CN112831127A

CN112831127A - Expandable polypropylene particles, modified polypropylene expanded beads and preparation thereof

Info

Publication number: CN112831127A
Application number: CN202011636987.8A
Authority: CN
Inventors: 张曼玲; 彭天晓
Original assignee: New Ziyuan Shanghai technology Development Co ltd
Current assignee: New Ziyuan Shanghai technology Development Co ltd
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2021-05-25

Abstract

The invention relates to expandable polypropylene particles, modified polypropylene expanded beads and preparation thereof, wherein the preparation process of the expanded polypropylene beads comprises the following steps: firstly, weighing 1-90 parts of random copolymerization polypropylene resin, 1-30 parts of a graft and 0.01-20 parts of a functional additive according to the parts by weight, mechanically blending, and then mixing and extruding and granulating by an extruder to obtain expandable polypropylene particles; then, placing the expandable polypropylene particles, water, surfactant, dispersant and foaming agent into a high-pressure reaction kettle, pressurizing and heating to foam to obtain the modified polypropylene expanded beads. Compared with the prior art, the modified polypropylene beads provided by the invention have good toughness, are not easy to adhere, and are beneficial to a forming process; in addition, the preparation method has simple process and convenient operation, and is beneficial to realizing industrialization.

Description

Expandable polypropylene particles, modified polypropylene expanded beads and preparation thereof

Technical Field

The invention belongs to the technical field of polypropylene expanded beads, and relates to expandable polypropylene particles, modified polypropylene expanded beads and preparation thereof.

Background

The polypropylene resin foam material (EPP) has the advantages of light weight, heat insulation, sound insulation, buffering, high specific strength, low price and the like, so the EPP is widely applied to the fields of packaging industry, agriculture, transportation industry, automobile industry, daily necessities and the like. 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; meanwhile, the weight of the product is light, and the product weight can be greatly reduced; in addition, EPP is also an environment-friendly material, is easily subjected to beta degradation, and PP foam is easily recycled, and is superior to other foam materials in environmental friendliness, thus being called "green" foam. Due to the excellent performance, EPP becomes a novel foam material with higher application value and market potential after polystyrene (EPS), polyurethane (EPU) and polyethylene (EPE) foam materials.

However, in the prior art, the polypropylene foaming material also has the defects of insufficient weather resistance, weak toughness, easy brittleness at low temperature and the like, and the application of the polypropylene foaming material is undoubtedly limited by the defects. Therefore, in recent years, studies on the improvement of properties of the foamed polypropylene have been focused. The preparation of the foam material with uniform cell structure, large cell density and excellent mechanical property by combining PP crosslinking or graft modification to improve the melt strength of PP becomes a research focus. For blending other resin modified polypropylene, the interaction at the interface of PP and the blended resin becomes strong, more bubble nuclei can be formed after blending, and the cell density is increased. Thus, the crystallinity of the PP can be effectively reduced, and the melt strength of the PP is improved. However, in practice, it is found that blending other resin modified polypropylene can not facilitate the diffusion of bubbles in PP due to the increase of melt strength, so that the cells of PP are difficult to successfully foam. The structure of the cells directly affects the properties of the product. In view of the cell problem, it is necessary to modify its properties to meet the application requirements.

Disclosure of Invention

The invention aims to provide expandable polypropylene particles, modified polypropylene expanded beads and preparation thereof, so that prepared expandable polypropylene particles have the advantages of uniform cell structure, high cell density and good cell state, and the problem of cell merging or cracking is solved.

The purpose of the invention can be realized by the following technical scheme:

on one hand, the invention provides an expandable polypropylene particle, which comprises the following raw material components in parts by weight: 1-90 parts of random copolymerization polypropylene resin, 1-30 parts of graft and 0.01-20 parts of functional auxiliary agent.

Further, the melt flow rate of the random copolymerization polypropylene resin is 0.1-10 g/10min, and the melting point is 130-165 ℃. Preferably, the melt flow rate is from 0.2 to 5g/10 min. The polypropylene of random copolymerization has low crystallinity, low melting point, lower temperature and pressure for foaming, reduced pressure load of production equipment and contribution to stable operation of the equipment.

Further, the graft is one or more of styrene, polyethylene or ethylene-vinyl acetate copolymer. The present inventors have found, through careful study, that since polypropylene resin is a semicrystalline polymer, there are few molecular chains having a branched structure. During processing, when the processing temperature is lower than the melting point, the polypropylene melt is basically in a non-flowing state, but when the processing temperature is higher than the melt, the viscosity of the polypropylene melt is rapidly reduced, so that the melt is difficult to enclose gas, and further, the gas escapes, so that a high-quality foaming material cannot be obtained. Therefore, the purpose of adding the graft in the invention is to introduce a branched structure, increase the cross-linking points among macromolecules, increase entanglement points, increase the internal friction resistance among molecules, make the slippage among molecules relatively difficult, slowly reduce the viscosity along with the temperature rise, and improve the melt strength, thereby providing enough strength for cell walls in the foaming process, enclosing foaming gas, and reducing the phenomena of collapse, breakage, combination and the like of bubbles.

Furthermore, the functional auxiliary agent is one or more of nucleating agent, antioxidant, antistatic agent, foaming auxiliary agent or crosslinking agent. The nucleating agent is one or more of calcium carbonate, montmorillonite, citric acid, zinc borate, titanium dioxide, silicon dioxide, aluminum oxide, talcum powder, magnesium carbonate, benzoic acid or adipic acid, and the crystallization nucleating particles are 0.5-5 mu m; the antioxidant is used for preventing the PP from having poor heat oxidation resistance and being subjected to degradation reaction when heated in processing; the foaming auxiliary agent is used for promoting the PP particles to be foamed, improving the foaming process, stabilizing the cell structure and improving the foam quality; the crosslinking agent is used for increasing the strength of the wall of the bubble hole and fixing the structure of the polypropylene cell wall, the crosslinking agent does not achieve the structural effect of solidifying the polypropylene cell wall in a small amount, and excessive polypropylene is easy to agglomerate, so that the processing performance is influenced. On the other hand, the invention also provides a preparation method of the expandable polypropylene particles, which comprises the steps of weighing 1-90 parts of random copolymerization polypropylene resin, 1-30 parts of graft and 0.01-20 parts of functional auxiliary agent according to the parts by weight, mechanically blending, mixing by an extruder, extruding and granulating to obtain the expandable polypropylene particles.

Further, a mixing area of the extruder is sequentially divided into ten areas according to the advancing direction of the materials, wherein the temperature of one area is 110 ℃; the temperature of the second zone is 140 ℃; the temperature of the three zones is 190 ℃; the temperature of the fourth zone is 195 ℃; the temperature of the fifth area is 200 ℃; the temperature of the sixth zone is 205 ℃; the temperature of the seventh zone is 215 ℃; the temperature of the eight regions is 215 ℃; the temperature of the nine areas is 220 ℃; the temperature of ten areas is 220 ℃; the temperature of the extrusion head was 230 ℃; the melt pressure was 14 MPa. Wherein, the purpose of the first zone and the second zone is to soften various raw materials and is not too high easily; the temperature of the subsequent heating area mixing process is controlled to be between 160 ℃ and 250 ℃, the temperature is lower than 160 ℃, and the raw material PP particles cannot be completely melted, so that the raw material PP particles are not uniformly mixed with other components; the heating temperature must not exceed 250 c, otherwise partial thermal decomposition of the polypropylene may occur.

On the other hand, the invention also provides modified polypropylene foaming beads, which comprise the following raw material components in parts by weight: 1-10 parts of expandable polypropylene particles, 80-95 parts of water, 0.1-0.5 part of surfactant, 0.1-0.5 part of dispersant and 1-10 parts of foaming agent.

Further, water is used as a liquid medium for dissolving the dispersing agent and dispersing the polypropylene particles; the surfactant reduces the surface tension and surface free energy of water and prevents the polypropylene particles from being adhered to each other; the dispersing agent is used for preventing the polypropylene resin particles from being adhered to each other in a heating and softening state, and the effect of separating the polypropylene resin particles cannot be achieved by a small amount of the dispersing agent; the blowing agent is selected from CO₂The amount of the carbon dioxide is used for controlling the foaming pressure of the polypropylene resin particles, and the small amount of the CO is₂The foaming ratio cannot be reached to an ideal value, and the CO content is too high₂Collapse of the expanded polypropylene.

In addition, the invention also provides a preparation method of the modified polypropylene expanded bead, which comprises the steps of weighing the expandable polypropylene particles, water, the surfactant, the dispersing agent and the foaming agent according to the parts by weight, placing the expandable polypropylene particles, the water, the surfactant, the dispersing agent and the foaming agent into a high-pressure reaction kettle, and pressurizing and heating the mixture to obtain the modified polypropylene expanded bead through foaming.

Further, the method is characterized in that the pressurizing and heating process specifically comprises the following steps: firstly heating to 150 ℃ at 130-6 MPa and keeping the temperature for 30min, then continuously heating to 160 ℃ at 150-6 MPa and keeping the temperature for 30 min. When the polypropylene particles are heated, the autoclave body is heated by the heater, heat is transferred from the autoclave body to the medium water, the polypropylene particles are heated by heat transfer between the solution and the polypropylene particles, and a hysteresis process exists. The main purpose is to soften the polypropylene particles, CO₂Part of the polypropylene particles enter the polypropylene particles and reach the first-stage temperature equilibrium; the second stage temperature is around the melting point of the polypropylene particles and is primarily aimed at promoting CO₂During the dissolution of polypropylene, the condition that polypropylene particles are overheated due to temperature feedback lag is avoided, and the normal operation of the preparation process of the polypropylene particles is ensured.

Compared with the prior art, the polypropylene random copolymer is selected as a research object, and the temperature and the pressure for foaming are lowerThe pressure load of the production equipment is reduced, and the stable operation of the equipment is facilitated; firstly, extruding and granulating Mini-PP particles in an extruder by a blending thermal method, wherein the Mini-PP particles are uniform in size, and the foamed particles have a double-peak melting characteristic and are easy to mold in a steam mold; the invention adopts a high-pressure reaction kettle to perform supercritical CO₂The method for preparing the PP beads by using the foaming agent is environment-friendly and pollution-free, and the cell structure of the foaming beads is good; the product prepared by the invention has high toughness, certain lubricity and easy demoulding recovery. Therefore, the modified polypropylene beads prepared by the invention can realize industrialization.

Drawings

FIG. 1 is a DSC melting curve of expanded polypropylene beads prepared in example 1;

FIG. 2 is a SEM sectional view of expanded polypropylene beads of the product prepared in example 1;

FIG. 3 is an SEM sectional view of expanded polypropylene beads of a product prepared in comparative example 1;

FIG. 4 is an SEM sectional view of expanded polypropylene beads of a product prepared in comparative example 2;

FIG. 5 is an SEM sectional view of expanded polypropylene beads of a product prepared in comparative example 3;

FIG. 6 is an SEM sectional view of expanded polypropylene beads of the product prepared in comparative example 4.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

In a specific embodiment, the invention provides a preparation method of expanded polypropylene beads, which comprises the following steps:

(1) after the random copolymerization polypropylene resin, the graft and the functional auxiliary agent are put into a high-speed stirrer to be mixed for 5min at high speed, the mixed material is put into a feed hopper of an extruder, and a mixing area of the extruder is sequentially divided into ten areas according to the advancing direction of the material, wherein the temperature of one area is 110 ℃; the temperature of the second zone is 140 ℃; the temperature of the three zones is 190 ℃; the temperature of the fourth zone is 195 ℃; the temperature of the fifth area is 200 ℃; the temperature of the sixth zone is 205 ℃; the temperature of the seventh zone is 215 ℃; the temperature of the eight regions is 215 ℃; the temperature of the nine areas is 220 ℃; the temperature of ten areas is 220 ℃; the temperature of the extrusion die head is 230 ℃; the melt pressure was 14 MPa.

And (4) drawing out the output lines through a granulator, and granulating through cold water to obtain expandable polypropylene particles with the particle size of 0.8-1.2 mm and the length of 1.2-1.5 mm.

Then, the specific foaming process is as follows; firstly, weighing 2 parts of expandable polypropylene particles, 95 parts of water, 0.2 part of surfactant, 0.1 part of dispersant and 2.7 parts of foaming agent in parts by weight, placing the materials in a high-pressure reaction kettle, and then adjusting the pressure in the kettle to reach the pressure required by foaming under the stirring state; namely, the temperature is firstly raised to 150 ℃ in the first section and is kept for 30min under the pressure of 3MPa, and then, the temperature is continuously raised to 154 ℃ in the second section and is kept for 30min under the pressure of 3.5 MPa. Finally, the discharge port of the autoclave was opened to discharge the contents of the autoclave into a collection tank, thereby obtaining polypropylene expanded beads.

Table one: names of various kinds of raw materials and their addition amounts in example 1

Polypropylene	Graft body	Nucleating agent	Foaming aid	Antioxidant agent	Crosslinking agent
						RD208CF	GPPS123	Zinc borate	Fatty acid zinc salt	B225	DCP
85	14.04	0.2	0.3	0.4	0.06

Table two: experimental raw materials and experimental conditions for preparing polypropylene foaming material by high-pressure kettle

Formulation and process requirements of table III respective proportion components

	Polypropylene	Graft body	Cell nucleating agent	Foaming aid	Crosslinking agent	Antioxidant agent
							Example 1	85	14.04	0.2	0.3	0.06	0.4
Comparative example 1	85	0	0.2	0.3	0.06	0.4
							Comparative example 2	85	14.04	0	0.3	0.06	0.4
Comparative example 3	85	14.04	0.2	0	0.06	0.4
							Comparative example 4	85	14.04	0.2	0.3	0	0.4

FIG. A is a DSC curve of the expanded polypropylene of example one showing a low temperature melting peak at a temperature of 131 ℃; the high-temperature melting peak appears at 150 ℃, and the high-temperature melting peak has good bimodal melting crystallization characteristics, which indicates that the high-temperature melting peak is suitable for steam molding. Comparative example 1: compared with example 1, most of them are the same except that the addition of the graft is omitted. The SEM cross-sectional view of the polypropylene beads is shown in FIG. 2, the cells of the polypropylene particles are totally collapsed, the sizes of the cells are not uniform, and gas escape occurs. It can be seen that the present example solves the phenomenon of cell coalescence or cracking by introducing grafted leaves, and the beads have higher toughness.

Comparative example 2: compared to example 1, most of them are the same except that the addition of nucleating agent is omitted. The SEM cross-sectional view of the polypropylene beads is shown in FIG. 3, and the cells of the polypropylene particles are not foamed and appear white mist, which shows that the nucleating agent polypropylene particles play a role in inducing foaming during foaming.

Comparative example 3: compared with example 1, the method is mostly the same except that the addition of the foaming aid fatty acid zinc is omitted. The SEM sectional view of the polypropylene bead is shown in FIG. 4, the polypropylene particle cells have the phenomenon of large cell merging, the cell size is not uniform, and the phenomenon of cell merging can be changed by adding the foaming auxiliary agent.

Comparative example 4: compared to example 1, most of them are the same except that the addition of the crosslinking agent is omitted. The SEM cross-section of the polypropylene beads is shown in FIG. 4, with no crosslinker added, and with an open cell structure. The addition of the cross-linking agent solves the problem of cell combination or cracking.

The polypropylene foam material provided in the embodiment has high toughness and certain lubricity, and is easy to demould and recycle. Therefore, the modified polypropylene beads prepared by the method disclosed by the invention are easy to prepare into various special shapes, are durable and have wide application prospects in the fields of buildings, packaging and the like.

Example 2-example 11:

compared with the embodiment 1, the nucleating agent is mostly the same except that the nucleating agent adopted in the embodiment is respectively replaced by equal parts by weight of calcium carbonate, montmorillonite, citric acid, titanium dioxide, silicon dioxide, aluminum oxide, talcum powder, magnesium carbonate, benzoic acid or adipic acid.

Example 12-example 14:

compared with the embodiment 1, the foaming agent is mostly the same, except that the foaming agent used in the embodiment is replaced by stearic acid, ethanolamine or urea with equal weight parts.

In the above examples, the addition amounts of the respective raw materials used may be arbitrarily adjusted within the following ranges as required: 1-90 parts of random copolymerization polypropylene resin, 1-30 parts of graft and 0.01-20 parts of functional auxiliary agent, wherein the functional auxiliary agent is arbitrarily adjusted to the end value or the middle value of the range value.

The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.

Claims

1. The expandable polypropylene particles are characterized by comprising the following raw material components in parts by weight: 1-90 parts of random copolymerization polypropylene resin, 1-30 parts of graft and 0.01-20 parts of functional auxiliary agent.

2. The expandable polypropylene particles as claimed in claim 1, wherein the melt flow rate of the random copolymer polypropylene resin is 0.1-10 g/10min, and the melting point is 130-165 ℃;

the graft is one or more of styrene, polyethylene or ethylene-vinyl acetate copolymer.

3. The expandable polypropylene particles of claim 1, wherein the functional additive is one or more of nucleating agent, antioxidant, foaming additive or crosslinking agent.

4. The expandable polypropylene particles of claim 3, wherein the nucleating agent is one or more of calcium carbonate, montmorillonite, citric acid, zinc borate, titanium dioxide, silica, alumina, talc, magnesium carbonate, benzoic acid, or adipic acid.

5. The expandable polypropylene particles of claim 3, wherein the foaming aid is one or more of zinc fatty acid, stearic acid, ethanolamine or urea.

6. The process for preparing expandable polypropylene particles according to any one of claims 1 to 5, wherein the expandable polypropylene particles are obtained by weighing the random copolymer polypropylene resin, the graft and the functional assistant in parts by weight, mechanically blending, mixing by an extruder, extruding and granulating.

7. The process for preparing expandable polypropylene particles according to claim 6, wherein the mixing zone of the extruder is divided into ten zones in order according to the traveling direction of the material, wherein the temperature of one zone is 110 ℃; the temperature of the second zone is 140 ℃; the temperature of the three zones is 190 ℃; the temperature of the fourth zone is 195 ℃; the temperature of the fifth area is 200 ℃; the temperature of the sixth zone is 205 ℃; the temperature of the seventh zone is 215 ℃; the temperature of the eight regions is 215 ℃; the temperature of the nine areas is 220 ℃; the temperature of ten areas is 220 ℃; the temperature of the extrusion head was 230 ℃; the melt pressure was 14 MPa.

8. The modified polypropylene expanded bead is characterized by comprising the following raw material components in parts by weight: 1-10 parts of expandable polypropylene particles according to any one of claims 1-5, 80-95 parts of water, 0.1-0.5 part of surfactant, 0.1-0.5 part of dispersant and 1-10 parts of foaming agent.

9. The method for preparing the modified polypropylene expanded beads according to claim 8, wherein the expandable polypropylene particles, water, the dispersing agent and the foaming agent are weighed according to the parts by weight and placed in a high pressure reactor, and the expandable polypropylene particles are expanded by heating under pressure to obtain the modified polypropylene expanded beads.

10. The method for preparing the modified polypropylene expanded beads according to claim 9, wherein the heating under pressure comprises the following steps: firstly heating to 150 ℃ at 130-6 MPa and keeping the temperature for 30min, then continuously heating to 160 ℃ at 150-6 MPa and keeping the temperature for 30 min.