Vol.:(0123456789) International Journal of Precision Engineering and Manufacturing-Green Technology https://doi.org/10.1007/s40684-019-00023-6 1 3 REGULAR PAPER 3D Printing of Ground Tire Rubber Composites Faez Alkadi 1  · Jeongwoo Lee 1  · Jun‑Seok Yeo 2  · Seok‑Ho Hwang 2  · Jae‑Won Choi 1 Received: 9 September 2017 / Revised: 20 November 2017 / Accepted: 12 January 2018 © Korean Society for Precision Engineering 2019 Abstract Recycled tire rubber is an environmentally and economically benefcial material. Ground tire rubber (GTR) as a fller in a polymer matrix was used as an ink material (composite material) for material extrusion in a 3D printing process. The maxi- mum allowable amount of GTR incorporated into the mixture without signifcantly altering the rheological behavior of the ink was set. Printability investigations revealed that pressure and speed show linear and power relationships, respectively, to the line width for three diferent amounts of GTR. Moreover, the post-curing time of 30 min at 115 °C was set as the full-cure condition to achieve polymerization of 80% or more for the 3D printed parts. Unidirectional tensile testing demonstrated that 3D printed specimens exhibit no degradation in tensile strength when compared to molded specimens. Moreover, print- ability and mechanical properties of functionalized GTR were investigated to determine if this material exhibits enhanced mechanical strength. Unidirectional tensile tests show that the maximum tensile strength for specimens with functionalized GTR was 20% higher than in specimens with non-functionalized GTR. In conclusion, 3D printing of GTR composites shows promise for using recycled GTR to create 3D structures with rubber-like properties. Keywords 3D printing · Recycled powder · Ground tire rubber · Direct-print · GTR surface modifcation List of symbols GTR Ground tire rubber PHR Part per hundred rubber DP Direct-print 1 Introduction Scrap (waste) tires have become a global environmental issue since they are fammable, non-biodegradable, and con- tain toxic substances. About 1.5 billion tires are produced every year around the world, and approximately 4 million tons of scrap tires were generated in the US alone in 2015 [1]. Therefore, much research has been conducted to fnd solutions for the problems related to scrap tires. The research in this area can be classifed into two major tracks: (1) how to deal with the scrap tires, and (2) recycling/reusing scrap tires and reclaiming raw materials from them [2–5]. As one method of recycling scrap tires, the production of ground tire rubber (GTR) has been considered due to its positive eco- logical and economic impacts. The manufacturing process for GTR is environmentally friendly that creates no pollu- tion; it is also economically benefcial, as it eliminates some of the processes needed to reclaim raw rubber. Moreover, the use of GTR as a fller in various raw materials can reduce the cost of manufactured goods [3, 6]. The amount of a fller in a matrix can be directly or inversely proportional to diferent mechanical properties of composite materials, such as tensile strength, compression strength, and abrasion resistance [7]. Moreover, the interac- tion of polymer molecules with the surface of fllers can Online ISSN 2198-0810 Print ISSN 2288-6206 * Jae-Won Choi jchoi1@uakron.edu Faez Alkadi faa23@zips.uakron.edu Jeongwoo Lee jl119@zips.uakron.edu Jun-Seok Yeo jsyeo@kitech.re.kr Seok-Ho Hwang bach@dankook.ac.kr 1 Department of Mechanical Engineering, The University of Akron, 244 Sumner St, Akron, OH 44325, USA 2 Department of Polymer Science and Engineering, Dankook University, Yongin, Gyeonggi 16890, Republic of Korea