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. 2023 Dec 13;15(24):4697.
doi: 10.3390/polym15244697.

Upcycling of HDPE Milk Bottles into High-Stiffness, High-HDT Composites with Pineapple Leaf Waste Materials

Taweechai Amornsakchai  1   2   3 , Sorn Duangsuwan  1
Affiliations

Upcycling of HDPE Milk Bottles into High-Stiffness, High-HDT Composites with Pineapple Leaf Waste Materials

Taweechai Amornsakchai et al. Polymers (Basel). .

Abstract

In the pursuit of sustainability and reduced dependence on new plastic materials, this study explores the upcycling potential of high-density polyethylene (HDPE) milk bottles into high-stiffness, high-heat-distortion-temperature (HDT) composites. Recycled high-density polyethylene (rHDPE) sourced from used milk bottles serves as the composite matrix, while reinforcing fillers are derived from dried pineapple leaves, comprising fibers (PALF) and non-fibrous materials (NFM). A two-roll mixer is employed to prepare rHDPE/NFM and rHDPE/PALF mixtures, facilitating filler alignment in the resulting prepreg. The prepreg is subsequently stacked and pressed into composite sheets. The introduction of PALF as a reinforcing filler significantly enhances the flexural strength and modulus of the rHDPE composite. A 20 wt.% PALF content yields a remarkable 162% increase in flexural strength and a 204% increase in modulus compared to neat rHDPE. The rHDPE/NFM composite also shows improved mechanical properties, albeit to a lesser degree than fiber reinforcement. Both composites exhibit a slight reduction in impact resistance. Notably, the addition of NFM or PALF substantially elevates HDT, raising the HDT values of the composites to approximately 84 °C and 108 °C, respectively, in contrast to the 71 °C HDT of neat rHDPE. Furthermore, the overall properties of both the composites are further enhanced by improving their compatibility through maleic anhydride-modified polyethylene (MAPE) use. Impact fracture surfaces of both composites reveal higher compatibility and clear alignment of NFM and PALF fillers, underscoring the enhanced performance and environmental friendliness of composites produced from recycled plastics reinforced with pineapple leaf waste fillers.

Keywords: HDPE milk bottle; high stiffness; natural fiber; pineapple leaf waste; upcycling.

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Conflict of interest statement

Author TA was employed by the company TEAnity Team Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.

Figures

Figure 1
Figure 1
HDPE milk bottles and rHDPE obtained after cutting, cleaning and drying.
Figure 2
Figure 2
Procedure for aligning NFM and PALF on a two-roll mill during the uniaxial composite prepreg preparation. The schematic on the right shows NFM and PALF alignment as represented by black lines and the machine direction represented with the arrow.
Figure 3
Figure 3
ATR-FTIR spectra of NFM and PALF.
Figure 4
Figure 4
SEM micrographs of different pineapple leaf waste materials: (a) NFM and (b) PALF.
Figure 5
Figure 5
Photographs of (a) rHDPE/NFM and (b) rHDPE/PALF composite prepregs. Images (c) and (d) depict magnified views of the regions of interest indicated by squares in images (a) and (b), respectively. The machine direction is vertical.
Figure 6
Figure 6
Three-dimensional X-ray computed tomography images of NFM (a) and PALF (b) composite sheets.
Figure 7
Figure 7
Representative flexural stress–strain curves of neat rHDPE and composite sheets containing different amounts of PALF, NFM, and adhesion promoter (MAPE). Closed symbols represent rHDPE/PALF composites, while the open symbols represent rHDPE/NFM composites.
Figure 8
Figure 8
Flexural strength and modulus of rHDPE composite sheets containing different types of reinforcement: (a) flexural strength and (b) flexural modulus at 1% strain. Gray bar represents neat rHDPE. Patterned bars indicate composites with MAPE.
Figure 9
Figure 9
Impact properties of rHDPE composite sheets containing different types of reinforcement. Gray bar represents neat rHDPE. Patterned bars indicate composites with MAPE.
Figure 10
Figure 10
DSC thermograms of the 1st heating (solid line) and 2nd heating (dash line) cycles of the (a) NFM and (b) PALF composites.
Figure 11
Figure 11
HDT of rHDPE composite sheets containing different types of reinforcement. Gray bar represents neat rHDPE. Patterned bars indicate composites with MAPE.
Figure 12
Figure 12
Impact fracture surfaces of rHDPE and composites containing different types of fillers at low (left column) and high (right column) magnifications. (a,b) neat rHDPE, (c,d) 20NFM, (e,f) 20NFM-MAPE, (g,h) 20PALF and (i,j) 20PALF-MAPE.
Figure 13
Figure 13
Predictions of apparent reinforcement modulus of PALF and NFM in rHDPE. Dotted line are linear fitted of the experimental results of PALF and NFM systems.
Figure 14
Figure 14
Bicycle mudguard made from rHDPE/PALF composite.
See this image and copyright information in PMC

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