Embedding Ultra-High-Molecular-Weight Polyethylene Fibers in 3D-Printed Polylactic Acid (PLA) Parts

Abstract

This study aims to assess whether ultra-high-molecular-weight polyethylene (UHMWPE) fibers can be successfully embedded in a polylactic acid (PLA) matrix in a material extrusion 3D printing (ME3DP) process, despite the apparent thermal incompatibility between the two materials. The work started with assessing the maximum PLA extrusion temperatures at which UHMWPE fibers withstand the 3D printing process without melting or severe degradation. After testing various fiber orientations and extrusion temperatures, it has been found that the maximum extrusion temperature depends on fiber orientation relative to extrusion pathing and varies between 175 °C and 185 °C at an ambient temperature of 25 °C. Multiple specimens with embedded strands of UHMWPE fibers have been 3D printed and following tensile strength tests on the fabricated specimens, it has been found that adding even a small number of fiber strands laid in the same direction as the load increased tensile strength by 12% to 23% depending on the raster angle, even when taking into account the decrease in tensile strength due to reduced performance of the PLA substrate caused by lower extrusion temperatures.

Keywords: Dyneema; UHMWPE; additive manufacturing; fiber reinforced.

Figure 1

Material extrusion 3D printing: (a) Process schematic—the extruder and the build platform move relative to one another in the XY plane in order to deposit a horizontal layer and in the Z direction in order to position for the next layer; (b) horizontal layer elements.

Figure 2

3D printing of an acrylonitrile butadiene styrene and polycarbonate (ABS+PC) thermoplastic material part viewed through a ThermaCAM SC640 (FLIR Systems, Wilsonville, OR, USA) thermographic camera on a Zortrax M200 (Zortrax, Olsztyn, Poland) machine: (a) Isometric view; (b) side view.

Figure 3

Break pattern of unfilled polylactic acid (PLA) specimens: (a) Specimen printed at 170 °C with 45°/−45° raster; (b) specimen printed at 220 °C with 45°/−45° raster.

Figure 4

Tensile testing results of unfilled PLA specimens: (a) Specimens printed at 170 °C showing an average tensile strength of 40.05 MPa and an average Young’s modulus of 2902 MPa when printed with 0° raster, and a tensile strength of 35.34 MPa and an average Young’s modulus of 2898 MPa for the 45°/−45° raster; (b) specimens printed at 220 °C showing an average tensile strength of 44.01 MPa and an average Young’s modulus of 3081 MPa when printed with 0° raster, and a tensile strength of 38.06 MPa and an average Young’s modulus of 2848 MPa for the 45°/−45° raster; (c) average tensile strength for unfilled specimens—bars on top of columns represent standard deviation.

Figure 5

Ultra-high-molecular-weight polyethylene (UHMWPE) fiber layout: (a) Fiber direction relative to extrusion pathing; (b) void formation in the case of transversal extrusion pathing at a 45° angle; (c) specimen rupture for 0° raster; (d) specimen rupture for 45°/−45° raster.

Figure 6

Tensile testing results of PLA specimens filled with unidirectional UHMWPE fibers: (a) Specimens printed with a 45°/−45° raster angle showing an average tensile strength of 46.72 MPa and an average Young’s modulus of 3151 MPa; (b) specimens printed with a 0° raster angle, showing an average tensile strength of 49.19 MPa and an average Young’s modulus of 3036 MPa; (c) average tensile strength for fiber specimens compared to unfilled samples; the bars represent standard deviations; (d) void content of test specimens—red square marker represents the average of three 45° samples, rhombic marker represents the average of three 0° raster samples, while round markers represent individual samples. Eight fibers per layer correspond to 2% by weight fiber.

Figure 7

Differential scanning calorimetry (DSC) thermogram (second heating cycle) showing thermal transitions of neat PLA, PLA/1wt% UHMWPE, and PLA/2wt% UHMPWE.