Modified polyvinyl alcohol and preparation method and application thereof

Abstract

The application relates to the field of polyvinyl alcohol, and discloses modified polyvinyl alcohol and a preparation method and application thereof.The modified polyvinyl alcohol comprises structural unit A shown in formula (1), structural unit B shown in formula (2) and structural unit C shown in formula (3); wherein R1, R3, R4, R5, R6 and R7 are each independently H or C1-C3 alkyl, R2 is a hydroxyl group or a structure shown in formula I; m is an integer of 0-6, n is an integer of 1-6, R is C1-C3 alkyl, the content of the structural unit A is 71-96 mol%, the content of the structural unit B is 1-23 mol%, and the content of the structural unit C is 3-14 mol%. 18 The modified polyvinyl alcohol contains long-chain alcohol, the ratio of the structural units is controlled to adjust the polymerization degree and alcoholysis degree, the melt index can be improved, and the fluidity is improved.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl alcohol, and more specifically to a modified polyvinyl alcohol, its preparation method, and its application. Background Technology

[0002] Polyvinyl alcohol (PVA) is one of the few water-soluble polymers with good crystallinity. It possesses excellent water solubility, film-forming properties, mechanical properties, and gas barrier properties, and is biodegradable under certain conditions. It is widely used in paper processing, fiber processing, adhesives, emulsion protective colloids, and water-soluble films. However, due to the large number of hydroxyl groups in the PVA molecular chain, forming strong intramolecular hydrogen bonds, and its high crystallinity, it has a high melting point, very close to its decomposition temperature. The melting temperature of medium-to-high degree-of-hydrolysis PVA is generally between 200℃ and 240℃, and its decomposition temperature also falls within this range. Therefore, melt processing of ordinary PVA is very difficult.

[0003] To solve the problem of polyvinyl alcohol melt processing, a large amount of plasticizer is usually added to lower its melting point and improve its fluidity. However, the addition of plasticizer will reduce the excellent properties of polyvinyl alcohol materials, such as reducing its strength and barrier properties, and lowering its water solubility temperature. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of poor melt processability of polyvinyl alcohol (PVA) and reduced mechanical properties of PVA after adding a large amount of plasticizer, in the existing technology. This invention provides a modified PVA and its preparation method. The modified PVA contains long-chain alcohols. At the same time, by controlling the proportion of each structural unit in the modified PVA, the degree of polymerization and degree of alcoholysis are adjusted, thereby increasing the melt index of the modified PVA, improving its fluidity, and lowering its melting point to improve its melt processability.

[0005] To achieve the above objectives, the first aspect of the present invention provides a modified polyvinyl alcohol, the modified polyvinyl alcohol comprising structural unit A of the structure shown in formula (1), structural unit B of the structure shown in formula (2), and structural unit C of the structure shown in formula (3);

[0006]

[0007] In this context, R1, R3, R4, R5, R6 and R7 are each independently H or C1-C3 alkyl groups, and R2 is a hydroxyl group or the structure shown in Formula I;

[0008]

[0009] m is an integer from 0 to 6, n is an integer from 1 to 6, and R is a C1-C2 integer. 18The alkyl group has an alkyl content of 71 mol%-96 mol%, an alkyl unit content of 1 mol%-23 mol%, and an alkyl unit content of 3 mol%-14 mol%.

[0010] A second aspect of the present invention provides a method for preparing modified polyvinyl alcohol, the method comprising:

[0011] S1. In the presence of an initiator and a solvent, the compound with the structure shown in Formula II is polymerized with an ethylene ester compound to obtain the polymer product;

[0012] S2. The polymerization product is subjected to alcoholysis to obtain modified polyvinyl alcohol;

[0013]

[0014] Wherein, R1', R2' and R3' are each independently H or C1-C3 alkyl groups, z is an integer from 1 to 6, and X is a hydroxyl group or the structure shown in Formula III;

[0015]

[0016] Wherein, R' is a C1-C6 alkyl group;

[0017] The conditions for the alcoholysis reaction include: an alcoholysis temperature of 30-50℃ and an alcoholysis time of 10-50 min.

[0018] A third aspect of the present invention provides a modified polyvinyl alcohol, wherein the modified polyvinyl alcohol is prepared by the method described in the second aspect of the present invention.

[0019] The fourth aspect of the present invention provides an application of the modified polyvinyl alcohol described in the first or third aspect of the present invention in the fields of blow molding, injection molding or textiles.

[0020] Through the above technical solutions, the modified polyvinyl alcohol and its preparation method and application provided by the present invention achieve the following beneficial effects: by introducing structural units provided by long-chain alcohols or ethylene esters into the modified polyvinyl alcohol, and by controlling the content ratio of each structural unit in the modified polyvinyl alcohol to adjust the degree of polymerization and degree of alcoholysis, the melt index of the modified polyvinyl alcohol is improved. Furthermore, when the modified polyvinyl alcohol is applied, only a small amount of plasticizer needs to be added to improve its fluidity and melt processability, while ensuring that the mechanical properties are not significantly reduced. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of the present invention provides a modified polyvinyl alcohol, the modified polyvinyl alcohol comprising structural unit A of the structure shown in formula (1), structural unit B of the structure shown in formula (2) and structural unit C of the structure shown in formula (3);

[0023]

[0024] In this context, R1, R3, R4, R5, R6 and R7 are each independently H or C1-C3 alkyl groups, and R2 is a hydroxyl group or the structure shown in Formula I;

[0025]

[0026] m is an integer from 0 to 6, n is an integer from 1 to 6, and R is a C1-C2 integer. 18 The alkyl group has an alkyl content of 71 mol%-96 mol%, an alkyl unit content of 1 mol%-23 mol%, and an alkyl unit content of 3 mol%-14 mol%.

[0027] In this invention, the modified polyvinyl alcohol contains long-chain alcohols. At the same time, by controlling the proportion of each structural unit in the modified polyvinyl alcohol, the degree of polymerization and degree of alcoholysis are adjusted, thereby increasing the melt index of the modified polyvinyl alcohol, improving its fluidity, and thus improving its melt processing performance.

[0028] Furthermore, when the content of each structural unit in the modified polyvinyl alcohol meets the above range, the modified polyvinyl alcohol can achieve good processing performance by adding only a small amount of plasticizer when used for melt processing, and can ensure that the mechanical properties are not significantly reduced.

[0029] According to a preferred embodiment of the present invention, in formula (1), R1, R3, R4, R5, R6 and R7 are each independently H, methyl or ethyl.

[0030] According to a preferred embodiment of the present invention, m is an integer from 0 to 4, and n is an integer from 1 to 4.

[0031] According to a preferred embodiment of the present invention, R is a C1-C6 alkyl group.

[0032] According to a preferred embodiment of the present invention, the content of structural unit A is 77 mol%-81 mol%, the content of structural unit B is 10 mol%-12 mol%, and the content of structural unit C is 9 mol%-11 mol%.

[0033] According to the present invention, the degree of polymerization of the modified polyvinyl alcohol is 500-2000.

[0034] Furthermore, the degree of polymerization of the modified polyvinyl alcohol is 800-1800.

[0035] According to the present invention, the melting temperature of the modified polyvinyl alcohol is Tm, the decomposition temperature of the modified polyvinyl alcohol is Td, and Td-Tm≥35℃.

[0036] In this invention, the decomposition temperature refers to the decomposition temperature of the modified polyvinyl alcohol.

[0037] Furthermore, the melting temperature of the modified polyvinyl alcohol is Tm, the decomposition temperature of the modified polyvinyl alcohol is Td, and Td-Tm≥70℃.

[0038] According to a particularly preferred embodiment of the present invention, the melting temperature of the modified polyvinyl alcohol is Tm, the decomposition temperature of the modified polyvinyl alcohol is Td, and Td-Tm≥110℃.

[0039] According to the present invention, the crystallization temperature of the modified polyvinyl alcohol is 140℃-185℃.

[0040] Furthermore, the crystallization temperature of the modified polyvinyl alcohol is 160-175℃.

[0041] According to the present invention, the modified polyvinyl alcohol has a melt index of 1-5 g / 10 min at a load of 10 kg and a temperature of 220 °C.

[0042] In this invention, the modified polyvinyl alcohol has a processing window that is more than 110°C wider between its melting temperature and decomposition temperature, while also having a high crystallization temperature and a melt index that meets the requirements, making it well suited for melt processing.

[0043] According to one embodiment of the present invention, the melting temperature Tm of the modified polyvinyl alcohol is 180℃-235℃, and the decomposition temperature Td is 270℃-310℃.

[0044] A second aspect of the present invention provides a method for preparing modified polyvinyl alcohol, the method comprising:

[0045] S1. In the presence of an initiator and a solvent, the compound with the structure shown in Formula II is polymerized with an ethylene ester compound to obtain the polymer product;

[0046] S2. The polymerization product is subjected to alcoholysis to obtain modified polyvinyl alcohol;

[0047]

[0048] Wherein, R1', R2' and R3' are each independently H or C1-C3 alkyl groups, z is an integer from 1 to 6, and X is a hydroxyl group or the structure shown in Formula III;

[0049]

[0050] Wherein, R' is a C1-C6 alkyl group;

[0051] The conditions for the alcoholysis reaction include: an alcoholysis temperature of 30-50℃ and an alcoholysis time of 10-50 min.

[0052] According to a preferred embodiment of the present invention, in Formula II, R1', R2' and R3' are each independently H, methyl or ethyl.

[0053] According to a preferred embodiment of the present invention, in Formula II, R' is a C2-C4 alkyl group, and z is an integer from 1 to 4.

[0054] According to a preferred embodiment of the present invention, the conditions for the alcoholysis reaction include: an alcoholysis temperature of 35-45°C and an alcoholysis time of 14-40 min.

[0055] According to the present invention, the mass ratio of the ethylene ester compound to the compound with the structure shown in Formula II is 100:2-18.

[0056] In this invention, the mass ratio of the ethylene ester compound to the compound with the structure shown in Formula II satisfies the above-mentioned range, which enables the content of each structural unit in the obtained modified polyvinyl alcohol to meet the requirements, thereby controlling the degree of polymerization and degree of alcoholysis of the modified polyvinyl alcohol, and thus making it suitable for different processing conditions.

[0057] According to a preferred embodiment of the present invention, the mass ratio of the ethylene ester compound to the compound with the structure shown in Formula II is 100:8-12.

[0058] According to the present invention, the mass ratio of the ethylene ester compound to the initiator is 100:0.01-0.6.

[0059] According to the present invention, the initiator is selected from at least one of azo initiators, peroxide initiators, or redox initiators.

[0060] In this invention, the initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobis(2-methylbutyronitrile), hydrogen peroxide, ammonium persulfate, potassium persulfate, tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-pentyl peroxide, tert-pentyl peroxide, tert-butyl peroxide acetate, bis(4-tert-butylcyclohexyl peroxide), and dibutyl peroxide.

[0061] Furthermore, the mass ratio of the ethylene ester compound to the initiator is 100:0.04-0.16.

[0062] According to the present invention, the polymerization conditions include: a polymerization temperature of 50-68°C and a polymerization time of 3-6 hours.

[0063] According to the present invention, the polymerization conditions satisfying the above-mentioned range enable the polymerization reaction to be complete, and the prepared modified polyvinyl alcohol has better melt processability.

[0064] According to the present invention, the polymerization reaction is selected from solution polymerization, emulsion polymerization or suspension polymerization, preferably solution polymerization.

[0065] In this invention, when the polymerization reaction is solution polymerization, there are no special requirements for the feeding method of the ethylene ester compound. For example, batch feeding or simultaneous feeding can be used. The feeding method of the compound with the structure shown in Formula II can be batch feeding or simultaneous feeding, preferably batch feeding.

[0066] In this invention, the compound with the structure shown in Formula II can be fed in batches to obtain a more uniform random copolymer, thereby improving the overall performance of the final modified polyvinyl alcohol product.

[0067] In this invention, preferably, the feeding interval during batch feeding is 0.5-1h.

[0068] According to the present invention, the solvent is a C1-C4 alcohol.

[0069] According to a preferred embodiment of the present invention, at least one of methanol, ethanol, propanol, n-butanol and tert-butanol is used.

[0070] In this invention, during the polymerization reaction, the initiator is preferably dissolved in the above-mentioned solvent and added to the polymerization reaction system.

[0071] According to the present invention, in step S1, the ethylene ester compound is selected from C1-C64. 18 Saturated fatty acid vinyl esters.

[0072] According to a preferred embodiment of the present invention, the vinyl ester compound is selected from at least one of vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl decanoate, vinyl laurate, vinyl palmitate, and vinyl stearate, preferably vinyl acetate.

[0073] According to the present invention, in step S2, the alcoholysis reaction is carried out in the presence of a catalyst.

[0074] According to a preferred embodiment of the present invention, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide.

[0075] In this invention, the catalyst is preferably added in the form of a methanol solution.

[0076] According to the present invention, the mass ratio of the catalyst to the polymerization product is 0.2-2.5:100, preferably 0.2-1:100, and more preferably 0.2-0.3:100.

[0077] In this invention, the inventors discovered that adjusting the concentration of the polymer product obtained in step S1 to 20-40 wt% before carrying out the alcoholysis reaction can ensure that the degree of alcoholysis of the prepared modified polyvinyl alcohol meets the requirements, thereby further improving the melt processability of the prepared modified polyvinyl alcohol.

[0078] In this invention, a gel is formed during alcoholysis. If the gel is soft, it can be directly broken up; if the gel is hard, it can be pulverized into gel particles after alcoholysis. There is no particular limitation on the size of the gel particles; they can be of conventional sizes in the art.

[0079] A third aspect of the present invention provides a modified polyvinyl alcohol, wherein the modified polyvinyl alcohol is prepared by the method described in the second aspect of the present invention.

[0080] In this invention, the modified polyvinyl alcohol has the same properties as the modified polyvinyl alcohol described in the first aspect of this invention, and will not be described again.

[0081] The fourth aspect of the present invention provides an application of the modified polyvinyl alcohol described in the first or third aspect of the present invention in the fields of blow molding, injection molding or textiles.

[0082] The present invention will be described in detail below through embodiments.

[0083] In the following examples, the melting temperature, crystallization temperature, and decomposition temperature of the modified polyvinyl alcohol were measured using a differential scanning calorimeter (DSC 250, TA, USA) and a thermogravimetric analyzer (TGA 550, TA, USA) at a heating rate of 10 °C / min under a nitrogen atmosphere. Melt index conditions: 10 kg, 220 °C.

[0084] The contents of structural unit A, structural unit B and structural unit C were determined by 1H NMR.

[0085] Method for testing the tensile strength of modified polyvinyl alcohol: 77wt% modified polyvinyl alcohol is crushed into 0.2-0.6 mm, 20wt% plasticizer (glycerin), 1wt% antioxidant (chlorogenic acid) and 2wt% smoother (polyether silicone WE3220) are added and mixed evenly. Then, it is injection molded into a sheet with a length of 100 mm, a width of 15 mm and a thickness of 2 mm at 225℃. The film strength is tested using a material tensile tester, and the average value is taken for three tests.

[0086] The unmodified polyvinyl alcohol involved in the comparative example has a degree of polymerization of 1000 and a degree of alcoholysis of 97 mol%.

[0087] Example 1

[0088] S1. 140g of methanol solution containing 0.2g of azobisisobutyronitrile, 40g of isopentenol (R1', R2' are methyl, R3' is H, z is 1, X is hydroxyl) were added to 500g of vinyl acetate and stirred until homogeneous. The polymerization reaction was carried out at 64℃ in a water bath for 4.5h. After the polymerization reaction was completed, the residual monomer was distilled off to obtain the polymer product.

[0089] S2. Take 300g of the above polymer product, add methanol to adjust the concentration of the polymer product to 30%, then add a methanol solution containing 0.7g sodium hydroxide, and carry out alcoholysis reaction at 45℃ for 14min. Then crush the resulting gel block, wash and filter it with methanol, and dry it in an oven at 85℃ to obtain modified polyvinyl alcohol A1.

[0090] The molar contents, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol A1 are shown in Table 1. The melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol A1 are shown in Table 2.

[0091] Example 2

[0092] S1. 250g of methanol containing 0.5g of azobisisoheptanenitrile, 20g of butenol (R1' is methyl, R2' and R3' are H, z is 2, and X is hydroxyl) are added to 500g of vinyl acetate and stirred until homogeneous. The polymerization reaction is carried out at a water bath temperature of 60℃ for 5h. After the polymerization reaction is completed, the residual monomer is distilled off to obtain the polymer product.

[0093] S2. Take 300g of the above polymer product, add methanol to adjust the concentration of the polymer product to 30%, then add a methanol solution containing 0.9g of potassium hydroxide, and carry out alcoholysis reaction at 40℃ for 30min. Then crush the resulting gel block, wash and filter it with methanol, and dry it in an oven at 85℃ to obtain modified polyvinyl alcohol A2.

[0094] The molar contents, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol A2 are shown in Table 1. The melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol A2 are shown in Table 2.

[0095] Example 3

[0096] S1. 125g of tert-butanol solution containing 0.08g of neodecanoate tert-butanol, 60g of isopentenyl acetate (R1', R2' are methyl, R3' is H, z is 1, X is the structure shown in formula III, R' is methyl) were added to 500g of vinyl acetate and stirred until homogeneous. The polymerization reaction was carried out at a water bath temperature of 68℃ for 6h. After the polymerization reaction was completed, the residual monomer was distilled off to obtain the polymer product.

[0097] S2. Take 300g of the above polymer product, add tert-butanol to adjust the concentration of the polymer product to 34%, then add a tert-butanol solution containing 0.6g sodium methoxide, and carry out alcoholysis reaction at 45℃ for 14min. Then crush the resulting gel block, wash and filter it with methanol, and dry it in an oven at 85℃ to obtain modified polyvinyl alcohol A3.

[0098] The molar contents, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol A3 are shown in Table 1. The melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol A3 are shown in Table 2.

[0099] Example 4

[0100] S1. 500g of methanol containing 1.2g of azobisisobutyronitrile and 10g of isopentenol (R1', R2' are methyl, R3' is H, z is 1, X is hydroxyl) were added to 500g of vinyl acetate and stirred until homogeneous. The polymerization reaction was carried out at 64℃ in a water bath for 5.5h. After the polymerization reaction was completed, the residual monomer was distilled off to obtain the polymer product.

[0101] S2. Take 300g of the above polymer product, add methanol to adjust the concentration of the polymer product to 38%, then add a methanol solution containing 1.5g of tetraethylammonium hydrogenation, and carry out alcoholysis reaction at 45℃ for 40min. Then crush the resulting gel block, wash and filter the product with methanol, and dry it in an oven at 85℃ to obtain modified polyvinyl alcohol A4.

[0102] The molar contents, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol A4 are shown in Table 1. The melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol A4 are shown in Table 2.

[0103] Example 5

[0104] S1. 330g of methanol containing 0.6g of azobisisobutyronitrile, 50g of butenyl acetate (R1' is methyl, R2' and R3' are H, z is 2, X is the structure shown in formula III, R' is methyl) were added to 500g of vinyl acetate and stirred until homogeneous. The mixture was then polymerized at 64℃ in a water bath for 5h. After the polymerization reaction was completed, the residual monomer was distilled off to obtain the polymerized product.

[0105] S2. Take 300g of the above-mentioned polymer product, add methanol to adjust the concentration of the polymer product to 32%, then add a methanol solution containing 1.2g of potassium methoxide, and carry out alcoholysis reaction at 35℃ for 20min. Then crush the resulting gel block, wash and filter it with methanol, and dry it in an oven at 85℃ to obtain modified polyvinyl alcohol A5.

[0106] The molar contents, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol A5 are shown in Table 1. The melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol A5 are shown in Table 2.

[0107] Example 6

[0108] The method of Example 1 was followed, except that the alcoholysis time was 11 min. Modified polyvinyl alcohol A6 was obtained. The molar content, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol A6 are shown in Table 1. The melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol A6 are shown in Table 2.

[0109] Example 7

[0110] Following the method of Example 1, except that during the polymerization process, isopentenol was divided into four equal portions and added to the reaction system in batches at 1-hour intervals. Modified polyvinyl alcohol A7 was obtained. The molar contents, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol A7 are shown in Table 1, and the melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol A7 are shown in Table 2.

[0111] Comparative Example 1

[0112] The method was followed as in Example 1, except that a methanol solution containing 0.6 g of sodium hydroxide was added during alcoholysis, and the alcoholysis time was 8 min. Modified polyvinyl alcohol B1 was obtained. The molar contents, degree of polymerization, and degree of alcoholysis of structural unit A, structural unit B, and structural unit C in modified polyvinyl alcohol B1 are shown in Table 1, and the melting temperature Tm, decomposition temperature Td, tensile strength Ts, and melt index MI of modified polyvinyl alcohol B1 are shown in Table 2.

[0113] Table 1

[0114]

[0115]

[0116] Comparison Example a Refers to unmodified polyvinyl alcohol

[0117] Table 2

[0118] serial number Tc / ℃ Tm / ℃ Td / ℃ Tm-Td / ℃ MI / g / 10min Ts / MPa Example 1 160 186 305 119 3.4 48 Example 2 150 208 280 72 2.2 53 Example 3 175 188 306 118 3 50 Example 4 145 190 298 108 2.8 40 Example 5 153 192 290 98 2.4 44 Example 6 140 160 310 152 3.8 38 Example 7 185 184 307 123 3.6 50 Comparative Example 1 138 150 315 165 4.2 22 <![CDATA[Control Example b > 135 220 275 55 1.0 54

[0119] Application examples

[0120] Furthermore, taking Example 2 as an example, the film was melt-processed and injection molded into a sheet with a length of 100 mm × width of 15 mm × thickness of 2 mm. The formulation consisted of 100 g of modified polyvinyl alcohol with a particle size of 0.2-0.6 mm, 20 g of plasticizer (glycerol), 1 g of antioxidant (chlorogenic acid), and 2 g of smoothing agent (polyether silicone WE3220). The film was injection molded at a temperature of 225 °C to a length of 100 mm, a width of 15 mm, and a thickness of 2 mm. The melt index and tensile strength of the resulting film were tested, and the results were: melt index of 2.2 g / 10 min and tensile strength of 53 MPa.

[0121] The unmodified polyvinyl alcohol from the control example was melt-processed using the same method described above to obtain a film. The formulation consisted of 100g of unmodified polyvinyl alcohol with a particle size of 0.2-0.6mm, 40g of plasticizer (glycerol), 1g of antioxidant (chlorogenic acid), and 2g of smoothing agent (polyether silicone WE3220). The film was injection molded at 225℃ to form a sheet with a length of 100mm, a width of 15mm, and a thickness of 2mm. The melt index and tensile strength of the obtained film were tested, and the results were: melt index of 2.2g / 10min and tensile strength of 32MPa.

[0122] The results above show that, when the melt flow index is basically the same, the amount of plasticizer added to unmodified polyvinyl alcohol is significantly increased, resulting in a significant decrease in its mechanical properties.

[0123] As can be seen from the results in Table 1, Example 7, which uses the modified monomer batch feeding method with the structure shown in Formula II of the present invention, has significantly better effects in terms of melting temperature, melt index, and tensile strength of the material.

[0124] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified polyvinyl alcohol, characterized in that, The modified polyvinyl alcohol comprises structural unit A of the structure shown in formula (1), structural unit B of the structure shown in formula (2), and structural unit C of the structure shown in formula (3). In this context, R1, R3, R4, R5, R6 and R7 are each independently H or C1-C3 alkyl groups, and R2 is a hydroxyl group or the structure shown in Formula I; m is an integer from 0 to 6, n is an integer from 1 to 6, and R is a C1-C2 integer. 18 The alkyl group has an alkyl content of 71 mol%-96 mol%, an alkyl unit content of 1 mol%-23 mol%, and an alkyl unit content of 3 mol%-14 mol%.

2. The modified polyvinyl alcohol according to claim 1, wherein, In formula (1), R1, R3, R4, R5, R6 and R7 are each independently H, methyl or ethyl; Preferably, m is an integer from 0 to 4, and n is an integer from 1 to 4; Preferably, R is a C1-C6 alkyl group; Preferably, the content of structural unit A is 77 mol%-81 mol%, the content of structural unit B is 10 mol%-12 mol%, and the content of structural unit C is 9 mol%-11 mol%. Preferably, the degree of polymerization of the modified polyvinyl alcohol is 500-2000.

3. The modified polyvinyl alcohol according to claim 1 or 2, wherein, The melting temperature of the modified polyvinyl alcohol is Tm, and the decomposition temperature of the modified polyvinyl alcohol is Td, where Td-Tm ≥ 35℃, preferably Td-Tm ≥ 70℃, and more preferably Td-Tm ≥ 110℃. Preferably, the crystallization temperature of the modified polyvinyl alcohol is 140℃-185℃; Preferably, the modified polyvinyl alcohol has a melt index of 1-5 g / 10 min at a load of 10 kg and a temperature of 220 °C.

4. A method for preparing modified polyvinyl alcohol, characterized in that, The method includes: S1. In the presence of an initiator and a solvent, the compound with the structure shown in Formula II is polymerized with an ethylene ester compound to obtain the polymer product; S2. The polymerization product is subjected to alcoholysis to obtain modified polyvinyl alcohol; Wherein, R1', R2' and R3' are each independently H or C1-C3 alkyl groups, z is an integer from 1 to 6, and X is a hydroxyl group or the structure shown in Formula III; Wherein, R' is a C1-C6 alkyl group; The conditions for the alcoholysis reaction include: an alcoholysis temperature of 30-50℃ and an alcoholysis time of 10-50 min.

5. The preparation method according to claim 4, wherein, In Formula II, R1', R2' and R3' are each independently H, methyl or ethyl; Preferably, in formula II, R' is a C2-C4 alkyl group, and z is an integer from 1 to 4; Preferably, the conditions for the alcoholysis reaction include: an alcoholysis temperature of 35-45°C and an alcoholysis time of 14-40 min.

6. The preparation method according to claim 4 or 5, wherein, The mass ratio of the ethylene ester compound to the compound with the structure shown in Formula II is 100:2-18, preferably 100:8-12; Preferably, the mass ratio of the ethylene ester compound to the initiator is 100:0.01-0.6, more preferably 100:0.04-0.16; Preferably, the initiator is selected from at least one of azo initiators, peroxide initiators, or redox initiators; Preferably, the polymerization conditions include: a polymerization temperature of 50-68℃ and a polymerization time of 3-6 hours; Preferably, the polymerization reaction is selected from solution polymerization, emulsion polymerization, or suspension polymerization, and solution polymerization is preferred; Preferably, the solvent is a C1-C4 alcohol.

7. The preparation method according to claim 4 or 5, wherein, In step S1, the ethylene ester compound is selected from C1-C64. 18 saturated fatty acid ethylene esters; Preferably, the vinyl ester compound is selected from at least one of vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl decanoate, vinyl laurate, vinyl palmitate, and vinyl stearate.

8. The preparation method according to claim 4 or 5, wherein, In step S2, the alcoholysis reaction is carried out in the presence of a catalyst; Preferably, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide; Preferably, the mass ratio of the catalyst to the polymerization product is 0.2-2.5:

100.

9. A modified polyvinyl alcohol, characterized in that, The modified polyvinyl alcohol is prepared by the method according to any one of claims 4-8.

10. The use of the modified polyvinyl alcohol according to any one of claims 1-3 or claim 9 in the fields of blow molding, injection molding or textiles.

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