High-expandable PP material and preparation method thereof

Abstract

The invention discloses a high-expandable PP (polypropylene) material and a preparation method thereof. The high-expandable PP material comprises the following components in parts by mass: 100 parts of polypropylene, 0-10 parts of a chain extension monomer, 0.01-5 parts of modified nano zinc oxide, 0-5 parts of an antioxidant and 0-5 parts of a foaming agent, according to the method disclosed by the invention, the high-expandable PP nano-foam can be stably and efficiently prepared, and the preparation process is high in controllability, low in processing difficulty and suitable for mass production.

Description

Technical Field

[0001] The invention relates to the technical field of general polymer material modification and foaming, in particular to a high-expandable PP material and a preparation method thereof. Background Art

[0002] Polypropylene (PP) is one of the most widely used resins in the world with the fastest production growth. Compared with other thermoplastic resins, PP has low density, high melting point, wide sources, low price, non-toxicity, easy processing, good mechanical properties and chemical stability. It is the product with the best heat resistance among general resins. It has become an indispensable basic raw material for packaging, light industry, construction, electronics, electrical appliances and automobile industries.

[0003] However, ordinary PP generally has a linear structure, a narrow relative molecular weight, and the processing softening point is very close to the melting point of the crystalline phase. Therefore, the melt strength is very low and the processing temperature range is very narrow. This leads to bubble collapse during the extrusion foaming process, uneven wall thickness of thick-walled containers during thermoforming, and edge curling and shrinkage during extrusion coating and calendering, which greatly restricts its scope of use.

[0004] Highly expandable PP, also known as high melt strength polypropylene (HMSPP), is a new PP product developed to solve the above problems. HMSPP has high melt strength, strain hardening, and a wide processing temperature range. It is widely used in thermoforming, extrusion foaming, coating, and blow molding, and is used in the production of automobiles, foam food packaging, and sports equipment. Current research results show that the melt strength of PP with high molecular weight, wide molecular weight distribution, and long chain branching (LCB) structure will be greatly improved, especially the presence of long chain branches has a more obvious effect on improving PP melt strength and expandability.

[0005] Patent CN105504498A uses modified polypropylene and sodium bicarbonate as a foaming agent for injection foaming to obtain a microporous material with a pore diameter between 75 and 185 μm; Patent CN101104716A provides an expandable polypropylene bead and a preparation method thereof, which uses polypropylene and low-density polyethylene to blend and foam in a kettle, so that the melt strength during foaming reaches a relatively ideal range, and finally obtains foamed beads. Most PP nano foam materials can be obtained by intermittent foaming. The above routes have not achieved continuous industrial production, and the production efficiency is limited. Patent CN112759826B discloses a foamable polypropylene composition and foamed polypropylene and a preparation method thereof. By grafting polar monomers and reacting with component A for extrusion foaming, a foamed product with a pore diameter of 100 to 200 μm is obtained. It can be seen that it is very difficult to achieve continuous preparation of PP nano foam materials due to the influence of PP melt strength. Nano foam refers to a pore size less than 1 μm and a pore density greater than 10 12 Pieces / cm 3 Nanoporous foam is a foaming material. It has great application potential in the fields of electronics, automotive industry, aerospace, construction and medical due to its light weight, high strength and high thermal insulation. However, PP continuous extrusion nanofoaming technology faces the problem of difficulty in achieving high production efficiency and high foaming ratio at the same time. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a highly expandable PP and a nano foam material thereof, so as to solve the problems of low production efficiency and low foaming ratio of PP nano foam materials.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A highly expandable PP material comprises the following components in parts by weight:

[0009] 100 parts of polypropylene, 0-10 parts of chain extension monomer, 0.01-5 parts of modified nano zinc oxide, 0-5 parts of antioxidant, 0-5 parts of foaming agent;

[0010] Preferably, the highly expandable PP material comprises: 100 parts of polypropylene, 0.01 to 2 parts of chain extension monomer, 0.05 to 3 parts of modified nano zinc oxide, 0.01 to 2.5 parts of antioxidant, and 0.01 to 2.5 parts of foaming agent.

[0011] Preferably, the density of the polypropylene is 0.8 to 1 g / cm 3 , melt flow rate <30g / 10min (190℃ / 2.16kg).

[0012] Preferably, the chain extending monomer is selected from at least one of dienes, carboxylic acids, phenolic acids, unsaturated linear polyesters and the like.

[0013] Preferably, the chain extension monomer is selected from phenolic acids, and the carboxylic acids are preferably one or more of p-hydroxycinnamic acid, p-hydroxyphenylacetic acid, and 3,4-dihydroxyphenylethanol.

[0014] The modified nano zinc oxide preparation method comprises the following steps:

[0015] 1) dissolving stearic acid in solvent one to form a stearic acid solution;

[0016] 2) dispersing zinc oxide in solvent 2 to form a suspension;

[0017] 3) adding the stearic acid solution to the zinc oxide suspension and stirring to coat the surface of the zinc oxide with stearic acid;

[0018] 4) filtering, washing and drying to obtain modified nano zinc oxide.

[0019] Preferably, the solvent 1 is an alcohol or silicone oil, preferably one or more of methanol, ethanol, and cyclopentasiloxane silicone oil;

[0020] Preferably, the second solvent is alcohol or silicone oil, preferably one or more of methanol, ethanol, and cyclopentasiloxane silicone oil;

[0021] Preferably, the mass ratio of stearic acid to zinc oxide is 20-40:50-80.

[0022] Preferably, the average particle size of the zinc oxide is nanometers ranging from 10 to 90 nm.

[0023] Preferably, in step 3), the prepared stearic acid ethanol solution is slowly added dropwise to the dispersed nano zinc oxide ethanol suspension, and a magnetic stirrer is turned on for stirring for about 4 to 6 hours to ensure that the stearic acid molecules fully cover the surface of the nano zinc oxide particles.

[0024] Preferably, in step 4), the modified nano zinc oxide is filtered and separated from the reaction solution, and the modified nano zinc oxide is washed with ethanol or water. The washed modified nano zinc oxide is placed in a vacuum drying oven or an oven for drying for 6 to 12 hours to remove moisture and residual solvent, and finally the modified nano zinc oxide is obtained.

[0025] Preferably, the antioxidant comprises a primary antioxidant and an auxiliary antioxidant; the primary antioxidant is a hindered classification primary antioxidant, preferably one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate octadecyl ester, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; the auxiliary antioxidant is a phosphite auxiliary antioxidant, preferably one or more of tris[2,4-di-tert-butylphenyl]phosphite, tris(nonylphenyl)phosphite and tetrakis(2,4-di-tert-butylphenyl-4-4'-biphenyl)-bisphosphate.

[0026] Preferably, the blowing agent is selected from physical blowing agents, preferably one or more of CO2, N2, butane, pentane, fluorinated olefins, alcohol, and water.

[0027] Preferably, the PP nanoporous foam has a pore size of less than 1 μm and a pore density of more than 10 12 Pieces / cm 3 , the foaming ratio can reach more than 10.

[0028] The present invention also provides a method for preparing the highly expandable PP material, comprising the following steps: adding polypropylene, optional chain extension monomers, optional modified nano zinc oxide, optional antioxidants, and optional foaming agents to a twin-screw tandem single-screw extruder to perform melt grafting modification on the materials, and extruding and foaming to obtain the highly expandable PP material.

[0029] The processing temperature of the twin-screw extruder is 190-210°C; the processing temperature of the single-screw extruder is 150-180°C; the temperature of the single-screw extruder head is 140-170°C; and the residence time is 1-15 minutes.

[0030] Preferably, the processing temperature of the twin-screw extruder is 200-210°C;

[0031] Preferably, the processing temperature of the single screw extruder is 160-180°C;

[0032] Preferably, the extruder head temperature is 140-160°C.

[0033] The beneficial effects of the present invention are as follows:

[0034] The present invention provides a method for preparing a highly expandable PP and a nano-foamed material thereof. The method utilizes a processing end melt grafting modification method to carry out modification and extrusion foaming in a double-stage extruder (a twin-screw extruder connected in series with a single screw) to obtain a nano-scale microporous material having a PP foam cell size of less than 1 μm, a cell density of more than 1012 cells / cm3, and a foaming ratio of more than 10.

[0035] Para-hydroxycinnamic acid is added to the polypropylene matrix as a chain extension monomer. Because it contains hydroxyl and carboxyl functional groups, it can combine with the polypropylene matrix side chains under certain temperature and pressure to increase the long molecular chain structure and enhance chain entanglement, thereby improving the matrix melt strength. By adding stearic acid-modified zinc oxide, on the one hand, it can serve as a bubble nucleation point to promote bubble nucleation and improve the uniformity of cell dispersion. On the other hand, it can combine with the chain extension monomer to improve the interface bonding force with the matrix, thereby ensuring the formation of a uniform and dense cell structure in the melt.

[0036] The modification method proposed in the present invention can stably and efficiently prepare highly expandable PP nano foam, has strong controllability in the preparation process, has low processing difficulty, and is suitable for mass production. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Examples 1-4

[0039] Step 1: Mix the raw materials according to the weight ratio in Table 1.

[0040] Step 2: Add the aforementioned components into a twin-screw tandem single-screw extruder for melt grafting modification at 190°C with a screw speed of 200 rpm, and take out the obtained high expandability PP for characterization.

[0041] Comparative Example 1

[0042] The polypropylene material was prepared by the same method as in Example 1, the main difference being that modified nano zinc oxide was not added.

[0043] Comparative Example 2

[0044] The polypropylene material was prepared by the same method as in Example 1, the main difference being that zinc oxide of the same mass as the modified nano zinc oxide was added without modification.

[0045] Table 1: Formula table of embodiments and comparative examples

[0046]

[0047]

[0048] According to the formulations of the embodiments and comparative examples in Table 1, the components were added into a twin-screw tandem single-screw extruder for melt grafting modification and extrusion foaming. The screw speed was 200 rpm to obtain an extruded PP foam product. The obtained PP foam product was taken out for characterization. The characterization data are shown in Table 2 below.

[0049] Table 2 Data of foam products obtained from examples and comparative examples

[0050]

[0051] From the above data comparison, it can be seen that the use of chain extension monomer grafting and modified nano zinc oxide reinforcement improves the melt strength of polypropylene, provides bubble nucleation sites, improves the cell density of the product, and successfully prepares high foaming ratio PP nanoporous foam. The method of the present invention achieves an ultra-high foaming ratio of more than 10 times while continuously extruding and foaming to prepare PP nanoporous foam. Under the optimal conditions, the foaming ratio was successfully increased from the original 1.2 times to 10.8 times, and the cell density reached 6.04×10 12 Pieces / cm 3 , and the average pore size reaches 318nm, and the pore structure is relatively ideal.

[0052] Finally, it should be noted that the above embodiments are merely examples for the purpose of clear explanation and do not mean that the present invention is limited thereto. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A highly expandable PP material, characterized in that: Contains the following components in parts by weight: 100 parts of polypropylene, 0-10 parts of chain extension monomer, 0.01-5 parts of modified nano zinc oxide, 0-5 parts of antioxidant, 0-5 parts of foaming agent; Preferably, the highly expandable PP material comprises: 100 parts of polypropylene, 0.01 to 2 parts of chain extension monomer, 0.05 to 3 parts of modified nano zinc oxide, 0.01 to 2.5 parts of antioxidant, and 0.01 to 2.5 parts of foaming agent.

2. The PP material according to claim 1, characterized in that: At 190°C and 2.16 kg, the density of the polypropylene is 0.8 to 1 g / cm 3 , melt flow rate <30g / 10min; Preferably, the chain extending monomer is selected from at least one of dienes, carboxylic acids, phenolic acids, unsaturated linear polyesters and the like; Preferably, the chain extension monomer is selected from phenolic acids and carboxylic acids, more preferably one or more of p-hydroxycinnamic acid, p-hydroxyphenylacetic acid and 3,4-dihydroxyphenylethanol.

3. The PP material according to claim 1 or 2, characterized in that: The modified nano zinc oxide preparation method comprises the following steps: 1) dissolving stearic acid in solvent one to form a stearic acid solution; 2) dispersing zinc oxide in solvent 2 to form a suspension; 3) adding the stearic acid solution to the zinc oxide suspension and stirring to coat the surface of the zinc oxide with stearic acid; 4) filtering, washing and drying to obtain modified nano zinc oxide.

4. The PP material according to claim 3, characterized in that: The first solvent is alcohol or silicone oil, preferably one or more of methanol, ethanol, and cyclopentasiloxane silicone oil; Preferably, the second solvent is alcohol or silicone oil, preferably one or more of methanol, ethanol, and cyclopentasiloxane silicone oil.

5. The PP material according to claim 3 or 4, characterized in that: The mass ratio of stearic acid to zinc oxide is 20-40:50-80; Preferably, the average particle size of the zinc oxide is nanometers ranging from 10 to 90 nm.

6. The PP material according to any one of claims 3 to 5, characterized in that: In step 3), the prepared stearic acid ethanol solution is slowly added dropwise to the dispersed nano zinc oxide ethanol suspension, and a magnetic stirrer is turned on for stirring for about 4 to 6 hours to ensure that the stearic acid molecules are fully covered on the surface of the nano zinc oxide particles; Preferably, in step 4), the modified nano zinc oxide is separated from the reaction solution by filtration, washed and dried to finally obtain modified nano zinc oxide.

7. The PP material according to any one of claims 1 to 6, characterized in that: The antioxidant includes a primary antioxidant and an auxiliary antioxidant; the primary antioxidant is a hindered primary antioxidant, preferably one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate octadecyl alcohol ester, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; the auxiliary antioxidant is a phosphite auxiliary antioxidant, preferably one or more of tris[2,4-di-tert-butylphenyl] phosphite, tris(nonylphenyl) phosphite and tetrakis(2,4-di-tert-butylphenyl-4-4'-biphenyl)-bisphosphate; Preferably, the blowing agent is selected from physical blowing agents, preferably one or more of CO2, N2, butane, pentane, fluorinated olefins, alcohol, and water.

8. The method for preparing the PP material according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: adding polypropylene, optional chain extension monomer, modified nano zinc oxide, optional antioxidant and optional foaming agent into a twin-screw series single-screw extruder to perform melt grafting modification on the materials, and extruding and foaming to obtain a highly expandable PP material.

9. The preparation method according to claim 8, characterized in that: The processing temperature of the twin-screw extruder is 190-210°C; the processing temperature of the single-screw extruder is 150-180°C; the temperature of the single-screw extruder head is 140-170°C; the residence time is 1-15 minutes; Preferably, the processing temperature of the twin-screw extruder is 200-210°C; Preferably, the processing temperature of the single screw extruder is 160-180°C; Preferably, the extruder head temperature is 140-160°C.

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