A method for preparing an adhesive from polyoxymethylene plastic waste

Abstract

The application discloses a method for preparing an adhesive by recycling polyformaldehyde, and belongs to the technical field of chemical materials. The method comprises the following steps: under catalytic conditions, biomass-derived diols and petroleum-based polyformaldehyde plastics are heated and stirred to generate a cyclic acetal product through dehydration condensation; a fraction containing the cyclic acetal product and water vapor is collected and cooled to obtain a liquid phase product; after salt precipitation and dehydration treatment, the cyclic acetal product is obtained; and then, the cyclic acetal product is subjected to ring-opening polymerization reaction with cyclic anhydride under catalytic conditions to generate the adhesive. The method provided by the application has low reaction cost, and the product has high added value. After refining, the fraction after depolymerization can obtain high-quality 1,3-dioxolane, i.e., the cyclic acetal product, which can be used as an organic solvent such as a lignin solvent, a chromatographic analysis solvent, a metal surface treatment agent or a medical intermediate and monomer; and the polymerization product, i.e., the adhesive, can be used for bonding non-polar surfaces such as wood and PET plates, realizes green, efficient and low-cost recycling of polyformaldehyde, and has high practical application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical materials, and particularly relates to a method for preparing an adhesive by recycling polyformaldehyde plastic. BACKGROUND

[0002] Polyformaldehyde (POM), also known as acetal resin, polyoxymethylene, and polyacetal, is a thermoplastic polymer with high heat resistance, bending strength, fatigue resistance, excellent wear resistance and electrical properties, and is known as "super steel" or "race steel". However, during use, polyformaldehyde may exhibit natural aging phenomena such as cracking, deformation, and pulverization, thereby generating a large amount of waste polyformaldehyde. In addition to slow natural weathering, the main methods for recycling polyformaldehyde include chemical recycling and mechanical physical recycling. Chemical recycling mainly includes chemical decomposition and depolymerization: for example, polyformaldehyde is subjected to thermal depolymerization or condensation polymerization to decompose it into small molecules or oligomers as new chemical raw materials. For example, a degradation method using strong acid as a catalyst is used, but the use of strong acid may pollute the environment, and the inevitable volatilization during use may also cause harm to the human body and equipment, and the generated waste residue is also difficult to handle.

[0003] Chinese patent CN106397325A discloses an imidazole ionic liquid and its application in degrading polyformaldehyde, and relates to the technical field of ionic liquids, providing a means for saving the amount of acid catalyst for degrading polyformaldehyde; the preparation method of the ionic liquid comprises the following steps: 1) preparation of [ATMIM]Cl3 (1,2,3-tri(N-methyl imidazolyl)-1-propylene trichloride); 2) dissolving [ATMIM]Cl3 in water, purging with inert gas, heating to room temperature-80℃, adding raw materials containing target anions, the molar ratio of [ATMIM]Cl3 to the raw materials of target anions being 1:(3-4), stirring and blowing gas to react until no HCl is detected, stopping the reaction, purifying, and obtaining the ionic liquid. The process conditions for preparing the ionic liquid of the present application are a two-step synthesis method, and the degradation product is formaldehyde, which needs to be collected at-30℃, and the subsequent treatment is difficult. Therefore, it is an urgent problem to be solved in the prior art to provide an efficient and economical degradation method for polyformaldehyde plastic. SUMMARY

[0004] The present application aims to provide a method for preparing an adhesive by recycling polyformaldehyde plastic. The method provided by the present application can recycle waste polyformaldehyde plastic and convert it into a high-value-added product, realizing green recycling of polyformaldehyde plastic and being economical and environmentally friendly.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The application provides a method for preparing an adhesive from polyformaldehyde, comprising the following steps:

[0007] (1) mixing polyformaldehyde, biomass-derived diol and a first catalyst to obtain a mixture;

[0008] (2) heating and stirring the mixture obtained in step (1) under a sealed condition, collecting a fraction and cooling to obtain a liquid-phase product;

[0009] sequentially salting out and dehydrating the liquid-phase product to obtain a cyclic acetal product;

[0010] (3) mixing cyclic anhydride, a solvent and a second catalyst to obtain a premix;

[0011] in an inert atmosphere, dropping the cyclic acetal product obtained in step (2) into the premix to perform a polymerization reaction, thereby obtaining an adhesive.

[0012] Preferably, the polyformaldehyde in step (1) has a molecular weight of 20,000-110,000.

[0013] Preferably, the biomass-derived diol in step (1) is one of ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,2-hexanediol or 1,3-hexanediol.

[0014] Preferably, the mass ratio of the biomass-derived diol to the polyformaldehyde in step (1) is (1-9):1.

[0015] Preferably, the first catalyst in step (1) is at least one of hydrochloric acid, sulfuric acid, trifluoromethanesulfonic acid, SnCl4·5H2O, SnCl4, SnCl2·2H2O, FeCl3·6H2O, ZnCl2 or AlCl3.

[0016] Preferably, the molar amount of the first catalyst in step (1) accounts for 0.2%-7% of the molar amount of the polyformaldehyde.

[0017] Preferably, the temperature of the heating and stirring in step (1) is 100-140℃, and the time of the heating and stirring is 1-6h.

[0018] Preferably, the cyclic anhydride in step (2) is at least one of glutaric anhydride, phthalic anhydride, itaconic anhydride, maleic anhydride and 1,2-cyclohexane dicarboxylic anhydride.

[0019] Preferably, the second catalyst in step (2) is at least one of trifluoromethanesulfonic acid and trifluoromethanesulfonic acid methyl ester.

[0020] Preferably, the temperature of the polymerization reaction in step (2) is 20-50℃, and the time of the polymerization reaction is 0.5-6h.

[0021] The application provides a method for preparing an adhesive by recycling polyformaldehyde, which comprises the following steps: mixing polyformaldehyde, biomass-derived diol and a first catalyst to obtain a mixture; heating and stirring the mixture under a sealed condition to obtain a liquid product; sequentially performing salting-out and dehydration on the liquid product to obtain a cyclic acetal product; mixing cyclic anhydride, a solvent and a second catalyst to obtain a premix; and adding the cyclic acetal product obtained in step (2) into the premix under an inert atmosphere to perform a polymerization reaction and obtain an adhesive. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The H-NMR spectrum of the cyclic acetal product prepared in Example 1 of the application 1

[0023] Figure 2 The H-NMR spectrum of the adhesive prepared in Example 1 of the application 1 DETAILED DESCRIPTION

[0024] The application provides a method for preparing an adhesive by recycling polyformaldehyde, which comprises the following steps:

[0025] (1) mixing polyformaldehyde, biomass-derived diol and a first catalyst to obtain a mixture;

[0026] (2) heating and stirring the mixture obtained in step (1) under a sealed condition, collecting a distillate and cooling to obtain a liquid product;

[0027] sequentially performing salting-out and dehydration on the liquid product to obtain a cyclic acetal product;

[0028] (3) mixing cyclic anhydride, a solvent and a second catalyst to obtain a premix;

[0029] adding the cyclic acetal product obtained in step (2) into the premix under an inert atmosphere to perform a polymerization reaction and obtain an adhesive.

[0030] In the application, the raw materials used are all commercially available products in the art unless otherwise specified.​​

[0031] The polyformaldehyde, the biomass-derived diol and the first catalyst are mixed to obtain a mixture.

[0032] In the present application, the molecular weight of the polyformaldehyde is preferably 20000-110000. In the present application, the polyformaldehyde is preferably waste polyformaldehyde plastic.

[0033] In the present application, the biomass-derived diol is preferably one of ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,2-hexanediol or 1,3-hexanediol. In the present application, the mass ratio of the biomass-derived diol to the polyformaldehyde is (1-9):1, and more preferably (1-8):1. The present application controls the molar ratio of the biomass-derived diol to the polyformaldehyde in the above range to prevent the decomposition of the product 1,3-dioxolane in an acidic environment due to its excessively high concentration.

[0034] In the present application, the first catalyst is preferably at least one of hydrochloric acid, sulfuric acid, trifluoromethanesulfonic acid, SnCl4·5H2O, SnCl4, SnCl2·2H2O, FeCl3·6H2O, ZnCl2 or AlCl3. In the present application, the molar amount of the first catalyst is preferably 0.2%-7% of the molar amount of the polyformaldehyde, and more preferably 0.5%-5%. The present application controls the amount of the first catalyst in the above range to ensure that the polyformaldehyde plastic can be effectively degraded.

[0035] After obtaining the mixture, the present application performs heating and stirring of the mixture under a sealed condition, collects the distillate and cools to obtain a liquid phase product.

[0036] In the present application, the temperature of the heating and stirring is preferably 100-140°C, and the time of the heating and stirring is preferably 1-6h, and more preferably 2-4h. The present application controls the temperature and time of the heating and stirring in the above range to ensure the efficient degradation of the polyformaldehyde plastic. The present application does not have a specific limitation on the rotation speed of the heating and stirring, and a rotation speed known in the art can be used to achieve uniform stirring.

[0037] In the present application, the heating and stirring is preferably accompanied by ultrasonic treatment, and the power of the ultrasonic treatment is preferably 200-300w, and more preferably 250W. The present application uses ultrasonic treatment as an external field to intensify the conditions, which can reduce the amount of catalyst, shorten the reaction time and reduce the reaction temperature, and improve the reaction efficiency.

[0038] The present application does not have a specific limitation on the cooling method, and a technical solution known in the art can be used to achieve condensation to obtain a liquid phase product.

[0039] After the collection of the distillate, the present application preferably continues the next cycle reaction with the residue in the reactor.

[0040] After obtaining the liquid phase product, the present application sequentially performs salting-out and dehydration on the liquid phase product to obtain the cyclic acetal product.

[0041] In the present application, the dehydrating agent used in the salting-out is preferably at least one of anhydrous calcium chloride, anhydrous sodium sulfate, anhydrous magnesium sulfate, and anhydrous sodium chloride.

[0042] In the present application, the molecular sieve used in the dehydration is preferably at least one of 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, and 13XAPG molecular sieve.

[0043] The present application mixes the cyclic anhydride, the solvent, and the second catalyst to obtain a premix;

[0044] In the present application, the cyclic anhydride is preferably at least one of glutaric anhydride, phthalic anhydride, itaconic anhydride, maleic anhydride, and 1,2-cyclohexane dicarboxylic anhydride. In the present application, the molar ratio of the cyclic anhydride to the cyclic acetal product is preferably (0.5-3.5):1, and more preferably (1-2.5):1. The present application controls the molar ratio of the cyclic anhydride to the cyclic acetal product in the above range to ensure that the polymerization product has higher alternation and larger molecular weight.

[0045] In the present application, the solvent is preferably at least one of dichloromethane, acetone, toluene, and ethyl acetate.

[0046] In the present application, the second catalyst is preferably at least one of trifluoromethanesulfonic acid and methyl trifluoromethanesulfonate.

[0047] After obtaining the cyclic acetal product and the premix, the present application performs a polymerization reaction by dropping the cyclic acetal product into the premix in an inert atmosphere to obtain an adhesive

[0048] In the present application, the inert atmosphere is preferably a nitrogen atmosphere.

[0049] In the present application, the temperature of the polymerization reaction is preferably 20-50°C, and more preferably room temperature. In the present application, the time of the polymerization reaction is preferably 0.5-6h, and more preferably 2-4h. The present application controls the temperature and time of the polymerization reaction in the above range to ensure that the polymerization of the monomers is completed to the maximum extent.

[0050] The method provided by the application is suitable for chemical degradation and recycling of waste polyformaldehyde plastics, can utilize simple biomass-derived diols to generate a cyclic acetal product through dehydration condensation under catalytic conditions, and can convert the cyclic acetal product into an adhesive applicable to a nonpolar surface, realizes functionalized reuse of waste plastics, has simple process operation, low requirements on reaction equipment and experimental conditions, and can realize recycling of a homogeneous catalyst, and has the advantages of green economy and sustainability.

[0051] The technical solutions in the application will be clearly and completely described below in combination with the embodiments in the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the application.

[0052] Embodiment 1

[0053] A method for preparing an adhesive from polyformaldehyde, comprising the following steps:

[0054] (1) 18.62 g of ethylene glycol, 3 g of polyformaldehyde with a molecular weight of 20000-110000, and 1.05 g of SnCl4·5H2O are placed in a reactor and uniformly mixed to obtain a mixture;

[0055] The mass ratio of the biomass-derived diol to the polyformaldehyde is 6.2:1; and the molar amount of the first catalyst SnCl4·5H2O accounts for 3% of the molar amount of the polyformaldehyde;

[0056] (2) The mixture obtained in the step (1) is heated and stirred to 130 DEG C under a sealed condition for 3 h, and a distillate is collected and naturally cooled to obtain a liquid-phase product, and the residual liquid in the reactor is continuously used for the next cycle of reaction;

[0057] The liquid-phase product is salted out with CaCl2, and after dehydration through 4A molecular sieves, a cyclic acetal product is obtained;

[0058] (3) 4.436 g of 1,2-cyclohexane dicarboxylic anhydride, 0.06 g of methyl trifluoromethanesulfonate, and 2 ml of CH2Cl2 are mixed to obtain a premix;

[0059] 1 mL of the cyclic acetal product obtained in the step (2) is added dropwise into the premix under a nitrogen atmosphere, and uniformly mixed, and after reaction at room temperature for 3 h, the solvent is removed through a vacuum oven to obtain an adhesive;

[0060] The molar ratio of the cyclic anhydride 1,2-cyclohexane dicarboxylic anhydride to the cyclic acetal product is 2:1.

[0061] The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1. 1 The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1. Figure 1 The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1. Figure 1 The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1.

[0062] The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1. 1 The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1. Figure 2 The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1. Figure 2 The H-NMR spectrum of the product of the cyclic acetal prepared in Example 1 is shown in Figure 1.

[0063] Examples 2-10

[0064] The adhesive was prepared according to the method of Example 1, except that the type and amount of the first catalyst used in Examples 2-10 were as shown in Table 1.

[0065] In order to study the effect of the type and amount of the first catalyst on the chemical degradation of polyformaldehyde in the method provided by the present application, the conversion rate of polyformaldehyde (i.e. POM) in Examples 2-10 was calculated by weighing the remaining unreacted polyformaldehyde, the yield of 1,3-dioxolane in the step (2) was detected by gas chromatography, and the detection results are shown in Table 1. In Table 1, when the first catalyst is HCl, 37% hydrochloric acid is added to the mixture until the pH is 3.45; "catalyst amount / mol%" represents the molar percentage of the first catalyst to POM.

[0066] Table 1 Effect of the type and amount of different first catalysts on the chemical degradation of polyformaldehyde

[0067]

[0068]

[0069] As shown in Table 1, SnCl4·5H2O is the best catalyst, and the product yield of the chemical degradation of polyformaldehyde plastic catalyzed by SnCl4·5H2O can reach 74%.

[0070] The chemical degradation of polyformaldehyde plastic was carried out according to the method of Example 1, and at the same time, the residual liquid in the reactor in Example 1 was continuously subjected to the next cycle reaction, the cycle process was repeated for 6 times, and the conversion rate of polyformaldehyde (i.e. POM) and the yield of 1,3-dioxolane in each cycle were detected by the above-mentioned detection method, the concentration of 1,3-dioxolane in the fraction was detected by gas chromatography, and the stability parameters of the cycle process of the chemical degradation of polyformaldehyde plastic by the method of Example 1 of the present application were obtained as shown in Table 2.

[0071] Table 2 Stability parameters of polyformaldehyde plastic chemical degradation cycle process

[0072]

[0073]

[0074] As shown in Table 2, the conversion rate of polyformaldehyde plastic is not reduced after 6 cycles, which proves the feasibility of the cycle, and the total 1,3-dioxolane yield is 85.35%.

[0075] Examples 12-15

[0076] The adhesive was prepared according to the method of Example 1, except that the molar ratio of the cyclic anhydride 1,2-cyclohexane dicarboxylic anhydride to the cyclic acetal product in Examples 12-15 was 1:1, 1.5:1, 2:1, and 2.5:1, respectively.

[0077] The adhesive prepared in Examples 12-15 was used to bond a single layer of wood board and PET board with a thickness of 3 mm, with 1 layer of each type of board, and the amount of adhesive used was 0.2 g / cm 2 , and the shear strength of the bonded PET board was tested using a M221C tester, and the performance test data is shown in Table 3.

[0078] Table 3 Bonding performance parameters of polymeric products

[0079]

[0080] As can be seen from the above, polyformaldehyde plastic can be converted into high-value degradation products such as cyclic acetals through chemical degradation due to the presence of ether bonds, and water and a small amount of trioxymethylene are by-products in the degradation products

[0081] , so that high-quality cyclic acetal products can be obtained through distillation and subsequent refining for final purification; or after dehydration treatment, they can be used as raw materials for adhesive together with cyclic anhydride to synthesize adhesives that can be applied to non-polar surfaces, with excellent bonding performance and degradability

[0082] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for preparing adhesives from recycled polyoxymethylene, characterized in that, Includes the following steps: (1) Mix polyoxymethylene, biomass-derived diol and the first catalyst to obtain a mixture; In step (1), the biomass-derived diol is one of ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,2-hexanediol, or 1,3-hexanediol. The first catalyst in step (1) is at least one of hydrochloric acid, sulfuric acid, trifluoromethanesulfonic acid, SnCl4·5H2O, SnCl4, SnCl2·2H2O, FeCl3·6H2O, ZnCl2 or AlCl3; (2) Under sealed conditions, the mixture obtained in step (1) is heated and stirred, the fraction is collected and cooled to obtain a liquid product; The liquid phase product was subjected to salting out and dehydration in sequence to obtain the cycloacetal product. (3) The cyclic anhydride, solvent and second catalyst are mixed to obtain a premix; In an inert atmosphere, the cycloacetal product obtained in step (2) is added dropwise to the premix to carry out a polymerization reaction and obtain an adhesive. In step (3), the second catalyst is at least one of trifluoromethanesulfonic acid or methyl trifluoromethanesulfonate.

2. The method according to claim 1, characterized in that, In step (1), the molecular weight of polyoxymethylene is 20,000 to 110,000.

3. The method according to claim 1, characterized in that, In step (1), the mass ratio of biomass-derived diol to polyoxymethylene is (1~9):

1.

4. The method according to claim 1, characterized in that, In step (1), the molar amount of the first catalyst accounts for 0.2% to 7% of the molar amount of polyoxymethylene.

5. The method according to claim 1, characterized in that, The heating and stirring temperature in step (1) is 100~140℃, and the heating and stirring time is 1~6h.

6. The method according to claim 1, characterized in that, In step (2), the cyclic anhydride is at least one of glutaric anhydride, phthalic anhydride, itaconic anhydride, maleic anhydride, and 1,2-cyclohexanedicarboxylic anhydride.

7. The method according to claim 1, characterized in that, The polymerization reaction in step (2) is carried out at a temperature of 20~50℃ and for a time of 0.5~6h.

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