actively studied. Here, we found that optimized curing was possible when the curing time was controlled via temperature adjustment. We first prepared basic alkali silicate solutions, containing sodium, potassium, and lithium silicate, and compromised them in terms of water resistance. Adhesive strength was measured according to ASTM D3165 using a universal testing machine. The target material, a stainless steel (SUS) specimen, was prepared as described by ASTM D3165. Moreover, to develop fast thermal curing, the effects of two parameters were investigated: curing time and temperature. The temperature range tested was 80–140 °C for 2–36 h; we assessed adhesive strength. The maximum shear strength was obtained after thermal curing at 80 °C for 36 h, 120 °C for 12 h, and 140 °C for 2 h. However, when thermal curing proceeded past the maximum shear strength, the shear strength decreased, attributable to a reduction in the adherent area.

Mechanical and Thermal Properties of Waterborne Polyurethane Coating Modified through One-Step Cellulose Nanocrystals/Graphene Materials Sols Method

Developing multifunctional coatings with excellent mechanical and thermal properties is highly desirable for wood-based composite application. The recent development of waterborne coatings for wood products suggests that a promising thermosetting material needs to also have properties like low volatile organic contents (VOCs), hardness, and fast curing. The cellulose nanocrystals/graphene materials (CNC/GM) sols were prepared through the one-step method as the thermally conductive and reinforced modifier for preparing waterborne polyurethane (WPU) coatings. The influence of this modifier on the thermal and mechanical properties such as thermal conductivity, abrasion resistance, and adhesion of WPU coatings was investigated. The results indicated that adding CNC/GM sols increased the hardness, abrasion resistance, and thermal conductivity of the WPU coatings, and meanwhile maintained the coating adhesion at the highest grade (level 1). The highest abrasion resistance value of 0.023 g/100 r was obtained for the modified WPU coating when the addition of GM was 3%.