CN114195959B - Polypropylene graft with low degradation degree and preparation method thereof - Google Patents

Abstract

The invention discloses a polypropylene graft with a low degree of degradation and a preparation method thereof. During the melt grafting process of polypropylene, under the action of an initiator, carbon-carbon bond breaks are likely to occur, leading to serious degradation of polypropylene. In order to inhibit the degradation of polypropylene, in the existing invention patents, one or more grafting aids are generally added in the process of polypropylene melt grafting modification. problem. Aiming at the deficiencies of the prior art, the invention provides a new method for grafting and modifying polypropylene. Its characteristic is that an active group that is easier to graft reaction with functionalized grafting monomers such as maleic anhydride than polypropylene free radicals is firstly introduced into the main chain of polypropylene. Subsequently, based on the introduced active groups, the grafting reaction with the functionalized grafting monomer under relatively mild conditions can greatly inhibit the degree of degradation of polypropylene during the grafting modification process, resulting in a polymer with higher molecular weight and higher density. Polypropylene graft with high grafting rate.

Description

A kind of polypropylene graft with lower degree of degradation and preparation method thereof

technical field

The invention belongs to the technical field of polypropylene modification, and in particular relates to a polypropylene graft with a low degree of degradation and a preparation method thereof.

Background technique

As a general-purpose polymer material, polypropylene has been widely used in many fields of people's lives. Due to the relatively low mechanical properties of polypropylene, it needs to be blended with nylon, glass fiber and other organic or inorganic fillers to make composite materials before it can be used as an engineering material. Since polypropylene is a non-polar polymer material, when polypropylene is blended with fillers such as nylon and glass fiber, it is difficult to be compatible between polypropylene and fillers on a micro or macro scale, resulting in local cracking of the composite material during use. , uneven fillers and even partial shedding, etc., seriously restrict the industrial application of polypropylene composite materials.

The current industrial solution is to introduce polar monomers into the main chain of polypropylene through copolymerization of propylene and polar monomers or subsequent graft modification of polypropylene to improve the relationship between polypropylene and polar fillers. compatibility. Among them, the method of subsequent graft modification of polypropylene products has the advantages of low cost and good effect. Commonly used grafting monomers are polar monomers such as maleic anhydride or acrylic acid. Methods for functional modification of polypropylene grafted polar monomers include solution method, melting method, solid phase method, ray radiation method, etc. Among them, the melting method is more convenient to operate and has been widely used in industry.

During the melt-grafting process of polypropylene, among all the hydrogen atoms on polypropylene, the hydrogen atoms on the tertiary carbon are the most active, and are most likely to be dissociated by the attack of oxygen-containing free radicals after the decomposition of the initiator. In general, the tertiary hydrogen on the main chain of polypropylene is activated and stripped, and the carbon-carbon bond is prone to breakage, which leads to the degradation of polypropylene and greatly reduces the mechanical properties of polypropylene. In addition, due to the low reactivity of maleic anhydride and the tendency to self-polymerize during the grafting reaction, it is difficult to introduce maleic anhydride molecules into the polypropylene molecular chain, resulting in a generally low grafting rate of maleic anhydride. Common solutions are to increase the amount of initiator, increase the concentration of maleic anhydride and use auxiliary grafting monomers. Increasing the amount of initiator can obtain higher concentration of active free radicals and provide more active sites for grafting reaction, but the use of a large amount of initiator will aggravate the degree of degradation of polypropylene, resulting in poor mechanical properties of polypropylene. Increasing the amount of maleic anhydride will lead to an increase of unreacted maleic anhydride, and more acidic residues will greatly increase the odor of polypropylene grafted products. Commonly used auxiliary grafting monomers are small organic molecules containing at least one carbon-carbon double bond, such as acrylic acid, acrylate, β-pinene, styrene, divinylbenzene, octene, decene, etc. Can be used alone or in combination. The use of auxiliary grafting monomers can not only reduce the degradation of polypropylene to a certain extent, but also improve the grafting rate of maleic anhydride. On the one hand, the auxiliary monomer can help stabilize the free radicals of polypropylene macromolecules and reduce the breakage of carbon-carbon single bonds; on the other hand, the auxiliary graft monomer can form copolymerization with unsaturated functional graft monomers such as maleic anhydride One grafting site on the main chain of polypropylene can introduce multiple maleic anhydride molecules to improve the problem of low grafting rate.

Chinese patent CN 104804143A introduces styrene auxiliary monomer in the melting grafting process of polypropylene. The specific method is to mix the initiator and styrene to form a styrene solution, and then mix polypropylene and maleic anhydride into a twin-screw extruder or In two twin-screw extruders connected in series, after melting, the mixture of initiator and styrene is added to different barrel sections of the extruder to carry out melt grafting reaction. When the amount of styrene was 7.5%, the melt flow rate MFR of polypropylene decreased from 160g/10min to 140g/10min, and the molecular weight of the obtained functionalized polypropylene and the raw material polypropylene did not decrease significantly.

In Chinese patent CN 101519477A and Chinese patent CN 101724128A, in addition to introducing styrene as the first auxiliary monomer during melt grafting modification of polypropylene, unsaturated molecules containing two or more carbon-carbon double bonds are also used as the second auxiliary monomer. Two auxiliary monomers, so as to improve the grafting efficiency of macromolecular polypropylene free radicals and obtain polypropylene grafts with higher molecular weight. Among them, the amount of maleic anhydride is 2%~5%, the amount of the first auxiliary monomer is about 3%~7%, and the ratio of the first monomer to the second monomer is about 1:4 to 7:13, two types When the amount of auxiliary monomer is generally not less than 5%, it can maintain the high molecular weight of polypropylene after the grafting reaction, that is, the low MFR value. Chinese patent CN 109467644A first soaks the mixture of polypropylene, initiator and maleic anhydride in styrene, and then performs grafting reaction on the swollen system. The amount of styrene used in this invention is as high as 5% to 25% relative to polypropylene. Chinese patent CN 106117445A carries out the reaction of grafting maleic anhydride to polypropylene in a reactor, and the same process introduces styrene as an auxiliary monomer, but this invention needs nitrogen protection, and vacuum removal of impurities is required for 30-120 minutes after the grafting reaction , after removing impurities, it needs to be taken out and granulated to shape, so the process is more cumbersome and the production cost is higher.

Contents of the invention

In order to suppress the breakage of the main chain of polypropylene during the melt grafting of polypropylene, the existing invention patents generally require the use of a higher amount of auxiliary additives, and cannot well solve the problem of polypropylene degradation. Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a new method for grafting and modifying polypropylene. It is characterized by first introducing an active site on the main chain of polypropylene that is easier to graft with functionalized grafting monomers than polypropylene free radicals, and then based on the introduced active site, under milder conditions Under the selective grafting reaction with maleic anhydride, the degradation of polypropylene in the grafting modification process can be greatly inhibited, and a polypropylene graft with a higher molecular weight and a higher grafting rate can be obtained.

It is therefore an object of the present invention to provide a polypropylene graft with a lower degree of degradation and a process for its preparation. Through the two-step reaction, the modification of the polypropylene molecular chain by the functionalized graft monomer is realized. The first step is to introduce high active sites on the main chain of polypropylene, which refers to the grafting reaction of polypropylene and a monomer A with active groups under the action of thermal initiation or initiator to obtain PP-A The second step is based on the grafting reaction between PP-A and functionalized grafting monomer B under relatively mild reaction conditions to obtain the target product PP-A-B.

The polypropylene graft in the present invention refers to a graft copolymer formed after introducing a functionalized graft monomer into a polypropylene resin macromolecular chain. One of the characteristics of the present invention is that the functionalized grafting monomers are efficiently grafted on the polypropylene molecular chain through two-step reactions. Another feature of the present invention is that the obtained polypropylene grafts are less degraded than the starting polypropylene material.

The polypropylene raw material used in the present invention is polypropylene powder that does not contain additives such as polypropylene antioxidants and deacidification agents before granulation in polypropylene production equipment, and can be produced under Unipol gas-phase fluidized bed process conditions Homopolypropylene powder, such as drawing material, injection molding and other product grades. The introduction of high active sites on the main chain of polypropylene in the present invention refers to the grafting reaction of polypropylene and a monomer A with active groups under the action of thermal initiation or peroxide initiator, on the one hand Significantly inhibit the degradation of polypropylene, and at the same time graft the active site on the main chain of polypropylene, and the product is marked as PP-A. The monomer A refers to a styrene derivative containing one or more alkyl substituent groups, wherein the styrene moiety acts similarly to the styrene molecule, which can stabilize polypropylene free radicals and inhibit polypropylene main The degradation of the chain; the hydrogen atom close to the benzene ring in the alkyl branch on the benzene ring is more active under the action of the benzene ring and is easily activated by the initiator. Monomer A can be 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 5-methylstyrene, 6-methylstyrene, 2-ethylstyrene, 3-ethylstyrene Styrene derivative compounds containing a single methyl group or other alkyl substituents containing 2 to 6 carbon atoms, such as methyl styrene, 4-ethyl styrene, 5-ethyl styrene, 6-ethyl styrene, etc. It can be a series of derivative compounds formed by the simultaneous or partial substitution of the hydrogen atoms on the benzene ring of styrene by the above-mentioned multiple alkyl radicals. The active site refers to the alkyl substituent group with 1 to 6 carbon atoms connected to the benzene ring, especially the part directly connected to the benzene ring in the alkyl radical, and the hydrogen atom on this position is The influence of the benzene ring is more easily activated to generate corresponding free radicals, and further grafting reaction occurs with functionalized grafting monomer B such as maleic anhydride, and the product is denoted as PP-A-B. In addition, in the PP-A produced after the reaction of monomer A and polypropylene, the alkyl radicals on the benzene ring protrude outside the main chain and are difficult to participate in the crystallization of polypropylene, and the steric hindrance is also higher than that on polypropylene. Tertiary hydrogens are more easily activated by initiator radicals.

When reacting PP-A containing active sites with functionalized graft monomer B, in order to inhibit the degradation of polypropylene, milder reaction conditions are preferred, such as lower reaction temperature, generally below 130°C, preferably 70°C ~110°C, more preferably 70~90°C. Under this temperature condition, compared with the hydrogen atoms on the polypropylene main chain, the alkyl radicals connected to the benzene ring in the monomer A that has been grafted on the polypropylene main chain can be better activated by the initiator, and then combined with The functionalized grafting monomer B is reacted, and the monomer B is grafted on the PP-A molecular chain, which effectively reduces the polypropylene degradation reaction caused by the activation of the tertiary hydrogen and the carbon-carbon bond breakage, and finally obtains a Functionalized polypropylene PP-A-B with high molecular weight and high grafting rate.

The initiator can be benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butyl peroxy)hexane, peroxide-3,5,5 -One or more of tert-butyl trimethylhexanoate.

The functionalized grafting monomer B can be unsaturated organic acid compounds such as maleic anhydride and acrylic acid.

In order to achieve the above object, the present invention adopts following technical scheme: a kind of preparation method of polypropylene graft with lower degree of degradation mainly comprises the following steps:

(1) The preparation process of PP-A is as follows:

1) Weigh 100 parts by weight of polypropylene powder without antioxidants, acid scavengers and other additives, 0.5-5 parts by weight of monomer A, 0-0.5 parts by weight of peroxide initiator, and 0-0.5 parts by weight of peroxide initiator When 0 parts by weight, it means that the reaction between polypropylene and monomer A is carried out under thermal initiation;

2) Transfer the above-mentioned raw materials to a high-speed mixer, and under stirring conditions, spray the monomer A and the peroxide initiator evenly on the surface of the polypropylene powder, and continue mixing for 1.0~10.0 min at a stirring speed of 300~ 1000 r/min;

3) Put the obtained mixture into the twin-screw extruder for melt grafting reaction, set the temperature of the main feeding port of the extruder to 130°C-155°C, and control the temperature of the rest of the barrel within 160-180°C. The rotation speed is 50~400 r/min, and then the extrudate is water-cooled, pelletized, and dried to obtain a PP-A product with a low degree of degradation;

(2) The preparation process of PP-A-B is as follows:

1) Dissolve 10 parts by weight of PP-A in 100 parts by weight of chlorobenzene to form a uniform dispersion at a temperature of 25-80°C;

2) Add 0.1-0.5 parts by weight of monomer B and 0.05-0.5 parts by weight of peroxide initiator to the above dispersion liquid, stir well and keep at 60-90°C for 2-10 hours;

3) After the reaction is over, add a large amount of acetone to the reaction system to precipitate the reaction product PP-A-B, and use acetone to wash it for no less than 3 times, and then dry it by blasting at 40°C and vacuum drying at 50°C After 2-10 hours, the PP-A-B product is obtained. The obtained PP-A-B product was subjected to a melt flow rate test, and the grafting rate was determined by acid-base titration.

Significant advantage of the present invention is:

The invention provides a method for effectively suppressing severe degradation of polypropylene in graft modification, and obtains a polypropylene resin graft copolymer with a lower degree of degradation. In the traditional method, the auxiliary grafting monomers such as styrene are generally directly involved in the grafting reaction between polypropylene and maleic anhydride and other monomers, because the auxiliary grafting monomers and maleic anhydride are easily reacted to form alternating copolymerization It will greatly reduce the concentration of grafting auxiliary monomers in the melt system, and reduce the stabilizing effect of auxiliary grafting monomers on polypropylene. In the first step of the present invention, functionalized grafting monomers are not involved, and only auxiliary grafting monomer A is used to stabilize polypropylene free radicals. At the same time, alkylphenyl groups are introduced into the main chain of polypropylene, which avoids the large-scale degradation of polypropylene. degradation. In the second step of the present invention, the reaction conditions are relatively mild, which can realize the grafting of the functionalized grafting monomer B while avoiding the breakage of the carbon-carbon bond in the main chain of polypropylene, and finally obtain a polypropylene graft with a lower degree of degradation. branches.

Detailed ways

In order to further disclose rather than limit the present invention, the present invention will be further described in detail below in conjunction with examples.

Example 1

A preparation method of a polypropylene graft with a lower degree of degradation, comprising the following steps:

(1) The preparation process of PP-A is as follows:

1) Weigh 100 parts by weight of polypropylene powder without additives such as antioxidants and acid scavenger (melt flow rate is 12-14 g/10min), 2 parts by weight of 4-methylstyrene, 2, 0.2 parts by weight of 5-dimethyl-2,5-bis(tert-butylperoxy)hexane;

2) Transfer the above raw materials to a high-speed mixer, and mix 4-methylstyrene and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane separately under stirring conditions Spray on the surface of polypropylene powder, continue mixing for 10.0 min, stirring speed 400 rpm;

3) Put the obtained mixture into a twin-screw extruder for melt grafting reaction, set the temperature of the barrel at the main feeding port of the extruder to 130°C, control the temperature of the die at 170°C, and control the temperature of the rest of the barrel at 170°C. The output speed is 300 r/min. Then the extrudate is water-cooled, pelletized and dried to obtain a PP-A product with a low degree of degradation.

(2) The preparation process of PP-A-B is as follows:

1) Dissolve 10 parts by weight of PP-A in 100 parts by weight of chlorobenzene to form a uniformly dispersed emulsion at a temperature of 80°C;

2) Add 0.5 parts by weight of maleic anhydride and 0.2 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane to the above emulsion, stir well and keep at 80°C for 10 Hour;

3) After the reaction is over, add 100 parts by weight of acetone to the reaction system to precipitate the reaction product PP-A-B, wash it with acetone for 4 times, and then dry it by blowing air at 40°C and vacuum drying at 50°C for 8 hours each. The PP-A-B product was obtained, and the test results related to the product are shown in Table 1.

Example 2

Replace 4-methylstyrene in Example 1 with 3,5-dimethylstyrene. Other experimental conditions are the same as in Example 1, and the product-related test results are shown in Table 1 for details.

Example 3

Change the amount of 2,5-dimethyl-2,5-bis(tert-butyl peroxy)hexane into 0 parts in Example 1, that is, do not use peroxide initiator, only carry out 4 under thermal initiation -Grafting reaction of methyl styrene; the barrel temperature of the main feeding port of the extruder is set at 130°C, the die head temperature is set at 170°C, and the temperature of the remaining barrels is controlled at 200°C. Other experimental conditions are the same as in Example 1, and the product-related test results are shown in Table 1 for details.

Example 4

In the preparation process of PP-A in Example 3, 4-methylstyrene was replaced by 3,5-dimethylstyrene. Other experimental conditions are the same as in Example 3, and the product-related test results are shown in Table 1 for details.

Comparative example 1

1) Weigh 100 parts by weight of polypropylene powder without antioxidant, 2 parts by weight of 4-methylstyrene, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane 0.2 parts by weight, 5 parts by weight of maleic anhydride powder;

2) Transfer the above mixture to a high-speed mixer, and mix 4-methylstyrene, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, horse The toric anhydride powder is uniformly dispersed in the polypropylene powder, and the mixing time is continued for 10.0 min, and the stirring speed is 400 r/min;

3) Put the obtained mixture into a twin-screw extruder for melt grafting reaction, set the temperature of the barrel at the main feeding port of the extruder to 130°C, control the temperature of the die at 170°C, and control the temperature of the rest of the barrel at 170°C. The output speed is 300 r/min. Subsequently, the extruded product is water-cooled, pelletized and dried to obtain a polypropylene graft.

Comparative example 2

In Comparative Example 1, set the barrel temperature of the main feeding port of the extruder at 130°C, the temperature of the die head at 170°C, and the temperature of the rest of the barrel at 190°C. Other experimental conditions are the same as those of Comparative Example 1, and the product-related test results See Table 1 for details.

Comparative example 3

In Comparative Example 2, 4-methylstyrene was replaced by styrene, and the other experimental conditions were the same as in Comparative Example 2. The test results related to the product are shown in Table 1.

Comparative example 4

In Example 1, 4-methylstyrene was replaced by styrene, other experimental conditions were the same as in Example 1, and the product-related test results are shown in Table 1.

Table 1. Summary of product performance index test results

The polypropylene graft obtained by the traditional melt graft modification method (Comparative Example 1-3) has an MFR value as high as 120-153g/10min, which is far greater than the starting material polypropylene, indicating that the traditional melt graft method is used , under the similar dosage of auxiliary grafting aids, the inhibitory effect of auxiliary grafting aids on polypropylene degradation is very limited. The polypropylene graft copolymer that obtains by embodiment 1-4, its MFR value is in the range of 15-17 g/10min, very close to the 12-14g/10min of starting material polypropylene powder, illustrates that the polypropylene graft copolymer provided by the present invention Propylene graft copolymers degrade less and have higher relative molecular weights. By comparing Examples 1-4 and Comparative Example 4, it can be obtained that in the process of using the two-step method to prepare the polypropylene compatibilizer, when using the specific monomer A of the present invention, the grafting rate is generally above 1.5%, which is much higher than that using 0.31% when styrene, it can be seen that under relatively mild reaction conditions, the use of specific monomer A can significantly improve the grafting rate of functionalized monomer maleic anhydride.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (4)

1. a preparation method of polypropylene graft, is characterized in that, specifically comprises the following steps: (1) The preparation process of PP-A is as follows: 1) Weigh 100 parts by weight of polypropylene powder, 0.5~5 parts by weight of monomer A, 0~0.5 parts by weight of peroxide initiator, and 0 parts by weight of peroxide initiator means that polypropylene is processed under thermal initiation. Reaction with monomer A; 2) Transfer the above-mentioned polypropylene powder to a high-speed mixer, and under stirring conditions, spray the monomer A and the peroxide initiator evenly on the surface of the polypropylene powder, continue mixing for 1.0~10.0 min, and stir Speed 300~1000 r/min; 3) Put the obtained mixture into the twin-screw extruder for melt grafting reaction, set the temperature of the main feeding port of the extruder to 130°C-155°C, and control the temperature of the rest of the barrel within 160-180°C. The rotation speed is 50~400 r/min, and then the extrudate is water-cooled, pelletized, and dried to obtain the PP-A product; (2) The preparation process of PP-A-B is as follows: 1) Dissolve 10 parts by weight of PP-A in 100 parts by weight of chlorobenzene to form a uniform dispersion at a temperature of 25-80°C; 2) Add 0.1-0.5 parts by weight of monomer B and 0.05-0.5 parts by weight of peroxide initiator to the above dispersion, stir well and keep at 60-90°C for 2-10 hours; 3) After the reaction is over, add a large amount of acetone to the reaction system to precipitate the reaction product PP-A-B, and use acetone to wash it for no less than 3 times, and then dry it by blasting at 40°C and vacuum drying at 50°C Each 2-10h, get PP-A-B product; Monomer A is 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3,5- One of dimethyl styrene. 2. preparation method according to claim 1 is characterized in that, peroxide initiator is benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert One or more of butyl peroxy) hexane, tert-butyl peroxy-3,5,5-trimethylhexanoate. 3. preparation method according to claim 1 is characterized in that, monomer B is maleic anhydride or acrylic acid. 4. the polypropylene graft that the arbitrary described preparation method of claim 1-3 makes.