A method for preparing maleic anhydride grafted polypropylene with high grafting rate

Abstract

The embodiment of the present invention discloses a method for preparing maleic anhydride grafted polypropylene with a high grafting rate. The method comprises: under nitrogen protection, adding polypropylene, maleic anhydride, xylene, and an initiator into a mixing kettle, stirring and heating to reflux, and obtaining a reaction raw material; the reaction raw material is pressurized and input into a tubular reactor, and a reaction product flows out; the reaction product is discharged after buffering and decompression, and then a precipitating agent is added, and the maleic anhydride grafted polypropylene is obtained through precipitation and filtration. The grafting rate of the maleic anhydride grafted polypropylene prepared by the method of the present invention is higher than 1.5%, which meets the requirements of high-end modified composite materials.

Description

Technical Field

[0001] The embodiment of the present invention relates to the technical field of polypropylene modification, and in particular to a method for preparing maleic anhydride grafted polypropylene with a high grafting rate. Background Art

[0002] As a general-purpose plastic, polypropylene is known for its large output, wide application, good quality and low price. However, polypropylene is non-polar and crystalline. In addition, its dyeing, adhesion, antistatic and hydrophilic properties are also poor. These shortcomings restrict its further promotion and application. By grafting polypropylene, a branch chain with appropriate polarity is introduced into its molecular chain. The polarity and reactivity of the branch chain are utilized to improve its performance deficiencies and add new properties. Strong polar side groups are introduced into the non-polar molecular main chain. Maleic anhydride grafted polypropylene can become a bridge to enhance the adhesion and compatibility between polar and non-polar materials.

[0003] Polypropylene grafted with maleic anhydride is used as an interface modifier for glass fiber and mineral-filled polypropylene, which gives polyolefin polarity and adhesion, and can greatly improve the adhesion between polypropylene and inorganic fillers such as glass fiber, talcum powder, and mica, and significantly improve the tensile strength, bending strength, and impact strength of modified polypropylene. Used as a compatibilizer for polypropylene and resin alloys containing polar groups: Maleic anhydride grafted polypropylene (compound grafting) has a wide range of applications and can be used as a compatibilizer for PA / PP and PA / PE blends to improve the processability and impact resistance of nylon, reduce water absorption, and improve the dimensional stability of products.

[0004] The grafting reaction of polypropylene and maleic anhydride can be carried out by solution grafting, melt grafting and solid phase grafting, but the grafting rates of these methods are generally very low (≤1.5%), which makes it difficult to meet the requirements of high-end modified composite materials. Summary of the invention

[0005] To this end, the present invention provides a method for preparing maleic anhydride grafted polypropylene with a high grafting rate. The grafting rate of the maleic anhydride grafted polypropylene prepared by the method is higher than 1.5%, meeting the requirements of high-end modified composite materials.

[0006] In order to achieve the above purpose, the embodiment of the present invention provides the following technical solutions:

[0007] A method for preparing maleic anhydride grafted polypropylene with a high grafting rate comprises the following steps:

[0008] (1) under nitrogen protection, polypropylene, maleic anhydride, xylene and initiator are added into a mixing kettle, stirred and heated to reflux to obtain a reaction raw material;

[0009] (2) the reaction raw materials are pressurized and then fed into a tubular reactor, and reaction products flow out;

[0010] (3) The reaction product is discharged after buffering and decompression, and then a precipitating agent is added, and the precipitate is filtered to obtain maleic anhydride grafted polypropylene.

[0011] The present invention finds that the above method can significantly improve the conditions for polypropylene grafting. Specifically, the first is to solve the problem that in the melt grafting method, due to the high temperature of 200°C and above during the melting process, polypropylene forms tertiary carbon radicals on its molecular chain under the action of free radical initiators, and β-fracture is easy to occur before the grafting reaction, which is easy to cause degradation and crosslinking, destroying the structure of polypropylene itself, and the degree of damage increases with the increase of the grafting rate, resulting in a decrease in the mechanical properties of the matrix, and due to the extremely high temperature, the reaction process is difficult to control, the product grafting rate is low, and maleic anhydride sublimates severely during the high-temperature extrusion reaction, and there are a series of problems such as a bad production environment; the second is to solve the dispersion problem, polypropylene is non-polar, maleic anhydride is polar, the compatibility of the two is very poor, the surface tension is large, it is not easy to disperse evenly, and the monomer cannot effectively and fully participate in the reaction during the melt reaction, resulting in a low grafting rate. In addition, compared with the low-temperature reaction (not exceeding 140°C) of the atmospheric pressure solution grafting method, this method increases the reaction temperature, improves the reaction rate, and greatly improves the grafting rate of maleic anhydride.

[0012] Furthermore, the temperature of the tubular reactor is 140-210° C., and the pressure is 5-10 MPa.

[0013] Furthermore, the temperature of the tubular reactor is 180° C. and the pressure is 7.2 MPa.

[0014] Furthermore, the residence time of the reaction raw materials in the tubular reactor is 30-100 min, preferably 55-65 min.

[0015] Furthermore, the weight ratio of the polypropylene to maleic anhydride is 12.5-500:1.

[0016] Furthermore, the initiator is a peroxide initiator, including dibenzoyl peroxide, dodecyl peroxide, cumene hydroperoxide or diisopropylbenzene hydroperoxide, and the amount of the initiator is 0.1%-1.0% of the mass of the polypropylene, preferably 0.5%.

[0017] Furthermore, the amount of xylene used is 3-15 times the mass of polypropylene.

[0018] Furthermore, the precipitation agent is acetone.

[0019] Furthermore, the method further comprises: (4) refining the maleic anhydride grafted polypropylene, wherein the refining method comprises: vacuum drying the maleic anhydride grafted polypropylene, adding xylene and heating to reflux, dissolving, pouring into acetone, standing and cooling to precipitate, filtering the precipitate, washing with acetone, and vacuum drying again to obtain refined maleic anhydride grafted polypropylene.

[0020] The embodiments of the present invention have the following advantages:

[0021] The invention prepares maleic anhydride grafted polypropylene with a high grafting rate through a tubular reaction, and further through the study of pressure, temperature, time and initiator content ratio, can prepare a high grafting rate qualified product with a grafting rate higher than 1.5%, meeting the market demand for high-end modified composite materials.

[0022] The method provided by the present invention can continuously feed and discharge materials, is simple to operate, has low energy consumption, and saves costs. In addition, the present invention avoids the pollution problems caused by PP degradation and MAH sublimation existing in other grafting methods, and the solvent can be recycled and reused, thereby reducing the generation of industrial waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0024] Figure 1 The DSC enthalpy change diagram of the polypropylene before and after grafting provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] This embodiment provides a method for preparing maleic anhydride grafted polypropylene

[0028] 1.1 Main raw materials

[0029] Polypropylene: commercially available; Xylene: industrial grade, commercially available;

[0030] Maleic anhydride: industrial pure, commercially available; Initiator: dibenzoyl peroxide;

[0031] Acetone: technical grade, commercially available.

[0032] 1.2 Process

[0033] 100 parts of polypropylene, 4 parts of maleic anhydride, 600 parts of xylene and 0.3 parts of initiator are added into a mixing kettle in proportion, heated to the normal pressure reflux temperature under stirring until completely dissolved, and then continuously pressurized into a tubular reactor through a feed pipeline (the pressure is controlled at 5 MPa and the temperature is 150°C), reacted in the tubular reactor for 55 minutes, and the outflowing reaction product is discharged after buffering and decompression, output to another kettle, and acetone at room temperature is added as a precipitating agent, and then the grafted product is obtained by precipitation filtration.

[0034] 1.3 Determination of grafted products

[0035] 1.3.1 Refining of grafted materials

[0036] The grafted material was vacuum dried at 90°C / 12h (to remove the residue on the surface), 5g of the dried grafted material was placed in 40ml of xylene for deheating and reflux to dissolve, and after complete dissolution, it was immediately poured into 100ml of acetone, allowed to stand and cool to precipitate, filtered and precipitated, and washed with acetone twice, and the obtained floccules were dried in a vacuum drying oven (90°C / 24h) to obtain a refined grafted material.

[0037] 1.3.2 Determination of grafting rate

[0038] Weigh 0.5g of the refined grafted material, place it in a 500ml three-necked flask, add 80ml of xylene, heat and reflux for 10min until the sample is completely dissolved, cool to 90℃, add 10ml of KOH-ethanol standard solution with a pipette, reflux at 100℃ for 1.5h to allow full reaction, cool to 70℃, quickly add 4 drops of phenolphthalein indicator, the solution should be dark red, titrate with HCl-isopropanol standard solution until colorless, repeat the titration 2-3 times and take the average value.

[0039] 1.3.3 Calculation method:

[0040] G1=M×(C1×V1-C2×V2)×10 -3 / 2m

[0041] M——is the molar mass of maleic anhydride, 98 mol / L;

[0042] C1——Concentration of sodium hydroxide-ethanol standard solution, mol / L;

[0043] V1——The volume of sodium hydroxide-ethanol standard solution used, mL; (10ml)

[0044] C2——Concentration of hydrochloric acid-xylene standard solution, mol / L;

[0045] V2——the volume of hydrochloric acid-xylene standard solution consumed in titration, mol / L;

[0046] m——sample mass, g;

[0047] 1.4 Measurement results

[0048] The grafting rate was measured to be 1.52%.

[0049] See also Figure 1 The peak temperature of enthalpy change of the grafted product decreased after grafting, indicating that polypropylene was successfully grafted.

[0050] Example 2

[0051] Based on Example 1, the effects of different pressures and temperatures on the grafting rate of grafted PP-g-MAH were investigated. The following conditions 1-4 differ from Example 1 only in temperature and pressure. The results are shown in Table 1.

[0052] Table 1

[0053] Temperature(℃) Pressure(MPa) Grafting rate G(%) Example 1 150 5.0 1.52 Condition 1 167 6.5 1.98 Condition 2 180 7.2 2.55 Condition 3 181 8.0 2.70 Condition 4 184 10 2.76

[0054] The results show that under different temperature and pressure conditions, the grafting rate of the grafted material shows great differences. The grafting rate increases significantly with the increase of pressure and temperature, but when the pressure and temperature reach a certain level, the growth of the grafting rate slows down. Considering various factors comprehensively, the temperature of 180℃ and the pressure of 7.2MPa are selected as the reaction conditions of the tubular reactor.

[0055] Example 3

[0056] Based on Example 1, a temperature of 180°C and a pressure of 7.2 MPa were selected as the reaction conditions of the tubular reactor to investigate the effect of different initiator contents on the grafting rate of PP-g-MAH. The following conditions 5-8 differ from condition 2 only in the initiator content. The results are shown in Table 2.

[0057] Table 2

[0058]

[0059] The results show that the initiator content also has a significant impact on the grafting rate. Considering the cost and other aspects, the initiator content of PP is selected to account for 0.5%.

[0060] Example 4

[0061] On the basis of Example 1, a temperature of 180°C and a pressure of 7.2 MPa were selected as the reaction conditions of the tubular reactor, and the initiator dosage was 0.5% of PP. The effect of different residence reaction times on the PP-g-MAH grafting rate was investigated. The results are shown in Table 3.

[0062] Table 3

[0063] Residence time (min) Grafting rate G(%) Condition 6 55 2.65 Condition 9 30 1.53 Condition 10 60 2.69 Condition 11 65 2.71 Condition 12 70 2.70 Condition 13 100 2.48

[0064] The results show that under the same conditions, only changing the reaction time in the tubular reactor can increase the grafting rate of the grafted product. However, when the reaction time is long enough, the grafting rate will not increase significantly, and may even show a downward trend. Therefore, considering the performance and energy consumption, 55-65 minutes is selected as the residence time of the reaction raw materials in the tubular reactor.

[0065] In summary, the optimal reaction conditions are: the temperature of the tubular reactor is 180°C, the pressure is 7.2 MPa, the amount of initiator is 0.5% of the mass of polypropylene, and the residence time in the tubular reactor is 55-65 min.

[0066] Test Example 1

[0067] The effects of different grafting reaction modes on the grafting rate of PP-g-MAH were investigated, and the results are shown in Table 4. Among them:

[0068] The amount of reaction raw materials used: 100 parts of polypropylene, 4 parts of maleic anhydride, 600 parts of xylene, and 0.5 parts of initiator.

[0069] Normal pressure solvent reaction: Reflux reaction at normal pressure for 4 hours.

[0070] Melt grafting: PP, MAH and initiator are uniformly mixed at a temperature of 200°C, and then grafted and extruded in a twin-screw extruder. The main engine temperature is: 165°C, 185°C, 195°C, 200°C, 200°C, 195°C, 185°C, the main engine speed is 90Hz, and the feeding is 20Hz.

[0071] High pressure tubular reactor grafting: Condition 6.

[0072] Table 4

[0073] Reaction Grafting rate G(%) Normal pressure solvent reaction 1.34 Melt grafting 1.45 High-pressure tubular reactor grafting 2.65

[0074] The results show that the grafting rate of the grafted product prepared by the method of the present invention is significantly better than that of the existing normal pressure solvent reaction and melt grafting.

[0075] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for preparing maleic anhydride grafted polypropylene with a high grafting rate, characterized in that: The steps include: (1) under nitrogen protection, polypropylene, maleic anhydride, xylene and initiator are added into a mixing kettle, stirred and heated to reflux to obtain a reaction raw material; (2) the reaction raw materials are pressurized and then fed into a tubular reactor, and reaction products flow out; (3) the reaction product is discharged after buffering and decompression, and then a precipitating agent is added, and the reaction product is filtered through precipitation to obtain maleic anhydride grafted polypropylene; The temperature of the tubular reactor is 150-210°C and the pressure is 5-10Mpa; The residence time of the reaction raw materials in the tubular reactor is 30-100 min; The initiator is a peroxide initiator, including dibenzoyl peroxide, dodecyl peroxide, cumene hydroperoxide or diisopropylbenzene hydroperoxide, and the dosage of the initiator is 0.3%-1.0% of the mass of the polypropylene.

2. The method according to claim 1, characterized in that The temperature of the tubular reactor is 180° C. and the pressure is 7.2 MPa.

3. The method according to claim 1, characterized in that The weight ratio of the polypropylene to maleic anhydride is 12.5-500:

1.

4. The method according to claim 1, characterized in that: The amount of xylene used is 3-15 times the mass of polypropylene.

5. The method according to claim 1, characterized in that: The precipitation agent is acetone.

6. The method according to claim 1, characterized in that The method further comprises: (4) refining the maleic anhydride grafted polypropylene, wherein the refining method comprises: vacuum drying the maleic anhydride grafted polypropylene, adding xylene and heating to reflux, dissolving the maleic anhydride grafted polypropylene, pouring the maleic anhydride grafted polypropylene into acetone, standing and cooling to precipitate, filtering the precipitate, washing with acetone, and vacuum drying again to obtain the refined maleic anhydride grafted polypropylene.

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