阅读说明：本技术 一种交联聚丙烯材料及其制备方法 (Cross-linked polypropylene material and preparation method thereof ) 是由 李勇进 何丽娜 吴桂英 蒋晓璐 傅华康 于 2021-06-30 设计创作，主要内容包括：本发明公开一种交联聚丙烯材料及其制备方法。由引发剂、茶多酚、聚丙烯、甲基丙烯酸缩水甘油酯(GMA)、苯乙烯(St)熔融共混制备而成。本发明采用化学自由基引发剂,引发聚合物大分子间的反应,通过分子链间的键合,形成交联网状结构,制备交联聚丙烯,得到融体强度较高的聚丙烯材料。本发明材料可作为发泡材料,得到泡孔尺寸小,孔密度大的聚丙烯发泡材料。(The invention discloses a cross-linked polypropylene material and a preparation method thereof. Is prepared by melting and blending initiator, tea polyphenol, polypropylene, Glycidyl Methacrylate (GMA) and styrene (St). The invention adopts a chemical free radical initiator to initiate the reaction among polymer macromolecules, and a cross-linked network structure is formed through the bonding among molecular chains to prepare the cross-linked polypropylene, so that the polypropylene material with higher melt strength is obtained. The material can be used as a foaming material to obtain a polypropylene foaming material with small cell size and high cell density.)

1. A cross-linked polypropylene material and a preparation method thereof are characterized by comprising the following steps:

step (1): vacuum drying polypropylene and tea polyphenol;

step (2): adding 0.01-5 parts by weight of initiator and 1-10 parts by weight of tea polyphenol to 100 parts by weight of polypropylene granules or powder, and uniformly mixing at normal temperature to obtain a mixture A;

and (3): uniformly mixing 0.01-15 parts by weight of Glycidyl Methacrylate (GMA) and 0.01-10 parts by weight of styrene (St) liquid to obtain a mixture B;

and (4): and adding the mixture A and the mixture B into a reaction device for melt blending to obtain the cross-linked polypropylene material.

2. The method according to claim 1, wherein the reaction equipment is an internal mixer, a single screw extruder or a double screw extruder, and the reaction temperature range is 160-230 ℃.

3. The method according to claim 2, characterized in that the rotor speed of the internal mixer is 50 to 150 rpm.

4. The method according to claim 2, wherein the screw rotation speed of the single-screw extruder and the screw rotation speed of the double-screw extruder are 30-600 rpm.

5. The method of claim 1, wherein the polypropylene is a homo-or co-polypropylene.

6. The method according to claim 1, wherein the initiator is a peroxide initiator, i.e. one or more of dicumyl peroxide (DCP), di-t-butylperoxyisopropyl benzene, t-butyl hydroperoxide, t-butyl benzoate peroxide, t-butyl dicarbonate peroxide, 2, 5-dimethyl-2, 5-bis (t-butylperoxy) hexane, 2, 5-dimethyl-2, 5-bis (t-butylperoxy) hexyne, and benzoyl peroxide.

7. A cross-linked polypropylene material produced by the method of any one of claims 1 to 6.

8. A polypropylene foam material, which is obtained by using the crosslinked polypropylene material of claim 7 through a supercritical carbon dioxide batch foaming method.

Technical Field

The invention belongs to the field of high polymer materials, and particularly relates to a preparation method of a cross-linked polypropylene material, wherein the cross-linking degree of the cross-linked polypropylene material is controllable.

Background

Polypropylene (PP) is one of 5 general plastics, has the characteristics of rich raw material sources, small density, low price, easy molding, excellent performance and the like, and is widely applied in the fields of automobile interior and exterior decoration, household appliances, packaging, building materials and the like. However, polypropylene has low melt strength and lacks strain hardening, which limits its application in foaming, extrusion molding, blow molding, and other fields. The low melt strength of polypropylene is mainly due to the fact that polypropylene is a semi-crystalline material, the softening point of the polypropylene is very close to the melting point, the temperature window of high melt strength between the softening point and the melting point is narrow, and the melt strength of polypropylene is rapidly reduced along with the temperature increase after the temperature exceeds the melting point. In addition, the polypropylene melt is substantially free of strain hardening phenomena due to the linear structure and narrow molecular weight distribution of the general purpose polypropylene. Therefore, general purpose polypropylene has limited applications in areas with melt strength requirements. In order to improve the melt strength of polypropylene, there are currently 4 methods, namely, radiation crosslinking, chemical crosslinking, PP blend modification, and PP/inorganic composite modification.

The PP blending modification is to blend and modify two or more polymer resin materials, can make up for the deficiency of single polymer performance, can also produce synergistic complementary effect, and prepare blending materials with excellent comprehensive performance. However, the compatibility of the blend determines the comprehensive performance of the mixed material, and if the two phases are completely incompatible, phase separation occurs, so that the interface bonding force is weak and the material performance is poor.

The modification of the PP/inorganic composite material is mainly to fill inorganic or organic fillers with lower price into polymers in the PP processing and forming process, but the comprehensive performance of the mixed material is also influenced by the good compatibility between the fillers and a matrix.

Radiation crosslinking is a modification method for crosslinking polymer macromolecules by energy supplied by high energy or radioactive isotopes (such as gamma rays, neutron rays and the like). The radiation crosslinking of PP is a very complex reaction, the crosslinking reaction and the cracking reaction of the main chain occur simultaneously and compete with each other, so the crosslinking efficiency is low, the radiation crosslinking process is complex and difficult to control, and the thickness of a PP sample is required during crosslinking, so the radiation crosslinking is not used in the field of polypropylene crosslinking modification at present.

The chemical crosslinking modification is mainly to modify linear or lightly branched polymers into three-dimensional network stereo structures by means of crosslinking, and the three-dimensional network stereo structures comprise organic peroxide crosslinking, silane water crosslinking and the like. There are two processes for silane crosslinking, one-step and two-step. The one-step method is that PP, silane coupling agent, initiator and catalyst are mixed and manufactured at one time, and the formed product is subjected to hydrolysis reaction for crosslinking; the two-step method is that silane is grafted to a PP molecular chain, the obtained grafted polymer can be stored in a dry environment, and is subjected to anhydrous mixed extrusion with a catalyst after being formed, and finally, the crosslinking reaction is carried out, so that the silane crosslinking preparation method is complex. After the initiator is added in the organic peroxide crosslinking, most of hydrogen-abstraction reaction of free radicals occurs on tertiary carbon atoms, and the generated tertiary free radicals are unstable and are easy to break at beta positions to generate beta cracking, so that macromolecular chains are degraded due to cracking and disproportionation, PP degradation and oxidation are caused, and the efficiency of the crosslinking reaction is influenced.

Aiming at the problems, a large number of experiments are carried out, reactive epoxy functional groups are introduced on polypropylene through grafting, tea polyphenol is introduced to serve as a crosslinking aid, and a crosslinking network is formed through the reaction of epoxy and phenolic hydroxyl at high temperature to prepare the crosslinked polypropylene. In order to improve the grafting rate of GMA and reduce the degradation problem of polypropylene in the grafting process, a second monomer styrene is added. The styrene can be grafted to the polypropylene tertiary carbon free radical chain segment more quickly, the formed polypropylene styrene free radical chain segment is more stable and cannot be broken, the degradation in the grafting process is inhibited, GMA is grafted to the polypropylene styrene free radical chain segment more easily, the grafting rate of GMA is improved, and the higher GMA grafting rate is more beneficial to the crosslinking of polypropylene. It is worth noting that grafting and crosslinking are performed simultaneously during the whole reaction process, but the GMA grafting speed is faster than the reaction speed of epoxy and phenolic hydroxyl groups to generate crosslinking of the whole system. The reaction activity of phenolic hydroxyl and epoxy of the tea polyphenol which is taken as a polyphenol substance is not very strong, and the tea polyphenol is selected as a crosslinking auxiliary agent, so that the crosslinking condition is met.

Disclosure of Invention

The invention aims to provide a preparation method of a cross-linked polypropylene material, which is simple and controllable in cross-linking degree, and particularly adopts a chemical free radical initiator to initiate the reaction among polymer macromolecules, and a cross-linked network structure is formed through the bonding among molecular chains to prepare the cross-linked polypropylene so as to obtain the polypropylene material with higher melt strength.

In order to achieve the purpose, the preparation method of the cross-linked polypropylene material comprises the following specific steps:

step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): directly adding 0.01-5 parts by weight of initiator and 1-10 parts by weight of tea polyphenol to 100 parts by weight of polypropylene granules or powder, and uniformly mixing at normal temperature to obtain a mixture A;

and (3): uniformly mixing 0.01-15 parts by weight of Glycidyl Methacrylate (GMA) and 0.01-10 parts by weight of styrene (St) liquid to obtain a mixture B;

and (4): adding the mixture A and the mixture B into a reaction device for melt blending to obtain a cross-linked polypropylene material;

the reaction equipment comprises an internal mixer, a single-screw extruder and a double-screw extruder, and the reaction temperature range is 160-230 ℃.

Preferably, the rotating speed of the rotor of the internal mixer is 50-150 rpm.

Preferably, the screw rotating speed of the single-screw extruder and the double-screw extruder is 30-600 rpm.

Preferably, the polypropylene is homo-polypropylene or co-polypropylene.

Preferably, the initiator is peroxide initiator, i.e. one or more of dicumyl peroxide (DCP), di-tert-butylperoxyisopropyl benzene, tert-butyl hydroperoxide, tert-butyl peroxybenzoate, tert-butyl peroxydicarbonate, 2, 5-dimethyl-2, 5-bis (tert-butylperoxy) hexane, 2, 5-dimethyl-2, 5-bis (tert-butylperoxy) hexyne and benzoyl peroxide.

Preferably, the tea polyphenol (C) is a polyhydroxy compound contained in tea leaves, and the main chemical component is a complex of catechins (flavanols), flavones and flavonols, anthocyanins, phenolic acids and depside acids, polymeric phenols, and the like. Wherein the catechin compounds are the main components of the tea polyphenol and account for 65 to 80 percent of the total weight of the tea polyphenol. The catechin compounds mainly comprise 4 substances of catechin (EC), gallocatechin (EGC), catechin gallate (ECG) and gallocatechin gallate (EGCG).

Another object of the present invention is to provide a crosslinked polypropylene material obtained by the above-mentioned preparation method.

The invention also aims to provide a polypropylene foaming material, which is obtained by adopting the crosslinked polypropylene material through a supercritical carbon dioxide intermittent foaming method.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the cross-linked polypropylene prepared by the invention has the advantages of simple preparation method and adjustable cross-linking degree;

(2) the invention applies the tea polyphenol to the cross-linked polypropylene system for the first time, is different from the application of the tea polyphenol in the fields of beverages, cosmetics, health care products and the like, expands the application range of the tea polyphenol and provides new possibility for the large-scale application of the tea polyphenol;

(3) the invention prepares the needed crosslinking polypropylene by melt blending of an internal mixer or an extruder, and the method has the possibility of industrial mass production.

(4) The material can be used as a foaming material to obtain a polypropylene foaming material with small cell size and high cell density.

Drawings

FIG. 1 is the storage modulus G' (ω) of pure polypropylene, comparative examples 1, 3 and the products of examples 1-3;

FIG. 2 is the loss tangent Tan δ (ω) of the pure polypropylene, the products of comparative examples 1, 3 and examples 1-3;

FIG. 3 is the complex viscosity | η | (ω) | of the pure polypropylene, the products of comparative examples 1, 3 and examples 1-3;

FIG. 4 is an SEM cross-sectional profile of a sample of expanded polypropylene: (A) comparative example 1, (B) example 1, (C) example 3.

Detailed Description

The present invention will be further illustrated with reference to examples.

A preparation method of a cross-linked polypropylene material comprises the following steps:

step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): directly adding 0.01-5 parts by weight of initiator and 1-10 parts by weight of tea polyphenol to 100 parts by weight of polypropylene granules or powder, and uniformly mixing at normal temperature to obtain a mixture A;

and (3): uniformly mixing 0.01-15 parts by weight of Glycidyl Methacrylate (GMA) and 0.01-10 parts by weight of styrene (St) liquid to obtain a mixture B;

and (4): adding the mixture A and the mixture B into a reaction device for melt blending to obtain a cross-linked polypropylene material;

the reaction equipment comprises an internal mixer, a single-screw extruder and a double-screw extruder, and the reaction temperature range is 160-230 ℃.

Preferably, the rotating speed of the rotor of the internal mixer is 50-150 rpm.

Preferably, the screw rotating speed of the single-screw extruder and the double-screw extruder is 30-600 rpm.

Preferably, the polypropylene is homo-polypropylene or co-polypropylene.

Preferably, the initiator is peroxide initiator, i.e. one or more of dicumyl peroxide (DCP), di-tert-butylperoxyisopropyl benzene, tert-butyl hydroperoxide, tert-butyl peroxybenzoate, tert-butyl peroxydicarbonate, 2, 5-dimethyl-2, 5-bis (tert-butylperoxy) hexane, 2, 5-dimethyl-2, 5-bis (tert-butylperoxy) hexyne and benzoyl peroxide.

Preferably, the tea polyphenol (C) is a polyhydroxy compound contained in tea leaves, and the main chemical component is a complex of catechins (flavanols), flavones and flavonols, anthocyanins, phenolic acids and depside acids, polymeric phenols, and the like. Wherein the catechin compounds are the main components of the tea polyphenol and account for 65 to 80 percent of the total weight of the tea polyphenol. The catechin compounds mainly comprise 4 substances of catechin (EC), gallocatechin (EGC), catechin gallate (ECG) and gallocatechin gallate (EGCG).

Melt index determination

The test is carried out on a high-iron melt index instrument according to the GB3682-83 standard: 230 ℃ and 2.16 kg.

Gel content determination

The gel content of the crosslinked polypropylene samples can be determined by soxhlet extraction experiments. The specific experimental conditions were as follows: solvent: o-xylene, temperature: extraction time at 190 ℃: and 72 h. After extraction, the sample is dried in a forced air oven at 100 ℃ for 12h to constant weight. Accurately weighing the mass of the crosslinked polypropylene sample before extraction and after extraction, and substituting the mass into the formula (1) for calculation. Three replicates were run for this experiment and the average was taken as the final gel content value for the sample.

In the formula (1), R_GelIs gel content, m₁And m₂The mass of the cross-linked polypropylene sample after extraction and before extraction are respectively.

Characterization of rheological behavior

The specific test conditions were as follows: the rheological properties of the samples were characterized by the SAOS test. The specific implementation conditions are as follows: frequency range: 0.01rad/s to 100rad/s, test amplitude: 5%, test temperature: at 200 ℃.

Preparation of polypropylene foaming material by supercritical carbon dioxide intermittent foaming method

Cutting the prepared polypropylene material into sample strips with the same size, placing the sample strips into a closed reaction kettle, introducing a small amount of carbon dioxide to exhaust air in the reaction kettle, and continuously introducing the carbon dioxide to enable the sample to be absorbed until the sample is saturated. In the reaction process, the saturation temperature is controlled to be 160 ℃, the saturation pressure is controlled to be 13.8MPa, and the saturation time is controlled to be 3 h. And then, quickly relieving the pressure, controlling the pressure relief time within 0.3s, and then placing the reaction kettle in an ice-water bath to shape the foam holes to obtain the corresponding foaming material.

Micro-morphology characterization of foamed polypropylene

The microscopic morphology of the cross section of the polypropylene material after foaming was characterized in detail by Scanning Electron Microscopy (SEM), wherein the test voltage was 3 kV. And quenching the sections of all samples to be tested in liquid nitrogen, and performing SEM test after gold spraying treatment.

The present invention will be described in detail with reference to examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited thereto. The polypropylene used in the examples below is either homopolypropylene or copolypropylene.

Comparative example 1: PP/DCP/GMA/St

Step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): PP/DCP was mixed in a weight ratio of 100/0.5 (wherein the polypropylene weighed 50g), stirred by hand to homogeneity, introduced into an internal mixer, followed by addition of 5phr of St in liquid form and 5phr of GMA in liquid form, and kneaded at 190 ℃ for 5min at 50 rpm.

And (3): discharging the mixture from the melt mixing equipment, and cooling to room temperature to obtain a grafting product.

Comparative example 2: PP/DCP/GMA/St/C, wherein C is 0.3 wt%

Step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): PP/DCP/C was mixed in a weight ratio of 100/0.5/0.3 (wherein polypropylene weighed 50g), stirred by hand to homogeneity, added to an internal mixer, followed by addition of 5phr of St in liquid form and 5phr of GMA in liquid form, and mixed at 190 ℃ for 5min at 50 rpm.

And (3): discharging the mixture from the melt mixing equipment, and cooling to room temperature to obtain a grafting product.

Comparative example 3: PP/DCP/GMA/St/C, wherein C is 0.5 wt%

Step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): PP/DCP/C was mixed in a weight ratio of 100/0.5/0.5 (wherein polypropylene weighed 50g), stirred by hand to homogeneity, added to an internal mixer, followed by addition of 5phr of St in liquid form and 5phr of GMA in liquid form, and mixed at 190 ℃ for 5min at 50 rpm.

And (3): discharging the mixture from the melt mixing equipment, and cooling to room temperature to obtain a grafting product.

Example 1: PP/DCP/GMA/St/C

Step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): PP/DCP/C was mixed in a weight ratio of 100/0.5/1 (wherein polypropylene weighed 50g) and stirred by hand to homogeneity, charged into an internal mixer, followed by addition of 2.5g of St in liquid form and 2.5g of GMA in liquid form, and kneaded at 190 ℃ for 5min at 50 rpm.

Example 2: PP/DCP/GMA/St/C

Step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): PP/DCP/C was mixed in a weight ratio of 100/0.5/2 (wherein polypropylene weighed 50g), stirred by hand to homogeneity, charged into an internal mixer, followed by addition of 2.5g of liquid St and 2.5g of liquid GMA, and kneaded at 190 ℃ at 50rpm for 5 min.

And (3): discharging the mixture from the melt mixing equipment, and cooling to room temperature to obtain a grafting product.

Example 3: PP/DCP/GMA/St/C

Step (1): vacuum drying polypropylene and tea polyphenol for 24-48 h at 80 ℃;

step (2): PP/DCP/C was mixed in a weight ratio of 100/0.5/3 (wherein polypropylene was weighed to 50g), stirred by hand to homogeneity, charged into an internal mixer, followed by addition of 2.5g of liquid St and 2.5g of liquid GMA, and kneaded at 190 ℃ at 50rpm for 5 min.

And (3): discharging the mixture from the melt mixing equipment, and cooling to room temperature to obtain a grafting product.

TABLE 1 melt index and gel content of crosslinked polypropylene systems

Melt index testing of comparative examples 1-3 and examples 1-3. The test results of the samples are shown in appendix Table 1. It can be seen that the addition of tea polyphenol decreases the melt index of the material, and as the addition amount of tea polyphenol increases, the melt index gradually decreases, and the melt strength and the melt index are in inverse proportion in value, that is, the lower the melt index, the higher the melt strength.

Gel content test of comparative examples 1-3 and examples 1-3. The test results of the samples are shown in appendix Table 1. It can be seen that the material generates gel after a certain amount of tea polyphenol is added, the gel content of the material is increased along with the increase of the addition amount of the tea polyphenol, the cross-linking degree of the material is improved, and the cross-linking structure is beneficial to improving the melt strength of the material.

Rheology tests of comparative examples 1-3 and examples 1-3. The test results of the samples are shown in the attached figures 1, 2 and 3. It can be seen that, as the addition amount of tea polyphenol increases, the storage modulus G' (ω) value gradually increases in fig. 1, which indicates that the elasticity of the material increases; meanwhile, the tea polyphenol has an end effect under the condition of high addition amount of tea polyphenol: g ' (omega) appears as a platform in the low frequency region, and shows the characteristic of ' solid-like '. tan δ (ω) has substantially the same tendency as the value of | η | (ω) | varies with ω: the tan delta (omega) value in fig. 2 decreases with increasing tea polyphenol addition, illustrating that the elastic contribution in the fluid increases significantly and the viscous contribution decreases gradually; in fig. 3, | η | (ω) | values are elevated in the low frequency region, indicating that intermolecular slip gradually decreases; the network of the material is gradually perfected along with the increase of the addition amount of the tea polyphenol, so that the molecular chain mobility is inhibited in a melt state.

The micro-topography of the sample after foaming is characterized by comparing example 1 with example 1 and example 3, and the test results of the sample are shown in the attached figure 4. It can be seen that the cells of examples 1 and 3 are more uniform than the cells of the foamed sample of comparative example 1. With the increase of the crosslinking degree of the foaming sample, the polypropylene foaming material with smaller cell size and higher cell density can be obtained.

The above embodiments are not intended to limit the present invention, and the present invention is not limited to the above embodiments, and all embodiments are within the scope of the present invention as long as the requirements of the present invention are met.