CN109265825B

CN109265825B - Polypropylene or polypropylene compound foamed product and preparation method thereof

Info

Publication number: CN109265825B
Application number: CN201811040415.6A
Authority: CN
Inventors: 周应国; 谭啸天
Original assignee: Jiangsu University of Science and Technology
Current assignee: Chongqing Shichuangxin Polymer Material Co ltd
Priority date: 2018-09-06
Filing date: 2018-09-06
Publication date: 2021-01-05
Anticipated expiration: 2038-09-06
Also published as: CN109265825A

Abstract

The invention discloses a polypropylene or polypropylene compound foaming product and a preparation method thereof, wherein polypropylene cold-drawn fibers are added into polypropylene or a blending material thereof according to a certain proportion, and the polypropylene or polypropylene compound foaming product with micropores with specific orientation is prepared by adopting any one mode of water foaming injection, chemical foaming injection, supercritical fluid foaming injection or chemical foaming/supercritical fluid foaming composite injection. The method has wide application range, and can be produced in a common injection machine and a supercritical fluid injection machine; compared with similar foaming injection products, the foaming product prepared by the method has obviously improved tensile strength and elongation at break.

Description

Polypropylene or polypropylene compound foamed product and preparation method thereof

Technical Field

The invention relates to a polypropylene or polypropylene composite foamed product and a preparation method thereof, belonging to the technical field of polymer materials.

Background

In recent years, polymer foamed products have been widely used in the industries of packaging, construction, automobile industry, aerospace, sports equipment and the like because of the advantages of sound insulation, shock absorption, heat insulation, raw material saving and the like. Among them, the polymer foaming injection products are more and more emphasized because of the characteristics of strong production adaptability, high efficiency, easy automatic operation, small shrinkage and warping amount of the products, and the like. Generally, the cells inside the foamed article are formed by the generation or addition of some gas from the plastic raw material during the forming process. According to the cell formation and the type of the foaming agent, chemical foaming, physical foaming, mechanical mixing foaming and the like can be included, and from the viewpoint of the processing method of the foamed product, there are mainly batch type, continuous extrusion method and injection molding method, and these methods have advantages and disadvantages, and thus have various degrees of application.

However, the mechanical properties of foamed products usually have large differences, and the differences are greatly influenced by structural parameters such as cell size, density, distribution and morphology, wherein the control of cell morphology and distribution is the most difficult and complicated. The problems to be solved by polypropylene foamed products are that the melt strength is improved, the escape of foaming gas is reduced, and the nucleation rate of the material is improved. Meanwhile, compared with similar solid products, the polypropylene foaming product often has the conditions of reduced tensile strength and greatly reduced elongation at break, the cells of the polymer microporous product are widely considered to be in a spherical or nearly spherical shape at present, and the cell shape is rarely considered to be regulated to a form more beneficial to improving the product performance.

Therefore, there is a need for a foaming method that can greatly improve the performance of polypropylene and its blend foamed products. The literature (Ying-Guo Zhou, Bei Su, Hai-Hong wu. effect of Cold-dry Fibers on the Self-compensation of the PP/LDPE Composites [ J ]. Journal of Materials Engineering and Performance, 2017, 26(8), 4072-4082.) studies that polypropylene or Composites thereof can be drawn below their heat distortion temperature to form Cold drawn Fibers which have a more stable thermodynamic structure than the original polypropylene or Composites thereof. The invention envisages that the addition of such cold drawn fibres may give the following effect to the foaming of the material: in the subsequent heating and melting process, a part of the microfilament is in a semi-molten state, namely a part of the microfilament is not completely molten, so that the final result is that a part of the microfilament can be used as a heterogeneous nucleating agent in the foaming process, the melt strength can also be improved, in addition, the crystallization process of polypropylene or a compound thereof can be accelerated in the material cooling process, the early locking of cells is caused, the gas is not easy to escape, and meanwhile, in the injection filling process, the microfilament can be oriented along the flow direction, and then the change of the micropore morphological structure can be induced in the subsequent foaming process. The above-mentioned various techniques can improve the expandability of polypropylene or a composite thereof, but the above-mentioned assumption is merely a theoretical analysis, and whether it is actually effective or not is to be further verified.

Disclosure of Invention

The purpose of the invention is as follows: the technical problem to be solved by the invention is to provide a polypropylene or polypropylene composite foamed product, which has good tensile strength and elongation at break because the foamed product has micropores consistent with the stress direction (flow direction) inside.

The technical problem to be solved by the invention is to provide the preparation method of the polypropylene or polypropylene compound foaming product agent, the method has wide application range, can be produced in a common injection machine and a supercritical fluid injection machine, has simple process and convenient operation when being produced in a common injection molding machine, and does not need to change any equipment; compared with the similar micro-foaming injection products, the foaming product prepared by the method has the advantages that the tensile strength and the elongation at break of the product are obviously improved.

The invention content is as follows: in order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a polypropylene or polypropylene composite foamed product, wherein micropores in the foamed product are arranged in a specific orientation, and the specific orientation is that the micropores are parallel to a flow direction.

The preparation method of the polypropylene or polypropylene compound foaming product comprises the steps of adding the polypropylene cold drawn fibers into the polypropylene or the blending material thereof according to a certain proportion, and preparing the polypropylene or polypropylene compound foaming product with micropores with specific orientation by adopting one mode of water foaming injection, chemical foaming injection, supercritical fluid foaming injection or chemical foaming/supercritical fluid foaming compound injection.

The polypropylene cold-drawn fiber is prepared by the following method: stretching polypropylene 500-800% below its crystallization temperature, and cutting the stretched material into grains; wherein the length of the particles is 3-15 mm, the width is 1-4 mm, and the thickness is 0.5-1.5 mm.

Further preferably, the preparation method of the polypropylene or polypropylene composite foamed product specifically comprises the following steps:

step 1, stretching polypropylene 500-800% below the crystallization temperature, and cutting the stretched material into particles; wherein the length of the particles is 3-15 mm, the width is 1-4 mm, and the thickness is 0.5-1.5 mm; the polypropylene is a homopolymerization or copolymerization product, the melt flow rate of the polypropylene is 1-20 g/10min (230 ℃, 21.6N), the melting temperature of the polypropylene is 160-166 ℃, and the elongation at break of the polypropylene exceeds 500%;

step 2, adding the particles into polypropylene or a blending material thereof according to 5-50% of the total mass of the mixing material, and uniformly mixing to prepare a mixing material; the polypropylene in the step 2 is the same as or different from the polypropylene for preparing the cold-drawn fibers (in the step 1), but in order to ensure that foaming injection can be carried out in a common injection machine, the flow rate of the polypropylene melt in the step 2 is not too high and is 1-50 g/10min (230 ℃, 21.6N); the other blending materials in the blending materials can be one or more of high-density polyethylene, low-density polyethylene or linear low-density polyethylene, namely, one or more of high-density polyethylene, low-density polyethylene or linear low-density polyethylene is/are added into polypropylene as the blending material, the adding amount of the blending material accounts for 0-50% of the total mass of all the blending materials, the melt flow rate of the low-density polyethylene used in the invention is 1-20 g/10min (190 ℃, 21.6kg), and the melt flow rate of the high-density polyethylene is 7.6g/10min (190 ℃, 21.6 kg);

step 3, putting the mixed material into an injection molding machine, and producing a foamed product with micropores with specific orientation through the action of a proper amount of gas; wherein the temperature of the melt in the injection molding machine is 166-172 ℃; wherein, the gas in the step 3 is gas obtained by compounding one or two of chemical foaming master batch decomposition or supercritical fluid decompression transformation, or gas obtained by water thermal decomposition.

Further preferably, the method for preparing the foamed product by combining the polypropylene cold-drawn fiber with the chemical foaming injection specifically comprises the following steps:

step 1, mixing the dried foaming agent, foaming auxiliary agent, nucleating agent, dispersing agent and carrier resin according to a certain proportion, and then obtaining a foaming master batch through an extruder;

step 2, stretching polypropylene 500-800% below the crystallization temperature, and cutting the stretched material into particles; wherein the length of the particles is 3-15 mm, the width is 1-4 mm, and the thickness is 0.5-1.5 mm;

step 3, adding the particles into polypropylene or a blending material thereof according to a proportion of 5-50% of the total mass of the mixing material, adding the foaming master batch prepared in the step 1 according to a certain proportion, wherein the mass ratio of effective components of a foaming agent in the foaming master batch is 0.4-1.0%, and uniformly mixing to obtain a mixing material;

and 4, putting the mixed material into an injection machine, wherein the temperature of a melt in the injection machine is 166-172 ℃.

In the step 1, the foaming master batch comprises the following components in parts by mass: 10-30 parts of foaming agent, 4-8 parts of dispersing agent, 5-10 parts of nucleating agent and 50-80 parts of carrier resin; wherein the addition amount of the foaming auxiliary agent is 10.5-11.3% of the mass of the foaming agent; the foaming agent is azodicarbonamide; the foaming auxiliary agent is one or the mixture of zinc oxide and barium oxide; the dispersing agent is PE wax; the nucleating agent is nano titanium dioxide or nano silicon dioxide; the carrier resin is polyethylene; the decomposition temperature of the chemical foaming master batch is 130-160 ℃, the temperature of an extruder is set to be 120-125 ℃ in the extrusion process, the foaming agent is likely to decompose in advance when the temperature is too high, and the plasticizing is not facilitated when the temperature is too low.

Further preferably, the method for preparing the foamed product by using the polypropylene cold-drawn fiber combined with water foaming injection specifically comprises the following steps:

step 1, stretching polypropylene 500-800% below the crystallization temperature, and cutting the stretched material into particles; wherein the length of the particles is 3-15 mm, the width is 1-4 mm, and the thickness is 0.5-1.5 mm;

step 2, mixing required amount of activated carbon, polypropylene and blends thereof, and then preparing a carrier material by a plastic extruder; the activated carbon accounts for 0.5-1.0% of the mass of the whole carrier material;

step 3, uniformly dispersing a proper amount of water in the carrier material prepared in the step 2 to form a water-containing mixed material; the used water is distilled water, the mass of the added water is 0.8-1.5% of the mass of the whole water-containing mixed material, one or more inorganic substances such as sodium chloride, calcium chloride or manganese chloride are added into the water and dissolved in the water to form a nucleating agent, and the using amount of the nucleating agent is 0.5-2% of the using amount of the water;

step 4, adding 5-50% of the particles prepared in the step 1 into the water-containing mixed material obtained in the step 3 by mass percent, and uniformly mixing to obtain a mixed material;

and 5, putting the mixed material into an injection machine, wherein the temperature of a melt in the injection machine is 166-172 ℃.

Further preferably, the method for preparing the foamed product by using the polypropylene cold drawn fiber and the supercritical fluid foaming injection specifically comprises the following steps:

step 2, adding the particles prepared in the step 1 into polypropylene or a blending material thereof according to 5-50% of the total mass of the mixing material, and uniformly mixing to obtain a mixing material;

step 3, putting the mixed material into an injection molding machine with a supercritical fluid injection device, and preparing a foamed product with micropores with specific orientation under specific process conditions (specific melt temperature); wherein the melt temperature in the injection molding machine is 166-172 ℃; the supercritical fluid is one or the composition of two of supercritical nitrogen or carbon dioxide, and the injection amount of the supercritical fluid is 0.3-1.0% of the mass of the foaming product.

If a composite injection mode of combining polypropylene cold-drawn fibers with chemical foaming/supercritical fluid foaming is adopted to prepare a foaming product, namely, foaming master batch is added in the step 2, the dosage of the supercritical fluid in the step 3 can be adjusted according to 2-4% of the addition amount of the foaming master batch, so that the dosage of the effective components of the foaming master batch and the dosage of the supercritical fluid are respectively controlled between 0.4-1.0% and 0.3-1.0%.

The principle of the preparation method of the invention is as follows: the polypropylene cold drawn fiber has a more stable thermodynamic structure than the original polypropylene, and in the subsequent heating and melting process, because the heating temperature is limited, the polypropylene cold drawn fiber is basically in a semi-molten state within 172 ℃, namely a part of the micro-filaments are not completely molten, the part of the micro-filaments can be used as heterogeneous nucleating agents in the foaming process, the melt strength is slightly improved, in addition, the crystallization process of the polypropylene or the compound thereof can be accelerated in the material cooling process, the early locking of foam holes is caused, the gas is not easy to escape, meanwhile, in the injection filling process, the foam holes can be oriented along the flow direction (the flow direction in the melt injection filling process), and then the change of the micro-pore structure can be induced in the subsequent foaming process. Because of the orientation of the cells in the direction of flow (cells aligned with the direction of flow) and this orientation can be fixed. The stretching direction of the part is parallel to the orientation direction of the foam pores, so that the mechanical property of the part is greatly improved, and the orientation of the micro pores of the part along the flow direction can ensure that the pores are easily communicated in the stretching process, so that the phenomenon that a bundle of fibers is stretched quickly appears, and the thin neck of the fiber is easily expanded in the stretching process and the elongation at break is high.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that:

the method can prepare the polypropylene or polypropylene compound microporous product with the oriented cells along the flow direction, and the cells of the product are easier to be mutually communicated when the product is stretched along the orientation direction of the micropores, so that the foamed product shows extremely high elongation at break, the elongation at break of the foamed product prepared by the method is over 500 percent, compared with the common foamed injection product, the mechanical property of the foamed product is greatly improved, the tensile strength of the foamed product is effectively improved by over 15 percent, and the ductility of the foamed product is over 3 times that of the common foamed injection product; the method has wide application range, can be produced in a common injection machine and a supercritical fluid injection machine, has simple process and convenient operation when being produced in the common injection molding machine, and does not need to change any equipment; several foaming injection methods used in the process do not have any residue that could affect the properties of the final foamed article; the cold-drawn fiber adopted by the method is also from a polypropylene material, and has no problem of compatibility difference with the polypropylene material for processing, thereby being simple and easy to implement.

Drawings

FIG. 1 is a process flow diagram of a foamed article of the present invention;

FIG. 2 is a diagram showing an embodiment of the production method of the present invention;

FIG. 3 is a scanning electron microscope image of the cell morphology of the foamed article perpendicular to the length direction (the longitudinal direction of the standard tensile bars in FIG. 2 is the length direction) prepared in example 1;

FIG. 4 is a scanning electron microscope image of the cell morphology of the foamed article parallel to the length direction prepared in example 1;

FIG. 5 is a scanning electron microscope image of the cell morphology of the foamed article perpendicular to the length direction prepared in comparative example 1;

FIG. 6 is a scanning electron microscope image of the cell morphology of the foamed article parallel to the length direction prepared in comparative example 1.

Detailed Description

The technical solution of the present invention is further described with reference to the following specific examples.

The process flow of the preparation method of the invention is shown in figure 1. In terms of raw materials, the polypropylene (PP) used is domestic T30S, the melt flow index of the low-density polyethylene (LDPE) is domestic 951-000, the melt flow index of the low-density polyethylene (LDPE) is domestic T30S, the melt flow index of the low-density polyethylene (LDPE) is domestic 951-000, the melt flow index of the high-density polyethylene (HDPE) is Taiwan plastic 8008, the melt flow index of the high-density polyethylene (HDPE) is 7.6g/10min (190 ℃, 2.16kg), the high-temperature AC foaming agent used is a commercially available Dn8 type, the average particle size of the high-temperature AC foaming agent is 6-8 mu m, the gas amount generated by complete decomposition exceeds 220ml/g, and the decomposition starting temperature is 192.2 ℃ and the decomposition peak value is 217.2 ℃ under the test condition of the temperature rising rate of 10 ℃/min by differential scanning calorimetry. The other used auxiliary agents are commercially available, wherein the foaming auxiliary agent adopts ZnO, the particle diameters of nano titanium dioxide, nano silicon dioxide and the like are all within 100 nanometers, the high-melting-point PE wax is used as a dispersing agent, and the melting point of the PE wax is about 105 ℃. In fig. 2, e is the profile of the article, and the longitudinal direction is the length direction of the article.

Example 1

This example utilizes a chemically foaming masterbatch to generate gas and then regulate the cell morphology of polypropylene and its blends to foam injection articles. The specific implementation path is shown in fig. 2, in the aspect of equipment, a common injection machine and an extruder are needed, the injection machine can be in hydraulic transmission, full-electric or electrohydraulic combination, the injection machine does not need to be additionally provided with a self-locking nozzle, a used mold is a standard stretching sample strip, and the extruder used for mixing raw materials can be in a single-screw or double-screw mode.

The method for preparing the foamed product by combining the polypropylene cold-drawn fiber with the chemical foaming injection specifically comprises the following steps:

step 1, manufacturing a foaming master batch: weighing the following raw materials by mass: LDPE (Low-Density polyethylene): 0.7995kg, AC: 0.1kg, ZnO: 0.0105kg, high melting PE wax: 0.04kg, nano titanium dioxide: 0.05 kg; respectively drying the raw materials, uniformly mixing in a mixing roll, and obtaining a foaming master batch through a double-screw extruder, wherein the melt temperature is 120 ℃ in the extrusion process (the decomposition temperature of the chemical foaming master batch is 130-160 ℃, and the decomposition temperature of the melt is 120 ℃ lower than the decomposition temperature so as to avoid the decomposition of the chemical foaming master batch);

step 2, preparing polypropylene cold-drawn fibers: placing polypropylene into an injection machine, stretching the polypropylene 700-800% in a room temperature environment, and cutting the stretched material section into polypropylene cold-drawn particles with the length of 3mm, the width of about 1mm and the thickness of about 0.5 mm;

step 3, weighing the raw material polypropylene: 5.4KG, polypropylene Cold drawn pellets: 4KG, foaming masterbatch: 0.6KG, and preparing a mixed material after uniformly mixing;

step 4, putting the mixed material into a common injection machine to process and produce a product; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

Finally, the prepared microporous polypropylene product is subjected to tensile property test, and the test results are shown in table 1.

To illustrate the effects of the present invention, comparative example 1 is illustrated, the raw material preparation process is similar to that of example 1, the preparation method of comparative example 1 is compared with example 1 without step 2 and without adding the polypropylene cold-drawn particles in step 3, and the polypropylene microporous article prepared in comparative example 1 is subjected to the tensile property test, and the test results are also shown in table 1. In addition, the samples of example 1 and comparative example 1 were characterized by Scanning Electron Microscopy (SEM) in the vertical and flow directions at the same positions in the middle, and the results are shown in fig. 3, 4, 5, and 6, respectively. Wherein FIGS. 3 and 5 are SEM results of cross-sectional cell morphology taken perpendicular to the length of the standard tensile bars shown in FIG. 2, FIGS. 4 and 6 are SEM results of cross-sectional cell morphology taken parallel to the length, and FIGS. 3 and 4 are taken for the article of example 1, and FIGS. 5 and 6 are the same for the article of comparative example 1. As is apparent from a comparison of fig. 3 and 5, fig. 3 shows that the article has a large number of internal micropores and a small size of micropores, and the distribution of micropores is relatively uniform, while fig. 5 shows the cell structure of comparative example 1, the number is small, the size is large, the difference in cell distribution is large, because of the sampling direction, the cells shown in figures 3 and 5 are circular, the holes in the actual article are not all spherical, which can be supplemented by the results of figures 4 and 6, as can be seen from a comparison of figures 4 and 6, the holes in fig. 4 have a more pronounced directionality (orientation), and this directionality is consistent with the direction of flow of the melt in the mold cavity, the pores are more ellipsoidal and are more elongated than the result in fig. 6, whereas the ellipsoids in fig. 6 are more circular and the micropores in fig. 6 also have no significant orientation.

It can be seen from the comparison between fig. 3 and 4 and fig. 5 and 6 and the data in table 1 that the microcellular foamed products prepared by the method of the present invention can be conveniently prepared in a common injection machine, and meanwhile, the cellular structures of the products are uniform, the cells have strong orientation in the flow direction (consistent with the flow direction of the melt in the mold cavity), the tensile strength of the products is improved by more than 17%, the ductility of the products is more than 5 times that of the conventional PP foamed products, and compared with the conventional PP solid products shown in comparative example 11, the tensile strength and the elongation at break of the products are both superior to those of the conventional PP solid products, thereby showing obvious application prospects.

Example 2

This example utilizes a chemically foaming masterbatch to generate gas and then regulate the cell morphology of polypropylene and its blends to foam injection articles. In the aspect of equipment, a common injection machine and an extruder are needed, the injection machine can be in hydraulic transmission, full-electric or electro-hydraulic combination, the injection machine does not need to be additionally provided with a self-locking nozzle, a used mold is a standard stretching sample strip, and the extruder used for mixing raw materials can be in a single-screw or double-screw mode.

first, a foaming master batch was produced: weighing the following raw materials by mass: LDPE (Low-Density polyethylene): 0.4861kg, AC: 0.3kg, ZnO: 0.0339kg, high melting point PE wax: 0.08kg, nano silica: 0.1 kg; respectively drying the raw materials, uniformly mixing in a mixing roll, and obtaining a foaming master batch through a double-screw extruder, wherein the melt temperature is 125 ℃ in the extrusion process;

secondly, polypropylene cold drawn fibers were prepared: placing polypropylene into an injection machine, stretching the polypropylene 700-800% in a room temperature environment, and cutting the stretched material section into polypropylene cold-drawn particles with the length of 15mm, the width of about 4mm and the thickness of about 1.5 mm;

then, weighing the raw material polypropylene: 27.5KG, polypropylene cold drawn pellets: 1.5KG, foaming masterbatch: 1KG, and preparing a mixed material after uniformly mixing;

then, the mixed material is put into a common injection machine to be processed into a product; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

To illustrate the effects of the present invention, comparative example 2 is further illustrated, wherein the raw material preparation process is similar to that of example 2, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 2 is subjected to tensile property test, and the test results are also shown in Table 1. It can be seen from the data in table 1 that although the polypropylene cold-drawn pellets added to the blend in the preparation method of example 2 are not much, the performance of the microporous article is also significantly improved.

Example 3

This example is the use of water as a blowing agent to decompose by heating to generate gas and then to regulate the cell morphology of polypropylene and its blends to foam injection articles. In the aspect of equipment, a common injection machine and an extruder are needed, the injection machine can be in hydraulic transmission, full-electric or electro-hydraulic combination, the injection machine does not need to be additionally provided with a self-locking nozzle, a used mold is a standard stretching sample strip, and the extruder used for mixing raw materials can be in a single-screw or double-screw mode.

The method for preparing the foamed product by utilizing the polypropylene cold-drawn fiber combined with the water foaming injection specifically comprises the following steps:

first, a polypropylene cold drawn fiber was prepared: placing polypropylene into an injection machine, stretching the polypropylene 700-800% in a room temperature environment, and cutting the stretched material section into polypropylene cold-drawn particles with the length of 10mm, the width of about 2mm and the thickness of about 1 mm;

secondly, manufacturing a carrier material: mixing activated carbon, polypropylene and blends thereof, and then preparing a carrier material by using a common plastic extruder; the active carbon accounts for 0.5 percent of the total mass of the whole carrier material;

thereafter, a mixed mass is formed: uniformly dispersing distilled water added with 0.5 mass percent of sodium chloride into the carrier master batch prepared in the step 1 to form a water-containing mixed material, wherein the mass content of the water is 0.8-1.5 percent of the mass content of the whole water-containing mixed material, adding the polypropylene cold-drawn particles into the water-containing mixed material according to the proportion of 20 mass percent of the mixed material, and uniformly mixing to prepare a mixed material;

then, processing the product: putting the mixed material into a common injection machine to process and produce a product; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

To illustrate the effects of the present invention, comparative example 3 is further illustrated, wherein the raw material preparation process is similar to that of example 3, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 3 is subjected to tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the foamed article obtained by adding 20% polypropylene cold-drawn particles are greatly improved.

Example 4

secondly, manufacturing a carrier material: mixing activated carbon, polypropylene and blends thereof, and then preparing a carrier material by using a common plastic extruder; the active carbon accounts for 1.0 percent of the total mass of the whole carrier material;

thereafter, a mixed mass is formed: uniformly dispersing distilled water added with 2.0 mass percent of sodium chloride into the carrier master batch prepared in the step 1 to form a water-containing mixed material, wherein the mass content of the water is 1.5 percent of the whole water-containing mixed material, adding the polypropylene cold-drawn particles into the water-containing mixed material according to the proportion of 30 mass percent of the mixed material, and preparing the mixed material after uniformly mixing;

and then, processing the product. Putting the mixed material into a common injection machine to process and produce a product; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

To illustrate the effects of the present invention, comparative example 4 is further illustrated, wherein the raw material preparation process is similar to that of example 4, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 4 is subjected to tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the foamed article obtained by adding 30% polypropylene cold-drawn particles are greatly improved.

Example 5

This example is to use supercritical fluid as blowing agent to control the cell morphology of polypropylene and its blend foaming injection products. On the equipment side, an injection machine with supercritical fluid injection function (for example, a commercialized MUCELL micro-foaming injection molding machine) and a common extruder are required, the mold used is a standard tensile bar, and the extruder used for raw material mixing may be a single screw or a twin screw.

The method for preparing the foaming product by utilizing the polypropylene cold-drawn fiber and the supercritical fluid foaming injection comprises the following steps:

secondly, manufacturing a mixed material: weighing: uniformly mixing 8KG polypropylene and 2KG polypropylene cold-drawn particles to prepare a mixed material;

thereafter, the article is processed: placing the mixed material into the supercritical fluid micro-foaming injection molding machine, and introducing supercritical nitrogen with the total injection mass of 1.0% to produce a foaming product with a specific micropore form; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

To illustrate the effects of the present invention, comparative example 5 is further illustrated, wherein the raw material preparation process is similar to that of example 5, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 5 is subjected to tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the foamed article obtained by adding 20% polypropylene cold-drawn particles are greatly improved.

Example 6

The embodiment utilizes the combined action of the supercritical fluid and the chemical foaming master batch as the foaming agent to regulate and control the cell morphology of the polypropylene and the blend foaming injection product thereof. On the equipment side, an injection machine with supercritical fluid injection function (for example, a commercialized MUCELL micro-foaming injection molding machine) and a common extruder are required, the mold used is a standard tensile bar, and the extruder used for raw material mixing may be a single screw or a twin screw.

The specific implementation steps of embodiment 6 are as follows:

first, a polypropylene cold drawn fiber was prepared: placing polypropylene into an injection machine to prepare a sample strip, stretching the sample strip by 700-800% at room temperature, and cutting the stretched material segment into polypropylene cold-drawn particles with the length of 10mm, the width of about 2mm and the thickness of about 1 mm;

next, a foaming master batch was produced: weighing the following raw materials by mass: LDPE (Low-Density polyethylene): 0.638kg, AC: 0.2kg, ZnO: 0.022kg, high melting PE wax: 0.06kg, nano silica: 0.08 kg; respectively drying the raw materials, uniformly mixing in a mixing roll, and obtaining a foaming master batch through a double-screw extruder, wherein the melt temperature is 125 ℃ in the extrusion process;

thirdly, manufacturing a mixed material: weighing: 7.8KG of polypropylene, 0.2KG of foaming master batch and 2KG of polypropylene cold-drawn particles are uniformly mixed to prepare a mixed material;

thereafter, the article is processed: putting the mixed material into the supercritical fluid micro-foaming injection molding machine, and introducing supercritical carbon dioxide which accounts for 0.4% of the total injection mass to produce a foaming product with a specific micropore shape; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

To illustrate the effects of the present invention, comparative example 6 is further illustrated, wherein the raw material preparation process is similar to that of example 6, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 6 is subjected to the tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the foamed article obtained by adding 20% polypropylene cold-drawn particles are greatly improved.

Example 7

Example 7 specific implementation procedure:

first, a foaming master batch was produced: weighing the following raw materials by mass: LDPE (Low-Density polyethylene): 0.7995kg, AC: 0.1kg, ZnO: 0.0105kg, high melting PE wax: 0.04kg, nano titanium dioxide: 0.05 kg; respectively drying the raw materials, uniformly mixing in a mixing roll, and obtaining a foaming master batch through a double-screw extruder, wherein the melt temperature is 120 ℃ in the extrusion process;

secondly, polypropylene cold drawn fibers were prepared: placing polypropylene into an injection machine to prepare a sample strip, stretching the sample strip by 700-800% at room temperature, and cutting the stretched material segment into polypropylene cold-drawn particles with the length of 3mm, the width of about 1mm and the thickness of about 0.5 mm;

then, weighing the raw material polypropylene: 4.75KG, low density polyethylene 2.25KG, polypropylene cold drawn pellets: 2KG, foaming master batch: 1KG, and preparing a mixed material after uniformly mixing;

To illustrate the effects of the present invention, comparative example 7 is further illustrated, wherein the raw material preparation process is similar to that of example 7, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 7 is subjected to the tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the PP/LDPE blend foamed product obtained after 20% of polypropylene cold-drawn particles are added are greatly improved.

Example 8

The specific implementation steps of embodiment 8:

secondly, manufacturing a mixed material: weighing: 5.5KG of polypropylene, 2.5KG of high-density polyethylene and 2KG of polypropylene cold-drawn particles are uniformly mixed to prepare a mixed material;

thereafter, the article is processed. Placing the mixed material into the supercritical fluid micro-foaming injection molding machine, and introducing supercritical nitrogen with the total injection mass of 0.3% to produce a foaming product with a specific micropore form; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

To illustrate the effects of the present invention, comparative example 8 is further illustrated, wherein the raw material preparation process is similar to that of example 8, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 8 is subjected to tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the PP/HDPE blend foamed product obtained by adding 20% of polypropylene cold-drawn particles are greatly improved.

Example 9

The specific implementation steps of embodiment 9:

secondly, manufacturing a mixed material: weighing: uniformly mixing 3KG polypropylene, 5KG low-density polyethylene and 2KG polypropylene cold-drawn particles to prepare a mixed material;

thereafter, the article is processed: putting the mixed material into the supercritical fluid micro-foaming injection molding machine, and introducing supercritical carbon dioxide with the total injection mass of 1.0% to produce a foaming product with a specific micropore shape; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

To illustrate the effects of the present invention, comparative example 9 is further illustrated, wherein the raw material preparation process is similar to that of example 9, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 9 is subjected to the tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the PP/LDPE blend foamed product obtained after 20% of polypropylene cold-drawn particles are added are greatly improved.

Example 10

The specific implementation steps of embodiment 10 are as follows:

thirdly, manufacturing a mixed material: weighing: uniformly mixing 2.9KG of polypropylene, 4.9KG of high-density polyethylene, 0.2KG of foaming master batch and 2KG of polypropylene cold-drawn particles to prepare a mixed material;

thereafter, the article is processed: placing the mixed material into the supercritical fluid micro-foaming injection molding machine, and introducing supercritical nitrogen gas accounting for 0.5 percent of the total injection mass to produce a foaming product with a specific micropore shape; the temperature of the melt of the injection machine is set between 166 and 172 ℃.

The polypropylene microporous article thus obtained was subjected to tensile property test, and the test results are shown in Table 1.

To illustrate the effects of the present invention, comparative example 10 is further illustrated, wherein the raw material preparation process is similar to that of example 10, but no polypropylene cold-drawn pellets are added, and the polypropylene microporous article obtained in comparative example 10 is subjected to the tensile property test, and the test results are also shown in Table 1. As can be seen from the data in Table 1, the tensile strength and elongation at break of the PP/HDPE blend foamed product obtained by adding 20% of polypropylene cold-drawn particles are greatly improved.

TABLE 1 comparison of tensile Properties of several materials

As can be seen from Table 1, the polypropylene and the blend thereof provided by the invention have a microcellular structure with a specific form, show the characteristics of low density (due to the existence of a large number of microcells in the product, the density of the product is reduced, the weight is reduced), excellent mechanical properties and excellent application prospect. The tensile strength and the elongation at break of the foamed product prepared by the method are improved at the same time, wherein the tensile strength is improved by at least 15 percent, and the problem that the tensile strength is reduced when the elongation at break of the product is increased by the traditional product toughening method is solved.

Claims

1. A preparation method of a polypropylene or polypropylene compound foaming product is characterized by comprising the following steps: adding the polypropylene cold-drawn fiber into polypropylene or a blending material thereof according to a certain proportion, and preparing a polypropylene or polypropylene compound foaming product with specific orientation micropores by adopting one mode of water foaming injection, chemical foaming injection, supercritical fluid foaming injection or chemical foaming/supercritical fluid foaming compound injection; micropores in the prepared foaming product are arranged in a specific orientation, and the specific orientation is that the micropores are parallel to the flow direction; the polypropylene cold-drawn fiber is prepared by the following method: stretching polypropylene 500-800% below the crystallization temperature, and cutting the stretched material into particles; wherein the length of the particles is 3-15 mm, the width is 1-4 mm, and the thickness is 0.5-1.5 mm;

the preparation method of the polypropylene or polypropylene compound foaming product comprises the following steps:

step 1, stretching polypropylene 500-800% below the crystallization temperature of the polypropylene, and cutting the stretched material into particles; wherein the length of the particles is 3-15 mm, the width is 1-4 mm, and the thickness is 0.5-1.5 mm;

step 2, adding the particles into polypropylene or a blending material thereof according to a certain proportion, and uniformly mixing to prepare a mixed material;

step 3, putting the mixed material into an injection molding machine, and producing a foamed product with micropores with specific orientation through the action of a proper amount of gas; wherein the temperature of the melt in the injection molding machine is 166-172 ℃.

2. The method for preparing a polypropylene or polypropylene composite foamed article according to claim 1, wherein: in the step 3, the gas is obtained by compounding one or two of chemical foaming master batch decomposition or supercritical fluid decompression transformation.

3. The method for preparing polypropylene or polypropylene composite foamed product according to claim 1, wherein the polypropylene cold drawn fiber is added into polypropylene or its blend material in a certain proportion, and the chemical foaming injection method is adopted to prepare the polypropylene or polypropylene composite foamed product with specific orientation micropores, which comprises the following steps:

step 2, stretching polypropylene 500-800% below the crystallization temperature of the polypropylene, and cutting the stretched material into particles; wherein the length of the particles is 3-15 mm, the width is 1-4 mm, and the thickness is 0.5-1.5 mm;

step 3, adding the particles prepared in the step 2 into polypropylene or a blending material thereof according to 5-50% of the total mass of the mixing material, adding the foaming master batch prepared in the step 1 according to a certain proportion, wherein the mass ratio of effective components of a foaming agent in the foaming master batch is 0.4-1.0%, and uniformly mixing to obtain a mixing material;

4. The method for preparing a polypropylene or polypropylene composite foamed article according to claim 3, wherein: in the step 1, the foaming master batch comprises the following components in parts by mass: 10-30 parts of foaming agent, 4-8 parts of dispersing agent, 5-10 parts of nucleating agent and 50-80 parts of carrier resin; wherein the addition amount of the foaming auxiliary agent is 10.5-11.3% of the mass of the foaming agent; the foaming agent is azodicarbonamide; the foaming auxiliary agent is one or the mixture of zinc oxide and barium oxide; the dispersing agent is PE wax; the nucleating agent is nano titanium dioxide or nano silicon dioxide; the carrier resin is polyethylene.

5. The method for preparing polypropylene or polypropylene composite foamed product according to claim 1, wherein the polypropylene cold drawn fiber is added into polypropylene or its blend material in a certain proportion, and the polypropylene or polypropylene composite foamed product with specific orientation micropores is prepared by water foaming injection, which comprises the following steps:

step 2, mixing required amount of activated carbon, polypropylene and blends thereof, and then preparing a carrier material by a plastic extruder;

step 3, uniformly dispersing a proper amount of water in the carrier material prepared in the step 2 to form a water-containing mixed material;

step 4, adding the particles prepared in the step 1 into the water-containing mixed material obtained in the step 3 according to 5-50% of the total mass of the mixed material, and uniformly mixing to obtain a mixed material;

6. The method for preparing polypropylene or polypropylene composite foamed product according to claim 1, wherein the polypropylene cold drawn fiber is added into polypropylene or its blend material in a certain proportion, and the polypropylene or polypropylene composite foamed product with specific orientation micropores is prepared by supercritical fluid foaming injection, which comprises the following steps:

step 3, putting the mixed material into an injection molding machine with a supercritical fluid injection device, and preparing a foaming product with specific orientation micropores under specific process conditions; wherein the melt temperature in the injection molding machine is 166-172 ℃.

7. The method of claim 6, wherein the polypropylene or polypropylene composite foamed article comprises: in the step 3, the supercritical fluid is one or the composition of two of supercritical nitrogen and supercritical carbon dioxide, and the injection amount of the supercritical fluid is 0.3-1.0% of the mass of the foaming product.