Abstract
Natural filler-based composites are an environmentally friendly and potentially sustainable alternative to synthetic or plastic counterparts. Recycling polymers and using agro-industrial wastes are measures that help to achieve a circular economy. Thus, this work presents the development and characterization of a 3D printing filament based on recycled polypropylene and cocoa bean shells, which has not been explored yet. The obtained composites were thermally and physically characterized. In addition, the warping effect, mechanical, and morphological analyses were performed on 3D printed specimens. Thermal analysis exhibited decreased thermal stability when cacao bean shell (CBS) particles were added due to their lignocellulosic content. A reduction in both melting enthalpy and crystallinity percentage was identified. This is caused by the increase in the amorphous structures present in the hemicellulose and lignin of the CBS. Mechanical tests showed high dependence of the mechanical properties on the 3D printing raster angle. Tensile strength increased when a raster angle of 0° was used, compared to specimens printed at 90°, due to the load direction. Tensile strength and fracture strain were improved with CBS addition in specimens printed at 90°, and better bonding between adjacent layers was achieved. Electron microscope images identified particle fracture, filler-matrix debonding, and matrix breakage as the central failure mechanisms. These failure mechanisms are attributed to the poor interfacial bonding between the CBS particles and the matrix, which reduced the tensile properties of specimens printed at 0°. On the other hand, the printing process showed that cocoa bean shell particles reduced by 67% the characteristic warping effect of recycled polypropylene during 3D printing, which is advantageous for 3D printing applications of the rPP. Thereby, potential sustainable natural filler composite filaments for 3D printing applications with low density and low cost can be developed, adding value to agro-industrial and plastic wastes.
Highlights
This study presents the development and characterization of a 3D printing composite filament based on recycled polypropylene and cocoa bean shells
The second phase occurs between 230 ◦ C and 290 ◦ C with a weight loss of around 29%, which indicates the degradation of the hemicellulose and cellulose
Hemicellulose and lignin identified in the thermogravimetric analysis (TGA) analysis are amorphous
Summary
Global environmental issues have become noticeable, including increased energy consumption, shortage of petrochemical resources, greenhouse gas exhaustion, and accumulation of plastic waste [1,2]. These environmental concerns and economic factors have motivated researchers to investigate environmentally friendly materials with sustainability benefits [3,4,5], where one of the benefits is the potential to move towards a circular economy [6]. Pulp, and bean shell, representing about 80 wt.%
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