阅读说明：本技术 一种悬浮聚合制备纳米碳纤维增强聚甲基丙烯酰亚胺泡沫的方法 (Method for preparing carbon nanofiber reinforced polymethacrylimide foam through suspension polymerization ) 是由 姚正军 祖嘉琦 焦自保 陈文静 钱崑 于 2019-12-02 设计创作，主要内容包括：本发明公开了一种悬浮聚合制备纳米碳纤维增强聚甲基丙烯酰亚胺泡沫的方法,步骤一、将分散介质和悬浮剂加入第一反应釜,进行搅拌；步骤二、将单体加入第二反应釜中,加热至反应温度,再加入引发剂和纳米碳纤维,然后在恒温的条件下,将第二反应釜置于超声分散仪中进行超声分散；步骤三、将第二反应釜中分散后的混合液倒入已加热至反应温度的第一反应釜中,搅拌进行悬浮聚合反应,得到预聚体；步骤四、在预聚体中加入交联剂和发泡剂,采用挤压机对其进行挤压；步骤五、将挤压后的混合物置于模具中进行发泡热处理成型,得到纳米碳纤维增强的聚甲基丙烯酰亚胺泡沫。本发明具有力学性能优异、反应时间短、成品率高、易于规模化生产等优点。(The invention discloses a method for preparing carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which comprises the following steps of adding a dispersion medium and a suspending agent into a first reaction kettle, and stirring; secondly, adding the monomer into a second reaction kettle, heating to a reaction temperature, adding an initiator and the carbon nanofibers, and then placing the second reaction kettle into an ultrasonic dispersion instrument for ultrasonic dispersion under a constant temperature condition; step three, pouring the mixed solution dispersed in the second reaction kettle into the first reaction kettle heated to the reaction temperature, and stirring for suspension polymerization reaction to obtain a prepolymer; step four, adding a cross-linking agent and a foaming agent into the prepolymer, and extruding the prepolymer by using an extruder; and fifthly, placing the extruded mixture in a mold for foaming heat treatment molding to obtain the carbon nanofiber reinforced polymethacrylimide foam. The invention has the advantages of excellent mechanical property, short reaction time, high yield, easy large-scale production and the like.)

1. A method for preparing carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization is characterized by comprising the following steps:

step one, adding a dispersion medium and a suspending agent into a first reaction kettle, and stirring;

secondly, adding the monomer into a second reaction kettle, heating to a reaction temperature, adding an initiator and the carbon nanofibers, and then placing the second reaction kettle into an ultrasonic dispersion instrument for ultrasonic dispersion under a constant temperature condition;

step three, pouring the mixed solution dispersed in the second reaction kettle into the first reaction kettle heated to the reaction temperature, and stirring for suspension polymerization reaction to obtain a prepolymer;

step four, adding a cross-linking agent and a foaming agent into the prepolymer, and extruding the prepolymer by using an extruder;

and fifthly, placing the extruded mixture in a mold for foaming heat treatment molding to obtain the carbon nanofiber reinforced polymethacrylimide foam.

2. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

and in the third step, in the stirring process, when the viscosity of the system is increased to have resistance, the stirring speed is reduced, the temperature is increased, the suspension polymerization reaction is continuously carried out until the system is in a viscoelastic state and the stirring is blocked, and the prepolymer is obtained.

3. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

wherein the monomers are methacrylonitrile and methacrylic acid;

the weight parts of the raw materials are as follows:

0.5-2 parts of nano carbon fiber;

30-60 parts of methacrylonitrile;

30-60 parts of methacrylic acid;

a dispersion medium, 120-;

0.5-5.0 parts of suspending agent;

initiator 0.1-0.4;

0.5-7.0 parts of foaming agent;

1.5-3.0 parts of cross-linking agent.

4. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

in the first step, the dispersion medium is deionized water;

the suspending agent is any one of methyl cellulose, polyvinyl alcohol and sodium polyacrylate;

the stirring speed is 100-300 r/min.

5. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

wherein, in the second step, the reaction temperature is 60-65 ℃;

the dispersion frequency is 5kHz-50kHz, and the dispersion time is 20-30 min;

the initiator is one of azo compounds or organic peroxides.

6. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

in the second step, the initiator is azobisisobutyronitrile.

7. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

and in the second step, a condensing pipe is inserted into the second reaction kettle, and circulating cooling water is introduced into the condensing pipe, so that the temperature of the second reaction kettle is controlled within the fluctuation range of +/-0.5 ℃.

8. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 2 by suspension polymerization, wherein:

wherein, in the third step, the initial stirring speed is 150-;

when the viscosity of the system increases to have resistance, the stirring speed is reduced to 100-200r/min, and the temperature is increased by 5-10 ℃.

9. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

in the fourth step, the cross-linking agent is one of acrylamide and allyl methacrylate;

the foaming agent is one of an expanded microsphere foaming agent and azodicarbonamide.

10. The method for preparing carbon nanofiber reinforced polymethacrylimide foam according to claim 1 by suspension polymerization, wherein:

and in the fifth step, the foaming heat treatment forming process is carried out by putting the mixture into a mould on a vulcanizing machine, the hydraulic pressure is 15-20 MPa, the foaming process is carried out by keeping the temperature at 160-180 ℃ for 30-40 min, and the heat treatment process is carried out by keeping the temperature at 200-220 ℃ for 1-2 h.

Technical Field

The invention belongs to the field of materials, relates to a preparation method of polymethacrylimide foam, and particularly relates to a method for preparing carbon nanofiber reinforced polymethacrylimide foam through suspension polymerization.

Background

The Polymethacrylimide (PMI) foam is a PMI foam which has obviously better strength and rigidity than other foam materials under the same density at present, and the density and the mechanical property enable the Polymethacrylimide (PMI) foam to be widely applied in the field of aerospace, and is mainly used as a core material to form a sandwich structure with a composite material. PMI foam is used for the first time on an A380 airplane for a main bearing structural part and applied to a rear pressure frame and inner and outer ailerons. In the future, higher requirements on the mechanical properties of polymethacrylimide foam can be provided, and the traditional method for improving the mechanical properties by increasing the density cannot meet the requirements in the fields of safety protection, transportation, mechanical manufacturing, aerospace and the like.

Thus, there is a need for foams with better mechanical properties. The invention patent with application number 201310502487.9 discloses a preparation method of a graphene reinforced polymethacrylimide foam material, which is to obtain a foam material with better mechanical property by reinforcing the polymethacrylimide foam through graphene, but because the surface of graphene is inert and does not contain any active group when the graphene is compounded with a polymer, and the acting force between the graphene and a polymer matrix is very small, the most critical step is to uniformly disperse the graphene into the polymer matrix, and ultrasonic dispersion cannot ensure the maximization of the contact surface between the graphene and the polymer matrix, and the mechanical property of the composite material can be directly influenced. Meanwhile, the preparation method adopts a body method, and the method combines the performances of graphene, so that the problems of implosion, additive sedimentation and the like are easily caused.

Disclosure of Invention

The invention provides a method for preparing carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which overcomes the defects of the prior art.

In order to realize the aim, the invention provides a method for preparing carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which comprises the following steps of firstly, adding a dispersion medium and a suspending agent into a first reaction kettle, and stirring; secondly, adding the monomer into a second reaction kettle, heating to a reaction temperature, adding an initiator and the carbon nanofibers, and then placing the second reaction kettle into an ultrasonic dispersion instrument for ultrasonic dispersion under a constant temperature condition; step three, pouring the mixed solution dispersed in the second reaction kettle into the first reaction kettle heated to the reaction temperature, and stirring for suspension polymerization reaction to obtain a prepolymer; step four, adding a cross-linking agent and a foaming agent into the prepolymer, and extruding the prepolymer by using an extruder; and fifthly, placing the extruded mixture in a mold for foaming heat treatment molding to obtain the carbon nanofiber reinforced polymethacrylimide foam.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: in the third step, in the stirring process, when the viscosity of the system is increased to have resistance, the stirring speed is reduced, the temperature is increased, the suspension polymerization reaction is continuously carried out until the system is in a viscoelastic state and the stirring is blocked, and the prepolymer is obtained.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: wherein, the monomers are methacrylonitrile and methacrylic acid; the weight parts of the raw materials are as follows: 0.5-2 parts of nano carbon fiber; 30-60 parts of methacrylonitrile; 30-60 parts of methacrylic acid; a dispersion medium, 120-; 0.5-5.0 parts of suspending agent; initiator 0.1-0.4; 0.5-7.0 parts of foaming agent; 1.5-3.0 parts of cross-linking agent.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: wherein, in the first step, the dispersion medium is deionized water; the suspending agent is any one of Methyl Cellulose (MC), polyvinyl alcohol (PVA) and sodium Polyacrylate (PAAS), and preferably, the suspending agent is Methyl Cellulose (MC); the stirring speed is 100-300 r/min.

Wherein the pH value of the deionized water is within 6-8, and Cl^-≤10×10^-6Conductivity of 1 × 10^-5Ω·cm^-1～1×10^-6Ω·cm^-1The hardness is less than or equal to 5, and no visible mechanical impurities exist.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: wherein, in the second step, the reaction temperature is 60-65 ℃; the dispersion frequency is 5kHz-50kHz, and the dispersion time is 20-30 min; the initiator is one of azo compounds or organic peroxides.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: in the second step, the initiator is azobisisobutyronitrile.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: and in the second step, a condensing pipe is inserted into the second reaction kettle, and circulating cooling water is introduced into the condensing pipe, so that the temperature of the second reaction kettle is controlled within the fluctuation range of +/-0.5 ℃.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: wherein, in the third step, the initial stirring speed is 150-; when the viscosity of the system increases to have resistance, the stirring speed is reduced to 100-200r/min, and the temperature is increased by 5-10 ℃.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: in the fourth step, the cross-linking agent is one of Acrylamide (AM) and Allyl Methacrylate (AMA), preferably, the cross-linking agent is Acrylamide (AM); the foaming agent is one of an expanded microsphere foaming agent and Azodicarbonamide (AC), and preferably, the crosslinking agent is the expanded microsphere foaming agent.

Further, the invention provides a method for preparing the carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, which can also have the following characteristics: and in the fifth step, the foaming heat treatment forming process is carried out by putting the mixture into a mould on a vulcanizing machine, the hydraulic pressure is 15-20 MPa, the foaming process is carried out by keeping the temperature at 160-180 ℃ for 30-40 min, and the heat treatment process is carried out by keeping the temperature at 200-220 ℃ for 1-2 h.

The invention has the beneficial effects that:

firstly, the invention adopts the suspension polymerization method, the free radical suspension polymerization process leads the monomer to be polymerized in the form of liquid drops, compared with other methods such as the free radical bulk polymerization method, the invention is not easy to generate the implosion phenomenon caused by the difficulty of dissipating a large amount of heat generated by the reaction, the suspension polymerization method leads the reaction heat to be easy to discharge, the polymerization time is short, the manufacturing period is short, a mould is not required to be manufactured every time, the production efficiency is high, the implosion phenomenon can not occur in the polymerization process, and the yield is high.

And each carbon atom of the carbon nanofiber is combined with three atoms around the carbon nanofiber through a covalent bond, two ends of the carbon nanofiber are closed, no suspended chemical bond exists, and a tight and compact structure is formed, so that the stability of the carbon nanofiber is stronger, and the number of defects is less. The charge acting force among the carbon atoms in the nanometer scale ensures that the carbon nanofiber has the mechanical properties of high strength, high elasticity, high rigidity and the like.

Due to the unique fiber structure, the specific surface area is large while the number of defects is small, the dispersibility is good, reactant molecules can well pass through the mesoporous structure, the mass transfer process is facilitated, the contact time of the mixture is obviously shortened, the method is simple, the operation is convenient, and the yield is high. And the nano carbon fiber has low density, high specific modulus and high specific strength, and can ensure that the nano carbon fiber achieves high mechanical property under the condition of adding a small amount of nano carbon fiber. The excellent characteristics of small addition amount, large specific surface area and good dispersibility of the carbon nanofibers effectively solve the problem that the carbon nanofibers cannot be uniformly dispersed in a matrix.

Meanwhile, the nano carbon fibers are added, so that the fibers are mutually wound to form an isotropic three-dimensional network structure, the reinforcing effect is well played in a matrix, and the sliding or cracking of the PMI foam plastic in any direction in the stress process is reduced.

The carbon nanofibers are added as a reinforcing item, so that the strength of the PMI foamed plastic can be greatly improved, excellent mechanical properties can be guaranteed to be achieved under the condition of low density, and the requirement standard of a bearing part is met in the form of a sandwich structure in the design of an aircraft part.

Compared with the foaming of common PMI foam, the carbon nanofiber reinforced PMI foam requires higher temperature for inhibiting the foaming process, and cracks can occur if the foaming temperature is not well adjusted, so that the mechanical property is influenced.

And fourthly, foaming and forming in a specific mould to obtain the workpiece with the required shape to obtain the product. The density of the final product can be regulated by regulating the amount of the prepolymer mixture, and industrialization can be realized.

The mechanical property of the PMI foam plastic can be greatly improved by adding a small amount of carbon nanofibers, so that the traditional mode of improving the mechanical property of the PMI foam plastic by improving the density of the PMI foam is broken through, the requirements on materials required by a light and high-strength specific application environment are met, the PMI foam plastic can be used as a favorable product to be applied to the fields of safety protection, mechanical manufacturing, transportation, aerospace and the like, and meanwhile, the carbon nanofibers have the effects of electromagnetic shielding and absorption, so that the PMI foam plastic has multiple benefits in the field of aviation.

According to the invention, the carbon nanofibers are added into the PMI foam as a reinforcing phase, so that the tensile strength, the bending strength and the compressive strength of the PMI foam are greatly improved, and compared with the conventional mode of improving the mechanical property by increasing the density, the carbon nanofiber is more beneficial to being applied to the fields of aviation, aerospace, trains, ships and the like.

Drawings

FIG. 1 is a flow chart of a method for preparing carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization.

Detailed Description

The invention is further described below with reference to the accompanying drawings and specific examples.

The invention provides a method for preparing carbon nanofiber reinforced polymethacrylimide foam by suspension polymerization, wherein the flow is shown in figure 1, and the weight ratio of the components in each embodiment is shown in table 1.

TABLE 1 examples of nanocarbon fibre-reinforced polymethacrylimide foams

The method comprises the following specific steps:

firstly, dissolving a suspending agent Methyl Cellulose (MC) in dispersion medium deionized water to prepare a suspending agent solution, then adding the suspending agent solution into a first reaction kettle, starting a stirring device to stir at the stirring speed of 300 r/min.

And step two, adding monomer methacrylonitrile and methacrylic acid into a second reaction kettle, heating to the reaction temperature of 60 ℃, and adding an initiator azobisisobutyronitrile and carbon nanofibers. And then placing the second reaction kettle in an ultrasonic disperser for ultrasonic dispersion under the condition of constant temperature, and performing ultrasonic dispersion for 25 minutes at the frequency of 10 kHz.

Wherein, preferably, a condensing pipe is inserted into the second reaction kettle, and circulating cooling water is introduced into the condensing pipe, so that the temperature of the second reaction kettle is controlled within the fluctuation range of +/-0.5 ℃.

And step three, pouring the mixed solution dispersed in the second reaction kettle into the first reaction kettle heated to the reaction temperature of 60 ℃, adjusting the rotating speed of a stirring device to be 150r/min, and stirring for suspension polymerization reaction to obtain the prepolymer.

In the stirring process, specifically, after 5 hours of reaction, the viscosity of the suspension of the system is increased and resistance is caused, the stirring speed is reduced to 100r/min, the reaction temperature is increased to 70 ℃, after 2 hours of suspension polymerization reaction, the system is in a viscoelastic state and is blocked in stirring, and the stirring is stopped, so that the prepolymer is obtained.

And step four, adding a cross-linking agent Acrylamide (AM) and a foaming agent expanded microsphere foaming agent into the prepolymer, extruding the prepolymer by using an extruder, and removing redundant water to obtain a mixture with viscoelasticity.

And fifthly, placing the extruded mixture in a specific mould according to the required density range requirement for foaming heat treatment molding to obtain the carbon nanofiber reinforced polymethacrylimide foam.

The foaming heat treatment forming process is carried out by putting the mixture into a mold on a vulcanizing machine, the hydraulic pressure is 15-20 MPa, the foaming process is carried out by keeping the temperature of the mixture on the vulcanizing machine at 200 ℃ for 30min, and the heat treatment process is carried out by keeping the temperature of the mixture at 220 ℃ for 1.5 h.

The foams prepared in the examples are limited to foaming according to specific moulds, and the densities are relatively close. The PMI foams prepared in the respective examples were subjected to mechanical property tests according to the relevant standards, and the test results are shown in table 2 below.

TABLE 2 mechanical Properties of PMI foams prepared in the examples

It can be seen from table 2 that, the carbon nanofibers are added as the reinforcing phase, so that the mechanical properties of the PMI foam are greatly improved compared with those of the PMI foam which is not added, and the mechanical properties of the PMI foam are multiplied along with the increase of the proportion of the carbon nanofibers, but when the weight of the carbon nanofibers reaches about 1 part, the trend of the increase of the mechanical properties of the foam becomes gentle, the carbon nanofibers are probably wound with each other along with the increase of the content of the carbon nanofibers, the reinforcing of the acting force of the carbon nanofibers plays a certain role in hindering the foaming process of the substrate, fine cracks are generated, and certain influence is generated on the mechanical properties of the PMI foam. Under the condition of adding the same nano carbon fiber content, the difference of the mechanical index value of the PMI foam is not large under the preparation of formulas with different contents. The density is higher and the mechanical property is better as the content of each component is increased.