Preparation of high performance radiation cross-linking polypropylene

Preparation method of high-performance radiation cross-linked polypropylene

The invention relates to a method for producing polypropylene with a high degree of crosslinking, and more specifically, to a method for producing polypropylene with a high degree of crosslinking through radiation crosslinking.

Generally, the cross-linking methods of thermoplastic polymers can be divided into chemical methods and radiation methods. Radiation crosslinking has the characteristics of low crosslinking temperature, does not affect the crystallinity of the polymer, and energy saving. For the crosslinking of polymers with stricter quality requirements, the radiation method is better than the chemical method. At present, the radiation cross-linking method has been widely used in the production of cross-linked polyolefin products such as heat-resistant wires, heat-shrinkable films and pipes, and foam plastics. However, the radiation method has encountered great difficulties in the application of cross-linked polypropylene. This is mainly due to the special tertiary carbon molecular structure in the polypropylene molecular chain, which makes it not only difficult to cross-link, but also in radiation cross-linking. The process is always accompanied by degradation, so the cross-linked polypropylene often has poor performance. The Journal of Radiation Physical Chemistry published in the United Kingdom, Vol. 26, No. 3, pages 339-346, discloses a method of radiation cross-linking of polypropylene, which uses a lower radiation dose, and mainly investigates the content of acrylate groups. Functional monomers have an effect on the properties of radiation cross-linked polypropylene, but this method cannot effectively inhibit the degradation reaction during the cross-linking process, and the mechanical properties at room temperature are not significantly improved.

The purpose of the present invention is to provide an improved method for the production of high-crosslinking polypropylene by the radiation method, which is characterized in that a certain amount of nucleating agent is added during the production process of radiation cross-linked polypropylene to overcome the above-mentioned existing technology. During the radiation cross-linking process, polypropylene degradation and normal temperature mechanical properties are not significantly improved, and cross-linked polypropylene with high gel content and excellent mechanical properties and heat resistance is obtained.

The method for producing high crosslinking degree polypropylene of the present invention is: in the presence of a multifunctional monomer crosslinking accelerator and an antioxidant, the polypropylene material is irradiated with high energy rays to cause a crosslinking reaction to obtain high crosslinking High-degree polypropylene, the radiation absorbed dose is less than 10kGy, which is characterized in that a nucleating agent is added during the preparation process of radiation cross-linked polypropylene.

High-energy radiation polypropylene has cross-linking reaction and degradation reaction at the same time. The nucleating agent is added in the radiation cross-linking process to reduce the occurrence of degradation reaction and improve the mechanical properties at room temperature. This is the radiation of the present invention compared to the prior art. Improvements made by the cross-linking method. In the present invention, due to the addition of the nucleating agent, the crystallinity of the polypropylene material is improved, the size of the spherulites is reduced, and the rate of oxygen infiltration into the polypropylene material is slowed down. At this time, oxygen is too late to penetrate into the polypropylene material, causing the internal "anoxia" of the material, reducing the oxidative degradation of the polypropylene material, increasing the radiation stability of the polypropylene, and improving the mechanical properties and heat resistance of the polypropylene. performance.

The nucleating agent added in the method of the present invention can be selected from aluminum benzoate, sodium sorbate, dibenzylidene sorbitol, bis(2,4-di-tert-butylphenol) sodium methylene phosphate (Sodium Salt of MethyleneBis- (2,4-di-t-butylphenol) acid phosphate), sebacic acid, benzoic acid, adipic acid, terephthalic acid, or a mixture thereof. The added amount of the nucleating agent is 0.1-5 wt% of the weight of the polypropylene material, preferably 0.2-0.6 wt%.

The high-energy ray source in the method of the present invention is one of electron rays, gamma rays, and heavy ion beam rays, and it is more convenient to use gamma rays or electron rays. The absorbed dose of radiation during irradiation should generally be less than 10kGy, and it is best to control it within 0.5-2kGy. Controlling the radiation dose is more critical in the present invention. Only when a lower dose is irradiated, the radiation stability of polypropylene containing a nucleating agent can be improved.

Completing the present invention does not have any special requirements for the environment, and it can be carried out at any room temperature and in the air.

In the present invention, it is necessary to add a crosslinking accelerator containing a multifunctional monomer. The radiation crosslinking reaction itself is a non-chain reaction, and the addition of multifunctional monomers can convert this non-chain reaction into a chain reaction to finally form a network-like macromolecular structure. The number of multifunctional groups of the crosslinking accelerator monomer is preferably 2 or 3. It can be selected from tetramethylene diacrylate (TEGDM), trimethylol propyl trimethacrylate (TMPTM), and triacrylic acid. One of trimethylol propyl ester (TMPTA) or their mixture is added in an amount of 0.1-4% of the weight of the polypropylene material, preferably 0.5-2%.

Generally, antioxidants for polyolefin processing can be used in the radiation crosslinking process of the present invention, such as aromatic amines or phenols. Aromatic amines include phenyl-β-naphthylamine, N,N"-di-β-naphthyl-p-phenylenediamine, N,N"-diphenyl-p-phenylenediamine, etc.; phenol series include 4,4 -thiobis(6-tert-butyl-3-methylphenol), 2,6-di-tert-butyl-p-cresol, 2,2-methylenebis(4-methyl-6- Tert-butyl phenol) and so on.

The "polypropylene material" mentioned in the present invention is a material selected from the following groups: (1) propylene homopolymer; (2) propylene and selected from ethylene, C4-C10 ene-1, C4-C10 two A block copolymer or random copolymer formed by one of the olefins. Among them, C4-C10 ene-1 includes linear and branched C4-C10 ene-1, such as butene-1, isobutylene, pentene-1, 3-methylbutene-1, hexene-1, 3 , 4-Dimethylbutene-1, heptene-1, octene-1 and so on. C4~C10 dienes include 1,3-butadiene, 1,4-pentadiene, isoprene, 1,5-hexadiene, 2,3-dimethyl-1,3-hexyl Diene and so on.

(3) The mixture of polypropylene and polypropylene copolymer described in (1) and (2) above, or a mixture of polypropylene, polypropylene copolymer, polyethylene, and ethylene-propylene rubber.

Due to the addition of the nucleating agent in the preparation process of the radiation cross-linked polypropylene, the present invention has the following advantages: the cross-linked polypropylene after being irradiated with a lower radiation dose, the nucleating agent is added compared to the non-additive The cross-linking constant of the core agent is basically unchanged, while the degradation constant is reduced, from 1.45×10-4 to 1.12×10-4 (according to the measured gel content data, the Charlesby -Pinner equation is calculated), that is, the radiation stability of polypropylene has been improved.

The addition of the nucleating agent increases the gel content of the radiation cross-linked polypropylene. For example, when the radiation dose is 1 kGy, the gel content increases from 88.8% to 93.9%.

In addition to the improvement in the radiation stability of polypropylene and the increase in gel content, the mechanical properties and heat resistance of polypropylene materials have also been significantly improved. See the results shown in Table 1:

Table 1 Changes in mechanical properties of crosslinked polypropylene after adding nucleating agent

It can be seen from the table that after adding the nucleating agent, the flexural modulus, flexural strength, thermal deformation temperature and other mechanical properties of the cross-linked polypropylene have been improved, and the impact strength has not been significantly reduced. For uncrosslinked polypropylene, the impact strength will be significantly reduced after adding a nucleating agent. Therefore, it can be considered that the cross-linked polypropylene obtained by the present invention maintains the characteristics of the radiation cross-linked polypropylene in the prior art, and adds the characteristics of excellent mechanical properties and heat resistance of the material.

Embodiment Example 1 3000 grams of polypropylene powder (produced by Huabei Oilfield Pharmaceutical Factory, MI=1.0g/10min), 1wt% of trimethylol propyl triacrylate (TMPTA), 3wt of nucleating agent two (2 , 4-di-tert-butylphenol) sodium methylene phosphate (NA-11 produced by Japan Adeka Argus Chemieal Co.; Ltd.) and 1wt of antioxidant 2,2-methylene bis(4-methyl- 6-tert-butyl phenol), after fully mixing, extrude with a BRABENDER extruder and then cut into pellets at an extrusion temperature of 210°C, then use an injection machine to inject the pellets into molding, and use 60Co-γ in the air. The radiation dose is 2kGy and the dose rate is 1Gy/s.

The mechanical properties of the irradiated splines were measured according to ASTM standards, and the results are shown in Table 1.

Comparative Example 1: The test method is the same as in Example 1, except that no nucleating agent is added to the polypropylene powder. The mechanical properties of the irradiated splines were measured according to ASTM standards, and the results are shown in Table 1. Put it into a 120-mesh copper mesh, soak in boiling xylene for 8 hours and then dry and have a constant weight. The proportion of the undissolved part is the gel content.

Comparative Example 2: The test method is the same as in Example 2 except that no nucleating agent is added to the polypropylene powder. The gel content of polypropylene after irradiation was measured, and the results are shown in Table 2.

Example 3: The test method is the same as that of Example 1, except that the radiation dose is changed to 0.7kGy. The gel content of polypropylene after irradiation was measured, and the results are shown in Table 2.

Comparative Example 3: The test method is the same as in Example 3 except that the nucleating agent is not added to the polypropylene powder. The gel content of polypropylene after irradiation was measured, and the results are shown in Table 2.

Example 4: The test method is the same as that of Example 1, except that the radiation dose is changed to 1kGy. The gel content of polypropylene after irradiation was measured, and the results are shown in Table 2.

Comparative Example 4: The test method is the same as in Example 4 except that the nucleating agent is not added to the polypropylene powder. The gel content of polypropylene after irradiation was measured, and the results are shown in Table 2.

Example 5: The test method is the same as that of Example 1, except that the radiation dose is changed to 3kGy. The gel content of polypropylene after irradiation was measured, and the results are shown in Table 2.

Comparative Example 5: The test method is the same as in Example 5 except that the nucleating agent is not added to the polypropylene powder. The gel content of polypropylene after irradiation was measured, and the results are shown in Table 2.

Table 2 The effect of nucleating agent on the content of polypropylene gel after irradiation

Note: The unit of gel content in the table is weight percentage (wt%)