20: 3-4 (2020) 128-133 ISSN: 2084-6096 ISSN (online): 2299-128X Praveen Kumar Balguri 1,2 *, D G Harris Samuel 3 , Chilumala Indira 4 , Govardhan Dussa 1 Tirupathi Rao Penki 5 , Udayabhaskararao Thumu 2 * 1 Department of Aeronautical Engineering, Institute of Aeronautical Engineering, Hyderabad 500043, India 2 Institute of Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu 610054, China 3 Department of Mechanical Engineering, Hindustan Institute of Technology and Science, Chennai 603103, India 4 Computer Centre, Institute of Aeronautical Engineering, Hyderabad 500043, India 5 Department of Chemistry, Bar Ilan University, Ramat Gan 52900, Israel *Corresponding author. E-mail: isr.praveenkumar@gmail.com Received (Otrzymano) 29.06.2020 TENSILE, FLEXURAL AND IMPACT PROPERTIES OF ULTRASMALL TiO2 NANOTUBES REINFORCED EPOXY COMPOSITES Ultrasmall TiO2 nanotubes (TiO2NTs) of the length ~250±20 nm and diameter ~20 nm are synthesized and TiO2NT reinforced (0.1 wt.%) epoxy composites are fabricated. The reinforcing effects are studied by means of tensile, flexural, and impact tests as per ASTM standards. TEM and XRD characterization techniques are used in this study. It is observed that TiO2NTs greatly enhanced the tensile strength by 85%, elongation by 7%, flexural strength by 55%, and the impact strength by 8%. The mechanical properties of the epoxy nanocomposites indicate that TiO2NTs are efficient fillers to enhance the performance of epoxy composites. Keywords: TiO2 nanotubes, epoxy nanocomposites, mechanical properties, polymer nanocomposites INTRODUCTION High performance and cost-effective designs for structural components are the top criteria of aerospace, automobile, civil, and alternative energy industries. These critical requirements of industries have led engi- neers to give high priority to designing high strength materials with reduced weight. The need for lightweight and strong materials has paved the way for polymer composites to industries. Most advanced polymer com- posites are made of epoxy, a thermosetting resin, due to the epoxy resin’s outstanding characteristics like good adhesion to fiber reinforcements, compatibility with a variety of curing systems, better thermal, mechanical, electrical, and chemical properties [1-3]. The performance of epoxy-based composites is im- proved by dispersing second phase materials as fillers in epoxy resin systems. By using fillers at the nanoscale (10 –9 m), several enhancements in the composite prop- erties are observed, which are mainly due to the im- proved interface and result in an improved load trans- ferring ability. An effective method to fabricate advanced composites is the incorporation of nanofillers in the epoxy, combining the benefits of both the epoxy and the nanomaterials [4, 5]. Because of their excellent properties, TiO 2 nanofillers have encouraged research- ers to enhance the mechanical properties of epoxy nanocomposites [6]. As TiO 2 (3D) particles have a lim- ited surface area, 1D TiO 2 nanotube-like structures are drawing attention due to their increased surface area. In this work, ultrasmall TiO 2 nanotubes are synthesized by the hydrothermal process. Epoxy composites are then fabricated with the obtained TiO 2 nanotubes (TiO 2 NTs) (0.1 wt.%) and the reinforcing effects are investigated through tensile, flexural, and impact tests as per ASTM standards. MATERIALS AND METHODS Materials TiO 2 (> 99, Sigma Aldrich), NaOH (98%, Alfa Aesar), epoxy (Araldite LY 556, Huntsman Advanced Materials), and hardener (Aradur HY 951, Huntsman Advanced Materials). Synthesis of TiO2 nanotubes The synthesis of TiO 2 NTs was carried out hydro- thermally, which is a green synthesis route and it has several advantages of producing phase-pure nanostruc- tures in a one-step reaction that is cost-effective and reproducible [7]. In the typical synthesis, it starts with an aqueous solution of NaOH (7 M) and TiO 2 powder (500 mg) kept in a pressure vessel of a Teflon-lined stainless steel autoclave and placed in a 120ºC pre-