Polymer Curing Process Research Articles

Monitoring polymer curing progress through optical attenuation coefficient variations

The curing process of polymers has a crucial influence on their final properties. In this work, the optical attenuation coefficient (OAC) of the polymer was developed to reveal the polymerization reaction and proposed a non-contacted cure monitoring method to estimate the curing degree based on the OAC measurement. The method involves acquiring the interference spectra of the polymer specimen using optical coherence tomography (OCT) and extracting the time-varied OAC from the amplitude-frequency of the spectra. Since polymer curing is accompanied by an increase in refractive index, the gradual convergence in the refractive index of the matrix and fillers leads to a decrease in the OAC. For validation, the reliability, repeatability, and stability experiments of this method were implemented successively on a dental polymer resin and verified its feasibility in monitoring the curing process. Then, the quantitative measuring performance under different curing conditions was further verified on another polymer composite. Finally, three commercial dental composite materials were successfully measured for the curing degree and confirmed the practicability of the OAC-OCT-based method in monitoring cure application.

Reinforced Epoxy Composites Modified with Functionalized Graphene Oxide.

The possibility of using graphene oxide as a modifying additive for polymer fiber-reinforced composites based on epoxy resin and basalt roving has been studied. The content of graphene oxide in the system has been experimentally selected, which has the best effect on the physico-mechanical properties of the obtained polymer composite material. The efficiency of the modification of the graphene oxide surface with APTES finishing additives and aminoacetic acid, which provides chemical interaction at the polymer matrix–filler interface, has been considered. The influence of graphene oxide and functionalizing additives on the polymer curing process was investigated using the thermometric method and differential scanning calorimetry.

Investigation of curing kinetics and internal strains to enhance performances of bisphenol A based shape memory polymers

Shape memory polymers (SMPs) are an emerging class of polymers that can memorise temporary shapes and recover permanent shapes upon an external stimulus. These multi-functional materials have attracted researchers' interest due to their endemism thermomechanical and shape memory properties. Extensive fundamental research has been done on this field and recently synthesised SMPs and their composites (SMPC) have shown great potential for innovative and high-tech applications such as space exploration, medical and biomimetic devices etc. To date, researchers have improved SMP properties via polymer synthesis techniques, matrix reinforcement and incorporation of nano additives. However, neither of work has investigated the effect of polymer curing process on SMP performances with the aid of curing kinetics and internal strains. In this research, a bisphenol A based SMP was synthesized, and the progress of the chemical reaction was experimentally monitored using DEA, DSC kinetic models and FTIR. The DEA has provided the start and end of the crosslink generation. Simultaneously, measured internal strain through a novel embedded distributed optical fibre sensing network showed the shrinkage and expansion of the SMP at curing, which also correlates with DEA results. Most importantly, SMP and SMPC recovery time has improved by 20 and 16% compared to the DGEBA/SMPC-100. Moreover, tensile strength and ultimate tensile modulus have been increased by 13% and 7%, respectively. Overall, the proposed research approach provides an act of courage to researchers to further enhance SMP thermomechanical and weak and delicate shape memory properties without changing chemical structure or composition.

Combination of imaging techniques allows for visualization of polymer curing processes

Researchers developed a method to monitor the curing behavior at depths within a polymer specimen.

Nondestructive rapid and quantitative analysis for the curing process of silicone resin by near‐infrared spectra

AbstractReactive group content was a key parameter in polymer curing process. However, the conventional methods to measure the curing were destructive and time consuming. In this article, near‐infrared spectra technology had been applied for reactive group analysis of the photothermal curing silicone to achieve rapid nondestructive and quantitative detection. The calibration model was developed about epoxy value and CC double bond value, with determination coefficient (R2) of 0.9631 and 0.9689. Root mean square error of prediction were 0.0179 and 0.0143 by partial least square regression. The optimized calibration model was used to predict the content of epoxy value and CC double bond value in the photothermal curing process, it proved that the silicone resin cured under UV‐radiation and heat. This novel method provided a promising approach to analysis the curing mechanism and quality parameters of resin.

Model validation of polymer curing processes using thermography

Abstract It would be advantageous to have a direct model validation of curing processes of epoxy resin systems. Since a direct measurement of the curing evolution and, thus, validation of curing processes is not yet possible, the temperature development based on the exothermic curing reaction is of particular interest. This aspect represents the main focus of this article, which is based on an experiment with a curing epoxy resin sample including suitable boundary conditions, which can be reproduced by numerical simulations. The heat transfer coefficient of natural convection is determined both by empirical formulations as well as by use of temperature measurements. Using a thermographic measuring system, the surface temperature of the sample is measured throughout the curing reaction while the properties of the sample surface constantly change. The thermographic measurements reveal initial fluid streams due to internal convection within the sample, which stop after short period of time. For validation purposes between the experiment and the simulation, we provide a method to map the recorded pixel temperatures to a geometric coordinate system located in the center of the sample surface. Further, the numerical treatment of curing processes is briefly summarized. Finally, the numerical results are compared to the experimental data analysis. Deviations are critically discussed regarding possible errors.

Modelling the curing process in particle-filled electro-active polymers with a dispersion anisotropy

Even for a moderate actuation, a large electric voltage requirement hinders the application of electro-active polymers (EAPs) in many areas. Hence, among other mechanisms, the actuation enhancement in EAPs is performed via inclusions of high-dielectric-permittivity fillers in the matrix material in the uncured stage. Moreover, to obtain an optimum advantage from the high-dielectric-permittivity fillers, an electric field can be applied during the curing process which helps the particles to align in a preferred direction. To be specific, recent experimental evidences show that these particles form a dispersed anisotropy rather than a perfect transverse anisotropic structure. The polymer curing process is a complex (visco-) elastic phenomenon where a liquid polymer gradually transforms into a solid macromolecular structure due to cross-linking of the initial solution of short polymer chains. This phase transition comes along with an increase in the material stiffness and a volume shrinkage. In this paper we present a phenomenologically inspired large strain framework for simulating the curing process of particle-filled electro-active polymers with a dispersion-type anisotropy that can work under the influence of an electro-mechanically coupled load. The application of the proposed approach is demonstrated with some numerical examples. These examples illustrate that the model can predict common features in particle-filled dispersed electro-active polymers undergoing curing processes in the presence of an electro-mechanically coupled load.

Invited commentary

Invited commentary

Electrical, Mechanical and Electromechanical Properties of Graphene-Thermoset Polymer Composites Produced Using Acetone-DMF Solvents.

Recently, graphene-polymer composites gained a central role in advanced stress and strain sensing. A fundamental step in the production of epoxy-composites filled with graphene nanoplatelets (GNPs) consists in the exfoliation and dispersion of expanded graphite in a proper solvent, in the mixing of the resulting GNP suspension with the polymer matrix, and in the final removal of the solvent from the composite before curing through evaporation. The effects of traces of residual solvent on polymer curing process are usually overlooked, even if it has been found that even a small amount of residual solvent can affect the mechanical properties of the final composite. In this paper, we show that residual traces of N,N′-Dimethylformamide (DMF) in vinylester epoxy composites can induce relevant variations of the electrical, mechanical and electromechanical properties of the cured GNP-composite. To this purpose, a complete analysis of the morphological and structural characteristics of the composite samples produced using different solvent mixtures (combining acetone and DMF) is performed. Moreover, electrical, mechanical and electromechanical properties of the produced composites are assessed. In particular, the effect on the piezoresistive response of the use of DMF in the solvent mixture is analyzed using an experimental strain dependent percolation law to fit the measured electromechanical data. It is shown that the composites realized using a higher amount of DMF are characterized by a higher electrical conductivity and by a strong reduction of Young’s Modulus.

Ultrafast Nanoscale Polymer Coating on Porous 3D Structures Using Microwave Irradiation

AbstractThin polymer coatings are very popular, but the coatings on uneven surfaces or porous 3D structures are difficult to obtain with traditional methods. The pores are easily clogged due to nonuniform polymer curing processes caused by inevitable macroscale temperature gradients from their hotter outer to colder inner sides. Here an ultrafast and simple fabrication method is developed to obtain nanoscale coating layers on the inner and outer surfaces of a porous 3D sponge‐like carbon nanotube (CNT). Microwave irradiation rapidly and selectively heats the CNT immersed in a mixture solution of an uncured polymer and a diluent solvent, solidifying the polymer only adjacent to the CNT with five repeated 3 s microwave irradiation. The coating layers can be controlled by adjusting the concentration of the uncured polymer in the solution and controlling the CNT temperature via microwave power and irradiation time. The nanoscale coating strongly ties the junction between CNTs without filling the pores with the polymer, resulting in excellent resilience to compressive stress with large strains (≈180 kPa at 60%), which is maintained throughout repeated 8000 cycles of 0–60% strain. The unfilled pores allow for maintaining the low thermal conductivity, ≈26 mW m−1 K−1, and the electrical resistance is varied with strain. This facile selective polymer curing methodology can be utilized in processing various materials with uneven surfaces or pores.

Encapsulation of Single Nanoparticle in Fast-Evaporating Micro-droplets Prevents Particle Agglomeration in Nanocomposites.

This work describes the use of fast-evaporating micro-droplets to finely disperse nanoparticles (NPs) in a polymer matrix for the fabrication of nanocomposites. Agglomeration of particles is a key obstacle for broad applications of nanocomposites. The classical approach to ensure the dispersibility of NPs is to modify the surface chemistry of NPs with ligands. The surface properties of NPs are inevitably altered, however. To overcome the trade-off between dispersibility and surface-functionality of NPs, we develop a new approach by dispersing NPs in a volatile solvent, followed by mixing with uncured polymer precursors to form micro-droplet emulsions. Most of these micro-droplets contain no more than one NP per drop, and they evaporate rapidly to prevent the agglomeration of NPs during the polymer curing process. As a proof of concept, we demonstrate the design and fabrication of TiO2 NP@PDMS nanocomposites for solar fuel generation reactions with high photocatalytic efficiency and recyclability arising from the fine dispersion of TiO2. Our simple method eliminates the need for surface functionalization of NPs. Our approach is applicable to prepare nanocomposites comprising a wide range of polymers embedded with NPs of different composition, sizes, and shapes. It has the potential for creating nanocomposites with novel functions.

Erosion-wear, mechanical and thermal properties of silica filled epoxy nanocomposites

Abstract Different nano- and micro-fillers are added to modify the mechanical properties, wear resistance, thermal properties and the curing process of polymers. A very important application for epoxy resins is to be used as coating for anti-cavitation painting. Pyrogenic silica is already used in adhesives and paints, being its application related to rheology. The objective of this work is to study the effect of pyrogenic silica on epoxy resins, usually not present in their formulation. SiO2/epoxy nanocomposites with two different loads of nano-silica, 3 and 5 wt% were manufactured. In particular, the study focuses on the influence that the addition of nano-silica has on the mechanical, wear and cavitation erosion properties as well as on the thermal properties and the curing reaction. To accomplish these goals, nanocomposite samples in bulk and as coating were prepared. Mechanical properties (hardness, bending and tensile strength), wear resistance (in bulk and coating) and cavitation erosion were evaluated. The epoxy curing process and the influence of nano-SiO2 additions on the glass transition temperature (Tg) were studied by Differential Scanning Calorimetry (DSC). In general, a plasticising effect was observed with nano-silica addition. Moreover, the resistance to erosion by cavitation, in terms of cumulative erosion and erosion rate, was higher for the nanocomposites than for clear resin.

Impact of Water on Rheological Behavior of Polyurethane Glues

Abstract Gluing of wood with great moisture content has challenge of water interaction with glue to give unwanted changes in glue properties and formed bond-line. Rheological measurements of polyurethane glues are sufficiently effective method to understand the polymer curing process and viscoelastic properties. Gel formation point is important parameter for a glue from the point of its application. When glue reaches the gel formation point, its viscosity drastically increases so that it could not properly wet the wood and it can result in poor bonds. One-component moisture curing polyurethane glues require water molecules for the polyadditional reaction. When water is involved in the curing reaction, it reacts with the isocyanate groups of glue and can lead to the formation of excessive carbon dioxide and thus can lead to glue penetration out of bond-line, additional backpressure. The dynamic viscoelastic parameters such as complex dynamic viscosity (ή), phase angle (δ), elastic storage modulus (G”), the viscous loss modulus (G”) of two kinds of polyurethane glues depending on added water amount (from 0.9% to 10.0%) at a constant frequency and deformation (oscillation mode) were determined using rheometer. The aim of the present study was to investigate impact of added water on rheological behavior of polyurethane glues. At the end of this study it was concluded that tested glues indicated various behavior depending on chemical composition and added water content. Gel formation point is higher in case of GlueI. However, gel formation time was higher in case of GlueII and was not dependent on added water content. Gel formation time was faster for GlueII. Nevertheless, faster formed gel is stronger than longer formed gel of GlueI.

Towards modelling the curing process in particle‐filled electro‐active polymers

AbstractA large actuation voltage is required to produce a desired mechanical deformation in dielectric elastomers. To reduce the amount of the actuation voltage, several mechanisms can be applied and the inclusion of high dielectric permittivity fillers in the matrix material in the uncured stage is one of them. Moreover, to obtain a maximum advantage from the high dielectric permittivity fillers, an electric field is applied during the curing process which helps the particles to align in a preferred direction. The stiffness gaining during curing is modelled by an appropriate constitutive relation where the temporal evolution of the material parameters is considered. In this paper we present a phenomenologically‐inspired large strain framework for simulating the curing process of polymers that can work under the use of an electro‐mechanically coupled load. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A multi-scale approach to model the curing process in magneto-sensitive polymeric materials

We propose a magneto-mechanically coupled multi-scale model for simulating the curing process of polymers. In the case of magneto-sensitive polymers, micron-size ferromagnetic particles are mixed with a liquid polymeric matrix in the uncured stage. The polymer curing process is a complex process that transforms a fluid to a solid with time. To transfer the constituent parameter information from the micro-scale to the macro-scale for a composite magneto-mechanically coupled polymeric material, an extended Mori–Tanaka semi-analytic homogenization procedure is utilized. The stiffness gaining phenomenon as in the case of a curing process is realized by time-dependent material parameters appearing within the composite piezomagnetic material tensors. Moreover, to compute the volume reduction during curing, a magnetic induction dependent shrinkage model is proposed. Several numerical examples show that the model proposed herein can capture major observable phenomena in the curing process of polymers under magneto-mechanically coupled infinitesimal deformations.

Modelling the curing process in magneto-sensitive polymers: Rate-dependence and shrinkage

This paper deals with a phenomenologically motivated magneto-viscoelastic coupled finite strain framework for simulating the curing process of polymers under the application of a coupled magneto-mechanical load. Magneto-sensitive polymers are prepared by mixing micron-sized ferromagnetic particles in uncured polymers. Application of a magnetic field during the curing process causes the particles to align and form chain-like structures lending an overall anisotropy to the material. The polymer curing is a viscoelastic complex process where a transformation from fluid to solid occurs in the course of time. During curing, volume shrinkage also occurs due to the packing of polymer chains by chemical reactions. Such reactions impart a continuous change of magneto-mechanical properties that can be modelled by an appropriate constitutive relation where the temporal evolution of material parameters is considered. To model the shrinkage during curing, a magnetic-induction-dependent approach is proposed which is based on a multiplicative decomposition of the deformation gradient into a mechanical and a magnetic-induction-dependent volume shrinkage part. The proposed model obeys the relevant laws of thermodynamics. Numerical examples, based on a generalised Mooney–Rivlin energy function, are presented to demonstrate the model capacity in the case of a magneto-viscoelastically coupled load.

Modelling the mechanical aspects of the curing process of magneto-sensitive elastomeric materials

In this paper, a phenomenologically motivated magneto-mechanically coupled finite strain elastic framework for simulating the curing process of polymers in the presence of a magnetic load is proposed. This approach is in line with previous works by Hossain and co-workers on finite strain curing modelling framework for the purely mechanical polymer curing (Hossain et al., 2009b). The proposed thermodynamically consistent approach is independent of any particular free energy function that may be used for the fully-cured magneto-sensitive polymer modelling, i.e. any phenomenological or micromechanical-inspired free energy can be inserted into the main modelling framework. For the fabrication of magneto-sensitive polymers, micron-size ferromagnetic particles are mixed with the liquid matrix material in the uncured stage. The particles align in a preferred direction with the application of a magnetic field during the curing process. The polymer curing process is a complex (visco) elastic process that transforms a fluid to a solid with time. Such transformation process is modelled by an appropriate constitutive relation which takes into account the temporal evolution of the material parameters appearing in a particular energy function. For demonstration in this work, a frequently used energy function is chosen, i.e. the classical Mooney–Rivlin free energy enhanced by coupling terms. Several representative numerical examples are demonstrated that prove the capability of our approach to correctly capture common features in polymers undergoing curing processes in the presence of a magneto-mechanical coupled load.

In-situ generation and application of nanocomposites on steel surface for anti-corrosion coating

Abstract Thin organic coatings directly on steel sheets provide excellent barrier protection in saline environment and meet deformability demands, but fail in providing active corrosion protection. We have put an effort to solve this problem by formulating composite coatings using in-situ generation of metal oxide nanoparticles (NPs) in the polymer matrix. Here we present a new synthesis method of high performance polyetherimide composite with TiO2, MgO, and Al2O3 nanoparticles and their application for anti-corrosion coatings in saline environment. We observed that in-situ synthesis of these metal oxide NPs in the polymer curing process leads to evenly distribution and uniform size of nanoparticles. Thermo-mechanical property was analyzed for these three kinds of free-standing composite film to assess elasto-plastic behaviour and compared to mother polymer film. Results indicated that thermal stability and elastic behaviour of composites film are not affected to the great extent by the presence of NPs. The potentiodynamic and the electrochemical impedance studies on these composite coated steel panels were carried out to identify active–passive behaviour. Results showed active corrosion protection from nanocomposite coating based on TiO2 and barrier protection was noticed from nanocomposite coating based on MgO and Al2O3.

Modeling and optimization for curing of polymer flooding using an artificial neural network and a genetic algorithm

An artificial neural network model was adopted to investigate the relationships between polymer curing process parameters (polymer concentration, agitation speed, and paddle type) and viscosity and curing time. The adequacy of established mathematical models was checked by analysis of variance (ANOVA). The interaction effects of process parameters on the mixing performance were investigated. The desirability function integrated with genetic algorithm was used to determine the optimum conditions of maximum viscosity and minimum curing time. The polymer concentration of 3798mg/L, the double helical ribbon-screw impeller I, and the agitation speed of 115r/min were optimal for the polymer curing process. The results showed that the optimal results predicted by the genetic algorithm were in good agreement with the experimental results, so this study provided an effective method to enhance the curing process of polymer flooding.

Degree of cure‐dependent modelling for polymer curing processes at small strains

AbstractIn this paper, a thermodynamically consistent small strain constitutive model is formulated that is directly based on the degree of cure, a key parameter in the curing (reaction) kinetics. The new formulation is also in line with the earlier proposed hypoelastic approach, cf. Hossain et al., 2010. The curing process of polymers is a complex phenomenon involving a series of chemical reactions which transform a viscoelastic fluid into a viscoelastic solid during which the temperature, the chemistry and the mechanics are coupled. Some representative numerical examples conclude the paper and show the capability of the newly proposed constitutive formulation to capture major phenomena observed during the curing processes of polymers. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)