Application of low melt flow index polyoxymethylene in improving polyoxymethylene spinning properties

Abstract

This invention relates to the field of polymer materials technology, specifically disclosing the application of low melt flow index (MFI) polyoxymethylene (POM) in improving the spinning performance of POM. Using heteropolyacids as catalysts, and controlling the polymerization temperature and the amount of heteropolyacid catalyst added, low MFI POM with a melt flow index of 0.1 g / 10 min to 2.5 g / 10 min was prepared. After compounding this low MFI POM with a heat-stabilizing agent in a certain proportion, it was blended with general-purpose POM and extruded into granules. Unexpectedly, the thermal stability of the POM was significantly improved, and it also exhibited moderate rheological properties. When applied to the melt spinning process, the spinnability of the POM was significantly improved. Compared with the POM without the addition of this low MFI, the draw ratio increased by approximately 1.4 times, and the tensile strength of the POM fiber reached 6–8 g / d, a maximum increase of approximately 1.4 times. The yield and strength of the finished fiber product were significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, and particularly relates to application of low-melt-index polyoxymethylene in improving spinning performance of polyoxymethylene. BACKGROUND

[0002] Polyoxymethylene (POM) is a linear high polymer engineering plastic with regular molecular chain structure and main chain structure of (CH2O) n , and has high yield strength, fatigue resistance, creep resistance, friction resistance, chemical resistance and the like, and is widely applied to the fields of automobiles, electronic devices, precision instruments, daily necessities and the like. Polyoxymethylene fiber is one of synthetic fibers, and has the following advantages: (1) high strength, compared with ordinary nylon fiber and polyester fiber, the strength of polyoxymethylene fiber is higher, and is 2-3 times that of ordinary nylon fiber and polyester fiber; (2) excellent friction resistance and wear resistance, the dynamic friction coefficient is lower than 0.25, and the static friction coefficient is lower than 0.3; (3) excellent tensile recovery performance, durability and chemical resistance, and can be widely applied to the fields of ropes, concrete, healds and civil textiles.

[0003] Due to the reasons that the crystallinity of polyoxymethylene is as high as 70% or more, the crystallization speed is fast and the process is difficult to control, and the molecular chain is broken under the action of heat oxygen, shearing and the like at high temperature, bubbles are generated, the melt rheological performance of the resin is affected, and the resin cannot be well applied to the spinning process, spinning is difficult, and high-strength polyoxymethylene fiber is difficult to obtain.

[0004] In the prior art, there are methods for improving the spinnability of fiber products by adjusting the crystallization of polyoxymethylene through the molecular structure, thereby improving the strength; and there are methods for improving the flowability of the spinning polyoxymethylene, optimizing the melt spinning process, improving the spinning efficiency, and stabilizing the spinning. However, the current methods have limited improvement on the spinning performance of polyoxymethylene, and the process is relatively complex, which is not conducive to the realization of industrial production. Therefore, it is necessary to provide a new method which is simple in process and can effectively improve the spinning performance of polyoxymethylene. SUMMARY

[0005] In view of the problems that the spinning performance of polyoxymethylene is poor in the prior art, and it is difficult to obtain high-strength polyoxymethylene fiber, the present application provides application of low-melt-index polyoxymethylene in improving the spinning performance of polyoxymethylene. The low-melt-index polyoxymethylene with a specific melt index is used as a modifier to improve the spinning performance of general-purpose polyoxymethylene, the draft ratio and fiber strength of the polyoxymethylene fiber are improved, the yarn breakage rate is reduced, the industrialization is easy, and the method has strong practicability.

[0006] To solve the above technical problems, the technical scheme provided by the present application is as follows:

[0007] The application of a low melt index polyoxymethylene in improving the spinning performance of polyoxymethylene, wherein the melt index of the low melt index polyoxymethylene is 0.1 g / 10 min to 2.5 g / 10 min.

[0008] The inventors found in the actual research and development process that the general-purpose polyoxymethylene is prone to thermal degradation during the melt spinning process due to poor thermal stability, releasing formaldehyde, which makes it difficult to continuously perform the spinning process and easily causes yarn breakage.

[0009] Through creative thinking, the inventors unexpectedly found that the decomposition temperature of 5% thermal weight loss of the polyoxymethylene is increased by more than 20℃, the volatile matter M value after 45 min of constant temperature at 222℃ is reduced to less than 0.35% by adding a specific low melt index polyoxymethylene as a modifier to the general-purpose polyoxymethylene, the thermal stability is significantly improved, and the viscosity and rheological properties are significantly improved. After being applied to the melt spinning process, the spinnability of the polyoxymethylene is significantly improved, the draw ratio and fiber strength of the polyoxymethylene finished fiber prepared are significantly enhanced, and the yarn breakage rate is significantly reduced, which has very important significance for expanding the application field of polyoxymethylene fibers.

[0010] Preferably, the melt index of the low melt index polyoxymethylene is 0.3 g / 10 min to 0.7 g / 10 min.

[0011] The low melt index polyoxymethylene can effectively improve the thermal stability and spinning performance of the general-purpose polyoxymethylene and improve the draw ratio of the polyoxymethylene fiber and the mechanical strength of the finished fiber.

[0012] Preferably, the preparation method of the low melt index polyoxymethylene comprises the following steps:

[0013] The trioxymethylene, the cyclic ether compound, the heteropoly acid catalyst, and the chain transfer agent are uniformly mixed, and a polymerization reaction is performed at 50℃ to 60℃, a terminating agent is added to terminate the polymerization reaction, and the low melt index polyoxymethylene is obtained after drying.

[0014] The mass ratio of the heteropoly acid catalyst to the trioxymethylene is (1-6) ppm:1.

[0015] In the research and development process, the inventors unexpectedly found that by controlling the temperature of the polymerization reaction and the amount of the heteropoly acid catalyst added, a low melt index polyoxymethylene with a melt index of 0.1 g / 10 min to 2.5 g / 10 min can be obtained, which can be used as a modifier for the general-purpose polyoxymethylene to improve the spinnability of the general-purpose polyoxymethylene.

[0016] Specifically, the preparation method of the low melt index polyoxymethylene comprises the following steps:

[0017] The trioxymethylene, the cyclic ether compound, the heteropoly acid catalyst and the chain transfer agent are mixed uniformly in a pipeline mixer, and then continuously fed into a first-stage double-screw kneading rotor reactor to perform a polymerization reaction at 50-60°C, and then the reaction product is fed into a second-stage polymerization reactor, and a terminating agent is added to perform an inactivation treatment, and then the reaction powder is dried to obtain low-melt-index polyoxymethylene.

[0018] Further, in combination with the above, the cyclic ether compound is at least one of oxirane, oxetane, oxabutane, epichlorohydrin, 1,3-dioxolane, cyclohexene oxide or oxetane.

[0019] Further, in combination with the above, the heteropoly acid catalyst is at least one of phosphotungstic acid, phosphomolybdic acid, phosphomolybdotungstic acid, phosphotungstovanadic acid, silicomolybdic acid, phosphomolybdotungstovanadic acid or silicomolybdotungstic acid.

[0020] It should be noted that, in order to improve the dispersion uniformity of the heteropoly acid catalyst in the system, the heteropoly acid catalyst can be prepared in the form of a solution and added dropwise to the reaction system. The concentration of the heteropoly acid catalyst solution in the present application is not specifically required, as long as the amount of the heteropoly acid catalyst added meets the specific proportion requirement described above. For example, the heteropoly acid catalyst is phosphotungstic acid, and the phosphotungstic acid solution is an acetone solution of phosphotungstic acid with a mass concentration of 0.1%-0.3%.

[0021] Further, in combination with the above, the chain transfer agent is at least one of methyl acetal, ethyl acetal or butyl acetal.

[0022] Further, in combination with the above, the terminating agent is at least one of triphenylphosphine, triethylamine, triethanolamine or ammonia.

[0023] Further, in combination with the above, the mass ratio of the cyclic ether compound to trioxymethylene is 2:98-5:95.

[0024] The mass ratio of the chain transfer agent to trioxymethylene is (5-100) ppm:1.

[0025] It should be noted that 1 ppm = 0.0001%.

[0026] Further, in combination with the above, the amount of the terminating agent added is 0.05%-1% of the mass of trioxymethylene.

[0027] Further, in combination with the above, the polymerization reaction time is 1-3 min.

[0028] The preparation method of low-melt-index polyoxymethylene provided by the present application is simple to operate, and the low-melt-index polyoxymethylene prepared therefrom has good thermal stability and is suitable for large-scale production.

[0029] In the second aspect, the present application further provides a polyoxymethylene fiber masterbatch, which comprises polyoxymethylene raw material, heat stabilizer additive and the low-melt polyoxymethylene.

[0030] Preferably, the low-melt polyoxymethylene is added in an amount of 0.01% to 0.5% of the mass of the polyoxymethylene raw material.

[0031] Preferably, the heat stabilizer additive is added in an amount of 0.3% to 1% of the mass of the polyoxymethylene raw material.

[0032] Preferably, the heat stabilizer additive comprises antioxidant, formaldehyde absorbent, formic acid absorbent, terminating agent and lubricant in a mass ratio of 6-10:3-2:1:4-7:3-6.

[0033] Preferably, the antioxidant is at least one of di-triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionate, di-3-(3-tert-butyl-4-hydroxy-methylphenyl) propionate or triethylene glycol.

[0034] The preferred antioxidant can prevent the polyoxymethylene raw material from undergoing thermal oxidative degradation reaction, maintain the excellent performance of the polyoxymethylene matrix and prolong the service life of the material.

[0035] Preferably, the formaldehyde absorbent is at least one of melamine, ethylene urea, dicyandiamide, methylol melamine, urea, guanidine, hydrazine, oxalic acid dihydrazide, polyacrylamide or benzoguanamine.

[0036] Further preferably, the formaldehyde absorbent is melamine.

[0037] Since the polyoxymethylene resin may be decomposed into free formaldehyde during storage and processing, the preferred formaldehyde absorbent can effectively remove the free formaldehyde.

[0038] Preferably, the formic acid absorbent is at least one of calcium stearate, magnesium stearate, zinc stearate, magnesium oxide or zinc oxide.

[0039] Preferably, the terminating agent is at least one of triphenylphosphine, triethylamine, triethanolamine or ammonia.

[0040] Preferably, the lubricant is at least one of polyethylene wax, calcium stearate, polyamide wax, pentaerythritol tetrastearate, methyl stearate or ethylene bis-stearamide.

[0041] The application significantly improves the thermal stability of the general-purpose polyformaldehyde by selecting low-melt polyformaldehyde with a specific melt index and other thermal stabilizers and controlling the adding proportion of the low-melt polyformaldehyde and the thermal stabilizers, and the improved polyformaldehyde matrix has moderate rheology and viscosity, thereby being beneficial to the preparation of high-strength polyformaldehyde fibers, and the prepared polyformaldehyde fibers can be better applied to the textile field such as concrete, ropes or fishing nets, and have high popularization and application value.

[0042] Illustratively, the melt index of the general-purpose polyformaldehyde raw material is 6 g / 10 min to 27 g / min, preferably 9 g / 10 min to 15 g / min.

[0043] In a third aspect, the application further provides a preparation method of the polyformaldehyde fiber masterbatch, comprising the following steps:

[0044] The polyformaldehyde raw material, the low-melt polyformaldehyde and the thermal stabilizer are uniformly mixed, and then are melted and extruded in a twin-screw extruder at 180℃ to 230℃ to obtain the polyformaldehyde fiber masterbatch.

[0045] Further, the rotating speed of the twin-screw extruder during the melt blending is 120 rpm to 180 rpm, and the vacuum degree is 70 KPa to 100 KPa.

[0046] The preparation method of the polyformaldehyde fiber masterbatch provided by the application has the advantages of simplicity and continuous production, and the prepared polyformaldehyde fiber masterbatch has stable quality and is convenient for scale production.

[0047] The polyformaldehyde fiber masterbatch prepared by the application can be used to prepare polyformaldehyde fibers through a conventional melt spinning process in the art.

[0048] Illustratively, during the spinning process, the temperature of the melt extrusion is 190 to 200℃, the temperature of the spinning assembly is 210℃, the temperatures of the hot rollers GR1, GR2 and GR3 are 143℃, 145℃ and 145℃ respectively, the rotating speed ratio of GR2 / GR1 is 5 to 7, the rotating speed ratio of GR3 / GR2 is 1.1 to 1.5, and the rotating speed ratio of GR3 / GR1 is the draw ratio of the polyformaldehyde spinning.

[0049] The present application adopts heteropoly acid as catalyst, and by controlling the temperature of polymerization reaction and the adding amount of heteropoly acid catalyst, low melt index polyformaldehyde with melt index of 0.1 g / 10 min to 2.5 g / 10 min is prepared. After the low melt index polyformaldehyde and thermal stability aid are compounded according to a certain proportion, and are blended and extruded with general polyformaldehyde, it is unexpectedly found that the thermal stability of polyformaldehyde is significantly improved, and has moderate rheological property. After being applied to melt spinning process, the spinnability of polyformaldehyde is obviously improved, the drawing multiple is increased by about 1.4 times compared with that without adding the low melt index polyformaldehyde, the tensile strength of polyformaldehyde fiber can reach 6-8 g / d, and is increased by about 1.4 times at most. The yield and strength of fiber product are obviously improved, and can be widely applied to the fields of concrete, rope and other civil construction materials, and fishing net and other textile products, and has high practical value. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 TGA graph of polyformaldehyde fiber masterbatch prepared for example 12 and comparative example 1 of the present application. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0052] In order to better illustrate the present application, the following examples are further illustrated by examples.

[0053] Unless otherwise specified, the instruments and reagents used in the following examples are commercially available products.

[0054] The test methods of various properties in the following examples are as follows:

[0055] Melt index (MFR) test: test according to GB / T 3682-2000, temperature set to 190℃, load 2.16 kg.

[0056] Isothermal thermal weight loss (M value) test: polyformaldehyde powder or granules are placed in a nitrogen oven at 222℃, and the change rate of mass before and after the sample is treated is tested after constant temperature for 45 min.

[0057] Molecular weight test: TRSEC MODEL 302 of Visker company is used to detect molecular weight and molecular weight distribution with hexafluoroisopropanol as mobile phase.

[0058] Polymerization conversion rate test: sample is taken at the discharge port of a first-order double screw kneading rotor reactor, washed with water, weighed, and determined by combining nuclear magnetic analysis method.

[0059] Thermal decomposition temperature test: using TG instrument, the temperature is raised to 600℃ at the rate of 10℃ / min, the temperature of the weight loss of 5% of the polyformaldehyde sample is tested.

[0060] Polyformaldehyde fiber strength test: the strength of polyformaldehyde fiber is tested by using XL-A type yarn strength tester, and the test conditions are: clamp distance 250mm, tensile speed 200mm / min, and pre-tension 5cN.

[0061] Example 1

[0062] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0063] Trioxymethylene, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 1ppm and 70ppm of the mass of trioxymethylene respectively, the flow rate of trioxymethylene is 40kg / h, after being fully mixed and uniformly distributed, the mixture is continuously sent into a first-order double screw kneading rotor reactor, and the polymerization reaction is carried out at 60℃ for 2min, then the reaction product is sent into a second-order polymerization reactor, 0.2% triphenylphosphine terminator of the mass of trioxymethylene is added for inactivation treatment, then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0064] Example 2

[0065] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0066] Trioxymethylene, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 1ppm and 70ppm of the mass of trioxymethylene respectively, the flow rate of trioxymethylene is 40kg / h, after being fully mixed and uniformly distributed, the mixture is continuously sent into a first-order double screw kneading rotor reactor, and the polymerization reaction is carried out at 60℃ for 2min, then the reaction product is sent into a second-order polymerization reactor, 0.2% triphenylphosphine terminator of the mass of trioxymethylene is added for inactivation treatment, then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0067] Example 3

[0068] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0069] The trioxane, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 3ppm and 50ppm of the mass of trioxane respectively, the flow rate of trioxane is 40kg / h, after being mixed uniformly, the mixture is continuously sent into a first-stage double screw kneading rotor reactor, and the polymerization reaction is carried out at 56℃ for 2min, then the reaction product is sent into a second-stage polymerization reactor, and 0.3% triphenylphosphine terminator of the mass of trioxane is added to inactivate the reaction product, then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0070] Example 4

[0071] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0072] The trioxane, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 3ppm and 50ppm of the mass of trioxane respectively, the flow rate of trioxane is 40kg / h, after being mixed uniformly, the mixture is continuously sent into a first-stage double screw kneading rotor reactor, and the polymerization reaction is carried out at 56℃ for 2min, then the reaction product is sent into a second-stage polymerization reactor, and 0.3% triphenylphosphine terminator of the mass of trioxane is added to inactivate the reaction product, then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0073] Example 5

[0074] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0075] The trioxane, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 3ppm and 50ppm of the mass of trioxane respectively, the flow rate of trioxane is 40kg / h, after being mixed uniformly, the mixture is continuously sent into a first-stage double screw kneading rotor reactor, and the polymerization reaction is carried out at 56℃ for 2min, then the reaction product is sent into a second-stage polymerization reactor, and 0.3% triphenylphosphine terminator of the mass of trioxane is added to inactivate the reaction product, then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0076] Example 6

[0077] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0078] The trioxane, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 4.5ppm and 20ppm of the mass of trioxane respectively, the flow rate of trioxane is 40kg / h, after being mixed uniformly, the mixture is continuously sent into a first-stage double screw kneading rotor reactor, and the polymerization reaction is carried out at 50℃ for 1.5min, then the reaction product is sent into a second-stage polymerization reactor, 0.2% triphenylphosphine terminator of the mass of trioxane is added to inactivate the reaction product, and then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0079] Example 7

[0080] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0081] The trioxane, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 4.5ppm and 20ppm of the mass of trioxane respectively, the flow rate of trioxane is 40kg / h, after being mixed uniformly, the mixture is continuously sent into a first-stage double screw kneading rotor reactor, and the polymerization reaction is carried out at 50℃ for 1.5min, then the reaction product is sent into a second-stage polymerization reactor, 0.2% triphenylphosphine terminator of the mass of trioxane is added to inactivate the reaction product, and then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0082] Example 8

[0083] The embodiment of the present application provides a preparation method of low-melt-index polyformaldehyde, which comprises the following steps:

[0084] The trioxane, 1,3-dioxolane, 0.2wt% phosphotungstic acid acetone solution and methylal are added into a pipeline mixer, wherein the adding amount of 1,3-dioxolane, phosphotungstic acid and methylal is 4wt%, 4.5ppm and 20ppm of the mass of trioxane respectively, the flow rate of trioxane is 40kg / h, after being mixed uniformly, the mixture is continuously sent into a first-stage double screw kneading rotor reactor, and the polymerization reaction is carried out at 50℃ for 1.5min, then the reaction product is sent into a second-stage polymerization reactor, 0.2% triphenylphosphine terminator of the mass of trioxane is added to inactivate the reaction product, and then the reaction powder is dried and devolatilized to obtain low-melt-index polyformaldehyde.

[0085] The performance test results of the low-melt-index polyformaldehyde prepared in the above examples 1-8 are shown in Table 1.

[0086] Table 1

[0087]

[0088] Examples 9-15

[0089] The low-melt-polyoxymethylene prepared in Example 5 is compounded with a thermal stabilizer aid in a certain proportion, then mixed uniformly with polyoxymethylene raw powder, and then melted, devolatilized, and granulated in a twin-screw extruder to prepare a polyoxymethylene fiber masterbatch.

[0090] The formula of the spinning-grade polyoxymethylene fiber masterbatch provided in Examples 9-15 is shown in Table 2.

[0091] Table 2

[0092]

[0093] In the above Examples 9-15, the thermal stabilizer aid is an antioxidant, a formaldehyde absorber, a formaldehyde absorber, a terminator, and a lubricant in a mass ratio of 10:2:1:6:5; the antioxidant is di-triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionic acid ester, the formaldehyde absorber is melamine, the formaldehyde absorber is calcium stearate, the terminator is triphenylphosphine, and the lubricant is ethylene bis-stearamide.

[0094] The preparation process of the polyoxymethylene fiber includes the following steps:

[0095] Step a, uniformly mixing general-grade polyoxymethylene raw material, low-melt-polyoxymethylene, antioxidant, formaldehyde absorber, formaldehyde absorber, terminator, and lubricant, and then extruding and granulating in a twin-screw extruder to obtain a polyoxymethylene fiber masterbatch;

[0096] Step b, melt-extruding the polyoxymethylene fiber masterbatch, spinning, drawing, and winding to obtain high-strength polyoxymethylene fiber; the temperature of melt-extrusion is 195°C, the temperature of the spinning assembly is 210°C, and the temperatures of the hot rollers GR1, GR2, and GR3 are 143°C, 145°C, and 145°C, respectively. The polyoxymethylene nascent fiber is drawn in two stages, the GR2 / GR1 rotation ratio is the first-stage draw, the GR3 / GR2 rotation ratio is the second-stage draw, and the GR3 / GR1 is the total draw ratio, and the draw ratio is selected based on the absence of broken filaments and continuous and stable winding for 20 min.

[0097] Comparative Example 1

[0098] This comparative example provides a polyoxymethylene fiber including general-grade polyoxymethylene fiber raw material and a thermal stabilizer aid, wherein the proportion of the thermal stabilizer aid relative to the general-grade polyoxymethylene fiber raw material is 0.7%, and the thermal stabilizer aid is di-triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionic acid ester, calcium stearate, triphenylphosphine, and ethylene bis-stearamide in a mass ratio of 10:2:1:6:5.

[0099] The above polyformaldehyde fiber components are prepared into polyformaldehyde fiber according to the same method as in Example 12.

[0100] Comparative Example 2

[0101] The present comparative example provides a polyformaldehyde fiber, which has the same raw material composition as in Example 12, except that the low melt index polyformaldehyde (0.5 g / 10 min) is replaced with an equal amount of low melt index polyformaldehyde having a melt index of 4 g / 10 min.

[0102] The preparation method of the above low melt index polyformaldehyde comprises the following steps:

[0103] Trimeric formaldehyde, 1,3-dioxolane, 0.2 wt% phosphotungstic acid acetone solution and methylal are added to a pipeline mixer, wherein the mass ratio of 1,3-dioxolane, phosphotungstic acid and methylal to trimeric formaldehyde is 4:96, 6 ppm and 40 ppm respectively, after being fully mixed and uniformly mixed, they are continuously sent into a first-order double screw kneading rotor reactor, and a polymerization reaction is carried out at 70°C for 2 min, then the reaction product is sent into a second-order polymerization reactor, and a triphenylphosphine terminator is added at the same time for inactivation treatment, then the reaction powder is dried and devolatilized to obtain low melt index polyformaldehyde, and the melt index is 4 g / 10 min.

[0104] The above polyformaldehyde fiber components are prepared into polyformaldehyde fiber according to the same method as in Example 12.

[0105] The performance test results of the polyformaldehyde fiber masterbatch and fiber prepared in Examples 9-15 are shown in Table 3.

[0106] Table 3

[0107]

[0108] The TGA graph of Example 12 and Comparative Example 1 is shown in Figure 1 From the graph, it can be seen that the thermal decomposition temperature of Example 12 is significantly higher than that of Comparative Example 1, which proves that the low melt index polyformaldehyde with a specific melt index in the present application can effectively improve the thermal stability of the general-purpose polyformaldehyde raw material.

[0109] The low melt index polyformaldehyde prepared in other examples of the present application in Examples 9-15 can achieve a technical effect basically equivalent to that of the original Examples 9-15.

[0110] The antioxidants, formaldehyde absorbers, formaldehyde absorbers, terminators and lubricants in Examples 9-15 are replaced with other substances defined in the present application, as long as the amount is within the range defined in the present application, and a technical effect basically equivalent to the corresponding example can be achieved.

[0111] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement or improvement made in the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. Use of a low-melt polyoxymethylene in improving the spinning properties of polyoxymethylene, characterized in that The low-melt-index polyformaldehyde is added to the polyformaldehyde raw material as a modifier; The polyformaldehyde fiber spinning method is as follows: the polyformaldehyde raw material, the low-melt-index polyformaldehyde and the thermal stabilizer are uniformly mixed, melted and extruded in a double-screw extruder at 180-230°C to obtain polyformaldehyde fiber masterbatch; The polyformaldehyde fiber masterbatch is melted and extruded, spun, drawn and wound to obtain high-strength polyformaldehyde fiber. The low-melt-index polyformaldehyde is added in an amount of 0.01%-0.5% of the mass of the polyformaldehyde raw material; and the low-melt-index polyformaldehyde has a melt index of 0.1-2.5 g / 10 min.

2. Use according to claim 1, wherein The low-melt-index polyformaldehyde has a melt index of 0.3-0.7 g / 10 min.

3. The use according to claim 1, wherein The preparation method of the low-melt-index polyformaldehyde comprises the following steps: The trioxymethylene, the cyclic ether compound, the heteropoly acid catalyst and the chain transfer agent are uniformly mixed, and a polymerization reaction is carried out at 50-60°C; a termination agent is added to terminate the polymerization reaction, and the product is dried to obtain the low-melt-index polyformaldehyde. The mass ratio of the heteropoly acid catalyst to the trioxymethylene is (1-6) ppm:

1.

4. Use according to claim 3, wherein the compound is ###0002### The cyclic ether compound is at least one of oxirane, oxetane, oxolane, epichlorohydrin, 1,3-dioxolane, cyclohexene oxide or oxetane; and / or The heteropoly acid catalyst is at least one of phosphotungstic acid, phosphomolybdic acid, phosphomolybdotungstic acid, phosphotungstovanadic acid, silicomolybdic acid, phosphomolybdotungstovanadic acid or silicomolybdotungstic acid; and / or The chain transfer agent is at least one of methyl acetal, ethyl acetal or butyl acetal; and / or The termination agent is at least one of triphenylphosphine, triethylamine, triethanolamine or ammonia water.

5. The use according to claim 3, wherein the compound is ###0002### The mass ratio of the cyclic ether compound to the trioxymethylene is 2:98-5:95; and / or The mass ratio of the chain transfer agent to the trioxymethylene is (5-100) ppm:1; and / or The termination agent is added in an amount of 0.05%-1% of the mass of the trioxymethylene; and / or The polymerization reaction is carried out for 1-3 min.

6. A polyoxymethylene fiber masterbatch, characterized by The low-melt-index polyformaldehyde is added to the polyformaldehyde raw material as a modifier; 7. Polyoxymethylene fibre masterbatch according to claim 6, characterised in that The low-melt-index polyformaldehyde is added in an amount of 0.01%-0.5% of the mass of the polyformaldehyde raw material; and / or The thermal stabilizer additive is added in an amount of 0.3%-1% of the mass of the polyformaldehyde raw material.

8. Polyoxymethylene fibre masterbatch according to claim 7, characterised in that The thermal stabilizer additive comprises antioxidants, formaldehyde absorbers, formic acid absorbers, termination agents and lubricants in a mass ratio of 6-10:3-2:1:4-7:3-6.

9. Polyoxymethylene fibre masterbatch according to claim 8, characterised in that The antioxidants are at least one of di-triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionic acid ester, di-3-(3-tert-butyl-4-hydroxy-methylphenyl) propionate or triethylene glycol; and / or The formaldehyde absorbers are at least one of melamine, ethylene urea, dicyandiamide, methylol melamine, urea, guanidine, hydrazine, oxalic acid dihydrazide, polyacrylamide or benzoguanamine; and / or The formic acid absorbers are at least one of calcium stearate, magnesium stearate, zinc stearate, magnesium oxide or zinc oxide; and / or The termination agents are at least one of triphenylphosphine, triethylamine, triethanolamine or ammonia water; and / or The lubricant is at least one of a polyethylene wax, calcium stearate, a polyamide wax, pentaerythritol tetrastearate, methyl stearate, or ethylene bis-stearamide. The lubricant is at least one of a polyethylene wax, calcium stearate, a polyamide wax, pentaerythritol tetrastearate, methyl stearate, or ethylene bis-stearamide.

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