UV-curable Systems Research Articles

NIR-II light-encoded 4D-printed magnetic shape memory composite for real-time reprogrammable soft actuator

For the intelligent 4D-printed actuators, the excellent performance, including quickly reversible spatial-shape transformation and locking, digital and precise shape manipulation in real-time, and remote actuation in special spaces or harsh environments, is significantly desirable but still challenging. Here, using a UV-curable system containing the shape memory polymer (SMP) and NdFeB particles, namely the magSMP composite, we fabricate a real-time reprogrammable soft actuator via high-resolution Digital Light Processing (DLP)-based 4D printing. The printed structure is composed of an array of physical binary magSMP composite elements (m-bits), analogous to digital bits. Owing to the NdFeB's photothermal effect, each m-bit can be independently and reversibly switched between unlocking or locking states (allowing or prohibiting responsive shape-morphing) in response to the on/off state of NIR-II light. Through projecting NIR-II light patterns for encoding a set of binary instructions onto 4D-printed actuators, the real-time light-programmed deformations are induced precisely under an actuation magnetic field due to the NdFeB's huge coercivity. Thus, the synergistic magnetic and light field-manipulated multimodal deformations of actuators, including mimosa shape changing, grasping, and wire guiding, are achieved. This study shines lights on the fabrication of soft structures of arbitrary sizes and provides their future perspectives in soft robot design.

UV light treatment (278 nm) for detoxification of aflatoxins and application in edible and medicinal herb coix seed

SummaryAflatoxins (AFs) are highly toxic and cancer‐causing compounds, which could be commonly found in agricultural products and feeds. However, different tactics for detoxification have significant limitations due to their unsuitability for use. In this study, an LED UV curing system (wavelength: 278 nm, irradiation energy: 100%, irradiation time: 10 min) could effectively reduce pure aflatoxin B1 (AFB1), pure aflatoxin B2 (AFB2) and pure aflatoxin G1 (AFG1) (detoxification rates are more than 80%). In addition, in vitro biocompatibility tests indicate that the hypertoxicity of the obtained AFs‐degraded solutions was significantly reduced, which might be because the unsaturated ketone structure in AFB1, AFB2 and AFG1 was broken. Moreover, in processed coix seed and dried boat‐fruited Sterculia seed samples, the amount of AF was greatly reduced, and the rate of degradation was more than 85% with irradiation for 30 min. These data adequately implied that the current work might offer a practical way to detoxify AFs in various medicinal plants and foods.

Progress in the development of acrylic resin-based powder coatings – an overview

Powder coatings, due to the lack of solvents and volatile organic compounds (VOCs), have gained in importance compared to conventional liquid systems. They fulfill key criteria such as effectiveness, economics, energy efficiency, environmental compliance, and excellent surface finish. Recently, low curing temperature and UV-cured systems have been increasingly used. These techniques offer a lot of advantages such as, application of powder coatings on the heat-sensitive materials and energy savings. Acrylic resins are rarely used in powder systems, mainly due to their price. Nevertheless, they are an attractive alternative in low temperature curing or UV-cured systems (free radical or cationic polymerization) thanks to their chemical structure. The review article focuses on the correlation between the chemical structure of the corresponding monomers in the resin and their properties and application in powder coatings. Moreover, the correlation between the structure of acrylic resin and the powder coating formulation process was described.

Tough hyperbranched polyaryletherketone-based photosensitive resins bearing excellent dielectric property and thermal resistence

Organic polymer materials with low dielectric properties have garnered significant attention due to their convenient preparation process, low cost, and commendable mechanical properties. Such polymers, especially with heteromorphic structures, exhibited great potential for future electronic devices and antennas, particularly accompanied with rapid manufacturing technologies like three-dimensional (3D) printing. In this study, a series of new allyl ether-ended hyperbranched fluorene-based polyaryletherketone (hb-PFAEK-Allyls) were developed. The content of allyl ether photosensitive groups and molecular weight were controlled by adjusting the molar ratio of OH:F loading. UV-curable resins were then prepared through blending between hb-PFAEK-Allyls with trimethylolpropane triacrylate (TMPTA) and ethylene glycol bis(3-mercaptopropionate) (EGBMP), resulting in thiol-allyl-acrylate ternary UV-cured system. The influence of molecular weight of the hyperbranched polymers on the thermal performance, mechanical properties, and dielectric properties of the UV-cured films was systematically investigated. The results show that due to the introduction of hyperbranched structure with high molecular weight, the Tg of the UV-cured film can reach up to 248 °C. Due to the increased molecular free volume in the hyperbranched structure, the dielectric constant of the UV-cured film can be reduced to as low as 2.74 at 1 GHz. Due to the design of thiol-allyl-acrylate ternary UV-cured system, the cured film has excellent mechanical properties, with the highest tensile strength of 61.0 MPa and the elongation at break of 7.0%. This study represents innovative progress on integrating fully aromatic-based photosensitive hyperbranched polyaryletherketone into UV-curable resin architecture. Overall, the herein hb-PFAEK-Allyls-based photosensitive resins exhibit outstanding comprehensive performance and holds great potential for application in advanced 3D printing technology.

Development and validation of a low-cost UV curing system for Direct Ink Write 3D printers

Existing Direct Ink Write 3D printers use three axis robotic drives with high-cost extrusion system and no inbuilt curing system to cure the polymer inks. This article focusses on the development of a low-cost photopolymer ultraviolet (UV) light curing system for Direct Ink Write 3D printers and optimizing the print parameters. An UV light-emitting diode (LED) light curing setup consisting of UV LED strips, UV LED holder, and a nozzle shield is designed and fabricated. The photocuring of the polymer ink is with the help of low-cost UV LED strips emitting UV light in the wavelength of 405 nm. The effect of nozzle type, stand-off distance and printing speed on the layer height and layer width were calculated. The gel content was determined by Soxhlet extraction and the maximum gel content was achieved in 120 s. The setup was also able to fabricate complex shapes like hollow cone and a hollow bend pipe without any supports which validates the effectiveness of the curing system.

Adhesion of Varnish Coatings as a Background for Analogue and Digital Printing Technologies

In analogue and digital printing technologies, from 3 up to 12 layers of lacquer products are applied. Technological parameters significantly influence the adhesion in the coating system. This article refers to the analysis of the influence of selected technological parameters, such as the number of layers, energy doses distributed by the radiators, and line speed, on the topography and adhesion of varnish coatings formed in the process of varnishing with rollers and UV-curing systems. The appropriately prepared surface can be used as a background layer for the analogue and digital printing technology. Manufacturers must adapt the production process to the particular varnish to obtain finished products with the best possible performance properties. The state of surface free energy and finally adhesion can be assessed by theoretically determining the possibility of an adhesive bonding between the product and the substrate, taking into account the assumptions of the adsorption theory of adhesion and measurement of the contact angle (Θ). An experimental confirmation of adhesion measurements included removing the coatings from the substrate via stamps glued to the coating.

Synthesis of mace silver nanorod with particles and water-alcohol room-temperature-curing UV conductive ink

At present, the silver nanorods of UV conductive ink have the problems of easy agglomeration of silver nanorods, and slow curing speed. In this paper, firstly mace-like silver nanorods with inorganic particles were synthesized by using polycarbonate fibers as soft-templates, AgNO3 as silver source. The diameters and lengths of silver nanorods were 0.25–0.35 μm and 2.1–5.1 μm. There are many wolf-tooth particles (0.20–0.35 μm) on the silver nanorods which prevented the silver nanorods from reuniting. The obtained silver nanorods were not easy to agglomerate. The minimum resistance value of the coating could reach 1∼10Ω. Secondly, a kind of water-alcohol UV conductive ink with low heat treatment temperature (140 °C), fast drying and curing speed and water-alcohol system was prepared. Water-alcohol soluble P(AA-r-HEMA)-g-GMA was used as the prepolymer, glycidyl triethylenetetraamine hexamethacrylate (TGMA) was used as the monomer, and 907 and ITX were used as photoinitiators. The effects of the types and contents of different photoinitiators (907:1%–5%, ITX: 0.2 %∼1 %), species and contents of prepolymer (30 %∼50 %), the number and content of monomers with different functional groups (30 %∼50 %) on the UV-curing rate were studied. The curing rate was the fastest when the mass fraction of photoinitiator ITX was 0.4 %, the mass fraction of the prepolymer with 30 % GMA content was 50 % and the mass fraction of monomer TGMA was 50 %. The curing speed can reach 2–3 s, and the ink film surface was smooth without bubbles. At last, UV conductive ink was prepared by using the obtained water-alcohol UV curing system as the bonding material and mace-like silver nanorods as the conductive filler. The influence of heat treatment temperature and time on the conductive properties of the coating was explored. The optimal heat treatment temperature was 140 °C, and the heat treatment time was 30 min.

Antistatic epoxy acrylate/graphene oxide UV-curable coatings with improved shrinkage and adhesion strength

This study presents a simple method for preparing antistatic UV curable coating based on graphene oxide (GO). For this aim, epoxy acrylate (EA) was selected as a UV-curable matrix and synthesized GO nanoplates were dispersed in the resin through solvent-mediated dispersion. Simultaneous crosslinking of UV-curable resin and photoreduction of GO nanoplatelets take place during UV irradiation. The effect of UV intensity and concentration of graphene oxide on the curing kinetics of UV-curable nanocomposite and reduction of GO nanoplatelets was investigated. The results show that the curing reactions of the UV-curable system are disturbed by GO nanoparticles to some extent (depending on UV intensity). They also show that the electrical resistance of the UV-cured EA/GO nanocomposites decreases during the UV curing process. It was found that the shrinkage of the formulations improved considerably with the incorporation of GO into the formulations. The adhesion strength of the cured EA/GO coatings to mild steel was also found to be significantly higher than that of EA coating.

DLP 3D printing of high strength semi-translucent zirconia ceramics with relatively low-loaded UV-curable formulations

DLP 3D printing is one of the additive manufacturing techniques, which allows the fabrication of ceramic parts with a complex shape, precisely controlled internal architecture and fine surface finishing. The method is based on the layer-by-layer solidification of a photosensitive ceramic suspension via UV-light projection followed by debinding of organic components and sintering and generally requires a high solid content of the ceramic filler to achieve good sintered densification. The present article aims to explore the possibility of fabricating high strength, fully dense and semi-translucent zirconia parts with relatively low-loaded UV-curable systems using a low-cost desktop DLP printer designed for printing polymers. For the slurry preparation, tetragonal zirconia powders from three different suppliers were evaluated. It was shown that with 35 vol% of zirconia content slurries, it was possible to fabricate zirconia semi-translucent ceramics with a density of 99.6%. No cracks or pores larger than 1 μm were observed on the sintered parts. According to ball-on-3-ball mechanical tests performed on the 13 × 1 mm discs an average flexural strength of the printed zirconia ceramics was 1566 MPa and a maximum of 1964 MPa could be achieved.

Continuous resin refilling and hydrogen bond synergistically assisted 3D structural color printing

3D photonic crystals (PCs) have attracted extensive attention due to their unique optical properties. However, fabricating 3D PCs structure by 3D printing colloidal particles is limited by control of assembly under a fast-printing speed. Here, we employ continuous digital light processing (DLP) 3D printing strategy with hydrogen bonds assisted colloidal inks for fabricating well-assembled 3D PCs structures. Stable dispersion of colloidal particles inside UV-curable system induced by hydrogen bonding and suction force induced by continuous curing manner cooperatively realize the simultaneous macroscopic printing and microscopic particle assembly, which endows volumetric color property. Structural color can be well regulated by controlling the particle diameter and printing speed, through which various complex 3D structures with desired structural color distribution and optical light-guide properties are acquired. This 3D color construction approach shows great potential in customized jewelry accessories, decoration and optical device preparation, and will innovate the development of structural color.

Bioresorbable Chitosan-Based Bone Regeneration Scaffold Using Various Bioceramics and the Alteration of Photoinitiator Concentration in an Extended UV Photocrosslinking Reaction.

Bone tissue engineering (BTE) is an ongoing field of research based on clinical needs to treat delayed and non-union long bone fractures. An ideal tissue engineering scaffold should have a biodegradability property matching the rate of new bone turnover, be non-toxic, have good mechanical properties, and mimic the natural extracellular matrix to induce bone regeneration. In this study, biodegradable chitosan (CS) scaffolds were prepared with combinations of bioactive ceramics, namely hydroxyapatite (HAp), tricalcium phosphate-α (TCP- α), and fluorapatite (FAp), with a fixed concentration of benzophenone photoinitiator (50 µL of 0.1% (w/v)) and crosslinked using a UV curing system. The efficacy of the one-step crosslinking reaction was assessed using swelling and compression testing, SEM and FTIR analysis, and biodegradation studies in simulated body fluid. Results indicate that the scaffolds had comparable mechanical properties, which were: 13.69 ± 1.06 (CS/HAp), 12.82 ± 4.10 (CS/TCP-α), 13.87 ± 2.9 (CS/HAp/TCP-α), and 15.55 ± 0.56 (CS/FAp). Consequently, various benzophenone concentrations were added to CS/HAp formulations to determine their effect on the degradation rate. Based on the mechanical properties and degradation profile of CS/HAp, it was found that 5 µL of 0.1% (w/v) benzophenone resulted in the highest degradation rate at eight weeks (54.48% degraded), while maintaining compressive strength between (4.04 ± 1.49 to 10.17 ± 4.78 MPa) during degradation testing. These results indicate that incorporating bioceramics with a suitable photoinitiator concentration can tailor the biodegradability and load-bearing capacity of the scaffolds.

Construction of Photoinitiator Functionalized Spherical Nanoparticles Enabling Favorable Photoinitiating Activity and Migration Resistance for 3D Printing.

A straight-forward method was exploited to construct a multifunctional hybrid photoinitiator by supporting 2-hydroxy-2-methylpropiophenone (HMPP) onto a nano-silica surface through a chemical reaction between silica and HMPP by using (3-isocyanatopropyl)-triethoxysilane (IPTS) as a bridge, and this was noted as silica-s-HMPP. The novel hybrid-photoinitiator can not only initiate the photopolymerization but also prominently improve the dispersion of nanoparticles in the polyurethane acrylate matrix and enhance the filler-elastomer interfacial interaction, which results in excellent mechanical properties of UV-cured nanocomposites. Furthermore, the amount of extractable residual photoinitiators in the UV-cured system of silica-s-HPMM shows a significant decrease compared with the original HPMM system. Since endowing the silica nanoparticle with photo-initiated performance and fairly lower mobility, it may lead to a reduction in environmental contamination compared to traditional photoinitators. In addition, the hybrid-photoinitiator gives rise to an accurate resolution object with a complex construction and favorable surface morphology, indicating that multifunctional nanosilica particles can be applied in stereolithographic 3D printing.

Hybrid Free-Radical/Cationic Phase-Separated UV-Curable System: Impact of Photoinitiator Content and Monomer Fraction on Surface Morphologies and Gloss Appearance.

Simultaneous photopolymerization of radical and cationic systems is one strategy to generate polymer network architectures named interpenetrating polymer networks (IPNs). In these hybrid systems, phase separation and final polymer morphology are ultimately governed by thermodynamic incompatibility and polymerization kinetics. This behavior is quite complex, as numerous factors can affect polymerization kinetics including monomer/oligomer viscosity and structure, light intensity, photoinitiator content and absorbance, cross-linking, vitrification, etc. In this work, the impact of photoinitiator concentration and monomer fraction on surface morphologies in a hybrid radical/cationic phase-separated system was examined. Wrinkles formed on the surface of photopolymerized films depend on the polymerization rate and acrylate/epoxy ratio. This phenomenon is partially explained by the rapid polymerization rate associated with the development of an epoxy matrix and a smaller acrylate domain. The size and shape of the wrinkles can be controlled by varying formulation parameters (mainly, composition) and photoinitiator content. It was possible to create surface roughness and consequently decrease the gloss by controlling the polymerization kinetics and phase-separated morphology. This study demonstrates that the morphology, polymerization kinetics, and film properties (e.g., gloss, transparency) can be manipulated with the ratio of the acrylate/epoxy mixture and the photoinitiator content.

3D quantum dot-lens fabricated by stereolithographic printing with in-situ UV curing for lighting and displays

3D polymer/quantum dots (QDs) nanocomposite QD-lens is fabricated by stereolithography (SLA) 3D printer with in-situ UV curing system. Various UV-curable polymer precursors are mixed with QDs to investigate their printability and optical performance. 2D QD-thin film and 3D QD-lens are printed and attached to a blue InGaN chip to form a light-emitting diode (LED) device. An air gap between the 3D QD-lens and the chip provides more uniform light emission at different angles and better heat dissipation. Compared with conventional QD-on-chip LED, the 3D QD-lens LED operated at 20 mA has ∼100% enhancement of half-lifetime (T 50 ) in a standard reliability test. The LED T 50 can be further improved 75% by coating the QD-lens with hydrophobic parylene as a gas barrier layer against water and oxygen. By mixing both green- (G-) and red- (R-) QDs in the 3D QD-lens, a white light-emitting 3D QD-lens LED is demonstrated to possess a color gamut of ∼130% NTSC standard.

Current capabilities of prototyping technologies for multilayer printed circuit boards on a 3D printer

A new direction in 3D printing was investigated – prototyping of single-sided, double-sided and multilayer printed circuit boards. The current capabilities and limitations of 3D printed circuit board printing technology were identified. A comparative analysis of the characteristics of two desktop 3D printers presented in the industry for prototyping radio electronics, as well as the first professional machine DragonFly LDM 2020, which is a mini-factory for prototyping multilayer printed circuit boards, was carried out. The first practical experience of working and printing on DragonFly LDM 2020 supplied to the megalaboratory “3D prototyping and control of multilayer printed circuit boards” of the Institute of Radio Engineering and Telecommunication Systems MIREA – Russian Technological University is presented. The first samples of electronic boards printed on a 3D printer by the method of inkjet printing were obtained. An additive technology for the production of multilayer printed circuit boards is considered: printing with two printheads with conductive and dielectric nano-ink with two curing systems: an infrared sintering system for conductive ink and a UV curing system for dielectric ink. The LDM (Dragonfly Lights-out Digital Manufacturing) production method with the necessary maintenance is presented. The method allows the system to work roundthe-clock with minimal human intervention, significantly increasing the productivity of 3D printing and expanding the possibilities of prototyping. The materials used for 3D printing of multilayer printed circuit boards and their characteristics were investigated: dielectric acrylate nano-ink (Dielectric Ink 1092 – Dielectric UV Curable Acrylates Ink), conducting ink with silver nanoparticles (AgCite™ 90072 Silver Nanoparticle Conductive Ink). The research carried out allows us to compare the technological standards of printed electronics with traditional methods of manufacturing multilayer printed circuit boards for a number of parameters.

Synthesis of Amino Acid-derived Curing Reagents Containing a Disulfide Bond and Their Application to Anionic UV Curing Materials

Anionic UV curing has been applied for many kinds of industrial resins, because it overcomes technical problems in conventional radical and cationic UV curing. In this study, a cystine-based latent curing reagent was designed, and synthesized from l- and d-cysteine. The reagents showed not only good solubility toward organic media, but also good thermal decomposition behavior in the presence of basic species. Using them with a photo-base generator and an epoxy resin having a disulfide bond, UV-cured films of B-to-3B grade of pencil-hardness were fabricated successfully, after 10 J/cm2 of 365 nm-light irradiation and subsequent heating at 120-160°C for 30 min. Furthermore, two glass substrates were adhered by using this anionic UV curing system, and 1.6-3.7 MPa of shear stress was recorded in the photo-adhesion and re-adhesion experiments.

Combining FDTD and Curing Kinetic Equations to Model the Degree of Conversion Evolution of UV-Curable Systems

The degree of conversion (DoC) is significantly linked with many material properties of a UV-cured resin. The current curing kinetic models provide insight into how DoC evolves with depth for a pur...

Functionalised PEGs with photo-dimerisable, anthracenyl end-groups: New UV-curable materials for use in inkjet formulations

The synthesis and characterisation of two novel poly(ethylene glycol)-based materials featuring UV-dimerisable anthracenyl end-groups are described. These low molecular weight polymers exhibited good solubility (ca. 100 g/L) in common organic solvents and were deposited successfully using a drop-on-demand (DOD) inkjet printhead to produce clear prints. UV–vis irradiation of a linear bis-anthracene terminated PEG material resulted in polymerisation via photodimerisation of the anthracenyl end-groups, maintaining polymer solubility in common organic solvents and enabling solution state analysis of the polymerisation process using UV–vis and 1H NMR spectroscopies. In contrast, UV irradiation of a three-armed, tris-anthracenyl-terminated PEG resulted in the formation of an insoluble cross-linked network, which was characterised using rheometry, differential scanning calorimetry and lap shear tensiometry. It was found that the incorporation of solvent-soluble dyes into formulations of the tris-anthracenyl PEG resulted in an increase in UV-cure time when compared to the polymer alone, but did not prevent curing. The results highlight the suitability of this latter material as a UV-curable system for inclusion in inkjet formulations.

High Efficiency and Low Migration Hyperbranched Silicone Contain Macrophotoinitiators for UV-Cured Transparent Coatings.

A kind of hyperbranched silicone containing macrophotoinitiators (HBSMIs) were synthesized from 2-hydroxy-2-methyl-1-phenyl propanone (HMPP) and the UV-curing behaviors of HBSMIs were investigated in UV-cured transparent polyurethane-acrylate (PUA) coatings. HBSMIs show higher UV-initiating efficiency than HMPP. The migration of HBSMIs from the UV-cured coatings can be as low as 1.7–6.0 wt%, which is obviously lower than the migration of HMPP. There is a remarkable improvement of the tensile strength of the UV-cured materials initiated by HBSMI in comparison to that of the materials prepared with the same PUA initiated by HMPP. Especially for the UV-cured materials prepared from PUA with 20 wt% 1,1,1-tris(hydroxymethyl)propane (TMP), the tensile strength and the strain at break increased from 6.81 MPa to 12.14 MPa and from 43.0% to 71.9%, respectively. The fraction of improvement for the tensile strength and the strain at break is as high as 78.9% and 67.2%, respectively. The coatings prepared with HBSMI also have better UV resistance ability than those coatings prepared with HMPP because they turn slightly yellow when they are aged by UV for about 15 min while the coating prepared with 4 wt% of HMPP will turn yellow only aged by UV for 2 min. These results suggest that preparation hyperbranched silicone containing macrophotoinitiators will be one of the good strategies to improve the curing efficiency of the UV-curing system, reduce the migration of UV initiator from cured material, improve the mechanical and UV resistance performance of UV-cured materials.

The Effect of Curing Temperature on the Morphology and Electro-Optical Properties of a Flexible UV-Cured Polymer Dispersed Liquid Crystal (PDLC)

In this work, the experimental data on flexible PDLC films at the industrial scale and the effect of cure temperature (Tc) on the morphology and electro-optical properties of a UV-cured PDLC system via polymer-induced phase separation (PIPS) method were studied. Under constant UV radiation intebsity and thickness, the morphological parameters such as dimension, number density, and volume fraction of the phase-separated liquid crystal droplets as well as the optical transmissions and switching voltages as a function of cure temperature were determined. The effect of cure temperature on the morphology and electro-optical properties of UV-cured PDLC films were analyzed.