Upcycling Post-Consumer Paint Pail Plastic Waste

Abstract

The need for ending plastic waste and creating a circular economy has prompted significant interest in developing a new family of composite materials through recycling and recovery of waste resources (including bio-sourced materials). In this work, a family of natural fiber-reinforced plastic composites has been developed from paint pail waste recycled polypropylene (rPP) and waste wool fibers of different diameter and aspect ratio. Composites were fabricated by melt processing using polypropylene-graft-maleic anhydride as a compatibilizer. The internal morphology, interfacial and thermal characteristics, viscoelastic behavior, water sorption/wettability, and mechanical properties of composites were studied using electron microscopy, high-resolution synchrotron Fourier transform infrared microspectroscopy, thermal analysis, rheology, immersion test, contact angle measurement, tensile test and flexural test. The composite matrix exhibited an internal morphology of coalescent micro-droplets due to the presence of polyethylene and dry paint in the rPP phase. In general, the rheological and mechanical properties of the composites comprising higher-aspect-ratio (lower diameter) fibers exhibited relatively superior performance. About an 18% increase in tensile strength and a 39% increase in flexural strength were measured for composites with an optimal fiber loading of 10 wt.%. Interfacial debonding and fiber pull-out were observed as the main failure mechanism of the composites. The developed composites have potential for applications in automotive, decking, and building industries.

Keywords: composites; mechanical properties; melt processing; recycled polypropylene; rheology; thermal analysis; waste wool fiber.

Figure 1

A schematic of the composite fabrication process. The red arrows indicate the direction of mechanical movement of equipment (left—mixer; right—press) parts.

Figure 2

SEM images of wool fibers: (a) WF1, and (b) WF2. (c) ATR-FTIR spectra of wool fibers, and melt-mixed recycled polypropylene (rPP) sample.

Figure 3

SEM images of the fracture surface morphology of melt-mixed (a) rPP, and (b) rPP with 5 wt.% polypropylene-graft-maleic anhydride compatibilizer (rPP-C) samples.

Figure 4

TGA thermograms: (a) weight loss profile, and (b) derivative curve of as-received wool fibers and fabricated composites.

Figure 5

DSC thermograms: (a) heating and (b) cooling curves of fabricated composites.

Figure 6

Schematic of interaction mechanism of polypropylene-graft-maleic anhydride on wool fibers in fabricated composites.

Figure 7

Dynamic rheology measurements: (a) storage (straight line) and loss (broken line) modulus, and (b) complex viscosity as function of oscillation strain.

Figure 8

Contact angle measurement displaying water droplets on the surface of compression-molded samples: (a) rPP, (b) rPP-C, (c) rPP-C-10WF1, (d) rPP-C-20WF1, (e) rPP-C-10WF2, and (f) rPP-C-20WF2.

Figure 9

Mechanical property measurements: stress–strain curves of (a) tensile and (b) flexural test.

Figure 10

SEM images of the fracture surface of tensile-tested fabricated samples: (a) rPP-C-10WF1, (b) rPP-C-20WF1, (c) rPP-C-10WF2, and (d) rPP-C-20WF2.

Figure 11

Synchrotron macro-ATR-FTIR results. Panel 1 (rPP-C-10WF1): (a) microscopic image, (b) chemical map of amide I band characteristic of WF1 in composite with colored markers demarcating line arrays across interfacial regions, and (c) comparison of individual spectra extracted from selected locations as indicated in panel (b). Panel 2 (rPP-C-10WF2): (d) microscopic image, (e) chemical map of amide I band characteristic of WF2 in composite with colored markers demarcating line arrays across interfacial regions, and (f) comparison of individual spectra extracted from selected locations as indicated in panel (e).