Enhanced Mechanical Properties of 3D-Printed Glass Fibre-Reinforced Polyethylene Composites

Abstract

Optimisation of the tensile strength of thermoplastic polymer-matrix composites remains a scientific as well as technological challenge for 3D printing technology due to the mass application of composite materials. Inadequate mechanical properties are due to the mismatch in the surface energies of the polymer and fillers. In this study, an additively manufactured composite was 3D-printed and tested. The composite consisted of a linear low-density polyethylene matrix filled with glass fibres. Composite filaments were extruded from neat and plasma-treated polymer powders. Plasma was sustained in oxygen at 100 Pa by a pulsed microwave discharge, and 250 g of polymer powder of average diameter 150 µm was placed into a dish and stirred during the plasma treatment. The O-atom density at the position of the dish containing polymer powder was about 2 × 10²¹ m^-3, and the treatment time was varied up to 30 min. A gradual improvement in the composites' tensile and flexural strength was observed at the plasma treatment time up to about 10 min, and the mechanical properties remained unchanged with prolonged treatment time. The tensile strength of composites prepared from plasma-treated polymer increased by one-third compared to those based on untreated powder. However, reinforcing the modified polyethylene with plasma-treated glass fibres did not result in further significant mechanical improvement compared to untreated fibres. In contrast, strength values doubled using glass fibres with silane sizing in combination with plasma-modified matrix. The results were explained by the increased surface energy of the polymer powder due to functionalisation with polar functional groups during plasma treatment.

Keywords: 3D print; adhesion; plasma modification; polyethylene.

Figure 1

Material flow of prepared composite specimens.

Figure 2

The inside view of the LA 400 reactor chamber for plasma modification.

Figure 3

XPS survey spectra for an untreated PE and modified powders (a) and high-resolution C1s spectra for an untreated PE (b); 5 min treated (c); 10 min treated (d); and 30 min treated PE powder (e).

Figure 4

DSC curves of untreated PE (a) and plasma-treated tPE (b).

Figure 5

SEM micrograph of tPE-GF30 filament.

Figure 6

Stress-strain curves of filaments containing unmodified PE and plasma-treated tPE with different concentrations of GF.

Figure 7

The tensile strength and the elongation at break of tPE-GF30 samples versus the nozzle temperature at a constant printing speed of 60 mm∙s⁻¹ (a), and versus the printing speed at the constant nozzle temperature of 240 °C (b).

Figure 8

Surface quality of 3D-printed tPE-GF30 samples using insufficient nozzle temperature (a); optimal printing parameters (b); high printing speed (c).

Figure 9

Tensile strength (a) and flexural strength (b) dependence on the amount of GF and the use of matrix plasma treatment in a composite print.

Figure 10

Tensile strength of printed tPE-GF30 composites versus treatment time of used polyethylene powder.

Figure 11

SEM images of printed composites with matrix from untreated PE (a–c) and plasma-modified tPE (d–f).

Figure 12

Strength values of composites from untreated (PE) and plasma modified polyethylene (tPE) filled by 30 wt.% glass fibres without any modification (GF), plasma treated (tGF) and silane coated (sGF).

Figure 13

Interaction between unmodified polyethylene (a) or plasma-treated polyethylene (b) and glass surface in a composite system.