(DATE PALM)

Technical Field

The present disclosure relates to preparations of high-performance fibers and, more particularly, to a method of preparing the high-performance fibers from natural fiber sources.

Background Art

The need for renewable fiber reinforced composites has never been as prevalent as it currently is. Due to many advantages of using natural resources, natural fibers have been used recently as a method of providing added strength and ductility to reinforced polymer composites. This is because of their availability, renewability, low density, cost effectiveness as well as their satisfactory mechanical properties, which makes them an attractive ecological alternative to glass, carbon and man-made fibers used for the manufacturing of bio-composites. Recently, natural fillers are gaining attention as potential fillers in bio-composite production, because of their cost effectiveness, worldwide environmental concerns and strict standards. In particular, environmental laws and eco- sustainable technologies have triggered competitive research interest in facilitating the natural fillers as reinforcement materials for plastic polymers used in a broad range of industrial applications, such as decking, flooring, doors, interior parts of cars, and indoor furniture.

Using renewable materials, like date palm agro-waste, for manufacturing bio-composites can contribute to reduce the shortage of raw materials for Wood Plastic Composites (WPC) industry as well as diminishing environmental problems regarding the residues disposal. The leaves, rachis, and pedicels of date palm trees are used in making ropes, baskets, and mats in many parts of the world. However, the bulk of the material is discarded as waste which is either used as landfill or burned.

Some research has been undertaken to study various properties of date palm leaves, mesh and rachis for their potential use in bio-composites. However, use of pedicel as a natural source to produce fibers that can be used as a reinforcement in industrial products is not known. Summary of Invention

In one aspect of the present disclosure, a method of preparing high-performance fibers from a natural fiber source is provided. The method includes separating raw fibers from the natural fiber source. The method further includes dewaxing the separated raw fibers with an alcoholic solution of ethanol and water for a predetermined time at a first predetermined temperature. The alcoholic solution includes a 1:1 amount of ethanol and water, and the predetermined time is about 30 minutes to about 5 hours. The method further includes sterilizing the dewaxed fibers with an acidified salt solution, such as acidified sodium chloride, at a second predetermined temperature. The acidified salt solution includes 30% acetic acid and 5 wt.% sodium chloride, and the second predetermined temperature is in a range of about 100°C to about 115°C. The method also includes alkalizing the sterilized fibers with an alkali solution at a third predetermined temperature to generate the high- performance fibers. The third predetermined temperature is in a range of about 60 °C to about 100 °C.

In various embodiments, the method further includes heating the separated raw fibers in a microwave at about 450W power and at a temperature range of about 72°C to about 76°C. The method further includes sterilizing the dewaxed fibers for about 15 minutes in a microwave at about 450W power and at a temperature range of about 100°C to about 115°C. The method also includes alkalizing the sterilized fibers using 5 wt.% sodium hydroxide for about 20 minutes in a microwave at about 250W power and at a temperature range of about 70 °C to about 100 °C.

In some embodiments, the high-performance fibers have a crystallinity of about 50% to about 70%, a tensile strength of about 255 MPa to about 517 MPa, an elongation at break of about 1% to about 3.75%, and a cross-sectional area of about 0.033 mm ² to about 0.046 mm ² .

Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of Drawings

FIG. 1 is a flowchart for a method of preparing high-performance fibers from a natural fiber source; FIG. 2 is a graph comparing transmittance of dewaxed fibers at a predetermined time across various wavelengths;

FIG. 3 is a graph comparing transmittance of untreated fibers, fibers dewaxed through heat- assisted process, and fibers dewaxed through microwave assisted process;

FIG. 4 is a graph showing results of an X-ray diffraction study of the treated fibers;

FIG. 5 shows electron microscopic images of the untreated fibers and the treated fibers;

FIG. 6 is a graph comparing tensile strengths of the untreated fibers, fibers treated through heat-assisted process, and fibers treated through microwave assisted process;

FIG. 7 is a graph comparing stiffness of untreated fibers, fibers treated through heat-assisted process, and fibers treated through microwave assisted process;

FIG. 8 is a graph comparing fracture strains of untreated fibers, fibers treated through heat- assisted process, and fibers treated through microwave assisted process;

FIG. 9 is a graph comparing cross-sectional areas of untreated fibers, fibers treated through heat-assisted process, and fibers treated through microwave assisted process; and

FIG. 10 is a graph comparing moisture absorption ability of untreated fibers, fibers treated through heat-assisted process, and fibers treated through microwave assisted process.

Description of Embodiments

Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. Moreover, references to various elements described herein, are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice-versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claim.

The present disclosure relates to a novel process for preparing high-performance fibers from natural fiber sources using microwave and heat-assisted multistep chemical treatment. The objective of the multistep chemical treatment process is to improve characteristics and microstructure of natural fiber. The fibers resulting from the multistep chemical treatment process can be considered as a stand-alone material and can be used as reinforcement for different types of plastics because of their cost-effectiveness, hygienic, ecological, biodegradable, and sustainable properties.

FIG. 1 illustrates a flowchart for a method 100 of preparing high-performance fibers from a natural fiber source. In one embodiment, the natural fiber source may be a date palm. The method 100, at step 110, includes separating raw fibers from the natural fiber source. More specifically, at step 110, pedicels are extracted from the date palm trees. To extract the raw pedicels, date palm pedicels are collected and are trimmed to separate pedicel branches. Subsequently, to dismantle fiber bundles from pulp of the pedicels, water retting process is followed in which the pedicels are soaked in water for one week, after scrapping date palm bark manually. With this process, the fibers can be extracted manually from the date palm pedicles. In another embodiment, the raw fibers may be extracted from soaked pedicles with the aid of a mechanical decorticator, which helps to maintain fiber quality and integrity. Further, the extracted fibers are kept in plastic bags to reduce moisture absorption from surroundings. The phrase‘raw fibers’ is alternatively referred to as‘untreated fibers’ in this description.

Prior to the multistep chemical treatment process, the extracted fibers are washed with water to remove impurities sticking on surface and the washed fibers are dried in a vacuum oven at lOO C for 24 hours. Later, the dried fibers are chopped using a blender. By doing so, the fibers are considered ready for the multistep chemical treatment process.

The multistep chemical treatment process can be processed either through accelerated heating via a microwave (M.W) assisted process (represented by numeral 120 in FIG. 1) or through a heat-assisted process, which includes boiling (represented by numeral 130 in FIG. 1).

The method 100, at step 140, includes dewaxing the separated raw fibers with an alcoholic solution of ethanol and water for a predetermined time and at a first predetermined temperature. In one embodiment, the predetermined time is about 30 minutes to about 5 hours. In an example, Soxhlet apparatus may be used for dewaxing the raw fibers. The alcoholic solution includes 1:1 amount of ethanol and water. In one example, the water used for preparing the alcoholic solution may be deionized (D.I) water. In one embodiment, dewaxing can be achieved by heating the separated raw fibers in a microwave at about 450W power and at a temperature range of about 72 C to about 76 C. The first predetermined temperature may be any temperature within the temperature range of about 72 C to about 76 C. In an example, the first predetermined temperature may be 75 C. The microwave power is set at desired range for effective power, to enhance the wax, gum, and impurities removal, and to prevent fiber structure damage. In another embodiment, the separated raw fibers may be treated with an alcoholic solution of toluene, ethanol and water in a ratio of 1 : 1 : 1 for the predetermined time and at the first predetermined temperature.

The dewaxed sample is collected every 15 minutes to observe the dewaxing results using Fourier-transform infrared spectroscopy (FT-IR). Referring to FIG. 2, a graph 200 is illustrated to compare transmittance of dewaxed fibers at various wavelengths at every 15 minutes. It can be seen from the graph 200, that highest transmittance percentage is achieved at 60 minutes. As used herein, the term‘transmittance’ refers to ratio of amount of light incident on the fiber to amount of light transmitted through the fiber. As such, the transmittance percentage can also indicate degree of dewaxing in the fiber. Based on the findings in FIG. 2, microwave assisted dewaxing is obtained after 60 minutes as the wax and impurities peak vanish in the untreated spectra at about 1750 cm ¹ . While the heat-assisted dewaxing requires subjecting the fiber to boiling temperature for at least 3 hours, that is only limited on the surface, the microwave-assisted fiber dewaxing can be achieved in 1 hour, including outer dewaxing, inner dewaxing, and cleaning dewaxing.

Further, referring to FIG. 3, a graph 300 is illustrated to compare the transmittance of raw fibers, otherwise known as untreated fibers (shown as UT), fibers dewaxed through heat- assisted process (shown as HA), and fibers dewaxed through microwave assisted process (shown as MA). As shown in the graph 300, the fibers subjected to dewaxing through microwave assisted heating are associated with transmittance greater than that of the fibers subjected to dewaxing through heat-assisted process and untreated fibers.

Referring to FIG. 1, at step 150, the method 100 further includes sterilizing the dewaxed fibers with an acidified salt solution at a second predetermined temperature. In an example, the sterilization may be performed in the Soxhlet apparatus. In one embodiment, the acidified salt solution includes 30 % acetic acid and 5 wt.% sodium chloride. The acidified salt solution is also referred to as the acidified sodium chloride in this description. However, a skilled artisan will appreciate that the acidified salt solution can be a mixture of any other acid and salt, where the mixture is capable of sterilizing the dewaxed fibers. In one embodiment, the second predetermined temperature is in a range of about lOO C to about 115 C. The sterilization may be performed for about 15 minutes in the microwave at about 450W power and at the temperature range of about 100 C to about 115 C. In an example, the second predetermined temperature may be 105 C.

The sterilized fibers are soaked in distilled water for a week in order to observe the change in water’s color. The desired time is then determined using washing the fiber several times at different settings. Fiber purification can be achieved by setting the microwave power and the second predetermined temperature to 450 W and 105 ± 5°C, respectively, for 15 min. Microwave assisted sterilization may be performed for about 15 minutes, while the heat- assisted sterilization may require subjecting the dewaxed fiber to boiling temperature of about 115°C for at least 2 hours.

Referring to FIG. 1, at step 160, the method 100 includes alkalizing the sterilized fibers with an alkali solution at a third predetermined temperature to generate the high-performance fibers. The third predetermined temperature is in a range of about 60 C to about 100 C. In one embodiment, the sterilized fibers are subjected to alkalization using 5 wt.% sodium hydroxide for about 20 minutes in the microwave at about 250W power and at a temperature range of about 70 C to about lOO C. In an example, the third predetermined temperature may be 80 C. Microwave assisted alkalization may be performed for about 20 minutes, while the heat-assisted alkalization may require subjecting the sterilized fiber to boiling temperature of about 100°C for about 20 minutes to 45 minutes.

The microwave assisted alkalization can enhance the non-cellulosic (amorphous) extraction from the bio-fiber composition especially, lignin A and B, and hemicellulose. However, the extraction is controlled to prevent the fiber structure from damage. The disclosed method 100 allows the fiber strength, flexibility, processability and compatibility to be preserved. Moreover, the advantage of using microwave is that the process becomes less expensive, safe, and efficient for desired fiber modification. The experimental data and crystallinity degree are shown in Table 1.

Table 1: Values of the process parameter for maximum, minimum, and in-range levels along with % crystallinity

In one embodiment, to investigate crystallinity percentage of both untreated and treated fibers, chipped samples may be analyzed at ambient temperature by step scanning on an X- ray powder diffractometer. In an example, the measurements may be carried out at 40 kV and 20 mA with a detector placed on a goniometer scanning the range from 5° to 60°, at a scan speed of 2° min ¹ using monochromatic CuKa radiation (l = 1.5406 nm). A peak fitting method may be used to analyze the spectrogram and determine whether the fitting was completed with the assistance of, for example, OriginPro 2016 software. The crystalline degree of the materials may then be calculated from the area of crystalline and non crystalline peaks. The percentage of crystallinity (Cr %) of both raw and alkali treated fibers can be calculated by using the following equation:

Cr (%) = ^(I ° ^02~Iam) x 100%

1(302

where, I002 represents maximum intensity of 002 lattice reflection of the crystallographic form of cellulose (I) at 2Q = 21-23°; and I _am represents the maximum intensity of the amorphous part at 2Q = 17 - 19°. A graph 400 showing results of a study when the fibers are subjected to the X-ray diffractogram can be seen in FIG. 4, which shows the variation of 2Q against arbitrary intensity units.

Based on the variations, three different process factors and levels are determined, which are experimentally and statistically analyzed and attenuated in order to produce the best fiber crystalline structure. The dewaxed and acetylated fibers are placed in a 250-mL alkali solution. The third predetermined temperature is kept constant throughout the runs at 75+5 °C, which is determined based on trial runs to keep the solution at boiling condition. A statistical approach using Design of Experiment (DoE) and Response Surface Methodology (RSM) contributed in investigating the response over the target factor design range. It is also possible to locate the region of interest with the desired response.

FIG. 5 illustrates electron microscopic images 500 of untreated and treated fibers obtained through heating, dewaxing, and alkalization steps of the method 100. As shown in FIG. 5, an advantage of the microwave assisted accelerated heating is that it provides better surface treatment of the fibers as compared to the heat-assisted process 130.

Referring to FIG. 6, a graph 600 comparing tensile strengths of untreated fibers, fibers treated through heat-assisted process 130, and fibers treated through microwave assisted process 120 is illustrated. Tensile tests are carried out according to ASTM-D 638 using a universal testing machine with a 1 kN load cell at a constant speed rate of 1 mm/s to evaluate the tensile properties of the fibers. A 30mm gauge length extensometer is attached to the samples during tensile test to record the tensile strength data, at least 8 samples of each category are evaluated. From the results shown in Table 2 below, and from FIG. 6, it can be observed that the fibers treated through microwave assisted accelerated heating exhibit greater tensile strength compared to that of the untreated fibers and fibers treated through heat-assisted process 130.

Table 2: Comparison of tensile strengths of untreated fibers, fibers treated through heat- assisted process, and fibers treated through microwave assisted process Referring to FIG. 7, a graph 700 comparing stiffness of untreated fibers, fibers treated through heat-assisted process 130, and fibers treated through microwave assisted process 120 is illustrated. From tables 3 - 6 below and from the graph 700, it can be observed that the fibers treated through microwave assisted accelerated heating exhibit greater stiffness compared to that of the untreated fibers and the fibers treated through the heat-assisted process 130.

Referring to FIG. 8, a graph 800 comparing fracture strains of untreated fibers, fibers treated through heat-assisted process 130, and fibers treated through microwave assisted process 120 is illustrated. From tables 3 - 6 below and from the graph 800, it can be observed that that the fibers treated through microwave assisted accelerated heating can include fracture strains values, or elongation at break (%), between such values for untreated fibers and the fibers treated through heat-assisted process 130.

Referring to FIG. 9, a graph 900 comparing cross-sectional areas of untreated fibers, fibers treated through heat-assisted process 130, and fibers treated through microwave assisted process 120 is illustrated. The measurement of fiber cross-sectional area allows for the tensile properties evaluation and the dewaxing effect observations. The cross-sectional measurement of the date palm fiber was obtained using (VHX-5000 series KEYENCE, USA) at magnification power of 300-1000x optical microscope. From Tables 3 - 6 below and from the graph 900, it can be observed that that cross-sectional area of fibers treated through microwave assisted accelerated heating is less than the cross-sectional areas of untreated fibers and fibers treated through heat-assisted process 130.

Table 4: Mechanical properties of fibers treated through heat-assisted process.

Table 5: Mechanical properties of fibers treated through microwave assisted process.

Table 6: Comparison of stiffness, fracture strain, and cross-sectional area of untreated fibers, fibers treated through heat-assisted process, and fibers treated through microwave assisted process In an embodiment, the high-performance fibers include a crystallinity of about 50% to about 70%, a tensile strength of about 255 MPa to about 517 MPa, an elongation at break of about 1% to about 3.75%, and a cross-sectional area of about 0.033 mm ² to about 0.046 mm ² .

Referring to FIG. 10, a graph 1000 comparing moisture absorption ability of untreated fibers, fibers treated through heat-assisted process 130, and fibers treated through microwave assisted process 120 is illustrated. It can be observed from the graph that the fibers treated through microwave assisted accelerated heating exhibit low moisture absorption ability as compared to the untreated fibers and fibers treated through heat-assisted process 130.

Although the present disclosure is described with respect to date palm, a skilled artisan will appreciate that the fibers can be extracted from any other natural fiber sources. It can be used to utilize high crystalline fibers from any other natural fiber sources, as the biomass is similar in all plant cells. However, similar trial work may be required to determine the optimized parameter for other types of fibers.

An objective of high-performance bio-composite production is to improve the strength of interfacial adhesion between the fillers and host matrix. Therefore, the natural filler and polymer compatibility and homogeneity will be enhanced to obtain better bio-composites characteristics. The natural fibers are bio -degradable with comparable properties, which makes them effective materials for several applications of bio-composites including building and construction industries (ceiling paneling, partition boards). In addition, a source of raw material in polymer industry can be a source of economic development for rural areas.

The method 100 of the present disclosure maximizes the utilization of agro-waste in form of fibers for various applications. Also, time and cost required for preparing the high- performance fibers are minimized. Further, processing or treating the fiber using microwave accelerates the fiber productivity and enhances the overall strength, appearance, and material characteristics. In addition, the microwave assisted accelerated heating is safer and cleaner. The required capital for fiber production line start-up should be affordable and does not require hi-tech investment. As such, this method 100 can enable design and production of products that are light, less expensive, recyclable, sustainable, renewable and biodegradable. The method 100 of the present disclosure can also improve the compatibility between fiber and hosting polymer in bio-composites. Further, the fiber surface tribology can be enhanced to improve efficiency of functional groups, such as hydroxyl group (-OH), which can be functionalized for high-performance bio-composites synthesis.

The method 100 is also able to enhance performance of the fiber. The strength and crystallinity of the fibers are enhanced by -450% and by -30% respectively, which is higher than the existing technology for fiber modification. Purification and surface modification of natural fibers are essential steps toward fiber-matrix bonding improvement as the method 100 modifies the fiber surface and enhance structure modification by surface dewaxing and impurities removal of non-crystalline parts of the fibers.

The microwave assisted accelerated heating leads to a short treatment time and is easy to implement with improved properties of the produced fibers. The produced fibers can be used in bio-plastic products as a potential alternative to the current Wood Plastic Composites (WPCs). Additionally, the produced fiber is considered as a stand-alone material, which can also be used in various industrial applications to manufacture products. The produced fiber can also be used as a substantial candidate as filler for bio-plastic composites.

The method 100 utilizes new natural fibers from the date palm waste. Further, the method 100 can be used for other lignocellulosic fibers and powders to enhance the post processability in many applications. Therefore, efficient use of this natural resource in preparing natural fibers can have a positive impact on the eco-system and can improve the economic standard of rural people.

The method 100 of the present disclosure also provides safer chemical transformation steps. For example, toluene is a restricted chemical generally used for partial dewaxing. However, in method 100, any alcoholic solvent can be used with or without toluene. Amongst a variety of alcoholic solvents, ethanol is less toxic and has been in use for several industrial processes. Ethanol therefore, can be used in method 100 in place of toluene. The process can be applied as outlined earlier. The chemicals used for dewaxing can be recycled.

While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled.