Polyethylene composition as well as preparation method and application thereof

Abstract

The invention discloses a polyethylene composition as well as a preparation method and application thereof. The polyethylene composition comprises the following components in parts by weight: 85-95 parts of low density polyethylene; 1-5 parts of a compatilizer; 0.1-1 part of a crystal point removing auxiliary agent; wherein the crystal point removing auxiliary agent comprises an antioxidant, an acid acceptor and a metal deactivator, and the mass ratio of the antioxidant to the acid acceptor to the metal deactivator is (1-3): (2-5): 1. The antioxidant, the acid acceptor and the metal deactivator are added into the low-density polyethylene according to a specific ratio, so that the generation of crystal points in the preparation process of the polyethylene film can be effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyethylene film materials and the technical field of halogen-free flame retardant materials, and particularly relates to a polyethylene composition, a preparation method thereof and an application thereof. Background Art

[0002] Polyethylene film, known for its excellent flexibility, chemical resistance, and processability, is widely used in a variety of fields, including packaging, agriculture, and construction. With growing environmental awareness and the need for resource recycling, the development and application of recycled polyethylene film materials are gaining increasing attention. However, existing polyethylene film materials (especially recycled polyethylene) often exhibit crystallization issues during their production.

[0003] The presence of crystal points not only affects the appearance quality of the film, causing defects on its surface and reducing its aesthetics, but also has a negative impact on the physical properties of the film. For example, in packaging applications, crystal points may become stress concentration points, reducing the tensile strength and puncture resistance of the film, causing the film to easily break during use, affecting the packaging effect; in agricultural greenhouse film applications, crystal points will affect the uniformity of light transmittance of the film, reducing the effective use of light by crops, and thus affecting the growth of crops. In the prior art, the reduction of crystal points is mostly from the perspective of the pre-treatment stage and the extrusion granulation processing technology, and there are few methods for reducing and removing crystal points in recycled films by formula design. The prior art CN112745547A discloses a recycled polyethylene material that is resistant to thermal oxidative aging, but the recycled polyethylene obtained in this invention is used for pipes, and no attention is paid to recycled polyethylene film materials. In addition, the recycled polyethylene material obtained in this invention is prone to crystal point problems in the preparation of film materials. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem of crystal points easily appearing in the preparation process of polyethylene films in the prior art, and to provide a polyethylene composition.

[0005] Another object of the present invention is to provide a method for preparing the polyethylene composition.

[0006] Another object of the present invention is to provide applications of the polyethylene composition.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions: A polyethylene composition comprising the following components calculated in parts by weight: 85-95 parts of low-density polyethylene; 1~5 parts of compatibilizer; 0.1~1 part of de-crystallization agent; The degranulation auxiliary agent includes an antioxidant, an acid absorber and a metal passivator, and the mass ratio of the three is (1-3): (2-5): 1.

[0008] In the present invention, low-density polyethylene is used as the base resin, and an antioxidant, an acid scavenger and a metal passivator are added in a specific ratio to effectively reduce the generation of crystal points; the antioxidant can capture carbon-centered free radicals, alkyl free radicals, hydrogen free radicals, etc., the acid scavenger can absorb acidic substances in the system, and the metal passivator quenches metal ions and chelates with the metal ions to passivate the metal ions. By adjusting the ratio of the three, the free radicals in the system can be reduced to catalyze the branching and cross-linking of the low-density polyethylene, thereby reducing crystal points.

[0009] It should be noted that, in the polyethylene composition of the present invention, the content of the low-density polyethylene is preferably not less than 80 wt.%.

[0010] It should be noted that the mass ratio of the antioxidant, acid scavenger and metal passivator in the decrystallization point aid described in the present invention is (1~3): (2~5): 1, for example but not limited to the mass ratio of 1:5:1, 1:4;1, 1:3:1, 1:2:1, 2:5:1, 2:4:1, 2:3:1, 2:2:1, 3:5:1, 3:4:1 or 3:2:1, etc., as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the specific point values ​​included in the range are no longer exhaustively listed in the present invention.

[0011] Furthermore, the mass ratio of the antioxidant, the acid absorber and the metal passivator in the devitrification point auxiliary agent is (1.5~2.5): (3~4):1.

[0012] It should be noted that the decrystallization point aid described in the present invention is 0.1~1 part, for example but not limited to 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part or 1 part, etc., as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the specific point values ​​included in the range are no longer exhaustively listed in the present invention.

[0013] It should be noted that, in the polyethylene composition of the present invention, the content of the devitrification agent is 0.1-1.2 wt%.

[0014] Furthermore, the antioxidant includes one or more of hindered phenol antioxidants, phosphite antioxidants or thioester antioxidants.

[0015] In some preferred embodiments, the antioxidant is a compound of a hindered phenol antioxidant and a phosphite antioxidant or a thioester antioxidant.

[0016] Specifically, the antioxidant is a compound of a hindered phenol antioxidant and a phosphite antioxidant in a mass ratio of (1-2):1, or a compound of a hindered phenol antioxidant and a thioester antioxidant in a mass ratio of (1-2):1.

[0017] Specifically, the hindered phenol antioxidants include β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2'-thioethylene glycol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene or N , N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyphenylpropionamide); the phosphite antioxidant includes one or more of tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol bisdiphosphite or bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphate; the thioester antioxidant includes one or more of distearyl thiodipropionate, 4,4'-thiobis(6-tert-butyl-m-cresol), pentaerythritol tetrakis(3-laurylthiopropionate) or didodecyl thiodipropionate.

[0018] Furthermore, the metal deactivator includes a hydrazide metal deactivator and / or an amide metal deactivator.

[0019] Furthermore, the metal passivator is a hydrazide metal passivator.

[0020] Specifically, the hydrazide metal passivator is N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazide.

[0021] The amide metal passivator is 2,2-oxalamido-bis[ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate.

[0022] Furthermore, the acid absorber includes calcium stearate and / or magnesium stearate.

[0023] Specifically, the acid scavenger has a fineness of ≥99% (passing a 0.075 mm 200 mesh sieve), a metal content of 1-10%, and a free acid content of ≤1%.

[0024] Furthermore, the low-density polyethylene is recycled low-density polyethylene and / or new low-density polyethylene.

[0025] Specifically, the recycling source of the low-density polyethylene recycled material is film-type polyethylene.

[0026] As a further improvement of the above solution of the present invention, the components of the low-density polyethylene recycled material include resin, filler, metal and impurities, the resin is polyethylene, and the filler includes at least one of talc, calcium carbonate and wollastonite; the filler content of the low-density polyethylene recycled material is ≤10%, and the density is ≤0.93g / cm 3 , polyethylene content ≥90%.

[0027] Furthermore, the low-density polyethylene has a melt flow rate of 0.2-5 g / 10 min at 190° C. and a load of 2.16 kg.

[0028] Specifically, the test standard for the melt flow rate of the low-density polyethylene is ISO 1133-1-2011.

[0029] Furthermore, the compatibilizer includes maleic anhydride grafted polyethylene.

[0030] Specifically, the maleic anhydride grafted polyethylene is maleic anhydride grafted metallocene polyethylene.

[0031] Furthermore, the compatibilizer has a melt flow rate of 0.5-2.5 g / 10 min at 2.16 kg and 190° C.

[0032] Specifically, the melt flow rate test standard of the compatibilizer is ASTM D1238-23.

[0033] Furthermore, the grafting rate of the polyethylene grafted maleic anhydride copolymer is 0.5% to 2wt%.

[0034] The present invention also provides a method for preparing the polyethylene composition, comprising the following steps: The components are mixed evenly, melt-blended and extruded into pellets to obtain a polyethylene composition.

[0035] Furthermore, the extruder is a twin-screw extruder.

[0036] Furthermore, the extrusion temperature is 160-190°C.

[0037] Furthermore, the extruder is equipped with a dual-channel non-stop screen changer.

[0038] Specifically, the filter screen of the dual-channel non-stop screen changer has a mesh size of 120-200.

[0039] Furthermore, the screw speed of the twin-screw extruder is 450-550 rpm.

[0040] Furthermore, the feeding rate of the twin-screw extruder is 350-400 kg / h.

[0041] The present invention also protects the use of the polyethylene composition in preparing films.

[0042] A low-crystal point polyethylene film is prepared by using the polyethylene composition.

[0043] Furthermore, the thickness of the low crystal point polyethylene film is 0.03±0.02 mm.

[0044] Specifically, the preparation method of the low crystal point polyethylene film is as follows: The polyethylene composition is dried and added into a film blowing machine, and a low crystal point polyethylene film is obtained by melt extrusion and film blowing.

[0045] Specifically, the film blowing temperature is 190-210°C.

[0046] Specifically, the drying temperature is 75-85°C.

[0047] Specifically, the drying time is 3.5 to 4.5 hours.

[0048] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a polyethylene composition. By adding an antioxidant, an acid absorber and a metal passivator compounded in a specific ratio into low-density polyethylene as a degranulation auxiliary agent, the three can be compounded to reduce the free radicals in the system that catalyze the branching and cross-linking of the low-density polyethylene, thereby reducing the degranulation point. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below with reference to specific examples. The examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0050] 1. Raw materials used in each embodiment and comparative example: Low-density polyethylene: Low-density polyethylene 1: low-density polyethylene recycled material, RLLDPE UCT-0112 PN41 (HYD), melt flow rate 1.6 g / 10 min (190°C, 2.16 kg), transparent, filler content ≤10%, purchased from Fuzhou Huayueda Trading Co., Ltd. Low-density polyethylene 2: recycled low-density polyethylene, RLLDPE ICT-0117 PB21 (STD), melt flow rate 2.7 g / 10 min (190°C, 2.16 kg), transparent, filler content ≤10%, purchased from Qingdao Sutongda Trading Co., Ltd. Low-density polyethylene 3: EXCEED 3518CB, melt flow rate 3.5 g / 10 min (190 °C, 2.16 kg), purchased from ExxonMobil; Compatibilizer: maleic anhydride grafted polyethylene, MC218, purchased from Ningbo Nengzhiguang New Materials; De-crystallization additives: Degranulation aid 1: antioxidant: acid scavenger: metal passivator = 2:4:1; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (1010): tris(2,4-di-tert-butylphenyl) phosphite (168) = 2:1, wherein 1010 and 168 are purchased from Lionlong, the metal passivator is N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl]hydrazine (MD1024), purchased from Lionlong, the acid scavenger is calcium stearate, model CS-P, purchased from Anhui Ruihua New Materials Co., Ltd. Degranulation aid 2: antioxidant: acid absorber: metal passivator = 2:4:1; the antioxidant is β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (1076): 168 = 1:1, 1076 and 168 are purchased from Lionlong, the metal passivator is MD-1024, purchased from Lionlong, and the acid absorber is calcium stearate, model CS-P, purchased from Anhui Ruihua New Materials Co., Ltd. Degranulation point aid 3: antioxidant: acid scavenger: metal passivator = 2:4:1; the antioxidant is 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H,3H,5H) -trione (3114): distearyl thiodipropionate (DSTDP) = 1.33:1, wherein 3114 and DSTDP are purchased from Lionlong, the metal passivator is 2,2'-oxalamido-bis [ethyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl)] propionate (MD-697), purchased from Lionlong, and the acid scavenger is magnesium stearate, model MS-P, purchased from Anhui Ruihua New Materials Co., Ltd. Degranulation aid 4: antioxidant: acid absorber: metal passivator = 2:4:1; the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (1010), purchased from Lionlong, the metal passivator is MD-1024, purchased from Lionlong, and the acid absorber is calcium stearate, model CS-P, purchased from Anhui Ruihua New Materials Co., Ltd. Degranulation agent 5: antioxidant: acid absorber: metal passivator = 1:2:1; the antioxidant ratio is 1010:168 = 2:1, where 1010 and 168 are both purchased from Rianlon, the metal passivator is MD1024, also purchased from Rianlon, and the acid absorber is calcium stearate, model CS-P, purchased from Anhui Ruihua New Materials Co., Ltd. Degranulation agent 6: antioxidant: acid absorber: metal passivator = 2:2:1; the antioxidant is 1010:168 = 2:1, where 1010 and 168 are both purchased from Rianlong, the metal passivator is MD-1024, also purchased from Rianlong, and the acid absorber is calcium stearate, model CS-P, purchased from Anhui Ruihua New Materials Co., Ltd. Degranulation agent 7: antioxidant: metal passivator = 2:1 (excluding acid absorbent); the antioxidant is 1010:168 = 2:1, 1010 and 168 are both purchased from Rianlong, and the metal passivator is MD1024, also purchased from Rianlong; Degranulation agent 8: antioxidant: acid absorber: metal passivator = 2:1:1; the antioxidant ratio is 1010:168 = 2:1, where 1010 and 168 are both purchased from Rianlong, the metal passivator is MD1024, also purchased from Rianlong, and the acid absorber is calcium stearate, brand CS-P, purchased from Anhui Ruihua New Materials Co., Ltd. Degranulation agent 9: antioxidant: acid absorber: metal passivator = 2:6:1; the antioxidant ratio is 1010:168 = 2:1, where 1010 and 168 are both purchased from Rianlong, the metal passivator is MD1024, also purchased from Rianlong, and the acid absorber is calcium stearate, brand CS-P, purchased from Anhui Ruihua New Materials Co., Ltd. It should be noted that the parallel experiments in the examples and comparative examples all used raw materials from the same source.

[0051] 2. In each embodiment and comparative example, polyethylene compositions were prepared according to the formulations in Tables 1 and 2, using the following preparation method: After the components are uniformly mixed, they are added to a twin-screw extruder (equipped with a dual-channel non-stop screen changer with a filter screen of 120-200 mesh), and melt blended and extruded into granules to obtain a polyethylene composition; the extrusion temperature is 160-190°C, the screw speed of the twin-screw extruder is 450-550 rpm, and the feed rate of the twin-screw extruder is 350-400 kg / h.

[0052] 3. Performance testing: (1) Crystal point detection: The polyethylene composition prepared in the above examples and comparative examples was dried at 80°C for 4 hours, added to a film blowing machine, and melt-extruded and blown to obtain a polyethylene film. The film blowing temperature was 190-210°C. After 5-6 meters of film blowing, sampling was started at intervals of 1 meter. A total of 10 groups of samples were taken, and the crystal point was tested and the average value was taken. The sampled polyethylene film had a thickness of 0.03±0.02mm, a width of 12±2cm, and a length of 100±5cm. The crystal points on the film were checked under the light and marked with a marker. The industry standards for determining crystal points are as follows:

[0053] (2) Elongation at break test: The polyethylene composition in each embodiment and comparative example was pressed into a sheet to prepare a sample, with a thickness of 1 mm, type 5, and a rate of 50 mm / min. The test was performed according to the method of GB / T 1040.3-2018, and the unit was %, which was recorded as the elongation at break before thermal oxidative aging. (3) Thermal oxidative aging performance test: The polyethylene compositions in the examples and comparative examples were pressed into sheets to prepare samples with a thickness of 1 mm, type 5, and a speed of 50 mm / min. The sheets were placed in a thermal oxidative aging oven at 100°C for 1000 h, taken out to room temperature, and tested according to the method of GB / T 1040.3-2018. The unit is %, which is recorded as the elongation at break after thermal oxidative aging. The elongation at break change rate is calculated according to the formula: elongation at break change rate (%) = (elongation at break before thermal oxidative aging - elongation at break after thermal oxidative aging) / elongation at break before thermal oxidative aging * 100%. Examples 1 to 11 and Comparative Examples 1 to 10 Table 1 Amount (unit: weight parts) and properties of each component in the polyethylene composition in Examples 1 to 11

[0054] Table 2 Amount (unit: weight parts) and properties of each component in the polyethylene composition in each comparative example

[0055] As can be seen from Table 1, the polyethylene composition prepared in the present invention has good thermal oxidative aging performance, and the crystal points of the film prepared by blown film are effectively reduced. Specifically, after aging at 100°C for 1000 hours, the change rate of elongation at break is within 20%, and the crystal points of the film are controlled within the standard range.

[0056] It can be seen from Comparative Examples 1 to 3 that if the devitrification auxiliary agent used does not contain an acid scavenger or the content of the acid scavenger is too much or too little, it is not conducive to the reduction of devitrification points. The acid scavenger can eliminate the acidic substances generated by the polyethylene recycled material during multiple uses and recycling. If the acid scavenger is not added or the content of the acid scavenger is too little to completely eliminate the acidic substances, the residual acidic substances will catalyze the generation of free radicals, promote the cross-linking of polyethylene, and generate devitrification points. If the acid scavenger is too much, the system becomes alkaline, and the alkaline ions will also promote the generation of free radicals, thereby promoting devitrification points.

[0057] It can be seen from Comparative Examples 4 and 5 that if the amount of decrystalline point agent used is too small, it cannot completely eliminate free radicals to achieve the effect of eliminating crystal points. If too much is used, it will cause the film to stick to the roller during use, and the ideal effect of reducing crystal points will not be achieved.

[0058] It can be seen from Comparative Examples 9 and 10 that if too little compatibilizer is added, the compatibility between different components of the system is poor, the initial mechanical properties deteriorate, and during the thermal oxidative aging process, due to poor interfacial bonding, it is more susceptible to oxygen attack, and aging is aggravated; if too much compatibilizer is added, precipitation will occur, and more unstable points and initiator residues will be introduced. During material processing or subsequent use, especially in a heated and aerobic environment, it will become a source of initiation for free radicals, greatly accelerating the onset of the oxidative degradation chain reaction.

[0059] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A polyethylene composition, characterized in that The composition comprises the following components calculated in parts by weight: 85-95 parts of low-density polyethylene; 1~5 parts of compatibilizer; 0.1~1 part of de-crystallization agent; The degranulation auxiliary agent includes an antioxidant, an acid absorber and a metal passivator, and the mass ratio of the three is (1-3): (2-5):

1.

2. The polyethylene composition according to claim 1, characterized in that The mass ratio of the antioxidant, the acid absorber and the metal passivator in the devitrification auxiliary agent is (1.5-2.5): (3-4):

1.

3. The polyethylene composition according to claim 1, characterized in that The antioxidant includes one or more of hindered phenol antioxidants, phosphite antioxidants or thioester antioxidants.

4. The polyethylene composition according to claim 1, characterized in that The metal deactivator includes a hydrazide metal deactivator and / or an amide metal deactivator.

5. The polyethylene composition according to claim 1, characterized in that The acid scavenger includes calcium stearate and / or magnesium stearate.

6. The polyethylene composition according to claim 1, characterized in that The low-density polyethylene is low-density polyethylene recycled material and / or low-density polyethylene new material.

7. The polyethylene composition according to claim 1, characterized in that The compatibilizer includes maleic anhydride grafted polyethylene.

8. A method for preparing the polyethylene composition according to any one of claims 1 to 7, characterized in that: The steps include: The components are mixed evenly, melt-blended and extruded into pellets to obtain a polyethylene composition.

9. Use of the polyethylene composition according to any one of claims 1 to 7 in the preparation of films.

10. A low crystal point polyethylene film, characterized in that: It is prepared using the polyethylene composition according to any one of claims 1 to 7.

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