CN114195959B

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

Info

Publication number: CN114195959B
Application number: CN202111584364.5A
Authority: CN
Inventors: 孙杰; 苏万福; 徐晓龙; 李禹善; 于莎; 武大庆; 徐人威
Original assignee: Sinochem Quanzhou Petrochemical Co Ltd; Sinochem Quanzhou Energy Technology Co Ltd
Current assignee: Sinochem Quanzhou Petrochemical Co Ltd; Sinochem Quanzhou Energy Technology Co Ltd
Priority date: 2021-12-23
Filing date: 2021-12-23
Publication date: 2023-06-30
Anticipated expiration: 2041-12-23
Also published as: CN114195959A

Abstract

The invention discloses a polypropylene graft with low degradation degree and a preparation method thereof, wherein the polypropylene is easily broken by carbon-carbon bond to cause serious degradation of polypropylene under the action of an initiator in the polypropylene melt grafting process. In order to inhibit the degradation of polypropylene, one or more grafting aids are generally added in the melt grafting modification process of polypropylene in the prior invention patent, the usage amount of the aids is high, and the difficult problem of polypropylene degradation cannot be well solved. Aiming at the defects of the prior art, the invention provides a novel polypropylene grafting modification method. The method is characterized in that an active group which is easier to carry out grafting reaction with functional grafting monomers such as maleic anhydride and the like than a polypropylene free radical is firstly introduced into a polypropylene main chain. Then, based on the introduced active groups, the modified polypropylene is subjected to grafting reaction with the functionalized grafting monomer under milder conditions, so that the degradation degree of the polypropylene in the grafting modification process can be greatly inhibited, and the polypropylene graft with higher molecular weight and higher grafting rate is obtained.

Description

Polypropylene graft with low degradation degree and preparation method thereof

Technical Field

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

Background

As a general-purpose polymer material, polypropylene has been widely used in many fields of people's life. Because the polypropylene has relatively low mechanical properties, the polypropylene can be used as engineering material only by being prepared into a composite material together with organic or inorganic fillers such as nylon, glass fiber and the like in a blending mode. Because polypropylene is a nonpolar polymer material, when polypropylene is blended with fillers such as nylon, glass fiber and the like, the polypropylene and the fillers are difficult to be compatible on microscopic or macroscopic scale, so that the problems of local cracking, uneven fillers and even local falling off of the composite material in the use process are caused, and the industrialized application of the polypropylene composite material is severely restricted.

The current industrial solution is to introduce polar monomers into the polypropylene main chain by copolymerization of propylene and polar monomers or subsequent graft modification of polypropylene, so as to improve the compatibility between polypropylene and polar filler. The subsequent grafting modification method of the polypropylene product has the advantages of low cost, good effect and the like. The grafting monomers generally used are polar monomers such as maleic anhydride or acrylic acid. The method for functionally modifying the polypropylene grafted polar monomer comprises a solution method, a melting method, a solid phase method, a radiation method and the like, wherein the melting method is convenient to operate and has been widely applied to industry.

In the melt grafting process of polypropylene, among all hydrogen atoms on polypropylene, the hydrogen atom on tertiary carbon is most active and is also most easily dissociated by oxygen-containing free radical attack after the decomposition of an initiator. Under general conditions, tertiary hydrogen on a polypropylene main chain is activated and stripped to easily break carbon-carbon bonds, so that the polypropylene is degraded, and the mechanical property of the polypropylene is greatly reduced. In addition, since maleic anhydride has low reactivity and is easily self-polymerized during the grafting reaction, it is difficult to introduce maleic anhydride molecules into polypropylene molecular chains, resulting in a generally low grafting ratio of maleic anhydride. The usual solutions are to increase the initiator amount, to increase the concentration of maleic anhydride and to use auxiliary grafting monomers. The higher active free radical concentration can be obtained by increasing the amount of the initiator, more activated sites are provided for the grafting reaction, but the degradation degree of the polypropylene is aggravated by the large amount of the initiator, so that the mechanical property of the polypropylene is poor. Increasing the amount of maleic anhydride results in an increase in unreacted maleic anhydride, and more acidic residues greatly increase the odor of the polypropylene grafted product. The auxiliary grafting monomer is small organic molecule containing at least one carbon-carbon double bond, such as acrylic acid, acrylic ester, beta-pinene, styrene, divinylbenzene, octene, decene and the like, and can be used independently or in combination. The auxiliary grafting monomer can reduce the degradation of polypropylene to a certain extent and can well improve the grafting rate of maleic anhydride. On one hand, the auxiliary monomer can help to stabilize polypropylene macromolecular free radicals and reduce the breakage of carbon-carbon single bonds; on the other hand, the auxiliary grafting monomer can form a copolymer with unsaturated functional grafting monomers such as maleic anhydride, and a plurality of maleic anhydride molecules can be introduced into one grafting site on the polypropylene main chain, so that the problem of low grafting rate is solved.

The Chinese patent CN 104804143A introduces styrene auxiliary monomer in the polypropylene melt grafting process, and specifically comprises the steps of mixing an initiator and styrene to prepare a styrene solution, mixing polypropylene and maleic anhydride, adding the mixture into a double-screw extruder or two double-screw extruders connected in series, adding the mixed solution of the initiator and the styrene into different barrel sections of the extruder after melting, and carrying out melt grafting reaction. When the styrene content is 7.5%, the melt flow rate MFR of the polypropylene is reduced from 160g/10min to 140g/10min, and the molecular weight of the obtained functionalized polypropylene and the molecular weight of the raw material polypropylene are not obviously reduced.

In addition to styrene as a first auxiliary monomer, the Chinese patent CN 101519477A and the Chinese patent CN 101724128A also use unsaturated molecules containing two or more carbon-carbon double bonds as a second auxiliary monomer during the melt grafting modification of polypropylene, so as to improve the grafting efficiency of macromolecular polypropylene free radicals and obtain polypropylene grafts with higher molecular weight. Wherein the amount of maleic anhydride is 2% -5%, the amount of the first auxiliary monomer is about 3% -7%, the ratio of the first monomer to the second monomer is about 1:4 to 7:13, and when the amount of the two auxiliary monomers is generally not less than 5%, the polypropylene can be maintained to have higher molecular weight, namely lower MFR value after the grafting reaction. Chinese patent CN 109467644a first treated a mixture of polypropylene, initiator and maleic anhydride with styrene and then the swollen system was subjected to grafting reaction. The usage amount of the styrene in the invention is 5% -25% relative to the polypropylene. The reaction of polypropylene grafting maleic anhydride is carried out in a reaction kettle in Chinese patent CN 106117445A, and styrene is used as an auxiliary monomer in the process, but nitrogen protection is needed in the invention, vacuum impurity removal is needed for 30-120 min after the grafting reaction, and the polypropylene grafting maleic anhydride is taken out for granulation molding after the impurity removal, so that the process is complex and the production cost is high.

Disclosure of Invention

In order to inhibit the polypropylene main chain from breaking in the polypropylene melt grafting process, the prior invention patent generally needs to use higher auxiliary agent dosage, and can not well solve the problem of polypropylene degradation. Aiming at the defects of the prior art, the invention aims to provide a novel polypropylene grafting modification method. The method is characterized in that an active site which is easier to carry out grafting reaction with a functional grafting monomer than a polypropylene free radical is firstly introduced into a polypropylene main chain, and then the grafting reaction is selectively carried out with maleic anhydride under a milder condition based on the introduced active site, so that the degradation of polypropylene in the grafting modification process can be greatly inhibited, and a polypropylene graft with higher molecular weight and higher grafting rate is obtained.

Therefore, the invention aims to provide a polypropylene graft with low degradation degree and a preparation method thereof. The modification of the functional grafting monomer to the polypropylene molecular chain is realized through two steps of reactions. The first step is to introduce high active site into polypropylene main chain, namely to graft polypropylene with a monomer A with active group under the action of thermal initiation or initiator to obtain PP-A; and the second step is to carry out grafting reaction with the functionalized grafting monomer B under milder reaction conditions based on the PP-A to obtain the target product PP-A-B.

The polypropylene graft refers to a graft copolymer formed by introducing a functional grafting monomer on a macromolecular chain of polypropylene resin. One of the characteristics of the invention is that the functionalized grafting monomer is grafted on the polypropylene molecular chain efficiently through two-step reaction. Another feature of the present invention is that the resulting polypropylene grafts are degraded to a lesser extent than the starting polypropylene material.

The polypropylene raw material used in the invention is polypropylene powder which does not contain additives such as polypropylene antioxidant, deacidification agent and the like before pelleting in a polypropylene production device, and can be homo-polymerization polypropylene powder produced under the Unipol gas-phase fluidized bed process condition, such as product marks such as wiredrawing materials, injection molding materials and the like. The invention introduces high active site on polypropylene main chain, namely, under the action of thermal initiation or peroxide initiator, polypropylene and a monomer A with active group are grafted, on one hand, degradation of polypropylene is obviously inhibited, and meanwhile, the active site is grafted on the polypropylene main chain, and the product is named PP-A. The monomer A is a styrene derivative containing one or more alkyl substituent groups, wherein the styrene part has the function similar to a styrene molecule, can play a role in stabilizing polypropylene free radicals and inhibits the degradation of a polypropylene main chain; the hydrogen atoms adjacent to the benzene ring in the alkyl branched chain on the benzene ring are more active under the action of the benzene ring, and are easy to be activated by the initiator. The monomer A may be a styrene derivative compound containing a single methyl group or other alkyl substituent groups having 2 to 6 carbon atoms, such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 5-methylstyrene, 6-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 5-ethylstyrene, 6-ethylstyrene, or a series of derivative compounds in which a hydrogen atom on the benzene ring of styrene is substituted with the above-mentioned plurality of alkyl radicals at the same time or in part. The active site refers to an alkyl substituent group containing 1-6 carbon atoms and connected with a benzene ring, particularly refers to a position directly connected with the benzene ring in the alkyl free radical, and a hydrogen atom on the position is more easily activated to generate a corresponding free radical under the influence of the benzene ring, so that further grafting reaction is carried out on the functional grafting monomer B such as maleic anhydride, and the product is named as PP-A-B. In addition, in PP-A produced after the reaction of the monomer A and the polypropylene, alkyl free radicals on benzene rings protrude outside the main chain and are difficult to participate in crystallization of the polypropylene, and are more easily activated by initiator free radicals in steric hindrance than tertiary hydrogen on the polypropylene.

In the reaction of the PP-A containing an active site with the functionalized grafting monomer B, for inhibiting the degradation of the polypropylene, milder reaction conditions, such as lower reaction temperatures, are preferred, generally below 130 ℃, preferably 70-110 ℃, more preferably 70-90 ℃. Under the temperature condition, compared with the hydrogen atom on the polypropylene main chain, the alkyl free radical connected with the benzene ring in the monomer A grafted on the polypropylene main chain can be activated by the initiator better, then reacts with the functionalized grafting monomer B, and grafts the monomer B on the PP-A molecular chain, thereby effectively reducing the polypropylene degradation reaction caused by the rupture of carbon-carbon bonds due to the activation of tertiary hydrogen, and finally obtaining the functionalized polypropylene PP-A-B with higher molecular weight and higher grafting rate.

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

The functional grafting monomer B can be unsaturated organic acid compounds such as maleic anhydride, acrylic acid and the like.

In order to achieve the above purpose, the invention adopts the following technical scheme: the preparation method of the polypropylene graft with low degradation degree mainly comprises the following steps:

the preparation process of the PP-A is as follows:

1) Weighing 100 parts by weight of polypropylene powder without additives such as an antioxidant, an acid scavenger and the like, 0.5-5 parts by weight of monomer A, 0-0.5 part by weight of peroxide initiator, wherein 0 part by weight of peroxide initiator indicates that the reaction between polypropylene and monomer A is carried out under the action of thermal initiation;

2) Transferring the raw materials into a high-speed mixer, respectively and uniformly spraying a monomer A and a peroxide initiator on the surface of polypropylene powder under the stirring condition, and continuously mixing for 1.0-10.0 min at the stirring speed of 300-1000 r/min;

3) Adding the obtained mixture into a double-screw extruder for melt grafting reaction, setting the barrel temperature of a main feeding port of the extruder to be 130-155 ℃, controlling the temperature of the other barrels to be within 160-180 ℃ and the rotating speed of the extruder to be 50-400 r/min, and then carrying out water cooling, granulating and drying on the extrudate to obtain a PP-A product with very low degradation degree;

the preparation process of the PP-A-B is as follows:

1) 10 parts by weight of PP-A is dissolved in 100 parts by weight of chlorobenzene, and uniform dispersion is formed at the temperature of 25-80 ℃;

2) Adding 0.1-0.5 weight part of monomer B and 0.05-0.5 weight part of peroxide initiator into the dispersion liquid, uniformly stirring, and keeping at 60-90 ℃ for 2-10 hours;

3) After the reaction is finished, adding a large amount of acetone into the reaction system to precipitate and separate out a reaction product PP-A-B, using the acetone to wash for a plurality of times, wherein the washing times are not less than 3 times, and then carrying out forced air drying at 40 ℃ and vacuum drying at 50 ℃ for 2-10 hours to obtain the PP-A-B product. The PP-A-B product obtained was subjected to a melt flow rate test and the grafting ratio was determined by acid-base titration.

The invention has the remarkable advantages that:

the invention provides a method for effectively inhibiting the polypropylene from being easily severely degraded in the graft modification process, and a polypropylene resin graft copolymer with low degradation degree is obtained. In the traditional method, auxiliary grafting monomers such as styrene and the like are generally directly involved in the grafting reaction between monomers such as polypropylene and maleic anhydride, and because the auxiliary grafting monomers and the maleic anhydride are easy to react to generate an alternating copolymer, the concentration of the grafting auxiliary monomers in a molten system can be greatly reduced, and the stability of the auxiliary grafting monomers on the polypropylene is reduced. In the first step of the invention, no functional grafting monomer is involved, only the auxiliary grafting monomer A is used for stabilizing the polypropylene free radical, and simultaneously, the alkyl phenyl group is introduced into the polypropylene main chain, thereby avoiding the great degradation of polypropylene. The reaction condition in the second step of the invention is mild, not only can the grafting of the functional grafting monomer B be realized, but also the breakage of carbon-carbon bonds of the main chain of the polypropylene can be avoided, and finally the polypropylene graft with lower degradation degree can be obtained.

Detailed Description

The invention is further described in detail below with reference to examples for the purpose of further disclosure, but not limitation.

Example 1

A method for preparing polypropylene grafts with low degradation degree, comprising the following steps:

the preparation process of the PP-A is as follows:

1) Weighing 100 parts by weight of polypropylene powder without additives such as an antioxidant, an acid scavenger and the like (with a melt flow rate of 12-14 g/10 min), 2 parts by weight of 4-methylstyrene and 0.2 part by weight of 2, 5-dimethyl-2, 5-bis (tert-butyl peroxy) hexane;

2) Transferring the raw materials into a high-speed mixer, respectively and uniformly spraying 4-methyl styrene and 2, 5-dimethyl-2, 5-bis (tert-butyl peroxy) hexane on the surface of polypropylene powder under the stirring condition, and continuously mixing for 10.0 min at the stirring speed of 400 rpm;

3) And adding the obtained mixture into a double-screw extruder to perform melt grafting reaction, wherein the barrel temperature of a main feeding port of the extruder is 130 ℃, the die head temperature is controlled to 170 ℃, the temperature of the other barrels is controlled to 170 ℃, and the rotating speed of the extruder is 300 r/min. And then carrying out water cooling, granulating and drying on the extrudate to obtain the PP-A product with low degradation degree.

The preparation process of the PP-A-B is as follows:

1) 10 parts by weight of PP-A is dissolved in 100 parts by weight of chlorobenzene, and uniformly dispersed emulsion is formed at 80 ℃;

2) Adding 0.5 weight part of maleic anhydride and 0.2 weight part of 2, 5-dimethyl-2, 5-bis (tert-butyl peroxy) hexane into the emulsion, uniformly stirring, and keeping at 80 ℃ for 10 hours;

3) After the reaction is finished, 100 parts by weight of acetone is added into the reaction system to precipitate and separate out a reaction product PP-A-B, the acetone is used for washing for 4 times, and then the PP-A-B product is obtained after drying by blowing at 40 ℃ and vacuum drying at 50 ℃ for 8 hours, and the relevant test results of the product are shown in Table 1.

Example 2

The 4-methylstyrene of example 1 is replaced by 3, 5-dimethylstyrene. Other experimental conditions were the same as in example 1, and the results of the product-related test are shown in Table 1.

Example 3

The grafting reaction of 4-methylstyrene was carried out under the action of thermal initiation without using peroxide initiator by changing the amount of 2, 5-dimethyl-2, 5-bis (t-butylperoxy) hexane used in example 1 to 0 parts; the barrel temperature of the main feeding port of the extruder is 130 ℃, the die head temperature is 170 ℃, and the rest barrel temperatures are controlled at 200 ℃. Other experimental conditions were the same as in example 1, and the results of the product-related test are shown in Table 1.

Example 4

The 4-methylstyrene of example 3 in the preparation of PP-A was replaced by 3, 5-dimethylstyrene. Other experimental conditions were the same as in example 3, and the results of the product-related test are shown in Table 1.

Comparative example 1

1) Weighing 100 parts by weight of polypropylene powder without an antioxidant, 2 parts by weight of 4-methylstyrene, 0.2 part by weight of 2, 5-dimethyl-2, 5-bis (tert-butyl peroxy) hexane and 5 parts by weight of maleic anhydride powder;

2) Transferring the mixture into a high-speed mixer, uniformly dispersing 4-methylstyrene, 2, 5-dimethyl-2, 5-bis (tert-butyl peroxy) hexane and maleic anhydride powder into polypropylene powder under stirring, and continuing mixing for 10.0 min at a stirring speed of 400 r/min;

3) And adding the obtained mixture into a double-screw extruder to perform melt grafting reaction, wherein the barrel temperature of a main feeding port of the extruder is 130 ℃, the die head temperature is controlled to 170 ℃, the temperature of the other barrels is controlled to 170 ℃, and the rotating speed of the extruder is 300 r/min. And then carrying out water cooling, granulating and drying on the extrudate to obtain the polypropylene graft.

Comparative example 2

The main feeding port barrel temperature of the extruder in comparative example 1 was set at 130 ℃, the die temperature was controlled at 170 ℃, the remaining barrel temperatures were controlled at 190 ℃, other experimental conditions were the same as those in comparative example 1, and the results of the product-related tests are shown in Table 1.

Comparative example 3

The 4-methyl styrene in comparative example 2 was replaced with styrene, and other experimental conditions were the same as those of comparative example 2, and the results of the product-related test are shown in Table 1.

Comparative example 4

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

TABLE 1 summarizing the results of product Performance index tests

The polypropylene graft prepared by the traditional melt grafting modification method (comparative examples 1-3) has an MFR value as high as 120-153 g/10min, which is far greater than that of the starting material polypropylene, indicating that the auxiliary grafting aid has limited inhibition effect on polypropylene degradation under the condition of similar auxiliary grafting aid dosage by using the traditional melt grafting method. The polypropylene graft copolymers obtained in examples 1-4 have MFR values in the range of 15-17 g/10min, very close to 12-14 g/10min of the starting polypropylene powder, indicating that the polypropylene graft copolymers provided by the invention have a lower degree of degradation and a higher relative molecular weight. As can be seen from the comparison of examples 1-4 and comparative example 4, the grafting ratio is generally over 1.5% when using the specific monomer a of the present invention, which is much greater than 0.31% when using styrene, in the preparation of the polypropylene compatibilizer using the two-step process, and thus it is seen that the grafting ratio of the functionalized monomer maleic anhydride can be significantly improved by using the specific monomer a under relatively mild reaction conditions.

The foregoing description is only of the preferred embodiments of the invention, and all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. The preparation method of the polypropylene graft is characterized by comprising the following steps:

the preparation process of the PP-A is as follows:

1) 100 parts by weight of polypropylene powder, 0.5-5 parts by weight of monomer A and 0-0.5 part by weight of peroxide initiator, wherein 0 part by weight of peroxide initiator indicates that the reaction between polypropylene and monomer A is carried out under the action of thermal initiation;

2) Transferring the polypropylene powder into a high-speed mixer, respectively and uniformly spraying a monomer A and a peroxide initiator on the surface of the polypropylene powder under the stirring condition, and continuously mixing for 1.0-10.0 min at the stirring speed of 300-1000 r/min;

3) Adding the obtained mixture into a double-screw extruder for melt grafting reaction, setting the barrel temperature of a main feeding port of the extruder to be 130-155 ℃, controlling the temperature of the other barrels to be within 160-180 ℃ and the rotating speed of the extruder to be 50-400 r/min, and then carrying out water cooling, granulating and drying on the extrudate to obtain a PP-A product;

the preparation process of the PP-A-B is as follows:

2) Adding 0.1-0.5 weight part of monomer B and 0.05-0.5 weight part of peroxide initiator into the dispersion liquid, uniformly stirring, and keeping at 60-90 ℃ for 2-10h;

3) After the reaction is finished, adding a large amount of acetone into a reaction system to precipitate and separate out a reaction product PP-A-B, flushing the reaction product PP-A-B for a plurality of times by using the acetone, wherein the flushing times are not less than 3 times, and then carrying out forced air drying at 40 ℃ and vacuum drying at 50 ℃ for 2-10 hours to obtain PP-A-B products;

the monomer A is one of 2-methyl styrene, 3-methyl styrene, 4-methyl styrene, 2-ethyl styrene, 3-ethyl styrene, 4-ethyl styrene and 3, 5-dimethyl styrene.

2. The preparation method according to claim 1, wherein the peroxide initiator is one or more of benzoyl peroxide, dicumyl peroxide, 2, 5-dimethyl-2, 5-bis (t-butylperoxy) hexane, and t-butyl peroxy-3, 5-trimethylhexanoate.

3. The process according to claim 1, wherein monomer B is maleic anhydride or acrylic acid.

4. A polypropylene graft prepared by the process of any one of claims 1 to 3.