A bio-based polyester nucleating agent, and a preparation method and application thereof

Abstract

A method for preparing a bio-based polyester nucleating agent is disclosed. This method uses rice bran wax or beeswax as raw materials, which, after refining and oxidative modification, react with calcium or sodium ions to form calcium or sodium salts, thus preparing a bio-based nucleating agent with excellent compatibility with PET and PA. The nucleating agent has a composite structure of a long-chain alkyl backbone and a polar carboxylate group. The long-chain alkyl group can arrange itself in an orderly manner in the molten state to form a template, while the carboxylate group generates ion-dipole interactions with the polyester molecular chain, providing abundant heterogeneous nucleation sites. This nucleating agent can significantly increase the crystallization temperature of polyester by 10-20℃, shorten the crystallization half-cycle by more than 50%, shorten the molding cycle by 20-30%, and improve the mechanical properties and dimensional stability of the product. The raw materials used are renewable, the preparation process is simple, it has excellent thermal stability, and it has a synergistic effect with reinforcing materials such as glass fiber. This invention's nucleating agent is applicable to the injection molding, extrusion, blow molding, film, and fiber processing of PET and PA, and has good application prospects.

Description

Technical Field

[0001] This invention belongs to the field of polymer material additives technology, specifically relating to a bio-based polyester nucleating agent, its preparation method, and its application. Background Technology

[0002] Polyethylene terephthalate (PET) and polyamide (PA), as two important engineering plastics, are widely used in electronics, automotive manufacturing, packaging materials, and textile fibers due to their excellent mechanical properties, chemical resistance, and good processability. In 2022, global PET production capacity exceeded 30 million tons, and PA production capacity approached 10 million tons, with an average annual growth rate of 4-6%, indicating continued strong market demand. However, as semi-crystalline polymers, PET and PA suffer from slow crystallization rates, long molding cycles, and susceptibility to warping and deformation during injection molding, severely limiting their application in high-end fields such as precision components and optical devices.

[0003] Crystallization behavior is a key factor determining the final properties of semi-crystalline polymers. An excessively slow crystallization rate requires a longer cooling time during injection molding, which not only reduces production efficiency but also easily leads to internal stress concentration in the product, causing warpage and dimensional instability. Studies show that the optimal crystallization temperature range for PET is 140-220℃, but under conventional injection molding conditions, its crystallization half-cycle can last 2-5 minutes, far from meeting the demands of efficient production. Similarly, while PA6 crystallizes faster at higher temperatures, its crystallization is insufficient at lower mold temperatures, affecting product performance.

[0004] Nucleating agents are key additives for solving the above problems. By providing heterogeneous nucleation sites and lowering the nucleation free energy barrier, they can significantly improve the crystallization rate and crystallinity of polymers, refine spherulite size, and thus improve the dimensional stability and mechanical properties of the product. An ideal nucleating agent should have the following characteristics: ① good compatibility with the matrix polymer; ② stability at processing temperatures; ③ the ability to provide abundant nucleation sites; ④ no introduction of impurities or impact on the appearance of the product.

[0005] Currently, commercially available nucleating agents are mainly classified into the following categories: (1) Inorganic nucleating agents, such as talc, silica, calcium carbonate, etc., have the advantages of low price and good thermal stability, but poor compatibility with polymer matrix, difficult dispersion, and decreased transparency of the product after addition; (2) Organic carboxylates, such as sodium benzoate, aluminum p-tert-butylbenzoate, etc., have good nucleating effect, but insufficient thermal stability and are easy to decompose during high-temperature processing; (3) Sorbitol transparent nucleating agents, see Chinese patent CN202010248819.5, such as Millad 3988, which has a significant effect on polypropylene, but limited nucleating effect on PET and PA; (4) Polymer nucleating agents, such as ionomers, polyester oligomers, etc., have good compatibility but high cost and complex preparation process.

[0006] With increasingly stringent environmental regulations and the deepening of the concept of sustainable development, the development of bio-based nucleating agents derived from renewable resources has become a research hotspot in the industry. The EU's Green Deal and my country's "dual carbon" targets have placed higher demands on the environmental performance of plastic additives, and the market share of bio-based additives is expected to reach over 30% by 2030. Against this backdrop, developing high-performance additives using agricultural byproducts and natural products not only has economic value but also significant social implications.

[0007] Rice bran wax is a byproduct of rice bran oil refining, with a global annual production of approximately 80,000-100,000 tons, mainly produced in Asia. my country is a major rice bran resource country, producing about 12 million tons of rice bran annually, and thus has abundant rice bran wax resources. The main components of rice bran wax are esters formed from higher fatty acids (C22-C34) and fatty alcohols (C24-C36), possessing a unique long-chain alkyl structure and a melting point of approximately 75-85℃. Beeswax, on the other hand, is a natural wax secreted by bees, with a global annual production of approximately 15,000 tons. It is rich in esters (70-75%), free fatty acids (10-15%), and hydrocarbons (10-15%), also possessing a long-chain hydrophobic structure and a melting point of 62-65℃. Both raw materials are abundant, inexpensive (rice bran wax approximately 15,000-25,000 RMB / ton, beeswax approximately 30,000-50,000 RMB / ton), and biodegradable, making them ideal raw materials for developing bio-based additives.

[0008] Rice bran wax and beeswax have poor compatibility with PET and PA matrices, making direct addition difficult to achieve nucleation. This is mainly because natural wax molecules have low polarity and lack sufficient interaction forces with polar polyester matrices. Therefore, chemical modification is needed to introduce polar functional groups that can strongly interact with the polyester matrix, while retaining their long-chain alkyl backbone to promote ordered arrangement, thereby optimizing nucleation performance. Studies have shown that carboxylate nucleating agents can form ion-dipole interactions with PET or PA molecular chains and are currently recognized as highly efficient nucleating agent systems. Oxidating natural waxes to introduce carboxyl groups before converting them into carboxylates holds promise for obtaining novel nucleating agents that combine bio-based origin and high-efficiency nucleation performance. Summary of the Invention

[0009] The first technical problem to be solved by this invention is to provide a method for preparing a bio-based polyester nucleating agent. This method uses rice bran wax or beeswax as raw materials, and through selective oxidation, hydrolyzes and oxidizes the ester group portion of the wax molecule, or introduces a carboxyl group at the end of the alkyl chain, and then reacts with calcium or sodium ions to form a carboxylate, thereby obtaining a highly efficient nucleating agent with good compatibility with PET and PA.

[0010] The second technical problem this invention aims to solve is to provide a bio-based polyester nucleating agent prepared by the above method. This nucleating agent possesses a unique "rigid-flexible" composite structure: the long-chain alkyl portion can arrange itself in an orderly manner through intermolecular forces during melting and cooling, forming a structure similar to a crystallization template, guiding the directional alignment of polyester molecular chains; the carboxylate portion generates strong ion-dipole interactions with the polyester molecular chains, providing abundant heterogeneous nucleation sites. This nucleating agent can effectively increase the crystallization temperature and crystallization rate of PET and PA, improving the mechanical properties of the products.

[0011] The third technical problem to be solved by this invention is to provide the application of the above-mentioned bio-based polyester nucleating agent in PET and PA processing. This nucleating agent is particularly suitable for injection molding, extrusion molding and blow molding processes, and can be used to produce food packaging, electronic and electrical components, automotive structural parts, textile fibers and other products.

[0012] To solve the first technical problem mentioned above, the present invention provides a method for preparing a bio-based polyester nucleating agent, comprising the following steps:

[0013] (1) Raw material pretreatment:

[0014] Rice bran wax or beeswax is melted at 60-80℃, and activated clay is added at 1-5% of the wax mass. The mixture is then decolorized and refined for 30-60 minutes under a vacuum of 0.05-0.09 MPa and a stirring speed of 200-400 rpm. The activated clay is then removed by filtration to obtain refined bio-based wax.

[0015] The purpose of this step is to remove pigments, colloids, and mechanical impurities from natural wax, thereby improving product purity. The adsorption effect of activated clay effectively removes colored substances such as chlorophyll and carotenoids from the wax, while vacuum conditions facilitate the removal of volatile impurities. After refining, the wax's color changes from brownish-yellow to light yellow or milky white, its acid value decreases slightly, and its purity increases.

[0016] (2) Oxidative modification:

[0017] Refined bio-based wax and oxidant were mixed at a mass ratio of 1:0.5~2 and reacted at 60~100℃ for 2~6 h in the presence of a catalyst. After the reaction was completed, the mixture was cooled to room temperature, washed three times with ethanol, and dried under vacuum to obtain oxidized bio-based wax.

[0018] Oxidation is one of the key steps in this invention. Under the action of a phase-transfer catalyst, the oxidant can enter the organic phase and fully contact the wax molecules, hydrolyzing and oxidizing the ester groups in the wax molecules to carboxyl groups, or introducing carboxyl groups at the alkyl chain ends and double bond positions. The degree of oxidation directly affects the nucleation performance of the final product: insufficient oxidation results in low carboxyl content, fewer active sites after salt formation, and limited nucleation effect; excessive oxidation may destroy the long-chain alkyl structure and reduce the template effect. By controlling the type and amount of oxidant and reaction conditions, the amount of carboxyl groups introduced can be adjusted, with the optimal carboxyl value range being 30~80 mg KOH / g.

[0019] (3) Salt formation reaction:

[0020] The obtained oxidized bio-based wax was dissolved in an organic solvent, and an alkaline calcium compound or an alkaline sodium compound was added. The mixture was reacted at 50-80°C for 1-3 hours. The pH was adjusted to neutral, and the mixture was filtered, washed, and vacuum dried to obtain a bio-based polyester nucleating agent.

[0021] Salt formation is a crucial step in converting oxidation products into highly efficient nucleating agents. The ionic bonds formed between carboxyl groups and metal ions can generate strong ion-dipole interactions with the ester or amide groups of polyester molecular chains, which is the main driving force for nucleation. Calcium salts exhibit high thermal stability and nucleation efficiency, but relatively poor dispersibility; sodium salts have excellent dispersibility, but slightly lower thermal stability. This invention covers both calcium and sodium salts, allowing selection based on specific application requirements.

[0022] Preferably, the oxidant in step (2) is one of potassium permanganate, hydrogen peroxide, concentrated nitric acid, potassium dichromate, and peracetic acid.

[0023] Preferably, the catalyst in step (2) is a phase transfer catalyst, selected from one of tetrabutylammonium bromide, hexadecyltrimethylammonium bromide or polyethylene glycol 400, and the amount used is 0.5 to 3% of the mass of the refined bio-based wax.

[0024] Preferably, in step (3), the alkaline calcium compound is selected from calcium hydroxide, calcium oxide, and calcium carbonate; and the alkaline sodium compound is selected from sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0025] To solve the second technical problem mentioned above, the present invention provides a bio-based polyester nucleating agent prepared by the above-mentioned method.

[0026] The nucleating agent prepared by this method retains the long-chain alkyl structure of natural waxes while introducing ionic groups that can interact with polyesters, achieving synergistic optimization of structure and function. This nucleating agent can effectively increase the crystallization temperature and crystallization rate of PET and PA, shorten the molding cycle by 10-30%, and improve the mechanical properties of the products (tensile strength increased by 8-15%, flexural modulus increased by 10-20%) and dimensional stability (shrinkage rate reduced by 15-25%).

[0027] To address the third technical problem mentioned above, this invention provides an application of a bio-based polyester nucleating agent in PET and PA processing.

[0028] This nucleating agent is particularly suitable for injection molding, extrusion molding and blow molding processes, and can be used to produce food packaging, electronic and electrical components, automotive structural parts, textile fibers and other products.

[0029] Preferably, the bio-based polyester nucleating agent is mixed with PET or PA resin at a mass ratio of 0.05-2.0%, premixed in a high-speed mixer for 5-10 minutes, then added to a twin-screw extruder for melt blending and extrusion, granulation, drying, and finally the product is obtained by injection molding, extrusion or blow molding.

[0030] Processing temperature: PET 260~285℃, PA6 230~260℃, PA66 270~300℃;

[0031] Timing of addition: Add during the mixing stage or in the form of masterbatch.

[0032] The nucleating agent content in the masterbatch is 5-20%. The addition amount of nucleating agent is 0.3-0.8%. Within this range, the best nucleation effect and cost balance can be obtained.

[0033] Advantages of this invention:

[0034] This invention provides a method for preparing polyester nucleating agents using bio-based rice bran wax or beeswax as raw materials through oxidative modification and salt formation reactions. The nucleating agent prepared by this method possesses excellent nucleating properties, good thermal stability, and outstanding dispersibility. It can significantly improve the crystallization rate and mechanical properties of PET and PA, shorten the molding cycle, broaden the high-value application pathways of natural waxes, and has good industrial application prospects and economic benefits.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. Renewable Raw Material Sources: Rice bran wax and beeswax are natural bio-based materials, widely available, inexpensive, and biodegradable. Rice bran wax is a byproduct of rice bran oil refining, achieving high-value utilization of agricultural waste; beeswax is a natural bee product, ensuring resource sustainability. This aligns with the principles of green chemistry and a circular economy, possessing significant environmental and social value.

[0037] 2. Significant Nucleation Effect: The modified wax molecules possess both a long-chain alkyl backbone and polar carboxylate groups, forming a unique "rigid-flexible" composite structure. The long-chain alkyl groups can arrange themselves in an orderly manner in the molten state to form a crystallization template, while the carboxylate groups provide abundant heterogeneous nucleation sites through ion-dipole interactions or hydrogen bonding with the PET or PA molecular chains. Adding 0.1-1% of the nucleating agent of this invention can increase the crystallization temperature of PET by 10-20°C, shorten the crystallization half-cycle by more than 50%, and reduce the supercooling by 15-20°C; it can also increase the crystallization temperature of PA6 by 8-15°C, refine the spherulite size from 20-30 μm to 5-10 μm, and significantly improve transparency. Attached Figure Description

[0038] Figure 1 This is a process flow diagram for preparing the bio-based polyester nucleating agent of this invention.

[0039] Figure 2 This is the 1H NMR spectrum of the oxidized wax.

[0040] Figure 3 These are curves showing the effect of different nucleating agents on the crystallization temperature of PET.

[0041] Figure 4 These are polarized light microscope images of the spherulite morphology of PET before and after adding the nucleating agent of this invention:

[0042] (a) Blank PET; (b) with 0.5% OMR-Ca added. Detailed Implementation

[0043] Example 1: Preparation of Oxidized Rice Bran Wax Calcium Salt Nucleating Agent

[0044] See Figure 1 , Figure 2100 g of rice bran wax was heated to 70℃ and melted. 3 g of activated clay was added, and the mixture was decolorized and purified for 45 min under vacuum of 0.08 MPa and stirring at 300 rpm. The purified rice bran wax was then filtered to obtain refined rice bran wax. The refined rice bran wax was mixed with 120 g of potassium permanganate, and 1 g of tetrabutylammonium bromide was added as a phase transfer catalyst. The mixture was reacted at 80℃ for 4 h. After the reaction, the mixture was cooled, washed three times with ethanol, and dried under vacuum to obtain oxidized rice bran wax, with a carboxyl value of 58 mg KOH / g. The oxidized rice bran wax was dissolved in 200 mL of ethanol, and 5 g of calcium hydroxide was added. The mixture was reacted at 70℃ for 2 h, filtered, washed three times with ethanol, and dried under vacuum at 60℃ for 12 h to obtain the calcium salt nucleating agent for oxidized rice bran wax (labeled OMR-Ca). The product was a light yellow powder with a melting point of 82℃ and a thermal decomposition temperature of 368℃.

[0045] Example 2: Preparation of sodium beeswax oxidized nucleating agent

[0046] See Figure 1 , Figure 2 100 g of beeswax was heated to 70℃ and melted. 3 g of activated clay was added, and the mixture was decolorized and purified for 45 min under vacuum of 0.08 MPa and stirring at 300 rpm. The purified beeswax was then filtered to obtain refined beeswax. The refined beeswax was mixed with 100 g of hydrogen peroxide (30%), and 1 g of hexadecyltrimethylammonium bromide was added as a phase transfer catalyst. The mixture was reacted at 80℃ for 4 h. After the reaction, the mixture was cooled, washed three times with ethanol, and dried under vacuum to obtain oxidized beeswax, with a carboxyl value of 46 mg KOH / g. The oxidized beeswax was dissolved in 200 mL of ethanol, and 4 g of sodium hydroxide was added. The mixture was reacted at 70℃ for 2 h, filtered, washed three times with ethanol, and dried under vacuum at 60℃ for 12 h to obtain sodium beeswax oxidized salt nucleating agent (labeled OBW-Na). The product was a milky white powder with a melting point of 76℃ and a thermal decomposition temperature of 352℃.

[0047] Example 3: Preparation of Oxidized Rice Bran Wax Sodium Salt Nucleating Agent

[0048] See Figure 1 , Figure 2 Oxidized rice bran wax (carboxyl value 58 mg KOH / g) was prepared according to the method in Example 1. The oxidized rice bran wax was dissolved in 200 mL of ethanol, and 4 g of sodium hydroxide was added. The mixture was reacted at 70°C for 2 h, filtered, washed three times with ethanol, and dried under vacuum at 60°C for 12 h to obtain the sodium salt nucleating agent of oxidized rice bran wax (labeled OMR-Na). The product was a light yellow powder with a melting point of 80°C and a thermal decomposition temperature of 355°C.

[0049] Example 4: Preparation of Calcium Salt Nucleating Agent for Oxidized Beeswax

[0050] See Figure 1 , Figure 2Oxidized beeswax (carboxyl value 46 mg KOH / g) was prepared according to the method in Example 2. The oxidized beeswax was dissolved in 200 mL of ethanol, and 5 g of calcium hydroxide was added. The mixture was reacted at 70°C for 2 h, filtered, washed three times with ethanol, and dried under vacuum at 60°C for 12 h to obtain the calcium salt nucleating agent of oxidized beeswax (labeled OBW-Ca). The product was a milky white powder with a melting point of 78°C and a thermal decomposition temperature of 365°C.

[0051] Example 5: The effect of nucleating agents in PET

[0052] See Figure 3 , Figure 4 The nucleating agent prepared in Example 4 was added to PET resin (intrinsic viscosity 0.80 dL / g) at 0.5% (mass fraction). The mixture was then melt-blended (temperature 270~285℃) using a twin-screw extruder, granulated, dried, and injection-molded into standard samples. The crystallization properties were tested using differential scanning calorimetry (DSC) under nitrogen atmosphere. The temperature was increased to 290℃ at 10℃ / min and held for 3 min to eliminate thermal history, then decreased to 50℃ at 10℃ / min. The crystallization curves were recorded. The results are as follows:

[0053]

[0054] The results show that the nucleating agent of the present invention significantly improves the crystallization temperature and crystallization rate of PET.

[0055] Example 6: The effect of nucleating agent in PA6

[0056] See Figure 3 , Figure 4 OBW-Ca was added to PA6 resin at 0.3%, and the mixture was melt-blended (temperature 230-250℃) using a twin-screw extruder, granulated, dried, and then injection-molded into standard samples. The mechanical properties and crystallization behavior were tested, and the results are as follows:

[0057]

[0058] The results show that the mechanical properties of PA6 are significantly improved, the crystallization rate is accelerated, and the molding cycle is shortened by nearly 30% after adding the nucleating agent of this invention, which has significant industrial application value.

Claims

1. A method for preparing a bio-based polyester nucleating agent, characterized in that, Includes the following steps: (1) Raw material pretreatment: Rice bran wax or beeswax is melted at 60-80℃, and activated clay is added at 1-5% of the wax mass. The mixture is then decolorized and refined for 30-60 minutes under a vacuum of 0.05-0.09 MPa and a stirring speed of 200-400 rpm. The activated clay is then removed by filtration to obtain refined bio-based wax. (2) Oxidative modification: Refined bio-based wax and oxidant were mixed at a mass ratio of 1:0.5~2 and reacted at 60~100℃ for 2~6h in the presence of a catalyst. After the reaction was completed, the mixture was cooled to room temperature, washed three times with ethanol, and dried under vacuum to obtain oxidized bio-based wax. (3) Salt formation reaction: The obtained oxidized bio-based wax was dissolved in an organic solvent, and an alkaline calcium compound or an alkaline sodium compound was added. The mixture was reacted at 50-80°C for 1-3 hours. The pH was adjusted to neutral, and the mixture was filtered, washed, and vacuum dried to obtain a bio-based polyester nucleating agent.

2. The method for preparing a bio-based polyester nucleating agent according to claim 1, characterized in that: The oxidant in step (2) is one of potassium permanganate, hydrogen peroxide, concentrated nitric acid, potassium dichromate, or peracetic acid.

3. The method for preparing a bio-based polyester nucleating agent according to claim 1, characterized in that: In step (2), the catalyst is a phase transfer catalyst, selected from one of tetrabutylammonium bromide, hexadecyltrimethylammonium bromide or polyethylene glycol 400, and the amount used is 0.5 to 3% of the mass of the refined bio-based wax.

4. The method for preparing a bio-based polyester nucleating agent according to claim 1, characterized in that: In step (3), the alkaline calcium compound is selected from calcium hydroxide, calcium oxide, and calcium carbonate; the alkaline sodium compound is selected from sodium hydroxide, sodium carbonate, and sodium bicarbonate.

5. A bio-based polyester nucleating agent prepared by the method for preparing a bio-based polyester nucleating agent according to any one of claims 1-4.

6. The application of the bio-based polyester nucleating agent according to claim 5 in the processing of PET and PA.

7. The application of a bio-based polyester nucleating agent according to claim 6 in PET and PA processing, characterized in that: The aforementioned bio-based polyester nucleating agent is mixed with PET or PA resin at a mass ratio of 0.05~2.0%, premixed in a high-speed mixer for 5~10 minutes, then added to a twin-screw extruder for melt blending and extrusion, granulation, drying, and finally obtained by injection molding, extrusion or blow molding to produce the product. Processing temperature: PET 260~285℃, PA6 230~260℃, PA66 270~300℃; Timing of addition: Add during the mixing stage or in the form of masterbatch.

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