An easily crystallizable biodegradable fat-aromatic copolyester composition and preparation method thereof

Abstract

The present invention relates to biodegradable polymer materials, and discloses a biodegradable fat-aromatic copolyester composition that is easily crystallized and a preparation method thereof. The composition comprises a base resin and a crystallization accelerator; the base resin is prepared by copolymerizing butanediol, a C4-C6 short-chain aliphatic dicarboxylic acid, and an aromatic dicarboxylic acid; the crystallization accelerator is prepared by copolymerizing butanediol, a C4-C6 short-chain aliphatic dicarboxylic acid, and an aromatic dicarboxylic acid; 10 ‑C 16 The present invention adopts a long-chain aliphatic-aromatic copolyester with a relatively high content as a crystallization accelerator, which has the dual effects of promoting crystal nucleation and crystal growth in the matrix resin. A small amount of addition can significantly promote crystallization. The obtained composition has excellent comprehensive crystallization performance, with the performance advantages of a short half-crystallization time, a high crystallization temperature, and a large crystallization enthalpy. While maintaining excellent biodegradability, the transparency is also significantly improved.

Description

Technical Field

[0001] The present invention relates to biodegradable polymer materials, in particular to an easily crystallizable biodegradable fat-aromatic copolyester composition and a preparation method thereof. Background Art

[0002] Aliphatic-aromatic copolyesters (copolyesters), made from butanediol, short-chain aliphatic dibasic acids (C4-C6), and aromatic dibasic acids, such as poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate-co-terephthalate) (PBST), poly(butylene adipate-co-furandicarboxylate) (PBAF), and poly(butylene succinate-co-furandicarboxylate) (PBSF), are all important biodegradable polymers. Within a suitable composition range, they exhibit excellent biodegradability and physical and mechanical properties comparable to those of polyolefins. They can replace traditional non-biodegradable polymers such as polyolefins and are used in disposable or short-term plastic products, such as shopping bags, garbage bags, packaging films, and agricultural mulch films. However, these copolyesters all suffer from poor crystallinity to varying degrees.

[0003] Crystallinity is one of the most important properties of polymer materials, directly impacting the ease of production and processing, as well as the quality of their application. Three primary indicators are used to evaluate crystallization performance: melt crystallization temperature (or supercooling), crystallization enthalpy (degrees), and crystallization half-time. While melt crystallization temperature encompasses a range of temperatures, it is typically expressed as the temperature at which the crystallization rate reaches its maximum. Supercooling is the difference between the equilibrium melting point and the melt crystallization temperature. The melt crystallization temperature, or supercooling, reflects the ease with which a material crystallizes; higher melt crystallization temperature or lower supercooling indicates greater crystallization efficiency. Crystallization enthalpy corresponds to the heat released during crystallization and reflects the degree of crystallization. The crystallization half-time, the time required for half the crystallization process to complete, reflects the speed of the crystallization process. From a production and application perspective, polymer materials with excellent crystallization properties should possess a high crystallization temperature, a high crystallization enthalpy, and a short crystallization half-time, such as polyethylene, polybutylene terephthalate (PBT), and nylon 66. However, common biodegradable copolyesters such as PBAT, while crystallizing rapidly, have low crystallization enthalpy. PBST not only has a low crystallization enthalpy but also crystallizes slowly under practical production and processing conditions (i.e., rapid cooling), severely impacting PBST's pelletizing and melt processing properties. Furandicarboxylic acid-based copolyesters PBAF and PBSF exhibit even poorer crystallinity than PBAT and PBST.

[0004] The most common technique for promoting polymer crystallization is to add a nucleating agent to the polymer. This increases the number of crystal nuclei, either directly or by induction, thereby increasing the crystallization temperature and rate and reducing crystal size. Currently available nucleating agents for crystallization modification of PBST and PBAT copolyesters include the following:

[0005] (1) Patent CN 102558521 A discloses a polyfumaric acid diol ester and its copolyester nucleating agent, 1wt% of which can be used to separate PBAT The melt crystallization temperatures of PBST and PBST at a cooling rate of 10°C / min increased to 77.8°C and 73.4°C, respectively, which were increased by 5.3°C and 10.9°C, but the melt crystallization enthalpy data were not given;

[0006] (2) Patent CN 102492248 A discloses the use of polyvinyl acetal as a nucleating agent. A dosage of 1 wt% can increase the melt crystallization temperature of PBAT at a cooling rate of 10°C / min to 81.4°C, an increase of 6.8°C. However, no melt crystallization enthalpy data are provided.

[0007] (3) CN 108384200 A discloses a melamine / cyanuric acid complex nucleating agent, which can increase the melt crystallization temperature of PBAT by 15.6°C and 21.7°C at a cooling rate of 10°C / min at 1wt% and 5wt%, respectively. The final crystallization temperatures are 68.2°C and 74.2°C, respectively, and the melt crystallization enthalpies are 17.1 J / g and 16.8 J / g, respectively.

[0008] (4) CN 111100272 A, CN 111100427 A, and CN 111100270 A respectively disclose the use of similar copolyester oligomers with high aromatic chain content and aromatic polyester oligomers as nucleating agents for aliphatic-aromatic copolyesters, but no DSC data are provided.

[0009] It can be seen that the existing crystallization modification technology of biodegradable copolyester has the following problems: (1) Although it has a good crystallization promoting effect under the conventional DSC cooling rate (such as 10℃ / min), it often has poor effect or is not disclosed under the conditions of rapid cooling required for actual production and processing (cooling rate often reaches tens of degrees Celsius per minute), and does not really have production and application value. (2) The more important purpose of crystallization modification is to increase the crystallization rate and achieve rapid crystallization. However, the evaluation of crystallization performance in the existing technology is only based on crystallization temperature and crystallization enthalpy, ignoring the speed of crystallization or the length of half-crystallization time, so it is difficult to confirm whether rapid crystallization is truly achieved. (3) The crystallization promoter used only plays the role of promoting crystal nucleation, and is a nucleating agent. There is a lack of crystallization promoters that can promote both crystal nucleation and crystal growth. (4) The nucleating agents used in some existing technologies are not biodegradable, and the biodegradability of the product obtained by mixing with the base resin will be affected. The product obtained is not a fully biodegradable material; (5) The nucleating agent used has an adverse effect on transparency after mixing with the base resin.

[0010] In summary, the development of fully biodegradable fat-aromatic copolyester materials with short half-crystallization time, high crystallization temperature, large crystallization enthalpy and unaffected transparency under actual processing conditions of rapid cooling is still a technical problem that needs to be solved urgently. Summary of the Invention

[0011] The present invention addresses the problems of low crystallization temperature, slow crystallization speed, and particularly long semi-crystallization time of biodegradable fat-aromatic copolyesters. The present invention provides a biodegradable fat-aromatic copolyester composition that can rapidly crystallize under rapid cooling conditions. The composition not only has the performance advantages of a short semi-crystallization time, a high crystallization temperature, and a large crystallization enthalpy, but also maintains transparency and biodegradability.

[0012] To achieve the above object, the technical solution adopted by the present invention is:

[0013] An easily crystallizable biodegradable fatty-aromatic copolyester composition comprising a base resin and a crystallization accelerator;

[0014] The base resin is prepared by copolymerizing butanediol, a C4-C6 short-chain aliphatic dicarboxylic acid, and an aromatic dicarboxylic acid; the crystallization accelerator is prepared by copolymerizing butanediol, a C10-C16 long-chain aliphatic dicarboxylic acid, and an aromatic dicarboxylic acid;

[0015] The content of the aromatic dibasic acid butylene glycol repeating unit in the base resin is 43-70 mol %, and the content of the aromatic dibasic acid butylene glycol repeating unit in the crystallization accelerator is 60-90 mol %.

[0016] The present invention is directed to the problem that the crystallization rate of biodegradable fat-aromatic copolyester is slow, and adopts the long-chain fat-aromatic copolyester with the high content of aromatic dibasic acid butylene glycol as a crystallization accelerator.Contain the aromatic dibasic acid butylene glycol repeating unit identical with the matrix resin structure but higher in content in this crystallization accelerator, so its crystalline structure is identical with the matrix resin but easier to crystallize, crystallization rate is faster, plays nucleation in the matrix resin, promotes crystal nucleation.This crystallization accelerator also contains flexible fat long-chain dibasic acid butylene glycol repeating unit simultaneously, is conducive to promoting the segment motion of the matrix resin, thereby plays the effect of promoting its crystal growth.So this crystallization accelerator has the dual effect of promoting crystal nucleation and crystal growth simultaneously, mixes the prepared composition with the matrix resin with the comprehensive crystallization performance excellence, and has the performance advantages of short half crystallization time, high crystallization temperature, large crystallization enthalpy concurrently.

[0017] In addition, since the crystallization accelerator has a chemical structure similar to that of the matrix resin, the two have good compatibility, and the crystallization accelerator can be easily and evenly dispersed in the matrix resin, which helps it to fully exert its crystallization promoting effect and is beneficial to improving the transparency.

[0018] The biodegradable fatty-aromatic copolyester composition comprises, by weight, 80-99.8 wt% of a base resin and 0.2-20 wt% of a crystallization accelerator. In the present invention, even a minimal amount of the crystallization accelerator is sufficient to promote crystallization. Preferably, the composition comprises 90-99.8 wt% of the base resin and 0.2-10 wt% of the crystallization accelerator; more preferably, the composition comprises 95-99 wt% of the base resin and 1-5 wt% of the crystallization accelerator.

[0019] Preferably, the base resin and the crystallization accelerator are prepared from the same aromatic dibasic acid. Using the same aromatic dibasic acid improves compatibility between the two, promotes crystal growth better, and improves the overall performance of the product, such as transparency and mechanical properties.

[0020] Preferably, the short-chain aliphatic dibasic acid comprises succinic acid and / or adipic acid; preferably succinic acid.

[0021] The long-chain aliphatic dibasic acid includes any one or more of sebacic acid, dodecanedioic acid, and tetradecanedioic acid; dodecanedioic acid is preferred. According to the inventors' practical experience, increasing the aliphatic diacid chain length in the repeating unit of the aliphatic diacid butanediol ester makes the chain of the crystallization accelerator more flexible, can more effectively promote the chain segment movement of the matrix resin, and is more conducive to the crystal growth of the matrix resin. However, if the aliphatic diacid chain length in the repeating unit is too long, it will adversely affect the crystallization of the aromatic diacid butanediol ester repeating unit.

[0022] The aromatic dibasic acid includes any one or more of terephthalic acid, furandicarboxylic acid, thiophenedicarboxylic acid, and pyridinedicarboxylic acid. Considering the cost and availability of the aromatic dibasic acid, terephthalic acid and furandicarboxylic acid are preferred, and terephthalic acid is more preferred.

[0023] More preferably, the short-chain aliphatic dibasic acid is succinic acid; and / or the long-chain aliphatic dibasic acid is dodecanedioic acid; and / or the aromatic dibasic acid is terephthalic acid.

[0024] Preferably, the content of aromatic dibasic acid butylene glycol repeating units in the base resin is 45-50 mol%, and the content of aromatic dibasic acid butylene glycol repeating units in the crystallization accelerator is 70-80 mol%. The higher the content of aromatic dibasic acid butylene glycol repeating units in the base resin, the worse its biodegradability. The higher the content of aromatic dibasic acid butylene glycol repeating units in the crystallization accelerator, the worse its biodegradability and the higher its melting point, and the higher the processing temperature required for melt mixing with the base resin.

[0025] Existing biodegradable aliphatic-aromatic copolyesters often struggle to achieve rapid crystallization under rapid cooling conditions, particularly due to long crystallization half-times. Furthermore, studies often focus solely on the melt crystallization temperature and crystallization enthalpy, while ignoring the length of the crystallization half-time or the crystallization rate, which are crucial factors in determining the cooling and molding speed during material processing. The biodegradable aliphatic-aromatic copolyester composition described in the present invention achieves a melt crystallization temperature above 55°C, a crystallization enthalpy above 16 J / g, and a crystallization half-time below 40 seconds at a cooling rate of 40°C / min. DSC results under rapid cooling conditions can reflect the crystallization ability of a polymer during actual processing and provide practical guidance.

[0026] Preferably, the biodegradable fatty-aromatic copolyester composition can achieve a melt crystallization temperature of above 56° C., a crystallization enthalpy of above 18 J / g, and a half-crystallization time of below 30 s at a cooling rate of 40° C. / min.

[0027] The present invention also provides a method for preparing the easily crystallizable biodegradable fat-aromatic copolyester composition, comprising the steps of melt-blending raw materials comprising the base resin and a crystallization accelerator to obtain the biodegradable fat-aromatic copolyester composition.

[0028] The mass ratio of the base resin to the crystallization accelerator is 80:20 to 99.8:0.2; and / or the melt blending temperature is 150-250°C.

[0029] Preferably, the method for preparing the easily crystallizable biodegradable fat-aromatic copolyester composition comprises the steps of: melt-blending raw materials comprising a base resin and a crystallization accelerator to obtain a masterbatch, and then melt-blending raw materials comprising the masterbatch and the base resin to obtain the biodegradable fat-aromatic copolyester composition.

[0030] Further preferably, the base resin and the crystallization accelerator are melt-mixed in a mass ratio of 70:30 to 90:10 to prepare a masterbatch; and the base resin and the masterbatch are then melt-mixed in a mass ratio of 96.7:3.3 to 50:50 to prepare the easily crystallizable biodegradable fat-aromatic copolyester composition.

[0031] The melt blending is carried out using common polymer resin processing equipment such as a stirring kettle, a static mixer, a twin-screw extruder, a single-screw extruder or an internal mixer.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) In the composition of the present invention, the crystallization promoter has the same crystal structure as the matrix resin and has a long flexible fatty dibasic acid chain that is beneficial to promoting the movement of the matrix resin chain segments, thereby having the dual effect of promoting crystal nucleation and crystal growth. The composition obtained by mixing with the matrix resin has excellent comprehensive crystallization performance and has the performance advantages of a short half-crystallization time, a high crystallization temperature, and a large crystallization enthalpy.

[0034] (2) The composition of the present invention can not only crystallize rapidly under a conventional DSC cooling rate (10°C / min), but can also crystallize relatively quickly under a rapid cooling condition (40°C / min).

[0035] (3) The crystallization accelerator in the present invention has a chemical structure similar to that of the matrix resin, and the two have good compatibility. The crystallization accelerator is easily and evenly dispersed in the matrix resin, which helps it to fully exert its crystallization-promoting effect and is beneficial to improving transparency.

[0036] (4) The crystallization accelerator of the present invention has a certain degree of biodegradability and is used in a small amount. The composition prepared by mixing it with the base resin is biodegradable.

[0037] (5) The composition of the present invention can be prepared by conventional plastic processing methods and equipment, which is simple and feasible and convenient for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The DSC cooling scan curves of the compositions of Comparative Examples 1-2 and Examples 1 to 5 are as follows: (A) a cooling rate of 10° C. / min; and (B) a cooling rate of 40° C. / min. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art will make modifications or equivalent substitutions based on understanding the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, and all should be encompassed within the protection scope of the present invention.

[0040] The materials used in the following embodiments were purchased commercially. Commercially available copolyesters can be used, but to accurately calculate the mole percentage of butylene terephthalate (BT) repeating units, homemade products were used in the following embodiments. The names and abbreviations of the copolyesters used in the embodiments of the present invention are as follows:

[0041] Poly(butylene succinate-co-terephthalate): PBST;

[0042] Poly(butylene sebacate-co-terephthalate): PBSeT;

[0043] Poly(dodecanedioic acid-co-butylene terephthalate): PBDoT;

[0044] Poly(tetradecanoic acid-co-butylene terephthalate): PBTdT;

[0045] The composition of the copolyester is expressed as the molar percentage of the aromatic repeating units. For example, for the copolyester PBST, the molar percentage of the butylene terephthalate (BT) repeating units x mol% is used to express the copolymer composition of PBST, and the sample is recorded as PBST. x Among them, PBST 71 PBDoT 80 It has a similar aromatic repeating unit mass content of about 76 wt%.

[0046] In the embodiments of the present invention, the copolyesters are all prepared from terephthalic acid, butanediol, and aliphatic dibasic acid via esterification-polycondensation, and the intrinsic viscosity of all the polyesters is within the range of 0.7 to 1.4 dL / g.

[0047] In the embodiment of the present invention, the aliphatic-aromatic composition comprises a base resin (such as PBST x ) and crystallization promoters (such as PBDoT y ), whose mass percentages are a wt% and b wt% respectively (a+b=100), so it is named a PBST x + b PBDoT y .

[0048] The analytical testing methods used in the present invention are described below.

[0049] Copolymer composition: The composition of the copolyester was determined by H-NMR spectroscopy.

[0050] Thermal Transitions: A TA Instrument Q200 differential scanning calorimeter was used to measure the polymer samples' thermal transition properties, including crystallization temperature, crystallization enthalpy, and crystallization half-period. A standard "heat-down-heat" procedure was used, with a heating rate of 10°C / min and a hold time of 5 minutes. Two cooling rates, slow and fast, were used: 10°C / min and 40°C / min, respectively.

[0051] Transmittance and Haze: A CS-821N Hangzhou Color Spectrum benchtop spectrophotometer was used to measure the sample's transparency indicators, including transmittance and haze, within the visible light wavelength range. The film used in the test was produced by hot pressing and had a thickness of 400 ± 20 μm.

[0052] PBST 48Preparation: Butanediol, terephthalic acid, and succinic acid in a molar ratio of 100:23:27 were placed in a reactor, heated to 220°C, and tetrabutyl titanate (TBT) catalyst was added at a catalyst dosage of 0.05 mol% of the dibasic acid. The esterification reaction was continued for 3 hours. The temperature was raised to 250°C, and an additional 0.05 mol% catalyst was added. The vacuum was reduced to below 100 Pa, and polycondensation was carried out for 2 hours to obtain a polymer with an intrinsic viscosity of 0.89 dL / g and a molar percentage of butylene terephthalate (BT) repeating units of 48 mol%. It was recorded as PBST. 48 .

[0053] PBST 71 Preparation: Butanediol, terephthalic acid, and succinic acid in a molar ratio of 100:35:15 were placed in a reactor, heated to 220°C, and tetrabutyl titanate (TBT) catalyst was added at a catalyst dosage of 0.05 mol% of the dibasic acid. The esterification reaction was continued for 3 hours. The temperature was raised to 250°C, and an additional 0.05 mol% catalyst was added. The vacuum was reduced to below 100 Pa, and polycondensation was carried out for 2 hours. The resulting polymer had an intrinsic viscosity of 0.77 dL / g and a molar percentage of butylene terephthalate (BT) repeating units of 71 mol%. It was recorded as PBST. 71 .

[0054] PBSE 70 Preparation: Butanediol, terephthalic acid, and sebacic acid in a molar ratio of 100:34:16 were placed in a reactor, heated to 220°C, and tetrabutyl titanate (TBT) catalyst was added at a catalyst concentration of 0.05 mol% based on the dibasic acid. The esterification reaction was allowed to proceed for 4 hours. The temperature was raised to 250°C, and an additional 0.05 mol% catalyst was added. The vacuum was reduced to below 100 Pa, and polycondensation was carried out for 2 hours. The resulting polymer had an intrinsic viscosity of 1.17 dL / g and a molar percentage of butylene terephthalate (BT) repeating units of 70 mol%. It is denoted as PBSeT. 70 .

[0055] PBDoT 70 Preparation: Butanediol, terephthalic acid, and dodecanedioic acid in a molar ratio of 100:34:16 are placed in a reactor, heated to 220°C, and tetrabutyl titanate (TBT) catalyst is added at a catalyst amount of 0.05 mol% of the dibasic acid. The esterification reaction is carried out for 4 hours. The temperature is raised to 250°C, and 0.05 mol% of the catalyst is added. At the same time, the vacuum degree is reduced to below 100 Pa and polycondensation is carried out for 2 hours. The resulting polymer has an intrinsic viscosity of 1.04 dL / g and a molar percentage of butylene terephthalate (BT) repeating units of 70 mol%. It is recorded as PBDoT 70 .

[0056] PBDoT 80Preparation: Butanediol, terephthalic acid, and dodecanedioic acid in a molar ratio of 100:39:11 were placed in a reactor, heated to 220°C, and tetrabutyl titanate (TBT) catalyst was added at a catalyst amount of 0.05 mol% of the dibasic acid. The esterification reaction was carried out for 4 hours. The temperature was raised to 250°C, and 0.05 mol% of the catalyst was added. At the same time, the vacuum degree was reduced to below 100 Pa and polycondensation was carried out for 2 hours. The resulting polymer had an intrinsic viscosity of 1.17 dL / g and a molar percentage of butylene terephthalate (BT) repeating units of 80 mol%. It was recorded as PBDoT. 80 .

[0057] PBT 70 Preparation: Butanediol, terephthalic acid, and tetradecanedioic acid in a molar ratio of 100:34:16 were placed in a reactor, heated to 220°C, and tetrabutyl titanate (TBT) catalyst was added at a catalyst concentration of 0.05 mol% based on the dibasic acid. The esterification reaction was continued for 4 hours. The temperature was raised to 250°C, and an additional 0.05 mol% catalyst was added. The vacuum was reduced to below 100 Pa, and polycondensation was continued for 2 hours. The resulting polymer had an intrinsic viscosity of 1.33 dL / g and a molar percentage of butylene terephthalate (BT) repeating units of 70 mol%. It was designated PBTdT. 70 .

[0058] Comparative Example 1 PBST 48

[0059] PBST 48 The matrix resin is used as comparative example 1, and the sample is recorded as PBST 48 .

[0060] Comparative Example 2 97 PBST 48 + 3 PBST 71

[0061] PBST with a mass ratio of 97:3 48 Matrix resin and PBST 71 The nucleating agent was melt-mixed in an internal mixer at 200°C for 5 minutes, and the obtained sample was recorded as 97 PBST 48 + 3 PBST 71 .

[0062] Example 1 97 PBST 48 + 3 PBDoT 70

[0063] PBST with a mass ratio of 97:3 48 Base resin and PBDoT70 The crystallization accelerator was melt-mixed in an internal mixer at 200°C for 5 minutes, and the obtained sample was recorded as 97 PBST 48 + 3 PBDoT 70 .

[0064] Example 2 97 PBST 48 + 3 PBDoT 80

[0065] PBST with a mass ratio of 97:3 48 Base resin and PBDoT 80 The crystallization accelerator was melt-mixed in an internal mixer at 200°C for 5 minutes, and the obtained sample was recorded as 97 PBST 48 + 3 PBDoT 80 .

[0066] Example 3 99 PBST 48 + 1 PBDoT 80

[0067] PBST with a mass ratio of 99:1 48 Base resin and PBDoT 80 The crystallization accelerator was melt-mixed in an internal mixer at 200°C for 5 minutes, and the obtained sample was recorded as 99 PBST 48 + 1 PBDoT 80 .

[0068] Example 4 97 PBST 48 + 3 PBSE 70

[0069] PBST with a mass ratio of 97:3 48 Base resin and PBSeT 70 The crystallization accelerator was melt-mixed in an internal mixer at 200°C for 5 minutes, and the obtained sample was recorded as 97 PBST 48 + 3 PBSE 70 .

[0070] Example 5 97 PBST 48 + 3 PBT 70

[0071] PBST with a mass ratio of 97:3 48 Base resin and PBTdT 70 The crystallization accelerator was melt-mixed in an internal mixer at 200°C for 5 minutes, and the obtained sample was recorded as 97 PBST 48 + 3 PBT 70 .

[0072] The DSC curves of the compositions of Comparative Examples 1-2 and Examples 1-5 at a cooling rate of 10°C / min and 40°C / min are shown in FIG. Figure 1 (A) and 1(B), the melt crystallization temperature (T c ), crystallization enthalpy (ΔH c ) and half crystallization time (t 1 / 2 )See Table 1.

[0073] Table 1 Melt crystallization parameters of the compositions of Examples and Comparative Examples at different cooling rates

[0074]

[0075] *: Matrix resin PBST 48 No obvious melt crystallization peak appeared at a cooling rate of 40℃ / min (nd means not detected), but cold crystallization peak and melting peak appeared during the second heating process; while other samples did not show cold crystallization peak during the second heating process, only melting peak.

[0076] DSC results (Table 1 and Figure 1 ) shows that in Comparative Example 1, the matrix resin PBST 48 At a cooling rate of 10°C / min, a higher melt crystallization temperature (62°C) and a higher melt crystallization enthalpy (20.6 J / g) were exhibited, and the crystallization performance looked good; however, at a cooling rate of 40°C / min (Note: the cooling rate in the actual melt processing process may be faster, and due to the limitations of the DSC instrument used, 40°C / min is the maximum cooling rate that can be used), it is difficult to observe PBST. 48 The melt crystallization peak of PBST under rapid cooling conditions 48 The slow crystallization is far from meeting the requirements of actual melt processing. Therefore, it is necessary to improve the crystallization of PBST under rapid cooling conditions.

[0077] In comparative example 2, the matrix resin PBST 48 PBST with the same structure but different composition (higher content of BT repeating units) 71 As nucleating agent, the dosage is 3wt% and PBST 48 The blended composition 97PBST 48 + 3 PBST 71 At a cooling rate of 40°C / min, the melt crystallization temperature is 50°C, the crystallization enthalpy is 15.5 J / g, and the half-crystallization time is 44 s. It can be seen that compared with the matrix resin PBST 48 While crystallization was difficult at a cooling rate of 40°C / min, the crystallinity of Comparative Example 2 was significantly improved.

[0078] In Example 1, the matrix resin PBST 48 Introducing 3wt% PBDoT 70 As a crystallization promoter, the resulting composition 97 PBST 48 + 3 PBDoT 70 At a cooling rate of 40°C / min, the melt crystallization temperature was 60°C, the crystallization enthalpy was 21.6 J / g, and the half-crystallization time was 30 seconds. It can be seen that at a cooling rate of 40°C / min, compared to Comparative Example 2, the crystallization of Example 1 was significantly and comprehensively improved. Whether in terms of crystallization temperature, crystallization enthalpy, or crystallization half-period, Example 1 was significantly superior to Comparative Example 2. In particular, the half-crystallization time was significantly shortened from 44 seconds in Comparative Example 2 to 30 seconds in Example 1. This is due to the unique structure of the crystallization accelerator of the present invention.

[0079] In the present invention, the crystallization accelerator (using PBDoT as an example) has, on the one hand, a structure partially identical to that of the matrix resin. Specifically, its aromatic repeating units are all butylene terephthalate (BT), resulting in a crystal structure identical to that of the matrix resin, but with a higher BT content. Therefore, the crystallization accelerator crystallizes more readily than the matrix resin, allowing nucleation and crystallization to occur at higher temperatures, thus playing a nucleating role. Furthermore, the crystallization accelerator has a different structure from the matrix resin. Specifically, the aliphatic repeating units of the matrix resin are short-chain structures, while the aliphatic repeating units of the crystallization accelerator of the present invention are long-chain structures. The presence of the long flexible dibasic acid chain promotes segmental motion in the matrix resin, thereby promoting faster crystallization, narrowing the crystallization peak, and shortening the half-crystallization time. Therefore, the crystallization accelerator of the present invention has the dual effects of providing crystal nuclei and accelerating crystal growth, thus exhibiting a better crystallization-promoting effect than conventional nucleating agents.

[0080] Compared with Example 1, the BT repeating unit content in the crystallization promoter in Example 2 is higher (80 mol% vs. 70 mol%), and the resulting composition 97 PBST 48 + 3 PBDoT 80At a cooling rate of 40°C / min, the melt crystallization temperature further increased to 65°C, the crystallization enthalpy was 21.5 J / g, and the half-crystallization time was further shortened to 24 s, indicating that its crystallinity was further improved.

[0081] Compared with Example 2, the crystallization promoter PBDoT in Example 3 80 The amount of is reduced from 3wt% to 1wt%, and the resulting composition 99 PBST 48 + 1 PBDoT 80 At a cooling rate of 40°C / min, the melt crystallization temperature was 59°C, the crystallization enthalpy was 20.4 J / g, and the crystallization half-time was 23 s. This indicates that reducing the amount of crystallization accelerator, while slightly decreasing the melt crystallization temperature and crystallization enthalpy, still maintained a comparable crystallization half-time to that of Example 2, effectively promoting the crystallization of the matrix resin.

[0082] In addition to PBDoT, the compositions based on other crystallization promoters included in the present invention also have excellent crystallization performance. 48 Introducing 3wt% PBSeT 70 As a crystallization promoter, the resulting composition 97 PBST 48 + 3 PBSE 70 At a cooling rate of 40°C / min, the melt crystallization temperature is 55°C, the crystallization enthalpy is 20.6 J / g, and the half-crystallization time is 30s. 48 Introducing 3wt% PBTdT 70 As a crystallization promoter, the resulting composition 97 PBST 48 + 3 PBT 70 At a cooling rate of 40°C / min, the melt crystallization temperature is 60°C, the crystallization enthalpy is 21.4 J / g, and the half-crystallization time is 32 s. Their comprehensive crystallization performance also has significant advantages over Comparative Example 2.

[0083] On the other hand, when studying the crystallinity of polymers using DSC, a slower cooling rate, such as 10°C / min, is typically used. However, at a cooling rate of 10°C / min, the addition of a nucleating agent (Comparative Example 2) or the crystallization accelerators of the present invention (Examples 1-5) significantly increased the crystallization temperature, but did not significantly increase the crystallization enthalpy or shorten the half-crystallization time. In fact, it was significantly prolonged in Comparative Example 2. This shows that DSC results obtained under slow cooling conditions (10°C / min) often lack practical guidance for application; whereas DSC results obtained under rapid cooling conditions can reflect the crystallization ability of polymers during actual processing and have practical guidance.

[0084] Existing techniques often focus solely on melt crystallization temperature and crystallization enthalpy, while ignoring the length of the half-crystallization time or the speed of crystallization, which are actually key factors determining the cooling and molding speed during material processing. The present invention uses the crystallization temperature, crystallization enthalpy, and half-crystallization time under rapid cooling conditions of 40°C / min as a basis to more comprehensively evaluate the crystallization ability of biodegradable copolyesters and their compositions.

[0085] The composition of the present invention has good compatibility with the matrix resin due to the similar chemical structure of the crystallization accelerator, which can avoid the decrease in transparency caused by microphase separation caused by the addition of a heterogeneous nucleating agent. On the other hand, the excellent nucleation effect of the crystallization accelerator increases the number of crystals and reduces the crystal size, which is conducive to the transmission of visible light. Therefore, the product made from the composition has better light transmittance. 48 The optical performance data of the film with a thickness of about 400 μm obtained by hot pressing the compositions of Examples 1 and 2 are shown in Table 2. Compared with the film made from the matrix resin, the film made from the composition of the present invention has higher light transmittance, lower haze and better transparency.

[0086] Table 2 Optical properties of Comparative Example 1 and Examples 1-2

[0087] Example Sample name Transmittance% Haze % Comparative Example 1 <![CDATA[PBST 48 ]]> 47.5 94.5 Example 1 <![CDATA[ 97 PBST 48 + 3 PBDoT 70 ]]> 55.6 88.4 Example 2 <![CDATA[ 97 PBST 48 + 3 PBDoT 80 ]]> 69.3 78.2

[0088] The thickness of the film used in the test is 400±20μm.

[0089] In addition, the crystallization promoter of the present invention is an aliphatic-aromatic copolyester having an aromatic chain content of 60-90 mol%, preferably 70-80 mol%, which still has a certain biodegradability (although the degradation is slow), and the addition amount can be as low as 1 wt%. Therefore, the composition prepared by melt blending it with a biodegradable base resin still has excellent biodegradability.

[0090] In summary, the present invention provides a fatty-aromatic copolyester composition with significantly improved crystallinity and a method for preparing the composition. The composition comprises a short-chain fatty-aromatic copolyester base resin with a low aromatic segment content and a long-chain fatty-aromatic copolyester crystallization accelerator with a high aromatic segment content. The preparation method is simple and easy. Compared to the base resin, the composition exhibits a shorter half-crystallization time, a higher crystallization temperature, a higher crystallization enthalpy, and significantly improved transparency under rapid cooling conditions, while maintaining excellent biodegradability.

Claims

1. A biodegradable fat-aromatic copolyester composition that is easily crystallized, characterized in that: including a base resin and a crystallization accelerator; The base resin is prepared by copolymerization of butanediol, C4-C6 short-chain aliphatic dicarboxylic acid and aromatic dicarboxylic acid; the crystallization accelerator is prepared by copolymerization of butanediol, C 10 -C 16 The aromatic dicarboxylic acid comprises any one or more of terephthalic acid, furandicarboxylic acid, thiophenedicarboxylic acid and pyridinedicarboxylic acid; The content of the aromatic dibasic acid butylene glycol repeating unit in the base resin is 43-70 mol%, and the content of the aromatic dibasic acid butylene glycol repeating unit in the crystallization accelerator is 60-90 mol%; Calculated by mass fraction, the biodegradable fatty-aromatic copolyester composition comprises 80-99.8 wt % of a base resin and 0.2-20 wt % of a crystallization accelerator.

2. The easily crystallizable biodegradable fat-aromatic copolyester composition according to claim 1, characterized in that: The base resin and the crystallization accelerator are prepared from the same aromatic dibasic acid.

3. The easily crystallizable biodegradable fat-aromatic copolyester composition according to claim 1, characterized in that: The short-chain aliphatic dibasic acid includes succinic acid and / or adipic acid; The long-chain aliphatic dibasic acid includes any one or more of sebacic acid, dodecanedioic acid, and tetradecanedioic acid.

4. The easily crystallizable biodegradable fat-aromatic copolyester composition according to claim 1, characterized in that: The short-chain aliphatic dibasic acid is succinic acid; and / or the long-chain aliphatic dibasic acid is dodecanedioic acid; and / or the aromatic dibasic acid is terephthalic acid.

5. The easily crystallizable biodegradable fat-aromatic copolyester composition according to claim 1, characterized in that: The content of the aromatic dibasic acid butylene glycol repeating unit in the base resin is 45-50 mol %, and the content of the aromatic dibasic acid butylene glycol repeating unit in the crystallization accelerator is 70-80 mol %.

6. The easily crystallizable biodegradable fatty-aromatic copolyester composition according to claim 1, characterized in that: The biodegradable fat-aromatic copolyester composition has a melt crystallization temperature of above 55° C. at a cooling rate of 40° C. / min, a crystallization enthalpy of above 16 J / g, and a half-crystallization time of below 40 s.

7. The method for preparing the easily crystallizable biodegradable fat-aromatic copolyester composition according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: melt-blending raw materials containing the base resin and the crystallization accelerator to obtain the biodegradable fat-aromatic copolyester composition.

8. The method for preparing the easily crystallizable biodegradable fat-aromatic copolyester composition according to claim 7, characterized in that: The mass ratio of the base resin to the crystallization accelerator is 80:20 to 99.8:0.2; and / or the melt blending temperature is 150-250°C.

9. The method for preparing the easily crystallizable biodegradable fat-aromatic copolyester composition according to claim 7, characterized in that: The method comprises the following steps: melt-blending raw materials containing a matrix resin and a crystallization accelerator to obtain a master batch, and then melt-blending raw materials containing the master batch and the matrix resin to obtain the biodegradable fat-aromatic copolyester composition.

Images