Low-smoke halogen-free phosphorus-free flame-retardant polypropylene composite material and preparation method thereof

Abstract

The invention discloses a low-smoke halogen-free phosphorus-free flame-retardant polypropylene composite material, which is prepared from the following ingredients in parts by weight: 40 to 50 parts of polypropylene, 20 to 40 parts of magnesium hydroxide, 8 to 20 parts of branched polyolefin materials, 5 to 15 parts of maleic anhydride grafted branched polyolefin materials and 0.1 to 3 parts of antioxidants. The branched polyolefin material has a long and short branched chain structure, and the weight-average molecular weight is 2000-8000000 g / mol; the branching degree is 40 to 250 / 1000 DEG C, and the melt index is 0.01 to 20 g / 10 min. The branching degree of the branched polyolefin material is improved, the toughening efficiency is improved, the compatibility is further improved by grafting the branched polyolefin material with maleic anhydride, magnesium hydroxide is relatively uniformly distributed at an interface between the maleic anhydride grafted branched polyolefin material and a polymer through step-by-step extrusion, the flame-retardant efficiency is improved, and the flame-retardant performance of the material is improved. The consumption of magnesium hydroxide is obviously reduced. The flame retardant property and the mechanical property of the polypropylene composite material are remarkably improved, and the polypropylene composite material has good processing fluidity and high market value.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials and their processing, and particularly relates to a low-smoke, halogen-free, phosphorus-free flame-retardant polypropylene composite material and a preparation method thereof. Background Art

[0002] Polypropylene (PP) materials have excellent mechanical properties and chemical stability. However, polypropylene has the disadvantages of too low oxygen index and easy flammability, and it needs to add flame retardants to increase its flame retardant performance before it can be used in fields with flame retardant requirements such as automobiles, household appliances, and cables.

[0003] Halogen flame retardants generate more smoke and corrosive gases during pyrolysis or combustion, seriously affecting the ecological environment and have been gradually phased out. Halogen-free flame retardants are the current research focus. Commonly used halogen-free flame retardants include phosphorus-containing flame retardants, intumescent flame retardants, inorganic metal flame retardants, etc. Phosphorus-containing flame retardants contain phosphorus elements, which may pose a threat to human health if exposed for a long time. Intumescent flame retardants are prone to moisture absorption, easy to undergo alcoholysis between components, and have poor anti-migration and compatibility, with a large amount of smoke evolution.

[0004] Inorganic metal flame retardants mainly refer to aluminum hydroxide and magnesium hydroxide. They can absorb a large amount of heat released during polymer combustion, inhibit the generation of smoke, do not produce secondary pollution, have good stability, are non-toxic, inexpensive and non-volatile, and are better smokeless and halogen-free flame retardants. Among them, the decomposition temperature of aluminum hydroxide is relatively low, close to the extrusion temperature of polypropylene, so its application is limited. The decomposition temperature of magnesium hydroxide is higher, and no toxic or harmful substances are produced during the decomposition process, meeting the requirements of green environmental protection.

[0005] However, magnesium hydroxide has the problem of low flame retardant efficiency. To achieve an ideal flame retardant effect, a high filling amount is usually required, generally at least more than 50% of the total mass of the polymer to have a better flame retardant effect. Moreover, magnesium hydroxide has strong polarity, is prone to agglomeration, and has poor compatibility with polymers. Directly adding it to PP has a greater impact on its mechanical properties.

[0006] The existing technologies to improve the mechanical properties of magnesium hydroxide include:

[0007] (1) Co-fire retard with co-fire retardants to reduce the addition amount of magnesium hydroxide. However, co-fire retardants may still bring environmental protection and health problems.

[0008] (2) Modify magnesium hydroxide. Commonly used are various coupling agents, fatty acid salts, etc. After modification, magnesium hydroxide has better compatibility with polypropylene, which is beneficial to improving the flame retardant performance. Modified magnesium hydroxide is already a relatively mature market product.

[0009] (3) Add compatibilizers, elastomers, etc. Compatibilizers improve compatibility, and elastomers can improve the adhesion between interfaces and improve the toughness of polymers.

[0010] However, in the prior art, the dosage of magnesium hydroxide is still relatively large, and it has a great impact on the mechanical properties of polymers, which limits the application of magnesium hydroxide flame-retardant polypropylene. Moreover, too much filler will cause the melt index of the polymer to decrease, and too low fluidity is not conducive to injection molding production. It is necessary to develop a high-strength, high-toughness and high-melt-index magnesium hydroxide flame-retardant polypropylene, which can improve its mechanical properties on the premise of ensuring the flame-retardant performance, is easy to process, and can be used in multiple application fields. Summary of the Invention

[0011] In view of this, the present invention aims to overcome the defects and deficiencies in the prior art, and proposes a low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material and its preparation method. Through the action of long and short branched chains of the branched polyolefin material, the dispersibility of the magnesium hydroxide flame retardant is improved, and good flame-retardant effect can be achieved with a lower dosage of magnesium hydroxide, while ensuring the mechanical properties of polypropylene, having a high melt index, and having good processing performance.

[0012] To achieve the above object, the technical solution adopted by the present invention is:

[0013] A low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material, characterized in that the low-smoke, halogen-free and phosphorus-free polypropylene composite material comprises the following components in parts by weight:

[0014] Polypropylene 40 - 50 parts

[0015] Magnesium hydroxide 20 - 40 parts

[0016] Branched polyolefin material 8 - 20 parts

[0017] Maleic anhydride grafted branched polyolefin material 5 - 15 parts

[0018] Antioxidant 0.1 - 3 parts.

[0019] Preferably, the melt index of the polypropylene is 1 - 30 g / 10 min, more preferably 5 - 15 g / 10 min, under the test conditions of 190 °C and a load of 2.16 kg.

[0020] The low-smoke, halogen-free and phosphorus-free polypropylene composite material may also be added with inorganic co-flame retardants, such as montmorillonite, zinc borate, etc. The dosage of the inorganic co-flame retardant is generally 5 - 20% of the mass of magnesium hydroxide.

[0021] In the present invention, the magnesium hydroxide is unmodified magnesium hydroxide or modified magnesium hydroxide, and the contact angle between the surface of the modified magnesium hydroxide and water is below 120 °C, preferably below 90 °C.

[0022] The modified magnesium hydroxide is prepared by reacting magnesium hydroxide with a surface modifier, and the surface modifier can be one or more of silane coupling agents, titanate coupling agents, dimethyl silicone oil, stearic acid, and stearates.

[0023] The antioxidant is any one or a mixture of two of phenolic antioxidants and phosphite antioxidants, such as antioxidant 1010, antioxidant 1035, antioxidant DSTP, etc.

[0024] The branched polyolefin material has long and short branched chain structures, with a weight-average molecular weight of 2000 - 8000000 g / mol; the degree of branching is 40 - 250 / 1000C, and the melt index under the conditions of 190°C and a load of 2.16 kg is 0.01 - 20 g / 10 min.

[0025] Furthermore, the branched polyolefin material is one or a combination of branched structure materials prepared from ethylene or a mixture of ethylene and C3 - C5 olefins as raw materials through a solution polymerization method. The branched polyolefin material is preferably a single ethylene branched polymerization product. The appearance of the branched polyolefin material can be in the form of an elastomer, rubber, oil, or wax.

[0026] Furthermore, the weight-average molecular weight of the branched polyolefin material is preferably 50000 - 500000 g / mol, the degree of branching is 60 - 150 / 1000C (more preferably 65 - 100 / 1000C), and the melt index under the conditions of 190°C and a load of 2.16 kg is 0.5 - 15 g / 10 min, more preferably 5 - 15 g / 10 min.

[0027] Furthermore, the melting point of the main component of the branched polyolefin material is -20°C to 90°C, preferably 20 - 80°C; the crystallinity is 0 - 15%, preferably 0.1 - 15%, more preferably 0.1 - 8%.

[0028] In the present invention, the branched polyolefin material can be prepared by the following method:

[0029] Add an organic solvent, a catalyst, and a cocatalyst into a reactor, control the temperature at 10 - 100°C, introduce ethylene into the reactor for a polymerization reaction, the ethylene pressure is 0.1 - 5 MPa, the reaction time is 10 - 90 min. After the reaction, add the reaction solution into acidified ethanol to terminate the reaction to obtain a solid precipitate. Wash and dry the solid precipitate to obtain the branched polyolefin material;

[0030] The catalyst is a late transition metal catalyst;

[0031] The late transition metal catalyst is a metal complex olefin polymerization catalyst with late transition metal atoms such as nickel (II), palladium (II), iron (II), cobalt (II), ruthenium (II), etc. as the active center, and the chelating ligand is selected from types such as N^N, P^N, N^O, P^O, etc. All kinds of late transition metal catalysts disclosed in the prior art that can catalyze the polymerization of ethylene to prepare branched polyolefins and can obtain the defined parameters of the branched polyolefin materials of the present invention can be applied to the present invention.

[0032] Furthermore, the late transition metal catalyst is a nickel / palladium complex; more preferably, it is an α-diimine nickel catalyst.

[0033] The cocatalyst is one or more of diethylaluminum chloride, dichloroethylaluminum, methylaluminoxane, polymethylaluminoxane, ethylaluminum sesquichloride (EASC), and preferably ethylaluminum sesquichloride.

[0034] The molar ratio of Al in the cocatalyst to Ni in the α-diimine nickel catalyst is 50 - 1000:1.

[0035] The polymerization reaction is carried out in an organic solvent, and the organic solvent is one or more of dichloromethane, toluene, and n-hexane.

[0036] Preferably, the reaction temperature of the polymerization reaction is 20 - 80 °C, and the reaction pressure is 0.5 - 3 MPa.

[0037] In the present invention, a branched structure with adjustable long and short chain branches is obtained by long-chain branched polymerization in solution using a late transition metal catalyst. Since the present invention is an in-situ polymerization of ethylene, the branches contain long chains and short chains, with a high degree of branching, and the long branches increase the crosslinking points, resulting in a lower crystallinity and improved elastomer properties.

[0038] The maleic anhydride grafted branched polyolefin material is prepared by reacting the branched polyolefin material of the present invention with maleic anhydride, and the grafting rate is 1.5 - 3.5%.

[0039] In the present invention, the maleic anhydride grafted branched polyolefin material is used to further improve the compatibility with the inorganic flame retardant, enhance the interfacial adhesion force, and through the feeding sequence, the magnesium hydroxide powder is mainly distributed at the interface boundary between the maleic anhydride grafted branched polyolefin material and the polymer matrix. Magnesium hydroxide can decompose in a timely and sufficient manner during combustion to play a flame retardant role.

[0040] Furthermore, preferably, the low-smoke, halogen-free, and phosphorus-free polypropylene composite material comprises the following components in parts by weight:

[0041] Polypropylene 40 - 50 parts

[0042] Magnesium hydroxide 25 - 30 parts

[0043] 15 - 20 parts of branched polyolefin material

[0044] 10 - 15 parts of maleic anhydride - grafted branched polyolefin material

[0045] 0.1 - 0.5 parts of antioxidant

[0046] The mass fraction of the magnesium hydroxide in the low - smoke, halogen - free, phosphorus - free polypropylene composite material is preferably 25 - 32%, more preferably 25 - 30%.

[0047] The present invention also provides a preparation method of the low - smoke, halogen - free, phosphorus - free polypropylene composite material, and the method is one of the following:

[0048] (1) Step - by - step method:

[0049] Take each raw material according to the formula ratio. For magnesium hydroxide, maleic anhydride - grafted branched polyolefin material, the first part of the branched polyolefin material, and if there is a co - flame retardant, add the co - flame retardant, and melt - extrude and pelletize with a twin - screw extruder to obtain an intermediate material; then melt - extrude the intermediate material, the remaining branched polyolefin material, polypropylene, and antioxidant with a twin - screw extruder to prepare the low - smoke, halogen - free, phosphorus - free polypropylene composite material;

[0050] Furthermore, the dosage of the first part of the branched polyolefin material is 50 - 75% of the total dosage of the branched polyolefin material;

[0051] The temperature of the melt - extrusion by the twin - screw extruder is preferably 140 - 230°C.

[0052] (2) One - step method:

[0053] For a twin - screw extruder equipped with a separate metering feeding system and capable of achieving segmented feeding, the one - step method can be adopted, and the steps are as follows:

[0054] Take each raw material according to the formula ratio. For magnesium hydroxide, maleic anhydride - grafted branched polyolefin material, the first part of the branched polyolefin material, and if there is a co - flame retardant, add the co - flame retardant, and feed them into the main feeding port of the twin - screw extruder according to the measurement; the remaining branched polyolefin material, polypropylene, and antioxidant are fed into the secondary feeding port that is at least 1 section of the barrel away from the main feeding port; finally, the low - smoke, halogen - free, phosphorus - free polypropylene composite material is prepared through one - time melt - extrusion.

[0055] The dosage of the first part of the branched polyolefin material is 50 - 75% of the total dosage of the branched polyolefin material;

[0056] The temperature of the melt - extrusion by the twin - screw extruder is preferably 140 - 230°C.

[0057] Further, the typical extrusion process of the twin-screw extruder is preferably as follows: the temperature of the conveying section is 90 - 150 °C, the temperature of the melting section is 140 - 230 °C, the temperature of the homogenizing section is 160 - 230 °C, the temperature of the die is 190 - 230 °C, and the screw speed is 50 - 150 rpm.

[0058] Compared with the prior art, the present invention has the following advantages:

[0059] (1) In the present invention, the degree of branching of the branched polyolefin material is increased, and different combinations of branch chain types and lengths endow the material with a special molecular chain entanglement structure and rheological properties, improving its toughening and dispersing effects. Moreover, by grafting maleic anhydride onto the branched polyolefin material, the compatibility between the inorganic flame retardant particles and the polymer is further improved, facilitating the dispersion of the inorganic particles and enhancing its flame retardant effect.

[0060] (2) In the preparation method, the maleic anhydride-grafted branched polyolefin material, a part of the branched polyolefin material, and magnesium hydroxide are first melt-extruded. The principle is that after the branched polyolefin material is grafted with maleic anhydride, its surface becomes polar, and the surface of magnesium hydroxide also contains polar hydroxyl groups. Therefore, the two have better compatibility, and magnesium hydroxide will be more distributed in the maleic anhydride-grafted branched polyolefin material. After the maleic anhydride-grafted branched polyolefin material, a part of the branched polyolefin material, and magnesium hydroxide are extruded, they are then melt-extruded with polypropylene and the remaining branched polyolefin material. The highly branched polyolefin material is conducive to the uniform dispersion of the intermediate material with magnesium hydroxide in polypropylene. After secondary extrusion, magnesium hydroxide is relatively evenly distributed at the interface between the maleic anhydride-grafted branched polyolefin material and the polymer. During combustion, it will not be wrapped by the branched polyolefin material and can decompose fully to absorb heat, thus improving its flame retardant efficiency and reducing the dosage of magnesium hydroxide. In the present invention, only 25 - 32% dosage of magnesium hydroxide is required to achieve a VO-level flame retardancy. Compared with polypropylene with the same flame retardant performance in the prior art, the dosage of magnesium hydroxide in the present invention is significantly reduced.

[0061] (3) The branched polyolefin material with long and short branch chain structures as a toughening agent can effectively improve the toughening efficiency of the matrix, enhance the impact strength and low-temperature toughness, and improve the filler loading effect. The branched polyolefin material and the maleic anhydride-grafted branched polyolefin material have good compatibility, improving the mechanical properties of the polypropylene composite material, and the toughening efficiency is very high. In the present invention, under the same dosage, using a low molecular weight and high melt index branched polyolefin material can achieve a toughening effect equivalent to or even better than that of conventional high molecular weight and low melt index POE. However, compared with low melt index POE, the high melt index branched polyolefin material in the present invention increases the melt index of the polypropylene composite material and significantly improves the processing fluidity.

[0062] The branched polyolefin material of the present invention has a large melt index and good fluidity, which is beneficial to improving the compatibility with polypropylene. Moreover, the inorganic flame retardant particles are more uniformly dispersed in polypropylene, which is beneficial to exerting its flame retardant effect and has a certain reinforcing effect. Therefore, the flame retardant performance and mechanical properties of the polypropylene composite material of the present invention are significantly improved, and it has good processing fluidity and great market value. Detailed Embodiments

[0063] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0064] The present invention will be described in detail below with reference to embodiments.

[0065] Example 1

[0066] Into 100 mL of n - hexane solvent, add α - diimine nickel catalyst (5 μmol) and sesquiethylaluminum chloride (2 mmol), control the temperature at 20 - 80 °C, introduce ethylene, and carry out the polymerization reaction. Start timing after the ethylene pressure is stable. The ethylene pressure is 0.1 - 5 MPa, and the reaction time is 10 - 70 min. After the reaction is completed, add the reaction solution into 200 mL of acidified ethanol, stir for 10 h, filter by suction, wash with ethanol, and dry under vacuum to obtain the branched polyolefin material;

[0067] The α - diimine nickel catalyst used in this example was prepared according to the following reaction formula:

[0068]

[0069] In the formula I, R1 is phenyl or substituted phenyl, and the substituted phenyl is p - aminophenyl, p - methylphenyl, p - methoxyphenyl or p - tert - butylphenyl;

[0070] R2 is phenyl or substituted phenyl, and the substituted phenyl is p - methylphenyl, p - methoxyphenyl, p - fluorophenyl or p - tert - butylphenyl;

[0071] R3 is phenyl or substituted phenyl, and the substituted phenyl is p - methoxyphenyl, p - fluorophenyl or p - tert - butylphenyl;

[0072] In toluene solvent, the aniline compound shown in formula II and butanedione are mixed in a molar ratio of 2 - 2.2:1, and under the action of a catalytic amount of p - toluenesulfonic acid, it is heated to 60 - 90 °C and reacted for 20 - 24 hours. Then, water is separated with a water separator and refluxed for 2 - 3 days to obtain the diimine ligand compound shown in formula III;

[0073] The diimine ligand compound shown in Formula III and (DME)NiBr2 are mixed at a molar ratio of 1:0.5 - 2, dissolved in dichloroethane solvent, and stirred under nitrogen protection for 10 - 24 h to obtain the α-diimine nickel catalyst shown in Formula I.

[0074] In this example, to prepare the α-diimine nickel catalyst where R1, R2, and R3 are all p-tert-butylphenyl, the specific method is as follows:

[0075] 2,4-Bis(p-tert-butylphenyl)-6-di(p-tert-butylphenyl)methylaniline (4 mmol) and butanedione (2 mmol) are dissolved in 100 mL of toluene, 10 mg of p-toluenesulfonic acid (PTSA) is added, and the mixture is stirred and refluxed at 80 °C for 24 h. Then it is refluxed with a Dean-stark water separator for 3 days. After the reaction solution is cooled to room temperature, part of the solvent is evaporated under reduced pressure to precipitate a solid. 400 mL of methanol is added to precipitate the solid product, which is filtered. The filter cake is washed with methanol and dried to obtain the diimine ligand compound with a yield of 81%.

[0076] Under nitrogen protection, the diimine ligand compound and (DME)NiBr2 (0.2 mmol) and the diimine ligand compound (0.20 mmol) are mixed and dissolved in 5 mL of dichloromethane, stirred at room temperature for 20 h. After removing dichloromethane under reduced pressure, ether is added to precipitate a red solid, which is filtered, washed with ether, and dried to obtain the α-diimine nickel catalyst. The yield is approximately 85%.

[0077] Using ethylene as the raw material, n-hexane as the solvent, the α-diimine nickel catalyst as the catalyst, and sesquiethylaluminum chloride as the cocatalyst, by adjusting the main-cocatalyst ratio, process, and product compounding combination, branched structure materials B1 (reaction temperature 30 °C, pressure 0.4 MPa, melt index 1.2 g / 10 min, molecular weight 130,000, branching degree 45 / 1000C, crystallinity 15%, melting point 75 °C), B2 (reaction temperature 48 °C, pressure 0.5 MPa, melt index 12 g / 10 min, molecular weight 160,000, branching degree 65 / 1000C, melting point 63 °C, crystallinity 8%), and B3 (melt index 5 g / 10 min, molecular weight 250,000, branching degree 80 / 1000C, melting point 60 °C, crystallinity 4%, reaction temperature 50 °C, pressure 0.6 MPa) are respectively prepared.

[0078] Using ethylene and octene as raw materials, alkane as the solvent, and a transition metal complex catalyst, a branched structure elastomer B4 (melt index 1.1 g / 10 min, molecular weight 200,000, branching degree 40 / 1000C, crystallinity 18%, melting point 60 °C) is prepared.

[0079] Prepare maleic anhydride grafted branched polyolefin materials:

[0080] In an acetone solvent, maleic anhydride and styrene were mixed in a mass ratio of 1:1. The resulting mixture was mixed with branched polyolefin material B2 in a mass ratio of 5:95. Then, 0.2% of initiator DCP was added, and it was melt-extruded at 180 °C using a twin-screw extruder. The solvent was removed by drying to obtain maleic anhydride-grafted branched polyolefin material, and the grafting rate was 3.1%.

[0081] The branched structural materials B1, B2, B3, the branched structural elastomer B4, and the maleic anhydride-grafted branched polyolefin material were used to prepare polypropylene composites. The specific steps were as follows:

[0082] 10 kg of branched polyolefin (branched structural material B1 was used in Experiment 1, branched structural material B2 was used in Experiment 2, branched structural material B3 was used in Experiment 3, and branched structural elastomer B4 was used in Experiment 4), 25 kg of modified magnesium hydroxide (particle size 1 - 3 μm, modified with sodium stearate, contact angle 88°), 10 kg of maleic anhydride-grafted branched polyolefin material were extruded and pelletized at 160 °C to obtain an intermediate material. Then, the intermediate material, 5 kg of branched polyolefin (branched structural material B1 was used in Experiment 1, branched structural material B2 was used in Experiment 2, branched structural material B3 was used in Experiment 3, and branched structural elastomer B4 was used in Experiment 4), 50 kg of polypropylene (MFR = 15 g / 10 min), 0.3 kg of antioxidant 1010, and 0.2 kg of antioxidant 168 were melt-extruded using a twin-screw extruder with a length-diameter ratio of 40:1. The extrusion conditions were: conveying section temperature 100 °C, melting section temperature 205 °C, homogenization section temperature 210 °C, die temperature 210 °C, and screw speed 120 rpm to obtain a low-smoke, halogen-free, and phosphorus-free polypropylene composite.

[0083] The low-smoke, halogen-free, and phosphorus-free polypropylene composites prepared in Experiments 1 - 4 were tested for mechanical properties and flame retardancy. The results are shown in Table 1 below.

[0084] Table 1

[0085]

[0086]

[0087] The experimental results proved that the degree of branching of the branched structural material B1 in Experiment 1 was only 45 / 1000C. Its melt index was relatively low, the molecular weight was also relatively low, and there were fewer long and short branches. The dispersibility of the intermediate material with magnesium hydroxide was poor, and the amount of magnesium hydroxide used was also small, only accounting for 25%. It was very difficult to achieve a good flame retardant effect with this conventional dosage ratio. Therefore, the flame retardancy of Experiment 1 was poor.

[0088] In addition, the mechanical properties of Experiment 1 were poor. On the one hand, this was related to the lower degree of branching and the poorer toughening performance. On the other hand, the poor dispersion of 25% inorganic filler added also led to a significant decrease in the tensile strength.

[0089] The elastomer in Experiment 4 was ethylene-octene copolymer, which had the lowest degree of branching among the four elastomers. However, it had a high molecular weight and a low melt index. Therefore, its mechanical properties were comparable to those of Experiment 1. However, the mechanical properties were also affected by the uneven distribution of magnesium hydroxide, and the tensile strength was poor.

[0090] The melt indices of the composites in Experiment 1 and Experiment 4 were both low, and the processing fluidity was poor.

[0091] The branched structure material B1 in Experiment 1 had a low degree of branching and a high crystallinity, so its melt index was also low; the ethylene-octene copolymer in Experiment 4 had a high molecular weight and a low melt index. Therefore, the melt indices of the polypropylene composites prepared in Experiment 1 and Experiment 4 were also low, which was not conducive to subsequent industrial processing.

[0092] The branched structure materials B2 and B3 in Experiment 2 and Experiment 3 themselves had a high melt index, good fluidity, and better dispersion of the filler. Therefore, the composites prepared had a high melt index and good processability.

[0093] Moreover, the branched structure materials B2 and B3 used in Experiment 2 and Experiment 3 had a high melt index and a low molecular weight, but the toughening effect was higher than that of the elastomer with a low melt index and a high molecular weight in Experiment 4. The notched Izod impact strength at room temperature and low temperature was significantly better than that of Experiment 4.

[0094] The flame retardant effect of Experiment 4 was also poor. Because the ethylene-octene copolymer had a low degree of branching, when the intermediate material with magnesium hydroxide was extruded for the second time, due to the effect of magnesium hydroxide, it could not be well dispersed in the polymer matrix, resulting in poor mechanical properties and flame retardant properties.

[0095] In Experiment 2 and Experiment 3, without using octene raw materials, the degree of branching of the ethylene copolymer was increased, and branched structure materials with a degree of branching of 65-80 / 1000C were used. The low-temperature impact resistance was significantly improved. Moreover, due to the high degree of branching and the matching of long and short branches, the intermediate material with magnesium hydroxide could be well dispersed into the polypropylene under its action, and the mechanical properties and flame retardant properties were also significantly improved compared with Experiment 1 and Experiment 4.

[0096] And in Experiment 2 and Experiment 3, under the condition of only using 25% magnesium hydroxide, the flame retardancy could reach the V0 level, significantly improving the flame retardant efficiency of magnesium hydroxide.

[0097] The possible mechanism is as follows:

[0098] After the branched polyolefin material is grafted with maleic anhydride, its surface becomes polarized, and the surface of magnesium hydroxide also contains polar hydroxyl groups. Therefore, the two have better compatibility. In the preparation process, first, the maleic anhydride-grafted branched polyolefin material, about 66% of the branched polyolefin material, and magnesium hydroxide are melt-blended and extruded. At this time, magnesium hydroxide will be more dispersed in the maleic anhydride-grafted branched polyolefin material, and the maleic anhydride-grafted branched polyolefin material and the branched polyolefin material also have good compatibility due to having the same matrix.

[0099] The intermediate material with magnesium hydroxide is then melt-extruded with polypropylene and the remaining about 33% of the branched polyolefin material. The highly branched branched polyolefin material enables the intermediate material with magnesium hydroxide to be better dispersed in the polypropylene matrix. In this process, magnesium hydroxide is more evenly distributed at the interface between the maleic anhydride-grafted branched polyolefin material and the polymer. During the combustion experiment, the magnesium hydroxide at the interface can decompose and absorb heat faster, and the released water vapor during combustion will not be wrapped by the branched polyolefin material, enabling it to fully decompose, absorb heat, and release water vapor for flame retardancy. Therefore, its flame retardancy efficiency is improved and the dosage of magnesium hydroxide is reduced. In Experiments 2 and 3, only 25% dosage of magnesium hydroxide is added to achieve a VO-level flame retardancy. Compared with polypropylene with the same flame retardancy performance in the prior art, the dosage of magnesium hydroxide in the present invention is significantly reduced.

[0100] Example 2

[0101] Charging is carried out according to the formulation in Table 2, and the raw materials and preparation process are the same as those in Example 1.

[0102] Table 2: Experimental formulation (kg)

[0103]

[0104] The mechanical properties and flame retardancy performance results of the low-smoke, halogen-free, and phosphorus-free polypropylene composites in Experiments 5 - 8 are shown in Table 3 below.

[0105] Table 3

[0106]

[0107] Judging from the results in Table 3, in Experiments 5 and 7, compared with Experiment 2, the content of magnesium hydroxide is increased, and its tensile strength does not change significantly. The flexural strength and flexural modulus increase with the increase of the filler. The impact resistance and low-temperature toughness also increase due to the increase in the dosage of the branched structure material.

[0108] Due to the increase in the content of magnesium hydroxide, the melt index decreases slightly. However, due to the relatively high melt index of the branched structure material B2 itself, the melt index of the final composite material is still relatively high.

[0109] As the content of magnesium hydroxide increases, the flame retardancy performance also improves accordingly.

[0110] However, when comparing Experiment 6 with Experiment 4, although the content of magnesium hydroxide was increased, branched elastomer B4 was used in Experiment 6, which had a relatively low degree of branching and poor load-bearing dispersion of magnesium hydroxide. Therefore, the flame retardancy was still poor and could not reach the V0 level. Moreover, due to the increase in the filler content, the tensile strength of Experiment 6 decreased significantly, and the melt index decreased significantly, which was not conducive to subsequent processing.

[0111] In Experiment 8, the maleic anhydride-grafted branched polyolefin material was not added, which led to a decrease in compatibility, a decrease in the interfacial bonding ability of the polymer, and a decrease in mechanical properties. In addition, magnesium hydroxide could not be distributed on the interface of the maleic anhydride-grafted branched polyolefin material, and part of the magnesium hydroxide was coated in the branched structural material B2, inhibiting or delaying the decomposition of magnesium hydroxide, which led to a significant decrease in flame retardancy.

[0112] Example 3

[0113] Experiment 9: Charge materials according to the formula of Experiment 2. However, change the preparation process as follows:

[0114] 15 kg of branched structural material B2, 10 kg of maleic anhydride-grafted branched polyolefin material, 50 kg of polypropylene (MFR = 15 g / 10 min), 25 kg of modified magnesium hydroxide (particle size 1 - 3 μm, modified with sodium stearate, contact angle 88°), 0.3 kg of antioxidant 1010, 0.2 kg of antioxidant 168. Use a twin-screw extruder for melt extrusion, with a length-diameter ratio of 40:1. The extrusion conditions are: conveying section temperature 100 °C, melting section temperature 205 °C, homogenization section temperature 210 °C, die temperature 210 °C, screw speed 120 rpm, to obtain a polypropylene composite material.

[0115] In Experiment 10, the raw materials and experimental steps were the same as those in Experiment 2. The difference was that the modified magnesium hydroxide (particle size 1 - 3 μm, modified with sodium stearate, contact angle 88°) was replaced with modified magnesium hydroxide with a contact angle of 135°.

[0116] The results of the mechanical properties and flame retardancy of the polypropylene composite materials in Experiments 9 - 10 are shown in Table 4 below.

[0117] Table 4

[0118]

[0119] In Experiment 9, the one-step extrusion method was adopted. At this time, magnesium hydroxide was more evenly distributed in the polymer matrix, rather than evenly distributed at the interface of the maleic anhydride-grafted branched polyolefin material. Therefore, some magnesium hydroxide was coated in the branched structure material B2, inhibiting or delaying the decomposition of magnesium hydroxide, which led to a decrease in flame retardancy. Therefore, the preferred preparation method of the present invention is to first melt-extrude magnesium hydroxide and the maleic anhydride-grafted branched polyolefin material, and the method of the first part of the branched polyolefin material, so that magnesium hydroxide is first distributed more in the maleic anhydride-grafted branched polyolefin material. During the second extrusion, it is beneficial for magnesium hydroxide to be more evenly distributed at the interface between the maleic anhydride-grafted branched polyolefin material and the polymer, improving its flame retardancy efficiency.

[0120] In Experiment 10, modified magnesium hydroxide with a larger contact angle was used. Since the contact angle is large, it means that after being treated with a surface modifier, its surface is more non-polar and has better compatibility with the polymer. Therefore, the mechanical properties have all increased. However, the modified magnesium hydroxide with a larger contact angle will be more evenly dispersed in the entire polymer matrix, and some magnesium hydroxide will be coated in the branched structure material B2, unable to be evenly distributed at the interface between the maleic anhydride-grafted branched polyolefin material and the polymer, resulting in low flame retardancy efficiency and poor flame retardancy performance.

[0121] Generally speaking, according to the conventional process, magnesium hydroxide usually needs to be added to more than 35% to have a good flame retardant effect, or it needs to be used in combination with other flame retardant aids. In this application, by using modified magnesium hydroxide to adjust its contact angle to a specific angle, it cannot be completely non-polar, and by adopting a segmented extrusion process, the flame retardancy efficiency of magnesium hydroxide is improved, and it can reach V0 flame retardant performance at a lower dosage and maintain good mechanical properties.

[0122] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-smoke, halogen-free, phosphorus-free flame-retardant polypropylene composite material, characterized in that The low-smoke, halogen-free, phosphorus-free polypropylene composite material comprises the following components in parts by weight: Polypropylene: 40 - 50 parts Magnesium hydroxide: 20 - 40 parts Branched polyolefin material: 8 - 20 parts Maleic anhydride grafted branched polyolefin material: 5 - 15 parts Antioxidant: 0.1 - 3 parts; The branched polyolefin material has long and short branched chain structures, a weight average molecular weight of 2000 - 8000000 g / mol; the degree of branching is 40 - 250 / 1000C, and the melt index at 190°C and a load of 2.16 kg is 0.01 - 20 g / 10 min.

2. The low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material according to claim 1, characterized in that The branched polyolefin material is one or a combination of branched structure materials prepared from ethylene or ethylene and C3 - C5 olefins as raw materials by a solution polymerization method.

3. The low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material according to claim 1, characterized in that The branched polyolefin material has a weight average molecular weight of 50000 - 500000 g / mol, a degree of branching of 60 - 150 / 1000C, and a melt index at 190°C and a load of 2.16 kg of 5 - 15 g / 10 min.

4. The low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material according to claim 1, wherein The melting point of the branched polyolefin material is -20°C - 90°C, and the crystallinity is 0 - 15%.

5. The low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material according to claim 1, characterized in that The maleic anhydride grafted branched polyolefin material is obtained by grafting the branched polyolefin material with maleic anhydride, and the grafting rate is 1.5 - 3.5%.

6. The low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material according to claim 1, characterized in that The magnesium hydroxide is modified magnesium hydroxide, and the contact angle between the surface of the modified magnesium hydroxide and water is below 120°.

7. The low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material according to claim 1, wherein The antioxidant is any one or a mixture of two of phenolic antioxidants and phosphite antioxidants.

8. The low-smoke, halogen-free and phosphorus-free flame-retardant polypropylene composite material according to claim 1, characterized in that The low-smoke, halogen-free, phosphorus-free polypropylene composite material comprises the following components in parts by weight: Polypropylene: 40 - 50 parts Magnesium hydroxide: 25 - 30 parts Branched polyolefin material: 15 - 20 parts Maleic anhydride grafted branched polyolefin material: 10 - 15 parts Antioxidant: 0.1 - 0.5 parts.

9. The preparation method of the low-smoke, halogen-free and phosphorus-free polypropylene composite material according to any one of claims 1 to 8, characterized in that The method is one of the following: (1) Step-by-step method: Take each raw material according to the formula ratio. Mix magnesium hydroxide, maleic anhydride grafted branched polyolefin material, the first part of the branched polyolefin material, and if there is a co-flame retardant, add the co-flame retardant, and melt and extrude and pelletize them with a twin-screw extruder to obtain an intermediate material; then melt and extrude the intermediate material, the remaining branched polyolefin material, polypropylene, and antioxidant with a twin-screw extruder to prepare the low-smoke, halogen-free, phosphorus-free polypropylene composite material; (2) One-step method: For a twin-screw extruder equipped with a separate metering feeding system and capable of achieving segmented feeding, the one-step method can be adopted, and the steps are as follows: Take each raw material according to the formula ratio. Feed magnesium hydroxide, maleic anhydride grafted branched polyolefin material, the first part of the branched polyolefin material, and if there is a co-flame retardant, add the co-flame retardant, into the main feeding port of the twin-screw extruder according to the measurement; feed the remaining branched polyolefin material, polypropylene, and antioxidant into the secondary feeding port at least 1 barrel section away from the main feeding port; finally, prepare the low-smoke, halogen-free, phosphorus-free polypropylene composite material through one-time melt extrusion.

10. The method according to claim 9, wherein The dosage of the first part of the branched polyolefin material is 50 - 75% of the total dosage of the branched polyolefin material.

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