Wear-resistant polyester material and method for producing same

Abstract

This invention discloses a wear-resistant polyester material and its preparation method, belonging to the field of polymer materials technology. The invention employs a two-stage separate esterification strategy: ethylene glycol is separately esterified with terephthalic acid and 2-hydroxyterephthalic acid, then the esterification products from the two stages are mixed and polycondensed, granulated, and dried to obtain the polyester material. The phenolic hydroxyl groups of 2-hydroxyterephthalic acid remain in the polyester backbone after polycondensation, forming intermolecular hydrogen bonds with adjacent ester carbonyl groups, acting as "pseudo-crosslinking points," increasing chain packing density and surface hardness, thereby significantly enhancing wear resistance and impact resistance while maintaining high transparency. Separate esterification ensures that the hydroxyl groups are uniformly distributed on the molecular chain, forming a complete hydrogen bond network. The resulting polyester material possesses excellent wear resistance, transparency, and flexibility, making it suitable for transparent packaging, optical films, and engineering plastic products.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a wear-resistant polyester material and its preparation method. Background Technology

[0002] Polyethylene terephthalate (PET) is currently the most produced saturated polyester engineering plastic. It possesses excellent chemical resistance, thermal stability, and electrical insulation properties, and is widely used in packaging, fibers, films, and engineering plastics. However, the PET molecular chain contains rigid benzene rings and is highly symmetrical, lacking a branched structure, resulting in poor flexibility (elongation at break of only about 3%) and insufficient surface abrasion resistance. In practical use, the surface of PET products easily loses its gloss due to scratches, affecting its appearance and service life.

[0003] To improve the abrasion resistance of polyester materials, existing technologies mainly employ physical blending modification by adding inorganic or organic abrasion-resistant additives (such as silicone, molybdenum disulfide, and polytetrafluoroethylene powder). However, the addition of abrasion-resistant additives usually leads to a significant decrease in material transparency and an increase in haze, limiting its application in transparent packaging, optical films, and other fields. Summary of the Invention

[0004] This invention addresses the technical problems of insufficient wear resistance in existing PET polyester materials and decreased transparency due to the addition of wear-resistant additives by providing a wear-resistant polyester material and its preparation method.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a wear-resistant polyester material includes the following steps: Step 1: In the first esterification reactor, terephthalic acid and ethylene glycol are mixed in a molar ratio and esterified under nitrogen protection to obtain the first esterification product; in the second esterification reactor, 2-hydroxyterephthalic acid and ethylene glycol are mixed in a molar ratio and esterified under nitrogen protection to obtain the second esterification product; wherein the total amount of ethylene glycol in the two reactors is 1.2-2.0 times the total molar amount of diacid. Step 2: Transfer the first esterification product and the second esterification product to the same polycondensation reactor, add the catalyst tetrabutyl titanate, heat under nitrogen protection, and evacuate. When the intrinsic viscosity of the reaction system reaches 0.65-0.80 dL / g, stop the reaction and introduce nitrogen to restore normal pressure to obtain the copolyester melt. Step 3: The copolyester melt obtained in Step 2 is cooled with water, granulated, and then vacuum dried at 80-100℃ for 4-6 hours to obtain wear-resistant polyester material.

[0006] Furthermore, in step 1, based on the total molar amount of diacids (terephthalic acid + 2-hydroxyterephthalic acid), the molar amount of terephthalic acid is 85-97 mol%, and the molar amount of 2-hydroxyterephthalic acid is 3-15 mol%. The molar amount of 2-hydroxyterephthalic acid is limited to 3-15 mol% because when the amount is less than 3%, sufficient intermolecular hydrogen bonds cannot be formed, and the improvement in wear resistance is not significant; when the amount is more than 15%, it is easy to cause oxidation of phenolic hydroxyl groups, resulting in yellowing of the product and a decrease in transparency and mechanical properties.

[0007] Furthermore, in step 2, the amount of tetrabutyl titanate added is 0.01-0.1% of the total reactant mass.

[0008] Further, the specific method for the esterification reaction described in step 1 is as follows: terephthalic acid and ethylene glycol are mixed at a molar ratio of 1:1.3-1.5, ultrasonically dispersed for 20-40 minutes, heated to 230-250℃ under nitrogen protection, and maintained at a pressure of 250-300 kPa for esterification reaction for 2-3 hours; 2-hydroxyterephthalic acid and ethylene glycol are mixed at a molar ratio of 1:2.0-3.0, and esterified under the same conditions for 2-3 hours.

[0009] Further, the specific method of the mixed polycondensation in step 2 is as follows: transfer the two esterification products to the polycondensation reactor, add tetrabutyl titanate, heat to 270-275°C under nitrogen protection, slowly evacuate to below 80 Pa within 30 minutes, maintain this vacuum level for 1-2 hours, and terminate the reaction when the stirring power no longer increases or the intrinsic viscosity reaches the target value.

[0010] Furthermore, the drying conditions described in step 3 are: vacuum drying at 90°C for 5 hours, with a product moisture content of less than 0.01%.

[0011] The present invention also discloses a wear-resistant polyester material prepared according to any one of the above preparation methods.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention introduces 2-hydroxy terephthalic acid units into the PET main chain, and the phenolic hydroxyl group forms intermolecular hydrogen bonds with the ester carbonyl group of the adjacent molecular chain, which acts as a "pseudo-crosslinking point" to improve the molecular chain stacking density and surface hardness.

[0013] (2) The copolymer unit disrupts the regularity of the PET molecular chain, inhibits the formation of large crystals, and keeps the material in an amorphous or microcrystalline state. The visible light transmittance is ≥87% and the haze is ≤5%, which is comparable to pure PET, overcoming the defect of traditional wear-resistant additives that reduce transparency.

[0014] (3) This invention strictly controls the reaction temperature, reaction time, and inert atmosphere, further suppressing the oxidation or side reactions of phenolic hydroxyl groups. Therefore, the phenolic hydroxyl groups are completely retained in the polyester backbone in the form of side groups, providing sufficient active sites for the subsequent formation of intermolecular hydrogen bonds. The formed hydrogen bond network provides an energy dissipation mechanism, enabling the material to absorb energy through the reversible breaking and recombination of hydrogen bonds when subjected to external forces.

[0015] (4) The present invention uses two separate esterification processes, which can avoid uneven copolymerization caused by the difference in esterification rates between 2-hydroxyterephthalic acid and terephthalic acid, and ensure that hydroxyl groups are evenly distributed on the molecular chain, thereby forming a more effective hydrogen bond network. Detailed Implementation

[0016] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0017] Example 1 A method for preparing a wear-resistant polyester material includes the following steps: Step 1: First esterification reactor: Weigh 0.45 mol (74.7 g) terephthalic acid (PTA) and 0.63 mol (39.1 g) ethylene glycol (EG), control the PTA:EG molar ratio to be 1:1.4, mix and ultrasonically disperse for 30 minutes, purge with nitrogen three times to replace air, raise the temperature to 240℃, maintain the pressure at 250 kPa, and esterify for 2 hours to obtain the first esterification product.

[0018] Second esterification reactor: Weigh 0.05 mol (9.1 g) of 2-hydroxyterephthalic acid (2-HTA) and 0.125 mol (7.8 g) of ethylene glycol, control the 2-HTA:EG molar ratio to be 1:2.5, mix and ultrasonically disperse for 30 minutes, add to the second esterification reactor, and esterify under the same conditions for 2 hours to obtain the second esterification product.

[0019] The total amount of EG used in the two reactors was 0.755 mol (1.51 times the total 0.5 mol of diacid).

[0020] Step 2: Transfer the first and second esterification products to a polycondensation reactor, add 0.05 g of tetrabutyl titanate (TBT) catalyst, heat to 270°C under nitrogen protection, slowly evacuate the system, and reduce the pressure to 80 Pa within 30 minutes. Maintain this vacuum level for 1.5 hours. The intrinsic viscosity of the product is measured to be 0.72 dL / g. Stop the reaction and purge with nitrogen to restore atmospheric pressure.

[0021] Step 3: Granulation and Drying The reaction melt was cooled with water, granulated, and then vacuum dried at 90°C for 5 hours to obtain abrasion-resistant polyester material.

[0022] In this embodiment, the total diacid composition is: PTA 90 mol%, 2-hydroxyterephthalic acid 10 mol%.

[0023] Example 2 The difference from Example 1 is as follows: First esterification reactor: PTA 0.475 mol (78.9 g), EG 0.665 mol (41.2 g), PTA:EG = 1:1.4.

[0024] Second esterification reactor: 0.025 mol (4.55 g) of 2-HTA, 0.0625 mol (3.9 g) of EG, 2-HTA:EG = 1:2.5.

[0025] The total amount of EG used in the two reactors was 0.7275 mol (1.455 times the total 0.5 mol of diacid).

[0026] The other steps are the same as in Example 1. The intrinsic viscosity was measured to be 0.69 dL / g.

[0027] Example 3 The difference from Example 1 is as follows: First esterification reactor: PTA 0.425 mol (70.6 g), EG 0.595 mol (36.9 g), PTA:EG = 1:1.4.

[0028] Second esterification reactor: 0.075 mol (13.65 g) of 2-HTA, 0.1875 mol (11.6 g) of EG, 2-HTA:EG = 1:2.5.

[0029] The total amount of EG used in the two reactors was 0.7825 mol (1.565 times the total 0.5 mol of diacid).

[0030] The other steps are the same as in Example 1. The intrinsic viscosity was measured to be 0.67 dL / g.

[0031] Example 4 The difference from Example 1 is as follows: First esterification reactor: PTA 0.485 mol (80.6 g), EG 0.679 mol (42.1 g), PTA:EG = 1:1.4.

[0032] Second esterification reactor: 0.015 mol (2.73 g) of 2-HTA, 0.0375 mol (2.3 g) of EG, 2-HTA:EG = 1:2.5.

[0033] The total amount of EG used in the two reactors was 0.7165 mol (1.433 times the total 0.5 mol of diacid).

[0034] The other steps are the same as in Example 1. The intrinsic viscosity was measured to be 0.68 dL / g.

[0035] Example 5 The difference from Example 1 is that the polycondensation temperature in step 2 was adjusted to 275°C, and the reaction time was adjusted to 1.2 hours. Other steps were the same as in Example 1. The intrinsic viscosity was measured to be 0.74 dL / g.

[0036] Comparative Example 1 The difference from Example 1 is that 2-hydroxyterephthalic acid was not added; only 0.5 mol (83.0 g) of PTA and 0.70 mol (43.4 g) of EG were used, and the PTA:EG ratio was controlled at 1:1.4 for single-pot esterification followed by polycondensation. Other steps were the same as in Example 1. The intrinsic viscosity was measured to be 0.67 dL / g.

[0037] Comparative Example 2 The difference from Example 1 is that in step 1, the amount of PTA used is 0.495 mol (82.2 g), and the amount of 2-HTA used is 0.005 mol (0.91 g), i.e., the molar ratio is 1 mol%. The total amount of EG used is calculated according to PTA:EG = 1:1.4 and 2-HTA:EG = 1:2.5. Other steps are the same as in Example 1. The intrinsic viscosity was measured to be 0.68 dL / g.

[0038] Comparative Example 3 The difference from Example 1 is that in step 1, the amount of PTA used is 0.35 mol (58.1 g), and the amount of 2-HTA used is 0.15 mol (27.3 g), i.e., the molar ratio is 30 mol%. The total amount of EG used is calculated according to PTA:EG = 1:1.4 and 2-HTA:EG = 1:2.5. Other steps are the same as in Example 1. The product is slightly yellow in color, and the intrinsic viscosity is measured to be 0.63 dL / g.

[0039] Comparative Example 4 The difference from Example 1 is that 2-hydroxyterephthalic acid was replaced with an equimolar amount of isophthalic acid (without hydroxyl groups), and the total diacid composition was: PTA 90 mol%, isophthalic acid 10 mol%. Other steps were the same as in Example 1. The intrinsic viscosity was measured to be 0.68 dL / g.

[0040] Comparative Example 5 Step 1: Weigh out 0.45 mol (74.7 g) of PTA, 0.05 mol (9.1 g) of 2-HTA, and 0.755 mol (46.8 g) of EG, and add them together to the same esterification reactor. After mixing, ultrasonically disperse for 30 minutes, purge the air with nitrogen three times, raise the temperature to 240℃, maintain the pressure at 250 kPa, and esterify for 2 hours to obtain a mixed esterification product.

[0041] Step 2: The above mixed esterification products were transferred to a polycondensation reactor, and 0.05 g of TBT was added. The mixture was heated to 270°C under nitrogen protection, and a vacuum was slowly applied to 80 Pa. The polycondensation reaction was carried out for 1.5 hours. The intrinsic viscosity was measured to be 0.65 dL / g (lower than 0.72 dL / g in Example 1).

[0042] Step 3: Granulation and drying are the same as in Example 1.

[0043] Performance testing Notched impact strength: according to GB / T 1043.1-2008 standard.

[0044] Tensile strength: according to GB / T 1040.2-2006 standard.

[0045] Taber wear: according to GB / T 1768-2006 standard.

[0046] Shore hardness: Tested according to GB / T 2411-2008 standard using a Shore D hardness tester. The sample thickness is 4mm, and there are no less than 5 test points. The average value is taken.

[0047] Visible light transmittance: Tested according to GB / T 2410-2008 standard using a transmittance / haze meter, with a sample thickness of 1 mm and a wavelength range of 380-780 nm.

[0048] Cross-scratch color difference ΔE: Using a scratch tester (compliant with GM 14688 standard), a cross-scratch was performed on the sample surface with a load of 10N and an angle of 45°. The L, a, and b values ​​before and after scratching were measured using a colorimeter (D65 light source, 10° viewing angle) to calculate the color difference.

[0049] Table 1 Performance test results of each embodiment and comparative example

[0050] As shown in Table 1, the polyester materials prepared in Examples 1-5 are significantly superior to Comparative Example 1 (pure PET) and Comparative Example 2 (with an addition of only 1 mol%) in terms of abrasion resistance and impact strength. Example 3 (15 mol% 2-HTA) exhibits the best abrasion resistance, with a Taber abrasion amount reduced by approximately 58% compared to Comparative Example 1, and a notched impact strength increased by approximately 127%.

[0051] The performance of Comparative Example 5 (total esterification) was significantly inferior to that of Example 1 (separate esterification), demonstrating the necessity of the dual-reactor separate esterification strategy of the present invention: separate esterification can avoid uneven copolymer composition caused by differences in esterification rate, ensure that hydroxyl groups are evenly distributed on the molecular chain, thereby forming a more complete hydrogen bond network.

[0052] Comparative Example 4 uses isophthalic acid without phenolic hydroxyl groups. Although it can destroy crystallinity, it cannot form hydrogen bonds. Its wear resistance is close to that of pure PET, which confirms that hydrogen bonds are the key to performance improvement.

[0053] In summary, this invention, through a separate esterification copolymerization strategy, uniformly introduces 2-hydroxyterephthalic acid units into the PET backbone. Utilizing the intermolecular hydrogen bonds between the phenolic hydroxyl groups and the ester carbonyl groups to form a "pseudo-crosslinked" network, it significantly improves the abrasion resistance, impact toughness, and surface hardness of the polyester material while maintaining excellent transparency. The overall performance is optimal when the molar ratio of 2-hydroxyterephthalic acid is 5-15%.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a wear-resistant polyester material, characterized in that, Includes the following steps: Step 1: In the first esterification reactor, terephthalic acid and ethylene glycol are mixed in a molar ratio and esterified under nitrogen protection to obtain the first esterification product; in the second esterification reactor, 2-hydroxyterephthalic acid and ethylene glycol are mixed in a molar ratio and esterified under nitrogen protection to obtain the second esterification product; the total amount of ethylene glycol in both reactors is 1.2-2.0 times the total molar amount of diacid. Step 2: Transfer the first esterification product and the second esterification product to the same polycondensation reactor, add the catalyst tetrabutyl titanate, heat under nitrogen protection, and evacuate. When the intrinsic viscosity of the reaction system reaches 0.65-0.80 dL / g, stop the reaction and introduce nitrogen to restore normal pressure to obtain the copolyester melt. Step 3: The copolyester melt obtained in Step 2 is cooled with water, granulated, and then vacuum dried at 80-100℃ for 4-6 hours to obtain wear-resistant polyester material.

2. The preparation method according to claim 1, characterized in that, In step 1, based on the total molar amount of terephthalic acid and 2-hydroxyterephthalic acid, the molar amount of terephthalic acid is 85-97 mol%, and the molar amount of 2-hydroxyterephthalic acid is 3-15 mol.

3. The preparation method according to claim 1, characterized in that, In step 2, the amount of tetrabutyl titanate added is 0.01-0.1% of the total reactant mass.

4. The preparation method according to claim 1, characterized in that, The specific method for the esterification reaction in the first esterification reactor in step 1 is as follows: terephthalic acid and ethylene glycol are mixed at a molar ratio of 1:1.3-1.5, ultrasonically dispersed for 20-40 minutes, heated to 230-250℃ under nitrogen protection, and maintained at a pressure of 250-300 kPa for esterification reaction for 2-3 hours.

5. The preparation method according to claim 1, characterized in that, The specific method for the esterification reaction in the second esterification reactor in step 1 is as follows: 2-hydroxyterephthalic acid and ethylene glycol are mixed at a molar ratio of 1:2.0-3.0, ultrasonically dispersed for 20-40 minutes, heated to 230-250℃ under nitrogen protection, and maintained at a pressure of 250-300 kPa for esterification reaction for 2-3 hours.

6. The preparation method according to claim 1, characterized in that, The specific method for the mixed polycondensation described in step 2 is as follows: transfer the esterification products from the two reactors to the polycondensation reactor, add tetrabutyl titanate, heat to 270-275°C under nitrogen protection, slowly evacuate to below 80 Pa within 30 minutes, maintain this vacuum level for 1-2 hours, and terminate the reaction when the stirring power no longer increases or the intrinsic viscosity reaches the target value.

7. The preparation method according to claim 1, characterized in that, The drying conditions described in step 3 are: vacuum drying at 90°C for 5 hours, and the product moisture content is less than 0.01%.

8. The wear-resistant polyester material prepared by the preparation method according to any one of claims 1-7.

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