Aliphatic polyester, polyester composition containing aliphatic polyester and application of aliphatic polyester

Abstract

The invention provides aliphatic polyester, a polyester composition containing the aliphatic polyester and application of the aliphatic polyester. The aliphatic polyester comprises dibasic acid residues, dihydric alcohol residues and branching agent residues. The diacid residues comprise the following residues: a1) 71-89 mol% of succinic acid residues based on 100 mol% of the total mole percentage content of a1) and a2); a2), 11-29 mol% of sebacic acid residues based on 100 mol% of the total mole percentage of a1) and a2); the dihydric alcohol residues are selected from 1, 4-butanediol residues which are at least equal to the dibasic acid residues in molar weight; when the total mass of the aliphatic polyester is 100 wt%, the mass percentage content of the branching agent residues is 0.09-0.22 wt%. The aliphatic polyester solves the problem of low heat sealing strength of aliphatic polyester.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyester materials, and particularly relates to an aliphatic polyester, a polyester composition containing the same, and their applications. Background Art

[0002] Biodegradable polyesters obtained from dicarboxylic acids and diols not only have biodegradable properties, but also have good extensibility and certain mechanical properties, and have properties similar to low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). Therefore, they are widely used in packaging bag fields such as shopping bags, express delivery bags, and fruit and vegetable bags.

[0003] For packaging bags, in order to meet the use requirements, heat sealing treatment is usually required during the processing. The quality of heat sealing directly affects whether the packaging bag is prone to edge bursting or bottom penetration during use. Heat seal strength is a key index for evaluating the quality of heat sealing. In addition to being affected by heat sealing processes (heat sealing time, temperature, pressure), the magnitude of heat seal strength is also closely related to the structure of the material itself. For aliphatic-aromatic polyesters, such as poly(butylene adipate-co-terephthalate) (PBAT), although they have relatively good mechanical properties, due to the presence of aromatic dicarboxylate chain segments, on the one hand, it will lead to poor degradation performance of the polyester material; on the other hand, it will lead to a relatively high melting point of the polyester, and the relatively high melting point requires a relatively high heat sealing temperature (usually exceeding 135 °C) during heat sealing. However, the too high heat sealing temperature will, on the one hand, cause the molecular chains of the material to diffuse faster, and within a relatively short heat sealing time, the molecular chain entanglement between interfaces is limited, thus reducing the heat seal strength; on the other hand, due to the too high temperature, the material undergoes a certain degree of thermal degradation during the heat sealing process, further reducing the heat seal strength.

[0004] For aliphatic polyesters, such as poly(butylene sebacate), although they have good degradation performance, no aromatic structure, and a low melting point, and do not require a relatively high heat sealing temperature to avoid the influence of heat sealing temperature on heat seal strength; however, the heat seal strength of aliphatic polyesters themselves is relatively low, which affects the performance of packaging bags and production efficiency.

[0005] Therefore, developing an aliphatic polyester with high heat seal strength is an urgent problem to be solved in this field. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an aliphatic polyester, a polyester composition containing the same, and their applications. The aliphatic polyester solves the problem that the low heat seal strength of aliphatic polyesters in the existing technology leads to easy edge bursting or bottom penetration of packaging bags.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an aliphatic polyester, which comprises dibasic acid residues, diol residues and branching agent residues; the dibasic acid residues comprise the following residues: a1), based on the total molar percentage content of a1) and a2) being 100 mol%, 71 to 89 mol% of succinic acid residues; a2), based on the total molar percentage content of a1) and a2) being 100 mol%, 11 to 29 mol% of sebacic acid residues; the diol residues are selected from 1,4-butanediol residues with at least an equimolar amount to the dibasic acid residues; the branching agent residues are derived from a branching agent with a functionality ≥ 3; based on the total mass of the aliphatic polyester being 100 wt%, the mass percentage content of the branching agent residues is 0.09 to 0.22 wt%.

[0009] In the present invention, by controlling the molar contents of succinic acid residues and sebacic acid residues within a specific range, while ensuring the mechanical properties, heat resistance and degradation properties of the aliphatic polyester, the melting point of the aliphatic polyester can be reduced (the melting point is lower than 100 °C), and the heat sealing temperature can be reduced, which is beneficial to improving the heat sealing strength; by including branching agent residues and controlling the content of the branching agent residues within a specific range, an aliphatic polyester with a specific branching structure can be formed, further improving the heat sealing strength of the aliphatic polyester; enabling the packaging bag including the aliphatic polyester to have a high heat sealing strength, avoiding problems such as bursting edges or bottom penetration of the packaging bag, and improving production efficiency.

[0010] It should be noted that the "residue" refers to any organic structure introduced into the polymer molecular chain by the relevant monomer through a polycondensation reaction, that is, an organic structure derived from the relevant monomer; for example, the dibasic acid residue refers to the structure derived from the dibasic acid monomer in the aliphatic polyester.

[0011] In the present invention, succinic acid and / or succinic acid derivatives are introduced into the polyester molecular chain through a polymerization reaction to form succinic acid residues; sebacic acid and / or sebacic acid derivatives are introduced into the polyester molecular chain through a polymerization reaction to form sebacic acid residues; if the content of succinic acid residues is too low or the content of sebacic acid residues is too high, the crystallization rate is slow, the strength is low, and the heat resistance is poor; if the content of succinic acid residues is too high or the content of sebacic acid residues is too low, the melting point is high, the heat sealing temperature is high, and the degradation property is poor.

[0012] In the present invention, the succinic acid derivatives include alkyl succinates. Exemplarily, the alkyl succinates can be at least one of dimethyl succinate, diethyl succinate, di-n-propyl succinate, di-isopropyl succinate, di-n-butyl succinate, di-isobutyl succinate, di-tert-butyl succinate, di-n-pentyl succinate, di-isopentyl succinate, and di-n-hexyl succinate; the alkyl succinates can be alkyl esters formed by succinic acid or alkyl esters formed by succinic anhydride, and preferably dimethyl succinate formed by succinic anhydride is used.

[0013] In the present invention, the sebacic acid derivative includes an alkyl sebacate; exemplarily, the alkyl sebacate may be at least one of dimethyl sebacate, diethyl sebacate, di-n-propyl sebacate, di-isopropyl sebacate, di-n-butyl sebacate, di-isobutyl sebacate, di-tert-butyl sebacate, di-n-pentyl sebacate, di-isopentyl sebacate, and di-n-hexyl sebacate; the alkyl sebacate may be an alkyl ester formed from sebacic acid or an alkyl ester formed from sebacic anhydride.

[0014] Preferably, the dibasic acid residue includes the following residues: a1), based on the total molar percentage content of a1) and a2) being 100 mol%, 74 to 83 mol% of succinic acid residue; a2), based on the total molar percentage content of a1) and a2) being 100 mol%, 17 to 26 mol% of sebacic acid residue; more preferably a1), based on the total molar percentage content of a1) and a2) being 100 mol%, 74 to 80 mol% of succinic acid residue; a2), based on the total molar percentage content of a1) and a2) being 100 mol%, 20 to 26 mol% of sebacic acid residue.

[0015] In the present invention, the mass percentage content of the branching agent residue is 0.09 - 0.22 wt%, for example, it can be 0.09 wt%, 0.092 wt%, 0.094 wt%, 0.098 wt%, 0.1 wt%, 0.102 wt%, 0.104 wt%, 0.106 wt%, 0.108 wt%, 0.11 wt%, 0.112 wt%, 0.114 wt%, 0.116 wt%, 0.118 wt%, 0.12 wt%, 0.122 wt%, 0.124 wt%, 0.126 wt%, 0.128 wt%, 0.13 wt%, 0.132 wt%, 0.134 wt%, 0.136 wt%, 0.138 wt%, 0.14 wt%, 0.142 wt%, 0.144 wt%, 0.146 wt%, 0.148 wt%, 0.15 wt%, 0.152 wt%, 0.154 wt%, 0.156 wt%, 0.158 wt%, 0.16 wt%, 0.162 wt%, 0.164 wt%, 0.166 wt%, 0.168 wt%, 0.17 wt%, 0.172 wt%, 0.175 wt%, 0.178 wt%, 0.18 wt%, 0.182 wt%, 0.185 wt%, 0.188 wt%, 0.19 wt%, 0.192 wt%, 0.195 wt%, 0.198 wt%, 0.2 wt%, 0.202 wt%, 0.205 wt%, 0.208 wt%, 0.21 wt%, 0.212 wt%, 0.215 wt%, 0.218 wt%, 0.22 wt% or the range between any of the above values. Preferably, the mass of the branching agent residue is 0.11 - 0.17 wt%.

[0016] In the aliphatic polyester of the present invention, the content of the branching agent residue can be tested by a liquid chromatography - mass spectrometry (LC - MS).

[0017] In the present invention, the addition of the polyfunctional branching agent causes the structure of the aliphatic polyester to change from a linear polyester to a branched polyester. As the addition amount of the branching agent increases, the number of molecules with long and short branches in the molecular chain segment increases. During the heat - sealing process, entanglement is more likely to occur at the interface, improving the heat - sealing strength. However, when the addition amount of the branching agent is too large, the crystallization rate of the polyester increases significantly, and the crystallinity increases. After the crystallization degree increases, more energy is required during the heat - sealing process to cause the material to melt and complete the heat - sealing. Therefore, too much branching agent content will instead lead to a decrease in the heat - sealing strength.

[0018] Preferably, at least one of hydroxyl, carboxyl or anhydride is contained in the molecular structure of the branching agent.

[0019] Preferably, the branching agent includes at least one of polyols, polyacids, polyol acids or polyacid anhydrides, and is further preferably a polyol.

[0020] Preferably, the polyol includes at least one of trimethylolpropane, trimethylolethane, pentaerythritol, polyether triol or glycerol.

[0021] Preferably, the polyacid includes at least one of 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid or 1,2,4,5-benzenetetracarboxylic acid.

[0022] Preferably, the polyol acid includes at least one of tartaric acid, citric acid or malic acid.

[0023] In the present invention, the polyol acid refers to a molecule structure containing at least one hydroxyl group and at least one carboxyl group.

[0024] Preferably, the polyacid anhydride includes 1,2,4-benzenetricarboxylic anhydride and / or pyromellitic dianhydride.

[0025] Preferably, the molecular weight distribution coefficient of the aliphatic polyester is 1.3 to 2.8, for example, it can be 1.3, 1.4, 1.5, 1.52, 1.54, 1.56, 1.58, 1.6, 1.62, 1.64, 1.66, 1.68, 1.7, 1.72, 1.74, 1.76, 1.78, 1.8, 1.82, 1.84, 1.86, 1.88, 1.9, 1.92, 1.94, 1.96, 1.98, 2, 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 2.6, 2.7, 2.8 or the range between any of the above values, and is further preferably 1.5 to 2.5.

[0026] In the present invention, the molecular weight distribution coefficient is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn); Mw and Mn can be obtained by testing with a gel permeation chromatograph, and then calculated. The branching agent and its content will affect the molecular weight distribution coefficient. When the content of the branching agent increases, the molecular weight distribution coefficient of the polyester becomes wider; in addition, the alcohol-acid ratio and polymerization conditions (such as temperature, time, pressure, etc.) will also affect the molecular weight distribution coefficient.

[0027] Preferably, at 190 °C and 2.16 kg, the melt flow rate of the aliphatic polyester is 1.2 to 10 g / 10 min, for example, it can be 1.2 g / 10 min, 1.4 g / 10 min, 1.6 g / 10 min, 1.8 g / 10 min, 2 g / 10 min, 2.2 g / 10 min, 2.4 g / 10 min, 2.6 g / 10 min, 2.8 g / 10 min, 3 g / 10 min, 3.2 g / 10 min, 3.4 g / 10 min, 3.6 g / 10 min, 3.8 g / 10 min, 4 g / 10 min, 4.2 g / 10 min, 4.4 g / 10 min, 4.6 g / 10 min, 4.8 g / 10 min, 5 g / 10 min, 5.2 g / 10 min, 5.4 g / 10 min, 5.6 g / 10 min, 5.8 g / 10 min, 6 g / 10 min, 6.2 g / 10 min, 6.5 g / 10 min, 6.8 g / 10 min, 7 g / 10 min, 7.2 g / 10 min, 7.5 g / 10 min, 7.8 g / 10 min, 8 g / 10 min, 8.2 g / 10 min, 8.5 g / 10 min, 8.8 g / 10 min, 9 g / 10 min, 9.2 g / 10 min, 9.5 g / 10 min, 9.8 g / 10 min, 10 g / 10 min or the range between any of the above values; more preferably, the melt flow rate is 2.2 to 6 g / 10 min.

[0028] In the present invention, the melt flow rate is tested according to the standard ISO 1133-2-2012, and the test conditions are 190 °C and 2.16 kg.

[0029] In the present invention, considering the hydrolysis resistance, aging resistance, biodegradability and cost, it is preferred that the carboxyl content of the aliphatic polyester is < 50 mol / t, more preferably the carboxyl content is < 30 mol / t, and particularly preferably the carboxyl content is < 15 mol / t.

[0030] In the present invention, the carboxyl content is obtained by testing according to GB / T 32366-2015; the carboxyl content can be controlled by changing conditions such as the acid-alcohol ratio, polymerization temperature, and polymerization time; in addition, the carboxyl content can also be controlled by inhibiting the types or amounts of impurities in raw materials such as nitrogen compounds and metal ions.

[0031] In the present invention, the preparation method of the aliphatic polyester is not particularly limited, and any method that can prepare the aliphatic polyester with a specific branched structure of the present invention is acceptable; preferably, the preparation method of the aliphatic polyester includes the following steps:

[0032] (1) React a dibasic acid, a diol and a branching agent to obtain an esterification product;

[0033] (2) Carry out a prepolymerization reaction on the esterification product obtained in step (1) to obtain a prepolymer product;

[0034] (3) Carry out a polycondensation reaction on the prepolymer product obtained in step (2) to obtain the aliphatic polyester.

[0035] In the present invention, the dibasic acid can be used alone or as a mixture of at least two kinds.

[0036] In the present invention, the molar ratio of the diol to the dibasic acid is (1.2 - 3):1. For example, it can be 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1 or the range between any of the above values. More preferably, it is (1.4 - 2):1.

[0037] In the present invention, the reaction in step (1) includes an esterification reaction and / or a transesterification reaction; the temperature of the reaction is 150 - 220 °C, the pressure is 0.7 - 1.2 bar, and the time is 2 - 7 h. Further preferably, the temperature of the reaction is 158 - 215 °C, the pressure is 0.75 - 1.15 bar, and the time is 2.5 - 6 h.

[0038] In the present invention, step (1) can be carried out in a mixing device. Mix the dibasic acid, diol and branching agent to obtain a reaction material mixture, and then raise the temperature to carry out the reaction.

[0039] In the present invention, the carboxyl content of the esterification product in step (1) ≤ 350 mol / t.

[0040] In the present invention, after the reaction in step (1), it further includes a step of removing the excessive diol by distillation. The removed diol can be purified by distillation and reused as a raw material. The purity of the purified diol ≥ 95%.

[0041] In the present invention, the temperature of the prepolymerization reaction in step (2) is 230 - 260 °C, the pressure is 0.3 - 0.8 bar, and the time is 70 - 200 min; further preferably, the temperature of the reaction is 235 - 245 °C, the pressure is 0.4 - 0.75 bar, and the time is 78 - 130 min.

[0042] In the present invention, step (2) can be carried out in a prepolymerization reactor.

[0043] In the present invention, the carboxyl content of the prepolymer product in step (2) ≤ 80 mol / t.

[0044] In the present invention, the temperature of the polycondensation reaction in step (3) is 230 - 260 °C, the pressure is 0.2 - 5 mbar, and the time is 35 - 120 min; more preferably, the reaction temperature is 238 - 255 °C, the pressure is 0.45 - 3 mbar, and the time is 40 - 115 min.

[0045] In the present invention, step (3) can be carried out in a finishing machine suitable for polycondensation reaction, such as a rotary reactor, a cage reactor, a horizontal reactor, etc.

[0046] In the present invention, the reaction in step (2) is carried out in the presence of a catalyst; the catalyst can be a tin compound, an antimony compound, a cobalt compound, a lead compound, a zinc compound, an aluminum compound or a titanium compound, more preferably a zinc compound, an aluminum compound or a titanium compound, and most preferably a titanium compound; the titanium compound can be tetrabutyl titanate or tetraisopropyl titanate; the titanium compound has less residue and lower toxicity in the product or downstream products compared with other compounds. It is particularly suitable for preparing biodegradable polyesters and can directly enter the environment in the form of compost bags or mulch films.

[0047] In the present invention, based on the total mass of the dicarboxylic acid, diol and branching agent being 100 wt%, the total mass of the catalyst is 0.001 - 1 wt%.

[0048] In the present invention, other additives can be added during the reaction in step (3) according to actual needs; the other additives include but are not limited to catalyst passivators, etc.

[0049] The catalyst passivator includes but is not limited to phosphorus compounds; the phosphorus compounds include but are not limited to one or more of phosphorous acid and phosphoric acid; based on the mass of the prepolymer being 100 wt%, the mass of the catalyst passivator is 0.001 - 0.1 wt%, preferably 0.01 - 0.05 wt%. Exemplarily, when a highly active titanium compound is selected as the catalyst, a catalyst passivator can be added, wherein the molar ratio of Ti to P is (1.1 - 1.5):1, and particularly preferably the molar ratio of Ti to P is (1.1 - 1.3):1.

[0050] In the present invention, after the polycondensation reaction, a chain growth reaction is further included, that is, reacting the product obtained from the polycondensation reaction (polycondensate) with a chain extender to obtain the aliphatic polyester.

[0051] In the present invention, the chain extender includes one or several of isocyanate, peroxide, epoxide, oxazoline, oxazine, caprolactam or carbodiimide.

[0052] In the present invention, the isocyanate may be an aromatic diisocyanate and / or an aliphatic diisocyanate, and the aromatic diisocyanate may be 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; diphenylmethane 2,2′-diisocyanate, diphenylmethane 2,4′-diisocyanate or diphenylmethane 4,4′-diisocyanate is particularly preferred. The aromatic diisocyanate may also be a polynuclear aromatic diisocyanate, such as tris(4-isocyanato-phenyl)methane with three rings, which may be formed in the process of producing a diisocyanate with one or two rings. The aliphatic diisocyanate may be a linear or branched alkylene diisocyanate containing 2 to 20 carbon atoms or a cycloalkylene diisocyanate containing 3 to 20 carbon atoms; for example, the aliphatic diisocyanate includes hexamethylene diisocyanate, pentamethylene diisocyanate, isophorone diisocyanate or methylene di(4-isocyanatocyclohexane) diisocyanate. Hexamethylene diisocyanate is particularly preferred.

[0053] In the present invention, based on the total mass of the polycondensation product, the mass of the isocyanate may be 0.05 to 2 wt %, particularly preferably 0.1 to 1.5 wt %.

[0054] In the present invention, the peroxide can be one or more of benzoyl peroxide, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-butylperoxy)methylcyclododecane, 4,4-di(butylperoxy)butyl valerate, dicumyl peroxide, tert-butyl peroxybenzoate, dibutyl peroxide, α,α-di(tert-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hex-3-yne or tert-butyl peroxide cumene.

[0055] In the present invention, based on the total mass of the polycondensation product, the mass of the peroxide may be 0.1 to 2 wt %, particularly preferably 0.2 to 1 wt %.

[0056] In the present invention, the epoxide may be one or more 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.

[0057] In the present invention, based on the total mass of the polycondensation product, the mass of the epoxide may be 0.1 to 2 wt%, preferably 0.2 to 1 wt%.

[0058] In the present invention, the oxazoline may be selected from one or more of 2,2′-bis(2-oxazoline), bis(2-oxazolinyl)methane, 1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane, 1,4-bis(2-oxazolinyl)butane, 1,4-bis(2-oxazolinyl)benzene, 1,2-bis(2-oxazolinyl)benzene or 1,3-bis(2-oxazolinyl)benzene. The oxazine may be selected from one or more of 2,2′-bis(2-dioxazine), bis(2-dioxazinyl)methane, 1,2-bis(2-dioxazinyl)ethane, 1,3-bis(2-dioxazinyl)propane, 1,4-bis(2-dioxazinyl)butane, 1,4-bis(2-dioxazinyl)benzene, 1,2-bis(2-dioxazinyl)benzene or 1,3-bis(2-dioxazinyl)benzene. The carbodiimide may be selected from one or more 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.

[0059] In the present invention, based on the total mass of the polycondensation product, the mass of the oxazoline, oxazine, caprolactam and carbodiimide is independently 0.1 to 2 wt%, preferably 0.2 to 1 wt%.

[0060] In the present invention, the temperature of the chain growth reaction is 170 - 240 °C, more preferably 180 - 220 °C; it is carried out under superatmospheric pressure or atmospheric pressure, varying with the system used.

[0061] In the present invention, the chain growth reaction can be carried out in an extruder, a continuous kneader (List reactor) or a static mixer. The extruder can be a single-screw extruder or a twin-screw extruder; for the static mixer, SMR, SMX or SMXL components, or a combination thereof can be used. Examples of the List reactor are a single-shaft DISCOTHERM B or a twin-shaft CRP or ORP reactor. Preferably, the chain growth reaction is carried out in an extruder, and the residence time in the extruder is 2 - 15 min, more preferably 4 - 12 min.

[0062] In the present invention, the aliphatic polyester can also be prepared by the following method: in step (1), succinic acid and / or succinic acid derivatives and sebacic acid and / or sebacic acid derivatives are respectively reacted with 1,4-butanediol to obtain two esterification products, and then the two esterification products are subjected to subsequent prepolymerization reaction, polycondensation reaction, and optional chain growth reaction.

[0063] Exemplarily, the preparation method specifically includes the following steps:

[0064] Step (1-1): React succinic acid and / or succinic acid derivatives, 1,4-butanediol with a branching agent at a temperature of 150 - 195 °C and a pressure of 0.7 - 1.1 bar for 2 - 6 h to obtain an esterification product A with a carboxyl content of 320 - 480 mol / t;

[0065] Step (1-2): React sebacic acid and / or sebacic acid derivatives with 1,4-butanediol at a temperature of 180 - 220 °C and a pressure of 0.6 - 1.1 bar for 2 - 6 h to obtain an esterification product B with a carboxyl content of 240 - 400 mol / t; then mix the esterification product A and the esterification product B and carry out prepolymerization reaction, polycondensation reaction and optional chain growth reaction; wherein, the conditions of the prepolymerization reaction, polycondensation reaction and optional chain growth reaction are selected from the same ranges as in step (2), step (3) and the aforementioned chain growth reaction.

[0066] In the present invention, the source of the succinic acid and / or succinic acid derivatives is not particularly limited, and it can be succinic acid and / or succinic acid derivatives derived from bio-based (i.e., the preparation raw material is biomass resources), or succinic acid and / or succinic acid derivatives derived from petroleum-based (i.e., the preparation raw material is petroleum resources).

[0067] In the second aspect, the present invention provides a polyester composition, which includes the biodegradable aliphatic polyester described in the first aspect.

[0068] Preferably, the polyester composition further comprises at least one of a second polymer, a filler or an additive.

[0069] Preferably, the second polymer comprises at least one of polylactic acid, polycaprolactone, polyhydroxyalkanoate, aliphatic polycarbonate or aliphatic-aromatic polyester (such as polybutylene terephthalate-adipate, polybutylene terephthalate-sebacate, etc.).

[0070] In the present invention, according to the standard ISO 1133-2-2012, at 190 °C and 2.16 kg, the melt flow rate of the second polymer is 0.5-50 g / 10 min.

[0071] Preferably, the filler comprises an inorganic filler and / or an organic filler.

[0072] In the present invention, the organic filler includes but is not limited to starch and / or cellulose; the starch can also be used in the form of allosteric and gelatinized forms. The starch can represent a continuous phase or a dispersed phase, and can be in a co-continuous form. The inorganic filler includes but is not limited to at least one of talcum powder, calcium carbonate, montmorillonite.

[0073] In the prior art, in order to improve the heat seal strength of the packaging bag, it is usually achieved by reducing the content of the filler in the polyester composition, and the reduction of the filling amount leads to an increase in the material cost; while the aliphatic polyester of the present invention, the polyester composition for filler filling, can not only improve the heat seal strength of the packaging bag, but also reduce the material cost.

[0074] In the present invention, the additive can be added according to actual needs, including but not limited to compatibilizers, antioxidants, lubricants, mold release agents, etc.; the compatibilizers include but are not limited to maleic anhydride grafted polyethylene, maleic anhydride grafted polyolefin elastomer, maleic anhydride grafted styrene-acrylonitrile copolymer, etc.; the antioxidants include but are not limited to any one of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant 164, antioxidant DLTP or antioxidant TPP; the lubricants include but are not limited to esters (such as polyethylene glycol esters, polyol esters), lignite salts, ethylene bisstearamide or polyethylene wax; the mold release agents include but are not limited to at least one of inorganic mold release agents (such as talcum powder, mica powder, clay, etc.), organic mold release agents (such as fatty acids, paraffin wax, glycerol, vaseline, etc.) or polymer mold release agents (such as silicone oil, polyethylene glycol, low molecular weight polyethylene, etc.).

[0075] As a preferred technical solution of the present invention, in parts by weight, the polyester composition comprises 50-70 parts (for example, it can be 50 parts, 55 parts, 60 parts, 65 parts, 70 parts or the range between any of the above values, preferably 52-68 parts, more preferably 58-66 parts) of the biodegradable aliphatic polyester described in the first aspect, 4-20 parts (for example, it can be 4 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts or the range between any of the above values, preferably 4.5-10.5 parts) of the second polymer, 15-35 parts (for example, it can be 15 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 25 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts, 35 parts or the range between any of the above values, preferably 17-27 parts) of the filler, and 0-15 parts (for example, it can be 1 part, 2 parts, 4 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 15 parts or the range between any of the above values) of the auxiliary agent.

[0076] In the present invention, the preparation method of the polyester composition comprises: mixing the biodegradable aliphatic polyester, the second polymer, the filler and optionally the auxiliary agent, and extruding to obtain the polyester composition; the extruder comprises a reactive extruder, and the extruder can be a single-screw extruder, a twin-screw extruder or a multi-screw extruder; the extrusion temperature is 140-220°C, and the rotation speed of the screw during extrusion is 200-500 rpm.

[0077] In the third aspect, the present invention provides a packaging bag, and the raw materials for preparing the packaging bag comprise the aliphatic polyester described in the first aspect or the polyester composition described in the second aspect.

[0078] In the present invention, other substances such as colorants can be added to the raw materials for preparing the packaging bag according to needs.

[0079] Preferably, the heat seal strength of the packaging bag ≥ 15 N / 15 mm, more preferably the heat seal strength ≥ 17.5 N / 15 mm, and particularly preferably the heat seal strength ≥ 21 N / 15 mm.

[0080] In the present invention, the heat seal strength of the packaging bag is obtained by testing the packaging bag obtained by setting the blown film processing temperature of the aliphatic polyester at 140°C, standing and adjusting for 24 h under the conditions of 25 ± 5°C and 55 ± 5% humidity according to the standard QB / T 2358-1998; specifically, the heat seal process is: the heat seal temperature is 100-130°C, the heat seal time is 1-5 s, and the heat seal pressure is 200-400 KPa.

[0081] In the present invention, the packaging bag includes shopping bags, express delivery bags, fruit and vegetable bags, etc.

[0082] The aliphatic polyesters, polyester compositions, and packaging films prepared therefrom according to the present invention are all biodegradable.

[0083] For the present invention, a substance or mixture of substances has the characteristic of "biodegradable" if it shows a degree of biodegradation percentage of at least 90%, as defined in DIN EN 13432.

[0084] 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 represented 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). After only a few days of composting, biodegradable polyesters and biodegradable polyester compositions usually show obvious signs of degradation, such as fungal growth, cracking, and perforation.

[0085] Other methods for determining biodegradability are also described in ASTM D5338 and ASTM D6400.

[0086] The numerical ranges described in the present invention not only include the point values listed above, but also any point values between the above numerical ranges not listed. Due to space limitations and for the sake of brevity, the specific point values included in the described ranges are not exhaustively listed in the present invention.

[0087] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0088] The aliphatic polyester provided by the present invention can improve the heat-sealing strength of the aliphatic polyester by controlling the molar contents of succinic acid residues and sebacic acid residues within a specific range, introducing branching agent residues, and controlling the content of branching agent residues within a specific range; enabling the packaging bags prepared from the aliphatic polyester to also have a high heat-sealing strength, avoiding problems such as bursting edges or bottom perforations of the packaging bags, and improving production efficiency. Specific Embodiments

[0089] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0090] In the present invention, the materials used can all be purchased commercially or prepared by conventional methods. Unless otherwise specified, the materials used in the present invention are as follows.

[0091] 1,4-Butanediol: Purchased from Xinjiang Meike Chemical Industry Co., Ltd.

[0092] Succinic acid: Purchased from Shandong Landian Biotechnology Co., Ltd.

[0093] Sebacic acid: Purchased from Hengshui Jinghua Chemical Co., Ltd.

[0094] Glycerol, pentaerythritol and tartaric acid: All purchased from Aladdin.

[0095] Tetrabutyl titanate: Purchased from Jianyi Chemical Import and Export Co., Ltd.

[0096] In the present invention, the test methods for the molecular weight distribution coefficient, melt flow rate, carboxyl content, molar percentage content of succinic acid residues and sebacic acid residues in the aliphatic polyester, and mass percentage content of branching agent residues are as follows.

[0097] 1. Molecular weight distribution coefficient: Tested by gel permeation chromatography (GPC); specifically: Using a chromatographic system at 40 °C, with a set of three columns in series (particle diameter of 5 μm and porosities of and ) and a refractive index detector, using chloroform as the eluent (elution flow rate of 1 mL / min), and polystyrene as the reference standard for determination to obtain Mw and Mn, and the molecular weight distribution coefficient = Mw / Mn; where the instrument model is: Waters1515 GPC, and the sample preparation method is: directly dissolve the aliphatic polyester in chromatographic grade THF to prepare a 1 mg / mL solution for testing.

[0098] 2. Melt flow rate: Tested according to standard ISO 1133-2-2012, and the test conditions are 190 °C and 2.16 kg.

[0099] 3. Carboxyl content: The test is carried out with reference to standard GB / T 32366-2015 as follows. Dissolve 1 g of the sample in 50 mL of a mixed solvent of phenol and chloroform with a volume ratio of 2:3; use an ethanol solution of potassium hydroxide with a concentration of 0.01 mol / L as the standard titrant, and a bromophenol blue solution with a concentration of 0.2% as the indicator; carry out a blank test according to the method of testing the carboxyl content of the above sample; the sample is tested in parallel twice, and the difference between the two test results is required to be less than or equal to 2 mol / t, and the final result is the average of the two test results.

[0100] 4. Molar percentage content: Tested by 1 the HNMR method; specifically: Take 20 mg of the aliphatic polyester sample and dissolve it in 0.6 mL of deuterated chloroform, and then use a Bruker AV 500 nuclear magnetic resonance spectrometer to measure its 11H NMR; Integrate the characteristic chemical shift peaks of succinic acid residues and sebacic acid residues (the characteristic chemical shift of succinic acid residues is about 2.63 ppm, representing 4 hydrogens on the two methylene groups -CH2-CH2- in succinic acid; the characteristic chemical shift of sebacic acid residues is about 1.30 ppm, representing 8 hydrogens on the four methylene groups -CH2-CH2-CH2-CH2- in the middle of sebacic acid). The respective molar percentages of succinic acid residues and sebacic acid residues in the aliphatic polyester are obtained based on the total molar percentage of 100 mol% of succinic acid residues and sebacic acid residues through the proportion of the peak areas. For example, if the integrated area of succinic acid residues is I1 and the integrated area of sebacic acid residues is I2, then the molar percentage of succinic acid residues in the aliphatic polyester based on the total molar percentage of 100 mol% of succinic acid residues and sebacic acid residues is I1 / (I1 + I2)×100%.

[0101] 5. Mass percentage of branching agent residues in the aliphatic polyester: Tested by LC-MS method. Specifically, take 0.5 - 1.5 g of the sample and add it to a three-necked flask, add 30 ml of 1 mol / L potassium hydroxide ethanol solution, carry out alkaline hydrolysis under reflux conditions until the aliphatic polyester is completely hydrolyzed. After cooling, filter under vacuum. Adjust a part of the filtrate to neutral with concentrated hydrochloric acid, dry it with anhydrous sodium sulfate, filter again, and perform qualitative and quantitative analysis of the branching agent residues on the filtrate by LC-MS.

[0102] Examples 1 - 17, Comparative Examples 1 - 5

[0103] Examples 1 - 17 and Comparative Examples 1 - 5 respectively provide an aliphatic polyester. The composition of the dibasic acid residues, the specific types and contents of the branching agent residues of the aliphatic polyester are shown in Table 1; among them, the content of the branching agent residues is based on 100 wt% of the mass of the aliphatic polyester. The molecular weight distribution coefficient, melt flow rate, and carboxyl content of the aliphatic polyester are shown in Table 1.

[0104] The preparation methods of the aliphatic polyesters provided in Examples 1 - 17 and Comparative Examples 1 - 5 are as follows.

[0105] Example 1

[0106] Provide a preparation method of the aliphatic polyester, which specifically includes the following steps:

[0107] (1) Physically mix 30.3 kg of succinic acid, 6.9 kg of sebacic acid, 35 kg of 1,4-butanediol, and 78 g of glycerol. After mixing, transfer the mixture to a 200 L esterification reactor, and carry out esterification reaction at a temperature of 190 °C and a pressure of 1.1 bar for 5 h to obtain an esterification product;

[0108] (2) Transfer the esterification product obtained in step (1) to a vertical reactor equipped with stirring, add 24 g of tetrabutyl titanate, and carry out a prepolymerization reaction at a temperature of 243 °C and a pressure of 0.60 bar for 80 min to obtain a prepolymer product;

[0109] (3) Transfer the prepolymer product obtained in step (2) to a horizontal reactor equipped with stirring, and carry out a polycondensation reaction at a temperature of 245 °C and a pressure of 1.2 mbar for 110 min to obtain the aliphatic polyester.

[0110] Example 2

[0111] Provide a method for preparing the aliphatic polyester, which specifically includes the following steps:

[0112] (1) Physically mix 25.8 kg of succinic acid, 11.4 kg of sebacic acid, 35 kg of 1,4-butanediol and 78 g of glycerol. After mixing, transfer the mixture to a 200 L esterification reactor, and carry out an esterification reaction at a temperature of 190 °C and a pressure of 1.0 bar for 5 h to obtain an esterification product;

[0113] (2) Transfer the esterification product obtained in step (1) to a vertical reactor equipped with stirring, add 26 g of tetrabutyl titanate, and carry out a prepolymerization reaction at a temperature of 242 °C and a pressure of 0.45 bar for 95 min to obtain a prepolymer product;

[0114] (3) Transfer the prepolymer product obtained in step (2) to a horizontal reactor equipped with stirring, and carry out a polycondensation reaction at a temperature of 243 °C and a pressure of 1.0 mbar for 95 min to obtain the aliphatic polyester.

[0115] Example 3

[0116] Provide a method for preparing the aliphatic polyester, which specifically includes the following steps:

[0117] (1) Physically mix 23.6 kg of succinic acid, 13.6 kg of sebacic acid, 35 kg of 1,4-butanediol and 80 g of glycerol. After mixing, transfer the mixture to a 200 L esterification reactor, and carry out an esterification reaction at a temperature of 180 °C and a pressure of 0.8 bar for 4 h to obtain an esterification product;

[0118] (2) Transfer the esterification product obtained in step (1) to a vertical reactor equipped with stirring, add 27 g of tetrabutyl titanate, and carry out a pre-polycondensation reaction at a temperature of 244 °C and a pressure of 0.52 bar for 90 min to obtain a prepolymer product;

[0119] (3) Transfer the prepolymer obtained in step (2) to a horizontal reactor with stirring, and carry out polycondensation reaction for 100 min at a temperature of 245 °C and a pressure of 1.1 mbar to obtain the aliphatic polyester.

[0120] Example 4

[0121] Provide a preparation method of the aliphatic polyester, which specifically includes the following steps:

[0122] (1) Physically mix 22.5 kg of succinic acid, 14.7 kg of sebacic acid, 35 kg of 1,4-butanediol and 76 g of glycerol. After mixing, transfer the mixture to a 200 L esterification reactor, and carry out esterification reaction for 4 h at a temperature of 180 °C and a pressure of 1.0 bar to obtain an esterification product;

[0123] (2) Transfer the esterification product obtained in step (1) to a vertical reactor with stirring, add 24 g of tetrabutyl titanate, and carry out prepolymerization reaction for 90 min at a temperature of 241 °C and a pressure of 0.70 bar to obtain a prepolymer;

[0124] (3) Transfer the prepolymer obtained in step (2) to a horizontal reactor with stirring, and carry out polycondensation reaction for 100 min at a temperature of 243 °C and a pressure of 1.1 mbar to obtain the aliphatic polyester.

[0125] Examples 5 to 10

[0126] Respectively provide a preparation method of the aliphatic polyester, which is different from that of Example 3 in that the content and type of the branching agent are different. Among them, in the preparation methods of Examples 5 to 10, the added masses of the branching agent are 68.0 g, 85.0 g, 55.0 g, 110.0 g, 80.0 g, and 80.0 g in sequence; other raw materials, dosages and preparation methods are the same as those of Example 3.

[0127] Example 11

[0128] Provide a preparation method of the aliphatic polyester, which is different from that of Example 3 in that step (1) includes the following steps:

[0129] (1-1) Physically mix 23.6 kg of succinic acid with 25 kg of 1,4-butanediol and 80 g of glycerol. After mixing, transfer the mixture to an esterification reactor, and carry out esterification reaction for 4 h at a temperature of 160 °C and a pressure of 1.0 bar to obtain an esterification product A;

[0130] (1 - 2) Physically mix 13.6 kg of sebacic acid with 10 kg of 1,4 - butanediol. After the mixing is completed, transfer the mixture to an esterification reactor and carry out an esterification reaction at a temperature of 200 °C and a pressure of 0.9 bar for 4 h to obtain an esterification product B; After mixing the esterification product A and the esterification product B, carry out steps (2) and (3). Other raw materials, steps, and preparation methods are the same as those in Example 3.

[0131] Example 12

[0132] Provide a method for preparing the aliphatic polyester, which is different from Example 11 in that

[0133] (1 - 1) Physically mix 23.6 kg of succinic acid with 25 kg of 1,4 - butanediol and 80 g of glycerol. After the mixing is completed, transfer the mixture to an esterification reactor and carry out an esterification reaction at a temperature of 180 °C and a pressure of 1.0 bar for 5 h to obtain an esterification product A;

[0134] (1 - 2) Physically mix 13.6 kg of sebacic acid with 10 kg of 1,4 - butanediol. After the mixing is completed, transfer the mixture to an esterification reactor and carry out an esterification reaction at a temperature of 210 °C and a pressure of 1.0 bar for 4 h to obtain an esterification product B;

[0135] (2) Transfer the esterification product A obtained in step (1 - 1) and the esterification product B obtained in step (1 - 2) to a vertical reactor with stirring, add 27 g of tetrabutyl titanate, and carry out a prepolymerization reaction at a temperature of 240 °C and a pressure of 0.65 bar for 85 min to obtain a prepolymer;

[0136] (3) Transfer the prepolymer obtained in step (2) to a horizontal reactor with stirring and carry out a polycondensation reaction at a temperature of 242 °C and a pressure of 1.4 mbar for 50 min to obtain a polycondensate.

[0137] (4) Extrude the polycondensate obtained in step (3) with hexamethylene diisocyanate (with a content of 0.28 wt% of the mass of the polycondensate) in a reactive extruder at a temperature of 210 °C, and the residence time is 8 min to obtain the aliphatic polyester.

[0138] Example 13

[0139] Provide a method for preparing the aliphatic polyester, which is different from Example 11 in that

[0140] (1-1) Physically mix 23.6 kg of succinic acid, 25 kg of 1,4-butanediol, and 32 g of glycerol. After mixing is complete, transfer the mixture to an esterification reactor and carry out an esterification reaction at a temperature of 170 °C and a pressure of 1.0 bar for 3 h to obtain an esterification product A;

[0141] (1-2) Physically mix 13.6 kg of sebacic acid, 10 kg of 1,4-butanediol, and 48 g of glycerol. After mixing is complete, transfer the mixture to an esterification reactor and carry out an esterification reaction at a temperature of 190 °C and a pressure of 1.0 bar for 3 h to obtain an esterification product B; Mix esterification product A and esterification product B and then carry out steps (2) and (3); Other raw materials, dosages, and preparation methods are the same as those in Example 11.

[0142] Example 14

[0143] Provide a method for preparing the aliphatic polyester, which is different from Example 3 in that in step (3), transfer the prepolymer obtained in step (2) to a horizontal reactor with stirring, and carry out a polycondensation reaction at a temperature of 248 °C and a pressure of 1.1 mbar for 110 min to obtain the aliphatic polyester. Other raw materials, dosages, and preparation methods are the same as those in Example 3.

[0144] Example 15

[0145] Provide a method for preparing the aliphatic polyester, which is different from Example 3 in that in step (3), transfer the prepolymer obtained in step (2) to a horizontal reactor with stirring, and carry out a polycondensation reaction at a temperature of 245 °C and a pressure of 1.3 mbar for 58 min to obtain the aliphatic polyester. Other raw materials, dosages, and preparation methods are the same as those in Example 3.

[0146] Example 16

[0147] Provide a method for preparing the aliphatic polyester, which is different from Example 3 in that in step (3), transfer the prepolymer obtained in step (2) to a horizontal reactor with stirring, and carry out a polycondensation reaction at a temperature of 240 °C and a pressure of 1.4 mbar for 45 min to obtain a polycondensation product,

[0148] In step (4), after the polycondensation reaction, it further includes extruding the obtained polycondensation product with hexamethylene diisocyanate (content is 0.34 wt% of the mass of the polycondensation product) in a reactive extruder at a temperature of 200 °C for a residence time of 10 min to obtain the aliphatic polyester. Other raw materials, dosages, and preparation methods are the same as those in Example 3.

[0149] Example 17

[0150] A method for preparing the aliphatic polyester is provided, which is different from Example 3 in that in step (3), the prepolymer obtained in step (2) is transferred to a horizontal reactor with stirring, and polycondensation reaction is carried out at a temperature of 242 °C and a pressure of 1.4 mbar for 50 min to obtain a polycondensate.

[0151] In step (4), after the polycondensation reaction, it further includes extruding the obtained polycondensate and hexamethylene diisocyanate (with a content of 0.36 wt% of the mass of the polycondensate) in a reactive extruder at a temperature of 210 °C for a residence time of 7 min to obtain the aliphatic polyester. Other raw materials, dosages, and preparation methods are the same as those in Example 3.

[0152] Comparative Example 1

[0153] A method for preparing the aliphatic polyester is provided, which specifically includes the following steps:

[0154] (1) Physically mix 32 kg of succinic acid, 5.2 kg of sebacic acid, 35 kg of 1,4-butanediol, and 80 g of glycerol. After mixing, transfer the mixture to a 200 L esterification reactor, and carry out an esterification reaction at a temperature of 190 °C and a pressure of 1.1 bar for 5 h to obtain an esterification product.

[0155] (2) Transfer the esterification product obtained in step (1) to a vertical reactor with stirring, add 27 g of tetrabutyl titanate, and carry out a prepolymerization reaction at a temperature of 243 °C and a pressure of 0.60 bar for 110 min to obtain a prepolymer.

[0156] (3) Transfer the prepolymer obtained in step (2) to a horizontal reactor with stirring, and carry out a polycondensation reaction at a temperature of 245 °C and a pressure of 1.2 mbar for 100 min to obtain the aliphatic polyester.

[0157] Comparative Example 2

[0158] A method for preparing the aliphatic polyester is provided, which specifically includes the following steps:

[0159] (1) Physically mix 20.9 kg of succinic acid, 16.3 kg of sebacic acid, 35 kg of 1,4-butanediol, and 80 g of glycerol. After mixing, transfer the mixture to a 200 L esterification reactor, and carry out an esterification reaction at a temperature of 180 °C and a pressure of 1.0 bar for 4 h to obtain an esterification product.

[0160] (2) Transfer the esterification product obtained in step (1) to a vertical reactor equipped with stirring, add 27 g of tetrabutyl titanate, and carry out a prepolymerization reaction for 90 min at a temperature of 241 °C and a pressure of 0.70 bar to obtain a prepolycondensation product;

[0161] (3) Transfer the prepolycondensation product obtained in step (2) to a horizontal reactor equipped with stirring, and carry out a polycondensation reaction for 100 min at a temperature of 245 °C and a pressure of 1.2 mbar to obtain the aliphatic polyester.

[0162] Comparative Example 3

[0163] Provide a method for preparing the aliphatic polyester, which specifically includes the following steps:

[0164] (1) Physically mix 23.6 kg of succinic acid, 13.6 kg of sebacic acid, 35 kg of 1,4-butanediol, and 147 g of glycerol. After mixing, transfer the mixture to a 200 L esterification reactor, and carry out an esterification reaction for 5 h at a temperature of 190 °C and a pressure of 1.1 bar to obtain an esterification product;

[0165] (2) Transfer the esterification product obtained in step (1) to a vertical reactor equipped with stirring, add 24 g of tetrabutyl titanate, and carry out a prepolymerization reaction for 100 min at a temperature of 240 °C and a pressure of 0.50 bar to obtain a prepolymerization product;

[0166] (3) Transfer the prepolymerization product obtained in step (2) to a horizontal reactor equipped with stirring, and carry out a polycondensation reaction for 90 min at a temperature of 242 °C and a pressure of 1.4 mbar to obtain the aliphatic polyester.

[0167] Comparative Example 4

[0168] Provide a method for preparing the aliphatic polyester, which is only different from Example 3 in that the content of glycerol is different, and other raw materials, dosages, and preparation methods are the same as those in Example 3.

[0169] Comparative Example 5

[0170] Provide a method for preparing the aliphatic polyester, which is only different from Example 3 in that there is no glycerol, and other raw materials, dosages, and preparation methods are the same as those in Example 3.

[0171] Table 1

[0172]

[0173]

[0174] Application Examples 1-17, Comparative Application Examples 1-5

[0175] Application Examples 1-17 and Comparative Application Examples 1-5 each provide a polyester composition. By weight, the polyester composition comprises 63 parts of aliphatic polyester, 4 parts of polylactic acid, 25 parts of starch, 4 parts of glycerol, 3 parts of water, and 1 part of other additives (0.5 part of a compound antioxidant composed of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1 and 0.5 part of lubricant ethylene bisstearamide); the aliphatic polyesters are respectively provided by Examples 1-17 and Comparative Examples 1-5; the preparation method of the polyester composition comprises: according to the formula amount, mixing each component and adding it to a twin-screw extruder (length-diameter ratio is 48:1; diameter is 40 mm), carrying out melt mixing, and extruding and pelletizing; the extrusion temperatures are successively: zone 1 at 120 °C, zone 2 at 160 °C, zones 3 to 9 at 180 °C, zone 10 at 170 °C, zone 11 at 170 °C, the die head at 190 °C, the screw speed at 380 rpm, and the vacuum at -0.60 kg / cm 2 , to obtain the polyester composition; wherein, the starch is purchased from Shandong Shouguang Jueneng Golden Corn Development Co., Ltd.; the polylactic acid is PLA, KB600 NF30, sourced from Zhuhai Jinfa Biomaterials Co., Ltd.

[0176] Performance Testing

[0177] The polyester compositions respectively comprising the aliphatic polyesters provided by Examples 1-17 and Comparative Examples 1-5 are subjected to blown film processing under the following conditions to obtain packaging bags; the heat seal strength of the packaging bags is tested. Among them, the heat seal process is: heat seal temperature 115 °C, heat seal time 3 s, heat seal pressure 300 KPa.

[0178] The screw length-diameter ratio is 32:1, a spiral flow channel die head is used, the air ring is a double-port air ring, the set value of the blown film processing temperature is 140 °C, the blow-up ratio is 3.5, and the blown film thickness is 25 ± 2 μm.

[0179] Under the conditions of 25 ± 5 °C and 55 ± 5% humidity, it is left standing and adjusted for 24 h, and the heat seal strength test is carried out according to the standard QB / T 2358-1998.

[0180] The specific test results are shown in Table 2.

[0181] Table 2

[0182]

[0183] As can be seen from Table 2, for the biodegradable aliphatic polyester of the present invention, by regulating the composition ratio of succinic acid residues and sebacic acid residues in the biodegradable polyester polybutylene succinate sebacate, and at the same time introducing branched agent residues and regulating the content of the branched agent residues within a specific range, the heat seal strength of the packaging bag comprising the biodegradable polyester is significantly improved, and the heat seal strength of the obtained packaging bag ≥ 15 N / 15 mm.

[0184] The specific embodiments described above further elaborate on the object, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An aliphatic polyester, characterized in that The aliphatic polyester comprises a dibasic acid residue, a diol residue and a branching agent residue; The dibasic acid residues include the following residues: a1) 71 to 89 mol % of succinic acid residues, based on the total molar percentage of a1) and a2) being 100 mol %; a2) 11 to 29 mol % of sebacic acid residues, based on the total molar percentage of a1) and a2) being 100 mol %; The diol residues are selected from 1,4-butanediol residues in at least an equimolar amount to the dibasic acid residues; The branching agent residue is derived from a branching agent having a functionality ≥ 3; Based on the total mass of the aliphatic polyester being 100 wt %, the mass percentage of the branching agent residue is 0.09 to 0.22 wt %.

2. The aliphatic polyester according to claim 1, characterized in that The dibasic acid residues include the following residues: a1) 74 to 83 mol % of succinic acid residues, based on the total molar percentage of a1) and a2) being 100 mol %; a2) 17 to 26 mol % of sebacic acid residues, based on the total molar percentage content of a1) and a2) being 100 mol %.

3. The aliphatic polyester according to claim 1 or 2, characterized in that Based on the total mass of the aliphatic polyester being 100 wt %, the mass percentage of the branching agent residue is 0.11-0.17 wt %.

4. The aliphatic polyester according to any one of claims 1 to 3, characterized in that The branching agent contains at least one of a hydroxyl group, a carboxyl group or an acid anhydride in its molecular structure; Preferably, the branching agent comprises at least one of a polyol, a polyacid, a polyol acid or a polyacid anhydride, and more preferably a polyol; Preferably, the polyol comprises at least one of trimethylolpropane, trimethylolethane, pentaerythritol, polyether triol or glycerol; Preferably, the polyacid comprises at least one of trimesic acid, trimesic acid or pyromellitic acid; Preferably, the polyol acid comprises at least one of tartaric acid, citric acid or malic acid; Preferably, the polyacid anhydride comprises trimellitic anhydride and / or pyromellitic dianhydride.

5. The aliphatic polyester according to any one of claims 1 to 4, characterized in that The molecular weight distribution coefficient of the aliphatic polyester is 1.3 to 2.8, preferably 1.5 to 2.5; Preferably, at 190°C and 2.16kg, the melt flow rate of the aliphatic polyester is 1.2 to 10 g / 10 min, and more preferably the melt flow rate is 2.2 to 6 g / 10 min; Preferably, the carboxyl content of the aliphatic polyester is less than 50 mol / t.

6. A polyester composition, characterized in that The polyester composition comprises the aliphatic polyester according to any one of claims 1 to 5.

7. The polyester composition according to claim 6, characterized in that The polyester composition further comprises at least one of a second polymer, a filler or an auxiliary agent; Preferably, the second polymer comprises at least one of polylactic acid, polycaprolactone, polyhydroxyalkanoate, aliphatic polycarbonate or aliphatic-aromatic polyester; Preferably, the filler includes an inorganic filler and / or an organic filler.

8. The polyester composition according to claim 6 or 7, characterized in that In parts by weight, the polyester composition comprises 50 to 70 parts of aliphatic polyester, 4 to 20 parts of a second polymer, 15 to 35 parts of a filler and 0 to 15 parts of an auxiliary agent.

9. A packaging bag, characterized in that: The raw material for preparing the packaging bag comprises the aliphatic polyester described in any one of claims 1 to 5 or the polyester composition described in any one of claims 6 to 8.

10. The packaging bag according to claim 9, characterized in that: The heat sealing strength of the packaging bag is ≥15N / 15mm.

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