Starch-filled biodegradable composition as well as preparation method and application thereof

Abstract

The invention relates to a starch-filled biodegradable composition as well as a preparation method and application thereof. The biodegradable composition is prepared from the following components in parts by weight: 55 to 78 parts of flexible biodegradable polyester, 8 to 30 parts of starch and 5 to 18 parts of polylactic acid. The Z average molecular weight Mz of the flexible biodegradable polyester ranges from 160000 Da to 300000 Da; the water content of the starch is less than or equal to 13.5 wt%. By regulating and controlling the Z-average molecular weight of the flexible biodegradable polyester and the water content of the starch in the starch-filled biodegradable composition, the lifting weight of the material is improved, and the biodegradable composition can be used for preparing film bags.

Description

Technical Field

[0001] This invention relates to the field of polymer technology, and in particular to a starch-filled biodegradable composition, its preparation method, and its application. Background Technology

[0002] Starch is widely used in bio-based biodegradable products due to its inherent degradability, abundant sources, diverse types, and low price. However, current starch-based biodegradable films generally suffer from insufficient load-bearing capacity, which restricts their application in the packaging field.

[0003] Currently, there are two main approaches in the industry to improve load-bearing capacity. One is to reduce the starch content in the material, but lower starch content can affect the material's processing stability and increase costs. The other is to add PLA (polylactic acid). PLA's high modulus effectively improves the stiffness of starch-based film bags, but as the amount added increases, the load-bearing capacity of the starch-based biodegradable film decreases. After PLA stiffening, its compatibility with the system decreases, and the starch-based film bags are prone to reduced lifting performance, making them unsuitable for use. Therefore, maintaining the key load-bearing capacity of the film bag after PLA stiffening is crucial and requires a breakthrough.

[0004] CN110845830A discloses a starch-filled PLA / PBAT fully biodegradable composite material and its preparation method. The method improves the compatibility of PLA in the material and reduces the decline in tear performance by using non-degradable plasticizers, coupling agents, and compatibilizers. However, the effect of this method is limited, and the large-scale addition of non-degradable additives is not permitted in the biodegradation industry.

[0005] Therefore, it is necessary to provide a starch-filled biodegradable composition that meets the lifting performance requirements of the material. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a starch-filled biodegradable composition, its preparation method, and its applications. By controlling the Z-average molecular weight of the flexible biodegradable polyester and the water content of the starch in the starch-filled biodegradable composition, this invention improves the lifting weight of the material, making it suitable for use in the preparation of film bags.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a starch-filled biodegradable composition, said biodegradable composition comprising, by weight parts:

[0009] 55-78 parts of flexible biodegradable polyester

[0010] 8-30 parts starch

[0011] 5-18 parts of polylactic acid;

[0012] The Z-average molecular weight Mz of the flexible biodegradable polyester is 160,000-300,000 Da (e.g., it can be 160,000 Da, 180,000 Da, 200,000 Da, 220,000 Da, 250,000 Da, 280,000 Da, 300,000 Da, etc.).

[0013] The water content of the starch is ≤13.5wt% (e.g., it can be 13.5wt%, 13.0wt%, 12.5wt%, 12.0wt%, 11.5wt%, 11.0wt%, 10.5wt%, 10.0wt%, etc.).

[0014] In this invention, the flexible biodegradable polyester can be, for example, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 78 parts, etc., preferably 58-76 parts; the starch can be, for example, 8 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, etc., preferably 10-28 parts; the polylactic acid can be, for example, 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, etc., preferably 6-15 parts.

[0015] This invention rationally blends flexible biodegradable polyester, starch, and polylactic acid in specific component proportions. By controlling the Z-average molecular weight (Mz) of the flexible biodegradable polyester and the water content of the starch, the dispersibility and compatibility of the blend can be effectively improved. The resulting composition exhibits an appropriate melt flow rate, increasing the lifting weight of the material. When the starch water content is too high, the resulting film bag becomes soft and prone to deformation, resulting in reduced load-bearing capacity.

[0016] Preferably, the biodegradable composition contains 60-75% by mass of flexible biodegradable polyester, more preferably 65-72%.

[0017] Preferably, the starch content in the biodegradable composition is 8-30% by mass, and more preferably 10-28%.

[0018] Preferably, the mass percentage of polylactic acid in the biodegradable composition is 3-25%, more preferably 5-20%.

[0019] Preferably, the flexible biodegradable polyester is an aliphatic-aromatic copolyester, preferably polybutylene terephthalate adipate (PBAT) and / or polybutylene sebacate terephthalate (PBSeT).

[0020] Preferably, in the polybutylene adipate terephthalate, the molar content of adipic acid units is 20-30%, and the molar content of terephthalic acid units is 20-30%.

[0021] Preferably, in the polybutylene sebacate terephthalate, the molar content of sebacate units is 20-30%, and the molar content of terephthalic acid units is 20-30%.

[0022] Preferably, the Z-average molecular weight Mz of the flexible biodegradable polyester is 180,000-280,000 Da (e.g., 180,000 Da, 200,000 Da, 220,000 Da, 250,000 Da, 280,000 Da, etc.), and more preferably 200,000-260,000 Da.

[0023] Preferably, the starch includes any one or a combination of at least two of corn starch, tapioca starch, or potato starch, and is preferably corn starch and / or tapioca starch.

[0024] Preferably, the water content of the starch is ≤13wt%.

[0025] Preferably, the polylactic acid includes any one or a combination of at least two of PLLA, PDLA, or PLLA / PDLA copolymer, and is preferably a PLLA / PDLA copolymer.

[0026] Preferably, the polylactic acid has a number-average molecular weight Mn of 50,000-120,000 (e.g., 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, etc.), and a weight-average molecular weight Mw to number-average molecular weight Mn ratio of 1.1-2.2 (e.g., 1.1, 1.2, 1.5, 1.8, 2, 2.2, etc.).

[0027] Preferably, the polylactic acid has a number-average molecular weight Mn of 70,000-100,000, more preferably 72,000-90,000, and a weight-average molecular weight Mw to number-average molecular weight Mn ratio of 1.2-1.5, more preferably 1.35-1.42.

[0028] Preferably, the D-lactic acid content of the PLLA / PDLA copolymer is 2-20 mol% (e.g., 2 mol%, 4 mol%, 6 mol%, 8 mol%, 10 mol%, 12 mol%, 16 mol%, 20 mol%, etc.), more preferably 6-12 mol%, more preferably 6.5-10.5 mol%, and even more preferably 6.7-7 mol%.

[0029] In this invention, the load-bearing capacity of the obtained film material can be further improved by further controlling the number-average molecular weight, weight-average molecular weight, and D-lactic acid content of polylactic acid.

[0030] Preferably, the biodegradable composition further includes 0.1 to 1 part of lubricant by weight (e.g., 0.1, 0.2, 0.5, 0.8, 1, etc.).

[0031] Preferably, the lubricant comprises any one or a combination of at least two of Fischer-Tropsch wax, monoglyceride, ethylene bis-stearamide, oleamide, or erucamide.

[0032] In a second aspect, the present invention provides a method for preparing a starch-filled biodegradable composition according to the first aspect, the method comprising: mixing raw materials, melt extruding, granulating, and obtaining the biodegradable composition.

[0033] In this invention, the flexible biodegradable polyester and polylactic acid are dried to a water content of less than 300 ppm before melt extrusion.

[0034] Preferably, in the twin-screw extruder used for melt extrusion, the temperature of zone one is 90-110℃ (e.g., 90℃, 95℃, 100℃, 105℃, 110℃, etc.), the temperature of zone two is 110-130℃ (e.g., 110℃, 115℃, 120℃, 125℃, 130℃, etc.), the temperature of zone three is 130-150℃ (e.g., 130℃, 135℃, 140℃, 145℃, 150℃, etc.), the temperature of zone four is 150-170℃ (e.g., 130℃, 135℃, 140℃, 145℃, 150℃, etc.), and the temperature of zone five is 150-170℃ (e.g., 130℃, 135℃, 140℃, 145℃, 150℃, etc.). The temperatures in Zone 6, Zone 7, Zone 8, Zone 9, and Zone 10 are all 150-170℃ (e.g., 130℃, 135℃, 140℃, 145℃, 150℃, etc.).

[0035] Preferably, the twin-screw extruder used for melt extrusion has a screw length-to-diameter ratio of 30-50:1 (e.g., 30:1, 35:1, 40:1, 45:1, 50:1, etc.). Preferably, the twin-screw extruder used for melt extrusion has a screw speed of 250-400 rpm (e.g., 250 rpm, 300 rpm, 350 rpm, 400 rpm, etc.).

[0036] Thirdly, the present invention provides a biodegradable membrane bag, wherein the raw materials for preparing the biodegradable membrane bag include a starch-filled biodegradable composition as described in the first aspect.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] This invention rationally blends flexible biodegradable polyester, starch, and polylactic acid in specific component amounts. By controlling the Z-average molecular weight (Mz) of the flexible biodegradable polyester and the water content of the starch, the dispersibility and compatibility of the blend can be effectively improved. The resulting composition has an appropriate melt flow rate, which improves the stiffness of the film and enhances the lifting capacity of the film, fully meeting the usage requirements of film bag products. Detailed Implementation

[0039] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0040] The material information used in the following embodiments is as follows:

[0041] A flexible biodegradable polyester

[0042] A1: PBAT, polybutylene adipate terephthalate, Mz=201000 Da, the molar contents of adipic acid, terephthalic acid and 1,4-butanediol units in the polymer are 26%, 24% and 50%, respectively.

[0043] A2: PBAT, polybutylene adipate terephthalate, Mz=235000 Da, the molar contents of adipic acid, terephthalic acid and 1,4-butanediol in the polymer are 26%, 24% and 50%, respectively.

[0044] A3: PBSeT, polybutylene sebacic acid terephthalate, Mz=258000 Da, the molar contents of sebacic acid, terephthalic acid and 1,4-butanediol in the polymer are 25%, 25% and 50%, respectively.

[0045] A4: PBAT, polybutylene adipate terephthalate, Mz=123000 Da, the molar contents of adipic acid, terephthalic acid and 1,4-butanediol in the polymer are 26%, 24% and 50%, respectively.

[0046] A5: PBAT, polybutylene adipate terephthalate, Mz=353000 Da, the molar contents of adipic acid, terephthalic acid and 1,4-butanediol in the polymer are 26%, 24% and 50%, respectively.

[0047] B starch

[0048] B1: Corn starch, water content 13.0 wt%, purchased from Golden Corn.

[0049] B2: Corn starch, water content 12.5%, purchased from Golden Corn.

[0050] B3: Tapioca starch, water content 13.0%, purchased from Taihua.

[0051] B4: Corn starch, water content 14.0 wt%, purchased from Golden Corn.

[0052] C-polylactic acid

[0053] C1: PLLA / PDLA copolymer, Mn=87200, Mw / Mn=1.39, D-lactic acid content is 6.9mol.

[0054] C2: PLLA / PDLA copolymer, Mn=72600, Mw / Mn=1.41, D-lactic acid content is 6.8mol.

[0055] C3: PLLA / PDLA copolymer, Mn=89600, Mw / Mn=1.40, D-lactic acid content is 9.9mol.

[0056] C4: PLLA / PDLA copolymer, Mn=57700, Mw / Mn=1.37, D-lactic acid content is 6.7mol.

[0057] C5: PLLA / PDLA copolymer, Mn=148200, Mw / Mn=1.38, D-lactic acid content is 7.0 mol.

[0058] C6: PLLA / PDLA copolymer, Mn=87300, Mw / Mn=1.40, D-lactic acid content is 19.9mol.

[0059] C7: PLLA / PDLA copolymer, Mn=87600, Mw / Mn=1.39, D-lactic acid content is 3.8mol.

[0060] D Lubricant

[0061] D1: Lubricant, YT-90, Fischer-Tropsch wax, commercially available.

[0062] The test methods for the properties of the above materials are as follows:

[0063] (1) Z-average molecular weight Mz: The GPC test method was adopted. The GPC test was performed using the Waters ACQUITY APC™ instrument at a test temperature of 40℃. XT45, XT200 and XT459 columns were used. The solvent was tetrahydrofuran and the mobile phase flow rate was 0.5 mL / min. Polystyrene standard was used as the standard sample. The result was the average of three measurements.

[0064] (2) Number-average molecular weight Mn and weight-average molecular weight Mw: The determination was performed using a chromatographic system at 40°C with a set of three tandem columns (particle diameter 5 μm and porosities of 500 Å, 1000 Å and 10000 Å, respectively), a refractive index detector, chloroform as eluent (flow rate 1 mL / min), and polystyrene as a reference standard.

[0065] (3) D-lactic acid content in polylactic acid: 100 mg of polylactic acid sample was placed in a hydrothermal reactor, 10 ml of methanol was added, and 1 drop of NaOH aqueous solution was added. The hydrothermal reactor was then sealed. The hydrothermal reactor was placed in a 150°C forced-air oven for 60 min. After 60 min, the hydrothermal reactor was removed and cooled to room temperature by running water. The filtered sample solution was transferred to a gas chromatograph (Agilent 8860 gas chromatograph, CP7502 column). The peaks corresponding to D-lactic acid methyl ester and L-lactic acid methyl ester were determined according to the retention time, and the peak areas of D-lactic acid methyl ester and L-lactic acid methyl ester were recorded. The content of D-lactic acid in polylactic acid was obtained by dividing the peak area of ​​D-lactic acid methyl ester by the sum of the peak areas of D-lactic acid methyl ester and L-lactic acid methyl ester.

[0066] (4) Content of each unit in flexible biodegradable polyester: In this invention, the specific operation of the T content detection method of flexible biodegradable polyester resin is as follows: Take 20 mg of resin sample and dissolve it in 0.6 mL of deuterated chloroform, and then use a Bruker AV 500 nuclear magnetic resonance spectrometer to determine 1H NMR at room temperature. The core of this method is to utilize the direct proportional relationship between the characteristic peak area and the number of hydrogen atoms. The specific method is to select the characteristic peaks of benzene ring hydrogen of terephthalic acid (about 8.1 ppm) and methylene hydrogen of adipic acid (about 2.3 ppm) for integration. The ratio of their peak areas is the molar ratio of the two acid monomers. Since the butanediol monomer and the dicarboxylic acid monomer are paired 1:1, their molar fraction is always 50%, and the specific molar fractions of terephthalic acid and adipic acid can be calculated from this.

[0067] (5) Water content of starch: Follow GB 5009.3-2016. Place a clean, flat weighing bottle (with the cap angled against the side of the bottle) in a drying oven at 101℃~105℃ and heat for about 1 hour. After removing it, cover it and place it in a desiccator to cool for half an hour, then weigh it. This process needs to be repeated until the difference between the two weighings does not exceed 2mg. At this point, the weighing bottle has reached "constant weight". Quickly grind the sample until the particles are less than 2mm, weigh 2-10g (accurate to 0.0001g) and put it into the constant-weighted weighing bottle. The sample thickness should be uniform, and the sample thickness generally does not exceed 5mm. Place the weighing bottle containing the sample (with the cap angled against the side) in a drying oven and dry it at 101℃~105℃. The initial drying time is usually 2-4 hours (about 4 hours for semi-solid / liquid samples). After removing it, cooling, and weighing, put it back in the drying oven to continue drying for about 1 hour, and weigh it again after cooling. Repeat this process until constant weight is achieved again (the difference between two consecutive weight measurements is ≤2mg). Calculate the moisture content based on the weight difference before and after drying.

[0068] Examples 1-7, Comparative Examples 1-5

[0069] The above embodiments and comparative examples each provide a starch-filled biodegradable composition, the composition and weight parts of which are shown in Table 1.

[0070] The preparation methods of the starch-filled biodegradable compositions in the above embodiments and comparative examples are as follows:

[0071] Weigh each component according to the formula, mix them evenly, and then feed them into a twin-screw extruder for melt extrusion and granulation to obtain a biodegradable polyester composition. The temperatures of the twin-screw extruder from zone one to zone ten are 100℃, 120℃, 140℃, 160℃, 160℃, 160℃, 160℃, 160℃, 160℃, and 160℃ respectively. The screw length-to-diameter ratio is 40:1, and the screw speed is 320 rpm.

[0072] The compositions provided in the above embodiments and comparative examples were subjected to the following performance tests, and the results are summarized in Table 1.

[0073] (1) The lifting tester was used to conduct the test according to GB / T38082-2019 standard. A simulated object of a specified weight was placed in the film bag, and the handle was suspended from the equipment. The thickness of the film bag was 10±2μm and the width of the handle was 6cm. The test was conducted with an upper and lower total amplitude of 302mm and a frequency of 3Hz for a total of 1800 cycles to verify the load-bearing performance of the film bag. Three film bag samples were used for each test, and all of them were considered qualified. The limit lifting weight was defined as the maximum weight that could be borne by all qualified samples. The test weight was increased in increments of 0.1kg (e.g., 0.8kg, 0.9kg, 1.0kg, 1.1kg, etc.).

[0074] Table 1

[0075]

[0076] Test results:

[0077] (1) As can be seen from Examples 1 to 7, by controlling the water content of Mz and starch in the flexible biodegradable polyester and the content of Mn, Mw and D-lactic acid in the flexible biodegradable polyester, the present invention can improve the dispersibility and compatibility of the composition, thereby meeting the load-bearing capacity of the film, with a lifting weight of 2.0-2.8 kg.

[0078] (2) By comparing Examples 1 and Examples 4-7, it can be seen that when the content of polylactic acid Mn is slightly lower or higher, and the content of polylactic acid D-lactic acid is slightly lower or higher, the load-bearing capacity of the membrane material decreases.

[0079] (3) As can be seen from the comparison between Example 1 and Comparative Examples 1-2, when the Mz of the flexible biodegradable polyester is too low or too high, the starch water content is too high, and the PLA content is too low or too high, the load-bearing capacity of the membrane material decreases. The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A starch-filled biodegradable composition, characterized in that, The biodegradable composition comprises the following components in parts by weight: 55-78 parts of flexible biodegradable polyester 8-30 parts starch 5-18 parts of polylactic acid; The Z-average molecular weight (Mz) of the flexible biodegradable polyester is 160,000-300,000 Da. The water content of the starch is ≤13.5wt%.

2. The biodegradable composition according to claim 1, characterized in that, The flexible biodegradable polyester is an aliphatic-aromatic copolyester, preferably polybutylene adipate and / or polybutylene sebacate.

3. The biodegradable composition according to claim 1, characterized in that, The flexible biodegradable polyester has a Z-average molecular weight Mz of 180,000-280,000 Da, preferably 200,000-260,000 Da.

4. The biodegradable composition according to claim 1, characterized in that, The starch includes any one or a combination of at least two of corn starch, tapioca starch, or potato starch, preferably corn starch and / or tapioca starch.

5. The biodegradable composition according to claim 1, characterized in that, The water content of the starch is ≤13wt%.

6. The biodegradable composition according to claim 1, characterized in that, The polylactic acid includes any one or a combination of at least two of PLLA, PDLA, or PLLA / PDLA copolymer, preferably PLLA / PDLA copolymer.

7. The biodegradable composition according to claim 1, characterized in that, The polylactic acid has a number-average molecular weight Mn of 50,000-120,000 and a weight-average molecular weight Mw to number-average molecular weight Mn ratio of 1.1-2.

2. Preferably, the polylactic acid has a number-average molecular weight Mn of 70,000-100,000 and a weight-average molecular weight Mw to number-average molecular weight Mn ratio of 1.2-1.

5.

8. The biodegradable composition according to claim 6, characterized in that, The D-lactic acid content of the PLLA / PDLA copolymer is 2-20 mol, preferably 6-12 mol.

9. A method for preparing a starch-filled biodegradable composition according to any one of claims 1-8, characterized in that, The preparation method includes: mixing raw materials, melt extruding, granulating, and obtaining the biodegradable composition.

10. A biodegradable membrane bag, characterized in that, The raw materials for preparing the biodegradable membrane bag include the starch-filled biodegradable composition as described in any one of claims 1-8.

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