Novel composite coatings prepared from 3,4-epoxy cyclohexylmethyl 3,4-epoxycyclohexane carboxylate (ECC) and different ceramic fillers have been prepared to improve the thermal dissipation of ...electronic devices. As latent cationic initiator, a benzylanilinium salt with triethanolamine has been used, which leads to a polyether matrix. Different proportions of Al₂O₃, AlN and SiC as fillers were added to the reactive formulation. The effect of the fillers selected and their proportions on the evolution of the curing was studied by calorimetry and rheometry. The thermal conductivity, thermal stability, thermal expansion coefficient and thermomechanical and mechanical properties of the composites were evaluated. An improvement of 820% in thermal conductivity in reference to the neat material was reached with a 75 wt % of AlN, whereas glass transition temperatures higher than 200 °C were determined in all the composites.
A series of boron nitride (BN) composites, with different BN content, were prepared and characterized by cationic curing of DGEBA/BN formulations. As cationic initiator a commercial benzylanilinium ...salt was used. This cationic system shows good latent characteristics that were not lost on adding the filler. The performance of the catalytic system was optimized by varying the amount of initiator and adding little proportions of glycerol. The kinetics of the curing process was evaluated by calorimetric measurements. The addition of BN allowed increasing thermal conductivity without loss of mechanical properties like Young modulus, impact resistance, adhesion and other thermal characteristics like Tg or thermal stability. In addition, dielectric properties were improved with the increment of filler.
A new series of high thermal boron nitride (BN) composites are prepared and characterized by several techniques. They are formed by an epoxy‐anhydride matrix and different BN contents, ranging from ...30 to 80 wt%, of 120 μm agglomerates. For high BN ratio (≥60 wt%), epoxy mixtures were compressed (75 MPa) during 1 minute before curing, eliminating voids due to the high increase of viscosity, improving the compactness of the material and enhancing the thermal conductivity (TC). The curing process evolution was studied by calorimetric measurements to see if there was an influence of the filler on the curing rate. Rheological tests were performed to obtain the percolation threshold. It was observed that BN filler did not affect negatively the thermomechanical properties of the materials and allowed to enhance the TC from 0.17 W/m K in the case of the neat epoxy, to 3.06 W/m K when 80 wt% of BN agglomerates were added, which represents an improvement of 1700%.
•BN and EG have been combined as fillers in epoxy composites.•Thermal conductivity have been enhanced up to 2.22 W/m K.•Electrical insulation have been preserved on adding 70% BN and 5% ...EG.•Mechanical performances have been improved by the addition of fillers.
Expanded graphite (EG) and boron nitride (BN) were used as fillers to impart thermal conductivity (TC) while maintaining electrical insulation of a homopolymerized cycloaliphatic epoxy matrix. Even though EG leads to a higher increase of TC than BN (550% of enhancement with only a 7.5 wt.% of EG), EG is also electroconductive and its ratio in the formulation must be lower than the percolation threshold. Formulations with proportions between 2.5–7.5 wt.% of EG as the filler and mixtures with EG and a 40 wt.% of BN were thermally polymerized and composites with 70 wt.% of BN and 2.5/5.0 wt.% of EG were also prepared under pressure and then cured in the oven. Over 2 W/m K was achieved (i.e. more than 1500% of enhancement in reference to the neat epoxy). The composites containing a 40 wt. % of BN and 2.5 wt % of EG or 70% wt. % of BN and 5 wt % of EG were found to keep the insulation character. Mechanical and thermal characteristics of the prepared materials were also evaluated.
Non-fossil feedstocks for the production of photocurable resins have attracted growing interest from the scientific community and industry in order to achieve more sustainable 3D-printing ...technologies. Herein, we report the successful photopolymerization process of three diallyl ester monomers, derived from succinic acid,
d
,
l
-malic acid and
l
-(+)-tartaric acid (natural acids), with poly(ethylene glycol) diacrylate, a petroleum-based co-monomer well-known for its fast UV light reaction response. The existence of hydroxyl groups beside the ester units in the malic and tartaric compounds did not influence either the kinetics or the thermal stability of the thermoset polymers. Therefore, the most prominent composition was formed by 50 wt% of the bio-derived diallyl succinate, and 50 wt% of the synthetic, having excellent thermal stability and very good dimensional resolution and transparency in DLP printed samples after light curing, and most importantly, such samples promptly undergo hydrolytic degradation thanks to the presence of the ester linkages that are incorporated by the natural monomer.
Renewable sources can be used to obtain bio-based monomers, in only one-step of synthesis, for further photopolymerization with synthetic reactive monomers in DLP printers.
Young’s modulus varies with crystallographic orientation, temperature and alloying, but also with cold working and heat treatment. In this work, the evolution of Young’s modulus in polycrystalline ...pure aluminium (99.5%) with different cold-working levels determined at room temperature is presented. The deformation process was carried out in a universal tension machine and measurements were performed by ultrasounds. The Young’s modulus diminished from 70 to 65 GPa for 0-5% of deformation (elongation) and then increased with successive cold-working (68 GPa for 8.5% of elongation). These values were obtained 8 hours after plastic deformation was applied. This behaviour is compared with the Young’s modulus determined by extensometry in the same material. In this case, the modulus decreased from 70 to 63 GPa (3.5% of elongation) and then increased until 68 GPa for 10% of elongation. Results obtained on pure iron (Armco) deformed in the same conditions are included for comparative purposes. Values of Young’s modulus measured during the springback process after plastic deformation at different level are also included. Values obtained are between 10-15% lower than those measured 8 hours after plastic deformation.
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