Crosslinking modified polypropylene, preparation method thereof and fiber reinforced composite material

Abstract

The invention belongs to the technical field of polypropylene modification, and provides cross-linked modified polypropylene, a preparation method thereof and a fiber reinforced composite material. The preparation method comprises the following steps: mixing polypropylene, a cross-linking agent, an auxiliary cross-linking agent and an antioxidant to obtain a mixture; carrying out melt extrusion on the mixture to obtain cross-linked modified polypropylene; the auxiliary cross-linking agent comprises one or more of allyl esters, sulfur and a polyolefin elastomer. The low-melting-point polypropylene and the recycled fiber (or high-melting-point polypropylene) are compounded to obtain the fiber reinforced composite material with good wettability and excellent mechanical property. The low-melting-point polypropylene and the fiber reinforced composite material thereof are suitable for manufacturing floors, handrails, decorative plates and building templates in public places, effective utilization of recycled resources is promoted, and the policy of low carbon, energy conservation and environmental protection is met.

Description

Technical Field

[0001] The invention relates to the technical field of polypropylene modification, and in particular to a cross-linked modified polypropylene and a preparation method thereof and a fiber-reinforced composite material. Background Art

[0002] Polypropylene raw materials are easily available and inexpensive. They have the advantages of low density, good processability, high strength, good electrical insulation, non-toxicity, strong chemical corrosion resistance and high operating temperature. They are widely used in various fields such as automobiles, building materials, and home appliances. However, polypropylene has poor low-temperature toughness and low melt strength. Usually, polypropylene is improved by chemical modification methods such as copolymerization modification, cross-linking modification, and grafting modification, or physical mixing modification methods such as filling modification and functional modification. Peroxide-induced free radical reaction is the most widely used in grafting and cross-linking modification. Polypropylene cross-linking can improve morphological stability, toughness, heat resistance, and melt strength.

[0003] The cross-linking of polypropylene is much more complicated than that of polyethylene. Only under a higher peroxide concentration (or high radiation dose) can polypropylene form cross-links, but the accompanying severe oxidative degradation reaction will have a very adverse effect on the performance of the cross-linked product. In order to inhibit the degradation of polypropylene and promote its cross-linking, some multifunctional monomers, such as divinylbenzene and trimethylolpropane trimethacrylate, have been used as cross-linking aids in the cross-linking reaction of polypropylene. However, due to the coexistence of the cross-linking reaction and degradation reaction of polypropylene, the cross-linked polypropylene in the prior art still has problems such as high melting point and poor mechanical properties.

[0004] Therefore, it is of great significance to study and obtain a cross-linked modified polypropylene and its fiber-reinforced composite materials with low melting point and good mechanical properties. Summary of the invention

[0005] The object of the present invention is to provide a cross-linked modified polypropylene and a preparation method thereof and a fiber-reinforced composite material in view of the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing cross-linked modified polypropylene, comprising the following steps:

[0008] 1) mixing polypropylene, a cross-linking agent, an auxiliary cross-linking agent and an antioxidant to obtain a mixture;

[0009] 2) melt-extruding the mixture to obtain cross-linked modified polypropylene;

[0010] The auxiliary cross-linking agent comprises one or more of allyl esters, sulfur and polyolefin elastomer.

[0011] Preferably, the allyl esters include one or more of diallyl phthalate, p-benzoquinone dioxime and triallyl isocyanurate; and the polyolefin elastomer includes styrene-butadiene-styrene block copolymer and / or ethylene-propylene copolymer.

[0012] Preferably, the crosslinking agent is an organic peroxide crosslinking agent, and the organic peroxide crosslinking agent includes one or more of diisopropylbenzene peroxide, benzoyl peroxide and diisopropylbenzene hydroperoxide;

[0013] The antioxidant comprises one or more of antioxidant 1010, antioxidant 1076, antioxidant CA and dilauryl thiodipropionate.

[0014] Preferably, the mass of the cross-linking agent is 1-3% of the mass of the polypropylene, and the mass of the antioxidant is 0.1-0.3% of the mass of the polypropylene.

[0015] Preferably, when the auxiliary cross-linking agent is allyl ester and / or sulfur, the mass of the auxiliary cross-linking agent is 0.2-0.4% of the mass of the polypropylene;

[0016] When the auxiliary cross-linking agent is a polyolefin elastomer, the mass of the auxiliary cross-linking agent is 3-8% of the mass of the polypropylene.

[0017] Preferably, in step 1), the mixing is performed by blending polypropylene, an auxiliary cross-linking agent and an antioxidant into granules, and the blend is then mixed with the cross-linking agent;

[0018] The temperature of the blending and granulation is 160-200°C, the speed of the blending and granulation is 100-150r / min, and the particle size of the blend is 1-3mm;

[0019] Step 2) The temperature of the melt extrusion is 180-220° C., and the speed of the melt extrusion is 100-150 r / min.

[0020] The invention also provides cross-linked modified polypropylene prepared by the preparation method.

[0021] The present invention also provides a fiber-reinforced composite material comprising the cross-linked modified polypropylene, wherein the fiber-reinforced composite material comprises the following raw materials in mass fractions: 50-70% of recycled fiber or high-melting-point polypropylene and 30-50% of cross-linked modified polypropylene.

[0022] Preferably, the recycled fiber comprises one or more of polyester fiber, nylon fiber, acrylic fiber, spandex fiber and polypropylene fiber.

[0023] The beneficial effects of the present invention include the following:

[0024] 1) The peroxide crosslinking agent of the present invention can induce free radicals in the polyolefin chain molecules, and the auxiliary crosslinking agent has multiple unsaturated crosslinking points and can play the role of a macromolecular crosslinking agent. The crosslinking agent and the auxiliary crosslinking agent jointly modify the polypropylene to form a complex three-dimensional structure, and many micro-crosslinking regions are formed in the continuous phase composed of the polypropylene material, thereby reducing the melting point of the polypropylene and improving its toughness and strength.

[0025] 2) The present invention reasonably selects the types of crosslinking agents and auxiliary crosslinking agents, and reasonably controls their dosage to crosslink and modify polypropylene, thereby preparing low-melting-point polypropylene with a low melt index; the low-melting-point polypropylene of the present invention is compounded with recycled fiber (or high-melting-point polypropylene) to obtain a fiber-reinforced composite material with good wettability and excellent mechanical properties. The low-melting-point polypropylene and its fiber-reinforced composite material of the present invention are suitable for the manufacture of floors, railings, decorative panels and building templates in public places, promoting the effective utilization of recycled resources and complying with the policy of low-carbon energy conservation and environmental protection. DETAILED DESCRIPTION

[0026] The present invention provides a method for preparing cross-linked modified polypropylene, comprising the following steps:

[0027] 1) mixing polypropylene, a cross-linking agent, an auxiliary cross-linking agent and an antioxidant to obtain a mixture;

[0028] 2) melt-extruding the mixture to obtain cross-linked modified polypropylene;

[0029] The auxiliary cross-linking agent comprises one or more of allyl esters, sulfur and polyolefin elastomer.

[0030] In the present invention, the polypropylene is preferably a random copolymer polypropylene or a homopolymer polypropylene;

[0031] In the present invention, the allyl esters preferably include one or more of diallyl phthalate, p-benzoquinone dioxime and triallyl isocyanurate; the polyolefin elastomer preferably includes styrene-butadiene-styrene block copolymer and / or ethylene-propylene copolymer.

[0032] In the present invention, the mass content of styrene in the styrene-butadiene-styrene block copolymer is preferably ≤50%, more preferably 45-50%; the mass content of ethylene in the ethylene-propylene copolymer is preferably 10-13%, more preferably 11-12%; the polyolefin elastomer can effectively improve the toughness and tensile strength of polypropylene without affecting the color and transparency of the polypropylene itself. The cross-linking between polypropylene and polyolefin elastomer improves the mutual solubility of the two molecules, and the mechanical properties between the two molecules are improved through chemical bonds.

[0033] In the present invention, the cross-linking agent is preferably an organic peroxide cross-linking agent, and the organic peroxide cross-linking agent preferably comprises one or more of diisopropylbenzene peroxide, benzoyl peroxide and diisopropylbenzene hydroperoxide;

[0034] The antioxidant preferably comprises one or more of antioxidant 1010, antioxidant 1076, antioxidant CA and dilauryl thiodipropionate.

[0035] In the present invention, a covalent bond is formed between the auxiliary crosslinking agent and the polypropylene macromolecular free radical, so that the free radical is transferred, the β-fracture of the tertiary carbon free radical is prevented, the degradation of the polypropylene is inhibited on the one hand, and the formation of the intermolecular crosslinking structure is promoted on the other hand. The peroxide crosslinking agent of the present invention generates highly active hydroxyl free radicals during the melt extrusion process, so that the molecular chains of the polypropylene and the auxiliary crosslinking agent are crosslinked, the intermolecular interaction force is enhanced, and the mechanical properties of the material are improved.

[0036] In the present invention, sulfur can effectively inhibit the degradation of polypropylene, promote the formation of cross-linked structures between molecules to a certain extent, hinder molecular movement, significantly reduce the melt index of polypropylene, and increase the tensile strength and elongation at break; if the amount of sulfur used is too large, the tensile strength and elongation at break of the modified polypropylene will decrease instead.

[0037] In the present invention, the mass of the crosslinking agent is preferably 1-3% of the mass of polypropylene, more preferably 1.5-2.5%, more preferably 2%, and the mass of the antioxidant is preferably 0.1-0.3% of the mass of polypropylene, more preferably 0.15-0.25%, more preferably 0.2%.

[0038] In the present invention, when the auxiliary crosslinking agent is allyl ester and / or sulfur, the total mass of the auxiliary crosslinking agent is preferably 0.2-0.4% of the mass of polypropylene, more preferably 0.25-0.35%, and more preferably 0.3%;

[0039] When the auxiliary crosslinking agent is a polyolefin elastomer, the mass of the auxiliary crosslinking agent is preferably 3 to 8%, more preferably 4 to 7%, and even more preferably 5 to 6% of the mass of the polypropylene.

[0040] In the present invention, the mixing in step 1) is preferably performed by blending and granulating polypropylene, an auxiliary crosslinking agent and an antioxidant, and the blend is then mixed with the crosslinking agent;

[0041] The temperature of the blending and granulation is preferably 160-200°C, more preferably 170-190°C, more preferably 180°C, the speed of the blending and granulation is preferably 100-150r / min, more preferably 110-140r / min, more preferably 120-130r / min, and the particle size of the blend is preferably 1-3mm, more preferably 1.5-2.5mm, more preferably 2mm;

[0042] Step 2) The temperature of the melt extrusion is preferably 180-220°C, more preferably 190-210°C, more preferably 200°C, and the speed of the melt extrusion is preferably 100-150r / min, more preferably 110-140r / min, more preferably 120-130r / min.

[0043] The invention also provides cross-linked modified polypropylene prepared by the preparation method.

[0044] The present invention also provides a fiber-reinforced composite material comprising the cross-linked modified polypropylene, wherein the fiber-reinforced composite material comprises the following raw materials in mass fractions: 50-70% of recycled fiber or high-melting-point polypropylene and 30-50% of cross-linked modified polypropylene.

[0045] In the fiber-reinforced composite material of the present invention, the mass fraction of recycled fiber or high melting point polypropylene is preferably 55-65%, more preferably 58-62%, and more preferably 60%; the mass fraction of cross-linked modified polypropylene is preferably 35-45%, more preferably 38-42%, and more preferably 40%.

[0046] In the present invention, the recycled fiber preferably comprises one or more of polyester fiber, nylon fiber, acrylic fiber, spandex fiber and polypropylene fiber.

[0047] In the present invention, the preparation method of the fiber reinforced composite material is: recycled fiber or high melting point polypropylene is blended with cross-linked modified polypropylene and then melt-extruded to obtain a fiber reinforced composite material containing cross-linked modified polypropylene; the melt extrusion temperature is preferably 130-150°C, more preferably 135-145°C, more preferably 140°C, and the melt extrusion rotation speed is preferably 150-200r / min, more preferably 160-190r / min, more preferably 170-180r / min.

[0048] In the present invention, the recycled fibers are preferably made into continuous fibers, and then the continuous fibers are blended with cross-linked modified polypropylene for melt extrusion; the method of making the recycled fibers into continuous fibers is preferably not limited to mixing, twisting, warp knitting, etc.

[0049] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0050] Example 1

[0051] The polypropylene is random copolymer polypropylene (molecular weight is 10000Da), the cross-linking agent is diisopropylbenzene peroxide, the mass of the cross-linking agent is 2% of the mass of the polypropylene, the antioxidant is antioxidant 1010, and the mass of the antioxidant is 0.2% of the mass of the polypropylene; the auxiliary cross-linking agents are triallyl isocyanurate and sulfur, and the masses of triallyl isocyanurate and sulfur are 0.2% and 0.2% of the mass of the polypropylene respectively.

[0052] The polypropylene, auxiliary crosslinking agent and antioxidant are blended and granulated at 180°C and a rotation speed of 120r / min to obtain a blend with a particle size of 2mm; the blend and the crosslinking agent are mixed evenly to obtain a mixture. The mixture is melt-extruded at 200°C and a rotation speed of 120r / min to obtain a crosslinked modified polypropylene.

[0053] Example 2

[0054] The polypropylene is a random copolymer polypropylene (molecular weight is 10000Da), the cross-linking agent is benzoyl peroxide, the mass of the cross-linking agent is 1.5% of the mass of the polypropylene, the antioxidant is antioxidant 1076, the mass of the antioxidant is 0.15% of the mass of the polypropylene; the auxiliary cross-linking agent is an ethylene-propylene copolymer (ethylene mass content is 11%), and the mass of the auxiliary cross-linking agent is 5% of the mass of the polypropylene.

[0055] The polypropylene, auxiliary crosslinking agent and antioxidant were blended and granulated at 170°C and a rotation speed of 110 r / min to obtain a blended material with a particle size of 1.5 mm; the blended material and the crosslinking agent were mixed evenly to obtain a mixed material. The mixed material was melt-extruded at 190°C and a rotation speed of 110 r / min to obtain a crosslinked modified polypropylene.

[0056] Example 3

[0057] The polypropylene is random copolymer polypropylene (molecular weight is 10000Da), the cross-linking agent is diisopropylbenzene hydroperoxide, the mass of the cross-linking agent is 2.5% of the mass of the polypropylene, the antioxidant is dilauryl thiodipropionate, the mass of the antioxidant is 0.25% of the mass of the polypropylene; the auxiliary cross-linking agent is diallyl phthalate, the mass of the auxiliary cross-linking agent is 0.3% of the mass of the polypropylene.

[0058] The polypropylene, auxiliary crosslinking agent and antioxidant are blended and granulated at 190°C and a rotation speed of 140 r / min to obtain a blend with a particle size of 2.5 mm; the blend and the crosslinking agent are mixed evenly to obtain a mixture. The mixture is melt-extruded at 210°C and a rotation speed of 140 r / min to obtain a crosslinked modified polypropylene.

[0059] Comparative Example 1

[0060] The sulfur in Example 1 was omitted, the random copolymer polypropylene was replaced by isotactic polypropylene (molecular weight of 80,000 Da), and the other conditions were the same as in Example 1.

[0061] Comparative Example 2

[0062] The mass of the ethylene-propylene copolymer in Example 2 was changed to 10% of the mass of polypropylene, the mass content of ethylene in the ethylene-propylene copolymer was changed to 5%, and the other conditions were the same as in Example 2.

[0063] Comparative Example 3

[0064] The diallyl phthalate in Example 3 was omitted, and other conditions were the same as those in Example 3.

[0065] The melt index of the cross-linked modified polypropylene of Examples 1 to 3 and Comparative Examples 1 to 3 was tested according to GB / T 3682.1-2018, and the results are shown in Table 1.

[0066] Table 1 Melt index of cross-linked modified polypropylene of Examples and Comparative Examples

[0067]

[0068] Application Example 1

[0069] The waste polyester fabric was washed and dried, and mechanically defibrated to obtain recycled polyester fibers; the recycled polyester fibers were twisted to form continuous polyester fibers (twist of 80 twists / 10 cm); 60 kg of the continuous polyester fibers and 40 kg of the cross-linked modified polypropylene of Example 1 were blended, extruded through an extruder at 140° C. and a speed of 250 r / min, and then naturally cooled to room temperature to obtain a fiber reinforced composite plate containing cross-linked modified polypropylene.

[0070] Application Example 2

[0071] The cross-linked modified polypropylene of Example 1 in Application Example 1 is replaced by the cross-linked modified polypropylene of Example 2, and other conditions are the same as those of Application Example 1.

[0072] Application Example 3

[0073] 60 kg of isotactic polypropylene (molecular weight of 100,000 Da) and 40 kg of the cross-linked modified polypropylene of Example 1 were blended, extruded at 140° C. and 250 r / min through an extruder, and then naturally cooled to room temperature to obtain a fiber reinforced composite plate containing cross-linked modified polypropylene.

[0074] Application Example 4

[0075] In Application Example 3, the cross-linked modified polypropylene of Example 1 is replaced by the cross-linked modified polypropylene of Example 2, and other conditions are the same as those of Application Example 3.

[0076] Comparative application example 1

[0077] The cross-linked modified polypropylene in Example 1 of Application Example 1 is omitted, and other conditions are the same as those of Application Example 1.

[0078] Comparative Application Example 2

[0079] The cross-linked modified polypropylene in Example 1 of Application Example 3 is omitted, and other conditions are the same as those of Application Example 3.

[0080] The tensile strength and elongation at break of the fiber reinforced composite materials prepared in Application Examples 1 to 4 and Comparative Application Examples 1 to 2 were tested in accordance with GB / T 1040.1-2018. The test results are shown in Table 2.

[0081] Table 2 Tensile strength and elongation at break of fiber reinforced composites

[0082] Different samples Tensile strength / MPa Elongation at break / % Application Example 1 48.95 65.6 Application Example 2 47.16 77.8 Application Example 3 43.96 82.9 Application Example 4 44.12 85.6 Comparative application example 1 38.6 45.2 Comparative Application Example 2 34.5 50.1

[0083] The present invention reasonably selects the types of crosslinking agents and auxiliary crosslinking agents, and reasonably controls the dosages thereof to perform crosslinking modification on polypropylene, thereby preparing low-melting-point polypropylene with a low melt index; compared with a composite material prepared from a single organic fiber obtained by defibrination of recycled fibers and a single high-melting-point polypropylene, the low-melting-point polypropylene of the present invention is composited with recycled fibers (or high-melting-point polypropylene) to obtain a fiber-reinforced composite material with good wettability and excellent mechanical properties, and the tensile strength and elongation at break of the fiber-reinforced composite material are significantly improved.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing cross-linked modified polypropylene, characterized in that: The following steps are included: 1) mixing polypropylene, a cross-linking agent, an auxiliary cross-linking agent and an antioxidant to obtain a mixture; 2) melt-extruding the mixture to obtain cross-linked modified polypropylene; The auxiliary cross-linking agent comprises one or more of allyl esters, sulfur and polyolefin elastomer.

2. The preparation method according to claim 1, characterized in that: The allyl esters include one or more of diallyl phthalate, p-benzoquinone dioxime and triallyl isocyanurate; the polyolefin elastomer includes styrene-butadiene-styrene block copolymer and / or ethylene-propylene copolymer.

3. The preparation method according to claim 1 or 2, characterized in that: The cross-linking agent is an organic peroxide cross-linking agent, and the organic peroxide cross-linking agent includes one or more of dicumyl peroxide, benzoyl peroxide and dicumyl hydroperoxide; The antioxidant comprises one or more of antioxidant 1010, antioxidant 1076, antioxidant CA and dilauryl thiodipropionate.

4. The preparation method according to claim 3, characterized in that: The mass of the cross-linking agent is 1-3% of the mass of the polypropylene, and the mass of the antioxidant is 0.1-0.3% of the mass of the polypropylene.

5. The preparation method according to claim 4, characterized in that: When the auxiliary cross-linking agent is allyl ester and / or sulfur, the mass of the auxiliary cross-linking agent is 0.2-0.4% of the mass of polypropylene; When the auxiliary cross-linking agent is a polyolefin elastomer, the mass of the auxiliary cross-linking agent is 3-8% of the mass of the polypropylene.

6. The preparation method according to claim 4 or 5, characterized in that: Step 1) The mixing is to blend polypropylene, an auxiliary cross-linking agent and an antioxidant to form granules, and the blend is then mixed with the cross-linking agent; The temperature of the blending and granulation is 160-200°C, the speed of the blending and granulation is 100-150r / min, and the particle size of the blend is 1-3mm; Step 2) The temperature of the melt extrusion is 180-220° C., and the speed of the melt extrusion is 100-150 r / min.

7. The cross-linked modified polypropylene prepared by the preparation method according to any one of claims 1 to 6.

8. A fiber-reinforced composite material comprising the cross-linked modified polypropylene according to claim 7, characterized in that: The fiber-reinforced composite material comprises the following raw materials in mass fractions: 50-70% of recycled fiber or high-melting-point polypropylene and 30-50% of cross-linked modified polypropylene.

9. The fiber-reinforced composite material according to claim 8, characterized in that: The recycled fiber includes one or more of polyester fiber, nylon fiber, acrylic fiber, spandex fiber and polypropylene fiber.

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