Usage of Near-Infrared Spectroscopy for Inline Monitoring the Degree of Curing in RTM Processes

Near-infrared spectroscopy (NIR) was implemented in the resin transfer molding (RTM) process to inline monitor the degree of curing of a bio-based epoxy resin, which consists of epoxidized linseed oil (resin) and citric acid (hardener), respectively. A NIR micro-spectrometer was used for the development of robust calibration models using partial least squares (PLS) regression. Since the micro-spectrometer offers a smaller wavelength range compared with conventional NIR devices, and typical absorbance peaks are not directly involved in the captured data range, the results show new insights for the utilization of this technology. Different pre-treatments of the spectroscopic data have been tested, starting with different reference spectra, i.e., uncured resin and polytetrafluorethylene (PTFE), and followed by chemometrical algorithms. As a reference method for the degree of curing, direct current (DC) supported by differential scanning calorimetry (DSC) was used. The results show the potential of these cost-efficient and compact NIR micro-spectrometers for the intended inline monitoring purpose to gain relevant information feedback during the process.

Experimental analysis and modelling of temperature- and humidity-controlled curing

There has been much discussion about modelling the reaction kinetics of a curing polymer. Typically, curing is described by the development of a variable called degree of curing as a function of temperature and time. The material considered in this paper exhibits two different curing mechanisms, namely temperature-activated and diffusion-based. To be able to describe the complex hardening process, the material is extensively analysed experimentally, and a thermodynamically consistent coupled reaction kinetics model is formulated based on experimental observations. This model enables the implementation of the thermal, caloric, and mechanical properties of the material into a finite element (FE) framework.

Investigating Curing Kinetics for a Thin-Walled Carbon Fibre Structure

The paper presents a computational method and an example of using it to derive parameters of a high-pressure filament-wound carbon fibre vessel designed for unmanned aerial vehicle applications. A feature of the vessel design is its variable thickness, which may result in temperature gradients, residual stresses, and diminished strength. We propose a method for assessing curing kinetics that takes into account the heat emitted during this process. We used the ESI PAM-RTM software package for simulation and determined that at the initial stage of the curing process the temperature and degree of curing in the thinner part of the product exceed those in its thicker part. As the degree of curing increases, the exothermic reaction taking place affects the temperature fields, which leads to an increase in temperatures and degree of curing in the thicker regions. In order to level the temperature gradients and degree of curing over the whole vessel, we propose to heat it at different rates. Our investigation results allowed us to establish the optimum manufacturing conditions ensuring the minimum temperature gradient values

Estudio del Contenido en gel del Material Encapsulante EVA, como una Medida de Calidad del Proceso de Laminación de Módulos Fotovoltaicos

The gel content is a test that tests the resistance of the material of the module encapsulation layer, ensuring that the current conduction pathways of the cells are hermetically isolated from the inclement weather. In order to guarantee a good lamination of a photovoltaic module and therefore, a long service life of the same it is necessary that the degree of curing of the encapsulant be find between 65% - 90%. The objective of this work was to study the gel content of the EVA, after rolling. The gel content was determined using the EVASA supplier test method, taking EVA samples, after the lamination process of the photovoltaic modules. The results obtained were 73 to 96%. It is concluded that the gel content is a parameter that serves to guarantee the lamination process, since in the curing process chemical bonds are formed transversely between the long molecules of the EVA, which are weakly bound together before the reaction . The percentages of gel content, mean the percentage of EVA in which said reaction took place.

Phenomenological Modeling of the Apparent Viscosity as a Function of the Degree of Curing of an EPDM Elastomer

The moving die rheometer technique (MDR) is used to measure the elastic and viscous components of rubber. The analysis of the rheometry and the kinetic behavior can be used to obtain mathematical models to predict the viscosity of elastomers as a function of the temperature, the time and the degree of curing. These predictions allow the control, the optimization and the design of the process. In this research the phenomenological model of Kamal-Sourour was used to describe the curing kinetics, while the Carreau Macosko model was used to describe the viscous behavior of an ethylene - propylene diene industrial type compound (EPDM). The mathematical parameters for each model where determined by using non-linear regression techniques. Since the viscosity increases significantly while the curing rate decreases, we proposed a mathematical model based on the Carreau expression in order to consider the influence of the kinetic of curing in the apparent viscosity behavior. It was found that after the curing rate reaches its maximum the viscosity tends to infinity; that is, the chemical transition process known as fluidity point or gel point occurs in the vicinity of maximum curing rate. According to the results, it is concluded that rubber viscosity is well described by considering the curing variations; the fluidity point in the vulcanization process can also be obtained by the practical method of phenomenological approach.

Research of Formal-Kinetic Regularities of the Curing Process of Low-Viscosity Epoxy Binder

The expanding range of components intended for manufacturing products of polymer composite materials is often not accompanied by comprehensive information on the characteristics and recommended technological curing modes. The relevance and practical significance of this investigation are based on the need to predict rational technological modes for curing products of polymer composite materials based on the low-viscosity epoxy binder Etal-Inject-SLM, which is in demand in the manufacture of products from polymer composite materials by cold curing. The purpose of this investigation is to determine kinetic patterns, which allow for predicting the time and degree of curing of the low-viscosity epoxy binder Etal-Inject-SLM for various isothermal curing conditions. The method of differential scanning calorimetry was used to measure the thermal effect of the curing reaction of the Etal-Inject-SLM epoxy binder at various heating rates. Based on the experimental calorimetric data and using the model-free (non-prior) Friedman method, using the specialized software Netzsch Kinetics Neo, the parameters characterizing the formal kinetic laws of the curing process were calculated. This allowed for plotting isothermal and iso-conversion thermokinetic diagrams necessary for predicting the time and degree of curing of the Etal-Inject-SLM binder at different temperatures and curing times. This results can be useful for optimizing technological processes in which the low-viscosity epoxy binder Etal-Inject-SLM is used.

Polymerization characteristics of colored compomers cured with different LED units

Aim: Incomplete polymerization of a resin material used for dental restoration affects the properties of the restoration. We evaluated the structural and mechanical properties of three different colored compomers cured with three different LED units to observe the characteristic changes occurring in different matches. Methods: Polytetrafluoroethylene molds (5 mm in diameter and 2 mm in thickness) were used to prepare disk-shaped sample specimens. Nine sample groups (each of five specimens) were prepared, three each of different compomer resin colors (gold, berry, and silver). Samples were cured using three different LED units (Optima, VALO, and Demi Ultra), according to the manufacturers’ instructions. Microstructural properties of samples were characterized by determining the degree of curing using Fourier-transform infrared spectroscopy and by analyzing sample morphology under a scanning electron microscope. The Vickers hardness, compressive strength, and elastic modulus of the samples were measured to investigate their mechanical properties. Results: The degrees of curing decreased in the order of silver > berry > gold for all curing units. Conversely, gold compomers exhibited poorer mechanical values than the berry and silver counterparts. The Optima 10 unit yielded slightly higher degrees of curing than the other devices, followed by Demi Ultra and VALO light-curing units, respectively. Conclusion: The resin color affected the structural and mechanical properties of the compomers, possibly as a result of the complex interactions and relationships between the irradiation light and resin material, such as light absorbance and reflectance; thus, depending on the color as well as the curing protocol.

Adhesive strength in a high voltage mica insulation system

The problem of maintaining a monolithic high-voltage mica insulation made by the Resin Rich technology for windings of electrical machines and conductors is considered. The violation of solidity like delaminations and peeling off from conductor can happen both during the process of manufacturing and during exploitation of constructions. The possibility of breaking the solidity is directly related to the magnitude of adhesion strength. Design and manufacturing technology of samples in laboratory and industrial conditions to determine the adhesion strength were developed. Adhesive strength is determined by the method of shear and tensile test method between insulation layers and in system of metal- mica insulation.The created method for the manufacture of samples made it possible to test samples with various designs of adhesive contact, materials of adhesive contact and technological parameters of the pressing process. The adhesion strength depends on the parameters of the thermal pressing process and the degree of curing of the binder in the initial resin rich tape. Adhesive contact of mica insulation to metal through fiberglass is more durable than through film