A biodegradable aliphatic polyester, its preparation method and application

Abstract

The present invention discloses a biodegradable aliphatic polyester and its preparation method and application. The biodegradable aliphatic polyester of the present invention comprises units derived from at least one aliphatic dicarboxylic acid and at least one aliphatic diol, and satisfies the following conditions: 1.54 ≤ Mw / Mn ≤ 1.98, Mw / q ≥ 50000; wherein, q is the mass percentage of the low molecular weight polymer with a molecular weight ≤ 1000 Dalton of the biodegradable aliphatic polyester measured by GPC. By regulating the molecular weight distribution of the biodegradable aliphatic polyester and the mass percentage of the low molecular weight polymer with a molecular weight lower than 1000 Dalton, the biodegradable aliphatic polyester of the present invention has both good barrier properties and excellent self-adhesion.

Description

Technical Field

[0001] The present invention relates to the technical field of high molecular compounds, and more specifically, to a biodegradable aliphatic polyester, a preparation method thereof, and an application thereof. Background Art

[0002] A food wrap is a thin film plastic packaging product. It can not only extend the storage time of food in the refrigerator, but also maintain the moisture of the stored food to keep its freshness. At the same time, when used for independent packaging of food, it can also effectively prevent the smell of food from mixing. More importantly, when it is used for opened beverages, fruits or tableware, it can also play a role in isolating bacteria and improve the hygienic safety. Therefore, food wraps are widely used in fields such as household life, supermarkets or industrial food packaging. However, most traditional food wraps are made of polyethylene films, biaxially oriented polyester (BOPET), BOPP films or CPP films, etc. These food wraps cannot be biodegradable, and it is extremely easy to cause the problem of "white pollution" after being discarded.

[0003] To alleviate the environmental problems caused by the abandonment of traditional food wraps, people have begun to use biodegradable polyester polybutylene terephthalate - co - polybutylene adipate (PBAT) materials to replace the above - mentioned traditional film materials to improve the biodegradable performance of food wraps. PBAT not only has the degradation performance of aliphatic polyesters, but also has the mechanical properties of aromatic polyesters, and has good ductility and elongation at break. However, the barrier property of the food wrap made of the biodegradable polyester PBAT is poor, resulting in the food that needs a long storage time being prone to rot during storage, and the long - term freshness - keeping effect is limited. At the same time, the food wrap also needs to have good self - adhesiveness to better meet the usage requirements. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects and deficiencies of the poor barrier property and self - adhesiveness of the existing biodegradable polyester PBAT, and provide a biodegradable aliphatic polyester.

[0005] Another purpose of the present invention is to provide a preparation method of the biodegradable aliphatic polyester.

[0006] Another purpose of the present invention is to provide the application of the above - mentioned biodegradable aliphatic polyester in the preparation of food packaging films, industrial packaging films or agricultural mulch films.

[0007] The above purposes of the present invention are achieved by the following technical solutions:

[0008] The present invention protects a biodegradable aliphatic polyester, which comprises units derived from at least one aliphatic dicarboxylic acid and at least one aliphatic diol, and satisfies the following conditions: 1.54 ≤ Mw / Mn ≤ 1.98, Mw / q ≥ 50000;

[0009] Among them, q is the mass percentage of the low molecular weight polymer with a molecular weight ≤ 1000 Dalton of the biodegradable aliphatic polyester determined by GPC.

[0010] Preferably, the Mw / Mn is 1.65 - 1.85, and 70000 ≤ Mw / q ≤ 110000.

[0011] The molecular weight of the polymer, the molecular weight distribution (Mw / Mn), as well as the type and content of the oligomer are affected by various factors, such as the type of monomers, the ratio of monomers, the type and addition amount of the branching agent and chain extender, the branching structure, the polymerization process (continuous method or batch method), the reaction temperature, the reaction time, and the reaction pressure, etc.

[0012] The number average molecular weight (Mn) of the biodegradable aliphatic polyester of the present invention is 45000 - 85000, specifically it can be 45000, 50000, 55000, 60000, 65000, 70000 or 80000; the weight average molecular weight (Mw) is 87000 - 132000, specifically it can be 90000, 95000, 100000, 105000, 110000, 115000, 120000, 125000 or 130000; the mass percentage (q) of the low molecular weight polymer with a molecular weight ≤ 1000 Dalton is less than 1.93%, specifically it can be 1.11%, 1.35%, 1.38%, 1.55%, 1.67%, 1.72% or 1.91%.

[0013] Optionally, the unit derived from the aliphatic dicarboxylic acid is an aliphatic dicarboxylic acid and its ester having 2 - 22 carbon atoms in the main chain. Specifically, the aliphatic dicarboxylic acid is at least one of succinic acid, adipic acid, azelaic acid, sebacic acid or tridecanedioic acid; preferably succinic acid and / or adipic acid.

[0014] Optionally, the unit derived from the aliphatic diol is an aliphatic diol having 2 - 13 carbon atoms in the main chain. Specifically, the aliphatic diol is at least one of 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol or 1,13-tridecanediol; preferably 1,4-butanediol and / or 1,3-propanediol.

[0015] Specifically, the biodegradable aliphatic polyester comprises the following components:

[0016] A) Aliphatic dicarboxylic acid component:

[0017] a1) Based on the total amount of a1) and a2), 65 to 100 mol% of succinic acid or its ester derivatives, or a mixture thereof;

[0018] a2) Based on the total amount of a1) and a2), 0 to 35 mol% of adipic acid or its ester derivatives, or a mixture thereof, wherein the total molar percentage of components a1) and a2) is 100 mol%;

[0019] B) The aliphatic diol component is 1,4-butanediol, and its molar ratio to the aliphatic dicarboxylic acid component is ≥1.

[0020] Preferably, a1) in the aliphatic dicarboxylic acid component is 73 to 80 mol% of succinic acid or its ester derivatives, or a mixture thereof; a2) in the aliphatic dicarboxylic acid component is 20 to 27 mol% of adipic acid or its ester derivatives, or a mixture thereof.

[0021] The biodegradable aliphatic polyester, according to the ASTM F1249-13 standard, at a sample thickness of 12 ± 2 μm, 40 °C and RH = 60%, has a water vapor transmission rate ≤ 750 g / (d·m 2 ), preferably, the water vapor transmission rate ≤ 480 g / (d·m 2 ); more preferably, the water vapor transmission rate ≤ 330 g / (d·m 2 ).

[0022] The biodegradable aliphatic polyester has good self-adhesion, which is characterized by the shear peel strength. The higher the shear peel strength, the better the self-adhesion of the film material. The biodegradable aliphatic polyester, according to the GB / T10457-2009 standard, at a sample thickness of 12 ± 2 μm, has a shear peel strength ≥ 0.60 N / cm 2 ; preferably, the shear peel strength ≥ 0.72 N / cm 2 ; more preferably, the shear peel strength ≥ 0.85 N / cm 2 .

[0023] The present invention also protects a preparation method of the above-mentioned biodegradable aliphatic polyester, comprising the following steps:

[0024] Step i): Mix the aliphatic dicarboxylic acid or its derivatives (component A) with the aliphatic diol (component B), and then carry out an esterification reaction or a transesterification reaction to obtain an esterification product;

[0025] Step ii): Carry out a prepolymerization reaction on the esterification product in step i) to obtain a prepolymer product;

[0026] Step iii): subject the prepolymer obtained in step ii) to polycondensation reaction until the acid value of the resulting polycondensate, as determined according to the standard of GB / T 32366-2015, is 15 to 50 mol / t, thereby obtaining the biodegradable aliphatic polyester;

[0027] Among them, the acid value of the esterification product described in step i), as determined according to the standard of GB / T 32366-2015, is 360 to 770 mol / t; the acid value of the prepolymer described in step ii), as determined according to the standard of GB / T 32366-2015, is 70 to 110 mol / t.

[0028] The above aliphatic dicarboxylic acid or its derivative can be used alone or in the form of a mixture of two or more. In the present invention, in step i), the molar ratio of component A to component B is 1:(1.2 to 2.4), and the specific values within 1.2 to 2.4 can specifically be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, etc.; more preferably 1:(1.4 to 1.8).

[0029] In step i), in the case where there are two or more aliphatic dicarboxylic acids or their derivatives, in addition to the above-described step i), in which all the aliphatic dicarboxylic acids or their derivatives are blended with the aliphatic diol (component B) for mixed esterification, it is also possible to separately carry out independent esterification of individual aliphatic dicarboxylic acids or their derivatives with the aliphatic diol (component B). For example, the aliphatic dicarboxylic acid a1) component is subjected to an esterification reaction with the aliphatic diol (component B), and the aliphatic dicarboxylic acid a2) component is subjected to an esterification reaction with the aliphatic diol (component B), and then the esterification products of the two are mixed.

[0030] In the case of adopting the independent esterification process, the molar ratio of component a1 to component B is 1:(1.1 to 1.8), and specifically can be 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6 or 1:1.7; the molar ratio of component a2 to component B is 1:(1.3 to 2.0), and the molar ratio can specifically be 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8 or 1:1.9. The temperature of the esterification reaction is 150 to 200 °C, preferably 180 to 195 °C; the pressure is 0.7 to 1.1 bar, preferably 0.8 to 1.0 bar, and the reaction time is 2 to 4 hours. Under the independent esterification conditions, the acid value of the esterification product corresponding to each esterification, as determined according to the standard of GB / T 32366-2015, is 360 to 770 mol / t.

[0031] Specifically, the above preparation method includes the following steps:

[0032] In step i), after mixing the aliphatic dicarboxylic acid or its derivative with the aliphatic diol, a catalyst may or may not be added. When adding a catalyst, it can be added all at once or in portions; the total mass of the catalyst is 0.001 - 1 wt% of the mass of the aliphatic polyester, for example, it can be 0.001 wt%, 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.02 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, etc.; preferably 0.03 - 0.2 wt%.

[0033] The above-mentioned catalyst generally includes zinc compounds, aluminum compounds, and titanium compounds. Especially titanium compounds, compared with the commonly used tin compounds, antimony compounds, cobalt compounds, and lead compounds in the literature, another advantage of titanium catalysts (such as tetrabutyl titanate or tetraisopropyl titanate) is that the residual amount of the catalyst remaining in the product or downstream products has low toxicity. Catalyst toxicity is particularly important in biodegradable polyesters because they can directly enter the environment in the form of compost bags or covering films.

[0034] In step i), based on the total weight of the aliphatic dicarboxylic acid or its derivative and the aliphatic diol, a crosslinking agent having at least three functional groups may also be included in an amount of 0 - 3 wt%; preferably 0.01 - 2 wt%, more preferably 0.05 - 1 wt%, and particularly preferably 0.08 - 0.20 wt%.

[0035] The above-mentioned crosslinking agent having at least three functional groups is a compound having 3 - 6 hydroxyl groups. Specifically, it can be at least one of tartaric acid, citric acid, malic acid, trimethylolpropane, trimethylolethane, pentaerythritol, polyether triol, glycerol, 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic anhydride, 1,2,4,5-benzenetetracarboxylic acid, or pyromellitic dianhydride; preferably a polyol, such as trimethylolpropane, pentaerythritol, or glycerol; particularly preferably glycerol.

[0036] After mixing the aliphatic dicarboxylic acid or its derivative with the aliphatic diol, the temperature is raised. In step i), the temperature of the reaction system is set to 150 - 200 °C, preferably 165 - 190 °C; the pressure is set to 0.7 - 1.1 bar, preferably 0.8 - 1.0 bar. Step i) can be carried out in a mixing device, and the specific reaction time is 2 - 4 hours, and an esterification product with an acid value of 360 - 770 mol / t as determined according to GB / T 32366 - 2015 can be produced.

[0037] The excess diol component in step (i) is generally removed by distillation and returned to the loop after distillation purification. The purity of the diol component after distillation purification is ≥95%.

[0038] In step (ii), the esterification product in step (i) (if the catalyst is added in multiple portions, together with the remaining catalyst) is added to a reactor suitable for the pre-condensation reaction. Reactors that have been proven suitable for the pre-polycondensation reaction include tube bundle reactors, cascade reactors (Kesselkaskade), or bubble cap towers, especially downflow cascade reactors, which may have a degassing unit if appropriate. The reaction temperature is usually set to 230 - 260 °C, preferably 235 - 245 °C; the reaction pressure is usually set to 0.3 - 0.6 bar, preferably 0.35 - 0.55 bar; the reaction time is 70 - 200 minutes, and a prepolymer product with an acid value of 70 - 110 mol / t as determined according to GB / T 32366-2015 can be produced; preferably, the acid value of the prepolymer product is controlled within the range of 82 - 100 mol / t.

[0039] In the polycondensation step (iii), the catalyst deactivator can be mixed with the prepolymer product according to the actual situation and requirements. Specifically, the above deactivator is a phosphorus compound, an organic phosphite (such as phosphorous acid), or phosphoric acid. For example, if a highly active titanium catalyst is used, a deactivator can be added. Based on the amount of the polymer after step (iii), the addition amount of the deactivator can be 0.001 - 0.1 wt%, preferably 0.01 - 0.05 wt%. The molar ratio of Ti / P is preferably (1.1 - 1.5):1, particularly preferably (1.1 - 1.3):1.

[0040] In addition, according to the actual situation and requirements, a color stabilizer for the condensation process can also be mixed with the prepolymer product in the polycondensation step (iii). The color stabilizers that can be used are mainly phosphorus compounds, specifically at least one of phosphoric acid, phosphorous acid, triphenyl phosphite, triphenyl phosphate, sodium hypophosphite, or sodium phosphite. Generally, the use of a color stabilizer usually reduces the condensation rate, but triphenyl phosphate is a particularly suitable color stabilizer because it has basically no adverse effect on the condensation rate.

[0041] Based on the amount of the polymer after step (iii), the addition amount of the color stabilizer can be 0.001 - 1.5 wt%, preferably 0.01 - 1.0 wt%. Preferably, the molar ratio of Ti / P is 1.0:(0.3 - 1.0); more preferably 1.0:(0.5 - 1.0).

[0042] Furthermore, according to actual situations and requirements, in the polycondensation step iii), the activator used in the condensation process can be mixed with the prepolymer product. Optionally, the activator is a phosphorus compound; specifically, it can be at least one of disodium hydrogen phosphate, calcium hypophosphite, calcium phosphite, calcium phosphate, sodium hypophosphite, sodium phosphite, triphenyl phosphite, triphenyl phosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, or tributyl phosphate. Preferably, the activator is disodium hydrogen phosphate and / or sodium phosphite.

[0043] Specifically, based on the amount of the polymer after step iii), the addition amount of the activator can be 0.001 - 1.5 wt%, preferably 0.01 - 1.0 wt%. Preferably, the molar ratio of Ti / P is (1.0 - 1.5):1; more preferably, the molar ratio of Ti / P is (1.1 - 1.3):1.

[0044] The color stabilizer can also be used in combination with the activator. For example, triphenyl phosphate as the color stabilizer is used in combination with disodium hydrogen phosphate as the activator.

[0045] The reactor for the polycondensation reaction in step iii) can be a rotary disk reactor or a cage reactor. The reaction temperature is usually 235 - 260 °C, preferably 240 - 255 °C; the pressure is usually 0.2 - 5 mbar, preferably 0.5 - 3 mbar; the reaction time is 45 - 110 minutes, preferably 60 - 90 minutes, and a polycondensation product with an acid value of 15 - 50 mol / t measured according to GB / T 32366 - 2015 can be produced.

[0046] Specifically, the polycondensation product in step iii) and the chain extender can be added together to an extruder (added to a continuous kneader (List reactor), or added to a static mixer) to carry out a chain growth reaction.

[0047] Specifically, the static mixer can use SMR, SMX, or SMXL components, or a combination thereof. The List reactor can be a single - shaft DISCOTHERM B or a twin - shaft CRP or ORP reactor. The extruder can be a single - screw extruder or a twin - screw extruder. Preferably, the above - mentioned chain growth reaction is carried out in an extruder. After chain growth, the final polyester obtained has an acid value of 15 - 50 mol / t measured according to GB / T 32366 - 2015.

[0048] Optionally, the above - mentioned chain extender includes at least one of isocyanate, peroxide, epoxide, oxazoline, oxazine, caprolactam, or carbodiimide.

[0049] Specifically, the isocyanate may be an aromatic diisocyanate or an aliphatic diisocyanate; for example, the aromatic diisocyanate may be at least one of toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, diphenylmethane 2,2'-diisocyanate, diphenylmethane 2,4'-diisocyanate, diphenylmethane 4,4'-diisocyanate, naphthalene 1,5-diisocyanate or xylene diisocyanate. Preferably, it is diphenylmethane 2,2'-diisocyanate, diphenylmethane 2,4'-diisocyanate or diphenylmethane 4,4'-diisocyanate.

[0050] The isocyanate that can also be used in the present invention includes tris(4-isocyanatophenyl)methane with three rings. This polynuclear aromatic diisocyanate can be formed during the production of diisocyanates with one or two rings.

[0051] For the present invention, the aliphatic diisocyanate may be any linear or branched alkylene diisocyanate or cycloalkylene diisocyanate containing 2 to 20 carbon atoms, preferably 3 to 12 carbon atoms. For example, it may be hexamethylene diisocyanate, pentamethylene diisocyanate, isophorone diisocyanate or the diisocyanate of methylene bis(4-isocyanatocyclohexane); preferably, it is hexamethylene diisocyanate.

[0052] Based on the total weight of the biodegradable aliphatic polyester, the dosage of the isocyanate may be 0.05 to 2 wt%, preferably 0.1 to 1.5 wt%.

[0053] Specifically, the above peroxides may be at least one of benzoyl peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)methylcyclododecane, n-butyl 4,4-bis(butylperoxy)valerate, dicumyl peroxide, tert-butyl peroxybenzoate, dibutyl peroxide, α,α-bis(tert-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hex-3-yne or cumene hydroperoxide.

[0054] Based on the total weight of the biodegradable aliphatic polyester, the dosage of the peroxide may be 0.1 to 2 wt%, preferably 0.2 to 1 wt%.

[0055] Specifically, the above-mentioned epoxides may be one or several of diglycidyl ether, hexamethylene diglycidyl ether, sorbitol diglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polybutylene glycol diglycidyl ether, and copolymers containing epoxy groups based on styrene, acrylate, and / or methacrylate.

[0056] Based on the total weight of the biodegradable aliphatic polyester, the dosage of the epoxide may be 0.1 to 2 wt%, preferably 0.2 to 1 wt%.

[0057] Specifically, the above-mentioned dioxazolines may be at least one of 2,2'-bis(2-oxazoline), bis(2-oxazolinyl)methane, 1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane, or 1,4-bis(2-oxazolinyl)butane; preferably at least one of 1,4-bis(2-oxazolinyl)benzene, 1,2-bis(2-oxazolinyl)benzene, or 1,3-bis(2-oxazolinyl)benzene.

[0058] Specifically, the above-mentioned dioxazines may be 2,2'-bis(2-dioxazine), bis(2-dioxazinyl)methane, 1,2-bis(2-dioxazinyl)ethane, 1,3-bis(2-dioxazinyl)propane, or 1,4-bis(2-dioxazinyl)butane; especially at least one of 1,4-bis(2-dioxazinyl)benzene, 1,2-bis(2-dioxazinyl)benzene, or 1,3-bis(2-dioxazinyl)benzene.

[0059] Specifically, the above-mentioned carbodiimides may be one or several of N,N'-di-2,6-diisopropylphenyl carbodiimide, N,N'-di-o-tolyl carbodiimide, N,N'-diphenyl carbodiimide, N,N'-dioctyldecyl carbodiimide, N,N'-di-2,6-dimethylphenyl carbodiimide, N-tolyl-N'-cyclohexyl carbodiimide, N,N'-di-2,6-di-tert-butylphenyl carbodiimide, N,N'-di-2,4,6-triisobutylphenyl carbodiimide, diisopropyl carbodiimide, dimethyl carbodiimide, diisobutyl carbodiimide, dioctyl carbodiimide, tert-butylisopropyl carbodiimide, di-β-naphthyl carbodiimide, or di-tert-butyl carbodiimide.

[0060] Based on the total weight of the biodegradable aliphatic polyester, the dosage of oxazoline, oxazine, caprolactam or carbodiimide can each be 0.1 - 2 wt%, preferably 0.2 - 1 wt%.

[0061] The above chain growth reaction is carried out under superatmospheric pressure or atmospheric pressure, the reaction temperature is 170 - 240 °C, preferably 180 - 240 °C; the reaction time is 2 - 15 minutes, preferably 4 - 10 minutes.

[0062] The biodegradable aliphatic polyester prepared according to the above preparation method usually has a melt mass flow rate (MFR) of 1.0 - 40.0 g / 10 min, preferably 2.5 - 32.0 g / 10 min, particularly preferably 3.5 - 22.0 g / 10 min according to ISO 1133 - 2 - 2011 (190 °C, 2.16 kg).

[0063] The present invention also protects a biodegradable aliphatic polyester mixture, which contains the above biodegradable aliphatic polyester; based on the total weight of the biodegradable aliphatic polyester mixture, the weight content of the biodegradable aliphatic polyester is 50 - 95 wt%, preferably 65 - 90 wt%.

[0064] In addition, the above biodegradable aliphatic polyester mixture may further contain at least one polymer from synthetic or natural sources. The polymer from synthetic sources may specifically be at least one of polylactic acid (PLA), polybutylene succinate (PBS), polybutylene adipate succinate (PBSA), polybutylene sebacate succinate (PBSSe), polybutylene sebacate (PBSe), polybutylene terephthalate succinate (PBST), polybutylene adipate terephthalate (PBAT), polybutylene terephthalate sebacate (PBSeT) or polybutylene adipate furandicarboxylate (PBAF). Based on the total weight of the biodegradable aliphatic polyester mixture, the weight content of the polymer from synthetic sources is 1 - 20 wt%, preferably 4 - 10 wt%.

[0065] The polymer from natural sources may specifically be at least one of starch, cellulose, chitin, chitosan, alginate, proteins (such as gluten, zein or casein), collagen, gelatin, natural rubber, rosin acid and its derivatives or lignin and its derivatives. Preferably, it is starch or a mixture of starch and other polymers from natural sources. Starch can be used in the allosteric and gelled form or in the form of a filler, and the starch can be distributed in the continuous phase, dispersed phase or in a co - continuous form. Based on the total weight of the biodegradable aliphatic polyester mixture, the mass content of the polymer from natural sources is 1 - 25 wt%, preferably 2 - 10 wt%.

[0066] Specifically, the above-mentioned biodegradable aliphatic polyester or biodegradable aliphatic polyester mixture can be prepared by reactive extrusion. The extruder used in the reactive extrusion process can be a single-screw extruder, a twin-screw extruder or a multi-screw extruder. The extrusion temperature is 140-220 °C and the screw speed is 200-500 rpm.

[0067] An application of the above-mentioned biodegradable aliphatic polyester or biodegradable aliphatic polyester mixture in the preparation of food packaging films, industrial packaging films or agricultural mulch films is also within the protection scope of the present invention.

[0068] For the present invention, if a substance or a mixture of substances shows a biodegradation percentage degree of at least 90%, as defined in DIN EN 13432, then the substance or the mixture of substances has the characteristic of "biodegradable".

[0069] According to DIN EN 13432, during the composting process, air without CO2 is introduced into the mature compost and the compost is subjected to a specific temperature process. Here, biodegradability is defined as the percentage degree of biodegradation expressed by the ratio of the net amount of CO2 released by the sample (after subtracting the amount of CO2 released by the compost without the sample) to the maximum amount of CO2 that the sample can release (calculated from the carbon content in the sample). Only a few days after composting, biodegradable polyesters and biodegradable polyester mixtures usually show obvious signs of degradation, such as fungal growth, cracking and perforation. Other methods for determining biodegradability are described, for example, in ASTM D5338 and ASTM D6400.

[0070] Compared with the prior art, the beneficial effects of the present invention are:

[0071] By regulating the molecular weight distribution of the biodegradable aliphatic polyester and the mass percentage of the low molecular weight polymer with a molecular weight lower than 1000 Dalton, the biodegradable aliphatic polyester of the present invention has both a low water vapor transmission rate and a high self-adhesion, and can endow the film material with good barrier properties and excellent self-adhesion. Specific Embodiments

[0072] The present invention will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventional raw material reagents purchased.

[0073] 1. The molecular weight Mw and Mn of the biodegradable aliphatic polyester are tested by gel permeation chromatography (GPC)

[0074] The chromatographic system can be used at 40 °C with a set of three columns in series (particle diameter 5 μm and porosities respectively and ) Determination was carried out using a refractive index detector, chloroform as the eluent (flow rate 1 mL / min), and polystyrene as the reference standard.

[0075] 2. Test for the mass percentage q of low molecular weight polymers with a molecular weight ≤ 1000 Dalton measured by GPC

[0076] The determination method is as follows: A sample (F1) of polyester (about 3 - 4 g) is placed together with 30 mL of chloroform in a 200 mL flask. After the polyester is completely dissolved, 100 mL of a 1:1 (v / v) mixed solution of methanol and acetone is added, and then the mixture is kept under stirring for 2 hours. Then the mixture is filtered through a paper filter with a pore size of 8 μm, and the polymer remaining on the filter is rinsed with acetone, and the methanol / acetone solution is completely evaporated by heating under an air stream at 70 °C, and the weight of the residual solid component (F2) is recorded. A sample of the solid component (about 10 mg) is dissolved in 10 mL of chloroform and analyzed by GPC according to the method disclosed above. Based on the molecular weight distribution curve recorded by the GPC instrument, the mass percentage (P1) of low molecular weight polymers with a molecular weight ≤ 1000 Dalton is determined. The mass percentage q of polyester oligomers with a molecular weight ≤ 1000 Dalton is calculated according to the following equation: q = (P1 * F2) / F1 * 100%; The above determinations of Mn, Mw, and q can be carried out on polyester pellets or on the film obtained therefrom.

[0077] 3. The water vapor transmission rate test was carried out with reference to the standard ASTM F1249 - 13.

[0078] A film with a thickness of 12 ± 2 μm was prepared using a blown film machine with a screw diameter of 40 mm, a blown film temperature of 120 - 160 °C, a die gap = 1 mm, a flow rate of 25 ± 0.5 kg / h, and a blow-up ratio of 3.0. The water vapor transmission rate of the sample film was determined according to the standard ASTM F - 1249.

[0079] 4. The shear peel strength test was carried out with reference to the standard GB / T 10457 - 2009.

[0080] Ten specimens with a length of 50 mm and a width of 25 mm were cut. Two specimens were taken as a group, with the adhesive surfaces of the specimens facing each other in the length direction, overlapping head to tail, with an overlapping part length of 15 mm and a width of 25 mm. The specimens were laid flat on a smooth plane, and a rubber roller (diameter 40 mm, length 100 mm, mass 300 g) was rolled back and forth 3 times on the overlapping part of the specimens to ensure that there was no air remaining between the two layers of the fresh-keeping film at the overlapping part. The prepared specimens were placed in the experimental environmental conditions for 20 min and then tested.

[0081] Tensile test each group of specimens on a tensile testing machine, measure the force required for the two specimens to separate, and take the arithmetic mean of 5 groups of specimens as the result. The tensile speed used in the test is 250 mm / min ± 50 mm / min.

[0082] Example 1

[0083] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0084] Step i). Physically mix 350 kg of succinic acid, 143 kg of adipic acid, 500 kg of 1,4-butanediol and 0.35 kg of glycerol. After mixing, transfer the mixture to an esterification reactor. The reaction mixture is subjected to esterification reaction at a temperature of 200 °C and a pressure of 1.1 bar for 3 hours, and the acid value of the obtained esterified product is 438 mol / t;

[0085] Step ii). Transfer the esterification product obtained in step i) to a vertical reactor with stirring, add 0.32 kg of tetrabutyl titanate, and the reaction mixture is subjected to prepolymerization reaction at 250 °C and a reactor pressure of 0.60 bar for 110 minutes. The acid value of the obtained prepolymer is 101 mol / t;

[0086] Step iii). Transfer the prepolymer product obtained in step ii) to a horizontal reactor with stirring, and carry out polycondensation reaction at 245 °C and a pressure of 2.3 mbar for 80 minutes. The acid value of the obtained biodegradable aliphatic polyester is 22.8 mol / t, and the melt index is 4.1 g / 10 min (the test standard and conditions are ISO 1133-2-2011, 190 °C, 2.16 kg).

[0087] Example 2

[0088] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0089] Step i). Physically mix 350 kg of succinic acid, 143 kg of adipic acid, 650 kg of 1,4-butanediol and 0.85 kg of glycerol. After mixing, transfer the mixture to an esterification reactor. The reaction mixture is subjected to esterification reaction at a temperature of 190 °C and a pressure of 1.0 bar for 4 hours, and the acid value of the obtained esterified product is 382 mol / t;

[0090] Step ii). Transfer the esterification product obtained in step i) to a vertical reactor with stirring, add 0.40 kg of tetrabutyl titanate, and the reaction mixture is subjected to prepolymerization reaction at 250 °C and a reactor pressure of 0.45 bar for 150 minutes. The acid value of the obtained prepolymer is 78 mol / t;

[0091] Step iii). Transfer the prepolymer obtained in step ii) to a horizontal reactor equipped with stirring, and carry out polycondensation reaction at 245 °C and a pressure of 1.6 mbar for 60 minutes. The acid value of the obtained biodegradable aliphatic polyester is 26.3 mol / t, and the melt index is 5.4 g / 10 min (the test standard and conditions are ISO 1133-2-2011, 190 °C, 2.16 kg).

[0092] Example 3

[0093] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0094] Step i). Physically mix 350 kg of succinic acid, 143 kg of adipic acid, 550 kg of 1,4-butanediol and 1.2 kg of glycerol. After mixing, transfer the mixture to an esterification reactor. The reaction mixture is subjected to esterification reaction at a temperature of 180 °C and a pressure of 0.95 bar for 2.5 hours. The acid value of the obtained esterified product is 501 mol / t;

[0095] Step ii). Transfer the esterification product obtained in step i) to a vertical reactor equipped with stirring, add 0.42 kg of tetrabutyl titanate. The reaction mixture is subjected to pre-polycondensation reaction at 243 °C and a reactor internal pressure of 0.35 bar for 90 minutes. The acid value of the obtained prepolymer is 84 mol / t;

[0096] Step iii). Transfer the prepolymer obtained in step ii) to a horizontal reactor equipped with stirring, and carry out polycondensation reaction at 243 °C and a pressure of 1.3 mbar for 70 minutes. The acid value of the obtained biodegradable aliphatic polyester is 20.5 mol / t, and the melt index is 4.0 g / 10 min (the test standard and conditions are ISO 1133-2-2011, 190 °C, 2.16 kg).

[0097] Example 4

[0098] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0099] Step i). Physically mix 350 kg of succinic acid, 143 kg of adipic acid, 510 kg of 1,4-butanediol and 1.0 kg of glycerol. After mixing, transfer the mixture to an esterification reactor. The reaction mixture is subjected to esterification reaction at a temperature of 170 °C and a pressure of 0.85 bar for 2.5 hours. The acid value of the obtained esterified product is 570 mol / t;

[0100] Step ii). Transfer the esterification product obtained in step i) to a vertical reactor equipped with stirring, add 0.38 kg of tetrabutyl titanate, and carry out a prepolycondensation reaction on the reaction mixture at 242 °C and a reactor internal pressure of 0.40 bar for 110 minutes. The acid value of the obtained prepolymer product is 95 mol / t;

[0101] Step iii). Transfer the prepolymer product obtained in step ii) to a horizontal reactor equipped with stirring, and carry out a polycondensation reaction at 248 °C and a pressure of 1.4 mbar for 65 minutes. The acid value of the obtained biodegradable aliphatic polyester is 21.4 mol / t, and the melt index is 9.8 g / 10 min (test standard and conditions: ISO 1133-2-2011, 190 °C, 2.16 kg).

[0102] Example 5

[0103] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0104] Step i). Physically mix 215 kg of succinic acid, 143 kg of adipic acid, 480 kg of 1,4-butanediol and 1.2 kg of glycerol. After the mixing is completed, transfer the mixture to an esterification reactor. Carry out an esterification reaction on the reaction mixture at a temperature of 180 °C and a pressure of 1.10 bar for 4.0 hours. The acid value of the obtained esterified product is 361 mol / t;

[0105] Step ii). Transfer the esterification product obtained in step i) to a vertical reactor equipped with stirring, add 0.35 kg of tetrabutyl titanate, and carry out a prepolycondensation reaction on the reaction mixture at 248 °C and a reactor internal pressure of 0.58 bar for 145 minutes. The acid value of the obtained prepolymer product is 71 mol / t;

[0106] Step iii). Transfer the prepolymer product obtained in step ii) to a horizontal reactor equipped with stirring, and carry out a polycondensation reaction at 255 °C and a pressure of 1.7 mbar for 100 minutes. The acid value of the obtained biodegradable aliphatic polyester is 28.9 mol / t, and the melt index is 5.2 g / 10 min (test standard and conditions: ISO 1133-2-2011, 190 °C, 2.16 kg).

[0107] Example 6

[0108] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0109] Step i). Physically mix 350 kg of succinic acid, 350 kg of 1,4-butanediol, and 1.8 kg of glycerol. After mixing is complete, transfer the mixture to an esterification reactor. The reaction mixture undergoes an esterification reaction at a temperature of 160 °C and a pressure of 0.70 bar for 2.0 hours, and the acid value of the resulting esterified product is 756 mol / t;

[0110] Step ii). Transfer the esterification product obtained in step i) to a vertical reactor equipped with stirring, add 0.40 kg of tetrabutyl titanate, and the reaction mixture undergoes a prepolymerization reaction at 250 °C and a reactor internal pressure of 0.30 bar for 85 minutes. The acid value of the resulting prepolymerized product is 110 mol / t;

[0111] Step iii). Transfer the prepolymerized product obtained in step ii) to a horizontal reactor equipped with stirring, and carry out a polycondensation reaction at 256 °C and a pressure of 2.5 mbar for 110 minutes. The acid value of the resulting biodegradable aliphatic polyester is 33.4 mol / t, and the melt index is 12.3 g / 10 min (test standard and conditions are ISO1133-2-2011, 190 °C, 2.16 kg).

[0112] Example 7

[0113] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0114] Step i-1). Physically mix 350 kg of succinic acid, 330 kg of 1,4-butanediol, and 1.3 kg of glycerol. After mixing is complete, transfer the mixture to an esterification reactor. The reaction mixture undergoes an esterification reaction at a temperature of 180 °C and a pressure of 1.0 bar for 100 minutes, and the acid value of the resulting esterified product is 370 mol / t;

[0115] Step i-2). Physically mix 143 kg of adipic acid and 150 kg of 1,4-butanediol. After mixing is complete, transfer the mixture to another esterification reactor. The reaction mixture undergoes an esterification reaction at a temperature of 195 °C and a pressure of 0.80 bar for 90 minutes, and the acid value of the resulting esterified product is 721 mol / t;

[0116] Step ii). After mixing the esterification products obtained in step i-1) and step i-2), transfer them to a vertical reactor equipped with stirring, add 0.45 kg of tetrabutyl titanate, and the reaction mixture undergoes a prepolymerization reaction at 245 °C and a reactor internal pressure of 0.40 bar for 100 minutes. The acid value of the resulting prepolymerized product is 86 mol / t;

[0117] Step iii). Transfer the prepolymer obtained in step ii) to a horizontal reactor equipped with stirring, and carry out polycondensation reaction at 247 °C and a pressure of 1.1 mbar for 45 minutes. The acid value of the obtained polycondensate is 15.8 mol / t;

[0118] Step iv), transfer the polycondensate obtained in step iii) into a static mixer, add 1.8 kg of hexamethylene diisocyanate, and carry out blending reaction at 210 °C for 7 min. The acid value of the obtained biodegradable aliphatic polyester is 16.7 mol / t, and the melt index is 4.0 g / 10 min (the test standard and conditions are ISO 1133-2-2011, 190 °C, 2.16 kg).

[0119] Comparative Example 1

[0120] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0121] Step i). Physically mix 350 kg of succinic acid, 143 kg of adipic acid, 900 kg of 1,4-butanediol and 3.2 kg of glycerol. After mixing is completed, transfer the mixture to an esterification reactor. The reaction mixture is subjected to esterification reaction at a temperature of 210 °C and a pressure of 0.65 bar for 3 hours. The acid value of the obtained esterified product is 221 mol / t;

[0122] Step ii). Transfer the esterified product obtained in step i) to a vertical reactor equipped with stirring, add 0.48 kg of tetrabutyl titanate, and the reaction mixture is subjected to pre-polycondensation reaction at 250 °C and a reactor internal pressure of 0.20 bar for 156 minutes. The acid value of the obtained prepolymer is 41 mol / t;

[0123] Step iii). Transfer the prepolymer obtained in step ii) to a horizontal reactor equipped with stirring, and carry out polycondensation reaction at 252 °C and a pressure of 1.2 mbar for 50 minutes. The acid value of the obtained biodegradable aliphatic polyester is 12.1 mol / t, and the melt index is 3.0 g / 10 min (the test standard and conditions are ISO 1133-2-2011, 190 °C, 2.16 kg).

[0124] Comparative Example 2

[0125] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0126] Step i). Physically mix 350 kg of succinic acid, 143 kg of adipic acid, and 410 kg of 1,4-butanediol. After mixing is completed, transfer the mixture to an esterification reactor. The reaction mixture is subjected to esterification reaction at a temperature of 160 °C and a pressure of 1.2 bar for 2 hours. The acid value of the obtained esterified product is 841 mol / t;

[0127] Step ii). Transfer the esterification product obtained in Step i) to a vertical reactor equipped with a stirrer, add 0.44 kg of tetrabutyl titanate, and carry out a prepolycondensation reaction on the reaction mixture at 230 °C and a reactor internal pressure of 0.70 bar for 120 minutes. The acid value of the obtained prepolymer product is 167 mol / t;

[0128] Step iii). Transfer the prepolymer product obtained in Step ii) to a horizontal reactor equipped with a stirrer, and carry out a polycondensation reaction at 245 °C and a pressure of 2.1 mbar for 90 minutes. The acid value of the obtained biodegradable aliphatic polyester is 58.2 mol / t, and the melt index is 15.2 g / 10 min (the test standard and conditions are ISO 1133-2-2011, 190 °C, 2.16 kg).

[0129] Comparative Example 3

[0130] A biodegradable aliphatic polyester is prepared by the following preparation method:

[0131] Step i). Physically mix 350 kg of succinic acid, 143 kg of adipic acid, 680 kg of 1,4-butanediol and 1.8 kg of glycerol. After the mixing is completed, transfer the mixture to an esterification reactor. The reaction mixture undergoes an esterification reaction at a temperature of 210 °C and a pressure of 0.8 bar for 3 hours. The acid value of the obtained esterified product is 327 mol / t;

[0132] Step ii). Transfer the esterification product obtained in Step i) to a vertical reactor equipped with a stirrer, add 0.28 kg of tetrabutyl titanate, and carry out a prepolycondensation reaction on the reaction mixture at 240 °C and a reactor internal pressure of 0.75 bar for 80 minutes. The acid value of the obtained prepolymer product is 112 mol / t;

[0133] Step iii). Transfer the prepolymer product obtained in Step ii) to a horizontal reactor equipped with a stirrer, and carry out a polycondensation reaction at 250 °C and a pressure of 1.4 mbar for 50 minutes. The acid value of the obtained polycondensation product is 21.3 mol / t;

[0134] Step iv). Introduce the polycondensation product obtained in Step iii) into a static mixer, add 2.0 kg of hexamethylene diisocyanate, and carry out a blending reaction at 220 °C for 10 min. The acid value of the obtained biodegradable aliphatic polyester is 23.1 mol / t, and the melt index is 4.4 g / 10 min (the test standard is ISO 1133-2-2011, 190 °C, 2.16 kg).

[0135] The physical property parameters and performances of the biodegradable aliphatic polyesters in Examples 1-7 and Comparative Examples 1-3 are shown in Table 1 and Table 2.

[0136] Table 1 Physical Property Parameters of the Biodegradable Aliphatic Polyesters in Each Example and Comparative Example

[0137]

[0138] Table 2 Performances of the Biodegradable Aliphatic Polyesters in Each Example and Comparative Example

[0139]

[0140]

[0141] According to the data in Table 2, it can be known that the water vapor transmission rate of the biodegradable aliphatic polyesters in Examples 1-7 is less than 750 g / (d·m 2 ), and at the same time, the shear peel strength reaches 0.60 N / cm 2 or above, indicating that the biodegradable aliphatic polyester of the present invention not only has good barrier properties, but also has excellent self-adhesion.

[0142] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A biodegradable aliphatic polyester, characterized in that, The biodegradable aliphatic polyester contains units derived from at least one aliphatic dicarboxylic acid and at least one aliphatic diol, and satisfies the following conditions: 1.54 ≤ Mw / Mn ≤ 1.98, Mw / q ≥ 50000; wherein q is the mass percentage of the low molecular weight polymer with a molecular weight ≤ 1000 Dalton of the biodegradable aliphatic polyester determined by GPC; The aliphatic dicarboxylic acid is succinic acid and / or adipic acid; the aliphatic diol is 1,4-butanediol and / or 1,3-propanediol.

2. The biodegradable aliphatic polyester according to claim 1, wherein The Mw / Mn is 1.65 to 1.85, and 70000 ≤ Mw / q ≤ 110000.

3. The biodegradable aliphatic polyester according to claim 1, wherein The biodegradable aliphatic polyester contains the following components: A) Aliphatic dicarboxylic acid component: a1) 65 to 100 mol% of succinic acid or its ester derivative, or a mixture thereof, based on the total amount of a1) and a2); a2) 0 to 35 mol% of adipic acid or its ester derivative, or a mixture thereof, based on the total amount of a1) and a2), wherein the total molar percentage of components a1) and a2) is 100 mol%; B) The aliphatic diol component is 1,4-butanediol, and its molar ratio to the aliphatic dicarboxylic acid component is ≥ 1.

4. The biodegradable aliphatic polyester according to claim 3, wherein a1) in the aliphatic dicarboxylic acid component is 73 to 80 mol% of succinic acid or its ester derivative, or a mixture thereof; a2) in the aliphatic dicarboxylic acid component is 20 to 27 mol% of adipic acid or its ester derivative, or a mixture thereof.

5. The biodegradable aliphatic polyester according to any one of claims 1 to 4, characterized in that The biodegradable aliphatic polyester, under the conditions of a sample thickness of 12 ± 2 μm, 40 °C, and RH = 60%, is measured to have a water vapor transmission rate ≤ 750 g / (d·m 2 ) according to the ASTM F1249-13 standard; 6. The biodegradable aliphatic polyester according to claim 5, wherein The water vapor transmission rate ≤ 480 g / (d·m 2 ).

7. The biodegradable aliphatic polyester according to claim 6, characterized in that, The water vapor transmission rate ≤ 330 g / (d·m 2 ).

8. The biodegradable aliphatic polyester according to any one of claims 1 to 4, characterized in that, The biodegradable aliphatic polyester, according to the standard of GB / T 10457-2009, under the condition that the sample thickness is 12±2μm, the shear peel strength ≥ 0.6N / cm 2 .

9. The biodegradable aliphatic polyester according to claim 8, wherein, The shear peeling strength ≥ 0.72 N / cm 2 .

10. The biodegradable aliphatic polyester according to claim 9, wherein, The shear peel strength ≥ 0.85 N / cm 2 .

11. A method for preparing the biodegradable aliphatic polyester according to any one of claims 1 to 10, characterized in that, Comprising the following steps: Step i): Mix the aliphatic dicarboxylic acid or its derivative with the aliphatic diol and then carry out an esterification reaction or a transesterification reaction to obtain an esterification product; Step ii): Carry out a prepolymerization reaction on the esterification product in step i) to obtain a prepolymer product; Step iii): Carry out a polycondensation reaction on the prepolymer product in step ii) until the acid value of the formed polycondensation product measured according to the GB / T32366-2015 standard is 15 to 50 mol / t, thereby obtaining the biodegradable aliphatic polyester; wherein the acid value of the esterification product in step i) measured according to the GB / T 32366-2015 standard is 360 to 770 mol / t; the acid value of the prepolymer product in step ii) measured according to the GB / T 32366-2015 standard is 70 to 110 mol / t.

12. Use of the biodegradable aliphatic polyester according to any one of claims 1 to 10 in the preparation of food packaging films, industrial packaging films or agricultural mulch films.

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