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Morphology, rheological, and electrical properties of flexible epoxy/carbon composites cured by UV technique Pollawat Charoeythornkhajhornchai1,a), Chavakorn Samthong2 1

Division of Materials Engineering, Faculty of Engineering, Burapha University, Muang, Chonburi 20131, Thailand Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Pathumwan, Bangkok 10330, Thailand a) Address all correspondence to this author. e-mail: [email protected] 2

Received: 7 April 2020; accepted: 3 June 2020

The aim of this research was to develop the UV-cured epoxy/carbon composites. The rheological properties of the uncured neat epoxy and epoxy composite with graphite, graphene, and multi-walled carbon nanotube (MWCNT) were evaluated to observe the macroscopic flow behavior and the microstructure by shear force. The results showed that epoxy/carbon composites at high filler content exhibited shear-thinning behavior with a high yield stress value and epoxy/MWCNT at 30 phr showed this characteristic obviously. The fractured surface and particle dispersion in the epoxy matrix were evaluated by scanning electron microscopy and transmission electron microscopy, respectively. Epoxy/carbon composites at high filler content displayed rough fracture surface with particle agglomeration, thus the electrical conductivity increased. The result showed that the epoxy/MWCNT composites had high potential to use as a conductive adhesive with a 3D printing process due to high electrical conductivity with high viscosity that could be formed easily during processing.

Introduction Nowadays, the technology for electronic application, i.e., mobile phone and hard disc drive, has been attracted great attention dramatically. The life cycle of electronic packaging becomes shorter than many fields of products. Electronic industries have intended to develop and design the electronic package to be smaller, lighter, and thinner with higher performances to meet the demands of customers. The adhesive resin is an important part for connecting the electronic assemblies together in the electronic product, while the packaging should be as thin as possible. Thus, the three-dimensional (3D) printing technology of adhesive resin would be the appropriate technique for this process. Many researchers have developed and applied 3D printing technology in terms of material processing to generate the suitable technique for the 3D printing application. There are several techniques to fabricate materials in the 3D printing process such as inkjet printing [1], powder-bed technology [1], stereolithography [2, 3, 4, 5, 6], fused deposition modeling [7, 8], solvent-cast 3D printing [1], conformal 3D printing [1], and direct-write assembly [9, 10, 11, 12, 13, 14, 15, 16]. Chen et al. [12] developed the fabrication process of tough epoxy blended with an acrylate resin by a direct-write 3D printing

© Materials Research Society 2020

process. There were two curing stages which were a rapid photo cure of acrylate resin and thermal cure of epoxy oligo