Additive Manufacturing of Liquid Rubber for Tire Applications

As countless vehicles on the road run ceaselessly around the world, scrap tires are regarded as environmental pollution^[1]. The need for sustainable and reusable tires are evident and thus recycling and reusing tires have become of interest for many researchers^[2,3,4]. The abrasion of tread is a decisive factor in the consumption of tires that is closely related to the safety of vehicles. The recovery of destroyed tires by wear not only can reduce the consumption of tires, but also may extend their lifespan. Additive manufacturing (AM) for tire tread provides the advantage of applying a new design tread easily and can be used for partial recovery from worn treads. Recently, liquid rubber materials have been attempted to be 3D-printed. Currently, a filament type of thermoplastic polymers has been commonly used but the printing technique using pre-polymers can be also fully polymerized through a post-treatment process, meaning that more types of a material can be used for 3D printing.

In this work, a liquid rubber was 3D printed on a surface through a DPP (direct-print photopolymerization) system^[5]. This includes an air pressure-driven extruder moving on a horizontal plane, enabled by an XYZ-stage. A viscous pre-polymer was used as a main matrix and it is polymerized through a post-heating treatment. The matrix has a shear-thinning property so it can retain the filament shape after dispensing. Isoprene rubber and butadiene rubber (Kuraray, Japan) were used as viscous pre-polymers which are the same kinds of polymer used in an actual tire. Liquid rubbers have a molecular weight of 30,000 and 5,500, respectively, having acrylic groups which can be crosslinked through the post-treatment process. In order to have higher viscosity and retain their shapes after printed, carbon black and fumed silica were used as reinforcement to make them appropriate for the printing process. Sulfur was added as a cross-linking agent for vulcanization. Finally, printed parts were fully polymerized through the post-baking process for vulcanization in an oven for 20 min at 140 °C.  

In summary, we fabricated a 3-dimensional structure with a synthetic rubber using an additive manufacturing process which can be applicable for 3D printing of various types of oligomers. The work presented in this study is believed to enhance the mechanical properties similar to actual tire treads. This can be partially printed on the surface of the wormed tire tread using conformal printing^[6], resulting in extending the lifespan of tire tread.

[1] Alkadi, Faez, Lee, Jeongwoo, Yeo, J.S, Hwang, S.H, Choi, J.W., 2019, “3D printing of ground tire rubber composites,” Int. J. of Precis. Eng. and Manuf.-Green Tech, Vol. 6, pp. 211 (12 pages)

[2] Coiai, Serena, Passaglia, Elisa, Ciardelli, Francesco, 2006, “Gradient density grafted polymers on ground tire ruvver paticles by atom transfer radical polymerization,” Macromolecular Chemistry and Physics, Vol.207, pp. 2289 (10 pages)

[3] Naskar, A.K., Bhowmick, A.K., De, S.K., 2004, “Thermoplastic elastomeric composition based on ground rubber tire,” Polymer Engineeing & Science, Vol. 41, pp. 2035 (12 pages)

[4] Luo, T., Isayev, A.I., 1998, “Rubber/plastic blends based on devulcanized ground tire rubber,” Journal of Elastomers & Plastics, Vol. 30, pp. 133 (28 pages)

[5] Vatani, Morteza, Choi, J.W., 2017, “Direct-print photopolymerization for 3D printing,” Rapid Prototyping Journal, Vol. 23, pp. 337 (7 pages)

[6] Alkadi, Faez, Lee, K.C., Bashiri, Abdullateef H, Choi, J.W., 2020, “Conformal additive manufacturing using a direct-print process,” Additive Manufacturing, Vol. 32, pp. 100975