阅读说明：本技术 具有优异耐慢速裂纹增长性能的耐热聚乙烯组合物及其制备方法 (Heat-resistant polyethylene composition with excellent slow crack growth resistance and preparation method thereof ) 是由 王群涛 袁辉志 郭锐 王日辉 高凌雁 唐岩 许平 苑东兴 石晶 于 2018-07-16 设计创作，主要内容包括：本发明涉及一种具有优异耐慢速裂纹增长性能的耐热聚乙烯组合物及其制备方法,属于聚乙烯改性技术领域。本发明所述的具有优异耐慢速裂纹增长性能的耐热聚乙烯组合物,包括以下重量份数的原料：PE-RT树脂100份,抗氧剂0.2-0.5份,加工助剂0.04-0.08份,反应剂0.06-0.1份。所述反应剂为马来酰亚胺类哌啶基氧化物。本发明所述的具有优异耐慢速裂纹增长性能的耐热聚乙烯组合物,耐压强度、熔体强度及全尺寸切口蠕变性能均得到显著提高,有利于保证管材满足不同使用环境下的性能要求和使用寿命；本发明同时提供了简单易行、节能环保的制备方法。(The invention relates to a heat-resistant polyethylene composition with excellent slow crack growth resistance and a preparation method thereof, belonging to the technical field of polyethylene modification. The heat-resistant polyethylene composition with excellent slow crack growth resistance comprises the following raw materials in parts by weight: 100 parts of PE-RT resin, 0.2-0.5 part of antioxidant, 0.04-0.08 part of processing aid and 0.06-0.1 part of reactant. The reactant is maleimide piperidyl oxide. The heat-resistant polyethylene composition with excellent slow crack growth resistance has the advantages that the compression strength, the melt strength and the full-size notch creep property are remarkably improved, and the pipe can meet the performance requirements under different use environments and is beneficial to prolonging the service life; the invention also provides a simple, energy-saving and environment-friendly preparation method.)

1. A heat-resistant polyethylene composition with excellent slow crack growth resistance is characterized by comprising the following raw materials in parts by weight: 100 parts of PE-RT resin, 0.2-0.5 part of antioxidant, 0.04-0.08 part of processing aid and 0.06-0.1 part of reactant;

the reactant is maleimide piperidyl oxide.

2. The heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 1, characterized in that: the PE-RT resin is a copolymer of ethylene and 1-hexene.

3. The heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 2, characterized in that: the PE-RT resin is produced by adopting a gas phase process and a metallocene catalyst, the reaction temperature is 91-93 ℃, and the reaction pressure is 2.0-2.2 MPa.

4. The heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 1, characterized in that: the density of the PE-RT resin is 0.934-0.938g/cm³(ii) a The mass flow rate of the melt under the load of 2.16 kilograms is 0.60 to 0.75g/10 min; the weight average molecular weight is 11-15 ten thousand, the molecular weight distribution is 2.8-3.5; the ratio of main chain end methyl group/1000C is 0.40-0.60.

5. The heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 1, characterized in that: the PE-RT resin is in the form of powder, the average particle diameter is 0.65-0.80mm, and the bulk density is 0.45-0.50g/cm³。

6. The heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 1, characterized in that: the antioxidant is a mixture of hindered phenol antioxidant and phosphite antioxidant.

7. The heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 1, characterized in that: the processing aid is a fluorine-containing high molecular polymer PPA.

8. The heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 1, characterized in that: the maleimide piperidyl oxide is one or two of 4-maleimide-tetramethylpiperidine oxide or 1-oxy-3-maleimide-tetramethylpiperidine oxide.

9. A method for preparing a heat-resistant polyethylene composition having excellent slow crack growth resistance according to any one of claims 1 to 8, characterized by comprising the steps of:

(1) putting the PE-RT resin, the antioxidant and the processing aid into a high-speed mixer, stirring and mixing, stopping stirring, adding the reactant, and stirring again;

(2) and (2) adding the material added with the reactant and stirred in the step (1) into a double-screw extruder for melting, plasticizing, extruding and granulating to obtain the heat-resistant polyethylene composition with excellent slow crack growth resistance.

10. The method of preparing a heat-resistant polyethylene composition having excellent slow crack growth resistance according to claim 9, wherein: in the step (1), the reaction agent is added and stirred at the stirring temperature of 45-60 ℃.

Technical Field

The invention relates to a heat-resistant polyethylene composition with excellent slow crack growth resistance and a preparation method thereof, belonging to the technical field of polyethylene modification.

Background

The heat-resistant polyethylene (PE-RT) pipe material is a polyethylene special material with excellent hydrostatic pressure resistance and no need of crosslinking, and has the characteristics of excellent stability, good low-temperature impact resistance, hot-melt connection and the like, so that the heat-resistant polyethylene (PE-RT) pipe material is applied to a plurality of fields in China, such as a ground heating pipe, a solar pipe, a heat pipe network and the like. The PE-RT pipe material should have excellent slow crack growth resistance to meet the long-term service life requirement of 50 years.

In recent years, with the improvement of the requirement on the service life of heat-resistant polyethylene pipes under complex construction and use environments, the requirement on the slow crack growth resistance of the pipe materials is further improved, but the performance of many pipe materials at home and abroad is difficult to meet the requirement, and the application field of the pipe materials is limited.

How to form a certain number of long-chain branches in a molecular chain to improve the slow crack growth resistance of the resin and meet the requirements of the resin on higher pressure resistance and crack resistance is always the key point of domestic and foreign research. At present, polyolefin production enterprises mainly introduce long-chain branches into molecular chains by means of adjusting catalysts, polymerization process technologies and the like, but the technical process is complex, the molecular chain structure is difficult to control, and the cost is high.

CN200480016156 discloses a method of forming a polyolefin resin having a relatively high density and a long chain branching index ("LCB") greater than about 1. The process of the present invention comprises forming a reaction mixture capable of forming a polyolefin resin by mixing molecular hydrogen, a first olefin, an optional second olefin, a diluent, and a catalyst system comprising vanadium at a sufficient temperature, and initiating polymerization of the reaction mixture.

CN201110325136 discloses a long-chain branched polyethylene resin, which is prepared from polyethylene, organic peroxide, vinyl functional monomer, and crosslinking inhibitor as raw materials, wherein the mass ratio of the raw materials is as follows based on the amount of polyethylene: polyethylene, organic peroxide is 100: 0.05-0.30; polyethylene, vinyl functional monomer 100: 1.0-4.0; polyethylene and a crosslinking inhibitor, wherein the crosslinking inhibitor is 100: 0.5-1.5. The invention also discloses a preparation method of the polyethylene resin.

Although the above patents all mention maleimide compounds, the maleimide/alpha-olefin copolymer containing maleimide and pyridyl and having C10-C22 long carbon chain has C10-C22 long carbon chain structure, and the use of the component as polypropylene stabilizer improves the photo-thermal cracking resistance; CN201110325136 discloses maleimide-terminated polymers for pharmaceutical compositions, and neither of the above two patents improves material melt strength, material slow crack cracking resistance and pipe compressive strength.

Disclosure of Invention

The invention aims to provide a heat-resistant polyethylene composition with excellent slow crack growth resistance, which has the advantages that the compression strength, the melt strength and the full-size notch creep property are obviously improved, and the pipe can meet the performance requirements and the service life under different use environments; the invention also provides a simple, energy-saving and environment-friendly preparation method.

The heat-resistant polyethylene composition with excellent slow crack growth resistance comprises the following raw materials in parts by weight: 100 parts of PE-RT resin, 0.2-0.5 part of antioxidant, 0.04-0.08 part of processing aid and 0.06-0.1 part of reactant.

Preferably, the feed comprises the following raw materials in parts by weight: 100 parts of PE-RT resin, 0.3-0.4 part of antioxidant, 0.05-0.07 part of processing aid and 0.07-0.09 part of reactant.

The PE-RT resin is a copolymer of ethylene and 1-hexene. The PE-RT resin is produced by adopting a gas phase process and a metallocene catalyst, the reaction temperature is 91-93 ℃, and the reaction pressure is 2.0-2.2 MPa.

The density of the PE-RT resin is 0.934-0.938g/cm³Preferably 0.935 to 0.937g/cm³The material has good flexibility, ensures good impact resistance, and is convenient to construct and use.

The melt Mass Flow Rate (MFR) of the PE-RT resin under the load of 2.16kg is 0.60-0.75g/10min, preferably 0.63-0.72g/10 min; the molecular weight (Mw/MD) distribution D is from 2.8 to 3.5, preferably from 2.9 to 3.3. MFR and D influence the processability and mechanical strength of the resin, and the PE-RT resin with the performance parameters ensures that the pipe material has good processability while having certain mechanical strength.

The weight average molecular weight (Mw) of the PE-RT resin is 11-15 ten thousand, preferably 12-14 ten thousand; the ratio of main chain terminal methyl group/1000C is 0.40-0.60, preferably 0.45-0.55. The Mw and the number of methyl groups at the end of the backbone affect the reaction efficiency and cooperativity of the reactants, i.e., the number and distribution of long chain branches introduced into the resin.

The PE-RT resin is in the form of powder, the average grain diameter is 0.65-0.80mm, and the bulk density is 0.45-0.50g/cm³And the dispersion of the auxiliary agent and the introduction of long-chain branches are facilitated.

When the tube material is in contact with air, it is oxidized by a chemical reaction with oxygen in the air, which is a typical radical reaction. The antioxidant is added into the pipe material and can react with oxidation free radicals R and ROO generated by oxidation in the plastic material to interrupt the growth of an active chain, thereby effectively inhibiting or reducing the degradation and aging processes of the plastic material and prolonging the service life of plastic products. The antioxidant is a mixture of hindered phenol antioxidant and phosphite antioxidant, and the mixing ratio is preferably 1: 1. Amine antioxidants hinder the chain reaction effect of the reactants with the resin and are not favorable for introducing long chain branches.

The hindered phenol antioxidant is tetra [ methyl-beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ] pentaerythritol ester, beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) n-octadecyl propionate, 1,3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) benzene or 1,3, 5-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) -1,3, 5-triazine-2, 4,6(1H,3H,5H) -trione; the phosphite antioxidant is tris [2, 4-di-tert-butylphenyl ] phosphite, bis (2, 4-di-tert-butylphenol) pentaerythritol diphosphite or pentaerythritol distearate diphosphite.

In order to improve the processing performance of the composition, a small amount of fluorine-containing high molecular polymer PPA is added as a processing aid.

The reactant is maleimide piperidyl oxide. Preferably, the maleimide oxide is one or two of 4-maleimide-tetramethylpiperidine oxide and 1-oxy-3-maleimide-tetramethylpiperidine oxide, and the mixing mass ratio is 1:1 when the maleimide oxide and the 1-oxy-3-maleimide-tetramethylpiperidine oxide are mixed.

The preparation method of the heat-resistant polyethylene composition having excellent slow crack growth resistance comprises the following steps:

(1) and (2) putting the PE-RT resin, the antioxidant and the processing aid into a high-speed mixer, stirring and mixing, stopping stirring, adding the reactant, and stirring again at the stirring temperature of 45-60 ℃.

(2) And (2) adding the material added with the reactant and stirred in the step (1) into a double-screw extruder for melting, plasticizing, extruding and granulating to obtain the heat-resistant polyethylene composition with excellent slow crack growth resistance.

In the steps, the first three components are mixed, then the stirring is stopped, and then the reactant is added, so that the reactant is favorably and uniformly dispersed in the resin and fully reacted with the resin, and the content and the performance of the long-chain branch in the resin are improved.

The performance parameters of the heat-resistant polyethylene composition prepared by the invention are as follows:

the melt strength is more than or equal to 0.28N, 20 ℃, 11.2MPa hydrostatic strength is more than or equal to 322h, 95 ℃, 4.3MPa hydrostatic strength is more than or equal to 5394h, FNCT (50 ℃, 2% TX-10, 8.0MPa) is more than or equal to 2811 h; the impact strength (23 ℃) of the notch of the simply supported beam is more than or equal to 70kJ/m²。

The invention has the following beneficial effects:

(1) according to the invention, the molecular structure and components of the resin are limited, the maleimide oxide is added into the PE-RT pipe material, and long-chain branches are introduced into the molecular chain of the resin through blending and melt extrusion, so that the compression strength, the melt strength, the full-size notch creep property and the like of the composition are improved, and the pipe can meet the performance requirements and the service life under different service environments;

(2) the heat-resistant polyethylene composition is widely applied to the production of heat-resistant polyethylene pipes, such as floor heating pipes, aluminum-plastic composite pipes and the like;

(3) the preparation method of the heat-resistant polyethylene composition is energy-saving, environment-friendly, simple and feasible.

Drawings

FIG. 1 is a Cole-Cole plot of PE-RT compositions and PE-RT resins without long chain branching according to the invention.

Detailed Description

The present invention is further illustrated by the following examples, which are not intended to limit the practice of the invention.