CN117586577A - Polypropylene resin foaming particle and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of polypropylene resin foaming materials, and discloses polypropylene resin foaming particles and a preparation method thereof, wherein the polypropylene resin foaming particles comprise, by mass, 80-90 parts of polypropylene, 5-10 parts of a toughening agent, 4-12 parts of a filler, 0.3-1 part of a stabilizer, 0.2-2 parts of a lubricant and 0.1-0.5 part of a nucleating agent. The beneficial effects of the invention are as follows: the polypropylene resin foaming particles consist of polypropylene, a toughening agent and a filler, and the toughening agent and the filler can improve the toughness and strength of the resin. The zeolite, the diatomite and the white carbon black activated by the coupling agent are used as the filler, the filler activated by the coupling agent has good compatibility with the polypropylene resin, and can be uniformly dispersed in the polypropylene resin, and the zeolite, the diatomite and the white carbon black all contain a large number of micropores, so that the cell nucleation efficiency can be improved, and the foaming quality can be improved.

Description

Polypropylene resin foaming particle and preparation method thereof

Technical Field

The invention belongs to the technical field of polypropylene resin foaming materials, and particularly relates to polypropylene resin foaming particles and a preparation method thereof.

Background

The expanded polypropylene (EPP) is a high crystalline polypropylene/CO with excellent properties ₂ Composite material, the fastest growing environment-friendly novel compression-resistant buffer heat-insulating material at present. The EPP product has excellent shock resistance and energy absorption performance, high recovery rate after deformation, good heat resistance, chemical resistance, oil resistance and heat insulation. In addition, the weight of the product is light, and the weight of the product can be greatly reduced. EPP is a green environment-friendly material, can be recycled and reused, and does not cause white pollution.

In general, PP exists in a stable alpha crystal form, and has good comprehensive properties, but the alpha crystal form PP has poor impact resistance, so that the application range of the PP is limited. The PP in the beta crystal form can improve the toughness, and is shown to have greatly improved elongation at break and impact strength compared with the PP in the alpha crystal form, but the rigidity of the PP is reduced to different degrees, and the tensile strength and the elastic modulus are reduced. However, the beta crystalline form is an unstable thermodynamic state and is difficult to obtain under normal conditions. The rare earth beta-crystal nucleating agent has high nucleating efficiency and good stability in PP, and the PP with beta-crystal form is easy to obtain.

The beta-crystal nucleating agent has better adsorption effect and template effect on polypropylene, and can induce the polypropylene to generate beta-crystal form, but when EPP is prepared, a large amount of CO2 gas enters the interface between polypropylene melt and the nucleating agent in the bubble nucleation stage of the foaming process, so that the adsorption effect of the beta-crystal nucleating agent on polypropylene and the crystallization template effect are reduced, the generation of beta-crystal is not facilitated, and the beta-crystal nucleating agent mainly induces bubble nucleation.

Disclosure of Invention

The invention aims to provide polypropylene resin foam particles which have the effect of promoting beta crystal form nucleation and bubble nucleation simultaneously.

The technical aim of the invention is realized by the following technical scheme: the weight portions of the components are 80 to 90 portions of polypropylene, 5 to 10 portions of toughening agent, 4 to 12 portions of filler, 0.3 to 1 portion of stabilizer, 0.2 to 2 portions of lubricant and 0.1 to 0.5 portion of nucleating agent.

The invention is further provided with: the toughening agent comprises at least one of ethylene-butene copolymer, ethylene-octene copolymer and propenyl elastomer; the stabilizer comprises at least one of hindered phenol heat stabilizer, phosphite ester heat stabilizer and hindered amine light stabilizer; the lubricant comprises at least one of calcium stearate, PE wax, zinc stearate, ethylene bis-stearamide and erucamide.

The invention is further provided with: the filler comprises at least one of zeolite, diatomite and white carbon black after being activated by a coupling agent.

The invention is further provided with: the nucleating agent is a rare earth complex nucleating agent.

The invention is further provided with: the preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, putting nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding stearic acid and trimesic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the trimesic acid-stearic acid rare earth complex.

The invention is further provided with: the molar ratio of nitrate, stearic acid and octanol is 1:2:1.

The invention is further provided with: the nitrate rare earth comprises cerium nitrate and/or lanthanum nitrate.

The invention is further provided with: the method comprises the following steps:

s1, adding polypropylene resin, a toughening agent, a filler, a stabilizer, a lubricant and a nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, then adding supercritical fluid into a homogenization section of the three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foaming polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

The invention is further provided with: the supercritical fluid is supercritical CO ₂ The addition amount is 2-10% of the mass of the polypropylene foaming material.

The beneficial effects of the invention are as follows:

1. the polypropylene resin foaming particles consist of polypropylene, a toughening agent and a filler, and the toughening agent and the filler can improve the toughness and strength of the resin. The zeolite, the diatomite and the white carbon black activated by the coupling agent are used as the filler, the filler activated by the coupling agent has good compatibility with the polypropylene resin, and can be uniformly dispersed in the polypropylene resin, and the zeolite, the diatomite and the white carbon black all contain a large number of micropores, so that the cell nucleation efficiency can be improved, and the foaming quality can be improved.

2. The nucleating agent is a rare earth complex nucleating agent, the rare earth complex nucleating agent can efficiently induce beta crystal formation, and meanwhile, the crystallization rate of polypropylene is improved, so that the beta crystal form nucleating efficiency in the polypropylene resin prepared in the application reaches more than 95%, and the polypropylene resin has good toughness and high toughness, and can be obtained by combining the polypropylene filler with high toughness and strength.

3. The rare earth complex nucleating agent is a trimesic acid-stearic acid rare earth complex, stearic acid and trimesic acid are matched with rare earth at the same time, stearic acid nonpolar organic matters have good compatibility with polypropylene, and the stearic acid rare earth complex has good beta-crystal induction efficiency. The trimesic acid is a polar organic matter and has poor compatibility with polypropylene, so that the nucleation energy barrier at the interface of the trimesic acid and the polypropylene is lower. During the bubble nucleation stage, a large amount of CO ₂ The gas enters the interface between the polypropylene melt and the nucleating agent, and the nucleation energy barrier at the interface between the trimesic acid and the polypropylene is lower, so that the CO ₂ In benzene-threeThe formic acid is gathered to form bubbles, thereby avoiding the influence of the foaming process on the beta crystal nucleation process of the stearic acid rare earth complex. Beta-crystal nucleation and bubble nucleation in polypropylene resin foaming particles can be simultaneously promoted by adopting trimesic acid-stearic acid rare earth complex.

4. Under the action of stearic acid, trimesic acid-stearic acid rare earth complex nucleating agent can be uniformly dispersed in polypropylene, and trimesic acid and stearic acid are simultaneously matched with rare earth, so that trimesic acid and stearic acid are uniformly and alternately distributed on rare earth molecules, and therefore points with lower nucleation energy barrier exist nearby stearic acid uniformly, and CO is promoted ₂ Where it aggregates, thereby reducing the inhibition of beta nucleation by the foaming process.

Detailed Description

The technical solutions in the embodiments will be clearly and completely described below. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.

Example 1

The preparation method of the polypropylene resin foam particles comprises the following steps:

s1, adding 90 parts of polypropylene, 5 parts of ethylene-butene copolymer, 12 parts of zeolite activated by a coupling agent, 0.3 part of hindered phenol heat stabilizer, 2 parts of calcium stearate and 0.1 part of trimesic acid-stearic acid rare earth complex nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, and then adding supercritical CO accounting for 10% of the mass of the polypropylene foaming material ₂ Filling the mixture into a homogenization section of a three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foamed polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

The preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, placing 30mol of nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding 60mol of stearic acid and 30mol of trimesic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the trimesic acid-stearic acid rare earth complex.

Example 2

The preparation method of the polypropylene resin foam particles comprises the following steps:

s1, adding 85 parts of polypropylene, 8 parts of a propylene-based elastomer, 8 parts of white carbon black activated by a coupling agent, 0.6 part of a hindered amine light stabilizer, 4 parts of ethylene bis stearamide and 0.3 part of a trimesic acid-stearic acid rare earth complex nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, and then adding supercritical CO accounting for 6% of the mass of the polypropylene foaming material ₂ Filling the mixture into a homogenization section of a three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foamed polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

The preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, placing 30mol of nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding 60mol of stearic acid and 30mol of trimesic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the trimesic acid-stearic acid rare earth complex.

Example 3

The preparation method of the polypropylene resin foam particles comprises the following steps:

s1, adding 80 parts of polypropylene, 10 parts of ethylene-octene copolymer, 4 parts of diatomite activated by a coupling agent, 1 part of phosphite ester heat stabilizer, 0.2 part of PE wax and 0.5 part of trimesic acid-stearic acid rare earth complex nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, and then adding 2% of supercritical CO by mass of the polypropylene foaming material ₂ Filling the mixture into a homogenization section of a three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foamed polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

The preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, placing 30mol of nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding 60mol of stearic acid and 30mol of trimesic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the trimesic acid-stearic acid rare earth complex.

Example 4

The preparation method of the polypropylene resin foam particles comprises the following steps:

s1, adding 85 parts of polypropylene, 8 parts of a propylene-based elastomer, 8 parts of white carbon black activated by a coupling agent, 0.6 part of a hindered amine light stabilizer, 4 parts of ethylene bis stearamide and 0.3 part of a trimesic acid-stearic acid rare earth complex nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, and then adding supercritical CO accounting for 6% of the mass of the polypropylene foaming material ₂ Filling the mixture into a homogenization section of a three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foamed polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

The preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, placing 30mol of nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding 60mol of stearic acid and 30mol of trimesic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the trimesic acid-stearic acid rare earth complex.

Example 5

The preparation method of the polypropylene resin foam particles comprises the following steps:

s1, adding 85 parts of polypropylene, 8 parts of a propylene-based elastomer, 8 parts of white carbon black activated by a coupling agent, 0.6 part of a hindered amine light stabilizer, 4 parts of ethylene bis stearamide, 0.3 part of trimesic acid and 0.3 part of a stearic acid rare earth complex nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, and then adding supercritical CO accounting for 6% of the mass of the polypropylene foaming material ₂ Filling the mixture into a homogenization section of a three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foamed polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

The preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, placing 30mol of nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding 60mol of stearic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the stearic acid rare earth complex.

Example 6

The preparation method of the polypropylene resin foam particles comprises the following steps:

s1, adding 85 parts of polypropylene, 8 parts of a propylene-based elastomer, 8 parts of white carbon black activated by a coupling agent, 0.6 part of a hindered amine light stabilizer, 4 parts of ethylene bis stearamide and 0.3 part of a stearic acid rare earth complex nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, and then adding supercritical CO accounting for 6% of the mass of the polypropylene foaming material ₂ Filling the mixture into a homogenization section of a three-screw extruder, controlling the die pressure to be 5-25 Mpa and the die temperature to be 110-160 DEG CInstantaneously releasing pressure through a die, and foaming to obtain superfine microporous foamed polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

The preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, placing 30mol of nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding 60mol of stearic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the stearic acid rare earth complex.

Example 7

The preparation method of the polypropylene resin foam particles comprises the following steps:

s1, adding 85 parts of polypropylene, 8 parts of a propylene-based elastomer, 8 parts of white carbon black activated by a coupling agent, 0.6 part of a hindered amine light stabilizer and 4 parts of ethylene bis stearamide into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, and then adding supercritical CO accounting for 6% of the mass of the polypropylene foaming material ₂ Filling the mixture into a homogenization section of a three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foamed polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

Test data

Polypropylene foam samples were prepared by the method of examples 1 to 7, and the beta-form relative content, expansion ratio, cell density of the foam samples were examined, and the test data are shown in table 1 below.

The method for detecting the relative content of the beta crystal form adopts a wide-angle X-ray diffractometer, and the test conditions are as follows: the Cu target has an incident wavelength of 0.15418nm, and adopts working voltage and current of 40kV and 40mA, and the scanning angle ranges from 5 degrees to 40 degrees (2 theta).

Expansion ratioThe ratio of the volume of the prepared foaming material to the volume of the non-foaming raw material can be converted into the ratio of the density of the non-foaming raw material to the density of the foaming material.

Cell density detection method:

the beta nucleating agent modified polypropylene foaming sample is put into a vacuum flask filled with liquid nitrogen to be sealed and soaked for 90min, then the sample is quickly brittle broken, the cross section appearance of the foaming sample is obtained, and the section is subjected to vacuum gold plating twice. And (3) placing the gold-plated sample on an environmental scanning electron microscope sample stage, observing the morphology, selecting a uniform area for photographing, and recording the microscopic morphology of the foaming sample. Using cell calculation software to count the number of cells in the SEM picture, the cell density in three-dimensional space can be calculated from the calculated number of cells, and the cell density ρc of the sample is calculated using the formula: ρc= (n/a) 3/2 where n represents the total number of cells of the statistical SEM photograph and a is the actual area of the SEM photograph.

Table 1 examples 1-7 sample test data

As can be seen from the test data in Table 1, the better nucleation rate and foaming effect of the beta crystal form can be obtained by adopting the proportion in the examples 1-3, wherein the proportion effect of the example 2 is the best; as can be seen from examples 1 to 4, the relation between the expansion ratio and the cell density and the addition amount of the filler is large, and when the addition amount of the filler is 8 parts, a good foaming effect can be obtained, and the nucleating agent can also play a role in inducing foaming under the condition of not adding the filler, but the foaming effect is not addedThe filler adding effect is good; as can be seen from examples 5-7, trimesic acid-stearic acid rare earth complex nucleators are used in CO ₂ Under the foaming condition, the beta crystal form induction efficiency is optimal.

Claims (9)

1. A polypropylene resin foam particle characterized in that: the weight portions of the components are 80 to 90 portions of polypropylene, 5 to 10 portions of toughening agent, 4 to 12 portions of filler, 0.3 to 1 portion of stabilizer, 0.2 to 2 portions of lubricant and 0.1 to 0.5 portion of nucleating agent.

2. The polypropylene resin foam particles as claimed in claim 1, wherein: the toughening agent comprises at least one of ethylene-butene copolymer, ethylene-octene copolymer and propenyl elastomer; the stabilizer comprises at least one of hindered phenol heat stabilizer, phosphite ester heat stabilizer and hindered amine light stabilizer; the lubricant comprises at least one of calcium stearate, PE wax, zinc stearate, ethylene bis-stearamide and erucamide.

3. The polypropylene resin foam particles as claimed in claim 1, wherein: the filler comprises at least one of zeolite, diatomite and white carbon black after being activated by a coupling agent.

4. The polypropylene resin foam particles as claimed in claim 1, wherein: the nucleating agent is a rare earth complex nucleating agent.

5. The polypropylene resin foam particles as defined in claim 4, wherein: the preparation method of the rare earth complex nucleating agent comprises the following steps:

s1, putting nitrate rare earth into a three-neck flask, and adding deionized water into the three-neck flask for dissolution to obtain a nitrate rare earth solution;

s2, adding stearic acid and trimesic acid into the nitrate rare earth solution, adding absolute ethyl alcohol for dissolution, and finally adding an alkali solution;

s3, connecting the reaction kettle to a condensing reflux device, and stirring and reacting for 6 hours at 120 ℃;

s4, after the reaction is finished, carrying out suction filtration to obtain a solid, and washing and drying the solid by using absolute ethyl alcohol and water to obtain the trimesic acid-stearic acid rare earth complex.

6. The polypropylene resin foam particles as defined in claim 5, wherein: the molar ratio of nitrate, stearic acid and octanol is 1:2:1.

7. The polypropylene resin foam particles according to claim 6, wherein: the nitrate rare earth comprises cerium nitrate and/or lanthanum nitrate.

8. The method for producing polypropylene resin foam particles according to claim 1, wherein: the method comprises the following steps:

s1, adding polypropylene resin, a toughening agent, a filler, a stabilizer, a lubricant and a nucleating agent into a high-speed mixer, and uniformly mixing at 10-20 ℃ to obtain a polypropylene foaming material;

s2, adding the polypropylene foaming material into a three-screw extruder, plasticizing and mixing, then adding supercritical fluid into a homogenization section of the three-screw extruder, controlling the die pressure to be 5-25 Mpa, controlling the die temperature to be 110-160 ℃, and then instantly releasing pressure through the die to foam so as to obtain superfine microporous foaming polypropylene;

s3, carrying out heat exchange cutting granulation, drying and sieving on the superfine microporous foamed polypropylene through die surface water to obtain polypropylene resin foamed particles.

9. The method for producing polypropylene resin foam particles according to claim 1, wherein: the supercritical fluid is supercritical CO ₂ The addition amount is 2-10% of the mass of the polypropylene foaming material.