Thermal Conductivity Of Resin Research Articles

Molecular insights of DGEBA/MeTHPA three-dimensional resin network from design to heat transfer mechanism: Dynamic simulation and experimental research

The epoxy resin composed of bisphenol A diglycidyl ether (DGEBA) and methyl tetrahydrophthalic anhydride (MeTHPA) has been found to enhance its thermal conductivity by increasing its molecular weight and crosslinking density. This was achieved through experiments and all-atom molecular dynamics simulations. Molecular dynamics was employed to calculate the root-mean-square displacement, free volume fraction, potential energy, density, and quantity of hydrogen bonds. The results showed the influence of molecular weight and crosslinking density on the system's thermal conductivity. The results showed that the high molecular weight epoxy resin system exhibited high thermal conductivity at elevated crosslinking densities. During the crosslinking process, the epoxy resin's thermal conductivity increased, starting with the center portion weakening and then strengthening. In addition, a simulation-verified free volume was found to have an inversely proportional connection with thermal conductivity. This study explored the thermal conductivity mechanism of epoxy resin by analyzing the structural changes at the micro level and correlating them with the changes in thermal conductivity at the macro level to enhance guidance for industrial production and practical application.

Study on Thermomechanical Properties and Morphology of an Epoxy Resin Thermally Conductive Adhesive under Different Curing Conditions.

An epoxy resin thermally conductive adhesive is a type of thermosetting polymer encapsulation material that exhibits comprehensive performance, and the thermomechanical properties of this adhesive vary significantly under different curing conditions. In this paper, spherical alumina was used as a filler for thermal conductivity to prepare an epoxy resin thermal conductivity adhesive using a multistage freezing mixing method. The effects of various curing conditions on the thermal-mechanical properties and fracture morphology of the epoxy resin thermal conductivity adhesive were studied. The results showed that the curing condition of 150 °C/2.5 h significantly improved the performance of the epoxy resin thermally conductive adhesive. Through the shear test of the composite material, the influence of the curing agent on the adhesion of the thermally conductive adhesive under fixed conditions was explored. It was found that the curing agent with a superbranched structure exhibited latent properties and greatly enhanced the toughness of the cured epoxy resin product. Altering the curing conditions increases the shear strength by up to 307%. With the increase in curing temperature and the extension of curing temperature, the glass transition temperature gradually increased from 103.9 to 159.8 °C. The initial decomposition temperature TIDT gradually increased from 295.4 to 310.1 °C, and the temperature at which the fastest decomposition rate occurs (Tmax) gradually increased from 312.48 to 330.33 °C. The thermal stability of the substance increased with both temperature and time. The curing time and curing temperature were increased, and the morphology of the fracture of the epoxy resin thermally conductive adhesive cured sample gradually showed a ductile fracture from a typical brittle fracture. The research results reveal the influence of curing conditions on the thermal conductivity and thermal stability of the epoxy resin thermally conductive adhesive, which has a specific reference value for improving the performance of the epoxy resin thermally conductive adhesive, optimizing its usage conditions, and improving production efficiency.

Effect of Tantalum Oxide Nanpowder on Heat Cure Acrylic Resin Thermal Conductivity and Surface Roughness

The main problem with heat cure acrylic is their poor thermal conductivity and their roughness. This study aims at evaluating the effect of tantalum oxide nanopowder on the thermal conductivity and surface roughness of heat cure acrylic resin. Material and Method: The Intention was to create a total of (60) specimens. Twenty samples were made without additives (control), and 40 had been made with tantalum oxide at two different amounts (1 %, 1.5%). Results: the thermal conductivity tests showed non-significant difference among studied groups. The surface roughness tests showed highly significant difference among studied groups. when tantalum oxide had added to heat cure acrylic at two different amounts (1%, 1.5%). Conclusion: adding tantalum oxide increases the thermal conductivity and decreases the surface roughness of the two experimental groups.

Thermal conductivity enhancement of liquid crystalline epoxy/MgO composites by formation of highly ordered network structure

AbstractTo develop a high thermal conductive composite, an MgO filler was incorporated into a liquid crystalline (LC) epoxy containing a mesogenic moiety. The thermal conductivity of the obtained composite was 1.41 W/(m∙K) at 33 vol% content, which was remarkably higher than the value predicted using Bruggeman's model. To investigate the reason for this significant enhancement of the thermal conductivity in the LC epoxy composites, the LC phase structure of the composite was analyzed by a polarized optical microscope, an X‐ray diffractometry (XRD) and a polarized IR mapping measurement. An XRD analysis indicated the local formation of a highly ordered smectic phase structure, even in the high‐loading composite. This result indicated the promotion of the self‐assembly of the mesogenic network polymer chains by the MgO filler loading. We considered that this highly ordered structural formation can lead to an increase in the matrix resin's thermal conductivity, which can result in the effective enhancement of the thermal conductivity in the LC epoxy/MgO composite.

Real-time inverse solution of the composites’ cure heat transfer problem under uncertainty

This paper addresses the development of an inversion scheme based on Markov Chain Monte Carlo integrating process modelling with monitoring data for the real-time probabilistic estimation of unknown stochastic input parameters such as heat transfer coefficient and resin thermal conductivity and process outcomes during the manufacture of fibrous composites materials. Kriging was utilized to build an efficient surrogate model of the composite curing process based on finite element modelling. The utilization of an inverse scheme with real-time temperature monitoring driving the estimation of process parameters during manufacture results in real-time probabilistic prediction of process outcomes.

Effects of the Encapsulating Resin on the Junction Temperature of the QFN16 and QFN32 Electronic Packages Subjected to Free Convection

ABSTRACTThe junction temperature of the quad flat no-lead with 16 and 32 leads (QFN16 and QFN32) electronic packages subjected to free convection is highly affected by their encapsulating resin's thermal conductivity. This study considers a variation of this conductivity between −80% and +100% of the average value measured on an industrial prototype by means of the Transient Plane Source method. The three dimensional numerical solution based on the control volume formulation shows that the thermal trend is of exponential type for these components but with different functions. The proposed relationships allow the calculation of the junction temperature of both QFN16 and QFN32 according to the power generated varying between 0.1 and 1W, and the inclinations relative to the horizontal plane in the range 0–90° (horizontal and vertical positions respectively). The law governing the influence of conductivity on the junction temperature shows that a more conductive resin does not significantly lower the junction temperature. However, for low conductivity values, the temperature can exceed the maximum recommended by the manufacturers, causing possible malfunction of the QFN and altering its technical performance that are directly related to its thermal state. In some cases, the device can be decommissioned.

Junction temperature of QFN32 and 64 electronic devices subjected to free convection. Effects of the resin's thermal conductivity

The thermal state of the electronic devices used in many engineering fields must be controlled. The maximum temperature does not exceed the value recommended by the manufacturer to prevent a decrease of their reliability, malfunction or decommissioning. The junction temperature of the Quad Flat Non-Lead (QFN) device which often equips the electronic assemblies is affected by the thermal characteristics of its components, in particular the thermal conductivity of the molding compound (resin) used for the package encapsulation. This work deals with the QFN32 and QFN64 models widely used in the field of smart building. These devices may be tilted of any angle from the horizontal and vertical positions, depending on where they are located in the considered building. The packages located in small boxes are subjected to air natural convection. The 3D numerical approach based on the volume control method considers several configurations obtained by varying the generated power between 0.01 and 0.1W by steps of 0.01W, corresponding to the partial operation. The junction thermal state is determined for many values of the resin's thermal conductivity ranging between −80% and +100% of its average value and inclination of the devices varying between 0 and 90° (horizontal and vertical positions respectively) by steps of 15°. The results of the numerical solution are confirmed by thermal and electrical measurements carried out in situ on various prototypes. The deviation between measurements and calculations is low, ranging between −3 and +7%. New and accurate relationships are proposed, allowing to improve the thermal design of the QFN32 and QFN64 packages by determining their junction temperature for any combination of the considered generated power, tilt angle and thermal conductivity of the encapsulating resin. The control of the thermal aspect allows to enhance substantially the reliability of these widely used electronic devices.

A comparative study on the effect of carbon fillers on electrical and thermal conductivity of a cyanate ester resin

Carbon fillers including multi-walled carbon nanotubes (MWCNTs), carbon black (CB) and graphite were introduced in a cyanate ester (CE) resin, respectively. The effects of the fillers on the electrical and thermal conductivity of the resin were measured and analyzed based on the microscopic observations. MWCNTs, CB and graphite exhibited percolation threshold at 0.1 wt%, 0.5 wt% and 10 wt%, respectively. The maximal electrical conductivity of the composites was 1.08 S/cm, 9.94 × 10−3 S/cm and 1.70 × 10−5 S/cm. MWCNTs showed the best enhancement on the electrical conductivity. The thermal behavior of the composites was analyzed by calorimetry method. Incorporation of MWCNTs, CB and graphite increased the thermal conductivity of CE resin by 90%, 15% and 92%, respectively. Theoretical models were introduced to correlate the thermal conductivity of the CE/MWCNTs composite. The interfacial thermal resistance between CE resin and MWCNTs was 8 × 10−8 m2K/W and the straightness ratio was 0.2. The MWCNTs were seriously entangled and agglomerated. Simulation results revealed that thermal conductivity of the CE/MWCNTs composites can be substantially elevated by increasing the straightness ratio and/or filler content of MWCNTs.

Effect of Liquid-Crystalline Epoxy Backbone Structure on Thermal Conductivity of Epoxy–Alumina Composites

In a series of papers published recently, we clearly demonstrated that the most important factor governing the thermal conductivity of epoxy–Al2O3 composites is the backbone structure of the epoxy. In this study, three more epoxies based on diglycidyl ester-terminated liquid-crystalline epoxy (LCE) have been synthesized to draw conclusions regarding the effect of the epoxy backbone structure on the thermal conductivity of epoxy–alumina composites. The synthesized structures were characterized by proton nuclear magnetic resonance (1H-NMR) and Fourier-transform infrared (FT-IR) spectroscopy. Differential scanning calorimetry, thermogravimetric analysis, and optical microscopy were also employed to examine the thermal and optical properties of the synthesized LCEs and the cured composites. All three LCE resins exhibited typical liquid-crystalline behaviors: clear solid crystalline state below the melting temperature (Tm), sharp crystalline melting at Tm, and transition to nematic phase above Tm with consequent isotropic phase above the isotropic temperature (Ti). The LCE resins displayed distinct nematic liquid-crystalline phase over a wide temperature range and retained liquid-crystalline phase after curing, with high thermal conductivity of the resulting composite. The thermal conductivity values ranged from 3.09 W/m-K to 3.89 W/m-K for LCE–Al2O3 composites with 50 vol.% filler loading. The steric effect played a governing role in the difference. The neat epoxy resin thermal conductivity was obtained as 0.35 W/m-K to 0.49 W/m-K based on analysis using the Agari–Uno model. The results clearly support the objective of this study in that the thermal conductivity of the LCE-containing networks strongly depended on the epoxy backbone structure and the degree of ordering in the cured network.

A Study on Nanocomposites Behavior at Heating

Published literature is rich with investigations of mechanical properties of composites, but fewer publications are focused on thermal properties. Several publications addressing different theoretical approaches for predicting thermal conductivity of composite materials have been noted. However, one of the publications has discussed both transverse and axial thermal conductivity of a carbon fiber composite. A non-linear increase in the thermal conductivity was reported with the increase of fiber volume fraction of plain weaves and no theoretical models are able to predict this non-linearity. The result of literature search even further identified the necessity and importance of carrying out further investigations on thermal behavior of composites materials. Thermal conductivity of composites is anisotropic in nature and data about thermal conductivity of resin is known to reduce stresses related to shrinkage of composites during cure and mismatch in thermal expansion coefficients. Before conducting experiments to determine thermal conductivity of various composites, knowledge about effect of different parameters influencing thermal conductivity is essential. This paper deals with an analytical study on few nanocomposites behavior at heating.

Theoretical Considerations on Fibre Reinforced Composites Thermal Conductivity Uncertainties

Thermal conductivity of composites is anisotropic in nature and data about thermal conductivity of resin facilitates to reduce stresses related to shrinkage of composites during cure and mismatch in thermal expansion coefficients. Before conducting experiments to determine thermal conductivity of various composites, knowledge about effect of different parameters influencing thermal conductivity is essential. The increasing use of composites, for various applications, emphasizes its importance/significance in the thermal property analysis of an engineering system. Published literature is rich with investigations of mechanical properties of composites, but fewer publications are focused on thermal properties. Several publications addressing different theoretical approaches for predicting thermal conductivity of composite materials have been noted. Various theoretical approaches are used to yield the thermal conductivity of a composite material so that the heat flow in anisotropic composite material in any direction can be estimated. In this paper few models will be considered and a theoretical study on thermal conductivity uncertainties will be conducted and discussed. The results identified the need and importance of carrying out further investigations on thermal behavior of composites materials.

Prediction of thermal conductivity of air voided-fiber-reinforced composite laminates part II: 3D simulation

Applying the fundamental definition of thermal conductivity to a unit cell of unidirectional fiber reinforced composite with air voids, one can deduce simple empirical formula to predict the thermal conductivity of the composite material with estimated air void volume percent. The inherent 3-D problem is modeled using finite element analysis. The model is tested at different fiber to resin volume ratios and various fibers to resin thermal conductivity ratios for three different air void volume percent. The air voids are modeled as cylindrical shapes with different lengths aligned with fiber direction. Two prediction schemes have been developed through the present work. One is to predict the longitudinal thermal conductivity and the other is to predict the transverse thermal conductivity of the fibers. Also, the model can be used to estimate the voids volume percent if the fiber thermal conductivity has been provided. Such expression can, also, serve as useful guides for quality and perfect bonding for material development.

Tribological behaviour of epoxy based composites for rapid tooling

Epoxy resin composites are frequently applied in moulds manufactured with rapid tooling technologies that are used for wax and polymer materials injection. With the propose of enlarging the application field of the polymer matrix systems, it is fundamental to select adequate dispersed phases and analyse their influence on the composite properties in order to reinforce the polymer matrix and tailor the properties according to the tools specifications. Thermal conductivity and wear resistance are critical parameters for a good service performance and durability of the mould. Metallic fillers allow significant improvement in the resin thermal conductivity. In this work, it was possible to show that small amounts of milled fibres enhance the wear resistance, with little changes in the processability and in the allowed aluminium concentration in the resin matrix. A tribological study of these materials was performed involving the neat resin, the aluminium filled resin and tri-phase composites composed by epoxy, aluminium particles and milled glass or carbon fibres. The study was focused on the role of the particles and fibres in the friction and wear at room temperature and at a typical plastic injection temperature of 160 °C.

Effects of graphite fiber and epoxy matrix physical properties on the temperature profile in a composite during cure

An investigation was carried out into the effects of graphite fiber and epoxy matrix physical properties on the temperature profile in their laminates during cure. An accurate prediction of the temperature profile within a composite is of paramount importance in determining the processing conditions. In this study, a model for the temperature profile was established first. Then, three physical parameters of composites that change during cure, namely, density, heat capacity, and thermal conductivity, were varied in magnitude, and the ensuing effect on the temperature profile was examined. The range of their variation was based upon the values measured in the laboratory as well as those reported in the literature. Changes in the neat resin thermal conductivity were found to significantly influence the temperature profile. 17 refs.