Abstract
Characterization of Ceiba aesculifolia (CA) fibers by various techniques is herein reported. The seed pods were collected, and the fibers surrounding the seeds were characterized or treated in an oven at 100 °C prior to characterization by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis coupled with a differential scanning calorimeter (TGA-DSC). The SEM micrographs showed that the natural material is comprised of tubes of external diameter of approximately 27 μm and a mean wall thickness of about 0.62 μm. The results also indicated that the tubes begin to decompose at approximately 220 °C.
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Physicochemical Characterization of Natural Fibers Obtained from Seed Pods of Ceiba aesculifolia
Ulises Carranza-Nuñez,a Salomon Ramiro Vasquez-Garcia,a,* Nelly Flores-Ramirez,b Hamdy Ahmed Abdel-Gawwad,c José Luis Rico,a Arlette Arizbe Santiago,d Joel Vargas,e and José Cruz-de-León b
Characterization of Ceiba aesculifolia (CA) fibers by various techniques is herein reported. The seed pods were collected, and the fibers surrounding the seeds were characterized or treated in an oven at 100 °C prior to characterization by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis coupled with a differential scanning calorimeter (TGA-DSC). The SEM micrographs showed that the natural material is comprised of tubes of external diameter of approximately 27 μm and a mean wall thickness of about 0.62 μm. The results also indicated that the tubes begin to decompose at approximately 220 °C.
Keywords: Ceiba aesculifolia; SEM; FTIR; DRX; TGA-DSC
Contact information: a: Department of Chemical Engineering, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, 58030, México; b: Department of Wood Engineering and Technology, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, 58030, México; c: Raw Building Materials Technology and Processing Research Institute, Housing and Building National Research Center (HBRC), Cairo, Egypt; d: Escuela Nacional de Estudios Superiores, Unidad Morelia, Universidad Nacional Autónoma de México, Morelia, 58190, México; e: 4 Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Morelia, 58190, México; *Corresponding author: salomon_vg@yahoo.com
INTRODUCTION
Natural fibers obtained from plants and animals are used in many applications. In nature, vegetal fibers commonly contribute to the stability of the plant, or they can serve as a protection in the case of animal fibers. The world natural fiber production was approximately 33 million tons in 2013. Among this 78.8% was cotton linter, 10% of jute, 3.6% of clean wool, 2.7% of coir, and 4.8% of other fibers such as hemp, kapok, abaca, flax, silk, ramie, and sisal (Townsend and Sette 2016). This information clearly shows the importance of vegetal fibers. These fibers may present interesting properties, for instance, high tensile and low bending and torsional rigidities. In addition, vegetal fibers with low density, are unexpansive, biodegradable, non-toxic, and easy to handle (Wambua et al. 2003; Cheung et al. 2009; Dittenber and GangaRao 2012). Due to these properties, vegetal fibers are used in many applications including housing, clothing, and packing. One recent and growing application of vegetal fibers is in the production of composites, for instance as a reinforcement of synthetic polymeric materials (Wambua et al. 2003; Cheung et al. 2009; Zakikhani et al. 2014; Djafari Petroudy 2017). Synthetic fibers present excellent mechanical properties that can be tuned according to the final application. However, these materials frequently possess ecological problems during disposal, due to their high stability under atmospheric and environmental conditions. Characterization of several vegetal fibers has been reported in the last decades (Zeriahene et al. 1998; Fiore et al. 2014; Reddy et al. 2014; Belouadah et al. 2015; Porras et al. 2015; Mohamad et al. 2017), in addition to the well-documented cotton. Ceiba aesculifolia (CA) is a neotropical species that belongs to the Mavales order, and to the Bombacaceae family; it is distributed from Mexico to Costa Rica (Cascante-Marín 1997; Herrerías-Diego et al. 2008). This tree gives beautiful flowers and can reach 15 m high. The thin trunk is protected with strong thorns. The ellipsoid fruits have seed pods of about 15 cm long and 8 cm wide that keep the seeds covered with abundant soft and white fibers (Carranza-González and Blanco-García 2000; Avendaño et al. 2006). These fibers are commonly used to make pillows, and the bark, stem, and branches are used as firewood (Carranza-González and Blanco-García 2000). The number of pods that a Ceiba aesculifolia can produce every season vary according to the age of the tree and the environmental conditions. A tree can give tens or hundreds of pods. The relative abundance of this tree in our region, the basic usage of its constituents and the scarce publications related to this tree motivated the present research interest. Furthermore, the white fibers of this tree resemble those of cotton buds, and their characterization was performed for the first time in the present study. The results will undoubtedly set the basis to allow envisage new possible applications of these fibers.
EXPERIMENTAL
Fibers from Ceiba aesculifolia
Figure 1 shows an open brown CA pod, which contains a husk, fibers, and seeds. As can be observed, the fibers resemble those of the raw cotton. Their color is bright white and the texture is smooth.
Fig. 1. Ceiba aesculifolia pod (a) and white natural fibers around the seeds (b)
The bunches of fibers used in the present study were collected after drying 10 pods under shade for a couple of months. Separation of seeds, husk, and fibers was performed. From these pods, 4.3, 8.3, and 87.4 wt% were determined for fibers, seeds, and husks, respectively. The results are in the range of those reported by Velázquez-Rosas et al. (2017). The fibers were then collected and kept for further characterization. Some were directly characterized, labelled as natural fibers (NF), or were washed with deionized water prior to further characterization. The washed fibers were denoted as WF.
Characterization
The aim of washing the fibers with deionized water was to remove some extractives and alkali metals from this material (Benítez-Guerrero et al. 2014; Rocha et al. 2017; He et al. 2018). By treating the fibers under dissimilar procedures, differences in fiber features were expected. A scanning electron microscope (SEM) (JSM-7600F, JEOL Ltd., Tokyo, Japan) provided with an energy dispersive X-ray spectrometer (EDS) was used to find fiber morphology and composition. To determine the mean diameter and wall thickness, 20 fibers were observed under the microscope. The FTIR spectra of the previously ground fibers were acquired directly with no KBr. The equipment used for this purpose was a Perkin Elmer Spectrum 400 (Waltham, MA, USA) provided with an attenuated total reflectance (ATR) accessory. Data were acquired in 64 scans with a resolution of 4 cm-1 in the range of 650 to 4000 cm-1 with a germanium crystal. The thermal stability of the fibers was evaluated in a thermal gravimetric analyzer (TGA)-differential scanning calorimeter (DSC) device (STA 449 F3 Jupiter; Netzsch, Selb, Germany). In a typical experiment, 6 mg of natural fibers was collocated into an aluminum crucible and placed into the TGA chamber to be treated under nitrogen flow from ambient temperature to 600 ℃ at a heating rate of 5 ℃/min.
RESULTS AND DISCUSSION
Natural and washed Fibers
The following figure shows photographs of Ceiba aesculifolia.
Fig. 2. Photographs of Ceiba aesculifolia: tree (a), flower (b), and pods (c)
Figure 3 presents images of the NF and WF obtained by SEM. No apparent differences were observed. These figures show that the fibers present in the pods of this tree are indeed comprised of tubes of centimeters in length. A mean diameter of ca. 27 μm and a wall thickness of ca. 0.62 μm were calculated after analyzing various SEM images.
Fig. 3. SEM images of the natural tubes found in pods of the CA tree at two magnifications: 1000X (a) and 2000X (b)
FTIR
It is expected that the development of the fibers of the CA pods follows various stages, as those for cotton fibers. For the latter fibers, the overlapping stages are differentiation, initiation, polar elongation, secondary cell wall development, and maturation. The FTIR spectra for cotton wool at different periods were measured and showed that vibration positions shift slightly during biogenesis (Nelson and Mares 1965; Sathishkumar et al. 2013). Figure 4 shows the FTIR spectra of the NF and WF.
Fig. 4. FTIR spectra of the natural (a) and washed fibers (b)
The FTIR spectra show that fibers of the CA pods are typically composed of cellulosic material, such as those reported for cotton by Abidi et al. (2014) and for Lygeum spartum L. fibers reported by Belouadah et al. (2015). Both spectra in Fig. 4 look similar, suggesting that washing was unnecessary. However, other physical properties which were not measured, such as tensile strength and bending, might be changed by this treatment. The broad band with a maximum at 3340 cm-1 was attributed to -OH stretching vibrations resulting from hydrogen bonding in cellulose, whereas those at approximately 2918 and 2850 cm-1 that are overlapped, were assigned to -CH2 asymmetrical and symmetrical stretching, respectively (Nelson et al. 1965) and could result from the presence of wax substances on the surface of the primary cell wall (Abidi et al. 2008). The peaks at approximately 1736, 1640, and 1594 cm-1 are attributed to C=O stretching of lignin and hemicellulose (Sathishkumar et al. 2013), while that at approximately 1594 cm-1 is assigned to the C=C groups of lignin (De Rosa et al. 2011). The signal at 1236 cm-1 was attributed to -COO groups of cellulose (Reddy et al. 2014). The peak at 1033 cm-1 is attributed to the stretching mode of C-O of cellulose (Ilharco et al. 1997); the signal located at 1157 cm-1 is assigned to the stretching vibration of bridge C–O–C of cellulose and hemicellulose (De Rosa et al. 2011), whereas that at 1104 cm-1 is due to anti-symmetric in-plane ring stretching band (Ilharco et al. 1997). The vibration at 1236 cm-1 is attributed to C=O stretching or NH2 deformation (Nelson et al. 1965). The peak at approximately 895 cm−1 is assigned to the -linkage (Alonso-Simón et al. 2011). The vibration located at 710 cm-1 is attributed to CH2 rocking vibration in cellulose I (Akerholm et al. 2004), which is also characteristic of the cellulose in native cotton (Abidi et al. 2014).
Thermogravimetric Analysis
The thermal stability of the fibers obtained from the pods of the CA tree was evaluated using TGA-DTG equipment. The profile for WF was similar to that for NF and it is not shown. Figure 5 displays the thermogravimetric profile of NF.