A polyolefin composite material with excellent processing properties and its preparation method

Abstract

This invention discloses a polyolefin composite material with excellent processing properties and its preparation method, belonging to the field of polymer material modification technology. The composite material comprises 40-90 parts of polyethylene A (melt expansion ratio greater than 1.5), 10-60 parts of high melt flow index polyolefin B (melt flow index greater than 20 g / 10min), and 0.001-0.2 parts of molecular structure modifier C. The core of the method lies in improving the compatibility of polyethylene A and polyolefin B through the action of the molecular structure modifier C, achieving high melt strength while ensuring the material is gel-free. The resulting composite material simultaneously possesses high fluidity, high melt strength, and a high melt expansion ratio.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, and particularly to a polyolefin composite material with excellent processing properties and its preparation method. Specifically, it is a composite material and its preparation method that introduces branched structures into the polyolefin molecular chain through molecular structure modification technology without generating gelation, thereby giving it excellent processing properties. Background Technology

[0002] Polyolefins, such as polyethylene (PE), are among the most widely produced and used general-purpose plastics due to their excellent chemical stability, processability, and low cost. The processing and application properties of a material are largely determined by its rheological properties, among which melt flow index (MFI) and melt strength are two crucial indicators.

[0003] Materials with high melt flow index (MFI) have good fluidity, are easy to fill molds, and are suitable for rapid processing and production of thin-walled products. However, these materials typically have low melt strength and a small melt expansion ratio (MFI), which can easily lead to problems such as melt fracture, severe sag, cell collapse, or unstable film bubbles in applications like blow molding, foaming, and blown film, severely limiting their application in high-quality products. Conversely, materials with high melt strength and a high MFI (such as traditional low-density polyethylene, LDPE) have good processing performance, but often have a low MFI, resulting in high processing energy consumption and low efficiency.

[0004] To address this issue, the industry commonly employs chemical crosslinking (such as peroxide crosslinking) or radiation crosslinking techniques to enhance the melt strength and melt expansion ratio of polyolefins. However, these traditional crosslinking methods inevitably create a three-dimensional network structure within the material, resulting in insoluble gels. The presence of gels causes the material to lose its thermoplasticity, rendering it unsuitable for melt processing and recycling. Simultaneously, it causes the melt index to plummet to near zero, severely impairing its flowability. This becomes a "strength-for-flowability" solution, failing to achieve a balance between high performance and low efficiency.

[0005] Therefore, developing a modification method that can significantly improve the melt strength of polyolefins while maintaining their high fluidity without generating gel, and thus prepare a new material with excellent comprehensive properties, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polyolefin composite material with excellent processing performance and its preparation method. The material prepared by this invention can achieve the construction of a long branched structure without the formation of gel, and at the same time has a high melt index and high melt strength.

[0007] The technical solution of the present invention is as follows: This invention provides a polyolefin composite material with excellent processing performance, wherein the composite material is made by molecular structure modification of polyethylene A and polyolefin B; The polyethylene A has a melt flow index of 0.3 ~ 10 g / 10min and a density of 0.910 ~ 0.935 g / cm³ at 190℃ and 2.16 kg load. 3 The number average molecular weight is 12,000 to 30,000, the ratio of weight average molecular weight to number average molecular weight (Mw / Mn) is 3 to 20, the melting point is 105 to 115 ℃, and the melt expansion ratio is 1.4 to 2. The polyolefin B has a melt flow index of 20 ~ 400 g / 10min and a density of 0.880 – 0.965 g / cm³ at 190℃ and 2.16 kg load. 3 The ratio of weight-average molecular weight to number-average molecular weight, Mw / Mn, is 2 to 10. The molecular structure modification treatment is performed by chemically induced modification using molecular structure modifier C; The composite material is gel-free and simultaneously meets the following properties: melt index of 4 ~ 15 g / 10min at 190℃ and 2.16 kg load, melt expansion ratio of 1.5 ~ 2, and melt strength of 5 ~ 20 cN.

[0008] According to a preferred embodiment of the present invention, the raw materials constituting the polyolefin composite material include, by weight, the following: Polyethylene A: 40-90 parts; Polyolefin B: 10-60 parts.

[0009] According to a preferred embodiment of the present invention, the raw material further comprises a molecular structure modifier C, wherein the molecular structure modifier C is 0.001-0.2 parts by weight, and the sum of the weights of A and B is 100 parts.

[0010] According to a preferred embodiment of the present invention, the polyethylene A is low-density polyethylene (LDPE) with a melt expansion ratio of 1.5 to 2 and a density of 0.915 to 0.930 g / cm³. 3 The weight-average molecular weight to number-average molecular weight ratio (Mw / Mn) is 4–16, and the melting point is 105–115 °C. The polyolefin B is one of high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE / LLDPE), ultra-low-density polyethylene (VLDPE), polypropylene (PP), or ethylene-propylene copolymer with a melt flow index greater than 20 g / 10 min, and a density of 0.890–0.960 g / cm³. 3The absolute value of the difference between the density of polyethylene A and the density of polyolefin B is 0 ~ 0.03 g / cm³. 3 .

[0011] According to a preferred embodiment of the present invention, the molecular structure modifier C is one or a mixture of silane compounds, organic peroxides, and polyallyl compounds, wherein the silane compounds are preferably vinyltrimethoxysilane or vinyltriethoxysilane, the organic peroxides are preferably dicumyl peroxide (DCP), bis-tert-butylperoxyisopropylbenzene (BIPB), di-tert-butyl peroxide (DTBP), or benzoyl peroxide (BPO), and the polyallyl compounds are preferably triallyl isocyanurate or trimethylolpropane trimethacrylate.

[0012] This invention also provides a method for preparing the above-mentioned polyolefin composite material with excellent processing properties, which includes the following steps: Step 1: Melt blend the polyethylene A and the high melt flow index polyolefin B to obtain a basic blend; wherein, the molecular structure modifier C is first mixed with the polyethylene A, or the molecular structure modifier C is first mixed with the polyolefin B, and then the polyethylene A and the polyolefin B are melt blended to obtain the basic blend. Step 2: Modify the molecular structure of the base blend by inducing a reaction at 160-300℃; Step 3: Cool and granulate the processed material to obtain the polyolefin composite material.

[0013] According to a preferred embodiment of the present invention, a premixed material is obtained by dissolving the molecular structure modifier C in a solvent and mixing it with the polyethylene A or the polyolefin B for 5 to 30 minutes; the solvent can be one of alcohols, ketones, saturated alkanes, etc., wherein the alcohols are low-carbon alcohols with 1 to 4 carbon atoms, such as methanol, ethanol, isopropanol, etc.; the ketones are acetone, butanone (MEK), etc.; and the saturated alkanes can be n-alkanes and isoalkanes with 4 to 10 carbon atoms, such as n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, etc.

[0014] According to another preferred embodiment of the present invention, the molecular structure modifier C is dissolved in a solvent and mixed with the polyethylene B to obtain a premixed material D. The premixed material D is dried to remove the solvent to obtain a premixed material E. Then, the premixed material E is melt-blended with the polyethylene A to obtain a basic blend.

[0015] According to a preferred embodiment of the present invention, a premixed material D is obtained by dissolving the molecular structure modifier C in a solvent and mixing it with the polyethylene A. The premixed material D is dried to remove the solvent and obtain a premixed material E. Then, the premixed material E is melt-blended with the polyolefin B to obtain a basic blend.

[0016] According to a preferred embodiment of the present invention, a premixed material D is obtained by dissolving the molecular structure modifier C in a solvent and mixing it with the polyethylene B, and then the premixed material D is melt-blended with the polyethylene A to obtain a basic blend.

[0017] According to a preferred embodiment of the present invention, a premixed material D is obtained by dissolving the molecular structure modifier C in a solvent and mixing it with the polyethylene A, and then the premixed material D is melt-blended with the polyolefin B to obtain a basic blend.

[0018] According to a preferred embodiment of the present invention, the molecular structure modifier C is directly melt-blended with polyethylene A, wherein the loss of the molecular structure modifier after blending does not exceed 5%.

[0019] According to another preferred embodiment of the present invention, the molecular structure modifier C is directly melt-blended with polyolefin B, wherein the loss of the molecular structure modifier after blending does not exceed 5%.

[0020] In step S2, the chemical induction process is carried out continuously in a twin-screw extruder or a reciprocating single-screw extruder, and the material residence time is 0.5-15 minutes, preferably 1-10 minutes.

[0021] The beneficial effects of this invention are as follows: 1. This invention, through specific component selection, component ratio, and molecular structure modification processes, can prepare polyolefin composite materials with excellent processing properties while suppressing gel formation. On one hand, polyolefin B has a low molecular weight, resulting in low molecular chain entanglement and low intermolecular collision frequency in the molten state. Free radical reactions are dominated by chain growth or grafting, significantly reducing the probability of intermolecular crosslinking and thus suppressing the risk of gelation. On the other hand, polyethylene A experiences an increase in molecular weight and branching degree under free radical initiation. At this point, the low molecular weight B component in the system can effectively reduce the entanglement network density, compensate for the viscosity increase caused by the branching of A, and ensure that the composite material has good melt flowability. Therefore, the prepared material can simultaneously possess high flowability, high melt strength, and high melt expansion ratio.

[0022] 2. The material prepared by the method of the present invention retains its thermoplasticity completely, is applicable to various conventional processing methods, and can be reused multiple times. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] The specific testing method is as follows: Molecular weight distribution: Characterization was performed using a PL-GC 220 high-temperature gel permeation chromatography (HT-GPC, Agilent). The test temperature was 150 ℃, the injection volume was 200 µL, the flow rate was 1.0 mL / min, and the mobile phase was a mixture of 1,2,4-trichlorobenzene and 0.05 wt% 2,6-di-tert-butyl-4-methylphenol. A calibration curve was established using polystyrene standards, and the relative molecular mass and molecular weight distribution of the samples were calculated.

[0025] Melt expansion ratio (SR): The melt expansion ratio of polyolefins and composites was measured using a melt flow indexer (HS-XNR-400A) at 190 ºC and a load of 2.16 kg. Specifically, the melt expansion ratio reflects the extrusion swell effect of the polymer, referring to the extrudate size when the polymer melt is forced to extrude from the die. dj The phenomenon where the cross-sectional shape changes when the die size is greater than D.

[0026]

[0027] In the formula D The diameter of the die. dj The diameter of the fully relaxed extrudate.

[0028] Melt flow index: The melt flow rate of polyolefins and composites was measured using a melt flow indexer (HS-XNR-400A) at 190 ºC and 2.16 kg load, in accordance with GB / T 3682.1-2018 standard.

[0029] Density: According to the national standard GB / T 1033.2-2010, the density gradient method is used to accurately determine the density of polyolefins and composite materials.

[0030] Gel content: Fold a 100-mesh copper mesh into a cage of suitable shape, place it in a flask, and weigh it. Record the mass as follows: m 0. Then, take about 0.2 g of the composite material, cut it into strips about 2 mm wide, put them into a copper cage, weigh them, and record their mass as . m 1. Next, place the cage in a flask, add 100 mL of xylene, connect a condenser, and heat in a 140 ºC oil bath to ensure the xylene boils for 8 hours. Finally, filter quickly, then place the cage in a 140 ℃ oven and heat for 3 hours. Weigh the cage and record its mass as follows. m2. Calculate the gel content of the sample using the following formula:

[0031] Melt strength: Measured on a Gottfert Rheotens melt strength tester with a capillary die connected to a 1 mm diameter orifice. The test sample was fed into the capillary die via a Happen single-screw extruder at 10 rpm and allowed to melt at 190 °C for 10 minutes to achieve equilibrium. The temperature at the capillary outlet was also set to 190 °C. At the start of the test, the sample was drawn out of the capillary die and uniaxially stretched to a set of accelerating rollers 60 mm below the die, with the roller acceleration set to 2.4 mm / s². 2 As the roll speed increases, the instrument records the tensile force during the stretching process. The force value in the plateau region measured before the sample fractures is defined as the melt strength of the sample, expressed in cN.

[0032] Example 1 (1) Raw material ratio (parts by weight): Polyethylene A: 60 parts; Polyolefin B: 40 parts; Organic peroxide (dicumyl peroxide, DCP): 0.05 parts.

[0033] Other properties of polyethylene and polyolefin B are shown in Table 1.

[0034] (2) Preparation method: Premixing: First, add the organic peroxide and polyolefin B to a high-speed mixer and mix for 5 minutes to obtain premix material D. Then, mix polyethylene A with the prepared premix material D.

[0035] Reactive extrusion: The premixed material is fed into the main feed port of a twin-screw extruder and melt-blended within the extruder to obtain the basic blend. The extruder temperatures are set as follows: Zone 1 160 ℃, Zone 2 170 ℃, Zone 3 175 ℃, Zone 4 195 ℃, and the die head 190 ℃. The screw speed is 120 rpm, and the material residence time is approximately 2 minutes.

[0036] Granulation: The melt is extruded through a die, cooled with water, dried and then granulated to obtain composite material particles.

[0037] (3) The properties of the material after the reaction are shown in Table 1.

[0038] Example 2 The difference from Example 1 is that (1) Raw material ratio (parts by weight): Polyethylene A: 70 parts; Polyolefin B: 30 parts; Organic peroxide (dicumyl peroxide, DCP): 0.02 parts.

[0039] Other properties of polyethylene and polyolefin B are shown in Table 1. The properties of the reacted materials are shown in Table 1.

[0040] Example 3 The difference from Example 1 is that (1) Raw material ratio (parts by weight): Polyethylene A: 75 parts; Polyolefin B: 25 parts; Organic peroxide (dicumyl peroxide, DCP): 0.04 parts.

[0041] Other properties of polyethylene and polyolefin B are shown in Table 1. The properties of the reacted materials are shown in Table 1.

[0042] Example 4 The difference from Example 1 is that (1) Raw material ratio (parts by weight): Polyethylene A: 85 parts; Polyolefin B: 15 parts; Organic peroxide (dicumyl peroxide, DCP): 0.04 parts.

[0043] Other properties of polyethylene and polyolefin B are shown in Table 1. The properties of the reacted materials are shown in Table 1.

[0044] Example 5 The difference from Example 1 is that (1) Raw material ratio (parts by weight): Polyethylene A: 60 parts; Polyolefin B: 40 parts; Organic peroxide (dicumyl peroxide, DCP): 0.05 parts.

[0045] Other properties of polyethylene and polyolefin B are shown in Table 1. The properties of the reacted materials are shown in Table 1.

[0046] Example 6 (1) Raw material ratio (parts by weight): Polyethylene A: 85 parts; Polyolefin B: 15 parts; Organic peroxide (bis-tert-butylperoxyisopropylbenzene, BIPB): 0.03 parts.

[0047] Other properties of polyethylene and polyolefin B are shown in Table 1.

[0048] (2) Preparation method: Premixing: First, add the organic peroxide and polyolefin B to a high-speed mixer and mix for 5 minutes to obtain premix material D. Then, mix polyethylene A with the prepared premix material D.

[0049] Reactive extrusion: The premixed material is fed into the main feed port of a twin-screw extruder and melt-blended within the extruder to obtain the basic blend. The extruder temperatures are set as follows: Zone 1 160 ℃, Zone 2 170 ℃, Zone 3 185 ℃, Zone 4 205 ℃, and the die head 200 ℃. The screw speed is 120 rpm, and the material residence time is approximately 2 minutes.

[0050] Granulation: The melt is extruded through a die, cooled with water, dried and then granulated to obtain composite material particles.

[0051] (3) The properties of the material after the reaction are shown in Table 1.

[0052] Comparative Example 1 (simple blend, unmodified) (1) Raw material ratio: Same as in Example 1 (without adding DCP).

[0053] (2) Preparation method: After mixing all materials directly, melt extrusion granulation is carried out under the same process parameters.

[0054] (3) Performance test: melt index 19.5 g / 10min, melt expansion ratio 1.42.

[0055] Comparative Example 2 (Excessive Crosslinking) (1) Raw material ratio: Based on Example 1, the amount of DCP is increased to 0.8 parts.

[0056] (2) Preparation method: Same as in Example 1.

[0057] (3) Performance test: Melt index and melt expansion ratio could not be measured (non-flowing), gel content 68%.

[0058] The properties of the composite materials obtained in each embodiment and comparative example are shown in Table 1 below.

[0059] Table 1 Summary of Implementation Conditions

[0060] Table 2 Performance Summary Table

[0061] As shown in Table 1, the present invention uses a chemically induced modification process to prepare a composite material that simultaneously possesses high fluidity and high melt strength. The method provided in the examples can achieve molecular structure construction without the formation of gel. The material prepared in the examples of the present invention significantly improves the melt strength and melt expansion ratio of polyolefins while maintaining high fluidity and thermoplasticity. It is applicable to various conventional processing methods and can be reused multiple times.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A polyolefin composite material with excellent processing properties, characterized in that, The composite material is made from polyethylene A and polyolefin B after molecular structure modification. The polyethylene A has a melt flow index of 0.3 ~ 10 g / 10min and a density of 0.910 ~ 0.935 g / cm³ at 190℃ and 2.16 kg load. 3 The number average molecular weight is 12,000 to 30,000, the ratio of weight average molecular weight to number average molecular weight (Mw / Mn) is 3 to 20, the melting point is 105 to 115 ℃, and the melt expansion ratio is 1.4 to 2. The polyolefin B has a melt flow index of 20 ~ 400 g / 10min and a density of 0.880 – 0.965 g / cm³ at 190℃ and 2.16 kg load. 3 The ratio of weight-average molecular weight to number-average molecular weight, Mw / Mn, is 2 to 10. The molecular structure modification treatment is performed by chemically induced modification using molecular structure modifier C; The composite material is gel-free and simultaneously meets the following properties: melt index of 4~15 g / 10min at 190℃ and 2.16 kg load, melt expansion ratio of 1.5~2, and melt strength of 5~20 cN.

2. The polyolefin composite material according to claim 1, characterized in that, The raw materials constituting the polyolefin composite material include, by weight, the following: Polyethylene A: 40-90 parts; Polyolefin B: 10-60 parts.

3. The polyolefin composite material according to claim 2, characterized in that, The raw material further includes a molecular structure modifier C, which is 0.001-0.2 parts by weight, and the sum of the weights of A and B is 100 parts.

4. The polyolefin composite material according to claim 1, characterized in that, The polyethylene A is low-density polyethylene (LDPE) with a melt expansion ratio of 1.5 to 2 and a density of 0.915 to 0.930 g / cm³. 3 The weight-average molecular weight to number-average molecular weight ratio (Mw / Mn) is 4 to 16, and the melting point is 105 to 115℃.

5. The polyolefin composite material according to claim 1, characterized in that, The polyolefin B is one of high-density polyethylene (HDPE), medium-density polyethylene (MDPE), high-pressure low-density polyethylene (LDPE / LLDPE), ultra-low-density polyethylene (VLDPE), polypropylene (PP), or ethylene-propylene copolymer with a melt flow index greater than 20 g / 10min, and a density of 0.890–0.960 g / cm³. 3 The absolute value of the difference between the density of polyethylene A and the density of polyolefin B is 0 ~ 0.03 g / cm³. 3 .

6. The polyolefin composite material according to claim 1, characterized in that, The molecular structure modifier C is one of or a mixture of silane compounds, organic peroxides, polyallyl compounds.

7. The polyolefin composite material according to claim 6, characterized in that, The silane-containing compound is vinyltrimethoxysilane or vinyltriethoxysilane, and the organic peroxide is preferably dicumyl peroxide (DCP), bis-tert-butylperoxyisopropylbenzene (BIPB), di-tert-butyl peroxide (DTBP), or benzoyl peroxide (BPO). The polyallyl compound is preferably triallyl isocyanurate or trimethylolpropane trimethacrylate.

8. A method for preparing a polyolefin composite material with excellent processing properties as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Melt blend the polyethylene A and the high melt flow index polyolefin B to obtain a basic blend; wherein, the molecular structure modifier C is first mixed with the polyethylene A, or the molecular structure modifier C is first mixed with the polyolefin B, and then the polyethylene A and the polyolefin B are melt blended to obtain the basic blend. Step 2: Modify the molecular structure of the base blend by inducing a reaction at 160-300℃; Step 3: Cool and granulate the processed material to obtain the polyolefin composite material.

9. The method according to claim 8, characterized in that, In step 1, the molecular structure modifier C is dissolved in a solvent and mixed with the polyethylene A or the polyolefin B for 5 to 30 minutes to obtain a premix. Then, the premix is ​​melt-blended with the unmixed material from step 1 to obtain a basic blend.

10. The method according to claim 9, characterized in that, In step 2, the molecular structure modification treatment is carried out continuously in a twin-screw extruder or a reciprocating single-screw extruder, and the material residence time is 0.5-15 minutes.

Images