Preparation method of regenerated cellulose fiber and regenerated cellulose fiber

Abstract

The invention belongs to the field of regenerated cellulose fibers, and discloses a preparation method of regenerated cellulose fibers and regenerated cellulose fibers.The preparation method comprises the following steps that 1, pretreatment is conducted, specifically, part of hydroxyl of cellulose pulp is subjected to substitution treatment, and modified cellulose pulp with the substitution degree of 0.001-2.0 is prepared; 2) mixing the unmodified cellulose pulp and the modified cellulose pulp, and then mixing and swelling with an NMMO solution; and 3) dissolving, spinning and post-processing under a vacuum condition to obtain a regenerated cellulose fiber product. The preparation method comprises the following steps: pretreating cellulose to obtain modified cellulose pulp of which hydroxyl is partially substituted; and then different fiber pulps are physically blended to prepare the spinning solution, so that the purpose of improving fibrillation can be achieved, and meanwhile, the mechanical property of the fiber can be ensured. Compared with a traditional cross-linking method, toxic chemicals, water washing, acid washing and the like are not introduced, emission of harmful substances and waste water is reduced, and meanwhile energy consumption caused by cross-linking agent reaction and the like is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of regenerated cellulose fibers, and specifically relates to a method for preparing regenerated cellulose fibers and regenerated cellulose fibers; more specifically, it relates to a method for pretreating cellulose pulp raw materials and a method for preparing cellulose fibers by mixing different cellulose raw materials. Background Art

[0002] Regenerated cellulose fiber is a man-made fiber made from natural cellulose or other cellulose-containing raw materials through chemical treatment. The raw materials of regenerated cellulose fiber can come from waste paper, wood pulp, crop straw, sugarcane bagasse, etc., which are transformed into spinnable fibers through multiple chemical treatment processes. Regenerated cellulose fiber has the characteristics of biodegradability, hygroscopicity and breathability. At the same time, it also has good dyeability and washability, is not easy to deform, has good elasticity, and has been widely used. However, regenerated cellulose fiber will cause poor fiber fibrillation under wet friction conditions, which seriously affects the quality of yarn and fabric. At present, the main way to solve the easy fibrillation of Lyocell cellulose fiber is to cross-link the fiber or fiber fabric after treatment, such as:

[0003] The patent with publication number CN104005225A reports that the fiber is immersed in a solution containing a cross-linking agent, a catalyst and a penetrant, and after preliminary rolling and drying, the fiber is pre-treated and baked to solidify the cross-linking, and then washed with warm soft water and cold soft water to obtain the anti-fibrillation Lyocell fiber. The method is simple in process and can be used in the industrial production line of lyocell fiber. However, the steps of preheating and baking time in this method will not only cause the mechanical properties of the fiber to decrease, but also the catalysts, surfactants and other substances introduced to improve the cross-linking efficiency also increase the discharge amount of wastewater and the difficulty of treatment.

[0004] The patent with publication number CN113718350A discloses a method of adding a crosslinking agent to an oil agent. To prevent the crosslinking agent from reacting with water, the crosslinking agent is first end-capped, and then the crosslinking agent is de-end-capped by setting the fiber drying temperature to achieve the effect of the crosslinking agent continuing to react with the hydroxyl groups in the cellulose. This method can effectively reduce the fibrillation of the fiber, and Lyocell fiber can be processed using only conventional preparation processes, saving steaming and other processes, and greatly saving costs; however, some functional groups of the crosslinking agent are easily activated and difficult to control when being de-end-capped.

[0005] The patent with publication number CN114457591A discloses a kind of cellulose fiber that is resistant to fibrillation and its preparation method. By adding an aldehyde-free crosslinking agent, a glycidyl ether type epoxy resin, during the spinning or post-treatment process of cellulose fiber, the glycidyl ether type epoxy resin is cross-linked to cellulose under appropriate content, proportion and reaction conditions to prepare cellulose fiber that is resistant to fibrillation, thereby solving the problem that cellulose fiber is easy to fibrillate. However, this method still needs to add a glycidyl ether type epoxy resin as a crosslinking agent, which is costly and requires subsequent processing.

[0006] In addition, the chemical cross-linking methods mentioned above generally have problems such as toxicity and insufficient process stability, which have changed the green and environmentally friendly properties of the new solvent-based cellulose fibers.

[0007] In summary, a green and simple method is currently needed to improve the fibrillation problem of Lyocell fiber while ensuring the mechanical properties of the fiber. This method can not only eliminate the toxic problems caused by the currently used cross-linking agents, but also reduce the wastewater discharge and NMMO recovery problems caused by the introduction of cross-linking agent catalysts, water washing and acid washing.

[0008] In view of this, the present invention is proposed. Summary of the invention

[0009] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing regenerated cellulose fiber and regenerated cellulose fiber. The present invention pre-treats cellulose to obtain modified cellulose pulp in which hydroxyl groups are partially substituted; then, unmodified cellulose pulp is pre-mixed with NMMO solution and then mixed with modified cellulose pulp, thereby achieving full swelling of unmodified cellulose pulp in NMMO solution and uniform dispersion of modified pulp in the mixed system, increasing the lateral bonding between molecular chains by hydrogen bonding of hydroxyl groups, affecting the change of fiber aggregation structure, and improving the anti-fibrillation performance of the fiber. In addition, the mixing method between the pre-treated pulp and the untreated pulp of the present invention is a purely physical method, without the need to add any reaction reagents, thereby reducing the energy consumption of later fiber washing.

[0010] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0011] The present invention provides a method for preparing solvent-processed regenerated cellulose fibers, comprising the following steps:

[0012] 1) Pretreatment: Substituting part of the hydroxyl groups of cellulose pulp to prepare modified cellulose pulp with a degree of substitution of 0.001 to 2.0;

[0013] 2) Mixing unmodified cellulose pulp with modified cellulose pulp, and then mixing with NMMO solution to swell,

[0014] 3) Dissolving, spinning and post-processing under vacuum conditions to obtain regenerated cellulose fiber products.

[0015] The present invention provides a method for preparing regenerated cellulose fiber by a new solvent method, wherein cellulose pulp is pretreated, heterochains / heterogroups are introduced, and modified cellulose pulp with partially substituted hydroxyl groups is obtained; then, unmodified cellulose pulp is mixed with modified cellulose pulp, and then mixed and swollen with NMMO solution, and then dehydrated and dissolved under certain vacuum conditions to obtain a uniformly dissolved cellulose solution. The pretreatment method provided by the present invention is simple and easy to control, does not affect the green preparation process of the fiber, and different pulps can be physically blended to achieve the purpose of improving fibrillation, while not affecting the mechanical properties of the fiber, ensuring the quality of the fiber, and not changing the existing process of fiber industrialization. Compared with the traditional crosslinking method, no toxic chemicals, water washing and acid washing are introduced, which reduces the discharge of harmful substances and wastewater, and reduces the energy consumption caused by the crosslinking agent reaction.

[0016] In the present invention, the modified pulp selectively replaces part of the hydroxyl groups in the cellulose molecular chain by introducing hybrid groups (carboxymethyl, methyl, hydroxyethyl or acetyl, etc.) on the original cellulose chain. When the cellulose chain crystallizes, the hybrid groups can only be dispersed in the amorphous region because it is difficult to enter the crystalline region. The arrangement of the cellulose chain where the hybrid groups are located is hindered, resulting in a decrease in the overall orderliness of the fiber arrangement, which is not conducive to fiber crystallization; at the same time, the molecular chains with reduced orderliness increase the lateral bonding through the action of hydroxyl groups. Therefore, after the modified pulp is mixed with the unmodified pulp, the hybrid groups also play a role in disrupting the molecular arrangement and strengthening the lateral bonding in the blending system. The fibrillation of Lyocell fibers is mainly caused by the highly ordered arrangement and orientation of the molecular chains, which leads to weak lateral connections between the molecular chains. Therefore, the present invention can achieve the purpose of improving fiber fibrillation mainly by mixing modified pulp and unmodified pulp (physical mixing). The mixing of modified cellulose pulp and unmodified cellulose pulp is purely physical mixing, which mainly relies on the hydrogen bonding of hydroxyl groups to increase the lateral bonding between molecular chains, affecting the change of fiber aggregation structure. Compared with cross-linked fibers, it shortens the process flow and greatly reduces the equipment investment and the complexity of the preparation process.

[0017] The water retention of cellulose is the best when no substitution reaction occurs. The higher the degree of substitution, the worse the water retention. The degree of substitution of the modified cellulose pulp is controlled within the range of 0.001 to 2.0.

[0018] The substitution degree range is mainly determined by the solubility of the modified pulp in NMMO. After pulp modification, the hydrophilicity decreases due to the presence of hybrid groups. The higher the substitution degree and the lower the hydrophilicity, the greater the possibility that the cellulose chain is insoluble in NMMO. For example, the carboxymethyl cellulose, methyl cellulose and hydroxyethyl cellulose mentioned in the invention can be better dissolved in NMMO solution and then mixed with unmodified pulp when the substitution degree range is 0.001-0.5 and the substitution degree range of cellulose acetate is 0.5-2.0.

[0019] In the present invention, different means can be used to pretreat cellulose pulp to obtain modified cellulose pulp with different degrees of substitution.

[0020] In a further embodiment, in step 1), the substitution treatment comprises esterification, carboxymethylation, methylation, oxidation or hydroxyethylation of the cellulose pulp.

[0021] In the present invention, the manner or means of esterification, carboxymethylation, methylation, oxidation or hydroxyethylation of cellulose pulp is not limited, and any existing technology can be used. The substitution treatment can be completed in one step or multiple steps, as long as the degree of substitution is controlled within the range of 0.001 to 2.0.

[0022] As a scheme, in step 1), the cellulose pulp is first alkalized and then subjected to an etherification reaction to generate carboxymethyl cellulose, methyl cellulose or hydroxyethyl cellulose with a degree of substitution of 0.001 to 0.5.

[0023] In a further embodiment, the reagents used in the etherification reaction include but are not limited to chloroacetic acid, chloroformic acid, dimethyl sulfate, etc., and the types of modified pulp prepared are different due to different etherification reagents.

[0024] In the present invention, the modified cellulose that meets the degree of substitution requirement can be directly prepared, or the cellulose with a high degree of substitution can be first prepared and then hydrolyzed to make the degree of substitution of the modified cellulose meet the requirement.

[0025] As another scheme, in step 1), cellulose pulp is subjected to esterification reaction to obtain cellulose acetate, and then subjected to secondary hydrolysis to make its degree of substitution 0.5 to 2.0;

[0026] Preferably, cellulose acetate needs to be physically crushed to a particle size of <1000 μm before hydrolysis, preferably <500 μm.

[0027] The purpose of crushing is to make the two pulps mix better. Since cellulose acetate is solid, it can be mixed more fully with unmodified pulp after crushing. Modified pulps such as methyl cellulose are basically water-soluble and can be fully mixed with unmodified pulp after being dissolved in NMMO, so crushing is not required.

[0028] In a further embodiment, the solution used for the secondary hydrolysis is selected from the group consisting of aqueous NaOH solution, NaOH and ethanol solution, acetic acid solution, and aqueous solution;

[0029] Preferably, the temperature of the solution used in the secondary hydrolysis is 10-125°C, the concentration is 0-1.0 mol / L, the secondary hydrolysis time is 0.1-15h, and the degree of polymerization of the pulp after hydrolysis is 200-800; after the secondary hydrolysis, the modified pulp is washed to neutrality for subsequent use.

[0030] Furthermore, after the preparation of the modified cellulose pulp is completed, it needs to be washed with water, and the pH range of the washing liquid is 7-12.

[0031] In a further embodiment, in step 2), the unmodified cellulose pulp is premixed with the NMMO solution and then mixed with the modified cellulose pulp.

[0032] Preferably, the modified cellulose pulp accounts for 1%-10% of the total weight of all raw pulp, preferably 1%-5%.

[0033] Furthermore, the degree of polymerization of the unmodified cellulose pulp is 500-1500.

[0034] In a further embodiment, unmodified cellulose pulp is premixed with a NMMO solution having a mass concentration of 70% to 84%, the mixing temperature is 70 to 100° C., and the time is ≥ 5 min, preferably 5 to 30 min;

[0035] Then, the mixture is rapidly mixed with modified cellulose pulp at a mixing temperature of 80-110° C. for a time of ≥2 min, preferably 2-10 min.

[0036] According to the required cellulose concentration, the mass ratio of NMMO to the total amount of raw pulp is determined. Of the total amount of raw pulp, modified cellulose pulp accounts for 1%-10%, and the rest is unmodified cellulose pulp. Modified cellulose pulp is a crushed pulp, and its mixing efficiency with solvent is high. Therefore, the method of premixing unmodified cellulose pulp with NMMO solvent and then mixing it with modified cellulose pulp can effectively reduce the solubility difference between pulps, which is conducive to the uniform dissolution of the cellulose system and makes the stock solution quality more excellent.

[0037] In a further embodiment, in step 3), the vacuum degree of the dissolution process is controlled to be 0-10Kpa absolute pressure and the temperature is 90-130°C;

[0038] Preferably, the absolute vacuum pressure during the dissolution process is controlled to be 3-8 KPa and the temperature to be 105-120°C.

[0039] In a further solution, in step 3), during spinning, the temperature of the spinning solution is controlled to be 90-130°C, the aperture of the spinneret is 0.05-0.3 mm, the air gap cooling height is 5-200 mm, and the process conditions of the post-processing system are adjusted at the same time, the cellulose fibers are subjected to a tension suitable for each preparation stage, and the tow is continuously spun at a spinning speed of 20-500 m / min to obtain a finished product. The fiber spinning process includes washing, oiling, drying, packaging and winding.

[0040] In addition, the method of the present invention has a wider range of dissolution and spinning conditions than conventional ones. Generally, the spinning speed of Lyocell fiber is about 38 m / min, while the spinning solution prepared by the present invention can be spun at a high spinning speed.

[0041] The present invention also provides a regenerated cellulose fiber prepared by the preparation method as described above, wherein the wet friction time of the regenerated cellulose fiber is greater than 10s, the dry tensile strength is 3.4-3.9 cN / dtex, and the dry elongation is 9%-10%;

[0042] Preferably, the wet friction time of the regenerated cellulose fiber is 11.9s to 18.4s.

[0043] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0044] 1) The preparation method of cellulose fiber provided by the present invention first modifies cellulose pulp by pretreatment, that is, esterification, carboxylmethylation, methylation, oxidation or hydroxyethylation of part of the hydroxyl groups. This process only introduces a small amount of heterochains, which are still cellulose derivatives, without introducing new substances, and has good compatibility with the Lyocell system. The pretreatment reaction steps are simple and easy to obtain.

[0045] 2) In the method for preparing cellulose fibers provided by the present invention, no chemical reaction occurs during the fiber preparation process, and the mixing of modified cellulose pulp and unmodified cellulose pulp is purely physical mixing, which mainly relies on the hydrogen bonding effect of hydroxyl groups to increase the lateral bonding between molecular chains, affecting the change of the fiber aggregation structure. Compared with cross-linked fibers, the process flow is shortened, and the equipment investment and the complexity of the preparation process are greatly reduced.

[0046] 3) The method for preparing cellulose fibers provided by the present invention does not require the introduction of new equipment in the mixing process of different cellulose pulps. The purpose is achieved mainly by controlling the pre-mixing and re-mixing temperature and time. The operation is simple and can be directly operated on the existing production line without adding additional costs.

[0047] 4) The preparation method of cellulose fiber provided by the present invention uses less modified pulp, and although the pretreatment process involves chemical reactions and water washing procedures, it significantly reduces the production cost compared to the water washing and drying energy consumption of cross-linked fibers.

[0048] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0050] Figure 1 It is a schematic diagram of the steps of the pulp pretreatment method of the present invention;

[0051] Figure 2 is a flow chart of the preparation of the fiber of the present invention;

[0052] Figure 3 is a morphology diagram of the regenerated cellulose fiber prepared in Example 2 of the present invention;

[0053] Figure 4 is a morphology diagram of the regenerated cellulose fiber prepared in Comparative Example 1 of the present invention;

[0054] The specific reference numerals are:

[0055] 1: Mixing kettle, 2: Discharging pump, 3: Vacuum pump, 4: Dissolving kettle, 5: Spinneret, 6: Coagulation bath, 7: Water washing device.

[0056] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0058] It should be noted that the spinning of the present invention can be carried out using conventional technical conditions in the art. As a scheme, when spinning, the temperature of the spinning solution is controlled to be 90-130°C, the spinneret aperture is 0.05-0.3mm, and the air gap cooling height is 5-200mm. At the same time, the process conditions of the post-processing system are adjusted so that the cellulose fibers are subjected to the tension suitable for each preparation stage, so that the filament bundle is continuously spun at a spinning speed of 20-500m / min to form the finished product. The Lyocell fiber spinning process includes washing, oiling, drying, packaging or winding in sequence.

[0059] The esterification reaction and etherification reaction described in the present invention all adopt conventional technical conditions.

[0060] It should be noted that the specific spinning conditions of the following embodiments and comparative examples of the present invention are the same.

[0061] Indicator detection method:

[0062] The wet friction test adopts FZ / T 52019-2018 "Lyocell Staple Fiber". Under a constant rotation speed, the wet friction time corresponds to the number of wet frictions. The longer the wet friction time or the more wet friction times, the stronger the anti-fibrillation ability.

[0063] The dry tensile strength / (cN / dtex) and dry elongation / (%) are measured for the mechanical properties of fibers with reference to GB / T 14337-2022 "Test method for tensile properties of chemical staple fibers".

[0064] Example 1

[0065] (1) Cellulose pulp is subjected to esterification reaction to generate cellulose acetate, which is then crushed in a grinder to a particle size of about 500 μm for later use. An appropriate amount of cellulose acetate is then placed in an alkaline alcohol solution (NaOH and ethanol solution) with a concentration of 0.5 mol / L and reacted at 40°C for 60 min. After washing with water, modified cellulose pulp (DP=1.75) is obtained.

[0066] (2) Unmodified cellulose pulp (DP=700) and NMMO solution with a concentration of 76% were placed in a mixing device at 85°C and pre-mixed for 20 minutes at a temperature of 85°C and a stirring rate of 300 rpm. After the unmodified cellulose pulp was fully dispersed, cellulose acetate was added (the added cellulose acetate accounted for 3% of the total mass of all raw material pulps), the temperature was raised to 90°C, the stirring rate was increased to 500 rpm, and mixing was continued for 5 minutes, and the cellulose concentration was 12%.

[0067] (3) The mixed material was then transported to a dissolving device at a temperature of 110°C, and vacuumed and dehydrated at a vacuum degree of 7 KPa until the cellulose was completely dissolved to obtain a uniform, transparent amber cellulose solution. The cellulose solution was then filtered and degassed, and spun to obtain a regenerated cellulose fiber product. The properties of the obtained regenerated cellulose fiber are shown in Table 1.

[0068] Example 2

[0069] (1) Cellulose is esterified to produce cellulose acetate, which is then crushed in a grinder to a particle size of about 500 μm for later use. An appropriate amount of cellulose acetate is then placed in an alkaline alcohol solution (NaOH and ethanol solution) with a concentration of 0.5 mol / L and reacted at 60°C for 60 min. After washing with water, modified cellulose pulp (DP=1.35) is obtained.

[0070] The methods of step (2) raw material mixing and step (3) fiber preparation are the same as those of Example 1.

[0071] Example 3

[0072] (1) Cellulose is esterified to produce cellulose acetate, which is then crushed in a grinder to a particle size of about 500 μm for later use. A small amount of cellulose acetate is then placed in an alkaline alcohol solution (NaOH and ethanol solution) with a concentration of 0.5 mol / L and reacted at 80°C for 60 minutes. After washing with water, modified pulp (DP=1.06) is obtained.

[0073] The methods of step (2) raw material mixing and step (3) fiber preparation are the same as those of Example 1.

[0074] Comparative Example 1

[0075] In this comparative example, the novel solvent-processed cellulose fiber was prepared by the following method:

[0076] Unmodified cellulose pulp (DP=700) and NMMO solution with a concentration of 76% were placed in a mixing device at 85° C. and mixed for 20 minutes at a temperature of 85° C. and a stirring rate of 300 rpm, wherein the cellulose concentration was 12%.

[0077] Then it was transported to a dissolving device at a temperature of 110°C, and vacuumed and dehydrated at a vacuum degree of 7Kpa until the cellulose was completely dissolved to obtain a uniform, transparent amber cellulose solution. The cellulose solution was then filtered and degassed, and spun to obtain a regenerated cellulose fiber product. The properties of the obtained regenerated cellulose fiber are shown in Table 1.

[0078] Comparative Example 2

[0079] (1) Cellulose is esterified to produce cellulose acetate, which is then crushed in a grinder to a particle size of about 500 μm for later use. An appropriate amount of cellulose acetate is then placed in an alkaline alcohol solution (NaOH and ethanol solution) with a concentration of 0.5 mol / L and reacted at 20°C for 40 minutes. After washing with water, modified cellulose pulp (DP=3) is obtained.

[0080] The methods of step (2) raw material mixing and step (3) fiber preparation are the same as those of Example 1.

[0081] Comparative Example 3

[0082] (1) Cellulose is esterified to produce cellulose acetate, which is then crushed in a grinder to a particle size of about 500 μm for later use. An appropriate amount of cellulose acetate is then placed in an alkaline alcohol solution (NaOH and ethanol solution) with a concentration of 0.5 mol / L and reacted at 20°C for 10 min. After washing with water, modified cellulose pulp (DP=4) is obtained.

[0083] The methods of step (2) raw material mixing and step (3) fiber preparation are the same as those of Example 1.

[0084] The properties of the regenerated cellulose fibers obtained in Examples 1-3 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0085] Table 1 Effect of different degrees of substitution (DS) modified pulp on fiber properties

[0086]

[0087]

[0088] Result analysis:

[0089] From the results in Table 1, it can be seen that compared with Comparative Example 1 in which no modified cellulose pulp was added, although the mechanical properties of the regenerated cellulose fibers prepared by adding modified cellulose pulp with a certain degree of substitution in Examples 1-3 were slightly reduced, they could still meet the subsequent use requirements, indicating that the acetyl group as a hybrid group would indeed reduce the overall arrangement order of the cellulose molecular chain, and reduce the fiber mechanical properties to a certain extent by reducing the fiber crystallization; the fiber molecular chain orientation decreased, and the hydroxyl groups (not completely substituted) on the modified pulp molecular chain and the hydroxyl groups of the unmodified cellulose molecular chain or the hydroxyl groups between the unmodified molecular chains were combined with each other through hydrogen bonding, which increased the lateral bonding between the molecular chains, thereby improving the anti-fibrillation performance of the fiber to a certain extent, which was manifested in a significant increase in the wet friction time.

[0090] The morphology of the regenerated cellulose fiber prepared in Example 2 is as follows Figure 3 As shown, the morphology of the regenerated cellulose fiber prepared in Comparative Example 1 is as follows Figure 4 As shown in the figure, it can be seen intuitively that the fibrillation degree of the fiber prepared in Example 2 has been greatly improved.

[0091] In Comparative Examples 2 and 3, the substitution degree of modified cellulose pulp is too high and the modified pulp is difficult to dissolve in the Lyocell system, which is equivalent to that the modified pulp is not added successfully. Therefore, the fiber properties are not significantly changed compared with Comparative Example 1.

[0092] When the degree of substitution exceeds 2, cellulose acetate cannot be dissolved in NMMO solvent. At this time, only unmodified pulp is dissolved in NMMO to make spinning solution and spun into fiber, and cellulose acetate is not successfully added to the system. The fiber performance is similar to that of Comparative Example 1.

[0093] Example 4

[0094] The preparation of modified cellulose pulp (DP=1.35), raw material mixing and fiber preparation process are the same as in Example 2, except that the cellulose acetate added in this example accounts for 1% of the total mass of all raw material pulps.

[0095] Example 5

[0096] The preparation of modified cellulose pulp (DP=1.35), raw material mixing and fiber preparation process are the same as in Example 2, except that the cellulose acetate added in this example accounts for 5% of the total mass of all raw material pulps.

[0097] Comparative Example 4

[0098] The preparation of modified cellulose pulp (DP=1.35), raw material mixing and fiber preparation process are the same as in Example 2, except that the cellulose acetate added in this example accounts for 12% of the total mass of all raw material pulps.

[0099] Comparative Example 5

[0100] The preparation of modified cellulose pulp (DP=1.35), raw material mixing and fiber preparation process are the same as in Example 2, except that the cellulose acetate added in this example accounts for 0.5% of the total mass of all raw material pulps.

[0101] The properties of the regenerated cellulose fibers obtained in Examples 4-5 and Comparative Examples 4-5 were tested, and the results are shown in Table 2.

[0102] Table 2 Effect of different contents of modified pulp on fiber properties

[0103]

[0104] Result analysis:

[0105] It can be seen from the results in Table 2 that compared with Comparative Example 1 in which no modified cellulose pulp is added, the wet friction time of the regenerated cellulose fibers prepared by adding modified cellulose pulp in an appropriate proportion in Examples 2 and 4-5 is greatly improved, which gives the fibers anti-fibrillation properties, and although the dry tensile strength is slightly reduced, it still meets the requirements of subsequent applications (the principle is the same as the analysis of Examples 1-3 and Comparative Example 1).

[0106] In Comparative Examples 4 and 5, the amount of modified cellulose pulp added is too low or too high. Due to the preparation process of cellulose acetate, the degree of polymerization of cellulose acetate has been significantly reduced compared with that of unmodified pulp. Therefore, after mixing with unmodified pulp, the small molecule cellulose acetate has a certain plasticizing effect in the system. Therefore, when the content is too high, although it is beneficial to weaken the fibrillation ability of the fiber, the mechanical properties of the fiber will be greatly reduced and cannot meet the subsequent use requirements; when the content is too low, the effect of cellulose acetate is not obvious, so the purpose of reducing fibrillation cannot be achieved or the effect is not obvious.

[0107] Example 6

[0108] Take an appropriate amount of cellulose pulp and 20% sodium hydroxide and ethanol solution at 35°C for alkalization, then add the prepared chloroacetic acid ethanol solution and etherify at 70°C for 3h. The final carboxymethyl cellulose detection standard is a transparent substance soluble in water (DS=0.1), then wash and dry for use.

[0109] The method of step (2) raw material mixing and step (3) fiber preparation is the same as that of Example 1, wherein the proportion of carboxymethyl cellulose is 3%.

[0110] Example 7 (Methylcellulose)

[0111] Take an appropriate amount of cellulose pulp and 20% sodium hydroxide and ethanol solution at 35°C for alkalization, then add the prepared methyl chloride reagent and react at room temperature to obtain methyl cellulose.

[0112] The method of step (2) raw material mixing and step (3) fiber preparation is the same as that of Example 1, wherein the proportion of carboxymethyl cellulose is 3%.

[0113] Example 8 (Hydroxyethyl Cellulose)

[0114] Take an appropriate amount of cellulose pulp and react it with a 35% sodium bicarbonate aqueous solution at room temperature. After 15 minutes, take it out, squeeze and crush it, then react it with ethylene oxide at room temperature for 1, and then wash it with alcohol to obtain hydroxyethyl cellulose.

[0115] The method of step (2) raw material mixing and step (3) fiber preparation is the same as that of Example 1, wherein the proportion of carboxymethyl cellulose is 3%.

[0116] Table 3 Effects of different types of modified pulp on fiber properties

[0117]

[0118] Result analysis:

[0119] From the results in Table 3, it can be seen that compared with the comparative example 1 without adding modified cellulose pulp, the wet friction time of the regenerated cellulose fibers prepared by adding different types of modified cellulose pulp in the present examples 2 and 6-8 is improved, giving the fibers anti-fibrillation performance, while the dry tensile strength and dry elongation are not much different, and the mechanical properties of the fibers are also guaranteed. It shows that the anti-fibrillation performance of the fibers prepared by the method of the present invention is improved, and although the fiber strength is slightly reduced, it does not affect the fiber use requirements, and the principle is the same as the analysis of the examples 1-3 and the comparative example 1.

[0120] Through the comparison of the above embodiments and comparative examples, it is found that the modified cellulose pretreatment method and the method for preparing cellulose fibers after mixing different cellulose raw materials provided by the present invention have good compatibility between the modified cellulose and the unmodified cellulose system, and the mixing process is purely physical mixing, which can not only achieve the purpose of improving fiber fibrillation, but also ensure the mechanical properties of the fiber. Compared with the traditional cross-linking method, the introduction of toxic cross-linking agents and the complicated cross-linking process are omitted, which can greatly save equipment investment and raw material consumption, and the operation is simple and can be directly used in the production line.

[0121] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with the present invention can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for preparing regenerated cellulose fiber, characterized in that: The following steps are involved: 1) Pretreatment: Substituting part of the hydroxyl groups of cellulose pulp to prepare modified cellulose pulp with a degree of substitution of 0.001 to 2.0; 2) Mixing unmodified cellulose pulp with modified cellulose pulp, and then mixing with NMMO solution to swell, 3) Dissolving, spinning and post-processing under vacuum conditions to obtain regenerated cellulose fiber products.

2. The preparation method according to claim 1, characterized in that: In step 1), the substitution treatment comprises esterification, carboxylmethylation, methylation, oxidation or hydroxyethylation of the cellulose pulp.

3. The preparation method according to claim 2, characterized in that: In step 1), cellulose pulp is first alkalized and then subjected to etherification reaction to generate carboxymethyl cellulose, methyl cellulose or hydroxyethyl cellulose with a degree of substitution of 0.001 to 0.

5.

4. The preparation method according to claim 2, characterized in that: In step 1), cellulose pulp is subjected to an esterification reaction to obtain cellulose acetate, which is then subjected to a secondary hydrolysis to obtain a degree of substitution of 0.5 to 2.0; Preferably, the cellulose acetate is crushed to a particle size of <1000 μm, preferably <500 μm, before being hydrolyzed.

5. The preparation method according to claim 4, characterized in that: The solution used for the secondary hydrolysis is selected from a NaOH aqueous solution, a NaOH and ethanol solution, an acetic acid solution, and an aqueous solution; Preferably, the temperature of the solution used in the secondary hydrolysis is 10-125°C, the concentration is 0-1.0 mol / L, the secondary hydrolysis time is 0.1-15h, and the degree of polymerization of the pulp after hydrolysis is 200-800; after the secondary hydrolysis, the modified pulp is washed to neutrality for subsequent use.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step 2), the unmodified cellulose pulp is premixed with the NMMO solution and then mixed with the modified cellulose pulp. Preferably, the modified cellulose pulp accounts for 1%-10% of the total weight of all raw pulp.

7. The preparation method according to claim 6, characterized in that: Unmodified cellulose pulp is premixed with NMMO solution having a mass concentration of 70%-84%, at a mixing temperature of 70-100°C for a time of ≥5 minutes, preferably 5-30 minutes; Then, the mixture is rapidly mixed with modified cellulose pulp at a mixing temperature of 80-110° C. for a time of ≥2 min, preferably 2-10 min.

8. The preparation method according to any one of claims 1 to 5, characterized in that: In step 3), the vacuum degree of the dissolution process is controlled to be 0-10Kpa absolute pressure and the temperature is 90-130°C; Preferably, the absolute vacuum pressure during the dissolution process is controlled to be 3-8 KPa and the temperature to be 105-120°C.

9. The preparation method according to any one of claims 1 to 5, characterized in that: In step 3), during spinning, the temperature of the spinning solution is controlled to be 90-130° C., the aperture of the spinneret is 0.05-0.3 mm, the air gap cooling height is 5-200 mm, and the filament bundle is continuously spun at a spinning speed of 20-500 m / min to obtain a finished product.

10. A regenerated cellulose fiber prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The regenerated cellulose fiber has a wet friction time of >10s, a dry tensile strength of 3.4-3.9 cN / dtex, and a dry elongation of 9%-10%; Preferably, the wet friction time of the regenerated cellulose fiber is 11.9s to 18.4s.

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