Environmentally friendly cellulosic waste recycle
阅读说明:本技术 环境友好的纤维素废料再循环 (Environmentally friendly cellulosic waste recycle ) 是由 刘航 张锦文 刘望成 于 2018-05-11 设计创作,主要内容包括:本文公开了将例如棉等纤维素废料化学地再循环的技术。在一个实施方案中,方法包括,水解棉废料并且将水解的棉废料中的纤维素溶解在包含碱和选自脲((NH<Sub>2</Sub>)<Sub>2</Sub>CO)、聚乙二醇、或硫脲(SC(NH<Sub>2</Sub>)<Sub>2</Sub>)中的一种或多种的水溶液中,以生产另一种包含溶解的纤维素的水溶液。然后可以将包含溶解的纤维素的另一种水溶液挤出至凝结浴中以使溶解的纤维素在挤出的溶液中凝结,从而将来自棉废料的溶解的纤维素再形成为再生纤维。(Disclosed herein are techniques for chemically recycling cellulosic waste, such as cotton. In one embodiment, the method comprises hydrolyzing cotton waste and dissolving cellulose in the hydrolyzed cotton waste in a solution comprising a base and a solvent selected from the group consisting of urea ((NH) 2 ) 2 CO), polyethylene glycol, or thiourea (SC (NH) 2 ) 2 ) In an aqueous solution of one or more of them to produce another packAn aqueous solution containing dissolved cellulose. Another aqueous solution containing dissolved cellulose may then be extruded into a coagulation bath to coagulate the dissolved cellulose in the extruded solution, thereby reforming the dissolved cellulose from the cotton waste into regenerated fibers.)
1. A method of recycling cellulose waste comprising cellulose, the method comprising:
hydrolyzing the cellulosic waste material such that the cellulose in the hydrolyzed cellulosic waste material has a degree of polymerization of about 240 to about 860;
dissolving the cellulose in the hydrolyzed cellulose waste having a degree of polymerization of about 240 to about 860 in a solvent comprising a base, and selected from the group consisting of urea ((NH)2)2CO), polyethylene glycol, or thiourea (SC (NH)2)2) To produce another aqueous solution comprising dissolved cellulose from the cellulose waste; and
extruding the other aqueous solution comprising the dissolved cellulose into a coagulation bath comprising a coagulant, the coagulation bath configured to coagulate the dissolved cellulose in the extruded solution, thereby reforming the dissolved cellulose from the cellulose waste into a regenerated fiber or film.
2. The method of claim 1, wherein the base comprises one or more of sodium hydroxide (NaOH), lithium hydroxide (LiOH), or potassium hydroxide (KOH).
3. The method of claim 1, wherein dissolving the cellulose comprises dissolving the cellulose by mixing the hydrolyzed cellulose waste with the aqueous solution at a temperature of about-5 ℃ to about 0 ℃.
4. The method of claim 1, wherein dissolving the cellulose comprises dissolving the cellulose by mixing the hydrolyzed cellulose waste with the aqueous solution at a temperature of about-5 ℃ to about 0 ℃ and under mechanical agitation.
5. The method of claim 1, wherein dissolving the cellulose comprises dissolving the cellulose to produce another aqueous solution having a cellulose concentration of about 2% to about 10%.
6. The method of claim 1, wherein the aqueous solution comprises a combination of sodium hydroxide (NaOH) and urea, or a combination of lithium hydroxide (LiOH) and urea.
7. The method of claim 1, wherein the aqueous solution comprises a combination of sodium hydroxide (NaOH) and urea in water at a weight ratio of 8.75:10:81.25, respectively, or a combination of lithium hydroxide (LiOH) and urea in water at a weight ratio of 7.5:12:80.5, respectively.
8. The method of claim 1, wherein the coagulant in the coagulation bath comprises sulfuric acid (H)2SO4) One or more of ethanol, butanol or acetone.
9. The method of claim 1, wherein:
hydrolyzing the cellulosic waste material comprises contacting the cellulosic waste material with a sulfuric acid solution or an enzyme solution having a concentration; and
the method further comprises adjusting one or more of hydrolysis time, hydrolysis temperature, or concentration of the sulfuric acid or the enzyme in solution to cause the hydrolyzed cellulosic waste material to have a degree of polymerization of about 240 to about 860.
10. The method of claim 1, wherein:
the cellulosic waste material comprises a dye; and
reforming the dissolved cellulose from the cellulose waste into the regenerated fiber includes reforming the dissolved cellulose from the cellulose waste into the regenerated fiber without removing the dye from the cellulose waste, the regenerated fiber having an inherent color.
Background
Cotton is a material widely used in consumer products such as apparel and textiles. The consumption of such cotton products has been steadily increasing over the last decades. With such increased consumption, cotton waste production also increases. Cotton waste can be classified as pre-consumer waste or post-consumer waste. Pre-consumer waste is generated during the production of yarns, fabrics and end products, while post-consumer waste is generated when cotton products are discarded after use.
Pre-consumer waste can be recycled generally for use in low-grade yarns and nonwoven products for automobiles, building insulation, furniture, and the like. However, it is difficult to recycle post-consumer waste using existing recycling techniques due to impurities remaining on the cotton product and/or tearing/abrasion during use. It is estimated that 95% of the post-consumer waste is ultimately landfilled or incinerated. Landfills or incinerated post-consumer waste can generate large quantities of greenhouse gases and/or toxic chemicals/odors.
Disclosure of Invention
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
Recycling post-consumer waste of cellulosic products, such as cotton products, can be challenging due to the large differences in the quality and tear/abrasion of the waste. Cotton fibers are difficult to dissolve in common solvents due to the strong intramolecular and/or intermolecular hydrogen bonding of cellulose in cotton. Instead, environmentally unfriendly solvents are often used. For example, rayon fiber manufacture may use carbon disulfide (CS) in the viscose process2) Or in the cuprammonium process using a solution of cuprammonium hydroxide complex and a heavy metal. The above chemicals are toxic to humans and animals and are difficult to recycle and reuse.
Several embodiments of the disclosed technology relate to techniques for recycling post-consumer waste of cellulosic products (e.g., cotton products) to produce regenerated fibers using environmentally friendly solvents. In one embodiment, the shredded post-consumer waste material may first be hydrolyzed using an acid (e.g., sulfuric acid) to reduce the degree of polymerization of the cellulose fibers in the cellulosic product, e.g., from about 1,800 to a range of about 240 to about 860. The hydrolyzed fibers can then be readily dissolved in an alkaline/urea solvent and adapted for wet spinning or other suitable techniques to form individual regenerated fibers or films.
In accordance with aspects of the disclosed technology, exemplary alkaline/urea solvents may include sodium hydroxide (NaOH) and urea ((NH)2)2CO) or lithium hydroxide (LiOH) and ((NH)2)2CO) in water. In other examples, the sodium hydroxide or lithium hydroxide in the aforementioned exemplary solvents may be replaced with potassium hydroxide (KOH) or other suitable kind of strong base. In other examples, urea in the aforementioned exemplary solvents may also be at least partially replaced with polyethylene glycol (PEG) and/or thiourea (SC (NH)2)2) Instead.
Certain experiments using the foregoing exemplary solvents have been conducted to test the effectiveness of recycling post-consumer waste of cotton products. During the experiment, Scanning Electron Microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and tensile tests were used to characterize the diameter, morphology, thermal properties, crystallinity and tensile properties of the regenerated fibers. Experimental results show that using embodiments of the recycling techniques discussed herein, recycled fibers can be produced from post-consumer waste of cotton products. The recycled fibers may have properties or qualities comparable to those of recycled fibers produced commercially from wood pulp. Thus, experiments have shown that post-consumer waste of cotton products can be suitably recycled to produce high quality regenerated fibres using environmentally friendly solvents instead of using toxic solvents such as Schweizer reagent, cadmium ethylene diamine (Cadoxen) and lithium chloride/dimethylacetamide.
By recycling post-consumer waste of cellulose products, such as cotton products, rather than landfilling or incinerating such waste, the amount of landfill space and greenhouse gases and toxic chemicals/odors from anaerobic decomposition of cellulose can be significantly reduced when landfilling and incinerating. Recycling post-consumer waste can also reduce the need for growing raw cotton (virgin cotton) or other types of cellulosic raw materials. Raw cotton planting involves the extensive use of chemicals such as insecticides, fungicides and defoliants. It is estimated that 25% of the world's pesticides are used in cotton plantation in 2.4% of the world's farmlands. Furthermore, scouring and bleaching of cotton fibers is also heavily dependent on chemicals, water and energy. Thus, by producing high quality regenerated fibers from cellulosic waste, the planting of raw cotton or other types of cellulosic raw materials and the negative environmental impact of such planting can be reduced.
Further, another aspect of the disclosed technology may relate to recycling post-consumer waste of the cellulose product without removing dye from the cellulose product during the recycling process. As a result, regenerated fibers made from colored cellulosic products can have an inherent color and therefore do not require further dyeing prior to end use. Reducing or even eliminating dye removal in recycled cellulose products can reduce the cost of recycled fiber and the contamination associated with dye removal and/or additional dyeing processes.
Drawings
Fig. 1 is a flow diagram illustrating a process for recycling cellulose waste in accordance with an embodiment of the disclosed technology.
FIG. 2 is a schematic diagram of a fiber dissolving apparatus suitable for certain operations in the recycle process of FIG. 1, in accordance with embodiments of the disclosed technology.
FIG. 3 is a schematic diagram of a fiber forming apparatus suitable for certain operations in the recycling process of FIG. 1, in accordance with embodiments of the disclosed technology.
Fig. 4 is a schematic diagram illustrating one possible mechanism of fiber dissolution in accordance with embodiments of the disclosed technology.
Fig. 5A-5F are example SEM images showing the morphology of the following fibers, respectively, in accordance with embodiments of the disclosed technology: (A) raw cotton fiber, (B) cross section of fiber, (C) 0.05% sulfuric acid (H) in lithium hydroxide (LiOH)2SO4) Regenerated fibres in the case of 3.25% cotton, (D) 0.2% H in LiOH2SO4Regenerated fibres in the case of 3.25% cotton, (E) 0.2% H in LiOH2SO4Recycled fibre in the case of 5% cotton, and (F) 0.2% H in sodium hydroxide (NaOH)2SO4Recycled fibres in the case of 5% cotton.
Fig. 6A-6D are example TGA curves obtained from raw cotton fibers, hydrolyzed cotton fibers, and regenerated cotton fibers, respectively, treated with the following conditions, according to embodiments of the disclosed technology: (A) 0.05% H in LiOH2SO4-3.25% cotton, (B) 0.2% H in LiOH2SO4-3.25% cotton, (C) 0.2% H in LiOH2SO45% Cotton, and (D) 0.2% H in NaOH2SO4-3.25% cotton.
Fig. 7 is an example XRD spectrum of raw, hydrolyzed, and regenerated cotton fibers and the corresponding crystallinity calculated by the XRD peak height method, in accordance with embodiments of the disclosed technology.
FIG. 8 is an example tenacity-tensile strain curve obtained from a tensile test of an example recycled fiber, with an inset showing the tensile break surface of the recycled fiber, in accordance with embodiments of the disclosed technology.
Detailed Description
Certain embodiments of systems, apparatuses, articles of manufacture, and processes for recycling cellulosic products are described below. In the following description, specific details of components are included to provide a thorough understanding of certain embodiments of the disclosed technology. One skilled in the relevant art will also appreciate that the disclosed technology may have additional embodiments, or may be practiced without several of the details of the embodiments described below with reference to fig. 1-8.
As used herein, "cellulosic waste" generally refers to an unwanted or unusable material that at least partially contains cellulose. One example cellulosic waste material may be "cotton waste" comprising undesirable or unusable material that at least partially comprises cotton. For example, cotton waste may include textiles, clothing, or other types of consumer products that contain cotton that is discarded, worthless, defective, or otherwise unusable after initial use. In other examples, the cotton waste may also include white cotton, colored cotton, and cotton blends (e.g., cotton/polyester and cotton/nylon blends). Cellulosic waste (e.g., cotton waste) can generally be classified as either pre-consumer waste or post-consumer waste of the cellulosic product. For example, pre-consumer waste is generated during the production of yarns, fabrics and end products (e.g., garments), while post-consumer waste is generated when cellulose-containing products are discarded after use. Even though several embodiments of the techniques discussed below are used to recycle post-consumer waste of cotton products, in other embodiments, the disclosed techniques may be applied to recycle pre-consumer waste of cellulose products, or to produce recycled fiber from other pre-or post-consumer waste (e.g., of wood, bamboo, etc.) in appropriate applications.
The term "regenerated fiber" or "regenerated cellulose fiber" also used herein generally refers to cellulose fiber produced by dissolving cellulose of plants (e.g., from wood, bamboo, cotton, etc.) in chemicals and reforming the dissolved cellulose into fiber again. One example of regenerated fibers is rayon, which is produced by dissolving cellulose of wood pulp in chemicals and reforming the dissolved cellulose into fibers via, for example, the viscose process. In another example, as discussed in more detail herein, several embodiments of the disclosed technology can be utilized to produce regenerated fibers by dissolving post-consumer waste of cellulosic products, such as cotton products, with environmentally friendly solvents. In contrast, the term "raw cotton fiber" generally refers to cotton fiber that is directly derived from cotton plants. The raw cotton fibers may be spun into yarns, which may then be woven or knitted into a fabric.
Cotton is used in consumer products (e.g., clothing and textiles such as towels and bedding) more than other fibrous materials as a natural material with attractive comfort and easy care properties. Cotton consumption has been steadily increasing with rapid fashion trends/disposable lifestyles, and the decline in apparel and textile prices as a result of global purchases. In the united states, about two-thirds by weight of textile waste is cotton products, accounting for 3.7% of the municipal solid waste produced.
However, cotton is difficult to dissolve and therefore difficult to recycle. The recycling rate of cotton waste is currently estimated to be about 5% and well below about 15% of the total textile recycling rate. Thus, cotton waste is buried in landfills or burned in incinerators, both of which produce large quantities of greenhouse gases (e.g., methane and carbon dioxide) and toxic chemicals/odors. Such treatment of cotton waste is detrimental to the environment and human health and is incompatible with the efficient use of natural cellulose resources.
Several embodiments of the disclosed technology relate to recycling post-consumer waste of cellulosic products, such as cotton products, by dissolving cellulosic fibers (e.g., from cotton) with environmentally friendly solvents and spinning the dissolved fibers into high quality regenerated fibers for a wide range of end uses. Embodiments of the disclosed technology can reduce cellulose waste for landfills or incinerators by using cellulose waste as a raw material and environmentally friendly solvents for fiber dissolution and spinning, thereby reducing emissions of greenhouse and toxic chemicals/odors. Embodiments and additional advantages of the disclosed technology are described in more detail below with reference to fig. 1-8.
Fig. 1 is a flow diagram illustrating a
In other embodiments, the pretreatment of the cellulosic waste material may also include various chemical treatment techniques. In one example, sulfuric acid (H), for example, may be used2SO4) The acid solution such as aqueous solution of (a) hydrolyzing the shredded cotton waste at a hydrolysis temperature for a hydrolysis reaction time. One or more of the hydrolysis temperature, the hydrolysis reaction time, or the concentration of acid may be adjusted to reduce the degree of polymerization of the cotton waste from about 1,800 to a range of about 240 to about 760, a range of about 550 to about 860, or other suitable range. Example values for the foregoing variables can be 120 deg.C, 12 minutes, and about 0.2% sulfuric acid, respectively. In further embodiments, cotton waste may also be pretreated with enzymes (e.g., cellulase) to enhance solubilization.
The
During fiber dissolution, one or more operating parameters may be adjusted to achieve sufficient reaction or cellulose dissolution so that the dissolved fibers in the produced fiber solution may be reformed into regenerated fibers. Example operating parameters may include the application of mechanical agitation and the associated degree of mechanical agitation, solvent temperature (e.g., about-15 ℃ to about 0 ℃ or about-5 ℃ to about 0 ℃), dissolution reaction time, and concentration and/or composition of the solvent 114. Without being bound by theory, it is believed that insufficient dissolution results in an excessively viscous fiber solution, while excessive dissolution results in an excessively aqueous fiber solution. Under both conditions, the dissolved fibers in the fiber solution may not be readily reformed into regenerated fibers. Example values of the aforementioned operating parameters during fiber dissolution are described in more detail below with reference to the experimental section.
Various processing equipment may be used to dissolve cotton waste in a continuous or batch mode. For example, as described in more detail below with reference to fig. 2, a Constant Stirred Tank Reactor (CSTR)110 (shown in fig. 2) may be used in a continuous mode for dissolving shredded cotton waste. In other examples, cotton waste may also be treated in a continuous mode using a plug flow reactor (not shown). In other examples, cotton waste may also be treated in batch mode using a tank reactor (not shown).
The
The
As described in more detail later herein, certain experiments have been tested for recycling post-consumer waste of cotton products as samples using the foregoing example solvents and similar operating stages below. The results of these experiments indicate that high quality recycled fiber can be produced from post-consumer waste of cotton products using embodiments of the recycling techniques discussed herein. The recycled fibers may have properties comparable to recycled fibers produced commercially from wood pulp. Thus, post-consumer waste of cotton products can now be recycled using environmentally friendly solvents to produce high quality recycled fibers.
By recycling post-consumer waste, rather than landfilling or incinerating cotton waste, landfill space, as well as both greenhouse gases and toxic chemicals/odors from anaerobic decomposition and incineration of cellulose, can be significantly reduced. Recycling post-consumer waste can also reduce the need for growing raw cotton or other cellulosic raw materials. Raw cotton planting involves the extensive use of chemicals such as insecticides, fungicides and defoliants. Furthermore, scouring and bleaching of cotton fibers is also heavily dependent on chemicals, water and energy. Thus, by producing regenerated fibers from cotton waste, the planting of raw cotton and the negative environmental impact of such planting can be reduced.
In addition, the use of cellulosic waste to make recycled fiber can reduce rayon production from wood pulp and the associated negative environmental impacts. The processing of industrial wood pulp is very water and energy consuming and has become an important factor in the deterioration of the environment. Current rayon production involves the use of carbon disulfide (CS)2) Or a solution of an ammonium copper dihydroxide complex. Carbon disulfide is highly toxic, volatile, and not recyclable. Cuprammonium rayon production involves the use of copper, which is difficult to recover from waste water.
Further, another aspect of
Fig. 2 is a schematic diagram of a
Also shown in fig. 2, the
The
In certain embodiments, the
In operation, the
During fiber dissolution, the
Fig. 3 is a schematic diagram of a
In the illustrated example, the
In operation, a fiber solution containing dissolved fibers is fed into the
Fig. 4 is a schematic diagram illustrating one possible mechanism of dissolution of cellulose fibers in a solvent comprising lithium hydroxide (LiOH) and urea, in accordance with embodiments of the disclosed technology. As shown in FIG. 4, the cellulosic fibers 150 may initially include a plurality of cellulosic molecular chains or
Experiment of
Experiments were conducted using certain alkaline/urea aqueous solvents disclosed herein to recycle post-consumer cotton fabric and produce regenerated cellulose fibers via wet spinning. In the experiments, white shirts of 100% cotton as post-consumer waste were selected as the raw material. A mild hydrolysis process is applied as a pre-treatment to reduce the molecular weight of the cotton fabric. As described in more detail below, two example solvents, an aqueous solution of LiOH/urea and an aqueous solution of NaOH/urea, were used to compare the dissolution operation and the properties of the regenerated fibers.
A 100% white cotton shirt knitted with single weft knit (single soft knit) was used as the raw material. Using lithium hydroxide monohydrate (LiOH. H)2O, purity 99.0%), urea (NH)2CONH2Purity not less than 98.0%), ammonium sulfate [ (NH)4)2SO4Purity is 98%]Sulfuric acid (H)2SO4Purity 95.0-98.0%), and sodium hydroxide (NaOH, purity 98%) as reagents. The cotton shirt was first shredded and pretreated to reduce its molecular weight. The shredded cotton is immersed in a solution of sulfuric acid and treated at elevated temperature for hydrolysis. Two different sulfuric acid concentrations were used, namely 0.05 wt% and 0.2 wt% in water. The cotton/acid mixture was autoclaved at 120 ℃ for 12 minutes at a pressure of 20 psi. After cooling to room temperature, the hydrolyzed cotton was collected by filtration and washed with distilled water until the pH of the wash solution reached about 7. The hydrolyzed cotton was then dried overnight in a conventional oven at about 50 ℃. Finally, the Degree of Polymerization (DP) of the hydrolyzed cotton was determined by viscometry in ammoniacal copper solution at 25 ℃.
After drying, the hydrolysed cotton was dissolved in LiOH/urea/H with three components in two different ratios of 8.75:10:81.25 and 7.5:12:80.5 by weight2O or NaOH/urea/H2O in an aqueous solution. Both the hydrolyzed cotton and the solvent were pre-cooled to-12.5 ℃ and then mixed together in an ice-liquid nitrogen bath at-5 ℃ for 40 minutes with vigorous stirring. Spinning solutions having different dissolved cotton or cellulose concentrations of about 3.25% and about 5% by weight were prepared and the corresponding viscosity values were measured. The effect of solvent composition and cotton concentration on regenerated fiber properties was analyzed.
Wet spinning was carried out using a wet spinning apparatus substantially similar to that shown in fig. 3. In particular, the wet spinning apparatus includes a polymeric cylinder reservoir with a spinneret for spinning the regenerated fibers, a coagulation bath, and a rotating fiber collector. After the prepared spinning solution was loaded into the cylinder reservoir, the spinning solution was extruded into a coagulation bath using compressed nitrogen. The coagulation bath contained H at ambient room temperature in a weight ratio of about 7.5:7.5:852SO4/(NH4)2SO4/H2And O. The diameter of the spinneret orifice was 80 μm. The coagulated regenerated fibers were collected by a rotating fiber collector, then washed with hot water, then with room temperature water. The regenerated fibers were then dried at room temperature for at least 24 hours prior to characterization. Samples of the regenerated fibers were evaluated for fiber diameter, morphology, thermal properties, crystallinity, and tensile properties.
In 1s-1The viscosity of the spinning solution was measured at the shear rate of (2). A cooling bath (water-ice) was applied to control the measurement temperature at about 4 ℃. The fibrils and regenerated fibers were observed using a field emission scanning electron microscope. The morphology of the fiber surface, cross section and tensile failure surface was studied. All samples were sputter coated with platinum having a thickness of about 2.8nm prior to characterization. The fiber diameter is determined by measuring a cross-sectional image of the fiber, and the total area of at least thirty fibers randomly selected from the image is measured to calculate the average fiber diameter.
The crystallinity of the fibrils, hydrolyzed fibers, and regenerated fibers was determined by analyzing the X-ray diffraction (XRD) pattern recorded using an X-ray diffractometer. N is a radical ofi filtered CuK alpha radiation
40kV, 25mA, and a scanning step size of about 2 ° in the range from 5 ° to 40 °. To determine the thermal decomposition of fibrils, hydrolyzed fibers, and regenerated fibers, a thermogravimetric analyzer was used. The experiment was conducted with a heating rate of about 10 deg.C/min increasing from ambient temperature to 600 deg.C under a nitrogen atmosphere at a flow rate of 100 mL/min. Samples loaded with about 5mg of fiber were used for the test.Tensile testing was performed on a universal tester. The distance between the two clamps was set at 25mm and the crosshead speed was maintained at about 5 mm/min. Fiber tenacity and percent elongation were calculated from the average of 40 measurements of tensile load and elongation. The strength is obtained from the average tensile load and the average fiber diameter.
The Degree of Polymerization (DP) of raw cotton fiber is about 1800, which results in its low solubility in solvents and extremely high viscosity. To obtain a solution with a viscosity range suitable for fiber spinning, acid induced hydrolysis was applied as a pre-treatment of the shredded cotton shirt. Samples were taken with about 0.05 wt% and about 0.2 wt% H2SO4Hydrolyzed to have a DP of about 760 and about 659, respectively. The viscosity η of the four hydrolyzed cotton solutions is set forth in the table below:
as indicated above, the viscosity number is from about 834 to about 88000 mPas. At a fixed cotton content, H2SO4Higher% results in lower η; and when H2SO4At% constant, higher cotton loading resulted in an increase in η. The viscosity value of the sample solution prepared in NaOH was 106 times the viscosity value of the sample solution prepared in LiOH. Without being bound by theory, cellulose in aqueous NaOH can form gels with high viscosity values. Urea can reduce or even prevent such gel formation. The use of urea makes it possible to obtain high solution viscosities without gel formation when the concentration of NaOH is about 6-8 wt.%. The NaOH content used was about 7 wt%.
FESEM images in fig. 5A-5E show the different morphologies between raw cotton fibers and recycled fibers. Fig. 5A shows a raw cotton fiber having a typical rough surface, and a twist (volumes) along the fiber length with a wide range of fiber thicknesses. In contrast, as shown in fig. 5C-5F, the regenerated fibers have a relatively smooth surface and a rod-like longitudinal morphology. No voids or defects were observed on the surface of the regenerated fibers. The structure of the regenerated fibers is generally uniform over the entire surface. The average diameter of the regenerated fibers ranges from about 27 μm to about 38 μm with a small standard deviation.
Thermogravimetric analysis (TGA) was used to evaluate the thermal behavior of fibrils, hydrolyzed fibers and regenerated fibers. According to fig. 6A-6D, all samples showed a small weight drop between 50 ℃ and 100 ℃ due to retained moisture loss and a significant weight loss between 300 ℃ and 400 ℃ due to thermal decomposition of cellulose. The initial decomposition temperature (Ti) of both the hydrolyzed and regenerated fibers was about 300 ℃, while the initial decomposition temperature of the raw cotton fibers was about 330 ℃. And no significant difference in Ti was observed between the hydrolyzed and regenerated samples.
As shown in fig. 7, fibrils, hydrolyzed fibers, and regenerated fibers were examined by using X-ray diffraction (XRD). The fibrils and the two hydrolyzed fiber samples had very similar crystallization patterns. Three diffraction peaks near 15.1 °, 17.2 °, and 22.9 ° at 2 θ were associated with the crystal planes of (110), and (200), showing the structural features of cellulose I, indicating that the crystalline form was unchanged before and after hydrolysis. During the fiber dissolution and regeneration process, some changes in the crystalline structure of the regenerated fiber occur. (110) The peaks of (1) and (110) are shifted to 12.5 ° and 20.9 °, and (200), which is a shoulder peak, is located at 20.1 °. These changes are a direct indication of the transition from cellulose I to cellulose II in the crystalline reconstitution during dissolution and fiber regeneration.
The regenerated fibers have a crystallinity of about 75-81% lower than the crystallinity of the fibrils and corresponding hydrolyzed fibers. The crystallinity (Xc) increases after hydrolysis. It is believed that hydrolysis begins in the amorphous regions of the fiber. H + ions can penetrate more easily into disordered molecular chains in amorphous regions than in highly ordered crystalline regions. Thus, the amorphous regions are partially removed during hydrolysis, which results in a higher degree of crystallinity of the hydrolyzed fiber compared to raw cotton.
The following table shows the results in different solvents, H2SO4Concentration, and cotton loading (cotton loading) tensile properties of the treated recycled fibers:
as shown above, for the samples prepared in LiOH-urea-DI, the linear density was: 0.2 to 5 percent>0.2%-3.25%>0.05% -3.25%, which may be related to the different fiber diameters shown in fig. 5E, 5D and 5C. Both tenacity and elongation vary with different formulations. The total fiber tenacity is comparable to commercial acetate fibers (acetate) and the tensile strength is comparable to cotton fibers. For two samples prepared with the same solvent system (LiOH-Urea-DI) and cotton concentration (3.25 wt%), due to the H used2SO4The increased concentration causes an increase in cotton hydrolysis, resulting in a decrease in strength of the regenerated fibers from 193MPa to 150MPa and a decrease in crystallinity from 81.2% to 78.3% as a result of the decreased DP.
Under the same solvent conditions (LiOH-urea-DI) and acid concentration (0.2 wt%), an increase in cotton loading from about 3.25 wt% to about 5 wt% resulted in a 35% strength increase. The LiOH system produced fibers with slightly higher tensile strength than 0.2% -3.25% samples prepared in two different solvent environments. The elongation at break of the fiber is 9.3% to 15.9%, falling within the typical range of textile fiber elongation that provides flexibility for both comfort and processability for yarn and fabric production. It is also believed that the mechanical properties of the regenerated fiber can be further improved by the drawing process after the fibers are coagulated.
A representative tenacity-strain curve recorded during the tensile testing of the regenerated fibers is shown in fig. 8. The recycled fibers exhibit a range of values of tenacity and percent strain, and exhibit good mechanical properties. An example of the tensile failure surface morphology is shown as an inset in fig. 8. The surface morphology shows typical particulate breaks, indicating the microstructure of the fibrous fibers. The non-smooth fractured surface is the fractured ends of particles comprising microfibrils, i.e., clusters of cellulose molecular chains formed during fiber coagulation.
As experiments have shown, post-consumer waste can be chemically recycled by using alkaline/urea aqueous solvents to produce recycled fibers with good gloss, inherent color and sufficient tensile strength for a wide range of applications in consumer products. The degree of hydrolysis, the dissolution temperature, mechanical agitation during dissolution, solvent composition, and coagulation bath composition can all be adjusted to obtain the proper quality in the regenerated fiber.
From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. In addition, many of the elements of one embodiment may be combined with other embodiments in addition to or in place of elements of other embodiments. Accordingly, the technology is not limited except as by the appended claims.