A rapid crystallization PET resin composition for engineering plastics, its preparation method and application

Abstract

This invention discloses a rapid crystallization PET resin composition for engineering plastics, its preparation method, and its applications. The PET resin composition, by weight, comprises the following components: 98-102 parts PET, 0.5-1.8 parts nucleating agent, and 2-5 parts hydrogel, wherein the nucleating agent is a metal salt nucleating agent, the hydrogel has an average particle size D50 of 29-48 μm, and the hydrogel has a water content of 42%-68%. The PET resin composition of this invention can improve the crystallization rate of PET while maintaining good mechanical properties of the material.

Description

Technical Field

[0001] This invention relates to the field of engineering plastics technology, and in particular to a rapid crystallization PET resin composition for engineering plastics, its preparation method, and its application. Background Technology

[0002] PET is a common polyester material, typically used for fibers, films, and bottle flakes, but rarely used in engineering plastics applications. PBT has superior mechanical properties, heat resistance, and electrical properties compared to PET, and is therefore widely used in engineering plastics. The only difference in their molecular structure lies in the number of methylene groups. PET has two methylene groups contributed by ethylene glycol residues, while PBT has methylene groups contributed by butanediol residues. This shortens the interchain spacing between benzene rings in the PET molecular chain, increasing structural rigidity. The high rigidity of PET is not conducive to crystal nucleation and grain growth during cooling. Therefore, when PET is used as an engineering plastic, high molding temperatures and long holding times are required, and sometimes annealing is necessary to achieve the desired crystallization state. A key challenge in using PET as an engineering plastic is improving its crystallization rate. Currently, a mature technology involves adding PET-specific nucleating agents and crystallization accelerators. Nucleating agents provide heterogeneous nucleation sites for PET and are essential for increasing its crystallization rate and refining its grain size. Commonly used nucleating agents are mainly divided into two categories: inorganic nucleating agents, such as talc, and organic nucleating agents, typically small-molecule metal salts. Crystallization accelerators are small-molecule or low-molecular-weight plasticizers used to enhance the mobility of PET molecular chains. While PET has unique advantages as an engineering plastic, its slow crystallization rate, coupled with sufficient time and temperature treatment, results in highly crystalline PET exhibiting higher strength and rigidity than PBT. Therefore, there is an urgent need to develop a PET composition with a fast crystallization rate to meet its requirements as an engineering plastic. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a rapid crystallization PET resin composition for engineering plastics, its preparation method, and its applications.

[0004] This invention provides a PET resin composition, comprising, by weight, the following components: 98-102 parts PET, such as 98, 99, 100, 101, or 102 parts; 0.5-1.8 parts nucleating agent, such as 0.5, 0.8, 1, 1.5, or 1.8 parts; and 2-5 parts hydrogel, such as 2, 2.5, 3, 4, or 5 parts.

[0005] Wherein, the nucleating agent is a metal salt nucleating agent, such as any one or more of dimethylolpropionic acid metal salt, hydroxyethylsulfonic acid metal salt or ethylene-methacrylate metal salt, the average particle size D50 of the hydrogel is 29-48 μm, such as 29, 30, 32, 35, 40, 45, 48 μm, and the water content of the hydrogel is 42%-68%, such as 42%, 45%, 48%, 50%, 52%, 55%, 56%, 60%, 68%;

[0006] Average particle size D50 determination: determined according to GB / T19077-2016 "Particle size analysis by laser diffraction", using a Mastersizer 3000 laser particle size analyzer; moisture content determination according to method A, gravimetric method, in GB / T14190-2017.

[0007] The PET content in the composition is not less than 72% by mass;

[0008] The hydrogel is selected from any one or more of catechol-modified chitosan hydrogel, catechol-chitosan hydrogel, and CS / PVA composite hydrogel.

[0009] The inventors accidentally discovered in an experiment where polyester was not dehumidified that the prepared PET-metal salt nucleating agent composition exhibited superior crystallization properties and a rapid crystallization rate. However, due to the lack of polyester dehumidification, hydrolysis was severe, resulting in insufficient mechanical properties of the obtained material. Based on this, the inventors further investigated the role of moisture in promoting the crystallization of the PET-metal salt nucleating agent composition and found that hydrogels with a certain water content can help increase the crystallization rate of the PET resin composition. Hydrogels are highly absorbent and water-retaining polymeric network materials. Because water exists within the network structure of the hydrogel, very little water escapes during short-term high-temperature processing. Adding hydrogels did not cause significant degradation of PET; instead, the composition exhibited higher tensile strength. The inventors further hypothesized that the role of moisture is to promote the dissociation of metal ions, which act as nucleating agents, thereby accelerating the crystallization nucleation process. Furthermore, hydrogels dispersed in the PET resin matrix can reduce van der Waals forces between molecular chains and increase the spacing between rigid molecular chains, exhibiting excellent crystallization properties without the need for additional small-molecule or low-molecular-weight crystallization promoters.

[0010] The average particle size and water content of hydrogels both affect their water retention. If the hydrogel particles are too large and the water content is too high, the hydrogel particles will retain too much water after absorbing it, resulting in soft, sticky particles that are difficult to form at the die head. Conversely, if the hydrogel particles are too small and the water content is too low, the hydrogel particles will retain too little water, and the improvement in crystallization speed will not be significant. If the hydrogel and PET are subjected to the same drying treatment, it is found that the crystallization properties of the resulting PET resin composition system differ significantly from those of the PET resin composition system with a hydrogel having a certain water content. In this case, the hydrogel only acts as a crystallization promoter.

[0011] Furthermore, the intrinsic viscosity of the PET is 0.67-0.86 dL / g, preferably 0.67-0.8 dL / g. Selecting a relatively low intrinsic viscosity PET facilitates rapid alignment of PET molecular chains during crystallization while preventing molecular chain entanglement. Intrinsic viscosity testing method: The intrinsic viscosity of PET is determined according to Method A (capillary viscometer method) in GB / T 14190-2017, using phenol and 1,1,2,2-tetrachloroethane (mass ratio 50:50).

[0012] Furthermore, the metal salt nucleating agent is a hydroxyalkyl metal salt, that is, an alkyl metal salt that simultaneously possesses a hydroxyl structure and a metal salt structure. Common hydroxyalkyl metal salts include hydroxyalkyl carboxylates, hydroxyalkyl sulfonates, etc., and the cation of the metal salt can be selected from Li. + Na + K + For example, taking hydroxyalkyl carboxylates, when PET and carboxylate metal salts are extruded at high temperatures, a chemical reaction occurs to form PET-COOX, where X is an alkali metal ion. At this time, ion clusters are formed between the PET melts with ion end groups. These ion clusters act as nucleating agents in the melt, causing the molecular chains to arrange themselves in a regular pattern and crystallize rapidly. Metal salts containing hydroxyl groups are more effective nucleating agents, presumably because the hydrophilicity of hydroxyl groups can help metal ions contact the hydrogel, thus facilitating better dissociation.

[0013] Furthermore, the hydroxyalkyl metal salt is selected from any one or more of dimethylolpropionic acid metal salt and hydroxyethylsulfonic acid metal salt.

[0014] Furthermore, the PET resin composition also includes glass fiber. Glass fiber reinforcement can significantly improve the tensile strength of engineering plastics. Generally, 10-50 parts of glass fiber can be added, for example, 10, 15, 20, 25, 30, 35, 40, 45, or 50 parts, among which 15 parts and 30 parts of glass fiber are more common. The retained length of the glass fiber can be 100-1000 μm, and the average diameter can be 6-18 μm, but is not limited thereto.

[0015] Furthermore, the PET resin composition further includes 0.5-1.5 parts of processing aids.

[0016] Furthermore, the processing aid is an anti-hydrolysis agent, which is selected from conventional carbodiimide anti-hydrolysis agents.

[0017] Furthermore, the moisture content of the PET is ≤0.1%. Polyester materials are sensitive to moisture and are prone to reverse hydrolysis at high temperatures; controlling the moisture content to ≤0.1% can improve this.

[0018] The present invention also provides a method for preparing the PET resin composition, comprising the following steps:

[0019] Weigh each component according to the specified weight, mix the components, and then extrude and pelletize them using a screw extruder to obtain a PET resin composition. The specific steps are as follows:

[0020] Raw material preparation: Select PET chips with intrinsic viscosity of 0.67-0.86 dL / g and dry them to moisture content ≤0.1%. Select hydrogel with an average particle size of 29-48 μm, or grind large hydrogel particles to an average particle size of 29-48 μm and adjust the water content of the hydrogel to 42%-68%.

[0021] Ingredients: Mix 98-102 parts PET chips, 0.5-1.8 parts metal salt nucleating agent, and 2-5 parts hydrogel. Glass fiber and / or processing aids may also be added.

[0022] Screw extrusion: The PET resin composition is obtained by screw extrusion process.

[0023] The screw extruder has a screw plasticizing temperature of 240-265℃ and a rotation speed of 400-1000rpm, which can be adjusted in a timely manner according to the specific components and processing efficiency.

[0024] The present invention also provides the application of the PET resin composition in the preparation of coil frames and air conditioning outlets.

[0025] In summary, compared with the prior art, the present invention achieves the following technical effects:

[0026] (1) The PET resin composition of the present invention has a fast crystallization rate.

[0027] (2) The PET resin composition of the present invention can achieve a balance between crystallization rate and mechanical properties after being reinforced with glass fiber, which meets the application requirements of the field of engineering plastics. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0029] Example 1

[0030] The present invention will be further illustrated below with reference to specific embodiments and comparative embodiments. The following specific embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the following embodiments, and are not in particular limited to the types of raw materials used in the following specific embodiments.

[0031] I. The sources and moisture content of the raw materials for the examples and comparative examples are as follows:

[0032] PET#1: Yizheng Chemical Fiber, grade FG600, intrinsic viscosity is 0.67 dL / g;

[0033] PET#2: Yizheng Chemical Fiber, grade FG720, intrinsic viscosity is 0.74 dL / g;

[0034] PET#3: Shanghai Yuanfang, grade CB-602, intrinsic viscosity is 0.8 dL / g;

[0035] PET#4: Shanghai Yuanfang, grade CB-608S, intrinsic viscosity is 0.86 dL / g;

[0036] Nucleating agent #1: Metal salt nucleating agent, potassium 2,2-dimethylolpropionate;

[0037] Nucleating agent #2: Metal salt nucleating agent, sodium hydroxyethyl sulfonate, CAS: 1562-00-1;

[0038] Nucleating agent #3: Metal salt nucleating agent, sodium salt of ethylene-methacrylic acid copolymer, brand name Surlyn 8920, DuPont;

[0039] Hydrogel #1: Catechol modified chitosan hydrogel, Xi'an Qiyue Biotechnology, brand name Q-0248530, powder particle size ground to an average particle size of 29μm;

[0040] Hydrogel #2: o-diphenol chitosan hydrogel, Xi'an Qiyue Biotechnology, brand name Q-0248528, powder particle size ground to an average particle size of 45μm;

[0041] Hydrogel #3: CS / PVA composite hydrogel, Xi'an Qiyue Biotechnology, brand name Q-0067311, powder particle size ground to an average particle size of 30μm;

[0042] Hydrogel #4: o-diol chitosan hydrogel, Xi'an Qiyue Biotechnology, brand name Q-0248528; powder particle size ground to an average particle size of 48μm;

[0043] Hydrogel #5: Catechol modified chitosan hydrogel, Xi'an Qiyue Biotechnology, brand name Q-0248530, powder particle size ground to an average particle size of 19μm;

[0044] Hydrogel #6: o-diphenol chitosan hydrogel, Xi'an Qiyue Biotechnology, brand name Q-0248528; powder particle size ground to an average particle size of 65μm;

[0045] Fiberglass: Jushi Fiberglass 960A, the same material was used in parallel tests;

[0046] Processing aids: anti-hydrolysis agent, carbodiimide anti-hydrolysis agent, the same substance was used in parallel tests.

[0047] The preparation method of the PET resin composition in the embodiments and comparative examples of the present invention includes the following steps:

[0048] Select PET with the desired intrinsic viscosity, dry it in an oven to the desired moisture content, grind the hydrogel to the desired average particle size D50, and treat the hydrogel for different times in a constant temperature and humidity chamber (40℃, 95%RH) to adjust the moisture content. Adjust the hydrogel to absorb moisture to the desired moisture content, weigh each component according to the weight parts, and extrude and pelletize the above component mixture to obtain the PET resin composition. In the embodiments and comparative examples of this invention, a plasticizing temperature of 250℃ and a rotation speed of 800rpm are used uniformly.

[0049] II. Performance Testing Methods

[0050] (1) Determination of half-crystallization time t 1 / 2 The half-crystallization time is the time required for crystallization to proceed to half its full extent. Its value can relatively characterize the crystallization rate of different PET samples. The half-crystallization time under non-isothermal crystallization conditions was determined using DSC. The DSC temperature program was set as follows: the sample was heated to 280°C at a rate of 30°C / min, held at 280°C for 5 min to eliminate thermal history, and then cooled to 30°C at a rate of 30°C / min. The crystallization peak was integrated, and the time corresponding to when half the crystallinity was reached was t. 1 / 2 .

[0051] (2) Tensile strength test: The tensile strength of the specimens was tested in accordance with GB / T1040.1-2018 "Determination of tensile properties of plastics - Part 1: General" and GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics". The test temperature was 23℃. The injection molding process selected a mold temperature of 80℃, an injection temperature of 260-270℃, an injection pressure of 60-65 bar, a holding time of 25 seconds, and a total injection cycle of 42 seconds.

[0052] Table 1. Technical solutions and effects of the embodiments (unit: parts by weight)

[0053]

[0054]

[0055] Table 2 Comparative examples of technical solutions and effects (unit: parts by weight)

[0056]

[0057]

[0058] Compared to the system with metal salt nucleating agents alone (Comparative Example 2), the combination of metal salt nucleating agents in Examples 1-11 with hydrogels having a water content of 42%-68% significantly improved the crystallization rate of PET resin. The half-crystallization time of the PET resin composition samples measured at a cooling rate of 30°C / min was 37-69 s, preferably 37-58 s, while the half-crystallization time of Comparative Example 2 measured under the same test conditions was 112 s. As a comparative experiment between Examples 6 and 10, the use of hydroxyl-containing alkyl metal salts showed a significantly better crystallization-promoting effect than the use of non-hydroxyl-containing alkyl metal salts.

[0059] For tensile strength, using the tensile strength of 30 parts of glass fiber reinforced resin to characterize the strength difference between different resin compositions is more intuitive than measuring the strength of resin without glass fiber filler. Therefore, the performance data of adding 30 parts of glass fiber reinforced resin is provided exemplary in the examples. The tensile strength is evaluated with the control group under the same test conditions. The same trend can be reproduced in pure resin system and other glass fiber reinforced systems. Through different formulations of PET resin combinations, the tensile strength of the 30 parts of glass fiber reinforced PET resin composition prepared in the examples reaches 141-153 MPa, which has a significant advantage over the comparative example and can effectively meet the high standards of customers and the market.

[0060] Compared with Example 6, Comparative Examples 1-6 differed only in that Comparative Example 1 contained 3.5 parts of nucleating agent. The excessive amount of nucleating agent is presumably due to the mechanism of metal salt nucleating agents, which involves molecular chain exchange with PET to form PET salts. This process breaks down the PET molecular chains, and excessive addition exacerbates PET degradation, leading to a decrease in the mechanical properties of the PET resin composition. Comparative Example 2 differed only in that no hydrogel was added. The composition showed a longer semi-crystallization time and reduced strength, indicating that introducing a hydrogel with a specific water content can help improve the crystallization rate. Comparative Example 3 differed only in that the water content of the hydrogel was adjusted to 1%. The composition also showed a longer semi-crystallization time and reduced strength, demonstrating that the water content in the hydrogel particles significantly affects the improvement in crystallization. Comparative Example 4 differed only in that the amount of hydrogel added was reduced to 0.5 parts. Insufficient hydrogel addition had no significant effect on improving the crystallization rate. The only difference between Comparative Example 5 and Example 6 is that the amount of hydrogel added was increased to 8 parts. Adding excessive hydrogel led to a decrease in mechanical properties; this may be due to degradation caused by the high content, or the excessive hydrogel itself affecting the mechanical strength of the material. The only difference between Comparative Example 6 and Example 6 is that the hydrogel was ground to an average particle size of 19 micrometers, the same as Comparative Example 2. The improvement effect of Comparative Example 6 was not ideal. This shows that when the hydrogel particle size is too small, under the same water content, the amount of water stored in a single hydrogel particle is too small, affecting the improvement of the crystallization rate.

[0061] Comparative Examples 7 and 8 are all compared to Example 9. The only difference between Comparative Example 7 and Example 9 is that the average particle size of the hydrogel is 65 micrometers. This may be due to excessive water stored in the hydrogel particles, which makes the hydrogel particles sticky and soft during processing, making it difficult for the die head to form. The only difference between Comparative Example 8 and Example 9 is that deionized water was sprayed onto the hydrogel, making its water content reach 105%, which also made it difficult to extrude and form.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A PET resin composition, characterized in that, By weight, it includes the following components: PET 98-102 parts; Nucleating agent 0.5-1.8 parts; 2-5 parts of hydrogel; The nucleating agent is a metal salt nucleating agent, the average particle size D50 of the hydrogel is 29-48 μm, and the water content of the hydrogel is 42%-68%. The metal salt nucleating agent is a hydroxyalkyl metal salt; The hydroxyalkyl metal salt is selected from any one or more of dimethylolpropionic acid metal salt and hydroxyethylsulfonic acid metal salt; The moisture content of the PET is ≤0.1%.

2. The PET resin composition according to claim 1, characterized in that, The intrinsic viscosity of the PET is 0.67-0.86 dL / g.

3. The PET resin composition according to claim 1, characterized in that, It also includes glass fiber.

4. The PET resin composition according to claim 1, characterized in that, It also includes 0.5-1.5 parts of processing aids.

5. The PET resin composition according to claim 4, characterized in that, The processing aid is an anti-hydrolysis agent.

6. A method for preparing the PET resin composition according to any one of claims 1-5, characterized in that, Includes the following steps: Weigh each component according to the weight parts, mix the components, and then extrude and pelletize them to obtain a PET resin composition.

7. The use of the PET resin composition according to any one of claims 1-5 in the preparation of coil frames and air conditioning outlets.

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