Low-temperature-impact-resistant polypropylene / polyethylene modified material and preparation method thereof

Abstract

The invention discloses a low-temperature impact resistant polypropylene / polyethylene modified material and a preparation method thereof. According to the invention, a certain amount of glycidyl methacrylate grafted polypropylene and glycidyl methacrylate grafted polyethylene are adopted, polyfunctional isocyanate and an epoxy ring-opening accelerant are added, and melt blending is carried out; the reaction efficiency of polyfunctional isocyanate with a polypropylene grafted epoxy group and the reaction efficiency of polyfunctional isocyanate with a polyethylene grafted epoxy group are greatly improved, and a copolymer with an esterified substance as the center is generated, so that a lacing structure of a polyethylene chain is introduced between polypropylene spherocrystals, and the low-temperature impact toughness of the polypropylene / polyethylene modified material is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material science, and in particular to a low-temperature impact-resistant polypropylene / polyethylene modified material and a preparation method thereof. Background Art

[0002] Polypropylene is a non-polar general-purpose thermoplastic with good processing performance, good comprehensive mechanical properties and relatively low price, but its low-temperature toughness is poor, which limits its application in many occasions. Below -15℃, polypropylene loses its segmental mobility. When subjected to low-temperature impact, the rigid polypropylene molecular chain is difficult to absorb strain energy, resulting in low-temperature brittleness. The most commonly used method is to use elastomers for toughening. Since there is only entanglement of molecular chains in the amorphous region between non-polar polypropylene and elastomers, the intermolecular force is low, and the elastomer toughening efficiency is greatly reduced, which also produces low-temperature brittleness. Although adding excessive elastomers can improve the low-temperature toughness of the material to a certain extent, it not only increases the material cost, but also greatly reduces the strength and stiffness of the material. Polyethylene is a hard plastic with a glass transition temperature below -40℃ and good low-temperature toughness, but polypropylene and polyethylene have poor compatibility and are both partially crystalline polymers. Crystallization-induced phase separation during melt blending further deteriorates the compatibility. Therefore, it is difficult to obtain good comprehensive mechanical properties through simple blending, especially to improve the low-temperature toughness of polypropylene. Under the premise of maintaining the excellent processing performance of polypropylene, the present invention generates a large number of polyethylene flexible chain tie structures between the spherulites of polypropylene. Under low-temperature impact, the polyethylene flexible molecular chains absorb a large amount of energy, and a low-temperature impact-resistant polypropylene / polyethylene blended modified material can be prepared. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a low-temperature impact resistant polypropylene / polyethylene modified material and a preparation method thereof, which has good low-temperature impact toughness.

[0004] The present invention is achieved as follows: a low-temperature impact resistant polypropylene / polyethylene modified material and a preparation method thereof, which comprises, by weight, 100 parts of polypropylene, 15 to 40 parts of polyethylene, 2 to 10 parts of glycidyl methacrylate (hereinafter referred to as GMA) grafted polypropylene, 2 to 10 parts of GMA grafted polypropylene, 0.5 to 3 parts of multifunctional isocyanate, and 0.1 to 0.5 parts of epoxy ring-opening accelerator.

[0005] The polypropylene is a common homopolymer or copolymer polypropylene, the polyethylene is a low-density, medium-density or high-density polyethylene; the multifunctional isocyanate is an isocyanate substance with a functionality greater than 2; the GMA grafted polypropylene is a GMA grafted polypropylene with a GMA grafting rate exceeding 0.5%; the GMA grafted polyethylene is a GMA grafted polyethylene with a GMA grafting rate exceeding 0.5%; the epoxy ring-opening accelerator is a substance that can promote the ring-opening of epoxy groups when melt-kneaded at above 150°C, including 2-ethyl-4-methylimidazole, stannous chloride, and boron trifluoride, but not limited to the listed substances.

[0006] Preparation method of low-temperature impact resistant polypropylene modified material: first mix the components evenly according to the above-mentioned mass fractions, add them to the upstream feeding port of the twin-screw extruder for mixing, set the temperature from the feeding port to the extrusion die of the twin-screw extruder to 110-230°C, extrude the pull rods and granulate to obtain the low-temperature impact resistant polypropylene modified material.

[0007] The scheme of the present invention adopts a certain amount of GMA grafted polypropylene and GMA grafted polyethylene, that is, epoxy groups have been grafted on the macromolecular chain. During melt blending, although the grafted epoxy groups form the intermolecular electrostatic force of polar groups, they repel each other when the polypropylene and polyethylene are crystallized separately. The crystallization-induced phase separation still cannot form the lacing structure of the polyethylene chain between the spherulites of the polypropylene, and the low-temperature brittleness cannot be significantly improved. When multifunctional isocyanate is added during melt blending, the isocyanate can react chemically with the grafted epoxy groups, especially under the action of the epoxy ring-opening accelerator, the epoxy groups are first opened, which greatly improves the reaction efficiency with the isocyanate. The multifunctional isocyanate reacts with the epoxy groups of the DMA grafted polypropylene and the DMA grafted polyethylene respectively, thereby connecting the two through chemical bonds to generate a copolymer centered on the esterified substance. The epoxy ring-opening accelerator causes the grafted epoxy groups to open the ring to generate hydroxyl groups, which have high reactivity with isocyanate. The two molecules are connected and esters are generated. The general reaction formula is:

[0008] R1-N=C=O+R2-OH——>R1-NH-COO-R2

[0009] R1 is a structure bonded to the isocyanate group, and R2 is a molecular chain grafted to GMA.

[0010] When polyethylene and polypropylene crystallize separately, some of the polypropylene chains and polyethylene chains on the resulting copolymer are merged into their own spherulites, and ligaments containing uncrystallized polyethylene chains are formed between the spherulites. Therefore, the low-temperature impact toughness of the blend is greatly improved. The improvement effect depends on the type of polyethylene and the number of ligaments.

[0011] In summary, the present invention utilizes chemical modification to generate a polypropylene / polyethylene long-chain copolymer centered on an esterified substance, and forms a lacing structure of a large number of polyethylene chains between polypropylene spherulites, so that the material has good low-temperature impact properties. DETAILED DESCRIPTION

[0012] The notched impact test was carried out at -40°C according to GB / T 1843-2008 to determine the low-temperature notched impact strength.

[0013] Example 1 (comparative group)

[0014] (1) Weigh polypropylene (homopolymer), polyethylene, DMA-grafted polypropylene, and DMA-grafted polyethylene according to the ratio in Table 1 and mix them evenly.

[0015] (2) Add the mixture to the upstream feed port of the screw extruder for mixing at a temperature of 100-230°C, and obtain the test material by extruding and granulating.

[0016] The material was injection molded into specimens and the mechanical properties were tested after being placed at 20°C for 24 hours. The results are shown in Table 7.

[0017] Table 1 Formulation of Example 1

[0018]

[0019] Example 2 (comparative group)

[0020] (1) Weigh polypropylene (copolymer), polyethylene, DMA-grafted polypropylene, and DMA-grafted polyethylene according to the ratio in Table 2 and mix them evenly.

[0021] (2) Add the mixture to the upstream feed port of the screw extruder for mixing at a temperature of 100-230°C, and obtain the test material by extruding and granulating.

[0022] The material was injection molded into specimens and the mechanical properties were tested after being placed at 20°C for 24 hours. The melt flow rate was tested using pellets. The results are shown in Table 7.

[0023] Table 2 Formulation of Example 2

[0024]

[0025] Example 3

[0026] (1) Weigh polypropylene, polyethylene, DMA-grafted polypropylene, DMA-grafted polyethylene, difunctional toluene diisocyanate (TDI), and epoxy ring-opening accelerator 2-ethyl-4-methylimidazole according to the ratio in Table 3, mix them evenly, and add them to the upstream feeding port of the screw extruder for mixing at a temperature of 110 to 230°C.

[0027] (2) The test material is obtained by extrusion, drawing and granulation.

[0028] The material was injection molded into specimens, and the mechanical properties were tested after being placed at 20°C for 24 hours. The melt flow rate was tested using pellets. The results are shown in Table 7.

[0029] Table 3 Formulation of Example 3

[0030]

[0031] Embodiment 4:

[0032] (1) According to the ratio in Table 4, weigh polypropylene, polyethylene, DMA-grafted polypropylene, DMA-grafted polyethylene, difunctional toluene diisocyanate (TDI), and epoxy ring-opening accelerator stannous octoate and mix them evenly.

[0033] (2) Add the mixture to the upstream feed port of the screw extruder for mixing at a temperature of 110-230°C, and obtain the test material by extrusion, drawing and granulation.

[0034] The material was injection molded into specimens, and the mechanical properties were tested after being placed at 20°C for 24 hours. The melt flow rate was tested using pellets. The results are shown in Table 7.

[0035] Table 4 Formulation of Example 4

[0036]

[0037] Embodiment 5:

[0038] (1) Weigh polypropylene, polyethylene, DMA-grafted polypropylene, DMA-grafted polyethylene, trifunctional triphenylmethane triisocyanate (TTI), and epoxy ring-opening accelerator 2-ethyl-4-methylimidazole according to the ratio in Table 5, mix them evenly, and add them to the upstream feeding port of the screw extruder for mixing at a temperature of 110 to 230°C.

[0039] (2) Add the mixture to the upstream feed port of the screw extruder for mixing at a temperature of 110-230°C, and obtain the test material by extrusion, drawing and granulation.

[0040] The material was injection molded into specimens, and the mechanical properties were tested after being placed at 20°C for 24 hours. The melt flow rate was tested using pellets. The results are shown in Table 7.

[0041] Table 5 Formulation of Example 5

[0042]

[0043] Embodiment 6:

[0044] (1) Weigh polypropylene, polyethylene, DMA-grafted polypropylene, DMA-grafted polyethylene, triphenylmethane triisocyanate (TTI), and epoxy ring-opening accelerator boron trifluoride according to the ratio in Table 6, mix them evenly, and add them to the upstream feeding port of the screw extruder for mixing at a temperature of 110 to 230°C.

[0045] (2) Add the mixture to the upstream feed port of the screw extruder for mixing at a temperature of 110-230°C, and obtain the test material by extrusion, drawing and granulation.

[0046] The material was injection molded into specimens and the mechanical properties were tested after being placed at 20°C for 24 hours. The melt flow rate was tested using pellets. The results are shown in Table 7.

[0047] Table 6 Formulation of Example 6

[0048]

[0049] Table 7 -40℃ notched impact strength test results of each embodiment

[0050]

[0051] After testing, in the comparison group of Examples 1 and 2, regardless of homopolymerized polypropylene or copolymerized polypropylene, after adding polyethylene and polypropylene DMA grafts, the value of -40°C low-temperature notched impact strength is still very low. According to the results of Examples 3 and 4, multifunctional isocyanate and epoxy ring-opening accelerator are added under the premise of the same material types and ratios as the comparison group Examples 1 and 2, respectively. Due to the aforementioned chemical modification, the -40°C low-temperature notched impact strength is greatly improved. The results of Examples 5 and 6 show that with the increase of polyethylene content, the -40°C low-temperature notched impact strength is further increased. The test results of the embodiments show that the technical solution can significantly improve the low-temperature impact toughness of polypropylene / polyethylene blends.

Claims

1. A low-temperature impact resistant polypropylene / polyethylene modified material, characterized in that: Calculated by mass, it includes 100 parts of polypropylene, 15-40 parts of polyethylene, 2-10 parts of glycidyl methacrylate grafted polypropylene, 2-10 parts of glycidyl methacrylate grafted polyethylene, 0.5-3 parts of multifunctional isocyanate and 0.1-0.5 parts of epoxy ring-opening accelerator.

2. The low-temperature impact resistant polypropylene / polyethylene modified material according to claim 1, characterized in that: The polypropylene is common homopolymer or copolymer polypropylene, and the polyethylene is common low-density, medium-density or high-density polyethylene.

3. The low-temperature impact resistant polypropylene / polyethylene modified material according to claim 1, characterized in that: The multifunctional isocyanate is an isocyanate substance with an isocyanate functionality greater than 2.

4. The low-temperature impact resistant polypropylene / polyethylene modified material according to claim 1, characterized in that: The glycidyl methacrylate grafted polypropylene is a glycidyl methacrylate grafted polypropylene with a grafting rate exceeding 0.5%; the glycidyl methacrylate grafted polyethylene is a glycidyl methacrylate grafted polyethylene with a glycidyl methacrylate grafting rate exceeding 0.5%.

5. The low-temperature impact resistant polypropylene / polyethylene modified material according to claim 1, characterized in that: The epoxy ring-opening accelerator is a substance that can promote the ring-opening of epoxy groups when melt-kneaded at above 150°C.

6. The low-temperature impact resistant polypropylene / polyethylene modified material according to claim 5, characterized in that: The epoxy ring-opening accelerator is a substance that can promote the ring-opening of epoxy groups when melt-kneaded at a temperature above 150° C., including 2-ethyl-4-methylimidazole, stannous chloride, and boron trifluoride.

7. A low-temperature impact resistant polypropylene / polyethylene modified material as described in claim 1, wherein the preparation method is as follows: the components are mixed evenly according to the above-mentioned mass fractions, the temperature from the feeding port to the extrusion die of the twin-screw extruder is set to 110-230°C, the components are added to the upstream feeding port of the twin-screw extruder for mixing, and the low-temperature impact resistant polypropylene / polyethylene modified material is obtained by extruding the pull rods and granulating.

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