The present disclosure relates to a method of obtaining rayon fibers, and more specifically, the present disclosure relates to the method of obtaining rayon fibers using gaseous ammonia.
Renewable and sustainable resources are considered to be major forms of energy by industries due to their renewability, biodegradability, low environmental risks, and minimal health hazards. The most abundant macromolecule found in nature is cellulose. Cellulose and derivatives of cellulose are of great importance for various human activities. Native cellulose fibers are used extensively in textile, pulp and paper industries such as, textiles, films, fibers, granules, and composite materials. One such highly used fiber is rayon, which is a regenerated cellulose fiber, that is chemically similar to cotton but differs in physical properties. Rayon is crystalline and has a molecular weight that is one-fifth of cotton.
Rayon's versatility is the result of the fiber being chemically and structurally engineered by making use of the properties of cellulose from which it is made. Rayon fibers are used in the apparel industry such as aloha shirts, blouses, dresses, jackets, lingerie, scarves, suits, ties, hats, and socks. Besides the textile industry, rayon textile-reinforced composites are used in tires, conveyor belts, hoses, and v-belts. Viscose rayon, cuprammonium rayon, and saponified cellulose acetate are some of the types of rayon formed by various conventional methods.
Conventional methods for obtaining various types of rayon fibers such as viscose rayon, cuprammonium rayon, and saponified cellulose acetate involve reacting copper hydroxide with liquid ammonia under various reaction conditions. This process is less desirable because a high amount of liquid ammonia is required to react with copper hydroxide, thereby making the process very expensive. Also, the long reaction time makes the process time-intensive. Moreover, most of the conventional methods used to prepare the rayon fibers involve the use toxic chemicals such as carbon disulfide. Hence, there is a need for efficient, eco-friendly, and inexpensive techniques to prepare the rayon fibers.
The present disclosure relates to a method of obtaining rayon fibers from cellulose waste. The method includes extracting alpha-cellulose from the cellulose waste. In one embodiment, the cellulose waste is recycled writing paper (RWP), cardboards and wood shavings. In one embodiment, the cellulose waste is RWP. In another embodiment, the method includes extracting alpha-cellulose from the cellulose waste by chemical maceration. In an embodiment, the chemical maceration involves treating the cellulose waste with 5% wt./wt. hydrogen peroxide and 5% wt./wt. citric acid. The macerated cellulose waste was further treated with mineral acid under reduced pressure. In an embodiment, the mineral acid is hydrochloric acid. The method further includes dissolving the alpha-cellulose in a cuoxam solution to obtain a chemically modified cellulose. The cuoxam solution is obtained by reacting gaseous ammonia with an aqueous solution of copper hydroxide. In an embodiment, the method includes reacting the gaseous ammonia with the aqueous solution of copper hydroxide at a temperature range of 5-15° C. under atmospheric pressure.
The aqueous solution of copper hydroxide may be prepared by reacting copper sulphate with sodium hydroxide at a temperature range of 25° C.-37° C. In one embodiment, a weight ratio (w/w) of copper sulphate to sodium hydroxide is in a range of 5:1 to 1:1. The method further includes extruding the chemically modified cellulose into an acid bath to obtain a precipitate, neutralizing the precipitate to obtain the rayon fibers. In an embodiment, the acid bath comprises citric acid. In another embodiment, a weight percentage of the citric acid in the acid bath is in a range of 8-15%. Furthermore, the method includes neutralizing the precipitate to obtain the rayon fibers.
In one embodiment, the rayon fibers have a staple length in a range of about 40 millimeters (mm) to about 50 mm, a linear density in a range of about 200 Tex to 250 Tex, and a fiber diameter in a range of 19 micrometers (μm) to about 20 μm. In another embodiment, the rayon fibers have a tensile strength in a range of about 218.3 Megapascals (Mpa) to about 236 Mpa, an elongation at break in a range of 14.3 Gigapascals (GPa) to about 15.6 GPa, and a modulus of elasticity in a range of 16.1 to about 36 Pa. In some embodiments, the rayon fibers have a breaking tenacity in a range of 27-58 cN/Tex. The rayon fibers are used to fabricate one or more of short fiber-staples, long fiber-staples, filament fibers, woven textiles, non-woven textiles, or any combination thereof.
The foregoing as well as other features and advantages of the present disclosure will be more fully understood from the following description, examples, and claims.
A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
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. A skilled artisan will appreciate that various alternate embodiments and forms may be prepared. Examples, therefore, given are only for illustration purposes without any intention to restrict the embodiments to a given set of examples. Specific functional aspects are provided merely to enable a person skilled in the art to perform the invention and should not be construed as limitations of the invention. Any method steps and processes described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.
As used herein, “alpha-cellulose” refers to an un-degraded high-molecular weight cellulose content in the pulp.
As used herein, “cuoxam solution” refers to the solution of cupric hydroxide in ammonia.
The term “extruding” refers herein to a process to thrust out, force out, push out or press out an object to form the desired shape.
As used herein, “extracting” refers to is a process in which one or more components are separated selectively from a liquid or solid mixture.
The use of the singular herein includes the plural (and vice versa) unless specifically stated otherwise.
The use of the terms “include,” “includes”, “including,” “have,” “has,” or “having,” “comprise,” “comprises,” “comprising” or the like should be generally understood as open-ended and non-limiting unless specifically stated otherwise.
It is understood that the order of steps or order for performing certain actions can be changed so long as the intended result is obtained. Moreover, two or more steps or actions may be conducted simultaneously.
As used herein, the term “about” or “between” refers to a ±20% to ±10% variation from the nominal value unless otherwise indicated.
Referring to
At step 104, the aqueous solution of copper hydroxide was obtained by reacting copper sulphate with sodium hydroxide. In an embodiment, the copper sulphate and sodium hydroxide may be reacted at a temperature range of 22° C. to about 40° C. In another embodiment, the copper sulphate and sodium hydroxide may be reacted at a temperature range of 25° C. to about 37° C. In yet another embodiment, the copper sulphate and sodium hydroxide may be reacted at a temperature range of about 28° C. to about 32° C. In some embodiments, a weight ratio (w/w) of copper sulphate to sodium hydroxide is in a range of about 5:1 to about 1:1.
At step 106, the method 100 includes reacting gaseous ammonia with the aqueous solution of copper hydroxide to obtain a cuoxam solution. The cuoxam solution (also known as tetra-ammine cupric hydroxide) is an aqueous solution of copper hydroxide and ammonia, and has the ability to dissolve the cellulose to successfully form rayon fibers. In an embodiment, the method 100 includes reacting gaseous ammonia with the aqueous solution of copper hydroxide at a temperature range of 3° C. to about 18° C. under atmospheric pressure. In another embodiment, the method 100 includes reacting gaseous ammonia with the aqueous solution of copper hydroxide at a temperature range of 5° C. to about 15° C. under atmospheric pressure. In yet another embodiment, the method 100 includes reacting gaseous ammonia with the aqueous solution of copper hydroxide at a temperature range of 8° C. to about 12° C. under atmospheric pressure.
At step 108, the method 100 includes dissolving the alpha-cellulose in the cuoxam solution to obtain a chemically modified cellulose. The chemically modified cellulose may be treated in various ways to obtain different end products. At step 110, the method 100 includes extruding the chemically modified cellulose into an acid bath or a hardening bath to obtain a precipitate. The acid bath may include acid such as, but not limited to, acetic acid, citric acid, etc. In an embodiment, the acid bath includes citric acid. In an embodiment, a weight percentage of the citric acid in the acid bath is in a range of 6% to about 17%. In another embodiment, a weight percentage of the citric acid in the acid bath is in a range of 8% to about 15%. In yet another embodiment, a weight percentage of the citric acid in the acid bath is in a range of 10% to about 13%. At step 112, the method 100 includes neutralizing the precipitate to obtain the rayon fibers. In an embodiment, the precipitate is neutralized with sodium carbonate, sodium bicarbonate, buffer solutions, other aqueous solutions that may assist in neutralizing the mixture to a pH of about 7. The precipitate may further be processed by spinning techniques to obtain thread-like structures. In some embodiments, the spinning techniques may be wet spinning, dry spinning, melt spinning, gel spinning, etc.
The rayon fiber obtained by the process of the present disclosure offers better qualities compared to the conventional process. In an embodiment, the rayon fibers have a staple length in a range of 35 millimeters (mm) to about 55 mm. In another embodiment, the rayon fibers have a staple length in a range of 40 mm to about 50 mm. In yet another embodiment, the rayon fibers have a staple length of about 45 mm. In one embodiment, the rayon fibers have a linear density in a range of 185 Tex to about 265 Tex. In another embodiment, the rayon fibers have a linear density in a range of 200 Tex to about 250 Tex. In yet another embodiment, the rayon fibers have a linear density in a range of 215 Tex to about 235 Tex. The Tex system is defined as the mass in grams per 1,000 meters. In an embodiment, the rayon fibers have a fiber diameter in a range of about 19 micrometers (μm) to about 20 μm.
The rayon fibers have a tensile strength in a range of 218.3 Mpa to about X Mpa. In one embodiment, the rayon fibers have an elongation at break in a range oft 16.1% to 36%. In another embodiment, the rayon fibers have a modulus of elasticity in a range of 14.3 to 15.6 Gigapascals (GPa). In yet another embodiment, the rayon fibers have a breaking tenacity in a range of 27 cN/Tex to about 58 cN/Tex. The rayon fibers may be selected from short fiber-staples, long fiber-staples, filament fibers, woven textiles, non-woven textiles, or any combination thereof. The rayon fibers prepared by the process of the present disclosure allows the use of gaseous ammonia effectively, obviating the drawbacks associated with time and costs. Further, the rayon fibers obtained from the process of the present disclosure shows good physical properties and chemical properties.
The disclosure will now be illustrated with examples, which are intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure.
Materials and Methods
The fundamental procedure performed to produce the rayon fibers from the RWP is mentioned below. The practical scheme is restricted to the following steps, namely: a) isolating or extracting the cellulosic fibers (alpha-cellulose) from the RWP by chemical maceration process. The chemical maceration process eliminates gum, ink, calcium carbonate from the cellulose waste. b) preparing an aqueous solution of Cu(OH)2; c) gaseous ammoniation process of the aqueous solution of Cu(OH)2 to synthesize the cuoxam solution, d) dissolving the cellulose fibers (alpha-cellulose) into the cuoxam solution, e) preparing the curing solution or hardening bath of citric acid (10%, wt/wt), f) regenerating the cellulose waste to the rayon fibers by extruding the rayon fibers in the hardening bath, and g) washing and neutralizing the extruded rayon fibers.
Raw Materials
Seven chemical reagents were used for the synthesis of the rayon fibers (Table 1). Four of them, namely copper sulphate, sodium hydroxide, ammonia gas, and citric acid were purchased in a commercial grade. The reminder CR, namely copper hydroxide and cuoxam solution were prepared in the laboratory.
Table 1. shows Chemical reagents (CR) and their formulas, concentrations, and reagent role in the production of cuprammonium rayon.
Copper Sulphate [CuSO4] Solution (5%)
Copper sulfate pentahydrate is the hydrate and a metal sulfate of copper (+2). It appears as blue crystalline granules with a melting point of 110° C., non-combustible nature, nauseating metallic taste, odorless smell, and white aspect when is dehydrated (Anonymous, 2021). About 50 g of CuSO4 was dissolved in one liter of deionized water to get a 5% concentration. After the complete dissolution, the supernatant was filtered using polypropylene textile having about 10-20 μm and stored until used.
Sodium Hydroxide (NaOH) Solution (1%)
Sodium hydroxide is also known as lye or soda, or caustic soda. At room temperature, It is a white crystalline odorless solid that absorbs moisture from the air. When dissolved in water or neutralized with acid, it releases substantial amounts of heat. NaOH is used to manufacture soaps, rayon, paper, explosives, dyestuffs, and petroleum products. It is also used in processing cotton fabric, laundering and bleaching, metal cleaning and processing, oxide coating, electroplating, and electrolytic extracting. In addition, it is considered the best alkaline pH controller agent (Anonymous, 2021). About 10 g of the NaOH was well-dissolved in one liter of deionized water to get a 5% concentration.
Synthesis of Copper Hydroxide [Cu(OH)2]
Cu(OH)2 was prepared in this study in two different scales, namely laboratory-scaled and prototype-scaled syntheses. It was formed due to the reaction between copper sulphate and caustic soda at room temperature with continuous stirring (Rana et al., 2014). 5% wt/wt of citric acid was added to the CuSO4 solution to prevent its hydrolysis.
CuSO4+NaOH→Cu(OH)2+NaSO4
Ammonia Gas for Ammoniation Process
Four ammonia groups via adding the ammonia gas was directly purged to the solution of Cu(OH)2 to obtain the cuoxam solution.
4NH4OH+Cu(OH)2→Cu(NH3)4(OH)2+4H2O
In an embodiment, the ammonia gas can be pressurized into the Cu(OH)2 paste within a pressure vessel to accelerate the rate of ammoniation process, as well as saving the gas lost or in an open system like a beaker.
Cuoxam Solution: Preparation by Direct Gaseous Ammoniation of Copper Hydroxide
Cuoxam solution was synthesized by treating copper hydroxide with ammonia gas (NH3), under cooling. Since this reaction is exothermic, a large amount of heat is generated during the reaction; therefore the reaction is performed under cooling either by ice or nitrogen liquid, since this reaction is exothermic.
[NH3+H2O]+Cu(OH)2→Cu(NH3)4(OH)2
NH3+H2O→NH4OH
One advantage of gaseous ammoniation is continuous maintaining of the ammonia groups (NH3−) concentration within the liquor all over the reaction duration. With the précised control of the gaseous ammonia-injection process within the copper hydroxide vessel to synthesize the cuoxam solution, the harmful effect of the ammonia smell released from using ammonium hydroxide liquid is eliminated. Also, the process of the present disclosure significantly increased the produced rayon quality and simplified the machinery system applied for rayon production.
The Hardening Bath Using Citric Acid
The cuoxam solution containing the dissolved cellulose was deposited in a controlled manner using a syringe pump and extruded through its fine nozzle.
Production of the Rayon fibers
I. The laboratory-Scaled Production
This was done in a one liter-volumetric scale by performing the following steps: a) 50 g of CuSO4.5H2O was weighed and dissolved into 1000 g of deionized water. The pH of the solution was adjusted at 3 by adding drops of citric acid (5%), to prevent hydrolysis of the CuSO4. The solution was stirred continuously with a magnetic stirrer until the clearance of the solution was obtained. The solution was further vacuum-filtrated through a fine polypropylene cloth (120 mesh) to obtain a precipitate. The cupric hydroxide precipitate was washed sufficiently with deionized water until the filtrate fails to give a positive test for sulphate ions with barium chloride solution. The neutralized pasty precipitate was further treated with ammonia gas in a beaker. The pasty precipitate then converted to a solution of tetra-ammine cupric hydroxide (cuoxam solution).
About 30 g of well-shredded RWP was converted into cellulosic pulp and was chemically purified using diluted HCl (0.2%, wt/wt), washed until neutralization, and oven-dried to obtain cellulose. Gums, polymers, and inks isolated by a hydromechanical machine, were cast from the surface of the RWP-solution due to their low densities. About 20 g of the cellulose was dissolved in the cuoxam solution with continuous stirring using a magnetic stirrer. This solution was named an uncured-rayon solution. The solution was filtered using a standard sieve (80 mesh) to eliminate undissolved cellulosic particles. After the filtration, the viscosity of the resultant pasty solution was adjusted, based on the desired thickness of the rayon fibers.
The process of the present disclosure uses citric acid (C6H8O7) solution (10%, wt/wt) for preparing the hardening bath since it is safer than the ordinary bath of sulphuric acid (10%, wt/wt) concerning the public health considerations. To prepare the 10%-concentration of citric acid in one-liter volume, about 100 g of citric acid was dissolved in about one liter of de-ionized water. Such a hardening bath can be reused multiple times with the frequent adjustment of its pH. The hardening bath was cooled by ice or liquid nitrogen since the curing reaction is exothermic or spontaneous that resulting in excess release of heat energy making the fibers weak and breaking them. In addition, the hardening container had an inner perforated vessel to facilitate exit of the cured rayon fibers from the hardening bath, and for quickly transferring to the subsequent washing step. For pressing the rayon fibers, spinning dope was discharged through the spinneret holes into the coagulation bath containing citric acid (10%, wt/wt) and leading to the formation of relatively thick filaments, that were subsequently stretched to reduce the fineness. For this purpose, an ordinary syringe pump was filled with un-cured rayon solution that was free of any particles of paper, to prevent clogging of the needle of the syringe.
The tip of the syringe was immersed into the solution and was pressed gently to extrude fibers into the bath (Jia et al., 2014). The rayon fibers that were formed in the hardening bath, on contact with the citric acid. The rayon fibers were allowed to stand in the hardening solution for about 15 minutes until decolorizing from blue (represented by gray in the image) to opaque white. As shown in
II. The Prototype-Scaled Production
Scaled up production was performed in a 60 liter-volumetric scale vessel. The process employed for scaled up production is similar to that of laboratory-scaled production except for the following points:
a) a pyrex tank of 60 L-capacity was used for preparation of the free calcium carbonate macerated cellulosic fibers obtained from the RWP as well as for storing and synthesis of copper hydroxide from copper sulphate and sodium hydroxide;
b) stirring solutions were done by using forced-air streams;
c) extrusion of the rayon fibers was done by spinnerets instead of the medical syringe used in the laboratory-scaled case; and
d) To prepare the 10%-concentration of citric acid in a 60-liter volume, about 6 kg of citric acid was dissolved in about 60 liters of deionized water.
The Different Rayon Products
Six products of rayon fibers were produced by the process of the present disclosures.
Processing the Rayon Fibers
The elementary products of rayon fibers synthesized by the process of the present disclosure were short fiber-staple, long fiber-staple, and filament fibers, while the final products were non-woven and woven textiles. However, to achieve these products, carding, spinning, and weaving processes were applied using primitive tools.
I. The Carding Process
The first step in this industry is the carding process in which the random rayon fibers were ordered and aligned by using a primitive carding machine.
II. The Spinning Process
It is the consequent process after the carding process, whereby staple fibers were converted into threads by using manual twisting beside a manual hand-spindle. The twisting process was performed to enhance the strength of the interfiber cohesion. The rayon yarn's strength and flexibility are extensively reviewed to be dependent on several factors, namely degree of fiber-to-fiber overlap, the surface characteristics of the fibers, the degree of twist, the tightness of the twist, and the fiber strength.
III. The Weaving Process
Weaving was performed by using a primitive weaving machine. The fabric was done, whereby two unique sets of threads were intertwined at right angles to construct a woven fabric. In the weaving process, weft yarns are inserted between two layers of warp yarns at an angle of 90° to the warp yarns. Two weaving structures were constructed in this study, namely, plain weave 1/1 and panama weave 2/2. Accordingly, two different types of textile architecture have been established: a) plain weave 1/1 in which the yarn was crossing over one warp yarn, and b) panama weave 2/2 in which the weft yarns are not crossing every warp yarn. Both architectures were different in their yarn density (the number of yarns related to the width).
IV. The Non-Woven Fabrication Process
Nonwoven fabrics are more-or-less random sheets of fibers, which are held together by adhesive bonding, entanglement, or stitching. One-dimensional assemblies are used in cords and ropes. Three-dimensional fabrics are used as composite preforms, either in the form of shaped sheets or thick structures, but also have other applications, such as knitted garments and conveyor belts.
Results
Elimination of Calcium Carbonate from the RWP
Monitoring the efficiency of discarding gums, polymers, and inks by hydromechanical treatment as well as eliminating CaCO3 by chemical purification using diluted HCl was studied, and the results are presented in
CaCO3+2H+→Ca2++H2O+CO2←
It was noticed that under the reduced pressure, the total acid consumed was reduced while maininting high dissolution. Increasing the dissolution of the CaCO3 with decreasing pressure can be explained by le Chatelier's Law, the stirring effect due to rising bubbles, and the cavitation effect.
The Scientific Illustration of the Rayon Formation
The cuoxam solution known as cuoxam's reagent is a metal ammine complex having the formula [Cu(NH3)4(H2O)2](OH)2]. It is featured by its deep-blue color and is useful to dissolve cellulose.
Physical Properties of the Rayon Fibers
The traits studied were the yields of α-cellulose isolated from RWP as well as the physical properties of the rayon synthesized from the α-cellulose, namely melting point, rayon yield, apparent density, moisture content, moisture regain, volumetric shrinkage, and crystallinity index (Table 2).
Table 2. Mean values of the yield of α-cellulose (YC) and the rayon properties of melting point (MP), rayon yield (RY), apparent density (AD), moisture content (MC), moisture regain (MR), volumetric shrinkage (VS), and crystallinity index (CI).
Melting Point (MP)
The MP of the rayon fibers was found to be about 181° C. that is in accordance with that for the standard value (above 150° C.). In addition, the MP average was greater than that measured by Shamsuddin et al. (2016) as shown in Table 2. Accordingly, the melting point of the rayon fibers of the present disclosure is satisfactory, since higher MP is indicative of the thermal resistance of the fibers. The higher MP of the rayon fibers suggests a greater thermal stability of the rayon fabrics.
The Yield of Cellulose (YAC)
The average of the YAC obtained from the RWP after the elimination of impurities such as calcium carbonate, gums, and inks was found to be about 90.3%. This productivity was higher than that found previously by Hindi and Abohassan (2015) as clear in Table 2. This result reflects the efficiency of the hydromechanical method along with the CaCO3-elimination reagent in isolating the cellulose from the RWP.
The Rayon Yield (RY)
The mean value of RY produced from the isolated cellulose was about 92.25%. This output was found to be higher than the RY range (72.47-88.27%) obtained by other researchers such as Zaman and Begum (2020) as clear in Table 2. Accordingly, it can be said that the higher the RY, the more profit can be gained.
The Apparent Density (AD)
The AD of the rayon fibers was found to be about 1.54 g/cm3. Comparing it with that reported by Shishir (2014), it was observed that the AD lies within the standard limits as obvious from Table 2.
The Moisture Content (MC)
As indicated from Table 2, the average of the MC of the rayon fibers was found to be 8.6%. This was lower than the MC range (10-12.75%) determined by Abdul Basit et al. (2018) and Zaman and Begum (2020).
The Moisture Regain (MR)
The MR values of cotton and regenerated cellulose are about 7.8% (Table 2). Due to its cellulosic nature, viscose has more amorphous regions giving more voids in its structure (Abu-Rous et al., 2006). This nano-structure of the rayon fibers has some moisture management properties among all viscose blends. It was found to have moisture absorption ability but it wicks less as compared to natural fibers such as cotton fibers (Abu-Rous et al., 2006; Abdul Basit et al. 2018).
Volumetric shrinkage (VS)
The mean value VS of the rayon fibers was determined to be about 1.8% that lies within the accepted region. This value is higher to some extent than that found by Nawaz et al. (2002) as presented in Table 2. Since the VS is the dimensional change resulting in a decrease in the length or width of a rayon fiber specimen due to losing some of its moisture content, their fabrics' dimensions are expected to decrease slightly when exposed to heat or evaporation conditions. However, the VS if the rayon fibers of the present disclosure was small enough to be undistorted for the final product fabrics of the rayon fibers. Since rayon fibers are composed mainly of cellulose that is well known to be hydrophilic in its nature, it can allow the water to soak into the fiber and swell as well as lose moisture and is shrunk. On the other hand, hydrophobic fibers such as cellulose triacetate will exhibit very little shrinkage (Kohler, 2012).
Crystallinity Index (CI) from X-Ray Diffraction (XRD)
Chemical Characterization of the Cuoxam Solution Saturated with Cellulose
Two chemical properties of the Cuoxam solution saturated with cellulose, namely molecular weight, and degree of polymerization were analyzed, as shown in Table 3.
The Molecular Weight (MW)
The MW of the cuoxam solution saturated with cellulose is presented in Table 3. The molecular weight of viscose is in the range of 90,000 to 110,000 KDa.
The Degree of Polymerization (DP)
The DP average of viscose polymer is in the range of 300-450 g/mol, as shown in Table 3. Since pulp fibers in their natural state are too short to be spun into yarns, they are dissolved and regenerated in filament form. The rayon fibers are made by the wet spinning principle.
Fibrous Properties of the Cuprammonium Rayon
Five fibrous properties, namely staple length, linear density, and fiber diameter of the rayon were investigated in this study and their mean values are presented in Table 4.
The Staple Length (SL)
The SL property was measured and the data were presented in Table 4. The mean SL value was found to be about 44 mm, which is longer than that produced by Abdul Basit et al. (2018) and lies within the ordinary limit. The average SL of a group of fibers was reported to be dependent on the origin of the fibers. Increasing the average staple length of the fibers can ultimately make the yarn softer. The rayon fibers can be produced in extremely fine deniers to obtain softness and handle characteristics similar to silk. The burning characteristic of this material was reported to be similar to viscose rayon, whereby it burns rapidly and chars at 181° C.
The Linear Density (LD)
The average LD was about 235 Tex, which is substantially higher than that range determined by Aytac et al. (2010) and lower than that found by Shamsuddin et al. (2016) as indicated from Table 4. Since the LD is used as a measure of fineness, it can be said that lower the LD value, the more fineness for the rayon fibers. The rayon fibers of the present disclosure have lower fineness than those synthesized by Shamsuddin et al. (2016). LD can be adjusted easily by controlling several parameters, such as diameter of the syringe's nozzles, the viscosity of the cuoxam/cellulose solution, and the pressure of the extruding force. Reducing the diameter of the syringe's nozzles, and reducing the viscosity of the cuoxam/cellulose solution, while increasing the extruding force can help to idealize the rayon fineness.
The Fiber Diameter (FD)
The FD character is an additional indicator for rayon fineness besides the LD. The FD value was estimated from the SEM image using its scale bar (
Mechanical Properties of the Cuprammonium Rayon
Mechanical properties, namely tensile strength, modulus of elasticity termed as Young's modulus, elongation at break, and breaking tenacity are the most important mechanical properties of regenerated cellulose including cuprammonium rayon.
Tensile Strength (TS)
TS is one of the important properties for describing the mechanical performance of the rayon fibers. A universal testing machine was used to determine the TS of the test specimen. ASTM D3039 standards (Arumugaprabu et al., 2019). The TS average value of the rayon is 218.3 MPa as indicated in Table 5. From Table 5 it is clear that there is a wide range of the TS showed by Miyake et al. (2000), Quazi et al. (2012), and Shamsuddin et al. (2016). The vast range is attributed to the difference in their rayon types tested. However, TS of the rayon fibers of the present disclosure is close to those found by Shamsuddin et al. (2016) as shown in Table 5. The lower strength of the rayon fibers compared to other regenerated cellulose can be attributed to the lower crystallinity and higher amorphous regions in the rayon structure and vice versa for Tencel material (Kreze and Malej, 2003; Stana-Kleinschek et al., 2003; Carrillo et al., 2004). Changes in tensile strength and elongation with wetting may depend mainly on the number of the molecular chain ends in the amorphous region (Miyake et al., 2000).
Modulus of elasticity (MOE)
The MOE is a very important character in handling rayon yarns during such weaving and stentering when sudden tensions are applied (Miyake et al., 2000). The M MOE of the rayon fibers was determined to be 14.3 GPa (as can be observed in Table 5). This average is close to the estimated range of rayon material (15-15.6 GPa) found by Seavey and Glasser (2001) and Shamsuddin et al. (2016).
Elongation at break (EB)
The mean average of EB estimated for the rayon fibers was found to be 16.1% (as can be observed in Table 5) which is a median of the global range. Ordinary viscose rayon has 10.6-36.8% EB at the break as determined previously by Schwarz and Wannow (1941), Miyake et al. (2000), Aytac et al. (2010), Iqbal & Ahmad (2011), and Abdul Basit et al. (2018) Changes in tensile strength and elongation with wetting may depend mainly on the number of the molecular chain ends in the amorphous region (Miyake et al., 2000).
Breaking Tenacity (BT)
The BT of the resulted rayon fibers had a high mean value as compared to that referred by Miyake et al. (2000). The BT average of the rayon fibers of the present disclosure lies within the determined range (4.42-58 cN/Tex) found in the literature (Schwarz and Winnow, 1941; Iqbal and Ahmad, 2011; Shaikh et al., 2012; Abdul Basit et al., 2018) as can be observed in Table 5.
The rayon fiber prepared by the process of the present disclosure offers several advantages over conventional methods. One advantage of the embodiments according to the present disclosure is the use of gaseous ammonia to react with the copper hydroxide to form the cuoxam solution is the faster rate of reaction thereby making the process substantially faster. Another advantage of the rayon fibers obtained by the process of the present disclosure is that it has high yield and better quality. The rayon fibers have shown good tensile strength, elongation at break, modulus of elasticity, and breaking tenacity. The fiber characteristics render them favorable for use in making sustainable semi-synthetic floss for either insulation purposes or spun threads, woven and non-woven textile clothing, surface coating as well as a binder for carbon briquettes for fluid purification. Yet another advantage of the process of the present disclosure is reusing, recycling, and converting cellulose waste material to value added products thereby enhancing the sustainability, biocompatibility; and other environmental benefits.
It is understood that the examples, embodiments, and teachings presented in this application are described merely for illustrative purposes. Any variations or modifications thereof are to be included within the scope of the present application as discussed.
The authors extend their appreciation to the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia for funding this research work through the project number “2021-090” and King Abdulaziz University, DSR, Jeddah, Saudi Arabia.
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