CN104861295A - Preparation method of modified PP (polypropylene) material with improved shock resistance - Google Patents

Abstract

The invention provides a preparation method of a modified polypropylene material with improved impact resistance. The preparation method is prepared by one-step blending modification of raw materials including the following components: 100 parts of polypropylene, 20-40 parts of main modifier, 2.5-10 parts of secondary modifier, 0.5 parts of crosslinking modifier -5 parts, 0.5-5 parts of cross-linking auxiliary agent, wherein, the main modifier is polyolefin elastomer, the secondary modifier is high-density polyethylene, the cross-linking modifier is organic peroxide, and the cross-linking auxiliary agent It is divinylbenzene with a content of 50%-60%, and the difference between the decomposition temperature of the crosslinking modifier and the melting temperature of PP when the half-life of the crosslinking modifier is 1 minute is 1-5°C. The invention can greatly improve the impact strength of the modified PP, endow the composite material with excellent impact resistance, rigidity, aging resistance, cold resistance and gasoline resistance, and at the same time, other properties are hardly affected.

Description

A preparation method of modified polypropylene material with improved impact strength

technical field

The invention belongs to the field of polymer composite materials, and in particular relates to a preparation method of a modified polypropylene material with improved impact resistance.

Background technique

Polypropylene (PP) is a thermoplastic resin polymerized from propylene monomers. It is one of the main materials for making front and rear bumpers of cars and light and mini cars. Due to the high glass transition temperature of PP, the low-temperature impact performance is poor , The molding shrinkage rate is large, which limits its application in the automotive industry, so people often use rubber materials to toughen PP. At present, using polyolefin elastomer (Polyolefin elastomer, POE), such as ethylene-octene copolymer, ethylene-hexene copolymer and ethylene-butene copolymer to modify PP is an effective method to improve its mechanical properties. The reason is that POE has a narrow relative molecular mass and short chain distribution, has high elasticity, high strength, high elongation and good low temperature performance, and also has excellent heat aging resistance and UV resistance. For example, in the ethylene-octene copolymer elastomer, the polyethylene segment crystalline region (resin phase) acts as a physical crosslinking point, and the introduction of a certain amount of octene weakens the polyethylene segment crystallization, forming an amorphous region that exhibits rubber elasticity ( Rubber phase), when POE is used to modify PP, the rubber state in POE can cause a lot of silver craze under the action of external impact force, while the matrix material PP produces shear yield, mainly by craze, shear band Absorb energy, thereby improving the mechanical properties of the matrix material.

Automobile bumper is a thin-walled large-scale structural component with large surface area and complex shape. All countries have formulated relevant technical standards for plastic bumpers for automobiles. As far as the bumper is concerned, the production raw materials must have excellent high and low temperature impact toughness, rigidity, aging resistance, heat resistance, cold resistance, gasoline resistance, and good flame retardancy, etc.; Raw materials are required to have good thermal stability, low molding shrinkage, and good mold release. Among them, the PP material suitable for making automobile bumpers must have ultra-high impact strength, the minimum at room temperature must be above 400J/m, and the common PP impact strength can only reach 50J/m at room temperature, and it must be modified before it can be used. (Zhang Shunxi. Development of super high impact strength polypropylene material for bumper. Plastic Science and Technology. 1995,108(4):10-13). Generally, POE is used as a toughening agent to carry out physical and mechanical blending modification of PP, that is, to obtain a composite material by mechanically blending PP matrix with POE elastomer and inorganic filler. Although the impact strength has been improved, the improvement is small. , the impact strength can only reach about 90J/m at most, which cannot meet the requirements of automobile bumpers.

Chinese patent document CN102251304A uses PP as the base material, adds high-density polyethylene (HDPE), POE, etc. to mix uniformly, mixes and granulates through twin-screws, prepares polypropylene modified masterbatch, and then reserves high-strength, high-modulus polymer through screw extrusion. Propylene fiber, this kind of polypropylene fiber has high strength, low elongation, high modulus of rupture, and excellent weather resistance, but no toughening effect is mentioned. Chinese patent document CN102746572A utilizes polyethylene, activated calcium carbonate, POE, HDPE, antioxidant, anti-ultraviolet agent and toner etc. It meets the above requirements, but the impact strength after modification is only increased by more than 30%.

Contents of the invention

purpose of invention

The purpose of the present invention is to provide a method for preparing a modified polypropylene material with improved impact strength, so that the impact strength can be greatly improved.

Summary of the invention

The preparation method of the modified polypropylene material with improved impact strength is prepared by one-step blending and modification of raw materials comprising the following components:

Among them, the main modifier is polyolefin elastomer, the secondary modifier is high-density polyethylene, the cross-linking modifier is organic peroxide, and the cross-linking auxiliary agent is divinylbenzene with a content of 50%-60%, The difference between the decomposition temperature of the cross-linking modifier and the melting temperature of PP when the half-life of the cross-linking modifier is 1 minute is 1-5°C.

The one-step method is a known polymer blending modification method, specifically refers to completing the crosslinking reaction of polymer modification and extrusion granulation on the same extruder. This requires adding various additives, powdery or liquid crosslinking agents and crosslinking aids to the melt kneading of the PP composition on the same extruder, and completing the crosslinking reaction and extrusion granulation. The requirements for the extruder are higher. The solution is: choose an extruder with a large aspect ratio (L/D) (30-35) and an exhaust function.

The cross-linking modifier provides active free radicals during the processing, so that the main chains of PP, POE and HDPE become active free radicals and undergo cross-linking reactions, ensuring that the modified polypropylene material has excellent impact resistance, cold resistance performance and aging resistance. Preferably, the cross-linking modifier is dicumyl peroxide. The cross-linking aid prevents the chain-severing degradation reaction of the PP main chain during processing, thereby achieving an ideal cross-linking effect. The crosslinking aid divinylbenzene is a commercially available product, which has three isomers of o-, m-, and p-divinylbenzene, and it is not necessary to separate the isomers when used in the present invention; the 50% used in the present invention -60% content of divinylbenzene is a more commonly used specification in commercially available products. Obviously, if other content of divinylbenzene (such as 80%) is used, as long as the actual amount of pure divinylbenzene added is the same, it can also be used. The same technical effect can be achieved. Said content is the mass percent content.

The main modifier POE is at least one of ethylene-octene copolymer, ethylene-hexene copolymer, and ethylene-butene copolymer; the secondary modifier HDPE is ethylene monomer through catalytic polymer The homopolymer obtained by the reaction is a commercially available product, and the molding shrinkage of PP is reduced by blending with PP to ensure that the modified polypropylene material has good toughness and gasoline resistance. Preferably, the density of the ethylene-octene copolymer at 25°C is 0.850-0.913g/cm ³ , the density of the ethylene-hexene copolymer at 25°C is 0.90-0.955g/cm ³ , and the ethylene-butene copolymer The density of the material at 25°C is 0.850-0.910g/cm ³ .

The PP in the present invention can adopt homopolymerization or copolymerization PP according to the performance or use requirements of the modified PP material. When the present invention is used to prepare modified PP materials for automobile bumpers, preferably homopolymerized PP is used, more preferably the melt index of the homopolymerized PP is 10-25g/10min, and the most preferred melt index of the homopolymerized PP is 10-25g/10min. It is 20-25g/10min. The melt index is obtained by testing according to the standard ASTM D1238 (2004) (test temperature and load are 230°C and 2.16kg respectively, and the standard mold size for molten resin extrusion is: 2.095×8mm).

The raw material in the present invention may also include various auxiliary agents commonly used in polypropylene blending modification. As a preferred option, the raw material may also include 5-10 parts of a reinforcing agent and 0.5-5 parts of a heat stabilizer, wherein the Strengthening agent is DH-1 strengthening agent (hereinafter referred to as DH-1), and described thermostabilizer is zinc stearate, and described strengthening agent is commercially available product, can improve the dispersibility and fluidity of resin, increase the stability of material products. Mechanical strength and rigidity can also reduce the molding shrinkage of PP, and the heat stabilizer can inhibit or delay the thermal decomposition or crosslinking of polymers to ensure the thermal stability of PP during processing. The raw material of the present invention can also include 5-10 parts of flame retardant, 0.5-5 parts of light stabilizer, and 0.5-5 parts of lubricant. The flame retardant can delay or prevent the burning of polymer plastics and ensure the modification PP has good flame retardancy, the light stabilizer can prevent PP and ethylene polymer from photoaging, and ensure that the modified PP has good light stability, and the lubricant can reduce the intermolecular and The friction between the polymer and the equipment increases the fluidity and release properties of the raw materials, ensuring that the modified PP has good release properties. Preferably, the flame retardant is diphenyl octyl phosphate, the light stabilizer is o-hydroxybenzophenone, and the lubricant is barium stearate. Because according to the present invention, when adopting described cross-linking modifier, cross-linking auxiliary agent, main modifier and secondary modifier to carry out blending modification to PP to improve impact strength, the remaining properties (such as rigidity, gasoline resistance properties, flame retardancy, light stability, mold release, thermal stability and fluidity of raw materials during processing, etc.) will not be significantly adversely affected. Therefore, when adding the above-mentioned various commonly used additives, use the existing technology The usual dosage is enough.

The specific preparation steps of the present invention are: mixing and dispersing the raw materials evenly, adding them to the twin-screw extruder, and granulating through melt extrusion. The twin-screw extrusion process conditions are: first zone: 220-240 ° C; -240°C; Three zones: 220-240°C; Four zones: 220-240°C; Five zones: 220-240°C; Six zones: 220-240; Head temperature: 220-240°C; Screw speed: 300 -350 revolutions per minute (r/min), the residence time of the material in the barrel: 3-5 minutes. Preferably, the raw materials are stirred at a high speed in a high-speed mixer, so that the raw materials are mixed and dispersed evenly, and then added to the twin-screw extruder. Generally, high-speed stirring is required for 10-20 minutes. Among them, high-speed stirring is a common mixing method in the field, and the rotating speed is generally 500 -800r/min. The above specific preparation steps are characterized by controlling the appropriate processing temperature to complete the chemical crosslinking and extrusion granulation of PP in one step, because at the processing temperature of PP, the half-life of the crosslinking modifier dicumyl peroxide is 1 minute The decomposition temperature (171°C) is close to the melting temperature (166-170°C) of PP, so that during the crosslinking process of PP, the dicumyl peroxide can be completely decomposed, so as not to delay the crosslinking time of PP , which in turn affects other properties of the final product PP/toughener blend.

The present invention uses modifiers such as POE and HDPE to carry out blending modification on PP, which can greatly improve the impact strength of the modified PP, and endow the composite material with excellent impact resistance, rigidity, aging resistance, cold resistance and gasoline resistance, Meanwhile, the rest of the performance is barely affected. When the PP base material adopts the above-mentioned optimal scheme, the modified PP can reach the impact strength required by the automobile bumper, and can be widely used in parts such as automobile bumpers, instrument panels, door inner panels, battery casings, windshield rings and fenders. processing.

Detailed ways

The following are the raw materials used in all comparative examples and examples:

Homopolymer PP, China Petrochemical Corporation, brand: HHP3, melt index 25g/10min;

Ethylene-octene copolymer, American DuPont Company, brand: 8130, density at 25°C is 0.913g/cm ³ ;

Ethylene-hexene copolymer, American Dow Chemical Company, brand name: Dowlex 2641G, density at 25°C is 0.9309g/cm ³ ;

Ethylene-butene copolymer, Japan Mitsui Chemicals Co., Ltd., brand: DF840, density at 25°C is 0.8908g/cm ³ ;

HDPE, China Petroleum Daqing Petrochemical Company, grade: 5000S;

Dicumyl peroxide, Jining Huide Chemical Co., Ltd., chemically pure;

Divinylbenzene, Beijing Jintong Letai Chemical Products Co., Ltd., analytically pure, divinylbenzene content: 55%;

DH-1, Beijing Weicheng Technology Energy Saving Co., Ltd., the appearance is free-flowing particles of natural transparent solid; melting point ≤ 60 ℃; tensile strength ≥ 10MPa, elongation at break ≥ 800%;

Octyl diphenyl phosphate, Aladdin's reagent, chemically pure;

o-Hydroxybenzophenone, Aladdin's reagent, chemically pure;

Zinc stearate: Jiangxi Hongyuan Chemical, chemically pure;

Barium stearate: Jiangxi Hongyuan Chemical, chemically pure.

Comparative example 1

Modified polypropylene material, the weight share of its each component is:

Comparative example 2

Modified polypropylene material, the weight share of its each component is:

Example 1

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 2

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 3

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 4

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 5

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 6

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 7

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 8

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 9

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 10

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 11

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 12

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 13

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 14

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

Example 15

The described modified polypropylene material that improves impact strength, the weight share of its each component is:

The preparation method of the modified polypropylene material that improves the impact resistance in the above-mentioned comparative examples 1-2 and embodiments 1-15 is as follows: take the required materials according to the proportion, and stir at a high speed in a high-speed mixer for 10-20 minutes; mix the The good material is fed into the twin-screw extruder, and granulated by melt extrusion; the residence time of the material in the barrel is 3-5 minutes.

Twin-screw extrusion process conditions are: Zone 1: 220-240℃; Zone 2: 220-240℃; Zone 3: 220-240℃; Zone 4: 220-240℃; Zone 5: 220-240℃; Zone 6 : 220-240°C; head temperature: 220-240°C; screw speed: 300-350r/min.

Double-stack extruder: Nanjing Juli Chemical Machinery Co., Ltd., model: SHJ-20, screw diameter D: 21.7mm, length-to-diameter ratio L/D: 35;

High-speed mixer: Shanghai Zhenxuan Electromechanical Technology Co., Ltd., model: SDF550

Performance Testing:

Tensile strength is tested according to ASTM D638 (2003) standard; flexural strength is tested according to ASTM D790 (2010) standard; notched impact strength is tested according to ASTM D256 (1997); the results are shown in Tables 1 and 2.

Table 1 The effect of the content change of crosslinking modifier dicumyl peroxide on the performance of PP

Table 2 POE content, divinylbenzene, HDPE content and POE type on PP performance table

It can be seen from Tables 1 and 2 that the notched impact strength of unmodified and toughened PP is only 45J/m. When POE and HDPE are added as toughening modifiers, the notched impact strength is greatly improved, reaching 223J/m. This shows that the impact strength of PP can be well improved by physical-mechanical blending of POE and HDPE. However, this strength value cannot meet the standards for the use of automobile bumpers. After chemical crosslinking and blending of PP by one-step method, even if the content of crosslinking agent is very small (0.5 parts), the notched impact strength can reach that of general mechanical and physical blending. 2.5 times (520J/m), and with the increase of the content of crosslinking agent, the flexural strength, flexural modulus and notched impact strength of the modified PP material are all enhanced. With the increase of benzene and HDPE content, the notched impact strength of PP increases; when the type of POE is changed, as in Examples 6, 12, and 13, the notched impact strength of the modified PP material can meet the standards for the use of automobile bumpers, where POE is ethylene When the ethylene-octene copolymer is used, the notched impact strength of PP is the largest, which shows that the ethylene-octene copolymer has the best toughening effect. The experimental results of the above examples fully meet the use standard of automobile bumpers (minimum 400J/m at room temperature), which shows that the present invention is an effective means for preparing high impact strength modified polypropylene materials, and the method is simple and easy to implement.

Although the embodiment of the present invention has been disclosed as above, it is not limited to the use listed in the specification and embodiment, it can be applied to various fields of the present invention, and it can be easily done by those familiar with the art Therefore, the invention is not limited to specific details without departing from the general concept defined by the claims and their equivalents.

Claims (10)

1. A preparation method for improving the modified polypropylene material of impact strength, characterized in that, it is prepared through one-step blending modification by the raw materials comprising the following components: Among them, the main modifier is polyolefin elastomer, the secondary modifier is high-density polyethylene, the cross-linking modifier is organic peroxide, and the cross-linking auxiliary agent is divinylbenzene with a content of 50%-60%, The difference between the decomposition temperature of the cross-linking modifier and the melting temperature of PP when the half-life of the cross-linking modifier is 1 minute is 1-5°C. 2. the preparation method of the modified polypropylene material that improves impact strength as claimed in claim 1 is characterized in that, described crosslinking modifier is dicumyl peroxide. 3. the preparation method of the modified polypropylene material that improves impact resistance as claimed in claim 1 is characterized in that, described polypropylene is homopolypropylene. 4. the preparation method of the modified polypropylene material that improves impact strength as claimed in claim 3 is characterized in that, the melt index of described homopolypropylene is 10-25g/10min. 5. the preparation method of the modified polypropylene material that improves impact resistance as described in any one in claim 1-4, is characterized in that, described raw material also comprises reinforcing agent 5-10 parts, heat stabilizer 0.5- 5 parts, wherein, the reinforcing agent is a DH-1 reinforcing agent, and the heat stabilizer is zinc stearate. 6. the preparation method of the modified polypropylene material that improves impact resistance as claimed in claim 5 is characterized in that, described raw material also comprises flame retardant 5-10 part, light stabilizer 0.5-5 part and lubricant 0.5-5 parts, the flame retardant is diphenyl octyl phosphate, the light stabilizer is o-hydroxybenzophenone, and the lubricant is barium stearate. 7. the preparation method of the modified polypropylene material that improves impact resistance as any one of claim 1-6 is characterized in that, described polyolefin elastomer is ethylene-octene copolymer, ethylene-hexane At least one of ethylene copolymers and ethylene-butene copolymers. 8. The method for preparing a modified polypropylene material with improved impact strength as claimed in claim 7, characterized in that the density of the ethylene-octene copolymer at 25°C is 0.850-0.913g/cm ³ , and ethylene The density of -hexene copolymer at 25°C is 0.90-0.955g/cm ³ , and the density of ethylene-butene copolymer at 25°C is 0.850-0.910g/cm ³ . 9. the preparation method of the modified polypropylene material that improves impact strength as described in any one in claim 1-8, it is characterized in that, join in the twin-screw extruder after raw material is mixed and dispersed uniformly, by melting Extrusion granulation, twin-screw extrusion process conditions are: Zone 1: 220-240℃; Zone 2: 220-240℃; Zone 3: 220-240℃; Zone 4: 220-240℃; Zone 5: 220- 240°C; six zones: 220-240°C; machine head temperature: 220-240°C; screw speed: 300-350 rpm, residence time of the material in the barrel: 3-5 minutes. 10. the preparation method of the modified polypropylene material that improves impact strength as claimed in claim 6 is characterized in that, raw material is stirred at high speed in high-speed mixer, after making raw material mix and disperse uniformly, join in the twin-screw extruder .