Optimization of thick layers photopolymerization systems applying experimental and analytical approach (original) (raw)
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Cure depth in photopolymerization: Experiments and theory
Journal of Materials Research, 2001
The depth of photocuring for a model resin system was investigated as a function of photoinitiator concentration. Direct measurements of gel thickness were made from thin films of cross-linked multifunctional methacrylate monomer. The monomer, 2,2-bis{4- [2-hydroxy-3-(methacryloxy)propoxy]phenyl}propane, was polymerized in a solution of trichloroethylene with an ultraviolet laser light source at 325 nm. The monomer solutions were photocured using varying levels of both photonic energy and photoinitiator concentration. An optimal photoinitiator concentration that maximized the gel cure depth was observed. Additionally, two regimes were shown to exist in which the shrinkage (upon solvent removal) was minimized or maximized. A model was developed to probe the physics of the system. Good agreement with experiment was obtained, and the model may be employed to predict both the existence and location of the optimal photoinitiator concentration and the corresponding cure depth. The study showed that photoinitiator plays a significant role in controlling the quality and performance of the formed gel network, with special regard to thickness of cured layers. This has potential application to fields as diverse as industrially cured coatings and dental fillings, and more generally, 3-dimensional rapid prototyping techniques.
NPDD model: a tool for photopolymer enhancement
Holography: Advances and Modern Trends II, 2011
The use of theoretical models to represent the photochemical effects present during the formation of spatially and temporally varying index structures in photopolymers, is critical in order to maximise a material's potential. One such model is the Non-local Photo-Polymerization Driven Diffusion (NPDD) model. Upon application of appropriate physical constraints for a given photopolymer material, this model can accurately quantify all major photochemical processes. These include i) non-steady state kinetics, (ii) non-linearity iii) spatially non-local polymer chain growth, iv) time varying primary radical production, v) diffusion controlled effects, vi) multiple termination mechanisms, vii) inhibition, (viii) polymer diffusion and ix) post-exposure effects. In this paper, we examine a number of predictions made by the NPDD model. The model is then applied to an acrylamide/polyvinylalcohol based photopolymer under various recording conditions. The experimentally obtained results are then fit using the NPDD model and key material parameters describing the material's performance are estimated. The ability to obtain such parameters facilitates material optimisation for a given application.
AIChE Journal, 2010
While high throughput and combinatorial techniques have played an instrumental role in materials development and implementation, numerous problems in materials science and engineering are too complex and necessitate a prohibitive number of experiments, even when considering high throughput and combinatorial approaches, for a comprehensive approach to materials design. Here, we propose a unique combination of high throughput experiments focused on binary formulations that, in combination with advanced modeling, has the potential to facilitate true materials design and optimization in ternary and more complex systems for which experiments are never required. Extensive research on the development of photopolymerizable monomer formulations has produced a vast array of potential monomer/comonomer, initiator and additive combinations. This array dramatically expands the range of material properties that are achievable; however, the vast number of potential formulations has eliminated any possibility of comprehensive materials design or optimization. This limitation is addressed by maximizing the benefits and unique capabilities of high throughput experimentation coupled with predictive models for material behavior and properties. The high throughput experimentation-model combination is useful to collect a limited amount of data from as few as 11 experiments on binary combinations of 10 analyzed monomers, and then use this limited data set to predict and optimize formulation properties in ternary resins that would have necessitated at least 1000 high throughput experiments and several orders of magnitude greater numbers of traditional experiments. A data analysis approach is demonstrated, and the model development and implementation for one model application in which a range of material properties are prescribed, and an optimal formulation that meets those properties is predicted and evaluated. V
Optimization of Photopolymerization Process of Dental Composites
Processes
The aim of this paper is to perform optimization of photopolymerization process of dental composites in order to obtain maximum hardness. Samples (5 mm diameter; 2, 3 and 4 mm thickness) were made of Universal Composite (UC), Bulk fill Composite (BC) and Flowable Composite (FC). Light curing of specimens was performed with 600, 1000 and 1500 mW/cm2 light intensity and an irradiation time of 20, 40 and 60 s. Vickers microhardness on the top and bottom surfaces of samples was measured. Optimization was carried out via regression analysis using QStatLab software. Photopolymerization process parameters were calculated using a specially designed MatLab software-based algorithm. For all composites, regression models for hardness on top and bottom surfaces of composite layer were established. Layer thickness as well as hardness on top and bottom surfaces of each composite was calculated for 21 curing modes varying with light intensity and irradiation time. It was established that photopoly...
Polymer, 2001
UV-light initiation is now commonly used to induce polymerization of multifunctional monomers. The highly crosslinked networks obtained have a wide variety of applications. The thermal effects which take place during polymerization can be the cause of non-homogeneity and defects in the ®nal material. These defects greatly alter the physical properties of the ®nal products, particularly the optical ones, which causes problems in the design of thick and optically perfect materials. To better control the homogeneity of photocured materials and to determine the in¯uence of different experimental parameters on them, conversion and temperature distribution pro®les within a material during photopolymerization were simulated numerically, using the general heat equation applied to one-dimensional system. To describe the true conditions of kinetic experiments, some necessary parameters were measured, like conversion, reaction rate, spectral irradiance of the Hg vapor lamp and dimethacrylate spectral absorbance. We focused our attention more particularly on the in¯uence of the irradiation wavelength. Indeed, the high values of the spectral absorbance coef®cient cause a great decrease in light intensity in the depth of the material and lead in turn to a sharp drop in conversion.
Rapid Prototyping Journal, 2014
Purpose – Over the last several years, the range of applications for the photopolymerisation process has been steadily increasing, especially in such areas as rapid prototyping, UV inks, UV coats and orthodontic applications. In spite of this increase, there are still several challenges to be overcome when the application concerns materials formulation and their mechanical properties. In this context, the main aim of this work is to outline the contribution of the formulation components for the parameters of the photopolymerisation process and the resultant mechanical properties of the material. Design/methodology/approach – For this research, the authors have applied multivariable analysis methods, which allow the identification of principal conclusions based on experimental results. For the experimental analysis, the authors applied design of experiment, while the material formulation was based on methyl methacrylate as a monomer, Omnrad 2500 as a photoinitiator and trimethylolpro...
Polymers
Photopolymers are an attractive option for large-format additive manufacturing (LFAM), because they can be formulated from structural thermosets and cure rapidly in ambient conditions under low-energy ultraviolet light-emitting diode (UV LED) lamps. Photopolymer cure is strongly influenced by the depth penetration of UV light, which can be limited in the 2–4 mm layer thicknesses typical of LFAM. Photoinitiator (PI) systems that exhibit photobleaching have proven useful in thick-section cure applications, because they generate a photoinitiation wavefront, but this effect is time-dependent. This study investigates the light transmission and through-thickness cure behavior in (meth)acrylate photopolymer formulations with the photobleaching initiator bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO). Utilizing an optical model developed by Kenning et al., lower concentrations (0.1 wt% to 0.5 wt%) of BAPO were predicted to yield rapid onset of photoinitiation. In situ cure measure...
A Feasibility Study of a Rapid Prototyping Technology Based on a Photopolymer
Rapid Prototyping (RP) is a layer manufacturing process which is based on adding material in successive flat layers. In this process, a 3D CAD model is used directly to generate all information required for the part building. Among the various methods of adding layers, there are technologies that process photopolymeric materials, using an ultraviolet (UV) light to perform a photopolymerization or photocure process. Currently in Brazil, it is possible to find only RP processes developed by foreign companies and this motivates the development of national technologies. This work presents some initial studies carried out to allow a deposition and a photopolymerization of a polymer aiming the development of a RP technology. A photopolymer has been formulated and a RP apparatus has been assembled to test the main idea. With this prototype, some initial studies to analyze the functional viability of the process have been carried out. This work presents the development so far and some initial results. The first results are promising but they point to the requirement of further and deeper studies to analyze the process feasibility.
A Feasibility Study of a Rapid Prototyping Technology Based on Photopolymer
Rapid Prototyping (RP) is a layer manufacturing process which is based on adding material in successive flat layers. In this process, a 3D CAD model is used directly to generate all information required for the part building. Among the various methods of adding layers, there are technologies that process photopolymeric materials, using an ultraviolet (UV) light to perform a photopolymerization or photocure process. Currently in Brazil, it is possible to find only RP processes developed by foreign companies and this motivates the development of national technologies. This work presents some initial studies carried out to allow a deposition and a photopolymerization of a polymer aiming the development of a RP technology. A photopolymer has been formulated and a RP apparatus has been assembled to test the main idea. With this prototype, some initial studies to analyze the functional viability of the process have been carried out. This work presents the development so far and some initi...
Mechanical behavior of photopolymerized materials
Journal of the Mechanics and Physics of Solids, 2021
The photopolymerization process used for the production of additively manufactured polymers employed in advanced applications, enables obtaining objects spanning a large dimensional scale thanks to the molecular size achievable by the solidification process. In fact, the photopolymerization is based on the physical-chemical network cross-linking mechanism taking place at the nanoscale. Since the starting raw material is a liquid resin that progressively becomes solid upon the irradiation by a suitable light source, the mechanical propertiesand so the corresponding mechanical response of the final printed structural materialheavily depend on the degree and distribution of the polymerization induced in the material itself. In the present study, starting from the governing equations of the light-induced polymerization process, we determine the chain density formed within the solid domain. Then, the mechanical response of photopolymerized elements obtained with different photopolymerization parameters is investigated. Moreover, the microstructure optimization of polymeric elements in relation to the achievement of the desired mechanical response with the least energy spent in the polymer's formation, is studied. Finally, some interesting considerations related to the modeling of the photopolymerization process are outlined.