Papers by Keyword: Photopolymerization

Abstract: This paper presents a concise review on 4D printing of shape memory polymers that focuses on the use of acrylate-based materials using photopolymerization. Stereolithography (SLA), Digital Light Processing (DLP), Inkjet Printing (IJP), and UV assisted Direct ink Writing (UV-DIW) are the photopolymerization printing techniques that uses acrylate-based materials. These acrylate-based feedstocks will be polymerized during printing by the presence of UV light to form shape memory polymers (SMPs). Acrylate-based SMPs will change their shape in response to heat, water, light, and pH. Demonstrated applications of these 4D printed acrylate-bases SMPs are in biomedical, soft robotics, flexible electronics, and structural materials. However, 4D printing is still in the early stage and there are a lot of challenges like enhancing mechanical properties, biocompatibility, limited kind of SMPs, high cost of 4D printing system, and many more that needs to be addressed before a viable product can be produced.

Abstract: Photopolymerisation of 2-Hydroxyethyl methacrylate (HEMA) through the use of N,N-Diethyldithiocarbamato-(1,2)-propanediol (DCPD) was studied. The photoinitiator DCPD was synthesized from sodium N,N-Diethyldithiocarbamate (NaSR) and 3-chloro-1,2-propanediol. For the photochemical decomposition of the C – S bond, UV light at 254 nm is used. The role of the monomer concentration, reaction time and DCPD to HEMA mol ratio on the conversion of HEMA to PHEMA were studied in this paper. It was found that percentage conversion of HEMA increased both with the rise in concentration of monomer and reaction time. Further, living radical nature of the poly2-Hydroxyethyl methacrylate (PHEMA) was ascertained by the photo block copolymerization of methyl methacrylate (MMA) with PHEMA to form PHEMA-b-PMMA. The PHEMA and PHEMA-b-PMMA were characterized by FTIR, ¹H-NMR, Thermogravimetry.

Abstract: Polymethyl methacrylate (PMMA) is one among few known photo-polymeric resin useful in lithography for fabricating structures having better mechanical properties to meet the requirement in electronics and biomedical applications. This study explores the effect of Photo Initiator (PI) concentration and also curing time on strength and hardness of Polymethyl methacrylate (PMMA) obtained by UV photopolymerization of Methyl methacrylate (MMA) monomer. The UV LED light source operating at the wavelength of 364 nm is used with Benzoin Ethyl Ether (BEE) as photo initiator. The curing of PMMA resin is supported with peltier cooling device placed at the bottom of the UV light source. The characterisation study of UV photo cured PMMA is analysed through nano indenter (Agilent Technologies-G200). The current work investigates the influence of PI concentration and curing time in achieving maximum mechanical properties for UV photopolymerized PMMA.

Abstract: The reactivity of 3,5-di-tert-butyl-o-benzoquinone and its bis-o-benzoquinone derivative in photoreduction reaction and polymerization of dimethacrylate (OCDMA) (in bulk and in the presence of 1-butanol) with using of them as photoinitiators under visible light irradiation under argon atmosphere or air were investigated. It was found that the kinetic parameters of the bis-o-quinone photoreactions have low sensitive to the presence of molecular oxygen. The high stability of the spectral characteristics of resulting polymers based on bis-o-quinones compositions for the long time was established.

Abstract: Digital light processing (DLP) can be used as a rapid photopatterning technique with micrometer resolution. To ensure high levels of precision and accuracy, it is required to clearly understand the actual dimensional capabilities in the horizontal plane of a patterning setup. A methodology to assess these capabilities was suggested in this study, and the following parameters were determined: The effective pixel size, the planar dimensional reproducibility, and the dimensional precision in dependence of the angular feature orientation in the x-y plane. Experimental verification of the suggested approach was carried out by using a DLP-based 3D printer. This demonstrated that the nominal pixel size stated in the technical data sheet can deviate from the effective pixel size by more than 1%. Furthermore, dimensional inaccuracies of ±5.1% depending on the feature location within the x-y plane were indicated. The dimensional precision was affected by the angular orientation in relation to the pixel grid, and small errors equivalent to ±0.05 pixels were only achievable with features placed in parallel or diagonal orientation. These results characterize the planar accuracy of DLP equipment and help minimize dimensional errors in the direct digital manufacture of microchannel and strut-like patterns.

Abstract: This study investigated the improvement of hardness and flexural properties of a commercial stereolithography (SLA) resin by reinforcement with silica-based fillers. Three types of fillers were studied: synthetic amorphous silica, milled fiberglass, and geothermal scale powder. Particle size and aspect ratio of fillers were estimated from scanning electron microscopy (SEM) images, while chemical structure was characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Fillers were added to SLA resin at 0, 10, and 20 vol%. Hardness and flexural properties of SLA composites are higher than unfilled resin. Moreover, both hardness and flexural properties of SLA composites are improved according to type (milled fiberglass > synthetic amorphous silica > geothermal scale powder) and loading (20 vol% > 10 vol%). The observed effect of filler type and loading on hardness and flexural properties of SLA composites is due to aspect ratio, intrinsic properties and dispersion of filler.

Abstract: In this paper we presented the synthesis of TEOS with photoresist in order to use it like a hybrid material for 3D printer on the micrometer scale by means of the two-photon polymerization process, in which two photon are absorbed simultaneously by the material using an ultrafast laser causing its polymerization. We analyzed the mix of TEOS and photoresist with UV-VIS and FTIR spectrometers, checking that complies with two important conditions: has an optical transmission at 780 nm and absorbs at 390 nm. Finally we fabricated micro-structures with a new hybrid material; TEOS does not absorb the laser in this system and does not interfere with the formation of a three-dimensional structure. After formation the 3D microstructure, samples were heated to form the SiO. These samples of microstructures were observed under digital microscope and SEM.

Abstract: UV-curable process is widely used for paints, inks and adhesives due to its rapid curing, low energy consumption, high efficiency and low volatile organic compounds (VOCs). The objective of this research is to prepare poly(lactic acid) (PLA) based UV-curable coating by using glycolyzed PLA. PLA was glycolyzed by ethylene glycol (EG) at 170°C for 90 minutes. The obtained glycolyzed PLA was reacted with methacrylic anhydride (MAAH) to provide PLA acrylate oligomer. The obtained PLA acrylate oligomer was used in coating formulations with various amounts of photoinitiator and cured under UV radiation. Physical properties of cured coating film were investigated such as pencil hardness, gloss and haze. The results showed that poly(lactic acid) (PLA) based UV-curable coating provided good physical properties.

Abstract: Within the large variety of different additive manufacturing technologies stereolithography excels in high precision and surface quality. Using the Digital Light Processing (DLP) Technology a stereolithography-based system was developed, which is specifically designed for the processing of highly filled photopolymers.The powder-filled suspension enables the 3D-fabrication of a so called ceramic green part. In order to get a dense ceramic structure, subsequent thermal processing steps after the 3D-printing process are necessary. First, the polymer-ceramic composites heated up to 400°C. During this processing step, called debinding, the organic components are burned out. The resulting part, consisting of powder particles stabilized by physical interactions, is further heated to sinter the particles together, and the final, fully dense ceramic part is obtained.The debinding step is the most critical process. The used components have different evaporation or decomposition temperatures and behaviors. Thereby a reduction in weight and also in dimension occurs, which depends on the portion and composition of the organic components and especially on the temperature cycle. Furthermore, the physical characteristics of the ceramic powder, such as the particle size and the size distribution influence the debinding behavior. To measure the changes in weight and dimension a thermo-gravimetric (TGA) and a thermo-mechanical analysis (TMA) can be used. To avoid too high internal gas pressures inside the green parts a preferably constant gas evolution rate is seeked. Also the ‘surface-to-volume ratio’ affects the debinding characteristics. Therefore, optimized debinding cycles for specific geometries allow the crack-free debinding of parts with a wall thickness up to 20 mm.

Abstract: Albeit widely established in plastic and metal industry, additive manufacturing technologies are still a rare sight in the field of ceramic manufacturing. This is mainly due to the requirements for high performance ceramic parts, which no additive manufacturing process was able to meet to date.The Lithography-based Ceramic Manufacturing (LCM)-technology which enables the production of dense and precise ceramic parts by using a photocurable ceramic suspension that is hardened via a photolithographic process. This new technology not only provides very high accuracy, it also reaches high densities for the sintered parts. In the case of alumina a relative density of over 99.4 % and a 4-point-bending strength of almost 430 MPa were realized. Thus, the achievable properties are similar to conventional manufacturing methods, making the LCM-technology an interesting complement for the ceramic industry.