Abstract
The thermally conductive structural film adhesive not only carries large loads but also exhibits excellent heat-transfer performance, which has huge application prospects. Herein, a novel epoxy (Ep) thermally conductive structural film adhesive was prepared using polyphenoxy (PHO) as the toughening agent and film former, boron nitride (BN) nanosheets as the thermally conductive filler, and polyester fabric as the carrier. When the amount of PHO in the epoxy matrix was 30 phr and the content of nano-BN was 30 wt.% (Ep/PHO30/nBN30), the adhesive resin system showed good film-forming properties, thermal stability, and thermal conductivity. The glass transition temperature of Ep/PHO30/nBN30 was 215 °C, and the thermal conductivity was 209.5% higher than that of the pure epoxy resin. The Ep/PHO30/nBN30 film adhesive possessed excellent adhesion and peeling properties, and the double-lap shear strength at room temperature reached 36.69 MPa, which was 21.3% higher than that of pure epoxy resin. The double-lap shear strength reached 15.41 MPa at 150 °C, demonstrating excellent high temperature resistance. In addition, the Ep/PHO30/nBN30 film adhesive exhibited excellent heat-aging resistance, humidity, and medium resistance, and the shear strength retention rate after exposure to the complicated environment reached more than 90%. The structural film adhesive prepared showed excellent fatigue resistance in the dynamic load fatigue test, the double-lap shear strength still reached 35.55 MPa after 1,000,000 fatigue cycles, and the strength retention rate was 96.9%, showing excellent durability and fatigue resistance.
Highlights
The structural adhesive is an interface material that transmits large static and dynamic loads [1,2], and it is widely used in the fields of aerospace [3,4], transportation [5,6], wind power [7], and construction [8]
In the temperature range of 50–80 ◦C, the viscosity of the epoxy/PHO blend was low when the PHO content was low, while that of the epoxy/PHO blend was too high to process when the PHO content was increased to 40 phr, which indicated that these situations were not conducive to the preparation of epoxy structural film adhesive
The increase in the content of boron nitride (BN) nanosheets improved the complex viscosity of the adhesive to a certain extent, the viscosity in the range of 50–80 ◦C is suitable for the preparation of film adhesive
Summary
The structural adhesive is an interface material that transmits large static and dynamic loads [1,2], and it is widely used in the fields of aerospace [3,4], transportation [5,6], wind power [7], and construction [8]. It is of great significance to systematically investigate the mechanical behaviors and mechanical properties of the thermally conductive epoxy structural film adhesive in different environments, as well as fatigue loads, which can offer instruction and reference for the design of the ultimate load in an actual complex environment to ensure the safety and reliability of the bonded parts in service [34]. A thermally conductive epoxy structural film adhesive is prepared using thermoplastic-toughened epoxy resin as the matrix, BN nanosheets as the thermally conductive filler, and polyester fabric as the carrier. The bonding performance, peeling performance, environmental resistance, and fatigue performance of the thermally conductive epoxy structural film adhesive are studied, and the failure modes of the test pieces under different conditions are explored.
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