Lignin-based pet nucleating agent, method for preparing same, and pet modification method

Abstract

The application provides a kind of lignin-based PET nucleating agent and its production method and PET modification method, belongs to the technical field of organic chemistry.The application uses aromatic polymer lignin with complex structure as PET nucleating agent.The cross-linked phenolic polymer structure of lignin makes it not easy to rot, and its rigid structure also makes it have good thermal stability.These advantages are also the necessary conditions for lignin to be used as PET heterogeneous nucleating agent.The application also carries out carboxylation modification on lignin, introduces carboxylic ion clusters on the phenolic hydroxyl and alcoholic hydroxyl of lignin, these ion clusters can chemically induce nucleation of PET, so as to further improve the crystallization rate and crystallinity of PET.In figure 4, from left to right, they are pure PET, PET-G1 and PET-G2 injection molded models, it can be seen that under the same injection molding conditions, the white area of PET that has not crystallized formed by adding the application is significantly reduced, which significantly improves the crystallinity of PET.

Description

Lignin-based PET nucleating agents and their preparation methods, and PET modification methods Technical Field

[0001] This invention belongs to the field of organic chemistry technology, specifically relating to nucleating agents for polyethylene terephthalate (PET) and their preparation methods. Background Technology

[0002] There are many precedents for the study of nucleating agents for PET. Due to the presence of rigid benzene rings in the repeating structural units of PET, the nucleation of PET is slow and the crystallization rate is low, resulting in poor comprehensive mechanical properties and poor heat resistance of PET, which limits its engineering applications. Therefore, nucleation modification of PET to improve its crystallization rate and crystallinity has become an urgent problem to be solved. In the current research status, PET nucleating agents are divided into four categories: (1) Inorganic filler nucleating agents: including clay, oxides and hydroxides, inorganic salts, Si3N4 and carbon nanotubes / graphite, etc., whose nucleation mechanism is heterogeneous nucleation. (2) Organic small molecule nucleating agents: involving carboxylates, diamines, bisamides and modified sorbitol, etc., among which the nucleation mechanism of carboxylates is ion cluster induced nucleation, while the others are all heterogeneous nucleation. (3) Organic polymer nucleating agents: divided into crystalline polymers, liquid crystal polymers, block copolymers and ion crosslinking polymers, etc.; the first three are heterogeneous nucleation, and the latter is ion cluster induced nucleation. (4) Composite nucleating agents: These are two or more nucleating agents (or nucleation mechanisms) used in combination to synergistically promote PET crystallization and nucleation. Comparative studies have shown that organic polymers combined with composite nucleating agents are more effective and do not cause PET degradation, making them excellent nucleating agents for PET.

[0003] Wood, as the only renewable resource among the four basic materials (steel, cement, plastics, and wood), is widely used in furniture, construction, energy, new materials, and other fields, and is closely related to people's lives. The main components of woody biomass materials are cellulose, hemicellulose, and lignin, which together often account for more than 90% of the dry weight of woody biomass. Previous literature shows that there are precedents for using biomass materials as nucleating agents for polyethylene terephthalate (PET) long ago, such as using thermotropic crystals of cellulose aromatic esters as heterogeneous nucleating agents for PET. This has opened up new avenues for the industrial utilization of biomass resources. This patent selects lignin-modified products from woody resources as nucleating agents for polyethylene terephthalate. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of slow crystallization speed and low crystallinity of PET, and to propose a novel PET nucleating agent.

[0005] Specifically, this invention addresses the mechanism of PET nucleation reactions by utilizing the amorphous aromatic polymer structure of lignin to synthesize carboxylated lignin as a PET nucleating agent. Lignin is an amorphous aromatic polymer with a complex molecular structure composed of various monomers linked together. The main linkage modes are β-O-4 and α-O-5, while other representative linkages include β-5, β-1, and 5-5. Its amorphous aromatic polymer structure allows it to better serve as a heterogeneous nucleating agent for PET. Carboxylation of lignin provides more nucleation reaction sites for PET. By adding this nucleating agent, the crystallization properties of PET are modified, accelerating crystallization and increasing crystallinity, thereby more fully leveraging the advantages of PET's high performance and low cost.

[0006] The PET nucleating agent of the present invention has the structural formulas shown in formulas (I) and (II):

[0007]

[0008] Here, R1 represents the remainder of lignin. And the remainder of lignin is composed of monomers:

[0009] Amorphous aromatic polymers linked by β-O-4, α-O-5, β-5, β-1, 5-5, etc. R2 represents the portion obtained by carboxylating R1. Formula (I) is product G1, and formula (II) is product G2.

[0010] The PET nucleating agent production method described in this invention includes the following steps:

[0011] Lignin pretreatment:

[0012] (a) If the production process requires a specific color for PET, the lignin can be bleached to remove the chromophores and thus the color of the lignin; or a lighter-colored lignin can be selected directly.

[0013] (b) The pretreated lignin is ground into powder to obtain powdered lignin, and at this time the nucleating agent G1 is obtained;

[0014] Carboxylation reaction part

[0015] (c) Introducing carboxyl groups into lignin in an alkaline environment, thereby introducing more nucleation sites;

[0016] (d) After the reaction, a carboxymethylated alkaline lignin solution was obtained;

[0017] (e) Freeze-dry the solution in (d) for 48 h to obtain a fluffy carboxymethylated alkali lignin solid;

[0018] (f) Crush the solid in (e) and sieve it to obtain carboxymethylated alkali lignin powder, thus obtaining PET nucleating agent powder, and at this time, nucleating agent G2 is obtained.

[0019] This invention also aims to protect the use of the above-mentioned PET nucleating agent in modified PET.

[0020] The PET modification method of the present invention includes: mixing the PET nucleating agent of the present invention with pure PET evenly, and extruding the mixture at a temperature range of 240 to 270°C, wherein the weight percentage of the PET nucleating agent in the modified PET is between 0.1% and 1%.

[0021] Compared with PET nucleating agents currently on the market, the advantages of this invention are:

[0022] 1) The nucleating agent of the present invention requires a smaller amount of addition.

[0023] 2) The nucleating agent of the present invention has a better nucleating effect, and the modified PET after adding the present invention has a higher degree of crystallinity.

[0024] 3) The nucleating agent preparation method in this invention is simple, low-cost, environmentally friendly, and will not cause any pollution to the environment. Attached Figure Description

[0025] Figure 1 shows the DSC charts of pure PET and modified PET.

[0026] Figure 2 shows the relationship between the relative crystallinity of pure PET and modified PET over time.

[0027] Figure 3 shows the Jeziorny fitting plots of pure PET and modified PET.

[0028] Figure 4 shows, from left to right, injection molded models of pure PET, PET-G1, and PET-G2. Detailed Implementation

[0029] The present invention will be further described below with reference to specific implementation examples and accompanying drawings.

[0030] Implementation Case 1 - Preparation of Pure Lignin Nucleating Agent

[0031] Pure lignin is extracted and then filtered through a sieve to obtain pure lignin PET nucleating agent.

[0032] Implementation Case 2 - Preparation of Carboxylated Lignin Nucleating Agent (High-Pressure Oxidation Crosslinking Method)

[0033] Step 1 - Oxidation of Lignin

[0034] Weigh 1g of lignin into a high-pressure reactor, add a 20% sodium hydroxide solution (by volume), add water to a final volume of 70ml, stir well, and then place the mixture into the high-pressure reactor. React at 80-140℃ for 60 minutes. After the reaction is complete, allow the reactor to cool naturally until the pressure is released through the exhaust valve. Then, pour out the product, adjust the pH to neutral, and dry it.

[0035] Step 2 - Crosslinking reaction

[0036] The dried sample was placed in a 50 ml single-necked flask, and 1.5 g of sodium hydroxide and 25 ml of 20% formaldehyde solution were added. The temperature was raised to 95 °C, and the reaction was carried out for 1 h. After acid precipitation, the crude product was obtained.

[0037] Step 3 - Purification

[0038] After grinding the crude product into powder, add it to 100ml of pure water, stir at 400r / min for 4 hours at 25℃, filter, and repeat washing more than 3 times.

[0039] Implementation Case 3 - Preparation of Carboxylated Lignin Nucleating Agent (Microwave Carboxymethylation Crosslinking Method)

[0040] Step 1 - Carboxymethylation reaction

[0041] Add 1g of lignin and 25ml of water to a microwave reaction vessel. Add a certain amount of sodium hydroxide solution for alkalization for a certain time and a certain amount of sodium chloroacetate. Then place the vessel in a microwave reaction device and heat it to a certain temperature. After the reaction time is over, adjust the pH of the sample to neutral and dry it.

[0042] Step 2 - Crosslinking reaction

[0043] The dried sample was placed in a 50ml single-necked flask, and 0.25g of sodium hydroxide and 10ml of 30% formaldehyde solution were added. The mixture was heated to 95℃ and reacted for 1 hour. After acid precipitation and filtration, the crude product was obtained.

[0044] Step 3 - Purification

[0045] After grinding the crude product into powder, add it to 100ml of pure water, stir at 400r / min for 4 hours at 25℃, filter, and repeat washing more than 3 times.

[0046] Implementation Case 4 - Preparation of Carboxylated Lignin Nucleating Agent (Conventional Carboxymethylation Method)

[0047] Step 1 - Carboxymethylation reaction

[0048] Prepare a solution by dissolving 1g of lignin in 60ml of sodium hydroxide solution with a pH of 10.7, heating the solution to 60°C, and slowly adding a mixture of 50ml of 2.0g chloroacetic acid solution and 3ml of 6.25mol / L sodium hydroxide solution. The addition should be completed within half an hour, and the reaction should continue for 2 hours to obtain the crude carboxymethylated lignin product.

[0049] Step 2 - Purification

[0050] After grinding the crude product into powder, add it to 100ml of pure water, stir at 400r / min for 4 hours at 25℃, filter, and repeat washing more than 3 times.

[0051] Implementation Case 5 - Modification of PET using lignin-based nucleating agents

[0052] The DSC glass transition temperature of the unmodified PET is 125℃, and the melting point is 250℃.

[0053] The modification steps for PET are as follows:

[0054] The lignin from Example 1 and the carboxymethylated lignin obtained from the arbitrary preparation of carboxymethylated lignin were vacuum dried at 80°C for 12 h, while unmodified PET was vacuum dried at 130°C for 12 h. Lignin was uniformly mixed in at 5% of the PET mass, and the mixture was co-extruded at 280°C using a twin-screw extruder to obtain a lignin-PET composite material. The carboxymethylated lignin-PET composite material was obtained using the same method. The DSC testing procedure was as follows: 3 mg of sample was placed in an aluminum crucible and then placed in the testing equipment. Under nitrogen atmosphere, the temperature was raised to 290°C and held for 5 min to remove thermal history. The temperature was then lowered to 30°C at a rate of 20°C / min, and the cooling curves were recorded. In the figure, the PET curve represents the result without the addition of a nucleating agent, the PET-G1 curve represents the result of the PET-lignin composite material, and the PET-G2 curve represents the result of the PET-carboxymethylated lignin composite material. Integrating the data in Figure 1 yielded Figure 2: the curve showing the change in relative crystallinity over time. Finally, the Avrami exponent n and crystallization rate Zt were obtained by Jeziorny fitting (Figure 3). The final DSC analysis results are shown in Table 1 below: (In the table, T1 is the crystallization termination temperature, T2 is the crystallization initiation temperature, ΔH (J / g) is the crystallization enthalpy, t represents the crystallization time, n is the Avrami exponent, and Zt is the crystallization rate)

[0055] Table 1

[0056]

[0057] Compared with the modified PET, it can be seen that the PET modified by this invention has significantly improved crystallization performance. The cooling crystallization peak in Figure 1 also shows obvious characteristic changes. The peak width of the modified PET crystallization peak is significantly shortened and the peak height is significantly increased. The Avrami index is also significantly increased. The significant reduction in crystallization time can also be clearly seen in Figure 2. The Zt crystallization rate index obtained in Figure 3 is also increased, which clearly shows the improvement in crystallization rate.

Claims

1. An application of modified lignin as a PET nucleating agent, characterized in that, The modified lignin is obtained by carboxylation of formula (I) to obtain the structural formula shown in formula (II), which is defined as product G2; In the formula, two guaiac-based lignin monomers are used to demonstrate the nucleating agent generated after the carboxylation of lignin; R1 represents the remaining lignin; and the remaining lignin is composed of monomers: Amorphous aromatic polymers are formed by five linkages: β--O--4, aO-5, β-5, β-1, and 5-5; R2 represents the portion obtained by carboxylating R1.

2. The application as described in claim 1, characterized in that, The modified lignin is prepared by carboxylating the alcoholic and phenolic hydroxyl groups in the raw lignin, grafting carboxyl groups onto it. The specific reaction is as follows:

3. The application as described in claim 1, characterized in that, The production method of PET nucleating agent includes the following steps: Lignin pretreatment (a) If the production process requires PET color, the lignin is bleached to remove the chromophores and thus remove the lignin color; or a lighter-colored lignin is directly selected; (b) The pretreated lignin is ground into powder to obtain powdered lignin, at which point the nucleating agent G1 is obtained; Carboxylation reaction (c) Carboxyl groups are introduced into the lignin in an alkaline environment to introduce more nucleation sites; (d) After the reaction, a carboxymethylated alkaline lignin solution is obtained; (e) The solution in (d) is freeze-dried for 48 hours to obtain a fluffy carboxymethylated alkaline lignin solid; (f) The solid in (e) is crushed and sieved to obtain carboxymethylated alkaline lignin powder, which is the PET nucleating agent powder, at which point the nucleating agent G2 is obtained.

4. A method for modifying PET, characterized in that, The method comprises: uniformly mixing the modified lignin used in the application of claim 1 with PET, and then extruding the mixture through a twin-screw extruder.

5. The method for PET modification as described in claim 4, characterized in that, The modified lignin is between 0.1% and 1% by mass of the mixture, and the extrusion temperature is between 250°C and 260°C.

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