Method for preparing foamed polypropylene with high melt strength through ultraviolet irradiation and raw materials

Abstract

The invention relates to a method for preparing foamed polypropylene with high melt strength through ultraviolet irradiation and raw materials, and the method comprises the following steps: firstly, weighing the raw materials: 100 parts of PP resin; 0.5 to 1.5 parts of a bridging auxiliary agent; 0.2 to 1.0 part of a photoinitiator; 0.1 to 1.5 parts of a stabilizing agent; 0.5-4 parts of a foaming agent; and 0.5-2 parts of an antioxidant. Then preparing: uniformly mixing the PP resin, the bridging auxiliary agent, the photoinitiator and the stabilizer to obtain a PP blend; fully melting the PP blend in a press vulcanizer, and then increasing the pressure step by step, so that the material is shaped in a molten state; performing ultraviolet irradiation on the material prepared in the step 2 to obtain high-melt-strength polypropylene; and finally, uniformly mixing the high-melt-strength polypropylene, the antioxidant and the foaming agent, fully melting in a press vulcanizer, pressurizing and shaping, putting into another press vulcanizer, and controlling process parameters to enable the foaming agent to be heated and fully decomposed and foam to obtain the foamed polypropylene material.

Description

Technical Field

[0001] The invention relates to a method for preparing high melt strength foamed polypropylene through ultraviolet irradiation and raw materials, belonging to the technical field of polymer engineering plastics. Background Art

[0002] In the field of communications engineering, foamed insulation is favored by the industry because it has a lower dielectric constant and dielectric loss than single dielectric insulation, and can better meet the low attenuation and low loss requirements of communication cables. Among them, the most widely used foam products are mostly made of high-density polyethylene (HDPE) through physical foaming. However, with the emergence of many emerging fields (such as electric locomotives and other on-board communication systems), higher requirements are placed on the operating temperature of foamed products. The application range of HDPE is limited due to its low melting temperature (about 130°C). Polypropylene (PP) can better meet the requirements of use under high temperature conditions due to its high crystalline melting temperature (up to 169°C) and crystallinity. However, when PP material is processed at high temperature, the crystalline phase melts, and the slip between linear long-chain molecules becomes easier, resulting in a rapid decrease in melt strength. The foaming process is very difficult, and it is difficult to obtain an independent, high-porosity foam. The present invention intends to modify PP resin by ultraviolet irradiation method, first preparing a PP material with high melt strength, and then mixing it with a foaming agent to prepare a PP-based foam material, hoping to obtain a high-quality PP-based foam material with fine and uniform pores and a high foaming rate. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a method for preparing high melt strength foamed polypropylene based on ultraviolet irradiation and special raw materials.

[0004] The method uses specific raw materials and undergoes steps such as melt blending and ultraviolet irradiation modification to produce foamed polypropylene with high melt strength.

[0005] To achieve the above object, the present invention adopts the following scheme:

[0006] A method for preparing high melt strength foamed polypropylene by ultraviolet irradiation comprises weighing the following raw materials: 100 parts of PP resin; 0.5 to 1.5 parts of bridging agent; 0.2 to 1.0 parts of photoinitiator; 0.1 to 1.5 parts of stabilizer; 0.5 to 4 parts of foaming agent; and 0.5 to 2 parts of antioxidant.

[0007] Then, prepare according to the following steps:

[0008] Step 1: uniformly mixing PP resin, bridging agent, photoinitiator and stabilizer to obtain a PP blend;

[0009] Step 2: Fully melt the PP blend in a flat vulcanizing press, and then gradually increase the pressure to allow the material to set in a molten state;

[0010] Step 3: irradiating the material prepared in step 2 with ultraviolet light to obtain high melt strength polypropylene;

[0011] Step 4: 4.1) uniformly mixing high melt strength polypropylene, antioxidant and foaming agent;

[0012] 4.2) Fully melted in a flat vulcanizing press;

[0013] 4.3) Boosting and finalizing;

[0014] 4.4) Place the material in another flat vulcanizing press, control the pressure and temperature, and allow the foaming agent to be fully decomposed and foamed by heating to obtain a foamed polypropylene material.

[0015] The preferred raw material selection is: the bridging auxiliary agent is trimethylolpropane trimethacrylate TMPTMA; the photoinitiator is benzophenone BP; the stabilizer is styrene St; the foaming agent is azodicarbonamide AC; the antioxidant is antioxidant 1010; the requirement for the PP resin is that the melt mass flow rate at 230°C and 2.16kg is 3.2±1.0g / 10min.

[0016] The preparation steps were further optimized as follows:

[0017] In step 1: PP resin, bridging agent, photoinitiator and stabilizer are placed in a torque rheometer according to their mass parts, and mixed evenly at a temperature of 180° C. and a rotation speed of 60 rpm to obtain a PP blend.

[0018] In step 2, the PP blend is first fully melted in a flat-plate vulcanizer at 180°C; then the pressure is gradually increased from 5 MPa / 5 min to 15 MPa to allow the material to be shaped in the molten state;

[0019] In step 3, the material obtained in step 2 is irradiated with ultraviolet light for 10 seconds; the wavelength of the ultraviolet light is 365 nm; the power of the ultraviolet light is 1600 mW / cm 2 ; The vertical distance between the material and the UV light source is 5 cm;

[0020] In step 4:

[0021] 4.1) Place high melt strength polypropylene, antioxidant, and foaming agent in a torque rheometer according to their mass fractions and mix them uniformly at a temperature of 180°C and a rotation speed of 60 rpm;

[0022] 4.2) Fully melted in a flat vulcanizing press at 180°C;

[0023] 4.3) Gradually increase the pressure to 15 MPa at a rate of 5 MPa / 5 min to finalize the shape;

[0024] 4.4) Place the mixture in a flat vulcanizer at 210°C and 3 MPa for 15 min to obtain a foamed polypropylene material.

[0025] The high melt strength ultraviolet irradiation foamed polypropylene prepared by this method has fine and uniform foaming and a high foaming rate, and is a good choice for parts with high operating temperatures and low dielectric constant and dielectric loss requirements.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The present invention utilizes ultraviolet irradiation to process and prepare high melt strength polypropylene under the premise that the mechanical properties of the matrix resin do not change significantly, and obtains foamed polypropylene under the action of a foaming agent. Through microscopic observation, it is found that the foamed material obtained has more uniform cell size, thinner bubble cell walls, more number per unit area, and stronger foaming wrapping, and the bubble is not easy to break and merge, and the foaming quality is excellent. Through broadband dielectric spectrum measurement, it is known that the foamed material still has lower dielectric constant and dielectric loss. Meanwhile, the polypropylene used in the present invention is a thermoplastic material, which can be melt-recovered, responding to the "dual carbon" strategic goal of the country's green environmental protection, and the polypropylene raw material price is low, easy to obtain, suitable for large-scale production, and adapted to the development trend of future communication cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 1 represents an ultraviolet light irradiation platform, in which: ultraviolet LED irradiation array 1, conveyor belt 2, sample 3, heating platform 4, cooling water 5, flame retardant cloth 6.

[0029] Figure 2 Represents the stress-strain curve of each component.

[0030] Figure 3(a) to Figure 3(f) Respectively represent the pore morphology of different component materials, where:

[0031] Figure 3(a) is comparative example 2, Figure 3(b) is comparative example 3, Figure 3(c) is embodiment 3, Figure 3(d) is embodiment 4, Figure 3(e) is embodiment 5, and Figure 3(f) is embodiment 6.

[0032] Figure 4(a) to Figure 4(d) Represent the dielectric spectra of different component materials respectively. DETAILED DESCRIPTION

[0033] The following examples further illustrate the technical solution of the present invention, but are not intended to be limiting. Any modification or equivalent substitution of the technical solution of the present invention that does not depart from the concept and scope of the technical solution of the present invention shall be included in the scope of protection of the present invention. The equipment and devices not specifically noted in the following experiments are conventional equipment and devices in the art, and raw materials not specifically noted are commercially available. The technical means not specifically noted are conventional means well known to those skilled in the art.

[0034] Overview

[0035] The invention discloses a method for preparing high melt strength foamed polypropylene through ultraviolet irradiation and raw materials, belonging to the technical field of polymer engineering plastics.

[0036] Since polypropylene resins with linear long-chain molecular structures generally have low melt strength and poor foamability, the present invention improves the melt strength of polypropylene through ultraviolet irradiation, thereby improving its foaming quality.

[0037] The method for preparing foamed polypropylene involves the following formula (by weight): 100 parts of polypropylene PP resin, 0.5-1.5 parts of bridging auxiliary agent, 0.2-1.0 parts of photoinitiator, 0.1-1.5 parts of stabilizer, 0.5-4 parts of foaming agent, and 0.5-2 parts of antioxidant.

[0038] The high-melt-strength foamed polypropylene provided by the present invention effectively avoids melt fracture during the foaming process and can be used at a relatively high temperature. This helps increase the transmission capacity of communication cables, reduces signal attenuation during transmission, increases transmission distance, and improves product structure. This allows polypropylene, with its abundant sources and low prices, to be used as a foaming material, promoting its application as a foaming material and the development of the communication cable industry. It also injects new vitality into the polypropylene resin market, resulting in excellent economic and social benefits.

[0039] Solution Description

[0040] The raw material for preparing high melt strength foamed polypropylene by ultraviolet irradiation comprises, by mass, 100 parts of PP resin; 0.5 to 1.5 parts of a bridging auxiliary agent; 0.2 to 1.0 parts of a photoinitiator; 0.1 to 1.5 parts of a stabilizer; 0.5 to 4 parts of a foaming agent; and 0.5 to 2 parts of an antioxidant.

[0041] Specifically:

[0042] The melt mass flow rate of the PP resin at 230° C. and 2.16 kg is 3.2±1.0 g / 10 min.

[0043] The bridging auxiliary agent is trimethylolpropane trimethacrylate (TMPTMA), which serves as an intermediate bridge to connect some molecular chains, increase the degree of molecular chain branching, and thus improve the melt strength of the polypropylene resin.

[0044] The photoinitiator is benzophenone (BP), which undergoes energy level transition when irradiated by ultraviolet light of a specific wavelength to capture hydrogen atoms on the tertiary carbon atoms of the polymer molecular chain, thereby generating macromolecular chain free radicals.

[0045] The stabilizer is styrene (St), which can effectively inhibit the β-degradation side reaction of PP macromolecular free radicals during the reaction process.

[0046] The foaming agent is azodicarbonamide (AC), and the antioxidant is antioxidant 1010.

[0047] The present invention provides a method for preparing ultraviolet irradiation foamed polypropylene with high melt strength:

[0048] Step 1: Place PP base resin, TMPTMA, BP, and St into a torque rheometer according to their mass fractions, and mix them uniformly at a temperature of 180° C. and a rotation speed of 60 rpm to obtain a PP blend;

[0049] Step 2: Fully melt the PP blend in a flat vulcanizer at 180°C, then gradually increase the pressure to 15 MPa at a rate of 5 MPa / 5 min to allow the material to set in the molten state;

[0050] Step 3: Place the molten material in a Figure 1 The UV irradiation platform shown is used to irradiate the polypropylene with high melt strength; the irradiation time is 10s; the wavelength of the UV light is 365nm; the power of the UV light is 1600mW / cm 2 ; The vertical distance between the material and the UV light source is 5 cm;

[0051] Step 4. Place high melt strength polypropylene, antioxidant 1010, and AC into a torque rheometer according to their mass fractions, mix them evenly at a temperature of 180°C and a speed of 60 rpm, then fully melt them in a flat vulcanizer at 180°C, then gradually increase the pressure to 15 MPa at 5 MPa / 5 min to finalize the shape, and finally place it in a flat vulcanizer at 210°C and 3 MPa pressure for 15 minutes to allow AC to be fully decomposed and foamed by heat to obtain high melt strength UV irradiated foamed polypropylene.

[0052] refer to Figure 1 The UV irradiation platform uses a UV LED irradiation array (dot matrix) 1 with a wavelength of 365nm. The UV power of a single array LED is 1600mW / cm 2The number of UV LED arrays used is 5 to 7, the conveyor belt 2 runs at a speed of 0.5 to 0.8 m / min, and the vertical distance between the upper surface of the sample 3 and the UV lamp is 5 cm. The UV LED irradiation array is cooled by cooling water 5. A heating platform 4 (which can be a PTC heating plate) is placed below the sample. Flame-retardant cloth 6 is placed between the heating platform 4 and the conveyor belt 2 to maintain the sample temperature at 180°C, ensuring that the sample remains molten and transparent, ensuring uniform UV light transmission.

[0053] experiment

[0054] In order to explore the method of improving the melt strength of polypropylene, the following examples and comparative examples are further described.

[0055] In this experiment, the raw materials used in the embodiments and comparative examples are:

[0056] Polypropylene (PP) is homopolymer polypropylene produced by China Petrochemical Corporation, with the brand name T30s;

[0057] Trimethylolpropane trimethacrylate (TMPTMA) was produced by Anhui Xiangyun Rubber & Plastic Co., Ltd.

[0058] Benzophenone (BP) was produced by Lianyungang Jinleiyuan Chemical Co., Ltd.

[0059] Styrene (St) was produced by Shanghai MacLean Biochemical Technology Co., Ltd.;

[0060] The antioxidant was antioxidant 1010 produced by Nantong Xinchang Chemical Co., Ltd.

[0061] The foaming agent is azodicarbonamide (AC) produced by Shanghai MacLean Biochemical Technology Co., Ltd., and its effective content is ≥98%.

[0062] The contents (parts by weight) of the formulation components of the comparative examples and embodiments are shown in Table 1;

[0063] Table 1 Examples and Comparative Examples

[0064]

[0065] The preparation method of the implementation and comparative example is:

[0066] PP basic resin, TMPTMA, BP, and St were placed into a torque rheometer according to their mass parts, and mixed uniformly at a temperature of 180°C and a rotation speed of 60 rpm to obtain a PP blend;

[0067] The PP blend was fully melted in a flat vulcanizing press at 180°C, and then the pressure was gradually increased from 5 MPa / 5 min to 15 MPa to allow the material to be shaped in the molten state;

[0068] The molten materials of Example 1 and Example 2 were then irradiated on a UV irradiation platform. In this experiment, the number of UV arrays was 5 and the conveyor belt speed was 0.6 m / min to obtain high melt strength polypropylene. Comparative Example 1 was not irradiated.

[0069] Melt flow index tests were performed on Example 1, Example 2, and Comparative Example 1. The specific process was as follows: the temperature of the melt flow index tester was set to 230°C. After the tester was heated to a constant temperature, appropriate amounts of the three groups of samples were placed in a barrel with a load set to 2.16 kg. The samples were melted and placed in a press rod to allow the material to flow out of the capillary evenly. The mass of the PP melt of each component flowing out of the standard aperture and the diameter of the material flowing out of the standard aperture within 10 minutes were measured. The average of the three measurements was taken as the final result, as shown in Table 2.

[0070] The tensile test was carried out on Example 1, Example 2 and Comparative Example 1. The specific process was as follows: the sample selected for the experiment was about 1mm thick and punched into a dumbbell-shaped specimen with a dumbbell cutter. The tensile speed was set to 50mm / min. Each material was tested 3 times and the stress-strain curve was plotted as shown in the figure. Figure 2 .

[0071] Table 2 Melt index of each component

[0072]

[0073] It is not difficult to see that the melt fluidity of the polypropylene material irradiated by ultraviolet light decreases, while the melt strength increases. Moreover, as the PP melt strength increases, the material exhibits better mechanical properties. With the addition of the bridging agent, the bridging agent containing three unsaturated C=C structures plays the role of a "bridge bond" during the UV irradiation modification of the material, causing partial connection between the polypropylene molecular chains, increasing the degree of molecular chain branching, enhancing the physical entanglement effect between the molecular chains, and improving the melt strength of the material. The test results show that with the increase in the amount of bridging agent added, the melt index decreases significantly and the melt strength of the material is significantly enhanced.

[0074] In order to explore the preparation method of ultraviolet irradiation foamed polypropylene with high melt strength, further elaboration is given in combination with the following Examples 3 to 6 and Comparative Examples 2 and 3, including melt blending, ultraviolet irradiation and foaming of the following components in parts by mass.

[0075] The contents (parts by weight) of the formulation components of the comparative examples and embodiments are shown in Table 3.

[0076] Table 3 Examples and Comparative Examples

[0077]

[0078] The preparation methods of the embodiments and comparative examples are as follows:

[0079] First, PP basic resin, TMPTMA, BP, and St were placed in a torque rheometer according to their mass parts and mixed uniformly at a temperature of 180°C and a rotation speed of 60 rpm to obtain a PP blend;

[0080] The PP blend was fully melted in a flat vulcanizing press at 180°C, and then the pressure was gradually increased from 5 MPa / 5 min to 15 MPa to allow the material to be shaped in the molten state;

[0081] The molten materials of Examples 3 to 6 were then irradiated on a UV irradiation platform with 5 UV arrays and a conveyor belt speed of 0.6 m / min to obtain high melt strength polypropylene. Comparative Examples 2 and 3 were not irradiated.

[0082] Then, the above PP-based material, antioxidant 1010, and AC were placed into a torque rheometer according to their mass parts, and mixed evenly at a temperature of 180°C and a rotation speed of 60 rpm;

[0083] Then fully melt it in a flat vulcanizing machine at 180℃ and gradually increase the pressure to 15Mpa at 5Mpa / 5min to set the shape;

[0084] Finally, the material was placed in a flat vulcanizer at 210°C and 3 MPa to thermally decompose the AC and foam it for 15 minutes, thereby obtaining a UV-irradiated foamed polypropylene material with high melt strength.

[0085] A USB digital microscope was used to photograph the pore morphology of six groups of foamed PP materials with different components, such as Figure 3(a) to Figure 3(f) shown.

[0086] Figures 3(a) and 3(b) show the cell morphologies of pure PP material with 1 and 3 phr AC additions, respectively. These two figures show that although foaming can occur when the foaming agent AC is mixed into pure PP at a certain temperature, the low melt strength and viscosity of PP itself prevent it from effectively encapsulating the gas in the molten state, allowing the gas to escape easily. The rough surface of the bubbles makes them prone to merging or rupturing, resulting in varying cell morphologies, varying diameters, and extremely uneven distribution.

[0087] Figures 3(c) and 3(d) show the cell morphologies of high-melt-strength polypropylene prepared at a 0.5 phr TMPTMA addition followed by the addition of 1 and 3 phr of foaming agent AC, respectively. Figures 3(e) and 3(f) show the cell morphologies of high-melt-strength polypropylene prepared at a 1.0 phr TMPTMA addition followed by the addition of 1 and 3 phr of foaming agent AC, respectively. Comparison reveals that the cell morphologies of Examples 3 and 4 exhibit poor pore size, uneven pore size, a low number of bubbles, and even some cell breakage. This is primarily due to the fact that, while the melt strength of these compositions has improved, it still does not meet the requirements for uniform and dense cell growth. In contrast, the compositions of Examples 5 and 6 exhibit more uniform pore size, thinner cell walls, a higher number of bubbles, and superior foaming quality. This indicates that UV-modified polypropylene, due to its higher melt strength, better encapsulates emitted bubbles, making them less likely to break or merge, significantly improving the quality of foaming. Furthermore, as the amount of TMPTMA added increases, the foaming quality improves, further demonstrating the importance of increasing polypropylene melt strength in enhancing foaming quality.

[0088] The dielectric properties test results of the comparative examples and embodiments are as follows: Figure 4(a) to Figure 4(d) As shown in the figure, the bridging agent TMPTMA and the foaming agent AC both contain polar groups. While this may negatively impact the dielectric loss of the foamed material in the low-frequency range, it does improve melt strength, resulting in more uniform cell size, thinner and more numerous cell walls, and stronger foaming properties. This prevents bubbles from breaking and merging, leading to excellent foaming quality and a significant reduction in the dielectric constant. Overall, the impact of polar groups on all aspects of foamed polypropylene can be ignored. Polypropylene is a thermoplastic material with a high operating temperature, meeting the call for green, low-carbon emission reduction. Furthermore, its low price makes it suitable for large-scale production.

Claims

1. A method for preparing high melt strength foamed polypropylene by ultraviolet irradiation, characterized in that First, weigh the raw materials: PP resin 100 parts; bridging agent 0.5-1.5 parts; photoinitiator 0.2-1.0 parts; stabilizer 0.1-1.5 parts; foaming agent 0.5-4 parts; antioxidant 0.5-2 parts; Then, prepare according to the following steps: Step 1, mixing PP resin, bridging agent, photoinitiator and stabilizer to obtain PP blend; Step 2: Fully melt the PP blend in a flat vulcanizer, and then gradually increase the pressure to shape the material in a molten state; Step 3, subjecting the material prepared in step 2 to ultraviolet irradiation to obtain high melt strength polypropylene; Step 4, 4.1) uniformly mixing high melt strength polypropylene, antioxidant and foaming agent; 4.2) Fully melted in a flat vulcanizing press; 4.3) Boosting and finalization; 4.4) Put it into another flat vulcanizing machine, control the pressure and temperature, so that the foaming agent is fully decomposed and foamed by heat to obtain foamed polypropylene material.

2. The method for preparing high melt strength foamed polypropylene by ultraviolet irradiation according to claim 1, characterized in that Ingredients: The bridging auxiliary agent is trimethylolpropane trimethacrylate TMPTMA; The photoinitiator is benzophenone BP; The stabilizer is styrene St; The foaming agent is azodicarbonamide AC; The antioxidant is antioxidant 1010; The requirement for the PP resin is that the melt mass flow rate at 230° C. and 2.16 kg is 3.2±1.0 g / 10 min.

3. The method for preparing high melt strength foamed polypropylene by ultraviolet irradiation according to claim 1 or 2, characterized in that In step 1: PP resin, bridging agent, photoinitiator and stabilizer are placed in a torque rheometer according to their weight fractions, and mixed evenly at a temperature of 180° C. and a rotation speed of 60 rpm to obtain a PP blend. In step 2: first, fully melt the PP blend in a flat vulcanizer at 180°C; then gradually increase the pressure to 15 MPa at 5 MPa / 5 min to shape the material in a molten state; In step 3: the material obtained in step 2 is irradiated with ultraviolet light for 10 seconds; In step 4: 4.1) Put high melt strength polypropylene, antioxidant and foaming agent into the torque rheometer according to their mass fractions, and mix them evenly at a temperature of 180°C and a rotation speed of 60 rpm; 4.2) Fully melted in a flat vulcanizing machine at 180°C; 4.3) Gradually increase the pressure to 15Mpa at 5Mpa / 5min to finalize the shape; 4.4) Place the mixture in a flat vulcanizer at 210°C and 3 MPa for 15 min to obtain a foamed polypropylene material.

4. The method for preparing high melt strength foamed polypropylene by ultraviolet irradiation according to claim 3, characterized in that in step 3: The wavelength of ultraviolet light is 365nm; the power of ultraviolet light is 1600mW / cm 2 ; The vertical distance between the material and the UV light source is 5cm.

5. A raw material suitable for the method for preparing high melt strength foamed polypropylene by ultraviolet irradiation as claimed in claim 1, characterized in that The formula includes, by weight: 100 parts of PP resin; 0.5 to 1.5 parts of bridging auxiliary agent; 0.2 to 1.0 parts of photoinitiator; 0.1 to 1.5 parts of stabilizer; 0.5 to 4 parts of foaming agent; and 0.5 to 2 parts of antioxidant.

6. The raw material according to claim 5, characterized in that The bridging auxiliary agent is trimethylolpropane trimethacrylate TMPTMA; The photoinitiator is benzophenone BP; The stabilizer is styrene St; The foaming agent is azodicarbonamide AC; The antioxidant is antioxidant 1010; The requirement for the PP resin is that the melt mass flow rate at 230° C. and 2.16 kg is 3.2±1.0 g / 10 min.

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