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. 2023 Dec 4;15(23):4614.
doi: 10.3390/polym15234614.

Assessment of Hydrothermal Treatment Effects on Coir Fibers for Incorporation into Polyurethane Matrix Biocomposites Derived from Castor Oil

Mayara de Oliveira Camillo  1 , Bárbara Maria Mateus Gonçalves  1 , Veronica Scarpini Candido  2 , Luciano Da Costa Dias  1 , Jordão Cabral Moulin  1 , Sergio Neves Monteiro  3 , Michel Picanço Oliveira  1
Affiliations

Assessment of Hydrothermal Treatment Effects on Coir Fibers for Incorporation into Polyurethane Matrix Biocomposites Derived from Castor Oil

Mayara de Oliveira Camillo et al. Polymers (Basel). .

Abstract

The incorporation of natural lignocellulosic fibers as reinforcements in polymer composites has witnessed significant growth due to their biodegradability, cost-effectiveness, and mechanical properties. This study aims to evaluate castor-oil-based polyurethane (COPU), incorporating different contents of coconut coir fibers, 5, 10, and 15 wt%. The investigation includes analysis of the physical, mechanical, and microstructural properties of these composites. Additionally, this study evaluates the influence of hydrothermal treatment on the fibers, conducted at 120 °C and 98 kPa for 30 min, on the biocomposites' properties. Both coir fibers (CFs) and hydrothermal-treated coir fibers (HTCFs) were subjected to comprehensive characterization, including lignocellulosic composition analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The biocomposites were subjected to water absorption analysis, bending tests, XRD, SEM, FTIR, and TGA. The results indicate that the 30 min hydrothermal treatment reduces the extractive content, enhancing the interfacial adhesion between the fiber and the matrix, as evidenced by SEM. Notably, the composite containing 5 wt% CF exhibits a reduced water absorption, approaching the level observed in pure COPU. The inclusion of 15 wt% HTCF results in a remarkable improvement in the composite's flexural strength (100%), elastic modulus (98%), and toughness (280%) compared to neat COPU. TGA highlights that incorporating CFs into the COPU matrix enhances the material's thermal stability, allowing it to withstand temperatures of up to 500 °C. These findings underscore the potential of CFs as a ductile, lightweight, and cost-effective reinforcement in COPU matrix biocomposites, particularly for engineering applications.

Keywords: PU; composites; lignocellulosic fibers; mechanical properties; natural coir fibers; polymeric.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Water absorption of biocomposites.
Figure 2
Figure 2
Percentage variation in CF and HTCF in the biocomposites vs. flexural properties: flexural strength (a); elastic modulus (b); total deflection (c); flexural toughness (d).
Figure 3
Figure 3
FTIR Spectra: (a) displays the FTIR spectra for the fibers and (b) presents the spectra for the biocomposites.
Figure 4
Figure 4
SEM Images of coir fibers: CF (a); HTCF (b).
Figure 5
Figure 5
SEM images of biocomposites: (a,b) depict the interfacial bond between the COPU matrix and CF fibers at magnifications of 100× and 200×, respectively. (c,d) illustrate the interfacial bond between the COPU matrix and HTCF fibers at magnifications of 100× and 200×. Arrows indicate interface details.
Figure 6
Figure 6
The interface between the COPU matrix and ECF was examined using SEM at magnifications of 500× (a) and 1000× (b). Arrows indicate connection points, emphasizing the continuity between the matrix and the fibers.
Figure 7
Figure 7
X-ray diffraction of coir fibers (a); X-ray diffraction of biocomposites (b).
Figure 8
Figure 8
Thermogravimetric analysis of fiber (a) and biocomposites (b); differential thermogravimetric of fiber (c) and biocomposites (d).
See this image and copyright information in PMC

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