RESUMEN
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.
RESUMEN
Nowadays the use of natural fiber composites has gained significant interest due to their low density, high availability, and low cost. The present study explores the development of sustainable 3D printing filaments based on rice husk (RH), an agricultural residue, and recycled polypropylene (rPP) and the influence of fiber weight ratio on physical, thermal, mechanical, and morphological properties of 3D printing parts. Thermogravimetric analysis revealed that the composite's degradation process started earlier than for the neat rPP due to the lignocellulosic fiber components. Mechanical tests showed that tensile strength increased when using a raster angle of 0° than specimens printed at 90°, due to the weaker inter-layer bonding compared to in-layer. Furthermore, inter layer bonding tensile strength was similar for all tested materials. Scanning electron microscope (SEM) images revealed the limited interaction between the untreated fiber and matrix, which led to reduced tensile properties. However, during the printing process, composites presented lower warping than printed neat rPP. Thus, 3D printable ecofriendly natural fiber composite filaments with low density and low cost can be developed and used for 3D printing applications, contributing to reduce the impact of plastic and agricultural waste.
RESUMEN
Plant-based fibers are a potential alternative to synthetic polymer fibers that can yield enhanced biocompatibility and mechanical properties matching those properties of tissue. Given the unique morphology of the bract of the Manicaria saccifera palm, being an interwoven meshwork of fibers, we believe that these fibers with this built-in structure could prove useful as a tissue engineering scaffold material. Thus, we first investigated the fiber's in vitro biocompatibility and immunogenicity. We cultured NIH/3T3 mouse fibroblasts, human aortic smooth muscle cells, and human adipose-derived mesenchymal stem cells on the fiber mats, which all readily attached and over 21 days grew to engulf the fibers. Importantly, this was achieved without treating the plant tissue with extracellular matrix proteins or any adhesion ligands. In addition, we measured the gene expression and protein secretion of three target inflammatory cytokines (IL-1ß, IL-8, and TNFα) from THP-1 human leukemia monocytes cultured in the presence of the biotextile as an in vitro immunological model. After 24 h of culture, gene expression and protein secretion were largely the same as the control, demonstrating the low immunogenicity of Manicaria saccifera fibers. We also measured the tensile mechanical properties of the fibers. Individual fibers after processing had a Young's modulus of 9.51 ± 4.38 GPa and a tensile strength of 68.62 ± 27.93 MPa. We investigated the tensile mechanical properties of the fiber mats perpendicular to the fiber axis (transverse loading), which displayed upwards of 100% strain, but with a concession in strength compared to longitudinal loading. Collectively, our in vitro assessments point toward Manicaria saccifera as a highly biocompatible biotextile, with a range of potential clinical and engineering applications.