Magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material and preparation method thereof

Abstract

The present invention discloses a magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material and a preparation method thereof; calculated by mass fraction, the raw material formula thereof consists of the following components: magnesium hydroxide 58.3-77.7%, linear low density polyethylene 19.25-39.05%, fluorine-containing small molecule liquid crystal 1.0-2.9%, antioxidant 0.1-0.3%, initiator 0.01-0.05%; the fluorine-containing small molecule liquid crystal is 4-fluoro benzoic acid-4'-allyloxy benzoic acid hydroquinone diester. The present invention uses a fluorine-containing small molecule liquid crystal containing unsaturated carbon-carbon double bonds as a processing aid, which not only has an obvious effect on the processing flow modification of the magnesium hydroxide and linear low density polyethylene blend system, but also forms a graft copolymer by melt grafting onto the main chain of linear low density polyethylene, and the obtained material has excellent tensile strength and impact strength.

Description

Technical Field

[0001] The present invention relates to the technical field of halogen-free flame-retardant polyethylene modification, and particularly relates to a magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material and a preparation method thereof, belonging to the technical field of polymer material modification. Background Art

[0002] Polyethylene is a flammable material with a limiting oxygen index (LOI) of only about 17.4, and there is a dripping phenomenon during combustion, which is extremely likely to cause a fire. Therefore, in practical applications, it is necessary to flame-retardantly modify polyethylene. Inorganic metal hydroxides such as magnesium hydroxide are the most commonly used halogen-free flame-retardant fillers in the field of linear low-density polyethylene flame retardancy. However, the flame-retardant efficiency of magnesium hydroxide is relatively low, and the filling amount usually needs to be more than 50 wt% to make the linear low-density polyethylene reach an ideal flame-retardant grade. Due to the poor compatibility between the polar inorganic filler and the non-polar matrix resin, it is difficult for magnesium hydroxide to disperse at a high filling amount, and serious agglomeration occurs in the matrix. At this time, the frictional resistance between the agglomerated particles will play a dominant role, resulting in an increase in the melt viscosity of the blend system, and further causing a significant decrease in its fluidity during the melt processing. In addition, the existence of agglomeration will also lead to poor mechanical properties of the formed composite material.

[0003] Usually, processing aids are added to improve the processing fluidity of the magnesium hydroxide flame-retardant modified linear low-density polyethylene system. Due to its low surface energy, the fluorine-containing processing aid tends to be distributed at the interface between the filler particles and the polymer matrix, and can improve the dispersion of the filler particles in the matrix, thereby playing a role in flow modification. Cao Bo et al. (Silicone / fluorine-functionalized flow modifier with low surface energy for improving interfaces in highly filled composites, composites science and technology, 2021, 214: 108994) designed and synthesized a linear silicon-fluorine processing aid (Si-DPF) with a number average molecular weight of 1.6×10 3 and applied it to the blend system of magnesium hydroxide (MH) flame-retardant modified linear low-density polyethylene (LLDPE) (MH / LLDPE = 80:20). When the addition amount of Si-DPF was 2.9 wt%, the notched impact strength of the obtained composite material increased from 1.8 kJ / m 2 to 3.5 kJ / m 2, the elongation at break increased from 0.4% to 1.9%, but the tensile strength decreased from 11.9 MPa to 8.0 MPa, a decrease of 32.8%. It has a certain improvement effect on the processing fluidity of the system and the toughness of the formed composite material, but it causes the decrease of the tensile strength of the material and so on.

[0004] Thermotropic liquid crystal polymers have relatively low melt viscosities during the melt processing process and are extremely prone to orientation along the flow direction to form microfibers, and are often used as processing aids. Guan Xiaoxiao et al. (Design and Synthesis of Polysiloxane Based Side Chain Liquid Crystal Polymer for Improving the Processability and Toughness of Magnesium Hydrate / Linear Low-Density Polyethylene Composites. Polymers, 2020, 12(4):911) designed and synthesized a polysiloxane side chain liquid crystal polymer (PSCTLCP), whose melting point and clearing point are 173.6 °C and 275.5 °C respectively, which are compatible with the processing temperature of linear low-density polyethylene. Applying PSCTLCP to the magnesium hydroxide flame-retardant modified linear low-density polyethylene blend system (MH / LLDPE = 60:40) has a certain effect on improving fluidity. When the addition amount of PSCTLCP is 2.9 wt%, the notched impact strength of the composite material increased from 9.1 kJ / m 2 to 11.5 kJ / m 2 , and the elongation at break increased from 6.9% to 17.7%. However, the tensile strength of the formed composite material decreased from 9.4 MPa to 7.9 MPa.

[0005] As can be seen from the above, the existing fluorine-containing or polysiloxane liquid crystal polymer processing aids have a significant effect on improving the processing fluidity of the magnesium hydroxide flame-retardant modified linear low-density polyethylene system. However, although the toughness of the formed composite material increases, it is still relatively low, and the tensile strength and so on decrease, and a composite material with good tensile strength and impact strength cannot be obtained. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects in the prior art, and provide a magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material with excellent processing fluidity and mechanical properties and its preparation method.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material. Calculated by mass fraction, its raw material formula consists of the following components: magnesium hydroxide 58.3 - 77.7%, linear low-density polyethylene 19.25 - 39.05%, fluorine-containing small molecule liquid crystal 1.0 - 2.9%, antioxidant 0.1 - 0.3%, initiator 0.01 - 0.05%; The fluorine-containing small molecule liquid crystal is 4-fluoro-benzoic acid-4'-allyloxybenzoic acid hydroquinone diester, and its structural formula is:

[0009]

[0010] To further achieve the purpose of the present invention, preferably, the antioxidant is any one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], n-octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or tris(2,4-di-tert-butylphenyl) phosphite.

[0011] Preferably, the initiator is any one of dicumyl peroxide, benzoyl peroxide or di-tert-butyl peroxide cumene.

[0012] Preferably, the fluorine-containing small molecule liquid crystal is prepared by the following steps:

[0013] (1). Dissolve 1,4-benzenediol in pyridine, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly dropwise add 4-allyloxybenzoyl chloride, controlling the molar ratio of 1,4-benzenediol to 4-allyloxybenzoyl chloride to be 4 - 6:1; After the dropping is completed, react for 16 - 24 h, pour the reaction solution into deionized water, precipitate, filter, wash, and dry to obtain 4-allyloxybenzoic acid-4'-hydroxybenzene ester, and its structural formula is:

[0014] (2). Dissolve 4-allyloxybenzoic acid-4'-hydroxybenzene ester in pyridine, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly dropwise add 4-fluorobenzoyl chloride, controlling the molar ratio of 4-allyloxybenzoic acid-4'-hydroxybenzene ester to 4-fluorobenzoyl chloride to be 1:1 - 1.1. After the dropping is completed, react for 16 - 24 h, precipitate, filter and dry to obtain 4-fluoro-benzoic acid-4'-allyloxybenzoic acid hydroquinone diester.

[0015] Preferably, in step (1), the dosage of pyridine is 4 - 6 times the mass of 1,4-benzenediol; the dosage of deionized water is 20 - 25 times the mass of 1,4-benzenediol.

[0016] Preferably, in step (2), the dosage of pyridine is 8-10 times that of 4-allyloxybenzoic acid 4'-hydroxyphenyl ester; the dosage of deionized water is 30-35 times that of 4-allyloxybenzoic acid 4'-hydroxyphenyl ester.

[0017] Preferably, in step (1), during washing, wash with hot water 3-5 times to remove unreacted 1,4-benzenediol; the precipitated solid is white; the 4-allyloxybenzoic acid 4'-hydroxyphenyl ester is a white solid product.

[0018] In step (2), the precipitation is obtained by pouring the reaction solution into deionized water, and a light yellow precipitate is precipitated; the 4-fluoro-benzoic acid 4'-allyloxybenzoic acid hydroquinone diester is a light yellow powder.

[0019] The preparation method of the magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material is as follows: according to the raw material formula, the dried magnesium hydroxide, linear low density polyethylene, fluorine-containing small molecule liquid crystal, initiator and antioxidant are mixed evenly, and then melted, kneaded, extruded, cooled, pelletized and dried through a twin-screw extruder to obtain the magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material.

[0020] Preferably, the drying is carried out continuously in a blast drying oven at 70-80 °C for 8-12 h.

[0021] Preferably, the temperature of each zone of the twin-screw extruder is controlled between 150-170 °C, and the screw speed is 80-120 rpm.

[0022] Compared with the prior art, the present invention has the following positive effects:

[0023] The present invention uses a fluorine-containing small molecule liquid crystal containing an unsaturated carbon-carbon double bond as a processing aid, which not only has an obvious effect on the processing flow modification of the magnesium hydroxide and linear low density polyethylene blend system, but also forms a graft copolymer by melt grafting onto the main chain of linear low density polyethylene. The obtained magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material has excellent tensile strength and impact strength. Compared with the prior art, the tensile strength, fracture energy and notch impact strength can be increased by 55.0%, 92.5% and 25.7% respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the infrared spectrum of the fluorine-containing small molecule liquid crystal LC-F.

[0025] Figure 2 It is the 1H nuclear magnetic resonance spectrum of the fluorine-containing small molecule liquid crystal LC-F. DETAILED DESCRIPTION OF THE INVENTION

[0026] To further understand the present invention, the present invention will be specifically described below in conjunction with the accompanying drawings and embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than constituting a limitation on the protection scope of the present invention.

[0027] The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The raw materials involved in the following embodiments are all ordinary commercially available products and can be obtained through market purchase without special instructions.

[0028] The 4-allyloxybenzoyl chloride used in the present invention is a product of Hubei Xin Hongli Chemical Co., Ltd., and its CAS number is 36844-51-6.

[0029] The 1,4-benzenediol used is a product of Beijing Innochem Science & Technology Co., Ltd., and the product number is A60547.

[0030] The 4-fluorobenzoyl chloride used is a product of Beijing Innochem Science & Technology Co., Ltd., and the product number is A55746.

[0031] The fluorine-containing small molecule liquid crystal can be prepared by the following three preparation methods:

[0032] A fluorine-containing small molecule liquid crystal synthesized by the present invention has a lower surface energy due to the fluorine atoms. In the blend system of magnesium hydroxide and linear low-density polyethylene, it tends to be distributed at the interface between the two, reducing the agglomeration of magnesium hydroxide particles, improving the processing fluidity of the blend system, and enhancing the dispersion of magnesium hydroxide in linear low-density polyethylene. And due to the presence of unsaturated carbon-carbon double bonds, under the action of peroxide initiators, it can be melt-grafted onto the main chain of linear low-density polyethylene to form a graft copolymer. In this way, its addition will not only not reduce the mechanical properties of the obtained composite material, but also increase the mechanical strength and toughness. Compared with the magnesium hydroxide / linear low-density polyethylene composite materials modified with other processing aids that cannot simultaneously take into account the tensile strength and notch impact strength, both the tensile strength and notch impact strength of the obtained magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material are improved.

[0033] The following provides a preparation method of the fluorine-containing small molecule liquid crystal 4-fluorobenzoic acid-4'-allyloxybenzoic acid hydroquinone diester.

[0034] Preparation Method 1

[0035] (1) Weigh 55.1 g of 1,4-benzenediol into a 500 mL two-necked flask, add 250 mL of pyridine to dissolve it, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly add dropwise 19.7 g of 4-allyloxybenzoyl chloride. After the addition is complete, react for 24 h. Pour the reaction solution into 1250 mL of deionized water. White precipitate will precipitate out. Filter by suction, wash with 200 mL of hot water three times to remove unreacted 1,4-benzenediol, and dry to obtain 20.3 g of a white solid product, which is 4'-hydroxy phenyl 4-allyloxybenzoate, with a yield of 75.2%. Its structural formula is:

[0036]

[0037] (2) Weigh 13.5 g of 4'-hydroxy phenyl 4-allyloxybenzoate into a 250 mL two-necked flask, add 100 mL of pyridine to dissolve it, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly add dropwise 7.9 g of 4-fluorobenzoyl chloride. After the addition is complete, react for 24 h. Pour the reaction solution into 400 mL of deionized water. Pale yellow precipitate will precipitate out. Filter by suction and dry to obtain 12.6 g of a pale yellow powdery product, which is 4-allyloxybenzoic acid 4'-fluoro benzoic acid hydroquinone diester (LC-F), with a yield of 61.5%. Its structural formula is:

[0038]

[0039] Take a small amount of the pale yellow powdery product LC-F sample obtained in step (2) for infrared spectrum analysis. The results are as Figure 1 , and the stretching vibration peak of C=O in the aromatic ester group appears at 1730 cm -1 in the spectrum, the stretching vibration peak of C=C appears at 1649 cm -1 , and the characteristic peak of C-F appears at 1155 cm -1 ; The nuclear magnetic resonance hydrogen spectrum of this sample is as Figure 2 . The solvent is deuterated dimethyl sulfoxide. The chemical shifts corresponding to each hydrogen atom (as shown in the structural formula) are marked on the spectrum. The chemical shifts corresponding to the hydrogen atoms at a are 5.31 ppm and 5.44 ppm, the chemical shift corresponding to the hydrogen atom at b is 6.08 ppm, the chemical shift corresponding to the hydrogen atom at c is 4.72 ppm, the chemical shift corresponding to the hydrogen atom at d is 7.16 ppm, the chemical shift corresponding to the hydrogen atom at e is 8.10 ppm, the chemical shifts corresponding to the hydrogen atoms at f and g are 7.38 ppm, the chemical shift corresponding to the hydrogen atom at h is 8.22 ppm, and the chemical shift corresponding to the hydrogen atom at i is 7.46 ppm; The above infrared spectrum and nuclear magnetic resonance hydrogen spectrum well prove that the product is LC-F.

[0040] Preparation method 2

[0041] (1) Weigh 13.2 g of 1,4-benzenediol into a 500 mL two-necked flask, add 80 mL of pyridine to dissolve it, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly add dropwise 3.9 g of 4-allyloxybenzoyl chloride. After the addition is complete, react for 20 h. Pour the reaction solution into 350 mL of deionized water. White precipitate will precipitate out. Filter it by suction, wash it 4 times with 200 mL of hot water to remove unreacted 1,4-benzenediol, and dry it to obtain 3.6 g of a white solid product, which is 4'-hydroxy phenyl 4-allyloxybenzoate, with a yield of 66.7%.

[0042] (2) Weigh 6.8 g of 4'-hydroxy phenyl 4-allyloxybenzoate into a 250 mL two-necked flask, add 70 mL of pyridine to dissolve it, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly add dropwise 4.4 g of 4-fluorobenzoyl chloride. After the addition is complete, react for 20 h. Pour the reaction solution into 250 mL of deionized water. Light yellow precipitate will precipitate out. Filter it by suction and dry it to obtain 6.1 g of a light yellow powdery product, which is LC-F, with a yield of 59.5%.

[0043] Take a small amount of the light yellow powdery product LC-F sample obtained in step (2) for infrared spectrum analysis and nuclear magnetic resonance hydrogen spectrum analysis. The results are consistent with Preparation Method 1, indicating that LC-F can also be prepared by Preparation Method 2.

[0044] Preparation Method 3

[0045] (1) Weigh 22.0 g of 1,4-benzenediol into a 500 mL two-necked flask, add 90 mL of pyridine to dissolve it, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly add dropwise 9.9 g of 4-allyloxybenzoyl chloride. After the addition is complete, react for 16 h. Pour the reaction solution into 500 mL of deionized water. White precipitate will precipitate out. Filter it by suction, wash it 5 times with 200 mL of hot water to remove unreacted 1,4-benzenediol, and dry it to obtain 8.8 g of a white solid product, which is 4'-hydroxy phenyl 4-allyloxybenzoate, with a yield of 65.0%.

[0046] (2) Weigh 10.2 g of 4'-hydroxy phenyl 4-allyloxybenzoate into a 250 mL two-necked flask, add 80 mL of pyridine to dissolve it, introduce nitrogen protection and place it in an ice-water bath, stir, and slowly add dropwise 6.2 g of 4-fluorobenzoyl chloride. After the addition is complete, react for 16 h. Pour the reaction solution into 300 mL of deionized water. Light yellow precipitate will precipitate out. Filter it by suction and dry it to obtain 8.5 g of a light yellow powdery product, which is LC-F, with a yield of 55.4%.

[0047] Take a small amount of the light yellow powdery product LC-F sample obtained in step (2) for infrared spectrum analysis and nuclear magnetic resonance hydrogen spectrum analysis. The results are consistent with Preparation Method 1, indicating that LC-F can also be prepared by Preparation Method 3.

[0048] The magnesium hydroxide (MH) used in the present invention is a product of Hefei Zhongke Flame Retardant New Materials Co., Ltd., with the brand number FR-2803. The linear low density polyethylene (LLDPE) used is a product of Sinopec Guangzhou Co., Ltd., with the brand number DFDA-7042. The antioxidant used is pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is a product of BASF Chemical Co., Ltd. of Germany, with the brand number antioxidant Irganox 1010. n-Octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is a product of BASF Chemical Co., Ltd. of Germany, with the brand number antioxidant Irganox 1076; tris(2,4-di-tert-butylphenyl) phosphite is a product of BASF Chemical Co., Ltd. of Germany, with the brand number antioxidant Irgafos 168. The initiator used is diisopropylbenzene peroxide (BIBP), which is a product of AkzoNobel, with the brand number 14S-FL; dicumyl peroxide (DCP) is a product of Nouryon Chemicals Co., Ltd., with the brand number Perkadox BC-FF; benzoyl peroxide (BPO) is a product of Nouryon Chemicals Co., Ltd., with the brand number Perkadox L-W35 FCC.

[0049] The following provides an example of a preparation method of a magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material.

[0050] Example 1

[0051] Controlling the total mass to be about 500 g, 77.7 wt% MH, 19.25 wt% LLDPE, 2.9 wt% LC-F (prepared by Preparation Method 3), 0.1 wt% antioxidant 1010 and 0.05 wt% initiator BIBP are uniformly mixed and then added to a twin-screw extruder. Through melting, kneading, extrusion, cooling, pelletizing, and drying, a magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material is obtained. The temperatures of each zone of the twin-screw extruder are 150 °C in the first zone, 155 °C in the second zone, 160 °C in the third zone, 160 °C in the fourth zone, 165 °C in the fifth zone, 165 °C in the sixth zone, 165 °C in the seventh zone, 165 °C in the eighth zone, 170 °C in the ninth zone, 170 °C at the head, and the screw speed is 80 rpm.

[0052] Example 2

[0053] The total controlled mass is about 500 g. After uniformly mixing 74.3 wt% MH, 24.59 wt% LLDPE, 1.0 wt% LC-F (prepared by Preparation Method 2), 0.1 wt% antioxidant 1076, and 0.01 wt% initiator DCP, it is added to a twin-screw extruder. Through melting, kneading, extrusion, cooling, pelletizing, and drying, a magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material is obtained. The temperature of each zone of the twin-screw extruder is 150 °C in the first zone, 155 °C in the second zone, 160 °C in the third zone, 160 °C in the fourth zone, 165 °C in the fifth zone, 165 °C in the sixth zone, 165 °C in the seventh zone, 165 °C in the eighth zone, 170 °C in the ninth zone, 170 °C at the die head, and the screw speed is 90 rpm.

[0054] Example 3

[0055] The total controlled mass is about 500 g. After uniformly mixing 69.0 wt% MH, 29.27 wt% LLDPE, 1.5 wt% LC-F (prepared by Preparation Method 1), 0.2 wt% antioxidant 1076, and 0.03 wt% initiator BPO, it is added to a twin-screw extruder. Through melting, kneading, extrusion, cooling, pelletizing, and drying, a magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material is obtained. The temperature of each zone of the twin-screw extruder is 150 °C in the first zone, 155 °C in the second zone, 155 °C in the third zone, 155 °C in the fourth zone, 160 °C in the fifth zone, 160 °C in the sixth zone, 165 °C in the seventh zone, 165 °C in the eighth zone, 170 °C in the ninth zone, 170 °C at the die head, and the screw speed is 100 rpm.

[0056] Example 4

[0057] The total controlled mass is about 500 g. After uniformly mixing 63.7 wt% MH, 34.06 wt% LLDPE, 1.9 wt% LC-F (prepared by Preparation Method 1), 0.3 wt% antioxidant 168, and 0.04 wt% initiator BPO, it is added to a twin-screw extruder. Through melting, kneading, extrusion, cooling, pelletizing, and drying, a magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material is obtained. The temperature of each zone of the twin-screw extruder is 150 °C in the first zone, 160 °C in the second zone, 160 °C in the third zone, 160 °C in the fourth zone, 160 °C in the fifth zone, 165 °C in the sixth zone, 165 °C in the seventh zone, 165 °C in the eighth zone, 170 °C in the ninth zone, 170 °C at the die head, and the screw speed is 110 rpm.

[0058] Example 5

[0059] The total controlled mass is about 500 g. After uniformly mixing 58.3 wt% MH, 39.05 wt% LLDPE, 2.4 wt% LC-F (prepared by Preparation Method 3), 0.2 wt% antioxidant 168, and 0.05 wt% initiator DCP, it is added to a twin-screw extruder. Through melting, kneading, extrusion, cooling, pelletizing, and drying, a magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material is obtained. The temperature of each zone of the twin-screw extruder is 150 °C in the first zone, 155 °C in the second zone, 155 °C in the third zone, 160 °C in the fourth zone, 160 °C in the fifth zone, 160 °C in the sixth zone, 165 °C in the seventh zone, 165 °C in the eighth zone, 170 °C in the ninth zone, 170 °C at the die head, and the screw speed is 100 rpm.

[0060] Example 6

[0061] The total controlled mass is about 500 g. After uniformly mixing 58.3 wt% MH, 38.57 wt% LLDPE, 2.9 wt% LC-F (prepared by Preparation Method 1), 0.2 wt% antioxidant 1010, and 0.03 wt% initiator BIBP, it is added to a twin-screw extruder. Through melting, kneading, extrusion, cooling, pelletizing, and drying, a magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material is obtained. The temperature of each zone of the twin-screw extruder is 150 °C in the first zone, 155 °C in the second zone, 160 °C in the third zone, 160 °C in the fourth zone, 160 °C in the fifth zone, 160 °C in the sixth zone, 165 °C in the seventh zone, 165 °C in the eighth zone, 170 °C in the ninth zone, 170 °C at the die head, and the screw speed is 110 rpm.

[0062] The twin-screw extruder model used in Examples 1 to 6 is LTE26 / 40 (LabTech Company, Germany).

[0063] Comparative Example 1

[0064] Taking the magnesium hydroxide / linear low-density polyethylene composite modified with polysiloxane side chain liquid crystal polymer (PSCTLCP) in the reference (Design and Synthesis of Polysiloxane Based Side Chain Liquid Crystal Polymer for Improving the Processability and Toughness of Magnesium Hydrate / Linear Low-Density Polyethylene Composites. Polymers, 2020, 12(4): 911) as Comparative Example 1, its formulation is 58.3 wt% MH, 38.8 wt% LLDPE and 2.9 wt% PSCTLCP, and the performance test results are shown in Table 2. This formulation has the same MH mass fraction as Examples 5-6.

[0065] Comparative Example 2

[0066] Taking the magnesium hydroxide / linear low-density polyethylene composite modified with linear silicon-fluorine processing aid (Si-DPF) in the reference (Silicone / fluorine-functionalized flow modifier with low surface energy for improving interfaces in highly filled composites, composites science and technology, 2021, 214: 108994) as Comparative Example 2, its formulation is 77.7 wt% MH, 19.4 wt% LLDPE and 2.9 wt% Si-DPF, and the performance test results are shown in Table 2. This formulation has the same MH mass fraction as Example 1.

[0067] Table 1 Formulations of Examples 1-6 and Flame Retardant Properties of the Obtained Composites

[0068]

[0069]

[0070] The relevant test methods are as follows:

[0071] Processing fluidity: The instrument used is a torque rheometer, model RTOI-55 / 20 (Guangzhou Putong Experimental Analysis Instrument Co., Ltd.), the rotor speed is 50rpm, the test temperature is 170°C, the total volume of the sample is controlled to be 45mL, the raw materials are weighed according to the formula of Examples 1 to 6, the raw materials are evenly mixed and added to the torque rheometer, and the equilibrium torque of the melt is measured after the blending system reaches equilibrium, and the processing fluidity is evaluated by the level of the equilibrium torque. This test method is the same as the equilibrium torque test method of Comparative Examples 1 to 2.

[0072] Tensile properties: tested according to ASTM D-638 standard, the instrument used is a tensile testing machine, model BTI-FR010TH.A50 (Zwick Roell, Germany), and the tensile rate is 50 mm / min.

[0073] Bending properties: The test was conducted in accordance with ASTM D-790. The instrument used was a universal material testing machine, model AGS-10KNI (Shimadzu Corporation, Japan). A three-point bending mode was adopted with a span of 64 mm. The specimen was bent at a rate of 10 mm / min at room temperature until the bending strength reached the maximum value.

[0074] Notched impact strength: tested according to ISO 178:2003 standard, the instrument used is a cantilever beam impact tester, model PTM2302 (Shenzhen Sansi Zongheng Technology Co., Ltd.), the pendulum range is 5.5J. The cantilever beam notched impact method is adopted.

[0075] Limiting oxygen index (LOI): According to ASTM D2863-97 standard, the instrument used is a limiting oxygen index tester, model FTA-SC48 (FTT Company, UK).

[0076] Vertical burning test: According to ASTM D3801-10 standard, the instrument used is a horizontal vertical burning tester, model UL94-SC50 (FTT Company, UK).

[0077] The composite materials obtained in Examples 1 to 6 were placed in a blast drying oven at 90°C for 10 hours, then injection molded into standard specimens, and placed in a dry room temperature environment for 48 hours before the performance test was performed. The formulations of Examples 1 to 6 and the flame retardant properties of the composite materials obtained are shown in Table 1; the performance test results of Examples 1 to 6 and Comparative Examples 1 to 2 are summarized in Table 2.

[0078] From the data results in Table 1 and Table 2, it can be seen that in the present invention, linear low-density polyethylene is graft-modified with fluorine-containing small molecule liquid crystals, and the magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composites obtained in each example have good flame retardancy and mechanical properties. Example 6 of the present invention and Comparative Example 1 have the same magnesium hydroxide filling amount and processing aid addition amount (both are 58.3 wt% and 2.9 wt%). Their balance torques are basically the same, but the mechanical properties are significantly improved compared with Comparative Example 1. Especially the improvement in strength is particularly remarkable. The tensile strength increases from 7.9 MPa to 12.2 MPa, a 54.4% increase; the elongation at break increases from 17.7% to 21.1%, a 19.2% increase, and the notched impact strength increases from 11.5 kJ / m 2 to 12.1 kJ / m 2 , a 5.2% increase.

[0079] For Example 1 and Comparative Example 2 with a higher magnesium hydroxide filling amount, the balance torque of Example 1 of the present invention is slightly higher than that of Comparative Example 2, with a difference of less than 8%. And the performance of Example 1 in terms of mechanical properties is far superior to that of Comparative Example 2. Its tensile strength, fracture energy and notched impact strength reach 12.4 MPa, 20.4 MJ / m 3 and 4.4 kJ / m 2 , respectively, which are increased by 55.0%, 92.5% and 25.7% compared with Comparative Example 2.

[0080] Table 2 Performance test results of Examples 1 - 6 and Comparative Examples 1 - 2

[0081]

[0082] Comparative Examples 1 and 2 modified the magnesium hydroxide flame-retardant modified linear low-density polyethylene system with fluorine-containing or polysiloxane side-chain liquid crystal polymer processing aids, and the improvement effect on the processing fluidity of the system is relatively significant. However, although the toughness of the formed composite material increases, the tensile strength and the like decrease more. In the present invention, by grafting fluorine-containing small molecule liquid crystals onto the molecular chain of linear low-density polyethylene, on the one hand, as a processing aid, the fluorine-containing small molecule liquid crystal has a low surface energy and can be distributed at the interface between magnesium hydroxide particles and the matrix resin to reduce the agglomeration of magnesium hydroxide particles, improve the dispersion of magnesium hydroxide in linear low-density polyethylene, and further improve the processing fluidity of the blend system and the toughness of the obtained composite material; on the other hand, by grafting modification, rigid side chains are introduced onto the molecular chain of linear low-density polyethylene, increasing the steric hindrance of the internal rotation of the molecular chain segments of linear low-density polyethylene, making the molecular chain more rigid, thereby improving the mechanical properties of the composite material and avoiding the damage of the processing aid to the tensile strength of the composite material.

[0083] It can be seen that the present invention overcomes the defect that when the existing fluorine-containing or polysiloxane liquid crystal polymer processing aids are used to modify the magnesium hydroxide flame-retarded linear low-density polyethylene system, a composite material with both good tensile strength and impact strength cannot be obtained. The obtained magnesium hydroxide flame-retarded fluorine-containing small molecule liquid crystal grafted linear low-density polyethylene composite material has both excellent tensile strength and impact strength, and the processing fluidity of the blending system is also improved well, providing a solution to the problems of "energy-consuming and time-consuming" in the production process of inorganic particle high-filled composite materials and the poor comprehensive performance of products. At the same time, the melt grafting can be completed in a twin-screw extruder without changing the existing industrial production process flow. Therefore, this method has broad application value.

[0084] The implementation manners of the present invention are not limited thereto. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement manners and are all included in the protection scope of the invention.

Claims

1. A magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material, characterized in that, In terms of mass fraction, its raw material formula consists of the following components : magnesium hydroxide 58.3 - 77.7%, linear low density polyethylene 19.25 - 39.05%, fluorine-containing small molecule liquid crystal 1.0 - 2.9%, antioxidant 0.1 - 0.3%, initiator 0.01 - 0.05%; the fluorine-containing small molecule liquid crystal is 4-fluoro-benzoic acid-4'-allyloxy benzoic acid hydroquinone diester, and its structural formula is: 。 2. The magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite according to claim 1, characterized in that: The antioxidant is any one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], n-octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate or tris(2,4-di-tert-butylphenyl) phosphite.

3. The magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material according to claim 1, characterized in that: The initiator is any one of dicumyl peroxide, benzoyl peroxide or diisopropylbenzene peroxide.

4. The magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite according to claim 1, characterized in that: The fluorine-containing small molecule liquid crystal is prepared through the following steps: (1) Dissolve 1,4-benzenediol in pyridine, introduce nitrogen for protection and place it in an ice-water bath, stir, and slowly dropwise add 4-allyloxybenzoyl chloride, controlling the molar ratio of 1,4-benzenediol to 4-allyloxybenzoyl chloride to be 4-6:1; after the dropwise addition, react for 16-24 h, pour the reaction solution into deionized water, precipitate out, filter by suction, wash, and dry to obtain 4'-hydroxy phenyl 4-allyloxybenzoate, and the structural formula is: ; (2) Dissolve 4-allyloxy benzoic acid-4'-hydroxy phenyl ester in pyridine, protect it by introducing nitrogen and place it in an ice-water bath, stir, slowly dropwise add 4-fluorobenzoyl chloride, control the molar ratio of 4-allyloxy benzoic acid-4'-hydroxy phenyl ester to 4-fluorobenzoyl chloride to be 1:1 - 1.1, after the dropping is completed, react for 16 - 24 h, precipitate, filter by suction and dry to obtain 4-fluoro-benzoic acid-4'-allyloxy benzoic acid hydroquinone diester.

5. The magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite according to claim 4, characterized in that: In step (1), the dosage of pyridine is 4 - 6 times the mass of hydroquinone; the dosage of deionized water is 20 - 25 times the mass of hydroquinone.

6. The magnesium hydroxide flame-retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite according to claim 4, wherein: In step (2), the dosage of pyridine is 8 - 10 times that of 4-allyloxy benzoic acid-4'-hydroxy phenyl ester; the precipitation is to pour the reaction solution into deionized water to precipitate a light yellow precipitate; the dosage of deionized water is 30 - 35 times that of 4-allyloxy benzoic acid-4'-hydroxy phenyl ester.

7. The magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite according to claim 4, wherein: In step (1), during washing, wash with hot water 3 - 5 times to remove unreacted hydroquinone; the precipitate is white; the 4-allyloxy benzoic acid-4'-hydroxy phenyl ester is a white solid product; In step (2), the 4-fluoro-benzoic acid-4'-allyloxy benzoic acid hydroquinone diester is a light yellow powder.

8. The preparation method of the magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material according to any one of claims 1-7, characterized in that, According to the raw material formula, uniformly mix the dried magnesium hydroxide, linear low density polyethylene, fluorine-containing small molecule liquid crystal, initiator and antioxidant, and melt, knead, extrude, cool, pelletize and dry through a twin-screw extruder to obtain a magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite material.

9. The preparation method of the magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite according to claim 8, characterized in that: The drying is carried out continuously in a blast drying oven at 70 - 80 °C for 8 - 12 h.

10. The preparation method of the magnesium hydroxide flame retardant modified fluorine-containing small molecule liquid crystal grafted linear low density polyethylene composite according to claim 8, characterized in that: The temperature of each zone of the twin-screw extruder is controlled between 150 - 170 °C, and the screw speed is 80 - 120 rpm.

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