Characteristics of Adhesion in 3D Printed Composites

Development of fused filament fabrication (FFF) printers has introduced the possibility of printing multiple plastics during a single print. In addition, new thermoplastic polymers are being introduced to filament printing. At this point, there has been very little research on the adhesion between these new materials and materials that have been used extensively for 3D prints.

Thermoplastic polyurethane (TPU) is a novel material that has recently been profiled to print through 3D printers. This plastic is classified as an elastomer, giving it characteristics to flex and bend. Using this plastic in combination with a hard plastic such as Acrylonitrile butadiene styrene (ABS) or Acrylonitrile Styrene Acrylate (ASA), composite parts can now be printed with soft-to-hard gradients. To understand the strength of adhesion between materials, ASTM D1002 lap shear tests were conducted, with ABS or ASA as the substrate (bar) and TPU acting as the adhesive (joint). These lap shear bars were printed using 3ntr’s A4v3 3D printer, a FFF printer introduced to the market as a mid-ranger price point printer with print qualities of higher priced industrial grade printers. The 3ntr printer has three extruder nozzles, giving the ability to print with multiple materials on the same print.

During the evaluation of lap shear experiments, it was discovered that the adhesion between plastics differs on the configuration of the print. It was found that TPU had better adhesion to the bottom substrate during print and delamination occurred strictly at the joint at the top substrate. The ultimate goals of the project are to determine the adhesion between TPU and the hard plastics and how the order the plastics are printed (TPU onto cool hard plastic or hot hard plastic onto cool TPU) effect the adhesion and mechanical properties.

Data on Bond Strength vs. plastic combination will be presented for plastics TPU, ABS, and ASA at print profile temperatures T_TPU = 218°C, T_ASA = 240°C, and T_ABS = 240°C. This bond strength is considered the minimum bond strength between plastics printed, as the ability to delaminate the TPU from the ABS or ASA is restricted to only one side. Thermal characterization of plastics will also be presented (Glass Transition Temperatures (T_g), Melt Temperatures (T_M) and Crystallization Temperatures (T_xtal)), as well as the viscosity (μ) of these plastics at temperatures within ±10°C of the print temperatures.