Structural and Mechanical Properties of Recycled HDPE with Milled GFRP as a Filler

Abstract

The increasing complexity and production volume of glass-fiber-reinforced polymers (GFRP) present significant recycling challenges. This paper explores a potential use for mechanically recycled GFRP by blending it with high-density polyethylene (HDPE). This composite could be applied in products such as terrace boards, pipes, or fence posts, or as a substitute filler for wood flour and chalk. Recycled GFRP from post-consumer bus bumpers were ground and then combined with recycled HDPE in a twin-screw extruder at concentrations of 10, 20, 30, and 40 wt%. The study examined the mechanical and structural properties of the resulting composites, including the effects of aging and re-extrusion. The modulus of elasticity increased from 0.878 GPa for pure rHDPE to 1.806 GPa for composites with 40 wt% recycled GFRP, while the tensile strength ranged from 36.5 MPa to 28.7 MPa. Additionally, the porosity increased linearly from 2.65% to 7.44% for composites with 10 wt% and 40 wt% recycled GFRP, respectively. Aging and re-extrusion improved the mechanical properties, with the tensile strength of the 40 wt% GFRP composite reaching 34.1 MPa, attributed to a reduction in porosity by nearly half, reaching 3.43%.

Keywords: glass fibers; high-density polyethylene; mechanical properties; microstructure; recycling.

Figure 1

Tested material preparation process: (a) pellets of rHDPE; (b) bus bumpers waste; (c) rGFRP after grinding; (d) composite pellets 60% rHDPE + 40% rGFRP; (e) dog-bone shaped specimen for mechanical tests; and (f) rGFRP scraps at higher resolution.

Figure 2

Scheme of material preparation.

Figure 3

FTIR spectrum of (a) rHDPE; (b) resin from rGFRP waste; and (c) white paint from rGFRP waste.

Figure 4

Microstructure observations: (a) image of cross-section of rGFRC material before milling; (b) image taken by Keyence VHX-1000 microscope of surface of the rHDPE pellets; (c) example of image of filler contamination analysis of rHDPE/rGFRC 40% sample; (d) example of image with fiber glass contamination analysis of rHDPE/rGFRC 40% sample; (e) surface of cross-section of rHDPE/rGFRC 40% sample; and (f) outer layer of rHDPE material with dimension.

Figure 5

Results of CT for composites of rHDPE containing (a) 10 wt%; (b) 20 wt%; (c) 30 wt%; and (d) 40 wt % of rGFRP.

Figure 6

Images of rHDPE/rGFRP material: (a) cross-section; and (b) surface of the sample.

Figure 7

Images of rHDPE/rGFRC material: (a) macro view on the image; and (b–d) close-up of selected area—brighter areas are elements with higher mass number.

Figure 8

Behavior of rHDPE/rGFRP composites during (a) second heating, and (b) cooling, obtained by DSC analysis.

Figure 9

Engineering stress–strain curves for tensile test samples: (a) with varying percentages of rGFRP; and (b) with 40 wt% rGFRP after additional processes.

Figure 10

Comparison of (a) modulus of elasticity; (b) yield strength; (c) tensile strength; and (d) strain for tensile strength analyzed for all studied composites.

Figure 11

Results of CT for composites of rHDPE containing 40 wt% rGFRP after (a) additional extrusion; (b) aging; (c) and extrusion and aging. Measured region: 1 mm × 1 mm × 1 mm region, with resolution 20.90 m.