Polyethylene foam and preparation method thereof

Abstract

The invention provides polyethylene foam and a preparation method thereof, and relates to the field of high polymer materials. The material comprises the following raw materials in parts by weight: 60-90 parts of low-density polyethylene, 20-30 parts of modified polystyrene, 5-10 parts of a thermoplastic elastomer, 5-10 parts of a bifunctional monomer, 5-10 parts of a coated foaming agent and 1-2 parts of an antioxidant, the modified polystyrene is a styrene-ethylene oxide segmented copolymer zinc salt compound; the difunctional monomer is an epoxy-acrylate difunctional monomer, and a molecular chain of the difunctional monomer comprises an epoxy group and acrylate double bonds; the coated foaming agent is of a core-shell structure with polylactic acid as a shell and azodicarbonamide as a core. Low-density polyethylene is used as a main component, modified polystyrene is added, the modified polystyrene has good compatibility with a polyethylene matrix, the modified polystyrene can be uniformly dispersed in the polyethylene matrix in the extrusion molding process, zinc loaded by the modified polystyrene can also be uniformly distributed in the polyethylene matrix, and the decomposition temperature of the foaming agent can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and in particular to a polyethylene foam and a preparation method thereof. Background Art

[0002] Polyethylene foam is a porous polymer material made from polyethylene (PE) through a physical or chemical foaming process. Polyethylene foam has a unique, independent, closed-cell structure. From a microscopic perspective, polyethylene molecules form a three-dimensional network through cross-linking, encapsulating gas into evenly distributed, closed bubbles. The bubble diameter typically ranges from 50 to 200 microns, resulting in excellent cushioning, thermal and sound insulation, and waterproof and moisture-resistant properties. Polyethylene foam can be divided into various types, including XPE (chemically cross-linked polyethylene foam), IXPE (irradiated cross-linked polyethylene foam), and EPE (electrodealing polyethylene foam).

[0003] In order to improve the cross-linking degree and mechanical properties of polyethylene foam, other polymers such as polypropylene, polyurethane, thermoplastic elastomers, etc. are usually added. The melting temperature of some polymers is high, which exceeds the decomposition temperature of the foaming agent, causing the foaming agent to decompose prematurely during the resin extrusion molding stage, thereby reducing the foaming rate and affecting the uniformity of the bubbles; inorganic fillers such as glass fiber, calcium carbonate, talcum powder, etc. are also added. These inorganic fillers have poor compatibility with polyethylene and cannot be evenly distributed in the polyethylene matrix during the extrusion molding cross-linking or radiation cross-linking process. Not only can they not effectively improve the rigidity of the polyethylene foam, but they can also affect the foaming ratio.

[0004] Therefore, there is an urgent need to provide a polyethylene foam with excellent rigidity, expansion ratio, bubble uniformity, etc. Summary of the Invention

[0005] The object of the present invention is to provide a polyethylene foam with high rigidity and uniform bubbles.

[0006] Another object of the present invention is to provide a method for preparing polyethylene foam. Combined with the formula of the polyethylene foam, the foaming agent will not decompose prematurely during extrusion molding to prepare the masterbatch, and the foaming effect of the foaming agent is good in the subsequent foaming process.

[0007] The present invention solves the technical problem by adopting the following technical solutions.

[0008] In one aspect, an embodiment of the present invention provides a polyethylene foam comprising the following raw materials in parts by weight:

[0009] 60-90 parts of low-density polyethylene, 20-30 parts of modified polystyrene, 5-10 parts of thermoplastic elastomer, 5-10 parts of bifunctional monomer, 5-10 parts of coated foaming agent, 1-2 parts of antioxidant;

[0010] The modified polystyrene is a styrene-ethylene oxide block copolymer zinc salt complex;

[0011] The bifunctional monomer is an epoxy-acrylate bifunctional monomer, and its molecular chain contains an epoxy group and an acrylate double bond;

[0012] The coated foaming agent has a core-shell structure with polylactic acid as the shell and azodicarbonamide as the core.

[0013] In some embodiments of the present invention, the modified polystyrene is prepared as follows:

[0014] Stir polyethylene oxide carboxyl end group, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine at 0-1°C for 30-40 minutes, then dropwise add polystyrene hydroxyl end group, raise the temperature to 20-25°C, and react at 20-25°C for 20-24 hours; filter, wash the precipitate with ether, and dry for 40-48 hours to obtain a block polymer;

[0015] The block polymer is mixed with tetrahydrofuran to obtain a mixed solution A, and anhydrous zinc acetate is mixed with tetrahydrofuran to obtain a mixed solution B; the mixed solution B is added dropwise to the mixed solution A under stirring, and the temperature is raised to 40-50° C. After the addition is completed, the stirring is continued for 5-10 hours;

[0016] Then, the mixed solution is added into ether, allowed to settle, and filtered to obtain the modified polystyrene.

[0017] In some embodiments of the present invention, the molar ratio of the polystyrene hydroxyl end group, the polyethylene oxide carboxyl end group, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is (1-1.1):1:(1-1.2):(0.1-0.2).

[0018] In some embodiments of the present invention, the preparation method of the coated foaming agent is as follows:

[0019] Adding azodicarbonamide powder to the polyethylene glycol aqueous solution and dispersing it evenly to obtain an aqueous phase;

[0020] Add polylactic acid to dichloromethane, heat and stir until the polylactic acid is dissolved to obtain an oil phase;

[0021] Under stirring, the water phase is added dropwise to the oil phase, dispersed and emulsified at high speed to obtain an emulsion;

[0022] Evaporation at normal pressure, filtration, collection of solids, washing, and drying are performed to obtain the coated foaming agent.

[0023] In some embodiments of the present invention, the bifunctional monomer is bisphenol A epoxy acrylate or novolac epoxy acrylate.

[0024] In some embodiments of the present invention, the thermoplastic elastomer is one of ethylene-octene copolymer, ethylene-vinyl acetate copolymer, and styrene-butadiene block copolymer.

[0025] On the other hand, an embodiment of the present invention provides a method for preparing polyethylene foam, comprising the following steps:

[0026] S1 adds each raw material into the extruder to prepare the masterbatch;

[0027] S2: subjecting the masterbatch to irradiation cross-linking treatment to obtain a cross-linked masterbatch;

[0028] S3: adding the cross-linked masterbatch into a foaming furnace for foaming to obtain the foam.

[0029] In some embodiments of the present invention, in step S2, the radiation dose rate of the radiation cross-linking is 8-10 kGy / min.

[0030] In some embodiments of the present invention, in step S3, the foaming temperature is 180-200° C., and the foaming time is 1-2 minutes.

[0031] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0032] The polyethylene foam provided by the present invention uses low-density polyethylene as a main component and is added with modified polystyrene. The modified polystyrene has good compatibility with the polyethylene matrix and can be evenly dispersed in the polyethylene matrix during the extrusion molding process. The loaded zinc can also be evenly distributed in the polyethylene matrix. The zinc salt is combined with the foaming agent evenly distributed in the polyethylene matrix, which can effectively reduce the decomposition temperature of the foaming agent.

[0033] On the other hand, adding thermoplastic elastomers and bifunctional monomers to the polyethylene matrix can form a highly rigid network structure with the polyethylene matrix, providing mechanical properties such as rigidity of polyethylene foam. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0035] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0036] In one aspect, an embodiment of the present invention provides a polyethylene foam, comprising the following raw materials, by weight: 60-90 parts of low-density polyethylene, 20-30 parts of modified polystyrene, 5-10 parts of thermoplastic elastomer, 5-10 parts of bifunctional monomer, 5-10 parts of coating foaming agent, and 1-2 parts of antioxidant;

[0037] The modified polystyrene is a styrene-ethylene oxide block copolymer zinc salt complex; the bifunctional monomer is an epoxy-acrylate bifunctional monomer, and its molecular chain contains epoxy groups and acrylate double bonds; the coated foaming agent is a core-shell structure with polylactic acid as the shell and azodicarbonamide as the core.

[0038] The modified polystyrene is prepared as follows: polyethylene oxide carboxyl end group, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine are stirred at 0-1°C for 30-40 minutes, and then polystyrene hydroxyl end group is added dropwise, and the mixture is heated to 20-25°C and reacted at this temperature for 20-24 hours; filtered, and the precipitate is washed with ether and dried for 40-48 hours to obtain a block polymer;

[0039] The block polymer is mixed with tetrahydrofuran to obtain a mixed solution A, and anhydrous zinc acetate is mixed with tetrahydrofuran to obtain a mixed solution B. Under stirring, the mixed solution B is added dropwise to the mixed solution A and the temperature is raised to 40-50°C. After the addition is completed, stirring is continued for 5-10 hours. The mixed solution is then added to ether, allowed to settle, and filtered to obtain the modified polystyrene. The molar ratio of the polystyrene hydroxyl end group, polyethylene oxide carboxyl end group, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is (1-1.1):1:(1-1.2):(0.1-0.2). Through electrostatic adsorption and hydrogen bonding, the zinc acetate salt is bound to the molecular chain of the block polymer to form a high-molecular composite zinc salt. During the preparation of the masterbatch, the molecular chain of the modified polystyrene can be entangled with the polyethylene matrix, thereby improving the compatibility of the zinc salt with the polyethylene matrix.

[0040] The preparation method of the coated foaming agent is as follows: adding azodicarbonamide powder to a polyethylene glycol aqueous solution and uniformly dispersing it to obtain an aqueous phase; adding polylactic acid to dichloromethane and heating and stirring until the polylactic acid dissolves to obtain an oil phase; while stirring, dropwise adding the aqueous phase to the oil phase, dispersing and emulsifying at high speed to obtain an emulsion; evaporating at normal pressure, filtering, collecting the solid, washing, and drying to obtain the coated foaming agent. Using polylactic acid as the shell improves the compatibility of the foaming agent with the polyethylene matrix. Furthermore, during the foam preparation process, the outer shell melts first, releasing azodicarbonamide, exerting a foaming effect. The zinc salt then binds to the modified polystyrene. The zinc salt reacts with azodicarbonamide to form an azocarboxylate, which has a high decomposition temperature, thereby increasing the decomposition temperature of the foaming agent.

[0041] The bifunctional monomer is bisphenol A epoxy acrylate or novolac epoxy acrylate. The thermoplastic elastomer is one of ethylene-octene copolymer, ethylene-vinyl acetate copolymer, and styrene-butadiene block copolymer. The double bonds on the bifunctional monomer can cross-link with molecules such as polyethylene and thermoplastic elastomer to form a rigid network of molecular chains, thereby improving the rigidity of the polyethylene foam. Furthermore, the epoxy groups in the bifunctional monomer provide high steric hindrance, which greatly hinders the movement of the molecular chains and thus improves the mechanical properties of the foam.

[0042] On the other hand, an embodiment of the present invention provides a method for preparing polyethylene foam, comprising the following steps:

[0043] S1 adds each raw material into the extruder to prepare the masterbatch;

[0044] S2: subjecting the masterbatch to irradiation cross-linking treatment to obtain a cross-linked masterbatch; the irradiation dose rate of the irradiation cross-linking is 8-10 kGy / min.

[0045] S3: adding the cross-linked masterbatch into a foaming furnace for foaming to obtain the foam; the foaming temperature is 180-200° C., and the foaming time is 1-2 minutes.

[0046] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0047] Example 1

[0048] 1. Ratio of raw materials

[0049] 90 parts of low-density polyethylene, 30 parts of modified polystyrene, 5 parts of thermoplastic elastomer (ethylene-octene copolymer), 10 parts of bifunctional monomer (bisphenol A epoxy acrylate), 10 parts of coated foaming agent, 1 part of antioxidant (1010);

[0050] 2. Modified polystyrene is prepared as follows:

[0051] Stir polyethylene oxide carboxyl end groups, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine at 0°C for 30 minutes, then dropwise add polystyrene hydroxyl end groups, raise the temperature to 20-25°C, and react at this temperature for 24 hours; filter, wash the precipitate with ether, and dry for 48 hours to obtain a block polymer;

[0052] The block polymer is mixed with tetrahydrofuran to obtain a mixed solution A, and anhydrous zinc acetate is mixed with tetrahydrofuran to obtain a mixed solution B; the mixed solution B is added dropwise to the mixed solution A under stirring, and the temperature is raised to 40° C. After the addition is completed, the mixture is stirred for 10 hours;

[0053] The mixed solution was then added to ether, allowed to settle, and filtered to obtain the modified polystyrene. The molar ratio of the polystyrene hydroxyl end group, the polyethylene oxide carboxyl end group, the dicyclohexylcarbodiimide, and the 4-dimethylaminopyridine was 1.1:1:1.2:0.1.

[0054] 3. The preparation method of the coated foaming agent is as follows:

[0055] Azodicarbonamide powder is added to a polyethylene glycol aqueous solution (40 vol%) at a mass-to-volume ratio of 5:100 and dispersed evenly to obtain an aqueous phase; polylactic acid is added to dichloromethane at a weight ratio of 5:100, and heated and stirred until the polylactic acid is dissolved to obtain an oil phase; the aqueous phase is added dropwise to the oil phase under stirring (800 rpm), and dispersed and emulsified at a high speed (3000 rpm) to obtain an emulsion; evaporation is performed at normal pressure, and filtration is performed through a 0.45 μm microporous membrane. The solid is collected, washed, and dried to obtain the coated foaming agent.

[0056] 4. Based on the above raw materials, the polyethylene foam of this embodiment was prepared as follows:

[0057] S1: adding the raw materials into the extruder to obtain the masterbatch; the extrusion temperature is 95-130℃;

[0058] S2: irradiating and crosslinking the masterbatch to obtain a crosslinked masterbatch; the irradiation dose rate of the irradiation crosslinking is 10 kGy / min;

[0059] S3: adding the cross-linked masterbatch into a foaming furnace for foaming at a temperature of 200° C. for 1 minute to obtain the foam.

[0060] The purchase information of some raw materials is as follows:

[0061] Polyethylene oxide carboxyl end group, Dow Chemical, ENGAGE™ POE 8407;

[0062] Polystyrene hydroxyl group, Beijing Beike New Materials Technology Co., Ltd., product model: PS-OH (hydroxyl-terminated polystyrene, molecular weight 5000);

[0063] Ethylene-octene copolymer, Tianjin Petrochemical, F231-8‌;

[0064] Bisphenol A epoxy acrylate, Guangzhou Shanghe, Guangdong, CAS 55818-57-0.

[0065] Example 2

[0066] The difference from Example 1 is that the formula of the polyethylene foam in this embodiment is as follows:

[0067] 80 parts of low-density polyethylene, 20 parts of modified polystyrene, 8 parts of thermoplastic elastomer (ethylene-octene copolymer), 8 parts of bifunctional monomer (bisphenol A epoxy acrylate), 8 parts of coated foaming agent, 2 parts of antioxidant (1010);

[0068] The remaining raw materials and preparation methods are the same as those in Example 1.

[0069] Example 3

[0070] The difference from Example 1 is that the formula of the polyethylene foam in this embodiment is as follows:

[0071] 60 parts of low-density polyethylene, 20 parts of modified polystyrene, 5 parts of thermoplastic elastomer (ethylene-octene copolymer), 5 parts of bifunctional monomer (bisphenol A epoxy acrylate), 5 parts of coated foaming agent, 1 part of antioxidant (1010);

[0072] The remaining raw materials and preparation methods are the same as those in Example 1.

[0073] Example 4

[0074] The difference from Example 1 is that the formula of the polyethylene foam in this embodiment is as follows:

[0075] 70 parts of low-density polyethylene, 25 parts of modified polystyrene, 5 parts of thermoplastic elastomer (ethylene-octene copolymer), 5 parts of bifunctional monomer (bisphenol A epoxy acrylate), 5-10 parts of coated foaming agent, 1 part of antioxidant (1010);

[0076] The remaining raw materials and preparation methods are the same as those in Example 1.

[0077] Example 5

[0078] The difference from Example 1 is that, in this embodiment,

[0079] Modified polystyrene is prepared as follows:

[0080] Stir polyethylene oxide carboxyl end groups, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine at 0°C for 30 minutes, then dropwise add polystyrene hydroxyl end groups, raise the temperature to 25°C, and react at this temperature for 24 hours; filter, wash the precipitate with ether, and dry for 48 hours to obtain a block polymer;

[0081] The block polymer is mixed with tetrahydrofuran to obtain a mixed solution A, and anhydrous zinc acetate is mixed with tetrahydrofuran to obtain a mixed solution B; the mixed solution B is added dropwise to the mixed solution A under stirring, and the temperature is raised to 40° C. After the addition is completed, the mixture is stirred for 10 hours;

[0082] The mixed solution is then added to ether, allowed to settle, and filtered to obtain the modified polystyrene. The molar ratio of the polystyrene hydroxyl end group, the polyethylene oxide carboxyl end group, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 1:1:1:0.2.

[0083] The rest of the ratios, preparation methods and raw materials are the same as those in Example 1.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that polystyrene is directly used instead of the modified polystyrene in Example 1, and the remaining raw materials and preparation methods are the same as those in Example 1.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that azodicarbonamide is directly used to replace the coated foaming agent in Example 1, and the remaining raw materials and preparation method are the same as those in Example 1.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that polystyrene is directly used instead of the modified polystyrene in Example 1, and azodicarbonamide is directly used instead of the coated foaming agent in Example 1. The remaining raw materials and preparation methods are the same as those in Example 1.

[0090] Comparative Example 4

[0091] The difference from Example 1 is that no bifunctional monomer is added to the formula, and the remaining raw materials and preparation method are the same as those of Example 1.

[0092] Experimental example

[0093] The polyethylene foams (thickness 1 cm) of Examples 1-5 and Comparative Examples 1-4 were used as test objects, their elastic moduli were tested, and the bubble morphologies on the surface and cross-section were observed. The results are shown in Table 1.

[0094] Table 1

[0095] Elastic modulus MPa Bubble shape Example 1 9.3 The surface is uniform, with more than 5 layers of bubbles and the bubble size is uniform. Example 2 8.9 The surface is uniform, with more than 5 layers of bubbles and the bubble size is uniform. Example 3 8.8 The surface is uniform, with more than 5 layers of bubbles and the bubble size is uniform. Example 4 9.1 The surface is uniform, with more than 5 layers of bubbles and the bubble size is uniform. Example 5 8.7 The surface is uniform, with more than 5 layers of bubbles and the bubble size is uniform. Comparative Example 1 6.2 The surface is uniform, with more than 5 layers of bubbles and the bubble size is uniform. Comparative Example 2 8.9 The surface is uniform, with more than 5 layers of bubbles, and the bubble uniformity is worse than that of Example 1-5. Comparative Example 3 6.1 The surface is uniform, with more than 5 layers of bubbles, and the bubble uniformity is worse than that of Example 1-5. Comparative Example 4 7.3 The surface is uniform, with more than 5 layers of bubbles, and the bubbles are uniform.

[0096] As can be seen from Table 1, the polyethylene foams of Examples 1-5 have high elastic moduli and uniform bubbles. Modified polystyrene can improve the rigidity of the polyethylene foam. Comparative Example 1, which does not include modified polystyrene, has an elastic modulus lower than that of Examples 1-5. Comparative Example 2, which does not include an encapsulated foaming agent, has poorer pore uniformity than that of Examples 1-5. This is because the foaming agent decomposes prematurely during the foam preparation process, resulting in uneven foaming.

[0097] In summary, the polyethylene foam provided in the embodiment of the present invention has low-density polyethylene as the main component and is added with modified polystyrene. The modified polystyrene has good compatibility with the polyethylene matrix and can be evenly dispersed in the polyethylene matrix during the extrusion molding process. The loaded zinc can also be evenly distributed in the polyethylene matrix. The zinc salt is combined with the foaming agent evenly distributed in the polyethylene matrix, which can effectively reduce the decomposition temperature of the foaming agent.

[0098] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. A polyethylene foam, characterized in that, Calculated by weight, it includes the following raw materials: 60-90 parts of low-density polyethylene, 20-30 parts of modified polystyrene, 5-10 parts of thermoplastic elastomer, 5-10 parts of bifunctional monomer, 5-10 parts of coated foaming agent, 1-2 parts of antioxidant; The modified polystyrene is a styrene-ethylene oxide block copolymer zinc salt complex; The bifunctional monomer is an epoxy-acrylate bifunctional monomer, and its molecular chain contains an epoxy group and an acrylate double bond; The coated foaming agent has a core-shell structure with polylactic acid as the shell and azodicarbonamide as the core.

2. The polyethylene foam according to claim 1, wherein The modified polystyrene is prepared as follows: Stir polyethylene oxide carboxyl end group, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine at 0-1°C for 30-40 minutes, then drop polystyrene hydroxyl end group into the mixture, heat to 20-25°C, and react at 20-25°C for 20-24 hours; Filter, wash the precipitate with ether, and dry for 40-48 hours to obtain a block polymer; The block polymer is mixed with tetrahydrofuran to obtain a mixed solution A, and anhydrous zinc acetate is mixed with tetrahydrofuran to obtain a mixed solution B; the mixed solution B is added dropwise to the mixed solution A under stirring, and the temperature is raised to 40-50° C. After the addition is completed, the stirring is continued for 5-10 hours; Then, the mixed solution is added into ether, allowed to settle, and filtered to obtain the modified polystyrene.

3. The polyethylene foam according to claim 2, characterized in that The molar ratio of the polystyrene hydroxyl end group, the polyethylene oxide carboxyl end group, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is (1-1.1):1:(1-1.2):(0.1-0.2).

4. The polyethylene foam according to claim 1, characterized in that The preparation method of the coated foaming agent is as follows: Adding azodicarbonamide powder to the polyethylene glycol aqueous solution and dispersing it evenly to obtain an aqueous phase; Add polylactic acid to dichloromethane, heat and stir until the polylactic acid is dissolved to obtain an oil phase; Under stirring, the water phase is added dropwise to the oil phase, dispersed and emulsified at high speed to obtain an emulsion; Evaporation at normal pressure, filtration, collection of solids, washing, and drying are performed to obtain the coated foaming agent.

5. The polyethylene foam according to claim 1, characterized in that The bifunctional monomer is bisphenol A epoxy acrylate or novolac epoxy acrylate.

6. The polyethylene foam according to claim 1, characterized in that The thermoplastic elastomer is one of ethylene-octene copolymer, ethylene-vinyl acetate copolymer and styrene-butadiene block copolymer.

7. A method for preparing the polyethylene foam according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1 adds each raw material into the extruder to prepare the masterbatch; S2: subjecting the masterbatch to irradiation cross-linking treatment to obtain a cross-linked masterbatch; S3: adding the cross-linked masterbatch into a foaming furnace for foaming to obtain the foam.

8. The method for preparing polyethylene foam according to claim 7, wherein: In the S2, the radiation dose rate of the radiation cross-linking is 8-10 kGy / min.

9. The method for preparing polyethylene foam according to claim 7, wherein: In the step S3 , the foaming temperature is 180-250° C., and the foaming time is 1-2 minutes.