CN113045781A

CN113045781A - Method for preparing high-strength cast nylon product

Info

Publication number: CN113045781A
Application number: CN202110295097.3A
Authority: CN
Inventors: 谢鹏程; 宋乐; 丁玉梅; 杨卫民
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2021-03-19
Filing date: 2021-03-19
Publication date: 2021-06-29

Abstract

The invention provides a method for preparing high-strength cast nylon products, which comprises the steps of mixing nylon particles with a certain amount of nano-iron oxide magnetic powder, spinning by utilizing melt electrostatic spinning, directionally winding fibers on a plate, and magnetizing the fibers in a strong magnetic field environment to enable the fibers to have certain magnetism; then cutting the magnetized fiber into magnetized short fibers with a certain length; the magnetized short fibers are respectively and uniformly dispersed in caprolactam solution added with alkaline catalyst and caprolactam solution added with activating agent to be used as component A and component B for reaction injection molding, the component A and the component B are fully mixed and injected into a specially designed mold by a reaction injection molding machine, the mold is heated to a temperature lower than the melting point of nylon under the action of a magnetic field to solidify the caprolactam, and finally, a product is obtained, and the fibers are directionally arranged under the action of the magnetic field, so that the mechanical property of the composite material in the stress direction is greatly improved.

Description

Method for preparing high-strength cast nylon product

Technical Field

The invention belongs to the field of high polymer material molding, and particularly relates to a method for preparing a high-strength cast nylon product.

Background

The cast nylon is prepared by using molten caprolactam monomer as raw material, basic substance as catalyst, activator and other assistants to prepare monomer to be polymerized, directly injecting the monomer into a mould preheated to a certain temperature, quickly polymerizing the material in the mould, condensing into tough solid blank, and processing by related processes to obtain the predetermined product. The cast nylon product is used as one of engineering plastics, replaces steel with plastics, has excellent performance and has extremely wide application. It has light weight, high strength, self-lubricating, wear resisting, anticorrosive, insulating and other unique performance, and is widely used engineering plastic. The reinforced casting technology is a technology combining a fiber reinforcement technology with a casting process. The technology can improve the hardness and the dimensional stability of the cast nylon product. Commonly used reinforcing materials include short fibers such as glass fibers, carbon fibers, nylon fibers, and inorganic mineral materials such as mica, talc, silica, and calcium carbonate. The method not only keeps the basic advantages of the cast nylon process, but also endows the cast nylon product with more excellent characteristics, can obviously improve the thermal stability and mechanical property of the material, and enables the material to be a high-quality material with high strength, high modulus and high thermal stability.

However, inorganic reinforcements present a significant disadvantage: recycling is difficult because these reinforcements cannot be melted and cannot be re-melt processed into new articles by chopping. Even if recovered by incineration, these reinforcements can remain as waste residues, causing significant environmental damage. This is undoubtedly a serious drawback of the reinforced molding technique in the context of the increasing demands on the plastic products in terms of their full life cycle. In this context, single polymer composites have come to light. The polymer fiber is highly oriented along the fiber direction after being stretched, and the highly regular molecular structure is arranged to have extremely high strength and modulus compared with isotropic polymer materials. The single polymer composite material utilizes the characteristic, and uses high-strength polymer fibers to reinforce a polymer matrix so as to obtain a novel material which has the characteristics of the composite material, wherein the reinforcement and the matrix are made of the same material. However, the processing of this new material generally requires complex procedures and strict temperature control during processing to avoid disrupting the orientation of the fibers. A novel preparation process which is simple to manufacture and can be used for large-scale production is urgently needed.

Disclosure of Invention

The invention provides a method for preparing a high-strength cast nylon product, which comprises the steps of mixing nylon particles with a certain amount of nano iron oxide magnetic powder, and spinning by utilizing melt electrostatic spinning to obtain superfine high-modulus high-strength fibers mixed with iron oxide. The fibers are directionally wound on a plate, and the plate is placed in a strong magnetic field environment for magnetization, wherein the direction of the magnetic field is consistent with the direction of the fibers, so that the fibers have certain magnetism. Cutting the magnetized fiber into magnetized short fibers with a certain length; the magnetized short fiber is respectively and uniformly dispersed in caprolactam solution added with alkaline catalyst and caprolactam solution added with activating agent as A component and B component of reaction injection molding, the A solution and the B solution are fully mixed and injected into a specially designed mould by utilizing a reaction injection molding machine, a strong magnetic field is arranged in a mould cavity corresponding to the position of a sample which is mainly stressed, the direction of a magnetic induction line is consistent with the stress direction, the magnetized fiber can be oriented along the direction of the magnetic induction line under the action of the magnetic field, the orientation direction is consistent with the stress direction of a material, the mould is heated to the temperature lower than the melting point of nylon, so that the caprolactam is solidified to obtain a product, and the solidification temperature of the caprolactam is far lower than the melting temperature of the nylon, therefore, the strength and the rigidity of the fiber can not be damaged due to high temperature, and the fiber is oriented and arranged under the action of the magnetic field, the mechanical property of the composite material in the stress direction is greatly improved.

The method comprises the following specific steps:

1) and (3) passing the nano ferroferric oxide powder through a 10000-mesh screen, and taking undersize products.

2) Adding the sieved ferroferric oxide powder and nylon 6 particles together according to the mass ratio of 4-20% into a plastic mixer for fully and uniformly mixing;

3) adding the mixed plastic particles into a melt electrostatic spinning machine for electrostatic spinning to obtain nano electro-spinning fibers mixed with ferroferric oxide powder;

4) the fiber is stretched as much as possible, then the fiber is horizontally arranged and wound on a strip-shaped plate in a directional mode, the arrangement direction of the fiber is consistent with the long side direction of the plate, the strip plate wound with the fiber is placed in a strong magnetic field environment for as long as possible, and the magnetic induction line of the magnetic field is as straight as possible and is consistent with the arrangement direction of the fiber.

5) Cutting the fiber treated in the magnetic field into short fibers of 3-6mm, heating two parts of caprolactam powder with the same amount to 80 ℃, melting the caprolactam powder into liquid, adding an alkaline catalyst into one part of the caprolactam powder, wherein the alkaline catalyst can be sodium hydroxide, adding an activating agent into the other part of the caprolactam powder, and the activating agent can be toluene diisocyanate, and then respectively stirring uniformly.

6) And (3) respectively adding the short fibers obtained in the step (5) into caprolactam mixed with an alkaline catalyst and an activating agent according to the proportion of 10-20%, fully and uniformly stirring, and placing in a vacuum defoaming machine to eliminate bubbles.

7) Adding the solution obtained in the last step into a reaction injection molding machine as a component A and a component B respectively, mixing and injecting the mixture into a mold preheated to a certain temperature by using the reaction injection molding machine, maintaining the pressure for a period of time, heating to a curing temperature to cure caprolactam to form a product, wherein the mold is made of a non-magnetic material, the mold is placed in a strong magnetic field environment, or a strong magnet is arranged in the mold, so that a magnetic induction line passes through a mold cavity corresponding to a main stress position of the molded product, and the direction of the magnetic induction line is consistent with the stress direction corresponding to the product; the curing temperature of the mold should be controlled between 160 ℃ and 190 ℃.

The invention provides a method for preparing a high-strength cast nylon product, which can adopt microwave heating to heat and solidify in a mould, utilizes the characteristic that ferroferric oxide generates heat under microwave irradiation to ensure that the ferroferric oxide in the fiber generates heat, can ensure that solidification and crystallization are carried out by taking the fiber as the center because the heat is emitted from the fiber, and induces the polymerized caprolactam to crystallize vertically to the surface of the fiber by the heterogeneous fiber nucleation principle to increase interface adhesion.

The invention provides a method for preparing a high-strength cast nylon product, which can add a cross-linking agent into caprolactam liquid, induce molecular chains to generate cross-linking in the microwave heating and curing process, and enhance the interface adhesion effect.

The invention has the beneficial effects that:

(1) the magnetized nylon 6 short fibers are highly orderly arranged in the nylon-based single polymer composite material under the action of a magnetic field, and the strength, the modulus and the impact resistance of the composite material are greatly improved due to the reinforcing effect of the high-strength fibers on a matrix in the arrangement direction of the fibers.

(2) The temperature of caprolactam reaction and solidification is far lower than the thermal relaxation temperature of the nylon 6 fiber, so that the loss of modulus and strength caused by the melting of the nylon 6 fiber under the high-temperature condition is avoided.

(3) The processing method is mainly based on the existing equipment, has low requirement on the equipment, is easy to realize large-scale continuous production, and has wide applicability.

(4) The produced product not only has strength far higher than that of a homogeneous nylon product, but also has good recyclability.

Drawings

FIG. 1 is a schematic view of a fiber magnetizing apparatus in a method of manufacturing a high strength cast nylon article according to the present invention;

FIG. 2 is a schematic view of a dumbbell-type tensile specimen mold in a method of producing a high-strength cast nylon article according to the present invention;

FIG. 3 is a schematic view of an elongated impact specimen die in a method of making a high strength cast nylon article according to the present invention;

FIG. 4 is a schematic view of a cylindrical compression sample mold in a method of making a high strength cast nylon article according to the present invention;

FIG. 5 is a side cross-sectional view of a cylindrical compression sample mold in a method of making a high strength cast nylon article according to the present invention.

In the figure: 1-fiber; 2-winding block; 3-magnetizing the magnet; 4-a flat heater; 5-front template, 6-rear template, 7-heating rod and 10-strong magnet; 11-impact the sample template; 12-magnetic front template, 13-compressed sample rear template, 14-front round magnet and 15-rear round magnet; s-magnet S-pole; n-magnet N-pole.

Detailed Description

The invention is further illustrated by the following examples:

example 1:

the method for preparing the high-strength cast nylon product is used for preparing the dumbbell type tensile sample product, and comprises the following specific steps:

1) preparing a proper amount of commercial nano ferroferric oxide powder, putting the commercial nano ferroferric oxide powder into a vibrating screen with a 10000-mesh screen, and fully sieving the powder to obtain undersize materials for later use; oversize materials can be collected and ground by a grinding mill and then recycled;

2) adding 9.6kg of fully dried nylon 6 particles and 0.4kg of nano ferroferric oxide powder sieved in the previous step into a plastic mixer, and fully and uniformly mixing.

3) And (3) adding the uniformly mixed particles in the last step into a melt electrostatic spinning machine with a screw for feeding, setting the spinning voltage to be 30KV, the receiving distance to be 110mm and the charging barrel temperature to be 300 ℃, and spinning to obtain the nylon 6 fine fiber mixed with the ferroferric oxide powder.

4) As shown in fig. 1, the fiber 1 obtained by the previous step of spinning is stretched as much as possible, and then wound on a winding block 2 made of polytetrafluoroethylene, wherein the winding block 2 is a long polytetrafluoroethylene block with an i-shaped cross section, the winding direction of the stretched fiber 1 is consistent with the length direction of the winding block 2, and the fiber 1 is wound in a groove of the winding block 2, and a large winding force is applied when the fiber 1 is wound; the magnetized magnet 3 is a U-shaped strong magnet, and the groove in the middle of the U shape has a wide width which is enough to transversely place the winding block 2 in the groove; the flat heater 4 is a temperature-adjustable flat heater, the winding block 2 wound with the fiber 1 is placed on the flat heater 4, the U-shaped notch of the magnetizing magnet 3 is placed on a plane in an inverted mode, the winding block 2 is transversely placed in the middle of the U-shaped notch of the magnetizing magnet 3, the temperature of the flat heater is adjusted to 70 ℃, and the flat heater is placed for 10 hours to enable the fiber to be fully magnetized.

5) Cutting the magnetized fiber with magnetism into short fiber with the length of 3 mm; melting 19Kg of caprolactam solution at 80 ℃, adding 1Kg of sodium hydroxide, and fully stirring and mixing; another 19Kg of caprolactam solution was melted at 80 deg.C, and 1KgTDI was added and mixed well.

6) Dividing the whole chopped fiber into two parts of 5Kg, respectively adding into liquid caprolactam mixed with alkaline catalyst and activating agent, stirring thoroughly, and placing in a vacuum defoaming machine to eliminate bubbles, wherein the temperature in the defoaming process should be controlled at 80-100 deg.C.

7) Adding the solution obtained in the last step into a reaction injection molding machine as a component A and a component B respectively, wherein the reaction injection molding machine can be a general nylon reaction injection molding machine, mixing and injecting the mixture into a mold preheated to 80 ℃, keeping the pressure for 1 minute after injection, and then heating the mold to 160 ℃ to solidify caprolactam to form a product.

The mold is made of polytetrafluoroethylene, and as shown in fig. 2, mainly comprises a front template 5, a rear template 6, a heating rod 7 and a strong magnet 10. The front template 5 and the rear template 6 are both made of polytetrafluoroethylene, the front template 5 is a rectangular flat plate, four corners of the front surface of the front template are provided with protruded cylindrical guide posts, the rear template 6 is a rectangular flat plate with the same size as the front template 5 and can be combined with the front template 5 to form a set of complete mold, a dumbbell-shaped sample cavity is arranged on the joint surface of the rear template 6, one end of the cavity is connected with a runner for injection, the plane of the cavity is provided with a U-shaped groove, the U-shaped gap ensures that two ends of the U-shaped sample cavity are just connected with two ends of the dumbbell-shaped sample cavity, and the dumbbell-shaped sample cavity is positioned in the U-shaped gap; the strong magnet 10 is a strong magnet which has the same shape with the U-shaped groove, two poles are positioned at two ends of the U-shaped groove, the strong magnet 10 is embedded in the U-shaped groove, holes corresponding to guide pillars of the front template 5 are arranged at four corners of the rear template 6, three holes are arranged on the side surface of the rear template 6, and the heating rod 7 is inserted into the holes.

In the above process: firstly, ferroferric oxide magnetic powder with the diameter of less than 1 mu m is obtained by screening, the magnetic powder is mixed into nylon 6 particles, nylon 6 fibers with the diameter of 4-10 mu m can be obtained by the electrostatic spinning process, the particle size of the ferroferric oxide powder is small enough, the strength of the fibers can be prevented from being damaged too much, and the fibers are magnetized after being placed in a strong magnetic field for a certain time due to the ferroferric oxide powder, so that certain magnetism is achieved, and the direction of the magnetism is consistent with the length direction of the fibers; after the fibers are cut up, the short fibers also have magnetism; the short magnetic fibers are added into a raw material for reaction injection molding and injected into a specially designed mold, because the mold is filled with a strong magnet, and the magnetic induction line direction of the magnetic field of the strong magnet is consistent with the stretching direction of a stretching sample, the short magnetic fibers can be oriented along the magnetic induction lines under the action of the magnetic field in 1min of pressure maintaining time before heating and curing, after heating and curing, the short fibers oriented along the magnetic induction lines play a role in strengthening the tension direction of the sample, the mechanical property of the material is improved, because the solidification temperature of caprolactam is far lower than the melting point of nylon 6 fibers, the short fibers can be ensured not to be melted in the curing process, the high strength and the high modulus can be still maintained, and the oriented arrangement state in the magnetic field is maintained, almost all components of the cast nylon product processed by the method are nylon 6, but the highly oriented fiber has high anisotropy, and although the fiber contains a small amount of nano ferroferric oxide particles, the content of the nano ferroferric oxide particles is small, and the particles are fine, so that the recovery performance of the material is not influenced.

Example 2:

different from example 1, the method for preparing a high-strength cast nylon product according to the present invention is used in this example to prepare an elongated impact specimen product, and comprises the following specific steps:

2) adding 8Kg of fully dried nylon 6 particles and 2Kg of nano ferroferric oxide powder sieved in the previous step into a plastic mixer, and fully and uniformly mixing.

5) Cutting the magnetized fiber with magnetism into short fiber with the length of 3 mm; melting 42.75Kg of caprolactam solution at 80 deg.C, adding 2.25Kg of sodium hydroxide, and mixing under stirring; another 42.75Kg of caprolactam solution was melted at 80 deg.C, 2.25Kg of TDI was added and mixed well.

7) And adding the solution obtained in the last step into a reaction injection molding machine as a component A and a component B respectively, wherein the reaction injection molding machine can be a general nylon reaction injection molding machine, mixing and injecting the mixture into a special mold preheated to 80 ℃ and described below by using the reaction injection molding machine, keeping the pressure for 1 minute after injection, and then heating the mold to 190 ℃ to solidify caprolactam to form a product.

The mold is made of polytetrafluoroethylene, and as shown in fig. 3, mainly includes a front template 5, an impact sample template 11, a heating rod 7, and a ferromagnetic body 10. The mold is substantially the same as the mold described in example 1, the only difference being that the rear mold 6 is replaced with an impact sample mold plate 11, and the impact sample mold plate 11 is compared with the rear mold 6, and the cavity of the impact sample mold plate 11 is a cavity corresponding to a rectangular sample, and the cavity is located in a notch of a U-shaped groove, and two ends of the cavity are connected with two ends of the U-shaped groove.

Example 3:

in distinction to example 1, this example utilized a method of the present invention for making high strength cast nylon articles to make cylindrical compressed sample articles, comprising the following specific steps:

2) 9Kg of fully dried nylon 6 particles and 1Kg of nano ferroferric oxide powder sieved in the previous step are added into a plastic mixer and fully and uniformly mixed.

5) Cutting the magnetized fiber with magnetism into short fiber with the length of 3 mm; melting 28.5Kg of caprolactam solution at 80 deg.C, adding 1.5Kg of sodium hydroxide, and mixing under stirring; another 28.5Kg of caprolactam solution was melted at 80 deg.C, and 1.5Kg of TDI was added and mixed well.

7) Adding the solution obtained in the previous step into a reaction injection molding machine as a component A and a component B respectively, wherein the reaction injection molding machine can be a general nylon reaction injection molding machine, mixing and injecting the mixture into a special mold preheated to 80 ℃ and described below by using the reaction injection molding machine, keeping the pressure for 1 minute after injection, and then heating the mold to 175 ℃ to solidify caprolactam to form a product.

The mold is made of polytetrafluoroethylene, and mainly comprises a magnetic front template 12, a compressed sample rear template 13, a heating rod 7, a front round magnet 14 and a rear round magnet 15 as shown in fig. 4 and 5. Different from the mold used in embodiment 1, the magnetic front template 12 and the compressed sample rear template 13 are made of polytetrafluoroethylene, the magnetic front template 12 is a rectangular flat plate, the front surface is a matched surface, four corners of the magnetic front template are provided with protruded cylindrical guide posts, the center of the back surface is provided with a circular groove, the front circular magnet 14 is a cylindrical strong magnet, the upper surface and the lower surface of the cylinder are respectively an S pole and an N pole, and the front circular magnet 14 is embedded in the circular groove of the magnetic front template 12; the compressed sample rear template 13 is a rectangular flat plate with the same size as the magnetic front template 12, and can be combined with the front template 5 to form a set of complete mold, a cylindrical sample cavity is arranged in the center of the joint surface of the compressed sample rear template 13, a runner for injection is connected to one end of the cavity, and a circular groove is arranged in the center of the back surface of the cavity; the rear round magnet 15 is a strong magnet which is completely the same as the front round magnet 14, two poles of the strong magnet are positioned on the upper surface and the lower surface of a cylinder, the strong magnet 10 is embedded in a circular groove of a rear template 13 of a compressed sample, four corners of the rear template 13 of the compressed sample are provided with holes corresponding to guide posts of the magnetic front template 12, the side surface of the rear template 13 of the compressed sample is provided with three holes, a heating rod 7 is inserted into the holes, the mounting direction of the front round magnet 14 and the rear round magnet 15 is adjusted when the front round magnet and the rear round magnet are mounted, so that the adjacent magnetic poles of the front round magnet and the rear.

In the embodiment, the compression direction of the compression sample is along the cylindrical axis direction, the magnetic field generated by the front round magnet 14 and the rear round magnet 15 is also the same as the cylindrical sample axis direction, and during the forming process, the magnetic field guides the short fibers to be oriented along the cylindrical axis direction, so that the strength and the rigidity of the product in the compression direction are enhanced.

Example 4:

in contrast to example 1, a dumbbell type tensile specimen article was produced by the method for producing a high strength cast nylon article of the present invention, which comprises the following steps in step 7: a microwave irradiation apparatus was installed outside the mold described in example 1, and the solution obtained in the previous step was added as a component a and a component B, respectively, to a reaction injection molding machine, which may be a general machine for nylon reaction injection molding, and mixed and injected by the reaction injection molding machine into a special mold described below preheated to 80 ℃, and after injection, pressure was maintained for 1 minute, and then the mold was irradiated with microwaves, and caprolactam and the mold were heated to 175 ℃, and the caprolactam was solidified to form a product.

The fiber contains ferroferric oxide powder, so the fiber can generate heat through microwave irradiation, after the fiber generates heat, the fiber transfers heat to surrounding caprolactam liquid to solidify caprolactam, and as the fiber generates heat firstly, the solidification and crystallization are carried out by taking the fiber as a core, the fiber is taken as a crystallization core, the crystallization after the caprolactam solidification can expand outwards by taking the fiber as a center to form a layer of transversely-grown crystal layer vertical to the surface of the fiber, and the transverse crystal layer has a remarkable enhancing effect on the interface adhesion of the fiber and a substrate, so the interface adhesion can be further increased, and the mechanical property of the material is improved.

Example 5:

different from example 4, a dumbbell type tensile sample product was prepared by using the method for preparing a high strength cast nylon product of the present invention, and a proper amount of a crosslinking agent was added to caprolactam as a raw material.

During microwave heating, the cross-linking agent promotes the molecular chains to be cross-linked, so that the bonding strength of the matrix and the fibers is further increased, and the mechanical property is improved.

The above examples are to be understood as merely illustrative in more detail and as illustrative of the invention, and the invention is not to be construed as limited in any way by the use of tensile, impact and compressive test specimens which are relatively simple to apply and which are constructed of materials and procedures known in the art for carrying out the invention, which, if not specifically described, are described in as much detail herein.

Claims

1. A method for preparing a high-strength cast nylon product is characterized by comprising the following specific steps:

step 1, passing the nano ferroferric oxide powder through a 10000-mesh screen, and taking undersize;

step 2, adding the sieved ferroferric oxide powder and nylon 6 particles together according to the mass ratio of 4-20% into a plastic mixer, and fully and uniformly mixing;

step 3, adding the mixed plastic particles into a melt electrostatic spinning machine for electrostatic spinning to obtain nano electro-spinning fibers mixed with ferroferric oxide powder;

step 4, stretching the fibers, horizontally and directionally arranging and winding the fibers on a strip-shaped plate, wherein the arrangement direction of the fibers is consistent with the long side direction of the plate, placing the strip plate wound with the fibers in a strong magnetic field environment for a certain time, and keeping the magnetic induction lines of the magnetic field consistent with the arrangement direction of the fibers;

step 5, cutting the fiber treated in the magnetic field into short fibers with the diameter of 3-6mm, heating two parts of caprolactam powder with the same quantity to 80 ℃ to melt the caprolactam powder into liquid, adding an alkaline catalyst into one part of the caprolactam powder, adding an activating agent into the other part of the caprolactam powder, and then respectively stirring the caprolactam powder and the activating agent uniformly;

step 6, respectively adding the short fibers obtained in the step 5 into caprolactam mixed with an alkaline catalyst and an activating agent according to the proportion of 10-20%, fully and uniformly stirring, and placing in a vacuum defoaming machine to eliminate bubbles;

and 7, adding the solution obtained in the step 6 into a reaction injection molding machine as a component A and a component B respectively, mixing and injecting the mixture into a mold preheated to a certain temperature by using the reaction injection molding machine, maintaining the pressure for a period of time, and heating to a curing temperature to cure caprolactam to form a product.

2. The method of making a high strength cast nylon article of claim 1, wherein: the basic catalyst is sodium hydroxide and the activator is toluene diisocyanate.

3. The method of making a high strength cast nylon article of claim 1, wherein: and (7) manufacturing the mould by using a non-magnetic material, placing the mould in a high-intensity magnetic field environment, or installing a strong magnet in the mould, so that magnetic induction lines pass through a mould cavity corresponding to the main stress position of the product, and the direction of the magnetic induction lines is consistent with the stress direction corresponding to the product.

4. The method of making a high strength cast nylon article of claim 1, wherein: the curing temperature of the mold in the step 7 is controlled between 160 ℃ and 190 ℃.

5. The method of making a high strength cast nylon article of claim 1, wherein: and (7) heating and curing in the mold by using microwave.

6. The method of making a high strength cast nylon article of claim 1, wherein: a crosslinking agent is added to the caprolactam liquid.