阅读说明：本技术 一种阻燃粘胶纤维的制备方法 (Preparation method of flame-retardant viscose fibers ) 是由 林庆辉 郭巍 黄志冰 姚锰 郑超 吴晓东 于 2020-12-09 设计创作，主要内容包括：本发明提供一种阻燃粘胶纤维的制备方法,选择无氯漂溶解木浆浆粕为原料,制备粘胶纺丝原液,送入纺丝机,凝固再生出初生纤维；初生纤维经牵伸、取向形成具有一定强度的纤维经切断后进入绒毛槽、精炼机,在精炼漂白工序采用低温活化氧漂工艺,并采用纤维的后整理法制备无卤环保阻燃粘胶纤维。本发明通过优选铵盐阻燃剂,所制备的阻燃粘胶纤维,甲醛含量少,白度较高、干强较高、阻燃性能较佳,有一定的耐洗性,纤维不含可吸附有机卤化物,可用于纺织和无纺领域。(The invention provides a preparation method of flame-retardant viscose fiber, which comprises the steps of selecting chlorine-free bleached and dissolved wood pulp as a raw material, preparing viscose spinning dope, feeding the viscose spinning dope into a spinning machine, and solidifying and regenerating nascent fiber; the method comprises the steps of drawing and orienting nascent fibers to form fibers with certain strength, cutting the fibers, feeding the fibers into a fluff tank and a refiner, adopting a low-temperature activation oxygen bleaching process in a refining bleaching process, and preparing the halogen-free environment-friendly flame-retardant viscose fibers by adopting a fiber post-finishing method. According to the invention, the ammonium salt flame retardant is preferably selected, so that the prepared flame-retardant viscose fiber has the advantages of low formaldehyde content, high whiteness, high dry strength, good flame-retardant property and certain washability, does not contain adsorbable organic halide, and can be used in the fields of textile and non-woven fabrics.)

1. The preparation method of the flame-retardant viscose fiber is characterized by comprising the following steps of:

(1) preparing viscose fibers:

the pulp is prepared from chlorine-free bleached softwood dissolving pulp and chlorine-free bleached hardwood dissolving pulp according to the weight ratio of 5-8: mixing dregs according to the mass ratio of 100, sequentially carrying out the steps of dipping, squeezing, crushing, ageing, yellowing, dissolving and ripening to prepare a viscose spinning solution, delivering the spinning solution to a spinning machine, spraying the spinning solution from a spinning nozzle through a metering pump, reacting with a coagulating bath in an acid bath, and coagulating to regenerate nascent fibers; drafting and orienting the solidified and regenerated nascent fiber to form fiber with certain strength, cutting the fiber, and feeding the fiber into a fluff tank; the steam bubbles sprayed from the small holes of the steam spraying pipe at the bottom of the fluff slot disperse the fibers to make the thickness of the fiber layer uniform;

(2) post-treatment of viscose fibers:

and (3) delivering the viscose staple fiber from the fluff tank into a refiner, and sequentially performing primary washing, desulfurization, secondary washing, bleaching, tertiary washing, final washing, oiling, dehydration and drying to obtain the flame-retardant viscose fiber.

2. The method for preparing flame retardant viscose fiber according to claim 1, wherein the chlorine-free bleached softwood dissolving pulp and the chlorine-free bleached hardwood dissolving pulp in step (1) have a pulp whiteness of 89% or more and a methyl cellulose content of 90% or more.

3. The method for preparing a flame retardant viscose fiber according to claim 1, wherein in the step (1):

in the dipping process, a surfactant V388 is added, and the mass ratio of the surfactant V388 to the pulp is 0.04: 100, respectively;

in the dissolving process, adding a fatty amine polyoxyethylene ether denaturant, wherein the mass ratio of the denaturant to the pulp is (2-4): 10000;

the coagulating bath comprises 110-120 g/L sulfuric acid, 300-320 g/L sodium sulfate, 9-13 g/L zinc sulfate and 10-11 g/L Berol Spin 653 surfactant;

the spinning speed of the spinning machine is 50-60 m/min.

4. The method for preparing the flame-retardant viscose fiber according to claim 1, wherein the first washing temperature in the step (2) is 70-75 ℃, the second washing temperature is 60-80 ℃, the third washing temperature is 55-70 ℃, and the final washing temperature is 70-75 ℃.

5. The preparation method of the flame-retardant viscose fiber according to claim 1, wherein the desulfurizing agent used in the desulfurizing process in the step (2) is one or two of sodium hydroxide and sodium sulfide, the concentration of the desulfurizing agent is 2-4 g/L, and the desulfurizing temperature is 70-80 ℃.

6. The preparation method of the flame-retardant viscose fiber according to claim 1, wherein the bleaching agent used in the bleaching process in the step (2) is hydrogen peroxide, and the addition amount is 4-12 g/L; an activator and a penetrant assistant are used in the bleaching process, wherein the addition amount of the activator is 0.6-4 g/L, and the addition amount of the penetrant is 0.1-0.2 g/L; the bleaching temperature is 60-70 ℃, the pH value of bleaching liquid is controlled to be 10-11, and the bleaching time is 3-3.5 min; the activating agent is an amide compound, and the penetrating agent is a fatty alcohol polyether surfactant containing a carboxylic acid group and a sulfonic acid group.

7. The method for preparing flame-retardant viscose fiber according to claim 1, wherein the oil bath component applied in step (2) comprises an oil agent for flame-retardant fiber, a flame retardant and a catalyst, the pH value of the oil bath is controlled according to the pH value of the finished fiber reaching 7.0 +/-0.2, and the oil bath temperature is 62-66 ℃; the flame retardant is an ammonium salt flame retardant containing element N, P, H, O, and the mass concentration of the flame retardant in the oil bath is 20-40%; the catalyst is dicyanodiamine; the mass ratio of the catalyst to the flame retardant is 1: 6-1: 3.

8. the method as claimed in claim 7, wherein the flame retardant in step (2) is ammonium aminotrimethylenephosphate or ammonium phytate.

9. The method as claimed in claim 1, wherein the drying temperature in step (2) is 130-145 ℃.

Technical Field

The invention relates to the technical field of chemical fiber processing, in particular to a preparation method of flame-retardant viscose fibers.

Background

Compared with synthetic fibers such as polyester, polyamide and the like, the viscose fiber has excellent performances such as better hygroscopicity and comfort, and has biodegradability, and the application range of the viscose fiber is expanded to various fields such as clothing, decoration, medical health and industrial products. With the progress of society and the improvement of safety awareness, people have increasingly higher requirements on flame retardance of fiber products. However, because of its chemical structure, viscose fiber is a high molecular polymer with flammable characteristics, and therefore it is necessary to research the flame retardant modification technology of viscose fiber.

The patent with the application number of CN201110252275.0 discloses a phosphorus-nitrogen flame retardant dispersion liquid and a preparation method thereof, and solves the problems that the flame retardant dispersion liquid prepared from a flame retardant for viscose fibers in the prior art is poor in stability and difficult to realize large-scale industrial production. Patent with application number CN201410292939.X discloses an environment-friendly flame retardant, a preparation method and application thereof, wherein the flame retardant adopts organosilane hydrolysis dispersion liquid as a main component of the flame retardant, has wide raw material sources and low price, overcomes the adverse effects of the traditional halogen flame retardant and phosphorus flame retardant on environment and safety, and has high flame retardant addition ratio. Patent application No. CN201210065248.7 discloses a flame-retardant silicate fiber, a coagulating bath for producing the flame-retardant silicate fiber and a method for preparing the flame-retardant silicate fiber, wherein the flame-retardant fiber is spun by adopting a four-component coagulating bath, so that the loss of a flame retardant in a strand silk can be reduced, the spinning spinnability is improved, the physical and mechanical performance indexes of the flame-retardant fiber are improved, the production cost of the flame-retardant viscose fiber is reduced, and the mechanical performance of the flame-retardant fiber is still poor.

Although the existing flame retardant technology makes certain progress, the flame retardant for modifying the flame retardance of the viscose fibers still has difficulty in meeting the requirements of environmental protection, high efficiency and low cost. The inorganic flame retardant has the advantages of good thermal stability, no generation of corrosive gas, no volatilization, lasting effect, no toxicity and the like, but has influence on the spinning forming process and the physical and mechanical properties of fibers; organic halogen-based flame retardants tend to emit toxic and harmful gases during combustion, and the flame retardant will tend to be selected to be halogen-free. However, in order to improve the whiteness of the flame-retardant viscose fiber, sodium hypochlorite is often used for bleaching in the production of the viscose fiber, for example, patent application No. CN201610717315.7 discloses a production process of a matt high-whiteness cellulose fiber with a flame-retardant function, and sodium hypochlorite and hydrogen peroxide are used for bleaching to prepare the flame-retardant matt high-whiteness cellulose fiber, so that some organic halides are remained in the finished fiber, which brings potential risks to human health, and therefore, it is necessary to further develop a flame-retardant viscose fiber without chlorine bleaching.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: aiming at the defects in the prior art, the preparation method of the chlorine-free bleaching flame-retardant viscose fiber is provided, wherein the whiteness of the fiber is higher, and the damage to the mechanical property of the fiber is less.

In order to solve the problems, the specific technical scheme of the invention is as follows:

a preparation method of flame-retardant viscose fibers comprises the following steps:

(1) preparing viscose fibers:

the pulp is prepared from chlorine-free bleached softwood dissolving pulp and chlorine-free bleached hardwood dissolving pulp according to the weight ratio of 5-8: mixing dregs according to the mass ratio of 100, sequentially carrying out the steps of dipping, squeezing, crushing, ageing, yellowing, dissolving and ripening to prepare a viscose spinning solution, delivering the spinning solution to a spinning machine, spraying the spinning solution from a spinning nozzle through a metering pump, reacting with a coagulating bath in an acid bath, and coagulating to regenerate nascent fibers; drafting and orienting the solidified and regenerated nascent fiber to form fiber with certain strength, cutting the fiber, and feeding the fiber into a fluff tank; the steam bubbles sprayed from the small holes of the steam spraying pipe at the bottom of the fluff slot disperse the fibers to make the thickness of the fiber layer uniform;

(2) post-treatment of viscose fibers:

and (3) delivering the viscose staple fiber from the fluff tank into a refiner, and sequentially performing primary washing, desulfurization, secondary washing, bleaching, tertiary washing, final washing, oiling, dehydration and drying to obtain the flame-retardant viscose fiber.

Further, the pulp whiteness of the chlorine-free bleached softwood dissolving pulp and the chlorine-free bleached hardwood dissolving pulp in the step (1) is more than 89%, and the methyl cellulose content is more than 90%.

Preferred parameters, in step (1):

in the dipping process, a surfactant V388 is added, and the mass ratio of the surfactant V388 to the pulp is 0.04: 100, respectively;

in the dissolving process, adding a fatty amine polyoxyethylene ether denaturant, wherein the mass ratio of the denaturant to the pulp is (2-4): 10000;

the coagulating bath comprises 110-120 g/L sulfuric acid, 300-320 g/L sodium sulfate, 9-13 g/L zinc sulfate and 10-11 g/L Berol Spin 653 surfactant;

the spinning speed of the spinning machine is 50-60 m/min.

Wherein the temperature of the first washing in the step (2) is 70-75 ℃, the temperature of the second washing is 60-80 ℃, the temperature of the third washing is 55-70 ℃, and the temperature of the final washing is 70-75 ℃.

The desulfurizer used in the desulfurization process in the step (2) is one or two of sodium hydroxide and sodium sulfide, the concentration of the desulfurizer is 2-4 g/L, and the desulfurization temperature is 70-80 ℃.

The bleaching agent used in the bleaching in the step (2) is hydrogen peroxide, and the addition amount is 4-12 g/L; an activator and a penetrant assistant are used in the bleaching process, wherein the addition amount of the activator is 0.6-4 g/L, and the addition amount of the penetrant is 0.1-0.2 g/L; the bleaching temperature is 60-70 ℃, the pH value of bleaching liquid is controlled to be 10-11, and the bleaching time is 3-3.5 min; the activating agent is an amide compound, and the penetrating agent is a fatty alcohol polyether surfactant containing a carboxylic acid group and a sulfonic acid group.

The oil bath component for oiling in the step (2) comprises an oiling agent for flame-retardant fibers, a flame retardant and a catalyst, the pH value of the oil bath is controlled according to the pH value of the finished fiber reaching 7.0 +/-0.2, and the temperature of the oil bath is 62-66 ℃; the flame retardant is an ammonium salt flame retardant containing element N, P, H, O, and the mass concentration of the flame retardant in the oil bath is 20-40%; the catalyst is dicyanodiamine; the mass ratio of the catalyst to the flame retardant is 1: 6-1: 3.

preferably, the flame retardant in step (2) is ammonium aminotrimethylene phosphate or ammonium phytate.

The temperature for drying in the step (2) is 130-145 ℃.

The technical parameters of the flame-retardant viscose fiber obtained by the invention are as follows: the fineness is 1.32-1.75 dtex; the length is 32-40 mm; the dry breaking strength is more than or equal to 1.9 cN/dtex; the dry breaking elongation is 16.0-20.0%; the whiteness is more than or equal to 78.0 percent; the limiting oxygen index is more than or equal to 28 percent. The invention uses chlorine-free bleaching to dissolve wood pulp to ensure that the fibers do not contain adsorbable organic halides.

The invention optimizes the spinning speed to obtain proper post-processing time and ensure the balance of yield and quality index.

The invention adopts the chlorine-free bleaching process to ensure that the fiber does not contain adsorbable organic halide, which is beneficial to reducing the reduction of the mechanical property of the flame-retardant fiber caused by the chlorine bleaching process.

The invention adopts ammonium salt flame retardant to avoid formaldehyde generated in the application of the prepared flame-retardant viscose fiber. The invention selects proper flame retardant concentration to reduce the reduction of the mechanical property of the fiber caused by overhigh content of the flame retardant.

The invention selects proper drying temperature to ensure that the flame retardant performance has washability and avoid the yellowing phenomenon of the flame retardant fiber caused by overhigh temperature in the drying process.

The ammonium salt fire retardant is prepared by reacting organic acid with urea, contains a small amount of unreacted organic acid, and can adjust the pH value of the fiber.

The preparation method of the flame-retardant viscose fiber provided by the invention has the following beneficial effects:

(1) the invention selects the ammonium salt flame retardant preferably, and the prepared flame-retardant viscose fiber has low formaldehyde content and certain washability and can be used in the fields of textile and non-woven.

(2) The invention adopts the hydrogen peroxide bleaching process, thereby avoiding the problem of organic chlorine compound pollution in the wastewater caused by adopting chlorine or chlorine compound bleaching.

(3) The method selects the chlorine-free bleaching pulp as a raw material, adopts a low-temperature activation bleaching process, is favorable for reducing the performance damage of the fiber and avoids the fiber containing adsorbable organic halide compared with the chlorine bleaching process.

(4) The invention selects an ammonium salt flame retardant preferably, and introduces the ammonium salt flame retardant to the fiber by adopting a post-treatment method, thereby being beneficial to avoiding the spinnability problem caused by the addition method before spinning and the waste liquid treatment problem caused by the loss of the flame retardant in the spinning process.

Detailed Description

The specific technical scheme of the invention is described by combining the embodiment.

Example 1

(1) Preparing viscose fibers:

dissolving pulp of chlorine-free bleached softwood dissolving pulp and chlorine-free bleached hardwood dissolving pulp according to the weight ratio of 5: mixing the materials according to the mass ratio of 100, preparing a viscose spinning solution by the steps of dipping, squeezing, crushing, ageing, yellowing, dissolving and ripening, delivering the spinning solution to a spinning machine, spraying the spinning solution from a spinning nozzle through a metering pump, reacting with a coagulating bath in an acid bath, and coagulating to regenerate nascent fibers; drafting and orienting the solidified and regenerated nascent fiber to form fiber with certain strength, cutting the fiber, and feeding the fiber into a fluff tank; the steam bubbles sprayed from the small holes of the steam spraying pipe at the bottom of the fluff slot disperse the fibers to make the thickness of the fiber layer uniform. The whiteness of the chlorine-free bleaching dissolving pulp is more than 89%, and the content of methyl fiber is more than 90%; the mass ratio of the added relative pulp in the pulp dipping process is 0.04: 100 of surfactant V388; in the dissolving step, a fatty amine polyoxyethylene ether denaturant is added, and the mass ratio of the denaturant to the pulp is 2: 10000; the coagulating bath comprises 110g/L sulfuric acid, 300g/L sodium sulfate, 9g/L zinc sulfate and 10g/L Berol Spin 653 surfactant; the spinning speed of the spinning machine is 50 m/min.

(2) Post-treatment of viscose fibers:

and (3) delivering the viscose staple fiber from the fluff tank into a refiner, and performing primary washing, desulfurization, secondary washing, bleaching, tertiary washing, final washing, oiling, dehydration and drying to obtain the flame-retardant viscose fiber. The first washing temperature is 70 ℃, the second washing temperature is 60 ℃, the third washing temperature is 55 ℃, and the final washing temperature is 70 ℃; the desulfurizer used in the desulfurization process is sodium hydroxide and sodium sulfide, the concentration of the sodium hydroxide is 2g/L, the concentration of the sodium sulfide is 2g/L, and the desulfurization temperature is 70 ℃; the bleaching agent is hydrogen peroxide, and the addition amount is 4 g/L; an activator and a penetrant auxiliary agent are used in the bleaching process, wherein the addition amount of the activator is 0.6g/L, and the addition amount of the penetrant is 0.1 g/L; the bleaching temperature is 60 ℃, the pH value of bleaching liquid is 10, and the bleaching time is 3.5 min. The activator is an amide compound. The penetrating agent is fatty alcohol polyether surfactant containing carboxylic acid group and sulfonic group. The oil bath component is added with a flame retardant and a catalyst besides an oil agent for flame-retardant fibers, the pH value of the oil bath is controlled according to the pH value of the finished fiber reaching 7.0 +/-0.2, and the oil bath temperature is 62 ℃. The flame retardant is ammonium phytate flame retardant, and the mass concentration of the flame retardant in the oil bath is 20%. The catalyst is dicyandiamide, and the mass ratio of the dicyandiamide to the flame retardant is 1: 6. the temperature of the drying is 130 ℃.

The technical parameters of the obtained flame-retardant viscose fiber are as follows: the fineness is 1.75 dtex; the length is 40 mm; the dry breaking strength is more than or equal to 1.9 cN/dtex; the dry elongation at break was 16.0%; the whiteness is more than or equal to 78.0 percent; the limiting oxygen index is more than or equal to 28 percent.

Example 2

(1) Preparing viscose fibers:

dissolving pulp of chlorine-free bleached softwood dissolving pulp and chlorine-free bleached hardwood dissolving pulp according to the weight ratio of 8: mixing the materials according to the mass ratio of 100, preparing a viscose spinning solution by the steps of dipping, squeezing, crushing, ageing, yellowing, dissolving and ripening, delivering the spinning solution to a spinning machine, spraying the spinning solution from a spinning nozzle through a metering pump, reacting with a coagulating bath in an acid bath, and coagulating to regenerate nascent fibers; drafting and orienting the solidified and regenerated nascent fiber to form fiber with certain strength, cutting the fiber, and feeding the fiber into a fluff tank; the steam bubbles sprayed from the small holes of the steam spraying pipe at the bottom of the fluff slot disperse the fibers to make the thickness of the fiber layer uniform. The whiteness of the chlorine-free bleaching dissolving pulp is more than 89%, and the content of methyl fiber is more than 90%; the mass ratio of the added relative pulp in the pulp dipping process is 0.04: 100 of surfactant V388; in the dissolving step, a fatty amine polyoxyethylene ether denaturant is added, and the mass ratio of the denaturant to the pulp is 4: 10000; the coagulating bath comprises 120g/L sulfuric acid, 320g/L sodium sulfate, 13g/L zinc sulfate and 11g/L Berol Spin 653 surfactant; the spinning speed of the spinning machine is 60 m/min.

(2) Post-treatment of viscose fibers:

and (3) delivering the viscose staple fiber from the fluff tank into a refiner, and performing primary washing, desulfurization, secondary washing, bleaching, tertiary washing, final washing, oiling, dehydration and drying to obtain the flame-retardant viscose fiber. The first washing temperature is 75 ℃, the second washing temperature is 80 ℃, the third washing temperature is 70 ℃, and the final washing temperature is 75 ℃; the desulfurizer used in the desulfurization process is sodium hydroxide, the concentration of the sodium hydroxide is 4g/L, and the desulfurization temperature is 80 ℃; the bleaching agent is hydrogen peroxide, and the addition amount is 12 g/L; an activator and a penetrant auxiliary agent are used in the bleaching process, wherein the addition amount of the activator is 4g/L, and the addition amount of the penetrant is 0.2 g/L; the bleaching temperature is 70 ℃, the pH value of bleaching liquid is controlled to be 11, and the bleaching time is 3 min. The activator is an amide compound. The penetrating agent is fatty alcohol polyether surfactant containing carboxylic acid group and sulfonic group. The oil bath component is added with a flame retardant and a catalyst besides an oil agent for flame-retardant fibers, the pH value of the oil bath is controlled according to the pH value of the finished fiber reaching 7.0 +/-0.2, and the oil bath temperature is 66 ℃. The flame retardant is an amino trimethylene ammonium phosphate flame retardant, and the mass concentration of the flame retardant in the oil bath is 40%. The catalyst is dicyandiamide, and the mass ratio of the dicyandiamide to the flame retardant is 1: 3. the temperature of the drying is 145 ℃.

The technical parameters of the obtained flame-retardant viscose fiber are as follows: the fineness is 1.32 dtex; the length is 32 mm; the dry breaking strength is more than or equal to 1.9 cN/dtex; the dry elongation at break was 18.0%; the whiteness is more than or equal to 79.0 percent; the limiting oxygen index is more than or equal to 31 percent.

Example 3

(1) Preparing viscose fibers:

dissolving pulp of chlorine-free bleached softwood dissolving pulp and chlorine-free bleached hardwood dissolving pulp according to the weight ratio of 6: mixing the materials according to the mass ratio of 100, preparing a viscose spinning solution by the steps of dipping, squeezing, crushing, ageing, yellowing, dissolving and ripening, delivering the spinning solution to a spinning machine, spraying the spinning solution from a spinning nozzle through a metering pump, reacting with a coagulating bath in an acid bath, and coagulating to regenerate nascent fibers; drafting and orienting the solidified and regenerated nascent fiber to form fiber with certain strength, cutting the fiber, and feeding the fiber into a fluff tank; the steam bubbles sprayed from the small holes of the steam spraying pipe at the bottom of the fluff slot disperse the fibers to make the thickness of the fiber layer uniform. The whiteness of the chlorine-free bleaching dissolving pulp is more than 89%, and the content of methyl fiber is more than 90%; the mass ratio of the added relative pulp in the pulp dipping process is 0.04: 100 of surfactant V388; in the dissolving step, a fatty amine polyoxyethylene ether denaturant is added, and the mass ratio of the denaturant to the pulp is 4: 10000; the coagulating bath comprises 120g/L sulfuric acid, 300g/L sodium sulfate, 11g/L zinc sulfate and 10g/L Berol Spin 653 surfactant; the spinning speed of the spinning machine is 55 m/min.

(2) Post-treatment of viscose fibers:

and (3) delivering the viscose staple fiber from the fluff tank into a refiner, and performing primary washing, desulfurization, secondary washing, bleaching, tertiary washing, final washing, oiling, dehydration and drying to obtain the flame-retardant viscose fiber. The first washing temperature is 75 ℃, the second washing temperature is 70 ℃, the third washing temperature is 60 ℃, and the final washing temperature is 75 ℃; the desulfurizer used in the desulfurization process is sodium hydroxide and sodium sulfide, the concentration of the sodium hydroxide is 3g/L, the concentration of the sodium sulfide is 1g/L, and the desulfurization temperature is 75 ℃; the bleaching agent is hydrogen peroxide, and the addition amount is 7 g/L; an activator and a penetrant auxiliary agent are used in the bleaching process, wherein the addition amount of the activator is 1.4g/L, and the addition amount of the penetrant is 0.2 g/L; the bleaching temperature is 70 ℃, the pH value of bleaching liquid is controlled at 10.5, and the bleaching time is 3.3 min. The activator is an amide compound. The penetrating agent is fatty alcohol polyether surfactant containing carboxylic acid group and sulfonic group. The oil bath component is added with a flame retardant and a catalyst besides an oil agent for flame-retardant fibers, the pH value of the oil bath is controlled according to the pH value of the finished fiber reaching 7.0 +/-0.2, and the oil bath temperature is 65 ℃. The flame retardant is an amino trimethylene ammonium phosphate flame retardant, and the mass concentration of the flame retardant in the oil bath is 30%. The catalyst is dicyandiamide, and the mass ratio of the dicyandiamide to the flame retardant is 1: 4. the temperature of the drying is 135 ℃.

The technical parameters of the obtained flame-retardant viscose fiber are as follows: the fineness is 1.70 dtex; the length is 40 mm; the dry breaking strength is more than or equal to 2.0 cN/dtex; the dry elongation at break was 20.0%; the whiteness is more than or equal to 80.0 percent; the limiting oxygen index is more than or equal to 30 percent.

Comparative example 1

(1) Preparing viscose fibers:

dissolving pulp of chlorine-free bleached softwood dissolving pulp and chlorine-free bleached hardwood dissolving pulp according to the weight ratio of 5: mixing the materials according to the mass ratio of 100, preparing a viscose spinning solution by the steps of dipping, squeezing, crushing, ageing, yellowing, dissolving and ripening, delivering the spinning solution to a spinning machine, spraying the spinning solution from a spinning nozzle through a metering pump, reacting with a coagulating bath in an acid bath, and coagulating to regenerate nascent fibers; drafting and orienting the solidified and regenerated nascent fiber to form fiber with certain strength, cutting the fiber, and feeding the fiber into a fluff tank; the steam bubbles sprayed from the small holes of the steam spraying pipe at the bottom of the fluff slot disperse the fibers to make the thickness of the fiber layer uniform. The whiteness of the chlorine-free bleaching dissolving pulp is more than 89%, and the content of methyl fiber is more than 90%; the mass ratio of the added relative pulp in the pulp dipping process is 0.04: 100 of surfactant V388; in the dissolving step, a fatty amine polyoxyethylene ether denaturant is added, and the mass ratio of the denaturant to the pulp is 2: 10000; the coagulating bath comprises 110g/L sulfuric acid, 300g/L sodium sulfate, 9g/L zinc sulfate and 10g/L Berol Spin 653 surfactant; the spinning speed of the spinning machine is 50 m/min.

(2) Post-treatment of viscose fibers:

and (3) delivering the viscose staple fiber from the fluff tank into a refiner, and performing primary washing, desulfurization, secondary washing, bleaching, tertiary washing, final washing, oiling, dehydration and drying to obtain the flame-retardant viscose fiber. The first washing temperature is 70 ℃, the second washing temperature is 60 ℃, the third washing temperature is 55 ℃, and the final washing temperature is 70 ℃; the desulfurizer used in the desulfurization process is sodium hydroxide and sodium sulfide, the concentration of the sodium hydroxide is 2g/L, the concentration of the sodium sulfide is 2g/L, and the desulfurization temperature is 70 ℃; the bleaching agent is sodium hypochlorite, and the addition amount is 2 g/L; the bleaching temperature is 60 ℃, the pH value of bleaching liquid is 10, and the bleaching time is 3.5 min. The oil bath component is added with a flame retardant and a catalyst besides an oil agent for flame-retardant fibers, the pH value of the oil bath is controlled according to the pH value of the finished fiber reaching 7.0 +/-0.2, and the oil bath temperature is 62 ℃. The flame retardant is an amino trimethylene ammonium phosphate flame retardant, and the mass concentration of the flame retardant in the oil bath is 20%. The catalyst is dicyandiamide, and the mass ratio of the dicyandiamide to the flame retardant is 1: 6. the temperature of the drying is 130 ℃.

The technical parameters of the obtained flame-retardant viscose fiber are as follows: the fineness is 1.75 dtex; the length is 40 mm; the dry breaking strength is more than or equal to 1.7 cN/dtex; the dry elongation at break was 16.0%; the whiteness is more than or equal to 77.0 percent; the limiting oxygen index is more than or equal to 28 percent.

Comparative example 2

(1) Preparing viscose fibers:

dissolving pulp of chlorine-free bleached softwood dissolving pulp and chlorine-free bleached hardwood dissolving pulp according to the weight ratio of 5: mixing the materials according to the mass ratio of 100, preparing a viscose spinning solution by the steps of dipping, squeezing, crushing, ageing, yellowing, dissolving and ripening, delivering the spinning solution to a spinning machine, spraying the spinning solution from a spinning nozzle through a metering pump, reacting with a coagulating bath in an acid bath, and coagulating to regenerate nascent fibers; drafting and orienting the solidified and regenerated nascent fiber to form fiber with certain strength, cutting the fiber, and feeding the fiber into a fluff tank; the steam bubbles sprayed from the small holes of the steam spraying pipe at the bottom of the fluff slot disperse the fibers to make the thickness of the fiber layer uniform. The whiteness of the chlorine-free bleaching dissolving pulp is more than 89%, and the content of methyl fiber is more than 90%; the mass ratio of the added relative pulp in the pulp dipping process is 0.04: 100 of surfactant V388; in the dissolving step, a fatty amine polyoxyethylene ether denaturant is added, and the mass ratio of the denaturant to the pulp is 2: 10000; the coagulating bath comprises 110g/L sulfuric acid, 300g/L sodium sulfate, 9g/L zinc sulfate and 10g/L Berol Spin 653 surfactant; the spinning speed of the spinning machine is 50 m/min.

(2) Post-treatment of viscose fibers:

and (3) delivering the viscose staple fiber from the fluff tank into a refiner, and performing primary washing, desulfurization, secondary washing, bleaching, tertiary washing, final washing, oiling, dehydration and drying to obtain the flame-retardant viscose fiber. The first washing temperature is 70 ℃, the second washing temperature is 60 ℃, the third washing temperature is 55 ℃, and the final washing temperature is 70 ℃; the desulfurizer used in the desulfurization process is sodium hydroxide and sodium sulfide, the concentration of the sodium hydroxide is 2g/L, the concentration of the sodium sulfide is 2g/L, and the desulfurization temperature is 70 ℃; the bleaching agent is sodium hypochlorite, and the addition amount is 2 g/L; the bleaching temperature is 60 ℃, the pH value of bleaching liquid is 10, and the bleaching time is 3.5 min. The oil bath component is added with a flame retardant and a catalyst besides an oil agent for flame-retardant fibers, the pH value of the oil bath is controlled according to the pH value of the finished fiber reaching 7.0 +/-0.2, and the oil bath temperature is 62 ℃. The flame retardant is ammonium phytate flame retardant, and the mass concentration of the flame retardant in the oil bath is 20%. The catalyst is dicyandiamide, and the mass ratio of the dicyandiamide to the flame retardant is 1: 6. the temperature of the drying is 130 ℃.

The technical parameters of the obtained flame-retardant viscose fiber are as follows: the fineness is 1.75 dtex; the length is 40 mm; the dry breaking strength is more than or equal to 1.9 cN/dtex; the dry elongation at break was 16.0%; the whiteness is more than or equal to 79.0 percent; the limiting oxygen index is more than or equal to 28 percent.