A plasma-assisted method for preparing modified aramid pulp

Abstract

The present invention discloses a plasma-assisted method for preparing modified aramid pulp, belonging to the field of synthetic fiber technology. This method constructs an integrated plasma impregnation and modified-aramid pulping process for preparing para-aramid modified fiber pulp. By utilizing the synergistic effect of the plasma treatment process and the pulping process, the method avoids the use of toxic chemical additives and reduces the impact of the plasma treatment on the performance of the modified aramid pulp as a polymer bulking filler. This method significantly shortens the process path, improves production efficiency, and reduces production costs, making it suitable for large-scale continuous industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of synthetic fibers, and particularly relates to a method for preparing modified aramid pulp with the aid of plasma. Background Art

[0002] Poly(p-phenylene terephthalamide) (PPTA) fiber, also known as aramid 1414 and para-aramid, is a new synthetic fiber with excellent mechanical properties and good chemical and thermal stability. Para-aramid pulp, a para-aramid product made from short para-aramid fibers, is an important raw material for aramid products such as aramid paper and aramid honeycomb. It is also a filler widely used to increase the volume and improve the wear resistance of rubber and thermoplastics.

[0003] Due to the strong chemical inertness of para-aramid fiber itself, para-aramid pulp has poor compatibility with thermoplastics or rubbers and is difficult to combine well. Therefore, when aramid pulp is used as a reinforcing filler, it must first be surface-modified and prepared into a modified para-aramid pulp with good compatibility with the target material before use. From the perspective of the aramid industry chain, the existing technology generally uses the modification of aramid pulp finished products to prepare modified para-aramid pulp, that is, the preparation of modified para-aramid pulp is achieved through two independent processes of first preparing the pulp finished product and then modifying the pulp finished product. From the perspective of industrial practice, the process of directly preparing modified para-aramid pulp from aramid raw yarn in one go is currently rare.

[0004] In industry, the finished product of para-aramid pulp is generally prepared by precipitation method or refining method, wherein the precipitation method mostly uses aramid stock solution or pre-dissolved aramid resin as raw material to produce aramid pulp. Affected by the source of raw materials, this method is mostly adopted by para-aramid source manufacturers. One type of refining method is a method of using para-aramid filaments, staple fibers or scraps with longer fiber lengths as raw materials to produce para-aramid pulp. Currently, units on the market that do not have aramid production capacity mostly use this method for pulp production. At the same time, this method can also be used for the recycling of aramid products or scraps, and its application is relatively wide. This method is to cut the longer para-aramid fibers into short pieces, refine them, and then break up the filament fibers to obtain para-aramid pulp. The Chinese patent document with publication number CN102535223A discloses a method for preparing and grading para-aramid pulp, in which the aramid filaments are cut and then mechanically ground and pulped, and then dried and loosened to prepare para-aramid pulp. Since para-aramid itself has a high mechanical strength, the efficiency of decomposing it into pulp simply by grinding is not good. In order to ensure the decomposition and pulping efficiency of para-aramid fibers, it is often necessary to add additives such as alkali solution during the pulping process to embrittle the aramid fibers through chemical etching. The Chinese patent document with publication number CN117127435A discloses a process for preparing high-permeability aramid pulp / molecular sieve adsorption paper, which uses potassium hydroxide and dimethyl sulfoxide as decomposition additives to pre-treat aramid to promote the pulping process. The use of additives has solved the problem of pulping efficiency to a certain extent, but these additives are all highly corrosive or toxic, resulting in the generation of a large amount of polluting wastewater during the decomposition process, and are highly corrosive to the pulping equipment.

[0005] Among the many methods for modifying aramid materials, plasma treatment combined with impregnation modification has received increasing attention in recent years. This method is to place the aramid material in a plasma treatment device, and by applying voltage or other methods, the gas is formed into a plasma rich in active free radicals, negative ions and free electrons. The plasma scours the aramid surface to react and generate a large number of active groups, and then graft coupling agents or other active substances on these groups by impregnation to enhance the compatibility of the aramid material surface with other polymer materials. The Chinese patent document with publication number CN109680478A discloses a method for improving the shear strength of the interface between aramid fiber and epoxy resin by plasma treatment combined with impregnation modification. After treatment, the surface activity of the aramid fiber is effectively enhanced and its compatibility with the matrix is ​​improved. Compared with conventional chemical impregnation modification methods, plasma treatment has high environmental protection and high efficiency. It produces less pollutants and is easy to collect and treat. The required active groups can be efficiently generated on the surface of high-efficiency aramid materials by adjusting the reaction atmosphere. However, due to the extremely high plasma activity during the treatment process, it is very easy to over-etch the aramid surface, causing the aramid material to become brittle, resulting in problems such as reduced strength of the treated aramid material, affecting its use as a reinforcing filler.

[0006] To control the impact of embrittlement on the performance of aramid materials, the plasma treatment power used in the prior art is generally not too high. For example, in the aforementioned Chinese patent document with publication number CN109680478A, the typical plasma treatment power used in its embodiments is 400W, and the treatment time to achieve good results is 1 minute. Chinese patent document with publication number CN114724873A discloses a method for plasma-treating aramid fibers to enhance dielectric barrier discharge insulating rods. The plasma treatment power used is 200W to 500W, and the treatment time is 1 minute to 3 minutes. Although lower-power plasma treatment has a smaller impact on the performance of aramid fibers, it requires a longer treatment time and has relatively low production efficiency. Summary of the Invention

[0007] The present invention provides a plasma-assisted method for preparing modified aramid pulp. This method is simple, has high pulping efficiency, and does not require the use of toxic chemical additives. This method can be used to prepare modified para-aramid pulp with lower equipment investment and production costs, and the resulting modified para-aramid pulp exhibits excellent polymer compatibility and mechanical properties.

[0008] To achieve the object of the present invention, the present invention provides a technical solution for a plasma-assisted method for preparing modified aramid pulp, comprising the following steps:

[0009] (1) cutting the para-aramid filaments into aramid staple fibers, and then performing plasma treatment to obtain treated aramid staple fibers;

[0010] (2) mixing the treated aramid staple fibers obtained in step (1) with the impregnation grinding liquid to form an original slurry, heating the slurry to 50° C. to 65° C., grinding and beating the slurry, and separating the slurry to obtain a primary abrasive;

[0011] (3) adding water to the primary abrasive obtained in step (2) to form a primary grinding pulp, and grinding to obtain a fine grinding pulp;

[0012] (4) Filtering the refined pulp obtained in step (3) to separate the solids, drying and loosening the solids to obtain modified aramid pulp.

[0013] Furthermore, in step (1), the length of the aramid staple fiber is 3 mm to 6 mm; the atmosphere used for plasma treatment is one of air, argon, and carbon tetrafluoride, the power is 2 kW to 3.5 kW, and the treatment time is 10 s to 15 s.

[0014] Furthermore, in step (2), the impregnation and grinding liquid is prepared by an aramid surface modifier, pure water and ethanol in a mass fraction ratio of 0.04-0.07:1:1, and acetic acid is added to adjust the pH to 3.5-4.5 before use; wherein the aramid surface modifier is one of KH550, KH560 or KH570.

[0015] Furthermore, in step (2), the aramid content in the original slurry is 12wt%~17wt%; the grinding and beating time is 10min~15min; and the liquid content in the initial abrasive is 50wt%~70wt%.

[0016] Furthermore, in the step (3), the aramid content in the primary grinding pulp formed after adding water is 5wt%~7wt%, and the grinding time is 7~10min.

[0017] Furthermore, in step (4), the drying and loosening temperature is 80°C to 110°C until the moisture content of the modified aramid pulp reaches below 6wt%.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] (1) The technical solution of the present invention, by constructing a new process scheme that integrates plasma-assisted beating and beating impregnation, utilizes the embrittlement effect of the plasma treatment process on aramid fibers, replacing the step of using chemical additives to embrittle the fibers before beating in the existing independent aramid pulp preparation process. While ensuring that the modified para-aramid pulp product has a high beating degree, the technical solution of the present invention effectively avoids the use of corrosive and toxic additives in the conventional chemical-assisted beating process, thereby improving the environmental friendliness of the process and reducing the corrosion resistance requirements of the equipment.

[0020] (2) The technical solution of the present invention, through a process arrangement of first plasma treatment and then beating, utilizes the characteristic of mechanical grinding during the beating process to eliminate the internal structural weaknesses of aramid, thereby reducing the amount of structural weaknesses caused by the embrittlement effect of plasma treatment in the modified para-aramid pulp product, and further enhancing the reinforcing effect of the product as a reinforcing filler on polymers. Compared with the modified para-aramid pulp produced by the prior art process of first preparing the finished aramid pulp product and then plasma treatment and impregnation modification, the aramid-polyoxymethylene composite material reinforced by the pulp product produced by the technical solution of the present invention has a tensile strength of up to 120% and a wear resistance of up to 157% of the former.

[0021] (3) The technical solution of the present invention reduces the effect of plasma treatment on the mechanical properties of the final modified para-aramid pulp product. This solution uses 4 to 7 times the power of the existing plasma treatment process to treat aramid fibers, which can effectively improve the plasma treatment efficiency and shorten the treatment time by four-fifths compared with the existing process solution.

[0022] (4) Compared with the existing modified aramid pulp preparation process in which the beating and modification processes are independent of each other, the technical solution of the present invention is simpler, significantly shortens the production path, saves a lot of process equipment investment and energy consumption expenditure, greatly reduces production costs, improves production efficiency, and is suitable for industrial continuous production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a process flow chart of a specific embodiment of the present invention;

[0024] In the figure: 1 is the raw silk coil, 2 is the cutting machine, 3 is the plasma treatment machine, 4 is the primary grinding system, 5 is the centrifugal squeezer, 6 is the fine grinding system, 7 is the nanofiltration system, 8 is the plate and frame filter press, 9 is the ultrafiltration system, 10 is the drying and fluffing machine, and 11 is the clarification and sedimentation tank. DETAILED DESCRIPTION

[0025] In order to more clearly understand the purpose, technical features and effects of the present invention, the following is a detailed description with reference to the accompanying drawings and embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] In one embodiment of the present invention, the plasma-assisted method for preparing modified aramid pulp is as follows: Figure 1 As shown, the device operates according to the following steps:

[0027] (1) Para-aramid raw yarn is unwound from the raw yarn reel 1, bundled and then sent to the cutting machine 2 for cutting. The cutting machine 2 is a rotary cutter, which cuts the raw yarn into aramid staple fibers of a predetermined length by adjusting the rotary cutter speed. The aramid staple fibers are then sent to the plasma treatment machine 3 via a conveyor belt for plasma treatment.

[0028] (2) The plasma processor 3 uses a dielectric barrier discharge plasma generator. The plasma generator operates at a specified processing power, ionizing the atmosphere used for plasma treatment in the internal cavity of the plasma processor 3 to generate plasma. The aramid staple fibers fed into the plasma processor 3 react with the plasma in the cavity and become embrittled. After a certain reaction time, the aramid staple fibers are processed and sent out of the plasma processor 3.

[0029] More specifically, the plasma treatment process involves the plasma treatment atmosphere filling the space between the upper and lower plates of the plasma generator during operation. A high voltage is applied between the plates to excite the atmosphere, forming a corresponding plasma. As the aramid staple fibers, laid flat on a conveyor belt, pass between the plates, they are infiltrated and eroded by the plasma, reacting with the free electrons and free radicals in the plasma. This creates active groups on the aramid fiber surface and weakens the fiber structure due to plasma etching. The time it takes for the aramid staple fibers to pass between the plasma generator's plates is the processing time of the plasma processor 3. This can be controlled by controlling the speed of the conveyor belt carrying the aramid fibers through the plasma processor 3. The processing power of the plasma treatment is adjusted by varying the power of the variable frequency power supply used by the plasma generator.

[0030] (3) The aramid staple fibers treated by the plasma treatment machine 3 are mixed with an appropriate amount of impregnation and grinding liquid to form an original slurry containing a certain mass fraction of aramid. The impregnation and grinding liquid is prepared by mixing aramid surface modifier, ethanol and water in a certain proportion, and acetic acid is added to adjust the pH value to a specified value. After the original slurry is mixed, it is sent to the primary grinding system 4 for grinding and beating. When the device is first started, the impregnation and grinding liquid prepared with fresh raw materials is used. After the device is started, the impregnation and grinding liquid prepared by supplementing the components according to the impregnation and grinding liquid formula after the material liquid recovered from each process stage is tested. The primary grinding system 4 is a knife-stick beating machine, which crushes the aramid fibers by shearing the slurry and then performs grinding and beating. A heating sleeve is set outside the beating barrel of the primary grinding system 4 to heat the slurry. After the original slurry enters the primary grinding system 4, it is first heated to a certain temperature and then continuously ground and beaten for a certain time at a fixed speed of 300 rpm. After grinding and beating, the aramid staple fibers in the slurry are initially broken, and at the same time, the aramid modifier in the impregnated grinding liquid combines with the active groups on the aramid surface, thereby completing the surface impregnation modification of the aramid.

[0031] (4) After the pulping, the original pulp is removed from the primary grinding system 4 and sent to the centrifugal squeezer 5, where it is squeezed out under the action of centrifugal force. By controlling the speed of the centrifugal squeezer 5, the original pulp is separated into primary grinding material with a specified liquid content and extrudate. After the primary grinding material is formed, water is added to prepare the primary grinding pulp with a specified aramid content, and then it is sent to the fine grinding system 6 for grinding for a certain time. The fine grinding system 6 is a disc refiner with a fixed working speed of 500rpm. After the primary grinding pulp enters the fine grinding system 6, it is further broken and fibrillated under the grinding action of the grinding disc to achieve a fiber morphology consistent with the finished pulp. At the same time, through the addition of pure water and the grinding action of the fine grinding system 6, the aramid fiber is washed as a whole, and most of the impregnation and grinding liquid components that have not been combined with the aramid surface are removed, preventing excessive residues of the impregnation and grinding liquid components from affecting the capacity-enhancing performance of the aramid pulp product for engineering plastics.

[0032] (5) After the primary pulp is ground through the fine grinding system 6, a refined pulp is formed, which is then fed into a plate and frame filter press 8 for pressure filtration to obtain aramid fiber solids. The solids are spread flat on a conveyor belt and fed into a dryer and fluffer 10 for drying and fluffing at a specified temperature to obtain a finished modified aramid pulp. In this embodiment, by controlling the residence time of the solids in the dryer and fluffer 10, the moisture content of the aramid pulp obtained in all comparative examples and examples is controlled to ≤6 wt%.

[0033] (6) The filtrate obtained by filtering the refined pulp by the plate and frame filter press 8 is input into the nanofiltration system 7 as raw water, and nanofiltration separation is performed at an operating pressure of 3.0 MPa and a recovery rate of 95% of the aramid surface modifier. Under the action of the nanofiltration system 7, most of the impregnating agent components in the filtrate are intercepted and concentrated on the nanofiltration concentrated water side to form nanofiltration concentrated water, and nanofiltration fresh water containing a small amount of impregnating pulp components is separated on the nanofiltration fresh water side. This nanofiltration fresh water is recovered and returned to step (3) for the preparation of primary refined pulp, thereby saving some water.

[0034] (7) After the nanofiltration concentrate carrying the impregnating agent components leaves the nanofiltration system 7, it is mixed with the extrudate in step (3) to form a mixed liquid and sent to the ultrafiltration system 9 for ultrafiltration operation at an operating pressure of 0.7 MPa and a concentrated water to fresh water ratio of 1:7. After ultrafiltration, the insoluble impurities in the mixed liquid are retained by ultrafiltration on the ultrafiltration concentrate side to form ultrafiltration concentrate. After the ultrafiltration concentrate leaves the ultrafiltration system 9, it enters the clarification and sedimentation tank 11 for clarification and sedimentation. A small amount of sludge generated after clarification and sedimentation is discharged as solid waste. The generated supernatant is combined with the ultrafiltration fresh water generated on the ultrafiltration fresh water side and then supplemented with relevant components according to the test and impregnation grinding liquid formula, and then returned to step (2) as the impregnation grinding liquid for preparing the original slurry, thereby maximizing the recycling of the impregnation grinding liquid components and water resources used in the process. Example 1

[0035] This example uses 200D aramid raw yarn to conduct an aramid pulp production test, with a total input of 500g of aramid raw yarn. The test process is carried out according to the specific implementation method, and the technical parameters of each step are as follows:

[0036] In step (1), the length of the aramid staple fibers obtained by cutting the aramid raw yarn by the cutting machine 2 is 3 mm, the power of the plasma treatment machine 3 during the plasma treatment is 3 kW, the treatment time is 12 s, and the atmosphere used for the plasma treatment is carbon tetrafluoride.

[0037] In step (2), the mass fraction ratio of the aramid surface modifier, pure water and ethanol in the impregnation grinding liquid is 0.05:1:1, and the pH value is adjusted to 4 after adding acetic acid. The aramid surface modifier in the impregnation grinding liquid is KH550. The amount of impregnation grinding liquid added to the original slurry is controlled to control the aramid content in the original slurry to 12wt%. The temperature of the original slurry during grinding and beating in the primary grinding system 4 is controlled to 50°C, and the grinding and beating time is 10 minutes.

[0038] In step (3), the rotation speed of the centrifugal squeezer 5 is controlled to control the liquid content of the separated primary abrasive to 60 wt%. The amount of water added to the primary abrasive is adjusted so that the aramid content in the formed primary pulp is 6 wt%. The grinding time of the primary pulp in the fine grinding system 6 is controlled to 7 minutes.

[0039] In step (4), the drying and loosening temperature is 80°C.

[0040] After the test, all the modified aramid pulp products were collected and stored at a constant temperature of 20° C. for future use. Example 2

[0041] This example uses 200 denier aramid yarn to conduct an aramid pulp production test, with a total input of 300g of aramid yarn. The test process is carried out according to the specific implementation method, and the technical parameters of each step are as follows:

[0042] In step (1), the length of the aramid staple fibers obtained by cutting the aramid raw yarn by the cutting machine 2 is 6 mm, the power of the plasma treatment machine 3 during the plasma treatment is 2 kW, the treatment time is 15 s, and the atmosphere used for the plasma treatment is air.

[0043] In step (2), the mass fraction ratio of the aramid surface modifier, pure water and ethanol in the impregnation and grinding liquid is 0.07:1:1, and the pH value is adjusted to 4.5 after adding acetic acid. The aramid surface modifier in the impregnation and grinding liquid is KH560. The amount of impregnation and grinding liquid added to the original slurry is controlled to control the aramid content in the original slurry to 15wt%. The temperature of the original slurry during grinding and beating in the primary grinding system 4 is controlled to 65°C, and the grinding and beating time is 15min.

[0044] In step (3), the rotation speed of the centrifugal squeezer 5 is controlled to control the liquid content of the separated primary abrasive to 70 wt%. The amount of water added to the primary abrasive is adjusted so that the aramid content in the formed primary pulp is 5 wt%. The grinding time of the primary pulp in the fine grinding system 6 is controlled to 10 minutes.

[0045] In step (4), the drying and loosening temperature is 110°C.

[0046] After the test, the modified aramid pulp product was collected and stored at a constant temperature of 20°C for future use. Example 3

[0047] This example uses 200D aramid raw yarn to conduct an aramid pulp production test, with a total input of 500g of aramid raw yarn. The test process is carried out according to the specific implementation method, and the technical parameters of each step are as follows:

[0048] In step (1), the length of the aramid staple fibers obtained by cutting the aramid raw yarn by the cutting machine 2 is 5 mm, the power of the plasma treatment machine 3 during the plasma treatment is 3.5 kW, the treatment time is 10 s, and the atmosphere used for the plasma treatment is argon.

[0049] In step (2), the mass fraction ratio of the aramid surface modifier, pure water and ethanol in the impregnation and grinding liquid is 0.04:1:1, and the pH value is adjusted to 3.5 after adding acetic acid. The aramid surface modifier in the impregnation and grinding liquid is KH570. The amount of impregnation and grinding liquid added to the original slurry is controlled to control the aramid content in the original slurry to 17wt%. The temperature of the original slurry during grinding and beating in the primary grinding system 4 is controlled to 60°C, and the grinding and beating time is 12 minutes.

[0050] In step (3), the rotation speed of the centrifugal squeezer 5 is controlled to control the liquid content of the separated primary abrasive to 50 wt%. The amount of water added to the primary abrasive is adjusted so that the aramid content in the formed primary pulp is 7 wt%. The grinding time of the primary pulp in the fine grinding system 6 is controlled to 9 minutes.

[0051] In step (4), the drying and loosening temperature is 95°C.

[0052] After the test, the obtained aramid pulp product was collected and stored at a constant temperature of 20°C for future use. Comparative Example 1

[0053] This comparative example simulates the existing technical process route, uses a chemical additive-assisted beating method to prepare aramid pulp, and uses conventional plasma treatment combined with an impregnation method to modify it. The aramid precursor used and the feed amount are consistent with those in Example 1. The specific implementation method is:

[0054] (1) The aramid raw yarn was cut into 3 mm aramid staple fibers by a cutting machine 2. The obtained aramid staple fibers were not subjected to plasma treatment. Instead, the obtained aramid staple fibers were mixed with sodium hydroxide and dimethyl sulfoxide in a mass ratio of 18:2:80. The mixed slurry was placed in a mixer and stirred at a speed of 80 rpm for 30 minutes to chemically pre-disintegrate the aramid staple fibers.

[0055] (2) After the pre-disintegration is completed, the slurry is sent to the centrifugal squeezer 5 for squeezing. The speed of the centrifugal squeezer 5 is controlled so that the liquid content of the solid obtained after squeezing is less than 60wt%. The obtained solid is then fully washed with pure water to remove residual dimethyl sulfoxide and sodium hydroxide, and an appropriate amount of pure water is added to prepare an original slurry with an aramid content of 12wt%.

[0056] (3) The raw slurry is fed into the primary grinding system 4 and ground and beaten at a temperature of 50°C for 10 minutes. After grinding, the ground raw slurry is removed from the primary grinding system 4 and then added with an appropriate amount of pure water to prepare a primary grinding pulp with an aramid content of 6 wt%.

[0057] (4) The primary pulp is sent to the fine grinding system 6 for grinding for 9 minutes to obtain a refined pulp. The refined pulp is sent to the plate and frame filter press 8 for filtration to obtain aramid fiber solids, and then sent to the drying and fluffing machine 10 for drying and fluffing at 80°C to obtain a crude aramid pulp.

[0058] (5) The obtained crude aramid pulp product is fed into a plasma treatment machine 3, and the crude aramid pulp product is subjected to plasma treatment using a power of 500 W for 1 minute in a carbon tetrafluoride atmosphere.

[0059] (6) The plasma-treated crude aramid pulp was mixed with an appropriate amount of impregnation and grinding liquid to form an impregnation liquid with an aramid content of 12 wt%. The impregnation and grinding liquid was prepared by mixing an aramid surface modifier, pure water, and ethanol in a ratio of 0.05:1:1, and acetic acid was added to adjust the pH to 4. The aramid surface modifier was KH550. The impregnation liquid was placed in a stirrer at 50 rpm and stirred for 10 minutes to impregnate the aramid fibers.

[0060] (7) After the impregnation is completed, the aramid fibers in the impregnation slurry are scooped out using a scooping net and washed thoroughly with pure water to remove the residual impregnation and grinding liquid components. The washed aramid fibers are filtered using a plate and frame filter press 8, and the solids obtained by filtration are sent to a drying and fluffing machine 10 for drying and fluffing at 80°C to obtain a finished modified aramid pulp product.

[0061] After the test, the modified aramid pulp product was collected and stored at a constant temperature of 20°C for future use. Comparative Example 2

[0062] This comparative example simulates the existing process route, using a chemical-assisted beating method to prepare aramid pulp, and then using plasma treatment at the power level of the technical solution of the present invention in combination with an impregnation method to modify it. The aramid precursor and feed amount used were consistent with those in Example 1, and the specific implementation process was basically the same as that of Comparative Example 1, with only the following steps being modified:

[0063] The power of the crude aramid pulp in step (5) of comparative example 1 during the plasma treatment 3 was changed to 3 kW, and the treatment time was changed to 12 s, which were consistent with those in example 1, and the other parameters remained unchanged.

[0064] After the test, the modified aramid pulp product was collected and stored at a constant temperature of 20°C for future use. Comparative Example 3

[0065] The modified aramid pulp samples prepared in Examples 1-3 and Comparative Examples 1 and 2 were taken, and the beating degree, surface area and fiber length of the samples were tested according to the methods specified in GB / T 3332-2004 "Determination of pulp beating degree (Schober-Riegle method)", GB / T 19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method" and GB / T 29779-2013 "Determination of pulp fiber length by non-polarized light method".

[0066] After the comparative example is implemented, the test data are summarized and shown in Table 1 below:

[0067]

[0068] It can be seen from the test data that compared with the modified aramid pulp samples prepared by comparative examples 1 and 2 according to the existing process flow using chemical additives to assist beating, the modified aramid pulp prepared according to examples 1-3 has a similar beating degree, and a higher specific surface area and fiber decomposition degree, indicating that the plasma treatment process significantly promotes the aramid pulp beating process, and its effect is better than the method of using chemical additives to assist beating.

[0069] Furthermore, the modified aramid pulp prepared by the methods described in Examples 1-3 exhibited longer fiber lengths. This is because, compared to methods that rely on the strong dissolving action of chemical additives to aid decomposition, plasma treatment has a moderately destructive effect on aramid fibers, allowing the treated aramid fibers to maintain a relatively long fiber length after decomposition. When used to reinforce polymers, aramid pulp with longer fiber lengths enhances the continuity of the composite structure formed within the polymer matrix, contributing to improved overall mechanical properties of the resulting composite material. Comparative Example 4

[0070] Modified aramid pulp samples were prepared from Examples 1-3 and Comparative Examples 1 and 2, and were blended with POM to prepare aramid-reinforced POM composite materials with an aramid addition amount of 10 wt%.

[0071] (1) Take an appropriate amount of modified aramid pulp sample and dry it at 80℃ for 24h.

[0072] (2) Take an appropriate amount of dried modified aramid pulp sample, POM masterbatch, antioxidant, lubricant, and anti-wear agent, and put them into a high-speed mixer in the mass ratio of 10:87:0.2:0.3:2.5, and stir and mix them thoroughly. The POM masterbatch is M270, the antioxidant is Irganox245, the lubricant is polyethylene wax, and the anti-wear agent is silica microspheres with a diameter range of 380nm~200nm.

[0073] (3) The mixed materials were transferred from the high-speed mixer to the hopper of the twin-screw extruder, and the twin-screw extruder was started. The materials were blended and extruded at 180°C, and then granulated into aramid-reinforced POM composite material particles with a size of 2 mm.

[0074] (4) The obtained aramid reinforced POM composite material particles were injection molded into test specimens at an injection molding temperature of 200°C using an injection molding machine according to the shape of the 1A specimen in GB / T 1040-2022 "Determination of tensile properties of plastics" and the friction test specimen in GB / T 3960-2016 "Plastics sliding friction and wear test method".

[0075] Take the corresponding test specimens and perform a tensile performance test according to the method specified in GB / T 1040-2022 "Determination of Tensile Properties of Plastics", and perform a wear resistance test according to the method specified in GB / T 3960-2016 "Plastics Sliding Friction and Wear Test Methods".

[0076] After the comparative example is implemented, the test data are summarized and shown in Table 2 below:

[0077]

[0078] According to test data, the aramid-reinforced POM composite materials prepared using the modified aramid pulp prepared by the method described in Examples 1-3 all exhibited superior tensile and abrasion resistance compared to the corresponding samples in Comparative Examples 1 and 2. This demonstrates that the modified aramid pulp prepared by the method described in the present invention exhibits significant performance advantages over aramid pulp prepared by chemically assisted beating methods for POM compatibilization and abrasion resistance modification.

[0079] Comparing the test data of Example 1 and Comparative Example 1, it can be seen that the aramid-reinforced POM composite material corresponding to Example 1 is superior to the latter in both tensile and wear resistance, with the tensile strength being 120% of that of Comparative Example 1 and the wear resistance being 157% of that of Comparative Example 1. This illustrates the beneficial effect of the present invention's technical solution of placing the plasma treatment process before the pulping process. Compared to the modified aramid pulp prepared by the existing process route of Comparative Example 1, the embrittlement effect of the plasma treatment process in Example 1 according to the present invention has little effect on the mechanical properties of the modified aramid pulp, effectively ensuring its anti-wear and volume-enhancing properties as a reinforcing filler for POM. At the same time, compared to Comparative Example 1, Example 1 achieves a treatment effect superior to that of Comparative Example 1 by increasing the plasma treatment power and using only one-fifth of the treatment time of Comparative Example 1, demonstrating the superiority of the present invention's technical solution over the prior art in terms of plasma treatment efficiency.

[0080] Comparing the test data of Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that the performance of the corresponding aramid-reinforced POM composite material formed in Comparative Example 2 using the plasma treatment parameters of Example 1 is further reduced compared to Comparative Example 1. The main reason for this is that the existing technical routes used in Comparative Examples 1 and 2 cannot withstand the plasma treatment power range used in the technical solution of the present invention. Within this power range, the modified aramid pulp produced by the conventional technical route is significantly affected by the embrittlement effect of the plasma treatment, the aramid fiber structure is severely damaged, and its performance as a polymer-modified filler is further reduced. This shows that the existing technical route of preparing modified aramid pulp by beating first and then plasma treatment is difficult to shorten the treatment time by increasing the plasma treatment power like the technology of the present invention.

Claims

1. A plasma-assisted method for preparing modified aramid pulp, characterized in that: The steps include: (1) cutting the para-aramid filaments into aramid staple fibers, and then performing plasma treatment to obtain treated aramid staple fibers; the atmosphere used for the plasma treatment is one of air, argon, and carbon tetrafluoride, the power is 2 kW to 3.5 kW, and the treatment time is 10 s to 15 s; (2) The treated aramid staple fibers obtained in step (1) are mixed with an impregnation and grinding liquid to form an original slurry, which is heated to 50°C to 65°C, ground and beaten, and separated to obtain a primary abrasive; the impregnation and grinding liquid is prepared by an aramid surface modifier, pure water, and ethanol in a mass fraction ratio of 0.04 to 0.07:1:1, and acetic acid is added to adjust the pH to 3.5 to 4.5 before use; wherein the aramid surface modifier is one of KH550, KH560, or KH570; (3) adding water to the primary abrasive obtained in step (2) to form a primary grinding pulp, and grinding to obtain a fine grinding pulp; (4) Filtering the refined pulp obtained in step (3) to separate the solids, drying and loosening the solids to obtain modified aramid pulp.

2. The plasma-assisted method for preparing modified aramid pulp according to claim 1, characterized in that: In the step (1), the length of the aramid staple fiber is 3 mm to 6 mm.

3. The plasma-assisted method for preparing modified aramid pulp according to claim 1, characterized in that: In step (2), the aramid content in the original slurry is 12wt%~17wt%; the grinding and beating time is 10min~15min; and the liquid content in the initial abrasive is 50wt%~70wt%.

4. The plasma-assisted method for preparing modified aramid pulp according to claim 1, characterized in that: In the step (3), the aramid content in the primary grinding pulp formed after adding water is 5wt%~7wt%, and the grinding time is 7~10min.

5. The plasma-assisted method for preparing modified aramid pulp according to claim 1, characterized in that: In the step (4), the drying and loosening temperature is 80°C to 110°C until the moisture content of the modified aramid pulp reaches below 6wt%.

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