CN118307952A - A high-strength, high-wear-resistant, self-lubricating cast nylon composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a high-strength and high-wear-resistant self-lubricating cast nylon composite material and a preparation method thereof. The composite material is characterized in that intermolecular covalent chemical reaction and hydrogen bonding are utilized, caprolactam monomer is used as a reactive solvent, toluene diisocyanate (TDI) is used as a bridging agent, active polysiloxane with self-lubricating properties is connected to a graphene oxide sheet through a grafting intercalation reaction through the reactivity of isocyanate group and hydroxyl/amino group, and then ultrasonic dispersion is performed, and the graphene oxide is reduced to graphene through microwave reduction to obtain polysiloxane/reduced graphene hybrid particles, and the inhibitory effect of oxygen-containing groups on anionic polymerization is reduced. Finally, the hybrid particles are introduced into a cast nylon system through an anionic in-situ polymerization reaction to prepare the cast nylon composite material.

Description

A high-strength, high-wear-resistant, self-lubricating cast nylon composite material and preparation method thereof

Technical Field

The invention belongs to the field of polymer material synthesis and processing, and in particular relates to a high-strength, high-wear-resistant, self-lubricating cast nylon composite material and a preparation method thereof.

Background technique

As an important variety of polyamide engineering plastics, cast nylon is made of caprolactam monomers through anionic ring-opening polymerization under the action of catalysts and activators. Compared with ordinary nylon 6, it has a large molecular weight, high melting point and crystallinity, excellent mechanical strength, wear resistance and self-lubrication, corrosion resistance and chemical stability, and its molding size is not restricted. It can replace metal and its alloy products and is widely used. Cast nylon is often used as friction parts such as gears, bearings, and sleeves. Under harsh working conditions such as high speed, high load and high temperature, the wear rate increases, which seriously affects its service life and puts higher requirements on its tribological properties. Therefore, it is of great theoretical significance and practical application value to modify cast nylon to be wear-resistant and self-lubricating to expand its scope of engineering application.

An appropriate amount of inorganic filler can improve the mechanical strength of the polymer matrix, bear the load and transfer stress during the friction process, form a protective layer at the friction interface, weaken the mechanical interlocking and plowing effect of the micro-convex bodies on the friction pair surface on the matrix, and thus improve its wear resistance. Li et al., Wear, 2010, 269(3):262-268, used glass fiber (GF) as a wear-resistant modifier for cast nylon. When the GF content was 5wt%, under low load, its volume wear rate decreased by 68.9%, and strip-shaped GF appeared on the wear surface. The wear mechanism was mainly abrasive wear and adhesive wear; under high load, its volume wear rate began to increase, and GF was pulled out of the wear surface accompanied by a large amount of fatigue deformation, and the wear mechanism changed to fatigue wear. Pan et al., Tribology Letters, 2014, 54(2):161-170, added a monolayer of boron nitride (SBN) to caprolactam monomer, stirred and ultrasonicated, and prepared cast nylon/SBN nanocomposites by in situ polymerization. The results showed that the wear rate of the composite material was reduced by 45% compared with pure cast nylon.

Introducing various lubricants into the polymer matrix is the main method to reduce the friction coefficient and improve its self-lubricating property, such as polytetrafluoroethylene, graphite, molybdenum disulfide, paraffin, silicone grease, white oil, etc. Qu Jianbin et al., Engineering Plastics Application, 1994, 22(3):11-14, added industrial lubricating oil to molten caprolactam monomer, prepared oil-containing cast nylon by in-situ polymerization, the oil evenly penetrated into the matrix and became part of its structure, and the tribological properties were significantly better than those of cast nylon without lubricating oil. Chinese patent CN201911156843.X discloses a cast oil-containing nylon and a preparation method thereof, which improves the wear resistance and impact strength of the cast nylon. Chinese patent CN201610213789.8 discloses a nanoparticle-reinforced self-lubricating cast nylon composite sleeve and a manufacturing method thereof, which has better load-bearing capacity and better anti-friction and wear resistance by adding nano-graphite fluoride and mica powder, reduces wear on the sleeve and increases service life. Although this method can significantly reduce the friction coefficient of the composite material and improve its wear resistance, its mechanical strength and hardness have decreased, and its application range is limited. Therefore, the preparation of high-strength, high-wear-resistant and self-lubricating cast nylon still needs further research.

Summary of the invention

The purpose of the present invention is to provide a method for preparing a high-strength, high-wear-resistant self-lubricating cast nylon composite material in view of the deficiencies in the prior art. The method is characterized in that intermolecular covalent chemical reactions and hydrogen bonding are utilized, toluene diisocyanate (TDI) is used as a bridging agent, and active polysiloxane with self-lubricating properties is connected to a graphene oxide sheet through a grafting intercalation reaction through the reactivity of isocyanate groups and hydroxyl/amino groups, and then ultrasonically dispersed in a caprolactam monomer, and the graphene oxide is reduced to graphene through microwave reduction to obtain polysiloxane/reduced graphene hybrid particles, and the inhibitory effect of oxygen-containing groups on anionic polymerization is reduced. Finally, the hybrid particles are introduced into a cast nylon system through an anionic in-situ polymerization reaction to prepare a cast nylon composite material. On the one hand, the self-lubricating property of polysiloxane and the high wear resistance of graphene are utilized to exert a synergistic enhanced friction reduction effect, and the wear rate and friction coefficient of cast nylon are reduced. On the other hand, through the design of the grafting intercalation reaction system, the uniform dispersion of siloxane/reduced graphene hybrid particles in the matrix is simultaneously achieved, the incompatibility of polysiloxane and nylon system is solved, and the respective lubrication and enhancement effects are better exerted, and the mechanical strength, wear resistance and self-lubricating properties of cast nylon are effectively improved. The high-strength, high-wear-resistant self-lubricating cast nylon composite material prepared by the present invention has a simple preparation method, excellent mechanical properties and friction properties, and can be used as a structural material in the engineering field.

The object of the present invention is achieved by the following technical scheme, wherein the raw material fractions are all mass fractions unless otherwise specified.

A method for preparing a high-strength, high-wear-resistant, self-lubricating cast nylon composite material, characterized in that the main raw materials of the composite material are composed of the following components, calculated by mass fraction:

Caprolactam 100 parts

Graphene oxide 0.8-6 parts

Reactive polysiloxane 0.5-8 parts

Toluene diisocyanate 1.6-12 parts

Catalyst 0.05-8 parts

Co-catalyst 0.03-3 parts

Wherein, the active polysiloxane is a polysiloxane with aminopropyl, hydroxyl or epoxy groups at the molecular chain end, and the molecular weight is 1200-5000 g/mol;

The catalyst is any one of sodium hydroxide, potassium hydroxide, sodium ethoxide, and sodium carbonate;

The co-catalyst is any one of toluene diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate;

A method for preparing a high-strength, high-wear-resistant, self-lubricating cast nylon composite material, characterized in that the method comprises the following steps:

Preparation of Cast Nylon Precursor

100 parts of caprolactam monomer are heated at 68-80°C until completely melted, 0.8-6 parts of graphene oxide are added, ultrasonically dispersed and stirred for 0.5-2 h, 1.6-12 parts of toluene diisocyanate are added as a bridging agent, ultrasonically dispersed for 10 min, and then active polysiloxane is added. After ultrasonication for 10-30 min, the mixture is transferred to a microwave oven and reduced for 1-5 min at a power of 400-1000 W and a frequency of 800-2450 MHZ to obtain a cast nylon precursor.

Preparation of high-strength, high-wear-resistant self-lubricating cast nylon composite materials

The cast nylon precursor is immediately transferred to a three-necked flask, heated to 130-145°C, stirred for 5-10 min, completely sealed, vacuumed, and distilled under reduced pressure for 20-40 min to remove trace moisture, and then 0.05-8 parts of catalyst are added, and vacuum dehydration is performed again for 15 min. After the temperature drops to 120°C, it is heated again to 140-155°C, and 0.03-6 parts of co-catalyst are quickly added, stirred evenly, vacuumed for 0.5-1 min, and quickly cast into a stainless steel mold preheated to 170°C, anionic polymerization reaction is carried out for 30-140 min, and demolding is performed after natural cooling to obtain a cast nylon composite material.

The invention has the following advantages: the tribological properties of cast nylon are closely related to its mechanical strength, wear rate and friction coefficient; the addition of inorganic filler can improve the mechanical strength and wear resistance, but the friction coefficient tends to increase, that is, the self-lubricating property is poor; the addition of lubricating additives such as lubricating oil contributes to reducing the friction coefficient, but often leads to an increase in the wear rate, a decrease in the mechanical strength and hardness, and thus a decrease in the final friction performance; and the compatibility of the lubricating additive with the cast nylon matrix is generally poor, and the dispersion is uneven, which limits its use effect. The present invention utilizes toluene diisocyanate as a bridging agent, connects polysiloxane with graphene oxide, reduces graphene oxide to graphene by microwave reduction, obtains polysiloxane/reduced graphene hybrid particles, prepares cast nylon composite materials by anion in-situ polymerization, utilizes the self-lubricating properties of polysiloxane and the high wear resistance of graphene, exerts a synergistic enhanced friction reduction effect, reduces the wear rate and friction coefficient of cast nylon, on the other hand, by the design of the grafting intercalation reaction system, synchronously realizes the uniform dispersion of siloxane/reduced graphene hybrid particles in the matrix, solves the incompatibility of polysiloxane and nylon system, better exerts their respective lubrication and enhancement effects, and effectively improves the mechanical strength, wear resistance and self-lubricating properties of cast nylon. The preparation step is simple, and the in-situ one-pot method realizes the preparation of composite materials, which has certain advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a transmission electron microscope image of the cross section of the cast nylon composite material polysiloxane/reduced graphene.

Figure 2 is a scanning electron microscope image of the worn surface of the cast nylon composite material.

Detailed ways

The present invention is further described below through specific embodiments. It should be noted that the embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make non-essential improvements and adjustments to the present invention based on the contents of the present invention described above.

Example 1

100 parts of caprolactam monomer were heated at 70°C until completely melted, 0.8 parts of graphene oxide were added, ultrasonically dispersed and stirred for 0.5 h, 1.6 parts of toluene diisocyanate were added as a bridging agent, ultrasonically dispersed for 10 min, and then terminal aminopropyl polysiloxane with a molecular weight of 1200 g/mol was added. After ultrasonication for 15 min, the mixture was transferred to a microwave oven and reduced at a power of 600 W and a frequency of 800 MHZ for 1 min to obtain a cast nylon precursor.

The cast nylon precursor was immediately transferred to a three-necked flask and heated to 130℃, stirred for 5 min, and then completely sealed and vacuumed and distilled for 20 min to remove trace water. Then 0.1 parts of sodium hydroxide were added and vacuumed and dehydrated for 15 min again. After the temperature dropped to 120℃, it was heated to 140℃ again, and 0.03 parts of toluene diisocyanate were quickly added. Stir evenly, vacuumed for 0.5 min, and quickly cast into a stainless steel mold preheated to 170℃. Anionic polymerization reaction was carried out for 30 min, and demolding was carried out after natural cooling to obtain a cast nylon composite material. The tensile strength of the cast nylon composite material was 76 MPa, the elongation at break was 22%, the volume wear rate was 4.41´10 ^-6 mm ³ /Nm, and the friction coefficient was 0.36.

Example 2

100 parts of caprolactam monomer were heated at 75°C until completely melted, 2 parts of graphene oxide were added, ultrasonically dispersed and stirred for 1 h, 4 parts of toluene diisocyanate were added as a bridging agent, ultrasonically dispersed for 10 min, and then terminal hydroxyl polysiloxane with a molecular weight of 1500 g/mol was added. After ultrasonication for 20 min, the mixture was transferred to a microwave oven and reduced at a power of 800 W and a frequency of 1000 MHZ for 2 min to obtain a cast nylon precursor.

The cast nylon precursor was immediately transferred to a three-necked flask and heated to 135℃, stirred for 6 min, completely sealed, vacuumed, and distilled under reduced pressure for 20 min to remove trace water, then 0.2 parts of potassium hydroxide were added, and vacuum dehydration was performed again for 15 min. After the temperature dropped to 120℃, it was heated to 140℃ again, and 0.06 parts of isophorone diisocyanate were quickly added, stirred evenly, vacuumed for 0.5 min, and quickly cast into a stainless steel mold preheated to 170℃. The anionic polymerization reaction was carried out for 45 min, and the mold was demolded after natural cooling to obtain a cast nylon composite material. The tensile strength of the cast nylon composite material was 78 MPa, the elongation at break was 26%, the volume wear rate was 3.85´10 ^-6 mm ³ /Nm, and the friction coefficient was 0.32.

Example 3

100 parts of caprolactam monomer were heated at 75°C until completely melted, 3 parts of graphene oxide were added, ultrasonically dispersed and stirred for 1.5 h, 6 parts of toluene diisocyanate were added as a bridging agent, ultrasonically dispersed for 10 min, and then terminal epoxy polysiloxane with a molecular weight of 1800 g/mol was added. After ultrasonication for 30 min, the mixture was transferred to a microwave oven and reduced at a power of 1000 W and a frequency of 1500 MHZ for 3 min to obtain a cast nylon precursor.

The cast nylon precursor was immediately transferred to a three-necked flask and heated to 140℃, stirred for 8 min, and then completely sealed and vacuumed and distilled for 30 min to remove trace water. Then 3 parts of sodium ethoxide were added and vacuumed and dehydrated again for 15 min. After the temperature dropped to 120℃, it was heated to 150℃ again, and 0.5 parts of hexamethylene diisocyanate were quickly added. Stir evenly, vacuumed for 1 min, and quickly cast into a stainless steel mold preheated to 170℃. The anionic polymerization reaction was carried out for 60 min, and the mold was demolded after natural cooling to obtain a cast nylon composite material. The tensile strength of the cast nylon composite material was 81 MPa, the elongation at break was 28%, the volume wear rate was 3.29´10 ^-6 mm ³ /Nm, and the friction coefficient was 0.28.

Example 4

100 parts of caprolactam monomer were heated at 80°C until completely melted, 5 parts of graphene oxide were added, ultrasonically dispersed and stirred for 2 h, 10 parts of toluene diisocyanate were added as a bridging agent, ultrasonically dispersed for 10 min, and then terminal aminopropyl polysiloxane with a molecular weight of 2000 g/mol was added. After ultrasonication for 30 min, the mixture was transferred to a microwave oven and reduced at a power of 1000 W and a frequency of 2000 MHZ for 3 min to obtain a cast nylon precursor.

The cast nylon precursor was immediately transferred to a three-necked flask and heated to 140℃, stirred for 10 min, and then completely sealed and vacuumed and distilled for 40 min to remove trace water. Then 4 parts of sodium hydroxide were added and vacuumed and dehydrated again for 15 min. After the temperature dropped to 120℃, it was heated to 140℃ again, and 0.8 parts of toluene diisocyanate were quickly added. Stir evenly, vacuumed for 1 min, and quickly cast into a stainless steel mold preheated to 170℃. The anionic polymerization reaction was carried out for 80 min, and the mold was demolded after natural cooling to obtain a cast nylon composite material. The tensile strength of the cast nylon composite material was 84 MPa, the elongation at break was 25%, the volume wear rate was 2.73´10 ^-6 mm ³ /Nm, and the friction coefficient was 0.23.

In summary, after adding polysiloxane and reduced graphene, the cast nylon composite material of the embodiment of the present invention has high mechanical strength, low volume wear rate and friction coefficient, excellent tribological properties, and can be applied to the engineering field. On the one hand, the self-lubricating properties of polysiloxane and the high wear resistance of graphene are utilized to exert a synergistic enhanced friction reduction effect, reduce the wear rate and friction coefficient of cast nylon, and on the other hand, through the design of the grafting intercalation reaction system, the uniform dispersion of polysiloxane/reduced graphene hybrid particles in the matrix is synchronously realized, the incompatibility of polysiloxane and nylon system is solved, and the respective lubrication and enhancement effects are better exerted, and the mechanical strength, wear resistance and self-lubricating properties of cast nylon are effectively improved. The high-strength, high-wear-resistant self-lubricating cast nylon composite material prepared by the present invention has a simple preparation method, excellent mechanical properties and friction properties, and can be used as a structural material in the engineering field.

The above embodiments describe the specific contents of the present invention in detail, but the present invention is not limited to the embodiments, and those skilled in the art can make equivalent substitutions, which should be included in the protection scope of the present invention.

Claims (4)

1. The high-strength high-wear-resistance self-lubricating cast nylon composite material is characterized by comprising the following main raw materials in parts by weight:

Caprolactam 100 parts

0.8-6 Parts of graphene oxide

0.5-8 Parts of active polysiloxane

Toluene diisocyanate 1.6-12 parts

0.05-8 Parts of catalyst

0.03-3 Parts of promoter

Wherein the active polysiloxane is polysiloxane with molecular chain end aminopropyl or terminal hydroxyl or terminal epoxy, and the molecular weight is 1200-5000 g/mol.

2. The high-strength high-wear-resistance self-lubricating cast nylon composite material according to claim 1, wherein the catalyst is any one of sodium hydroxide, potassium hydroxide, sodium ethoxide and sodium carbonate.

3. The high-strength high-wear-resistance self-lubricating cast nylon composite material according to claim 1, wherein the cocatalyst is any one of toluene diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate.

4. A method for preparing the high-strength high-wear-resistance self-lubricating cast nylon composite material according to claim 1, which is characterized by comprising the following steps:

S1, preparation of casting nylon precursor

Heating 100 parts of caprolactam monomer to be completely melted at 68-80 ℃, adding 0.8-6 parts of graphene oxide, performing ultrasonic dispersion, stirring to 0.5-2 h, adding 1.6-12 parts of toluene diisocyanate as a bridging agent, performing ultrasonic dispersion for 10min, adding active polysiloxane, performing ultrasonic treatment for 10-30 min, transferring to a microwave oven, and reducing for 1-5 min under the conditions of power of 400-1000W and frequency of 800-2450 MHZ to obtain a casting nylon precursor;

S2, preparation of high-strength high-wear-resistance self-lubricating cast nylon composite material

Immediately transferring the casting nylon precursor into a three-neck flask, heating to 130-145 ℃, stirring 5-10 min, vacuumizing after complete sealing, distilling under reduced pressure to 20-40 min, removing trace moisture, then adding 0.05-8 parts of catalyst, performing vacuum dewatering again to 15 min, heating again to 140-155 ℃ after the temperature is reduced to 120 ℃, quickly adding 0.03-3 parts of cocatalyst, stirring uniformly, vacuumizing to 0.5-1 min, rapidly casting into a stainless steel mould preheated to 170 ℃, performing anionic polymerization to 30-140 min, naturally cooling, and demoulding to obtain the casting nylon composite material.