Cellulose / acetyl cellulose composite fiber and method for producing the same

Abstract

The present application provides a cellulose / acetyl cellulose composite fiber and a preparation method thereof, the preparation method comprising the following steps: mixing and crushing cellulose pulp and acetyl cellulose sheets, adding a low-concentration NMMO solution and a surfactant for stirring and impregnation, and obtaining a suspension after the material is fully mixed and impregnated; obtaining a blending spinning solution after the suspension is subjected to two-stage reduced-pressure evaporation and dehydration; and spinning the blending spinning solution by dry-jet wet spinning to obtain the composite fiber. The composite fiber prepared by the present application has the performance advantages of lyocell fiber and acetyl cellulose, excellent mechanical properties, and improved fibrillation performance. The fabric has the advantages of air permeability, skin friendliness, moisture absorption, easy drying, comfort, natural degradation, green environmental protection, and good application prospect in high-end textiles and garments.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cellulose fiber manufacturing, and particularly relates to a cellulose / acetate cellulose composite fiber and a preparation method thereof. BACKGROUND

[0002] Under the background of the increasingly serious environmental pollution caused by the shortage of petroleum resources and the extensive use of petrochemical products, the development of environmentally friendly renewable materials has become a major trend in material development. Regenerated cellulose fiber processed from natural cellulose has good moisture absorption, anti-static, strong air permeability, good dyeing properties, easy to textile processing, biodegradable and other advantages, and has been popular in the textile market for a long time, widely used in clothing, home textiles, medical and health fields, and deeply favored by consumers, becoming an important chemical fiber product for sustainable development of circular economy.

[0003] Lyocell fiber is known as "green fiber in the 21st century", which is a regenerated cellulose fiber spun by dry-wet method with wood pulp as raw pulp and N-methyl morpholine-N-oxide (NMMO) as solvent. Lyocell fiber production process is simple, the flow is short, the solvent is safe and non-toxic, the dissolution and regeneration is a physical process without chemical reaction, the solvent is closed cycle utilization, the recovery rate reaches more than 99.5%, which fundamentally eliminates the three wastes pollution caused by traditional viscose production of regenerated cellulose fiber, realizes the clean production of regenerated cellulose fiber; Lyocell fiber has high strength, good moisture absorption, better wrinkle resistance and shape retention than viscose fiber, and has incomparable advantages over other chemical fiber varieties; the product can be naturally degraded without secondary pollution problem, and is completely green and environmentally friendly.

[0004] Due to the unique high crystallinity and high orientation structure of lyocell fiber, the transverse bonding force between micro fibrils is weak, which is easy to absorb water and swell in wet environment. After mechanical external friction, the fibrils between the fibrils will separate, thus causing obvious fibrillation phenomenon, resulting in problems such as pilling, color change and fabric aging of the fabric, which seriously affects the appearance of the fabric. At present, the problem of lyocell fiber fibrillation tendency is mainly solved by crosslinking treatment of the fiber or its fabric. The crosslinking agent is mostly selected from compounds containing reactive groups, which can react with cellulose hydroxyl groups, such as polyaldehyde compounds, oligomeric polyacid, C2-C6 polyacid, triazine compounds and the like. The post-treatment crosslinking production process is long, the process is complicated, the amount of crosslinking agent is large, the wastewater is difficult to treat, the treatment time is long, the production energy consumption is high, the irritating toxic gas is produced, the mechanical properties of the fiber are greatly affected, and the anti-fibrillation effect is not durable enough.

[0005] Cellulose acetate fiber (also known as acetate fiber) is a semi-synthetic fiber obtained by chemical treatment of natural cellulose to cellulose acetate, and then spun into a kind of semi-synthetic fiber. It retains the excellent properties of cellulose such as good biocompatibility, degradability and good stability, and has the advantages of softness, smoothness, elegant luster, good moisture absorption and quick drying performance, and is widely used in high-end textiles, cigarette filters and other fields. Cellulose acetate fibers are generally dissolved in organic solvents such as acetone and dichloromethane, and then spun into fibers by dry or wet spinning. The dry strength of the fiber is only 1.0-1.3 cN / dtex, the fiber strength is low, the fiber processing difficulty increases in the later stage, and the application and promotion are limited. In the field of textile and clothing, acetate fiber is mainly blended with other fibers to make up for the lack of mechanical properties and to produce various high-performance fabrics.

[0006] If existing cellulose solvent spinning technology can be used to blend cellulose and cellulose acetate to produce composite fibers, in addition to the performance advantages of lyocell fiber and acetate fiber, by changing the aggregation state structure of the macromolecules inside the fiber, the fibrillation tendency of the fiber can be inhibited, and a new type of anti-fibrillation regenerated cellulose fiber can be developed, which has important significance.

[0007] Patent CN107475782A discloses a kind of acetate fiber and its preparation method, cellulose acetate is dissolved in NMMO aqueous solution to obtain spinning solution, and then acetate fiber is prepared by dry-jet wet spinning. This method can significantly improve the mechanical properties of the fiber, and the dry breaking strength is 3.5-5.6 cN / dtex, and the wet breaking strength is 2.6-4.5 cN / dtex. Because the degree of polymerization of cellulose acetate is low, the concentration of cellulose acetate in the spinning solution needs to be increased to prepare a high-viscosity spinning solution that meets the requirements of dry-jet wet spinning. In addition, because the cellulose acetate molecule chain has a large number of acetyl groups, its hydrophilicity is weaker than that of cellulose, and its solubility in NMMO solution is obviously not as good as that of cellulose, so increasing the composition of the spinning solution will affect the dissolution efficiency and effect, resulting in a decrease in production efficiency.

[0008] Patent CN113512777B discloses a lyocell fiber containing plant essential oil and its preparation method, plant essential oil / nano inorganic powder is mixed with functional mother liquor base solution to obtain functional mother liquor, wherein the functional mother liquor base solution is composed of cellulose, cellulose acetate, NMMO and water. The functional mother liquor is blended with lyocell spinning solution to prepare lyocell fiber containing cellulose and cellulose acetate. However, the patent does not provide a specific method for preparing the functional mother liquor base solution, and the purpose of adding cellulose acetate is only to reduce the crystallinity of the fiber by using the space hindered acetate group contained in cellulose acetate, so as to have more micropores in micro-nano size, and to accommodate and coat the plant essential oil. The influence of the addition of cellulose acetate on other properties of the fiber, such as fibrillation, moisture absorption, etc. is not mentioned.

[0009] For preparing cellulose / acetate composite fiber, the method that the person skilled in the art easily thinks of is to prepare lyocell spinning solution and acetate solution respectively, then blend the two solutions and spin by NMMO solvent method, but its disadvantages are long production process, need to increase special acetate dissolving device and mixing equipment, and the two high viscosity solutions are not easy to mix uniformly, and the production efficiency is low. Therefore, it is difficult to carry out large-scale industrial application.

[0010] There is no report in the prior art that cellulose pulp and acetate sheet raw materials are dissolved by NMMO solvent to prepare a blended spinning solution of cellulose pulp and acetate sheet, and then the blended spinning solution is spun to prepare cellulose / acetate composite fiber.

[0011] Most of the hydroxyl groups in cellulose acetate are substituted by acetyl groups, and its hygroscopicity and hydrophilicity are weaker than those of cellulose. The infiltration and swelling speed of cellulose acetate in NMMO solution is obviously slower than that of cellulose. In the previous test, the applicant found that when the blended spinning solution of cellulose pulp and acetate sheet was prepared according to the conventional preparation method of pure lyocell fiber spinning solution, the gel solution formed by the cellulose that dissolved faster wrapped the surface of the acetate cellulose particles that dissolved slower, forming a layer of mucous membrane, which hindered the diffusion of NMMO and the removal of internal moisture, and produced “white core”, resulting in incomplete dissolution of acetate cellulose, and the prepared blended spinning solution was turbid and had poor transparency. A large number of undissolved fragments or particles in the spinning solution could not be normally spun. After adjusting part of the process, the spinning stability was still poor, and the strength and elongation at break of the prepared composite fiber were low. SUMMARY

[0012] In order to solve the problems of the prior art, the present application provides a cellulose / acetate composite fiber and a preparation method thereof, which realizes the following purposes: improving the anti-fibrillation ability of the composite fiber, improving the homogeneity and spinnability of the spinning solution, and improving the strength and elongation at break of the composite fiber.

[0013] In order to realize the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0014] A preparation method of a cellulose / acetate composite fiber, the preparation method of the composite fiber comprising the following steps:

[0015] (1) After mixing and crushing the cellulose pulp and acetate sheet, low-concentration NMMO solution and surfactant are added and stirred for impregnation, so that the materials are fully mixed and infiltrated, to obtain a suspension;

[0016] (2) The suspension is subjected to two-stage evaporation and dewatering under reduced pressure to obtain a blended spinning solution;

[0017] (3) The blended spinning solution is filtered, and then is spun by dry-jet wet spinning, is solidified and shaped in a coagulation bath, and then is drawn, washed, and dried to obtain the composite fiber.

[0018] In the step (1), the cellulose pulp has a polymerization degree of 600-1000.

[0019] In the step (1), the cellulose acetate sheet has a polymerization degree of 200-400 and a substitution degree of 1.7-2.6, preferably 2.2-2.5.

[0020] In the step (1), the mixed mass of the cellulose and the cellulose acetate is 70-95:5-30, preferably 80-90:10-20.

[0021] In the step (1), the mass concentration of the NMMO solution is 50-65%.

[0022] In the step (1), the immersion bath ratio (total mass of the cellulose and the cellulose acetate:NMMO solution mass) is 1:8-20, the stirring speed is 20-60 rpm, the immersion temperature is 50-60°C, the immersion time is 20-60 min, preferably 20-40 min, and the immersion pressure is 15-40 kPa.

[0023] In the step (1), the surfactant can improve the wetting and penetration effect of the NMMO solution on the cellulose and the cellulose acetate sheet. The surfactant is one or more of a fatty alcohol polyoxyethylene ether, a fatty amine polyoxyethylene ether, and an aromatic polyoxyethylene ether, and is added in an amount of 0.02-0.1% of the total mass of the cellulose and the cellulose acetate.

[0024] The present application prolongs the immersion time of the NMMO solution on the raw material by setting the immersion process, so that the solvent fully penetrates and diffuses into the raw material particles, which is a prerequisite and guarantee for preparing a spinning solution with good homogeneity.

[0025] In the present application, the raw material is crushed and mixed with a low-concentration NMMO solution which has no dissolving ability for cellulose at a low temperature. The large immersion bath ratio can make the raw material rapidly and uniformly dispersed in the NMMO solution, ensuring the uniformity of the mixture of the raw material and the NMMO solution. At the same time, it also avoids the increase in viscosity of the system caused by the too fast and excessive swelling of the cellulose in a high-temperature and high-concentration NMMO solution, which hinders the penetration and diffusion of the solvent into the interior of the raw material particles. The immersion is carried out under reduced pressure, which can remove the air in the micropores in the interior of the raw material particles, so that the solvent can more easily penetrate into the interior of the particles, which is beneficial to shorten the immersion time. The addition of the surfactant can accelerate the penetration of the solvent into the interior of the raw material particles, increase the swelling of the raw material, shorten the immersion time, and improve the uniformity of the immersion.

[0026] In the step (2), in the two-stage evaporation dehydration under reduced pressure, the first-stage evaporation dehydration under reduced pressure is carried out under the conditions of stirring and dehydration temperature of 80-90 DEG C, the dehydration pressure is controlled to be between 5-15 kPa, and the dehydration time is 20-60 min; the mass ratio of NMMO to water in the pre-swelling solution is 74-82:18-26.

[0027] In the first-stage evaporation dehydration under reduced pressure, the concentration and temperature of the NMMO solution are increased to a range suitable for swelling, and the dehydration speed is controlled by the dehydration pressure, the swelling time is prolonged, and the material is ensured to swell slowly, uniformly and sufficiently, so that the cellulose is prevented from swelling too fast to form a package to hinder the diffusion of the solvent, and the cellulose is prevented from swelling insufficiently, and the uniformity and sufficiency of the dissolution are affected.

[0028] In the step (2), in the two-stage evaporation dehydration under reduced pressure, the second-stage evaporation dehydration under reduced pressure is carried out under the conditions of stirring and dehydration temperature of 95-105 DEG C, the dehydration pressure is controlled to be between 3-10 kPa, and the residual excess water is removed, and the material is dissolved to obtain a homogeneous blending spinning solution.

[0029] In the step (2), in the blending spinning solution, the total mass concentration of the cellulose and the cellulose acetate is 8-15%, preferably 10-14%.

[0030] In the step (3), in the dry-jet wet spinning, the air gap length is 20-60 mm, the coagulation bath is a 10-25 wt% NMMO solution, the coagulation bath temperature is 10-25 DEG C, the spinning speed is 38-42 m / min, and the spinning air blowing temperature is 19-21 DEG C.

[0031] In the composite cellulose, the content of the cellulose acetate is 5-30%, preferably 10-20%.

[0032] The application utilizes the characteristics that the cellulose and the cellulose acetate can be dissolved in the NMMO solution, and through the processes of immersion, swelling and dissolution of the cellulose and the cellulose acetate raw materials in the NMMO solutions with low, medium and high concentrations, the technical problems caused by the differences in the dissolution performance and efficiency of the cellulose and the cellulose acetate are solved, a homogeneous blending spinning solution is finally prepared, and the blending spinning solution has good spinnability; the dry-jet wet spinning is adopted, which is beneficial to high-ratio drafting, and the prepared composite fiber has good mechanical properties. Since the hydroxyl groups in the cellulose macromolecule are hydrophilic, and the hydroxyl groups on the cellulose macromolecule in the cellulose acetate are mostly replaced by hydrophobic acetyl groups, the cellulose composite fiber prepared by the application can absorb and remove water from the human body surface layer, and has certain moisture absorption and quick-drying properties, and the fabric processed therefrom is more comfortable to wear.

[0033] The introduction of cellulose acetate in the present application, in the process of spinning and solidification, the cellulose macromolecule is hindered by part of the cellulose acetate molecules when crystallizing and orienting, the high crystallization tendency of the cellulose macromolecule is reduced, the degree of crystallization and orientation is reduced, the size of the crystal region is reduced, the micro-aggregated structure of the obtained fiber is more uniform, the tendency of the intermolecular aggregation into microfibrils is weakened, and the anti-fibrillation performance of the fiber is enhanced.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] (1) The present application directly dissolves the cellulose and cellulose acetate blend in the NMMO solution to prepare a blended spinning solution, the homogeneity and spinnability of the spinning solution are good, the transparency of the spinning solution is high, the raw materials are fully dissolved, and the spinning is stable.

[0036] (2) The cellulose / cellulose acetate composite fiber prepared by the present application has the performance advantages of lyocell fiber and acetate fiber, and has excellent mechanical properties, and the fibrillation performance is improved. The dry breaking strength of the composite fiber prepared by the present application is 3.1-4.0 cN / dtex, the wet breaking strength is 2.7-3.6 cN / dtex, the dry breaking elongation is 11.4-14.6%, the moisture absorption rate is 9.8-11.2%, and the fibrillation index is 2.8-3.6.

[0037] (3) The present application relies on the existing mature Lyocell fiber production device, and is easy to realize industrialized production and has application value.

[0038] (4) The present application is environmentally friendly, the raw materials used come from natural and renewable cellulose, the processing process is green and environmentally friendly, the product has natural degradability and biocompatibility, and will not cause secondary pollution, which meets the needs of sustainable development of today's society. The fabric prepared by the composite fiber of the present application is breathable, skin-friendly, smooth and soft, moisture-absorbing and easy to dry, and can better meet the use requirements of high-end textiles and garments, and has good market prospect. DETAILED DESCRIPTION

[0039] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the claims attached hereto.

[0040] Example 1

[0041] Cellulose pulp with a degree of polymerization of 760 and acetate sheet with a degree of polymerization of 300 and a degree of substitution of 2.2 were mixed and crushed in a mass ratio of 95:15, then added to a 60wt% NMMO solution, the mass ratio of the total mass of cellulose and cellulose acetate to the mass of the NMMO solution was 1:11, and a fatty alcohol polyoxyethylene ether was added, the amount of which was 0.05% of the total mass of cellulose and cellulose acetate, under the conditions of a pressure of 20kPa, a temperature of 60℃, and a stirring speed of 40rpm, the material was impregnated for 40min to obtain a well-dispersed suspension.

[0042] The suspension was subjected to two-stage vacuum evaporation dehydration under stirring and heating to obtain a pre-swelling liquid and a blended spinning liquid, respectively. In the first stage of vacuum evaporation dehydration, the suspension was heated to 85℃, the dehydration pressure was controlled between 5~15kPa, and the dehydration time was 35min to obtain a viscous pre-swelling liquid, the mass ratio of NMMO to water in the pre-swelling liquid was 78:22; in the second stage of vacuum evaporation dehydration, the pre-swelling liquid was heated to 98℃, the dehydration pressure was controlled between 3~10kPa, and the material was gradually dehydrated to a mass ratio of NMMO to water in the system of about 87:13, after the material was fully dissolved, a homogeneous blended spinning liquid was obtained, the total mass (total solid mass) content of cellulose and cellulose acetate in the blended spinning liquid was 11.7%.

[0043] The blended spinning liquid was filtered and subjected to dry-jet wet spinning, the spinning speed was 40m / min, the air gap length was 30mm, the spinning air blowing temperature was 20℃, the coagulation bath was a 20wt% NMMO aqueous solution, the temperature was 20℃, after solidification, drawing and washing, the cellulose / cellulose acetate composite short fiber was obtained.

[0044] The final cellulose composite short fiber had a dry breaking strength of 3.6cN / dtex, a wet breaking strength of 3.1cN / dtex, a dry breaking elongation of 13.2%, a moisture absorption rate of 10.7%, and a fibrillation index of 2.8.

[0045] Example 2

[0046] Cellulose pulp with a degree of polymerization of 930 and acetate sheet with a degree of polymerization of 200 and a degree of substitution of 2.6 were mixed and crushed in a mass ratio of 70:30, then added to a 50wt% NMMO solution, the mass ratio of the total mass of cellulose and cellulose acetate to the mass of the NMMO solution was 1:20, and a fatty alcohol polyoxyethylene ether was added, the amount of which was 0.1% of the total mass of cellulose and cellulose acetate, under the conditions of a pressure of 15kPa, a temperature of 60℃, and a stirring speed of 60rpm, the material was impregnated for 20min to obtain a well-dispersed suspension.

[0047] The suspension is subjected to two-stage evaporation dehydration under stirring and heating to obtain a pre-swelling liquid and a blending spinning liquid, wherein the suspension is heated to 80°C in the first-stage evaporation dehydration, the dehydration pressure is controlled to be between 5-15 kPa, and the dehydration is performed for 60 min to obtain a viscous pre-swelling liquid, and the mass ratio of NMMO to water in the pre-swelling liquid is 74:26; in the second-stage evaporation dehydration, the pre-swelling liquid is heated to 95°C, the dehydration pressure is controlled to be between 3-10 kPa, and the dehydration is gradually performed until the mass ratio of NMMO to water in the system is about 87:13, and the homogeneous blending spinning liquid is obtained after the material is fully dissolved, and the total mass content (total solid mass content) of cellulose and cellulose acetate in the blending spinning liquid is 8.1%.

[0048] The blending spinning liquid is filtered and subjected to dry-jet wet spinning, the spinning speed is 40 m / min, the air gap length is 20 mm, the spinning air blowing temperature is 20°C, the coagulation bath is a 10 wt% NMMO aqueous solution, the temperature is 25°C, the nascent fiber is obtained after solidification in the coagulation bath and drawing, and then the cellulose / cellulose acetate composite short fiber is obtained after washing, oiling and drying.

[0049] The finally obtained cellulose composite short fiber has a dry breaking strength of 3.1 cN / dtex, a wet breaking strength of 2.7 cN / dtex, a dry breaking elongation of 11.4%, a moisture absorption rate of 9.8%, and a fibrillation index of 3.1.

[0050] Example 3

[0051] The cellulose pulp with a degree of polymerization of 600 and the acetate sheet with a degree of polymerization of 400 and a degree of substitution of 1.7 are mixed and crushed at a mass ratio of 95:5, and then added to a 65 wt% NMMO solution, the mass ratio of the total mass of cellulose and cellulose acetate to the mass of the NMMO solution is 1:8, and a fatty amine polyoxyethylene ether is added at an amount of 0.02% of the total mass of cellulose and cellulose acetate, and the material is fully mixed and infiltrated under the conditions of a pressure of 40 kPa, a temperature of 50°C, and a stirring speed of 20 rpm to obtain a well-dispersed suspension.

[0052] The suspension is subjected to two-stage evaporation dehydration under stirring and heating to obtain a pre-swelling liquid and a blending spinning liquid, wherein the suspension is heated to 90°C in the first-stage evaporation dehydration, the dehydration pressure is controlled to be between 5-15 kPa, and the dehydration is performed for 20 min to obtain a viscous pre-swelling liquid, and the mass ratio of NMMO to water in the pre-swelling liquid is 82:18; in the second-stage evaporation dehydration, the pre-swelling liquid is heated to 103°C, the dehydration pressure is controlled to be between 3-10 kPa, and the dehydration is gradually performed until the mass ratio of NMMO to water in the system is about 87:13, and after the material is fully dissolved, a homogeneous blending spinning liquid is obtained, and the total mass (total solid mass) content of cellulose and cellulose acetate in the blending spinning liquid is 14.4%.

[0053] After the blending spinning liquid is filtered, dry-jet wet spinning is performed, the spinning speed is 40 m / min, the air gap length is 60 mm, the spinning air blowing temperature is 20°C, the coagulation bath is a 25wt% NMMO aqueous solution, the temperature is 10°C, and after solidification, drawing in the coagulation bath, nascent fibers are obtained, and then after washing, oiling and drying, cellulose / cellulose acetate composite short fibers are obtained.

[0054] The finally prepared cellulose composite short fibers have a dry breaking strength of 4.0 cN / dtex, a wet breaking strength of 3.6 cN / dtex, a dry breaking elongation of 14.6%, a moisture absorption rate of 11.2%, and a fibrillation index of 3.6.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that only cellulose pulp (i.e., the mass ratio of cellulose to cellulose acetate is 100:0) is used to prepare pure lyocell fibers, and other processes and conditions are the same as those in Example 1.

[0057] The finally prepared pure lyocell fibers have a dry breaking strength of 4.2 cN / dtex, a wet breaking strength of 3.7 cN / dtex, a dry breaking elongation of 13.9%, a moisture absorption rate of 11.7%, and a fibrillation index of 6.7.

[0058] As can be seen from Comparative Example 1 and Examples 1-3, with the increase of the cellulose acetate content in the fiber, the mechanical strength of the fiber decreases, which is related to the structural change of the fiber. On the one hand, the degree of polymerization of the cellulose acetate is relatively low, the length of the macromolecular segment is short, and the hydroxyl groups on the cellulose acetate macromolecule after acetylation are less, the molecular force is weak, and the hydrogen bonds between the cellulose macromolecules are less, resulting in the decrease of the mechanical strength of the fiber; on the other hand, the addition of cellulose acetate changes the aggregate structure of the cellulose macromolecule to some extent, such as the decrease of the crystallinity and orientation degree, the decrease of the size of the crystalline region, etc., which is also an important factor leading to the decrease of the mechanical strength of the composite fiber. It can also be seen that the anti-fibrillation performance of the composite fiber obtained after adding cellulose acetate is obviously improved compared with the pure lyocell fiber.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is only that the first-stage dehydration by evaporation under reduced pressure is omitted, and the suspension is directly subjected to dehydration and dissolution under the process conditions of the second-stage dehydration by evaporation under reduced pressure to obtain the blended spinning solution. The other process procedures and conditions are the same as those of Example 1.

[0061] Compared with Example 1, the homogeneity of the blended spinning solution prepared in this comparative example is slightly poor, the transparency is low, a large number of gel groups can be observed in the spinning solution under a microscope, the spinning stability is poor, the breakage rate is high, and the strength of the finally spun fiber is obviously low.

[0062] The dry breaking strength of the cellulose composite short fiber prepared in Comparative Example 2 is 2.9 cN / dtex, the wet breaking strength is 2.4 cN / dtex, the dry breaking elongation is 11.6%, the moisture absorption rate is 10.4%, and the fibrillation index is 2.9.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 1 is that the dipping process is cancelled, and the other process procedures and conditions are the same as those of Example 1.

[0065] The blended spinning solution prepared in this comparative example is turbid, a large number of undissolved fragments or particles can be observed in the spinning solution under a microscope, and normal spinning cannot be carried out.

[0066] Comparative Example 4

[0067] The cellulose pulp with a degree of polymerization of 760 and the acetate sheet with a degree of polymerization of 300 and a degree of substitution of 2.2 are mixed and crushed in a mass ratio of 95:15, then added to a 74wt% NMMO solution, the mass ratio of the total mass of cellulose and cellulose acetate to the mass of the NMMO solution is 1:9, and the pre-swelling liquid is obtained by soaking and swelling at normal pressure, a temperature of 80℃, and a stirring speed of 40rpm for 40min; then the pre-swelling liquid is heated to 98℃, the dehydration pressure is controlled between 3~10kPa, and gradually dehydrated until the mass ratio of NMMO to water in the system is about 87:13, after the material is dissolved, the blending spinning liquid is obtained, and the total mass (total solid mass) content of cellulose and cellulose acetate in the blending spinning liquid is 11.7%.

[0068] The blending spinning liquid prepared in the present comparative example is turbid, has a "white core" phenomenon, and a large number of undissolved fragments or particles can be observed under a microscope, and normal spinning cannot be performed.

[0069] The above only describes the preferred embodiments of the present application and is not used to limit the present application. The remaining matters of the present application belong to the common knowledge of those skilled in the art. Based on the basic principles of the present application, combined with the technical solution features of the foregoing embodiments and the description in the specification, those skilled in the art can still make several modifications, equivalent replacements, or improvements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing a cellulose / acetyl cellulose composite fiber, characterized by: The preparation method of the composite fiber comprises the following steps: (1) After mixing and crushing cellulose pulp and cellulose acetate sheets, low-concentration NMMO solution and a surfactant are added for stirring and impregnation to fully mix and soak the materials, so as to obtain a suspension; The surfactant is one or more of fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether and aromatic polyoxyethylene ether, and the addition amount is 0.02-0.1% of the total mass of the cellulose pulp and the cellulose acetate; The impregnation bath ratio is 1:8-20, the stirring speed is 20-60 rpm, the impregnation temperature is 50-60℃, the impregnation time is 20-60 min, and the impregnation pressure is 15-40 kPa; (2) After two-stage reduced-pressure evaporation and dehydration of the suspension, a blended spinning solution is obtained; The two-stage reduced-pressure evaporation and dehydration comprises first-stage reduced-pressure evaporation and dehydration and second-stage reduced-pressure evaporation and dehydration; the first-stage reduced-pressure evaporation and dehydration is performed by heating the suspension to 80-90℃, controlling the dehydration pressure to be 5-15 kPa, and dehydrating for 20-60 min; the mass ratio of NMMO to water in the material obtained after the first-stage reduced-pressure evaporation and dehydration is (74:26)-(82:18); The second-stage reduced-pressure evaporation and dehydration is performed by heating the material obtained after the first-stage reduced-pressure evaporation and dehydration to 95-105℃, controlling the dehydration pressure to be 3-10 kPa, to obtain the blended spinning solution; the total mass concentration of cellulose and cellulose acetate in the blended spinning solution is 8-15%; (3) The blended spinning solution is spun by dry-jet wet spinning to obtain the composite fiber.

2. The method of producing a cellulose / cellulose acetate composite fiber according to claim 1, characterized by: In step (1), the degree of polymerization of the cellulose pulp is 600-1000; the degree of polymerization of the cellulose acetate sheets is 200-400, and the degree of substitution is 1.7-2.6; the mass ratio of the cellulose pulp to the cellulose acetate sheets is (70-95):(5-30); and the mass concentration of the NMMO solution is 50-65%.

3. The method of producing a cellulose / cellulose acetate composite fiber according to claim 1, characterized by: In step (3), when the dry-jet wet spinning is performed, the air gap length is 20-60 mm, the coagulation bath is 10-25 wt% NMMO solution, and the coagulation bath temperature is 10-25℃.

4. A cellulose / acetyl cellulose composite fiber produced by the production method according to any one of claims 1 to 3, characterized by: The content of cellulose acetate in the composite fiber is 5-30%, the dry breaking strength is 3.1-4.0 cN / dtex, the wet breaking strength is 2.7-3.6 cN / dtex, the dry breaking elongation is 11.4-14.6%, the moisture absorption rate is 9.8-11.2%, and the fibrillation index is 2.8-3.6.