Modified aramid pulp and aramid pulp composite material prepared from modified aramid pulp

Abstract

The invention discloses a modified aramid pulp and an aramid pulp composite material prepared from the modified aramid pulp, and belongs to the field of high polymer materials, the modified aramid pulp adopts a deep eutectic solvent (DES) as a modifier, entanglement of microfibers can be reduced, interface interaction between the aramid pulp and a rubber molecular chain can be improved, and the performance of the aramid pulp is improved. The mechanical property of the prepared rubber aramid pulp composite material is obviously improved; the modified aramid pulp composite material is prepared from the following components in parts by mass: 100 parts of raw rubber, 2 to 10 parts of zinc oxide, 1 to 3 parts of stearic acid, 0.5 to 2.5 parts of sulfur, 0.5 to 3 parts of dibenzothiazyl disulfide, 40 to 65 parts of reinforcing agent and 0.5 to 6 parts of modified aramid pulp.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, and particularly relates to a modified aramid pulp and an aramid pulp composite material made from the modified aramid pulp. Background Technology

[0002] Aramid pulp is a differentiated product obtained by fibrillating the surface of aramid short fibers. It also has the characteristics of aramid fibers, such as high modulus, insect resistance, high strength, high temperature resistance, chemical corrosion resistance and dimensional stability. Filling rubber with aramid pulp can endow rubber with high modulus, tear resistance, cut resistance and crack propagation resistance.

[0003] However, aramid pulp has a high electrostatic tendency and a large number of microfibers on its surface. The amide groups on the surface of these microfibers readily form hydrogen bonds, and the entanglement of these microfibers leads to severe agglomeration of the aramid pulp. If aramid pulp is added directly to rubber without any treatment, it is prone to agglomeration in the rubber matrix, becoming stress concentration points and causing a decline in the overall performance of the material. In addition, due to the shielding effect of the benzene ring on the amide groups in its molecular structure, aramid pulp has low reactivity and is difficult to achieve high interfacial adhesion with the rubber matrix. Therefore, aramid pulp needs to be pre-modified to improve its dispersibility and interfacial adhesion in rubber.

[0004] Based on the above problems, the commonly used method is to prepare aramid pulp predispersed masterbatch by mixing aramid pulp with modifiers, solid or liquid penetrating and isolating agents, and rubber carriers. This method is complex, and the resulting aramid pulp predispersed masterbatch contains approximately 40 wt% pulp. Due to the high content of additives, it affects the processing and properties of the rubber. Furthermore, there are many types of rubber, and to meet the needs of different rubber types, different rubber carriers need to be selected to prepare aramid pulp predispersed masterbatch separately, resulting in poor versatility. Summary of the Invention

[0005] The purpose of this invention is to provide a modified aramid pulp and an aramid pulp composite material made from the modified aramid pulp. The eutectic solvent is used as a modifier for the aramid pulp, which can reduce the entanglement of microfibers and improve the interfacial interaction between the aramid pulp and the rubber molecular chain, resulting in a significant improvement in the mechanical properties of the prepared rubber composite material.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing modified aramid pulp, comprising the following steps: heating and stirring [2-(acryloyloxy)ethyl]trimethylammonium chloride and a hydrogen bond donor to obtain a clear and transparent eutectic solvent; dispersing the aramid pulp in the eutectic solvent, stirring evenly, adding ethanol for dilution, filtering and drying to obtain modified aramid pulp.

[0007] Preferably, the hydrogen bond donor includes any one of ethylene glycol, glycerol, polyethylene glycol, xylitol, sorbitol, urea, acetamide, and acrylamide; the molar ratio of [2-(acryloyloxy)ethyl]trimethylammonium chloride to the hydrogen bond donor is 1:2 to 1:3; and the ratio of aramid pulp to eutectic solvent is 1g:40mL to 1g:80mL.

[0008] This invention provides an aramid pulp composite material comprising the following components in parts by weight: 100 parts raw rubber, 2-10 parts zinc oxide, 1-3 parts stearic acid, 0.5-2.5 parts sulfur, 0.5-3 parts dibenzothiazole disulfide, 40-65 parts reinforcing agent, and 0.5-6 parts modified aramid pulp.

[0009] Preferably, the raw rubber is one or more of natural rubber, nitrile rubber, styrene-butadiene rubber, cis-butadiene rubber, ethylene propylene rubber, or chloroprene rubber.

[0010] Preferably, the reinforcing agent includes any one of silica, carbon black, kaolin, diatomaceous earth, or mica powder.

[0011] More preferably, the reinforcing agent is silica, and the silica has a mass fraction of 40-60 parts.

[0012] This invention provides a method for preparing the above-mentioned aramid pulp composite material, comprising the following steps: adding raw rubber, zinc oxide, stearic acid, dibenzothiazole disulfide, reinforcing agent and modified aramid pulp sequentially into a mixer for mixing, discharging the rubber, adding sulfur thinner, and sheeting to obtain the aramid pulp composite material.

[0013] Preferably, the mass ratio of the raw rubber, zinc oxide, stearic acid, sulfur, reinforcing agent, dibenzothiazole disulfide, and modified aramid pulp is 100:2-10:1-3:0.5-2.5:0.5-3:40-65:0.5-6.

[0014] Preferably, the internal mixer rotor speed is 60-75 rpm, the mixing time is 10 min, and the mixing is passed through 5-8 times.

[0015] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: (1) The present invention uses the eutectic solvent DES as a modifier for aramid pulp. The hydrogen bond donor in DES can break the hydrogen bonds formed between amide bonds in the molecular chain of aramid pulp and form new hydrogen bonds with the amide bonds, reduce the entanglement of microfibers, and improve the dispersibility of aramid pulp in the matrix, so as to give full play to its reinforcing advantages. (2) The DES in the modified aramid pulp prepared by the present invention contains acrylate groups. When the modified aramid pulp is used to prepare rubber composites, the acrylate groups can be attached to the rubber molecular chain through the vulcanization reaction of diene rubber or through the epoxy group in epoxy rubber via reaction bonds during the rubber vulcanization process, thereby improving the interfacial interaction between the aramid pulp and the rubber molecular chain and enhancing the mechanical properties of the composite material.

[0016] This invention utilizes the eutectic solvent DES as a modifier to prepare modified aramid pulp. The natural rubber composite material prepared from the modified aramid pulp exhibits a tensile strength of 22.1-28.6 MPa, a tear strength of 53.8-96.3 kN / m, an M100 of 6.2-11.5 MPa, and an elongation at break of 268-347%. The nitrile butadiene rubber composite material prepared from the modified aramid pulp exhibits a tensile strength of 18.9-24.1 MPa, a tear strength of 38.6-76.0 kN / m, an M100 of 8.3-16.7 MPa, and an elongation at break of 200-287%.

[0017] (3) In this invention, [2-(acryloyloxy)ethyl]trimethylammonium chloride is selected as the hydrogen bond acceptor in DES to modify aramid pulp. During the rubber vulcanization process, many rubber fillers are acidic (such as silica, kaolin, diatomaceous earth, and bentonite), which adsorb basic dibenzothiazole disulfide, causing a decrease in the vulcanization rate of rubber. However, [2-(acryloyloxy)ethyl]trimethylammonium chloride is alkaline and can neutralize the acidity of the filler, solving the problem of acidic fillers delaying rubber vulcanization. In addition, this compound belongs to the quaternary ammonium salt eutectic solvent and has antistatic properties, which can effectively solve the static electricity problem of aramid pulp during opening.

[0018] (4) The modifier DES used in this invention is prepared by inexpensive and readily available industrial reagents, which has the advantages of low cost and repeated recycling. Furthermore, the modification process of aramid pulp does not require complex equipment, thus saving equipment costs.

[0019] (5) The technical solution of the modified aramid pulp adopted in this invention is simple to operate. First, the process of preparing the modifier DES is relatively simple. DES can be obtained by mixing the quaternary ammonium salt and the hydrogen bond donor in a certain proportion and heating and stirring for a certain period of time. Second, the operation of modifying aramid pulp with DES is simple. The modification process can be completed by mixing the aramid pulp and the prepared DES in a certain proportion and stirring for a period of time. Then, the modified aramid pulp can be obtained by diluting with ethanol, filtering, and drying the filter cake.

[0020] (6) The present invention utilizes DES-modified aramid pulp, which is applicable to a variety of rubber types with different properties. Unlike the pre-dispersed masterbatch for preparing aramid pulp, it does not require the selection of different carrier rubbers for different types of rubbers, thus solving the technical problem of poor versatility of pre-dispersed masterbatch for aramid pulp in the prior art. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. For the numerical ranges disclosed in this specification, the endpoint values ​​of each range, the endpoint values ​​of each range and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges. These numerical ranges should be regarded as specifically disclosed in this specification.

[0022] The para-aramid pulp used in the following examples is Typrolon Aramid Pulp 1820, the silica is Zeosil 1165MP, and the other reagents are all commercially available products. Example 1

[0023] (1) Add [2-(acryloyloxy)ethyl]trimethylammonium chloride and hydrogen bond donor ethylene glycol to a three-necked flask at a molar ratio of 1:2 and stir at 80°C for 1 h to obtain clear and transparent DES-1#; (2) Add 5 g of aramid pulp to 300 mL of DES-1#, disperse and stir for 3 h, then dilute with ethanol to 500 mL and filter to remove excess DES. Dry the filter cake at 75 °C to remove ethanol and obtain modified aramid pulp AP-M1.

[0024] In other embodiments of the present invention, the molar ratio of the hydrogen bond donor, [2-(acryloyloxy)ethyl]trimethylammonium chloride, and the ratio of the hydrogen bond donor, as well as the ratio of aramid pulp to eutectic solvent, were verified. When the molar ratio of [2-(acryloyloxy)ethyl]trimethylammonium chloride to the hydrogen bond donor was 1:3; when the ratio of aramid pulp to eutectic solvent was between 1 g:40 mL and 1 g:80 mL; and when the hydrogen bond donor was selected from any one of glycerol, polyethylene glycol, xylitol, sorbitol, acetamide, and acrylamide, the same technical effects as in Example 1 could be achieved. Example 2

[0025] 5 g of aramid pulp was added to 400 mL of DES-1# and dispersed and stirred for 3 h. The mixture was then diluted with ethanol to 500 mL, and excess DES-1# was removed by filtration. The filter cake was dried at 75 °C to remove the ethanol, yielding the modified aramid pulp, which was named AP-M2. Example 3

[0026] (1) Add [2-(acryloyloxy)ethyl]trimethylammonium chloride and hydrogen bond donor ethylene glycol to a three-necked flask at a molar ratio of 1:3 and stir at 80°C for 1 h to obtain clear and transparent DES-2#; (2) Add 5 g of aramid pulp to 300 mL of DES-2#, disperse and stir for 3 h, then dilute with ethanol to 500 mL and filter to remove excess DES-3#. Dry the filter cake at 75 °C to remove ethanol and obtain modified aramid pulp, which is named AP-M3. Example 4

[0027] (1) Add [2-(acryloyloxy)ethyl]trimethylammonium chloride and hydrogen bond donor urea to a three-necked flask at a molar ratio of 1:2 and stir at 80°C for 1 h to obtain clear and transparent DES-3#; (2) Add 5 g of aramid pulp to 300 mL of DES-3#, disperse and stir for 3 h, then dilute with ethanol to 500 mL and filter to remove excess DES-4#. Dry the filter cake at 75 °C to remove ethanol and obtain modified aramid pulp, which is named AP-M4.

[0028] To verify the versatility of modified aramid pulp for various rubber types, one polar and one non-polar rubber type were selected for testing. The non-polar rubber type was natural rubber (NR), and the polar rubber type was nitrile rubber (NBR). The specific formulations are shown in Tables 1 and 2, with units in g. The experimental examples used modified aramid pulp, while the comparative examples used unmodified aramid pulp.

[0029]

[0030]

[0031] The specific preparation steps are as follows: (1) Add raw rubber, zinc oxide, stearic acid, dibenzothiazole disulfide, silica and modified aramid pulp into a mixer in sequence and mix. The rotor speed of the mixer is 60-75 rpm and the mixing time is 10 min. (2) After the glue is discharged onto the open mill, sulfur is added and the mixture is passed through the mill 5-8 times before being sheeted to obtain aramid pulp composite material.

[0032] Test standards and methods for aramid pulp composites: The positive vulcanization time was tested according to standard GB / T 9872-2018, the tensile strength, stress at a given elongation and elongation at break were tested according to standard GB / T 528-2009, and the tear strength was tested according to standard GB / T 529-2008.

[0033]

[0034] As shown in Table 3, the use of modified aramid pulp can significantly shorten the vulcanization time of the compound and improve production efficiency. This is because the surface of the modified aramid pulp is bonded to DES through hydrogen bonding, and the synthesized DES contains alkaline quaternary ammonium salts, which can neutralize the acidity of the silica surface, thus solving the problem of acidic fillers adsorbing alkaline dibenzothiazole and delaying the vulcanization of rubber.

[0035] In addition, after being filled with DES-modified aramid pulp, the tensile strength and 100% elongation stress (M) of NR and NBR were improved. 100 Both tensile strength and tear strength are significantly improved. These improvements in mechanical properties are mainly attributed to the modification effect of DES on aramid pulp. On one hand, after modification with [2-(acryloyloxy)ethyl]trimethylammonium chloride / hydrogen bond donor type DES, the hydrogen bond donor in DES can disrupt the hydrogen bonds between the micro- and nano-fibers surrounding the aramid pulp and form new hydrogen bonds with the amide bonds in the aramid pulp structure, reducing microfiber entanglement and making the aramid pulp easier to disperse in the rubber matrix. On the other hand, the acrylate groups in [2-(acryloyloxy)ethyl]trimethylammonium chloride can undergo co-vulcanization reactions with natural rubber and nitrile rubber during rubber vulcanization and directly bond to the rubber molecular chain. DES, as an interfacial compatibilizer between aramid pulp and rubber, improves the interfacial strength between the two. Considering both of these factors, the tensile strength and tear strength of NR and NBR are significantly improved. 100 Both tear strength and tensile strength are significantly improved.

[0036] Because the dispersion of aramid pulp in rubber is improved after DES modification, and the interfacial strength between aramid pulp and rubber is increased, defects in the vulcanized rubber are reduced, avoiding premature failure of the material due to stress concentration caused by defects. Therefore, the elongation at break of the vulcanized rubber is also increased.

[0037] In other test examples of the present invention, the types of raw rubber and the proportions of raw rubber with zinc oxide, stearic acid, sulfur, dibenzothiazole disulfide, reinforcing agent, and modified aramid pulp were verified. Besides natural rubber and nitrile rubber, the raw rubber was selected from one or more of styrene-butadiene rubber, butadiene rubber, ethylene propylene rubber, or chloroprene rubber, and when the mass ratio of raw rubber, zinc oxide, stearic acid, sulfur, dibenzothiazole disulfide, reinforcing agent, and modified aramid pulp was 100:2-10:1-3:0.5-2.5:0.5-3:40-65:0.5-6, the same technical effects as in Test Examples 1-20 were achieved.

Claims

1. A modified aramid pulp, characterized in that, The method for preparing the modified aramid pulp includes the following steps: [2-(acryloyloxy)ethyl]trimethylammonium chloride and hydrogen bond donor were heated and stirred to obtain a clear and transparent eutectic solvent; aramid pulp was dispersed in the eutectic solvent, stirred evenly, diluted with ethanol, filtered and dried to obtain modified aramid pulp.

2. The modified aramid pulp according to claim 1, characterized in that, The hydrogen bond donor includes any one of ethylene glycol, glycerol, polyethylene glycol, xylitol, sorbitol, urea, acetamide, and acrylamide; the molar ratio of [2-(acryloyloxy)ethyl]trimethylammonium chloride to the hydrogen bond donor is 1:2 to 1:3; the ratio of aramid pulp to eutectic solvent is 1g:40mL to 1g:80mL.

3. An aramid pulp composite material, characterized in that, The components include the following parts by weight: 100 parts raw rubber, 2-10 parts zinc oxide, 1-3 parts stearic acid, 0.5-2.5 parts sulfur, 0.5-3 parts dibenzothiazole disulfide, 40-65 parts reinforcing agent, and 0.5-6 parts modified aramid pulp as described in claim 1 or 2.

4. The aramid pulp composite material according to claim 3, characterized in that, The raw rubber is one or more of natural rubber, nitrile rubber, styrene-butadiene rubber, cis-butadiene rubber, ethylene propylene rubber, or chloroprene rubber.

5. The aramid pulp composite material according to claim 3, characterized in that, The reinforcing agent includes any one of silica, carbon black, kaolin, diatomaceous earth, or mica powder.

6. The aramid pulp composite material according to claim 3, characterized in that, The preparation method of the aramid pulp composite material includes the following steps: raw rubber, zinc oxide, stearic acid, dibenzothiazole disulfide, reinforcing agent and modified aramid pulp are added to a mixer in sequence and mixed. After the rubber is discharged, sulfur is added and the mixture is sheeted to obtain the aramid pulp composite material.

7. The aramid pulp composite material according to claim 3, characterized in that, The mass ratio of the raw rubber, zinc oxide, stearic acid, sulfur, reinforcing agent, dibenzothiazole disulfide, and modified aramid pulp is 100:2-10:1-3:0.5-2.5:0.5-3:40-65:0.5-6.

8. The aramid pulp composite material according to claim 3, characterized in that, The internal mixer rotor speed is 60-75 rpm, the mixing time is 10 min, and the mixing is done 5-8 times.

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