CN117285803B - An easily crystallizable biodegradable fat-aromatic copolyester composition and preparation method thereof - Google Patents
An easily crystallizable biodegradable fat-aromatic copolyester composition and preparation method thereofInfo
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- CN117285803B CN117285803B CN202311269306.2A CN202311269306A CN117285803B CN 117285803 B CN117285803 B CN 117285803B CN 202311269306 A CN202311269306 A CN 202311269306A CN 117285803 B CN117285803 B CN 117285803B
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- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
- C08L67/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
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- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
- C08G63/16—Dicarboxylic acids and dihydroxy compounds
- C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
- C08G63/181—Acids containing aromatic rings
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Abstract
本发明涉及生物降解高分子材料，公开一种易结晶的可生物降解脂肪‑芳香共聚酯组合物及其制备方法，该组合物包括基体树脂和结晶促进剂；所述基体树脂由丁二醇、C4‑C6的短链脂肪族二元酸和芳香族二元酸共聚制得；所述结晶促进剂由丁二醇、C10‑C16的长链脂肪族二元酸和芳香族二元酸共聚制得；所述基体树脂中BT的含量为43‑70mol％，所述结晶促进剂中BT的含量为60‑90mol％。本发明采用含量较高的长链脂肪‑芳香共聚酯作为结晶促进剂，在基体树脂中有促进晶体成核和促进晶体生长的双重效果，少量添加即可实现显著促进结晶的效果，所制得的组合物的综合结晶性能优异，兼具半结晶时间短、结晶温度高、结晶焓大的性能优势，且在保持优异生物降解性的同时，透明性亦显著改善。
The present invention relates to a biodegradable polymer material, and discloses a biodegradable aliphatic-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 C10 - C16 long-chain aliphatic dicarboxylic acid, and an aromatic dicarboxylic acid; the BT content in the base resin is 43-70 mol%, and the BT content in the crystallization accelerator is 60-90 mol%. The present invention adopts a relatively high content of long-chain aliphatic-aromatic copolyester as a crystallization accelerator, which has the dual effects of promoting crystal nucleation and promoting crystal growth in the base resin; a small amount of addition can significantly promote crystallization; the prepared composition 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. While maintaining excellent biodegradability, the transparency is also significantly improved.
Description
Technical Field
The invention relates to a biodegradable high molecular material, in particular to a biodegradable fat-aromatic copolyester composition easy to crystallize and a preparation method thereof.
Background
Aliphatic-aromatic copolyesters (abbreviated copolyesters) made from butanediol, short chain aliphatic dibasic acids of C 4-C6 and aromatic dibasic acids, such as poly (butylene adipate-co-terephthalate) (abbreviated PBAT), poly (butylene succinate-co-terephthalate) (abbreviated PBST), poly (butylene adipate-co-furandicarboxylate) (abbreviated PBAF), poly (butylene succinate-co-furandicarboxylate) (abbreviated PBSF), are important biodegradable polymers. They have excellent biodegradability and physical and mechanical properties substantially equivalent to those of polyolefin in a suitable composition range, and can be used for replacing conventional non-biodegradable polymers such as polyolefin, and for plastic products for disposable or short-term use, such as shopping bags, garbage bags, packaging films, and agricultural mulching films. However, these copolyesters have a problem of poor crystallinity to a different extent.
Crystallinity is one of the most important properties of a polymer material, and directly affects the difficulty and easiness of the polymer production and processing process and the advantages and disadvantages of application properties. The crystallization performance is evaluated by three main indexes, namely melt crystallization temperature (or supercooling degree), crystallization enthalpy (degree) and semi-crystallization time. The melt crystallization temperature is actually a temperature range, but is usually expressed as the temperature at which the crystallization speed is the maximum, and the supercooling degree is the difference between the equilibrium melting point and the melt crystallization temperature, and reflects the difficulty in crystallization of the material, and the higher the melt crystallization temperature or the lower the supercooling degree, the easier the crystallization. The enthalpy of crystallization corresponds to the amount of heat evolved during crystallization, reflecting the degree of crystallization. The semi-crystallization time is half of the time when the crystallization process is completed, and reflects the speed of the crystallization process. From the production and application point of view, the high molecular material with excellent crystallinity should have high crystallization temperature, large crystallization enthalpy and short semi-crystallization time, such as polyethylene, polybutylene terephthalate (PBT) and nylon 66. However, common biodegradable copolyesters such as PBAT have a low enthalpy of crystallization despite faster crystallization, and PBST has a low enthalpy of crystallization, but also has a slow crystallization under practical production and processing conditions (i.e., rapid cooling conditions), severely affecting the pelletization and melt processability of PBST. The furandicarboxylic acid based copolyesters PBAF and PBSF are less crystalline than PBAT and PBST.
The most common technique for promoting crystallization of polymers is to add a nucleating agent to the polymer, and by increasing the number of nuclei directly or by induction, the crystallization temperature and crystallization rate can be increased, and the crystal size can be reduced. The presently disclosed nucleating agents that can be used for crystallization modification of PBST, PBAT copolyesters are as follows:
(1) Patent CN 102558521A discloses a poly (fumaric acid) glycol ester and its copolyester nucleating agent, wherein the dosage of 1wt% can respectively make PBAT And the melt crystallization temperature of PBST at a cooling rate of 10 ℃ per minute is respectively increased to 77.8 ℃ and 73.4 ℃, which are increased by 5.3 ℃ and 10.9 ℃, but no melt crystallization enthalpy data are given;
(2) Patent CN 102492248A discloses a technique using polyvinyl acetal as a nucleating agent, the amount of 1wt% can raise the melt crystallization temperature of PBAT to 81.4 ℃ at a temperature-lowering speed of 10 ℃ per min, 6.8 ℃ is raised, and melt crystallization enthalpy data is not given;
(3) CN 108384200A discloses a melamine/cyanuric acid complex nucleating agent, the use of 1wt% and 5wt% can raise the melt crystallization temperature of PBAT at 10 ℃ per minute by 15.6 ℃ and 21.7 ℃ respectively, the final crystallization temperature is 68.2 ℃ and 74.2 ℃ respectively, the melt crystallization enthalpy is 17.1J/g and 16.8J/g respectively;
(4) CN 111100272A, CN 111100427A, CN 111100270A respectively disclose techniques of using high aromatic mer content similar copolyester oligomers, aromatic polyester oligomers as nucleating agents for aliphatic-aromatic copolyesters, but do not provide DSC data.
It can be seen that the existing crystallization modification technology of biodegradable copolyester has the following problems that (1) although the existing crystallization modification technology has a good crystallization promoting effect under the conventional DSC cooling speed (such as 10 ℃ per minute), the rapid cooling (the cooling speed often reaches tens of ℃ per minute) required by actual production and processing is often not good or disclosed, and the existing crystallization modification technology has no real production and application value. (2) The more important purpose of crystallization modification is to increase the crystallization rate and realize rapid crystallization, while the prior art only uses crystallization temperature and crystallization enthalpy as the basis to evaluate crystallization performance, and neglects the speed of crystallization or the length of semi-crystallization time, so that it is difficult to confirm whether rapid crystallization is actually realized. (3) The crystallization accelerator used only plays a role in promoting crystal nucleation, is a nucleating agent, and lacks a crystallization accelerator which plays a role in promoting crystal nucleation and crystal growth at the same time. (4) Part of the nucleating agents used in the prior art have no biodegradability, the biodegradability of the product obtained by mixing the nucleating agents with matrix resin is affected, the obtained product is not a fully biodegradable material, and (5) the transparency is adversely affected after the nucleating agents are mixed with the matrix resin.
In view of the above, development of a fully biodegradable aliphatic-aromatic copolyester material with short semi-crystallization time, high crystallization temperature, large crystallization enthalpy and unaffected transparency under the actual processing condition of rapid cooling is still a technical problem to be solved.
Disclosure of Invention
Aiming at the problems of low crystallization temperature, low crystallization speed and long crystallization time, particularly the biodegradable fat-aromatic copolyester composition can be quickly crystallized under the condition of quick cooling, and has the performance advantages of short crystallization time, high crystallization temperature and large crystallization enthalpy, and can keep transparency and biodegradability.
In order to achieve the above purpose, the invention adopts the following technical scheme:
An easily crystallized biodegradable aliphatic-aromatic copolyester composition comprises a matrix resin and a crystallization promoter;
The matrix resin is prepared by copolymerizing butanediol, short-chain aliphatic dibasic acid of C4-C6 and aromatic dibasic acid, and the crystallization promoter is prepared by copolymerizing butanediol, long-chain aliphatic dibasic acid of C10-C16 and aromatic dibasic acid;
The content of the aromatic dibasic acid butanediol ester repeating unit in the matrix resin is 43-70mol%, and the content of the aromatic dibasic acid butanediol ester repeating unit in the crystallization accelerator is 60-90mol%.
Aiming at the problem of low crystallization speed of biodegradable aliphatic-aromatic copolyester, the invention adopts long-chain aliphatic-aromatic copolyester with high content of aromatic dibasic acid butanediol as a crystallization accelerator. The crystallization accelerator contains the aromatic dibasic acid butanediol ester repeating unit which has the same structure as the matrix resin but has higher content, so that the crystallization accelerator has the same crystal structure as the matrix resin but is easier to crystallize and has higher crystallization speed, and plays a nucleation role in the matrix resin to promote the nucleation of crystals. The crystallization promoter also contains flexible aliphatic long-chain dibasic acid butanediol ester repeating units, which is favorable for promoting the chain segment movement of matrix resin, thus playing a role in promoting the crystal growth. Therefore, the crystallization accelerator has the dual effects of simultaneously accelerating crystal nucleation and crystal growth, and the composition prepared by mixing the crystallization accelerator with matrix resin has the advantages of excellent comprehensive crystallization performance, short crystallization time, high crystallization temperature and large crystallization enthalpy.
In addition, the crystallization promoter has a chemical structure similar to that of the matrix resin, so that the crystallization promoter and the matrix resin have good compatibility, and the crystallization promoter is easy to uniformly disperse in the matrix resin, thereby being beneficial to fully playing the crystallization promoting role and improving the transparency.
The biodegradable fat-aromatic copolyester composition comprises 80-99.8wt% of matrix resin and 0.2-20wt% of crystallization promoter. The crystallization accelerator of the present invention is added in an extremely small amount to achieve the effect of accelerating crystallization, and preferably comprises 90 to 99.8wt% of the matrix resin and 0.2 to 10wt% of the crystallization accelerator, and further preferably comprises 95 to 99wt% of the matrix resin and 1 to 5wt% of the crystallization accelerator.
Preferably, the matrix resin and the crystallization promoter are prepared using the same aromatic dibasic acid. The same aromatic dibasic acid is adopted, so that the compatibility of the aromatic dibasic acid and the aromatic dibasic acid is better, the crystal growth promoting effect is better, and the product has better comprehensive properties such as transparency and mechanical property.
Preferably, the short chain aliphatic dibasic acid comprises succinic acid and/or adipic acid, preferably succinic acid.
The long-chain aliphatic dibasic acid comprises any one or more of sebacic acid, dodecanedioic acid and tetradecanedioic acid, and preferably dodecanedioic acid. According to the practical experience of the inventor, the chain flexibility of the crystallization promoter is stronger due to the increase of the chain length of the aliphatic diacid in the aliphatic diacid butanediol ester repeating unit, the chain segment movement of the matrix resin can be promoted more effectively, the crystal growth of the matrix resin is facilitated, and the crystallization of the aromatic diacid butanediol ester repeating unit is adversely affected due to the overlong chain length of the aliphatic diacid in the repeating unit.
The aromatic diacid comprises any one or more of terephthalic acid, furandicarboxylic acid, thiophenedicarboxylic acid and pyridinedicarboxylic acid. Terephthalic acid and furandicarboxylic acid are preferred, and terephthalic acid is further preferred, in view of cost and source universality.
Further preferably, the short chain aliphatic diacid is succinic acid, and/or the long chain aliphatic diacid is dodecanedioic acid, and/or the aromatic diacid is terephthalic acid.
Preferably, the content of the aromatic dibasic acid butanediol ester repeating unit in the matrix resin is 45-50mol%, and the content of the aromatic dibasic acid butanediol ester repeating unit in the crystallization accelerator is 70-80mol%. The higher the content of the aromatic dibasic acid butanediol ester repeating unit in the matrix resin, the poorer the biodegradability, the higher the content of the aromatic dibasic acid butanediol ester repeating unit in the crystallization accelerator, the poorer the biodegradability, and the higher the melting point, the higher the processing temperature required for melt mixing with the matrix resin.
The biodegradable aliphatic-aromatic copolyester in the prior art is difficult to realize the effect of rapid crystallization under the condition of rapid cooling, particularly has long crystallization time, and only focuses on the crystallization temperature and crystallization enthalpy of a melt, but ignores the length of the crystallization time or the crystallization speed, and the latter is actually a key factor for determining the cooling forming speed in the material processing process. The biodegradable fat-aromatic copolyester composition can realize melt crystallization temperature above 55 ℃ at a cooling rate of 40 ℃ per minute, crystallization enthalpy above 16J/g and semi-crystallization time below 40 s. DSC results under the condition of rapid cooling can reflect the crystallization capability of the polymer in the actual processing process, and have practical guiding significance.
Preferably, the biodegradable aliphatic-aromatic copolyester composition can realize melt crystallization temperature above 56 ℃ at a cooling rate of 40 ℃ per minute, crystallization enthalpy above 18J/g and semi-crystallization time below 30 s.
The invention also provides a preparation method of the biodegradable fat-aromatic copolyester composition easy to crystallize, which comprises the step of carrying out melt blending on raw materials comprising the matrix resin and the crystallization promoter to obtain the biodegradable fat-aromatic copolyester composition.
The mass ratio of the matrix resin to the crystallization promoter is 80:20-99.8:0.2, and/or the melt blending temperature is 150-250 ℃.
Preferably, the preparation method of the biodegradable fat-aromatic copolyester composition easy to crystallize comprises the steps of carrying out melt blending on raw materials comprising matrix resin and crystallization promoter to obtain master batch, and carrying out melt blending on raw materials comprising the master batch and the matrix resin to obtain the biodegradable fat-aromatic copolyester composition.
Further preferably, the matrix resin and the crystallization promoter are melted and mixed according to the mass ratio of 70:30-90:10 to prepare a master batch, and the matrix resin and the master batch are melted and mixed according to the mass ratio of 96.7:3.3-50:50 to prepare the biodegradable aliphatic-aromatic copolyester composition easy to crystallize.
The melt blending is performed by common polymer resin processing equipment such as a stirring kettle, a static mixer, a double-screw extruder, a single-screw extruder or an internal mixer.
Compared with the prior art, the invention has the following beneficial effects:
(1) In the composition, the crystallization accelerator has the same crystal structure as that of the matrix resin, and has the flexible fatty dibasic acid long chain which is beneficial to promoting the chain segment movement of the matrix resin, so that the composition has the dual effects of promoting the crystal nucleation and the crystal growth, and the composition prepared by mixing the crystallization accelerator with the matrix resin has the advantages of excellent comprehensive crystallization performance, short semi-crystallization time, high crystallization temperature and large crystallization enthalpy.
(2) The composition of the invention not only can be rapidly crystallized under the conventional DSC cooling speed (10 ℃ per minute), but also can be rapidly crystallized under the rapid cooling (40 ℃ per minute) condition.
(3) The crystallization promoter has a chemical structure similar to that of the matrix resin, has good compatibility, is easy to uniformly disperse in the matrix resin, is favorable for fully playing the crystallization promoting role, and is favorable for improving the transparency.
(4) The crystallization accelerator has certain biodegradability and small dosage, and the composition prepared by mixing the crystallization accelerator with matrix resin is biodegradable.
(5) The composition of the invention can be prepared by adopting a conventional plastic processing method and equipment, and the method is simple and feasible and is convenient for industrial production.
Drawings
FIG. 1 shows DSC cooling scan curves of the compositions of comparative examples 1-2 and examples 1-5, (A) cooling rate of 10℃per minute, and (B) cooling rate of 40℃per minute.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. Modifications and equivalents will occur to those skilled in the art upon understanding the present teachings without departing from the spirit and scope of the present teachings.
Materials used in the following embodiments are commercially available, and the copolyester may be commercially available, but the molar percentage of the polybutylene terephthalate (BT) repeating unit is calculated accurately, and the homemade product is used in the following embodiments. The names and abbreviations of the copolyesters used in the examples of the invention are as follows:
Poly (butylene succinate-co-terephthalate): PBST;
poly (sebacic acid-co-butylene terephthalate): PBSeT;
poly (dodecanedioic acid-co-butylene terephthalate): PBDoT;
Poly (tetradecanedioic acid-co-butylene terephthalate): PBTdT;
The composition of the copolyester is expressed in terms of mole percent of aromatic repeat units therein, for example, for the copolyester PBST, the copolymer composition of PBST is expressed in terms of mole percent x mole percent of Butylene Terephthalate (BT) repeat units, and the sample is designated PBST x. Wherein PBST 71、PBDoT80 has a comparable/similar aromatic repeat unit mass content of about 76wt%.
In the embodiment of the invention, the copolyester is prepared by using terephthalic acid, butanediol and aliphatic dibasic acid as raw materials and carrying out esterification-polycondensation, and the intrinsic viscosity of all the polyesters is in the range of 0.7-1.4 dL/g.
In an embodiment of the present invention, the aliphatic-aromatic composition comprises a matrix resin (e.g., PBST x) and a crystallization promoter (e.g., PBDoT y) in a weight percent, b weight percent, respectively. (a+b=100), so it is designated aPBSTx+bPBDoTy.
Analytical testing methods used in the present invention are described below.
Copolymer composition the composition of the copolyester was determined using nuclear magnetic hydrogen spectroscopy.
Thermal transition the crystallization temperature, enthalpy of crystallization, half-cycle of crystallization, and other thermal transition properties of the polymer samples were tested using a TA Instrument Q200 differential scanning calorimeter. The temperature rise speed is 10 ℃ per minute, the heat preservation time is 5 minutes, and the temperature reduction speeds are 10 ℃ per minute and 40 ℃ per minute respectively.
And the light transmittance and the haze are measured by adopting a CS-821N Hangzhou color spectrum desk-top spectrocolorimeter. The film used for the test was prepared by hot pressing and had a film thickness of 400.+ -.20. Mu.m.
The preparation method of PBST 48 comprises the steps of placing butanediol, terephthalic acid and succinic acid in a molar ratio of 100:23:27 in a reactor, heating to 220 ℃, adding a tetrabutyl titanate (TBT) catalyst, wherein the addition amount of the catalyst is 0.05mol% of the dibasic acid, and carrying out esterification reaction for 3 hours. Heating to 250 ℃, adding 0.05mol% of catalyst, simultaneously reducing the vacuum degree to below 100Pa, and polycondensing for 2 hours to obtain a polymer, wherein the characteristic viscosity number of the obtained polymer is 0.89dL/g, and the mole percentage of a Butylene Terephthalate (BT) repeating unit is 48mol%, which is recorded as PBST 48.
PBST 71 is prepared by placing butanediol, terephthalic acid and succinic acid in a molar ratio of 100:35:15 in a reactor, heating to 220 ℃, adding a tetrabutyl titanate (TBT) catalyst with the addition amount of 0.05mol% of dibasic acid, and carrying out esterification reaction for 3 hours. Heating to 250 ℃, adding 0.05mol% of catalyst, simultaneously reducing the vacuum degree to below 100Pa, and polycondensing for 2h. The intrinsic viscosity of the obtained polymer was 0.77dL/g, and the molar percentage of the repeating units of Butylene Terephthalate (BT) was 71mol%, which was designated as PBST 71.
PBSeT 70 preparation, namely, placing butanediol, terephthalic acid and sebacic acid in a molar ratio of 100:34:16 into a reactor, heating to 220 ℃, adding a tetrabutyl titanate (TBT) catalyst with the addition amount of 0.05mol% of dibasic acid, and carrying out esterification reaction for 4 hours. Heating to 250 ℃, adding 0.05mol% of catalyst, simultaneously reducing the vacuum degree to below 100Pa, and polycondensing for 2h. The intrinsic viscosity of the polymer obtained was 1.17dL/g, and the molar percentage of the repeating units of Butylene Terephthalate (BT) was 70mol%, which was designated PBSeT 70.
PBDoT 70 preparation, namely, placing butanediol, terephthalic acid and dodecanedioic acid in a molar ratio of 100:34:16 into a reactor, heating to 220 ℃, adding a tetrabutyl titanate (TBT) catalyst with the addition amount of 0.05mol percent of dibasic acid, and carrying out esterification reaction for 4 hours. Heating to 250 ℃, adding 0.05mol% of catalyst, simultaneously reducing the vacuum degree to below 100Pa, and polycondensing for 2h. The intrinsic viscosity of the polymer obtained was 1.04dL/g, and the molar percentage of the repeating units of Butylene Terephthalate (BT) was 70mol%, which was designated PBDoT 70.
PBDoT 80 preparation, namely, placing butanediol, terephthalic acid and dodecanedioic acid in a molar ratio of 100:39:11 into a reactor, heating to 220 ℃, adding a tetrabutyl titanate (TBT) catalyst with the addition amount of 0.05mol percent of dibasic acid, and carrying out esterification reaction for 4 hours. Heating to 250 ℃, adding 0.05mol% of catalyst, simultaneously reducing the vacuum degree to below 100Pa, and polycondensing for 2h. The intrinsic viscosity of the polymer obtained was 1.17dL/g, and the molar percentage of the repeating units of Butylene Terephthalate (BT) was 80mol%, which was designated PBDoT 80.
PBTdT 70 preparation, namely, placing butanediol, terephthalic acid and tetradecanedioic acid in a molar ratio of 100:34:16 into a reactor, heating to 220 ℃, adding a tetrabutyl titanate (TBT) catalyst with the addition amount of 0.05mol% of the dibasic acid, and carrying out esterification reaction for 4 hours. Heating to 250 ℃, adding 0.05mol% of catalyst, simultaneously reducing the vacuum degree to below 100Pa, and polycondensing for 2h. The intrinsic viscosity of the polymer obtained was 1.33dL/g, and the molar percentage of the repeating units of Butylene Terephthalate (BT) was 70mol%, which was designated PBTdT 70.
Comparative example 1 PBST 48
The sample was designated PBST 48 using PBST 48 matrix resin as comparative example 1.
Comparative example 2 97PBST48+3PBST71
The PBST 48 matrix resin and PBST 71 nucleating agent in a mass ratio of 97:3 were melt mixed in an internal mixer at 200 ℃ for 5 minutes, and the obtained sample was designated 97PBST48+3PBST71.
Example 1 97PBST48+3PBDoT70
The PBST 48 base resin and the PBDoT 70 crystallization accelerator in a mass ratio of 97:3 were melt-mixed in an internal mixer at 200 ℃ for 5 minutes, and the obtained sample was designated as 97PBST48+3PBDoT70.
Example 2 97PBST48+3PBDoT80
The PBST 48 base resin and the PBDoT 80 crystallization accelerator in a mass ratio of 97:3 were melt-mixed in an internal mixer at 200 ℃ for 5 minutes, and the obtained sample was designated as 97PBST48+3PBDoT80.
Example 3 99PBST48+1PBDoT80
The PBST 48 base resin and the PBDoT 80 crystallization accelerator were melt-mixed in an internal mixer at 200 ℃ for 5 minutes at a mass ratio of 99:1, and the obtained sample was designated as 99PBST48+1PBDoT80.
Example 4 97PBST48+3PBSeT70
The PBST 48 base resin and the PBSeT 70 crystallization accelerator in a mass ratio of 97:3 were melt-mixed in an internal mixer at 200 ℃ for 5 minutes, and the obtained sample was designated as 97PBST48+3PBSeT70.
Example 5 97PBST48+3PBTdT70
The PBST 48 base resin and the PBTdT 70 crystallization accelerator in a mass ratio of 97:3 were melt-mixed in an internal mixer at 200 ℃ for 5 minutes, and the obtained sample was designated as 97PBST48+3PBTdT70.
DSC curves of the compositions of comparative examples 1-2 and examples 1-5 at cooling rates of 10℃and 40℃are shown in FIGS. 1 (A) and 1 (B), and melt crystallization temperatures (T c), enthalpies of crystallization (. DELTA.H2 c), and crystallization half times (T 1/2) are shown in Table 1.
Table 1 melt crystallization parameters for the compositions of examples and comparative examples at different cooling rates
* The substrate resin PBST 48 has no obvious melt crystallization peak (nd is not detected) at the temperature reduction rate of 40 ℃ per minute, but has a cold crystallization peak and a melting peak in the secondary temperature rise process, and other samples have no cold crystallization peak and only have a melting peak in the secondary temperature rise process.
DSC results (Table 1 and FIG. 1) show that in comparative example 1, the matrix resin PBST 48 shows a higher melt crystallization temperature (62 ℃) and higher melt crystallization enthalpy (20.6J/g) at a cooling rate of 10 ℃ per minute, and the crystallization performance looks good, but at a cooling rate of 40 ℃ per minute (note: the cooling rate in a real melt processing process may be faster, limited by the DSC instrument used, and 40 ℃ per minute is the maximum cooling rate that can be adopted), the melt crystallization peak of PBST 48 is difficult to observe, indicating that PBST 48 is slow to crystallize under the condition of rapid cooling, and can not meet the requirement of actual melt processing. It is therefore necessary to improve the crystallinity of PBST under rapid cooling conditions.
In comparative example 2, in which PBST 71 having the same structure as the matrix resin PBST 48 but different in composition (having a higher content of BT repeating units) was used as a nucleating agent in an amount of 3wt%, the composition 97PBST48+3PBST71 obtained by blending with PBST 48 had a melt crystallization temperature of 50℃at a cooling rate of 40℃per minute, a crystallization enthalpy of 15.5J/g, and a crystallization half-crystallization time of 44s, it was found that the crystallinity of comparative example 2 was significantly improved as compared with the case where the matrix resin PBST 48 was difficult to crystallize at a cooling rate of 40℃per minute.
In example 1, 3wt% of PBDoT 70 was introduced into the matrix resin PBST 48 as a crystallization accelerator, and the resulting composition 97PBST48+3PBDoT70 had a melt crystallization temperature of 60℃and a crystallization enthalpy of 21.6J/g and a crystallization half time of 30s at a cooling rate of 40℃/min. It can be seen that the crystallinity of example 1 is significantly more improved and overall than that of comparative example 2 at a cooling rate of 40 ℃ per minute, and that example 1 is significantly better than comparative example 2, in particular the crystallization half-period, regardless of the crystallization temperature, the crystallization enthalpy or the crystallization half-period, from 44s of comparative example 2 to 30s of example 1. This benefits from the unique structure of the crystallization promoters of the present invention.
In the present invention, the crystallization accelerator (PBDoT is exemplified by the present invention) has the same structure as that of the matrix resin portion, that is, the aromatic repeating units are Butylene Terephthalate (BT) and thus the crystal structure is the same as that of the matrix resin, but the BT content is higher, so the crystallization accelerator is easier to crystallize than the matrix resin, and can nucleate and crystallize at a higher temperature, and thus can perform nucleation, on the other hand, the crystallization accelerator has a structure different from that of the matrix resin, that is, 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, and the existence of the flexible diacid long chain can promote the segment movement of the matrix resin, thus promoting the faster growth of crystals, thereby enabling the crystallization to be faster, the crystallization peak to be narrowed, and the crystallization time to be shortened. Therefore, the crystallization accelerator of the present invention has a dual effect of providing crystal nuclei and accelerating crystal growth, and thus has a better crystallization accelerating effect than a general nucleating agent.
Compared with example 1, the crystallization accelerator of example 2 has a higher content of BT repeating units (80 mol% vs.70 mol%), the resulting composition 97PBST48+3PBDoT80 has a further improved crystallization temperature of the melt to 65℃at a cooling rate of 40℃/min, a crystallization enthalpy of 21.5J/g and a further reduction in crystallization time to 24s, which is seen to further improve the crystallinity.
Compared with example 2, the amount of crystallization accelerator PBDoT 80 in example 3 was reduced from 3wt% to 1wt%, and the resulting composition 99PBST48+1PBDoT80 had a melt crystallization temperature of 59 ℃ and a crystallization enthalpy of 20.4J/g and a crystallization half time of 23s, respectively, at a cooling rate of 40 ℃ per minute. It can be seen that the crystallization promoter is reduced in amount and, although the melt crystallization temperature and enthalpy of crystallization are slightly reduced, the crystallization of the matrix resin is still effectively promoted while maintaining a crystallization half time comparable to that of example 2.
In addition to PBDoT, compositions based on other crystallization promoters comprised by the present invention also have excellent crystallization properties. In example 4, 3wt% of PBSeT 70 was introduced into the matrix resin PBST 48 as a crystallization accelerator, and the resulting composition 97PBST48+3PBSeT70 had a melt crystallization temperature of 55℃and a crystallization enthalpy of 20.6J/g and a crystallization half time of 30s at a cooling rate of 40℃/min. In example 5, 3wt% of PBTdT 70 was introduced into the matrix resin PBST 48 as a crystallization accelerator, and the resulting composition 97PBST48+3PBTdT70 had a melt crystallization temperature of 60℃and a crystallization enthalpy of 21.4J/g and a crystallization half time of 32s at a cooling rate of 40℃/min. Their overall crystallization properties are also of significant advantage over comparative example 2.
On the other hand, in researching the crystallinity of the polymer by DSC, a slower cooling rate such as 10 ℃ per minute is generally adopted, but at a cooling rate of 10 ℃ per minute, the nucleating agent (comparative example 2) or the crystallization accelerator of the present invention (examples 1 to 5) is added, and the crystallization enthalpy is not significantly increased, and the crystallization half time is not shortened, but rather is significantly prolonged in comparative example 2, except that the crystallization temperature is significantly increased. Therefore, DSC results under the condition of slow cooling (10 ℃ per minute) often lack practical significance of guiding application, and DSC results under the condition of fast cooling can reflect the crystallization capability of the polymer in the practical processing process, so that the method has practical guiding significance.
In the prior art, only the crystallization temperature and the crystallization enthalpy of a melt are often concerned, but the length of the semi-crystallization time or the crystallization speed is ignored, and the latter is actually a key factor for determining the cooling forming speed in the material processing process. The invention is based on crystallization temperature, crystallization enthalpy and semi-crystallization time under the condition of rapid cooling at 40 ℃ per minute, and more comprehensively evaluates the crystallization capability of the biodegradable copolyester and the composition thereof.
The composition of the invention has good compatibility with the matrix resin because the crystallization promoter and the matrix resin have similar chemical structures, and can avoid the decrease of transparency caused by microphase separation when the heterogeneous nucleating agent is added. On the other hand, the excellent nucleation of the crystallization promoter increases the number of crystals, and the crystal size becomes smaller, facilitating the transmission of visible light, so that the article produced from the composition has better light transmittance. The optical property data of the films having a thickness of about 400 μm obtained by hot pressing the compositions of comparative example 1, PBST 48 and examples 1 and 2 are shown in Table 2, and the films obtained by the composition of the present invention have higher light transmittance, lower haze and better transparency than those obtained by the base resin.
Table 2 optical properties of comparative example 1 and examples 1 to 2
| Examples | Sample name | Transmittance% | Haze% |
| Comparative example 1 | PBST48 | 47.5 | 94.5 |
| Example 1 | 97PBST48+3PBDoT70 | 55.6 | 88.4 |
| Example 2 | 97PBST48+3PBDoT80 | 69.3 | 78.2 |
The film thickness used for the test was 400.+ -.20. Mu.m.
In addition, the crystallization promoter of the present invention is an aliphatic-aromatic copolyester having an aromatic unit content of 60 to 90mol%, preferably 70 to 80mol%, which still has a certain biodegradability (although degradation is slow), and may be added in an amount of as little as 1wt%, so that a composition prepared by melt blending it with a biodegradable matrix resin still has excellent biodegradability.
In summary, the invention provides a fat-aromatic copolyester composition with remarkably improved crystallinity and a preparation method thereof, wherein the composition comprises short-chain fat-aromatic copolyester matrix resin with lower aromatic chain unit content and long-chain fat-aromatic copolyester crystallization promoter with higher aromatic chain unit content, and the preparation method is simple and easy to implement. Compared with matrix resin, the composition has the effects of short semi-crystallization time, high crystallization temperature, large crystallization enthalpy and remarkably improved transparency under the condition of rapid cooling, and simultaneously maintains excellent biodegradability.
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