A mixture for the preparation of biodegradable polymer material, biodegradable polymer material and use
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- ÚSTAV POLYMÉROV SLOVENSKEJ AKADÉMIE VIED VEREJNÁ VÝSKUMNÁ INŠTITÚCIA
- Filing Date
- 2024-07-25
- Publication Date
- 2026-06-10
AI Technical Summary
Current biodegradable polymer mixtures, particularly those containing thermoplastic starch (TPS), face challenges such as high cost, compatibility issues with non-polar plastics, and sensitivity to water, which limit their widespread adoption in packaging applications.
A mixture comprising 1 to 99 parts by weight of a biodegradable polymer with at least 30% secondary or tertiary hydrogens, 99 to 1 parts by weight of thermoplastic starch or native starch with a plasticizer, 0.02 to 12 parts by weight of a compatibilizer formed by oligomeric polymers of liquid rubbers, and 0.1 to 5 parts by weight of an organic peroxide initiator, which enhances compatibility and processing properties.
The proposed mixture achieves significantly improved mechanical properties, such as increased toughness and reduced brittleness, while maintaining cost-effectiveness, making it suitable for large-scale production and use in packaging materials.
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Abstract
Description
[0001] A mixture for the preparation of biodegradable polymer material, biodegradable polymer material and use
[0002] Field of technology
[0003] The invention relates to biodegradable polymer mixtures for packaging materials.
[0004] Background art
[0005] The economic and societal importance of biodegradable and environmentally friendly materials has grown substantially over the past decade, as increasing public awareness and environmental concerns about solid waste disposal have spurred the creation of stricter plastic disposal laws, sustainability concepts, the growth of the recycling industry, and the use of biodegradable and / or biopolymers as substitutes for petroleum-based plastics, especially in the packaging applications. There is a strong request to develop biodegradable products for packaging and mulching films, as these are high-volume plastic applications that degrade rapidly while still maintaining satisfactory performance. Plastics used for these applications of synthetic origin and non-biodegradable, can have a significant negative impact on the environment as they cause serious visual pollution after disposal, take a long time to decompose and also tend to degrade soil quality by reducing water and nutrient permeability if used, for example, as mulch films. Biodegradable plastic materials (BDP) would be an acceptable choice for these applications as they could be safely and efficiently disposed of in soil or compost, as their degradation products do not irreversibly harm soil, flora or fauna. BDP can be of natural or petrochemical origin. For example, polyfbutylene adipate-co- terephthalate) (PBAT) is an aromatic-aliphatic copolyester and an example of a BDP of petrochemical origin. It is a synthetic semi-crystalline thermoplastic copolyester with mechanical and thermal properties similar to some types of polyethylene. PBAT is fully biodegradable in municipal landfills (it is "compostable"), can be processed in conventional polymer processing equipment (mixers, extruders, injection molding machines, etc.) and is relatively stable under processing conditions. In addition, it has some interesting barrier properties for a material that can be formed into films for the food packaging industry. Despite this, the volume of its applications is only around 1% compared to, for example, polyethylene, although compared to polyethylene, PBAT has a lower oxygen permeability, which means that it provides food with a longer shelf life. The reason for this situation is the higher price, which reaches 1.5 to twice the price of polyethylene.
[0006] The comparison of other BDP with plastics that are not compostable is similar, for example polyhydroxybutyrate with strength and modulus equal to or higher than polypropylene is on the market at prices three times or even more expensive.
[0007] This aspect of BDP's higher price is commonly addressed by blending it with cheaper polymers. In terms of price and availability, the most widely used additive is starch, especially its thermoplastic form (thermoplastic starch, TPS). Applications of TPS, either alone or in mixtures with other plastics, are largely limited due to unsatisfactory mechanical properties and sensitivity to moisture.
[0008] Combining TPS with another biodegradable polymer is an option for obtaining a cheaper compostable product, therefore mixtures of TPS with PBAT, polylactic acid (PLA), polycaprolactone (PCL) and other polyesters as well as poly(hydroxyalkanoates) are frequently mentioned in the literature. The main problems associated with these mixtures are their cost, the tolerance of the less polar biopolymer with the highly polar starch (compatibility), and the sensitivity to water with increasing TPS content. The latter property limits the use of TPS materials in applications where contact with water may occur.
[0009] To increase the compatibility of starch with non-polar plastics, so-called compatibilizers are applied that have a bipolar character, so that one part of the compatibilizer molecule interacts mainly by physical forces with the starch and the other less polar part of the compatibilizer molecule is more easily mixed into the polymer phase. The use of compatibilizers, especially at high TPS contents, is essential if a good set of properties is to be achieved. Several compounds such as soybean oil, citric and tartaric acids, maleic anhydride, glycidyl methacrylate, as well as maleated TPS, maleated PBAT and starch nanoparticles were used as compatibilizers for the above mixtures with varying effectiveness. However, the most effective compatibilizers are starch copolymers with structures similar or identical to the polymer to be mixed with starch. In their pure form, however, such materials are not commonly available in sufficient quantities, because due to the large number of different polymers, it would be necessary to synthesize a compatibilizer for more or less each group of polymers, so the availability and thus the price of the compatibilizer itself would be too high.
[0010] The patent literature contains a number of patents that address the improvement of the properties of BDP mixtures with starch, especially of the TPS type, in which the addition of TPS is primarily intended to improve the economy of production and bring it closer to the cost of producing packaging films from materials based on fossil raw materials, especially oil, at unchanged utility properties of the final product. However, for such materials with a higher TPS content, sufficiently effective compatibilizers, which would be available in high-volume amounts at an acceptable competitive price, are still lacking.
[0011] The aim of this invention is the production of inexpensive biodegradable and compostable polymer material with significantly improved ultimate properties such as increased toughness and reduced brittleness. Such material is suitable as packaging material.
[0012] Summary of invention
[0013] The first aspect of this invention is a mixture for the preparation of a biodegradable polymer material which contains:
[0014] - 1 to 99 parts by weight of at least one biodegradable polymer (component A), which in the basic chain contains at least 30% of carbons with secondary or tertiary hydrogens from the total number of carbons in the chain without carbons forming aromatic rings,
[0015] - 99 to 1 part by weight of thermoplastic starch or native starch and plasticizer, (component B), - 0.02 to 12 parts by weight of a compatibilizer formed by oligomeric polymers of the type of liquid rubbers with a molar mass between 3,000 and 50,000, the skeleton of which is formed by an elastomer containing at least two different functional groups, one of which is polar and is capable of forming hydrogen bonds with hydroxyl groups on the starch macromolecule bonds and the second functional group is formed by double bonds capable of reacting with free radicals, especially of the oxyl radical type, created by thermal decomposition of organic peroxides,
[0016] - 0.1 to 5 parts by weight of the initiator of radical processes consisting of an organic peroxide whose decomposition temperature is higher than the melting temperature of all the components of the mixture mentioned above.
[0017] The compatibilizer according to this invention is a substance compatible with both polar and non-polar components of the mixture.
[0018] It was surprisingly found that several oligomeric polymers of the type of liquid rubbers are suitable as compatibilizers in the process of preparing a biodegradable polymer material containing thermoplastic starch, because they contain at least two different functional groups, one of which is capable of forming with hydroxyl groups on the starch macromolecule the so-called hydrogen bonds (as examples of such groups can be hydroxyl, carboxyl, sulfonic and other polar groups) and the second functional group is formed by double bonds capable of reacting with free radicals, especially of the oxyl radical type, created by thermal decomposition of organic peroxides.
[0019] Oligomeric polymers are currently used commercially in the form of so-called liquid rubbers. Currently, they are applied as additives to rubbers, where they improve processing properties and also serve as secondary thermal stabilizers, including in tires. Types containing polar functional groups are applied as additives to increase adhesion in hot melt adhesives, as well as to increase the interactions of rubbers and some plastics with reinforcing particle fillers, in rubber compounds for tires also increase the adhesion of vulcanized rubber to metal reinforcing components, in other cases they serve to increase the adhesion of rubber to metal substrates of any geometry. The use of these substances as compatibilizers for the production of biodegradable polymer material containing thermoplastic starch was not known until now.
[0020] The compatibilizer according to the present invention can be liquid carboxylated polyisoprenes or polybutadienes, liquid polybutadienes functionalized with hydroxyl groups, liquid polybutadienes terminated with -OH, -SH, -COOH, -NCO, -NH2 groups. Polar functional groups capable of forming hydrogen bonds with hydroxyl groups on the starch macromolecule are hydroxyl, carboxyl, sulfonic groups in the compatibilizer molecule.
[0021] Biodegradable polymer (component A) is a material based on any polymer that meets the conditions of biodegradability and compostability in accordance with valid standards defining environmentally degradable materials. Such a polymer must contain in the basic chain at least 30% of carbons with secondary or tertiary hydrogens from the total number of carbons on the chain, excluding carbons forming aromatic rings. This polymer can also contain other elements, primarily oxygen and nitrogen, as well as common additives providing additional properties for specific plastics, such as increasing strength and modulus by adding commonly used stiffening fillers, increasing thermal stability by adding antioxidants, fire resistance, modifying barrier properties and processing parameters and processable by one or more technologies commonly used in the processing of polymeric materials (especially homogenization and shaping). Examples of these biodegradable polymers include polylactic acid (PLA), polyhydroxyalkanoates (PHA), such as polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate copolymer (PHBV), as well as polybutylene adipate- co-terephtate (PBAT), polycaprolactone (PC), or mixtures of the above-mentioned polymers, but other polymers and copolymers based on polyolefins, polyesters, polyamides and others can also be used if they meet the standards for biodegradability and compostability and the requirement for the chain structure, mentioned above.
[0022] Thermoplastic starch according to the present invention (component B) is in the form of either native starch (most often powder), which before use is modified by known procedures to a state that allows molding at a higher temperature, which is achieved by adding plasticizers, especially glycerol, but also sorbitol, urea, formaldehyde and a range of other suitable plasticizers, as well as various mixtures of plasticizers, or directly in the form of thermoplastic starch (TPS). In the simplest and at the same time typical case, TPS is prepared in the first step separately by mixing native starch with plasticizers at an elevated temperature, most often almost exclusively with glycerol. In our procedure, in this first step, an appropriate amount of compatibilizer, which is soluble in glycerol, is mixed together with the glycerol. If a commercial TPS is used for the preparation of the mixture, in the first step of the preparation of the mixture according to the presented patent, a compatibilizer is mixed into this TPS.
[0023] The initiator of radical processes is an organic peroxide, the decomposition of which takes place mainly or exclusively into oxyl radicals. For this purpose, practically any organic peroxide can be used, the decomposition of which takes place at a higher temperature than the temperature during homogenization of the individual components of the mixture and other additives.
[0024] Alternatively, the mixture for the preparation of the biodegradable polymer material according to the present invention may also contain other additives for adjusting the strength, antistatic and antibacterial properties, fire resistance, or a decrease of gas permeability.
[0025] The second aspect of this invention is a biodegradable polymer material that can be prepared from the mixture according to the first aspect of this invention by the following steps:
[0026] - homogenization by mixing the components of the mixture at a temperature higher than the melting temperature of the individual components of the mixture but lower than the decomposition temperature of the initiator of radical processes and subsequently,
[0027] - with constant stirring, heating the mixture at least to the temperature of the decomposition of the initiator of radical processes and maintaining the temperature for at least 6 times the half-time of the decomposition of the initiator of radical processes at the given temperature; - subsequently, the material is shaped using a standard procedure.
[0028] All the components are gradually added to the mixing device at a temperature lower than the decomposition temperature of the organic peroxide, but higher than the melting temperature of all the components of the mixture, while after a mixing time sufficient for the homogenization of the components of the mixture, which can be indicated by the stabilization of the torque value on the display of the mixing device device at the final lowest value, the temperature, without removing the mixture from the mixing device, is increased to the peroxide decomposition temperature, which is maintained with continued mixing for at least 6 times the half-life of the peroxide decomposition at the given temperature.
[0029] Alternatively, the biodegradable polymeric material can be prepared from the mixture according to the first aspect of the present invention by the following steps:
[0030] - the compatibilizer is mixed with the plasticizer and native starch at a temperature higher than the melting point of the individual components of the mixture, and subsequently
[0031] - this mixture is mixed with at least one biodegradable polymer and an initiator of radical processes at a temperature lower than the decomposition temperature of the initiator of radical processes,
[0032] - subsequently, the material is shaped at a temperature higher than or equal to the decomposition temperature of the initiator of radical processes for at least 6 times the half-time of the decomposition of the initiator of radical processes at the given temperature.
[0033] In the first step, thermoplastic starch (TPS) is prepared, composed of appropriate amounts of native starch, plasticizer and compatibilizer, in the second step, TPS is mixed with a biodegradable polymer (component A) and any organic peroxide at an elevated temperature and mixing time that is lower than 0.2 of the half-life of the selected peroxide at the given temperature, and the mixture prepared in this way is then shaped above the melting temperature of the mixture by extrusion in the form of a foil, or by extrusion into a mold of the desired shape, or by compression molding into a mold in a press.
[0034] Any mixing devices commonly used for mixing polymer blends (e.g. extruders or kneaders) can be used for mixing.
[0035] The organic peroxide (initiator) upon raising the temperature above the decomposition temperature initiates the reaction between the compatibilizer and the non-polar polymer component, and the compatibilizer interacts with both polar and non-polar polymer components of the mixture by forming covalent, physico-chemical, hydrogen and I or other types of bonds between the compatibilizer and the polymer components mixtures. This achieves a high degree of compatibility between the basic components A and B, thereby ensuring substantially improved performance properties of the resulting mixed material.
[0036] The described procedure does not preclude the use of the addition of other additives to modify the properties essential for the intended application of a particular material (increasing strength by adding reinforcing fillers, additions of antistatic, antibacterial additives, or fillers that increase resistance to gas permeability or fire.
[0037] Another aspect of this invention is also a method of producing a biodegradable polymer material as described above.
[0038] Another aspect of this invention is the use of oligomers of the liquid rubber type with a molar mass between 3,000 and 50,000, the skeleton of which is formed by an elastomer containing at least two different functional groups, one of which is polar and is capable of forming hydrogen bonds with hydroxyl groups on the starch macromolecule and the second functional group is formed by double bonds capable of reacting with free radicals, especially of the oxyl radical type, created by thermal decomposition of organic peroxides, as a compatibilizer for the production of biodegradable polymer material according to the second aspect of this invention. Oligomeric polymers can be based on liquid carboxylated polyisoprenes or polybutadienes, liquid polybutadienes functionalized with hydroxyl groups, as well as liquid polyisoprenes or polybutadienes with chains terminated by -OH, -SH, -NCO, - NH2 groups.
[0039] The mixture for the preparation of biodegradable polymer material according to the present invention enables an increase in the number and volume of applications of these ecological materials, especially in packaging technology, consisting in a replacement for plastic materials produced from fossil sources that are not compostable, while in addition to improving several useful properties compared to the packaging materials currently used, including applied biodegradable mixtures, also has an advantage related to the economic side of high-volume production, consisting in the reduction of material costs due to the possibility of using thermoplastic starch with marginal or no need for compromise concerning the ultimate properties.
[0040] Examples
[0041] Example 1
[0042] In the first step, thermoplastic starch was prepared from a mixture of native starch powder and plasticizer, which was glycerol in a ratio of 2:1. After standing in a beaker for 16 hours at a temperature of 80 °C, the mixture was stirred in a laboratory mixer at a temperature of 130 °C for about 10 minutes. Subsequently, one part of the TPS prepared in this way was mixed with two parts of the polymer polybutylene adipate- co-terephthalate (PBAT) at a temperature of 130 °C for 12 minutes. After removing the mixture from the kneader, test specimens were compression molded in a laboratory press at a temperature of 130 °C for 2 minutes to dertermine mechanical properties and dynamic-mechanical properties (DMTA). The properties of the material are listed in Table 1.
[0043] Example 2
[0044] The procedure was the same as in example 1, with the difference that 3 wt. parts of dicumyl peroxide per 100 wt. part of the same mixture of biodegradable polymer polybutylene adipate-co-terephthalate and thermoplastic starch as in example 1. Test bodies for measuring mechanical properties and dynamic-mechanical properties (DMTA) were pressed at 180 °C for 6 minutes. After pressing at 180 °C for 6 minutes, the mechanical properties and dynamic-mechanical properties listed in Table 1 were achieved.
[0045] Example 3:
[0046] TPS was prepared similarly to example 1, but with addition of 3 wt. part of the compatibilizer, which was carboxylated polyisoprene, then the prepared TPS 33 wt. parts mixed with 67 wt. parts of the biodegradable polymer polybutylene adipate-co- terephthalate at a temperature of 130 °C for 15 minutes. 1 wt. part of dicumyl peroxide was added to 100 parts by weight of the mixture of TPS, compatibilizer and PBAT. After pressing at 180 °C for 6 minutes, the mechanical properties and dynamicmechanical properties listed in Table 1 were achieved.
[0047] Example 4
[0048] The same mixture of polymers as in example 3 and the same amount of compatibilizer were used, but 3 parts by weight of dicumyl peroxide were added. After pressing at 180 °C for 6 minutes, the mechanical properties and dynamic-mechanical properties listed in Table 1 were achieved.
[0049] Examples 5 to 14
[0050] The procedure was the same as in example 3, and the compositions of the biodegradable polymer mixtures are listed in Table 1.
[0051] In example 12, polyhydroxybutyrate (PHB) was used as a biodegradable plastic.
[0052] In Example 13, polyhydroxybutyrate-co-valerate (PHBV) copolymer was used as a biodegradable plastic.
[0053] In example 14, polylactic acid (PLA) was used as a biodegradable plastic.
[0054] The results of mechanical properties and dynamic-mechanical properties are shown in Table 1.
[0055] Example 15 The composition of the mixture was identical to the composition in example 3. First, all the components of the mixture, powdered starch, PBAT and glycerol, were put into the chamber of a laboratory kneader heated to 130 °C, and after three minutes of mixing, the compatibilizer and dicumyl peroxide were added. After mixing for another 2 minutes, the chamber was heated, up to 180 °C in about 4 minutes. This temperature was maintained for 6 minutes, since the half-time of decomposition of dicumyl peroxide according to data from the literature at 180 °C is 1 minute. Subsequently, the mixture was removed from the chamber and testing specimens were prepared in a laboratory press at a temperature of 140 °C for measuring the properties. The results of mechanical properties and dynamic-mechanical properties are shown in Table 1.
[0056] Example 16
[0057] The procedure was the same as in Example 15, with the difference that polycaprolactone was used instead of PBAT. The chamber was heated to 170 °C and this temperature was maintained for 12 minutes with constant mixing of the mixture, since the half-time of decomposition of dicumyl peroxide at 170 °C is approximately 2 minutes.
[0058] Examples 17 to 20
[0059] In these examples, the procedure was the same as in Example 3, with the difference that a different compatibilizer was used in each example. The compositions of the biodegradable polymer mixtures as well as the used compatibilizers are defined in Table 1. Table 1 also shows the results of the mechanical properties of the produced materials.
[0060] Analysis of results:
[0061] It is clear from Table 1 that the mechanical properties of the mixtures given in the examples exceed the basic mixture, consisting only of biodegradable plastic and thermoplastic starch without a compatibilizer, after applying the compatibilizer and peroxide and using the described procedures in all cases. The strength increased in all cases, in several cases significantly (more than twice) and the value of the elongation at break, which is proportional to the material's toughness and impact resistance, also increased in most cases. The addition of TPS will significantly reduce the material costs for the production of products from such mixtures, and the products can be composted after the end of their useful life.
[0062] Table 1: Composition of materials shown in Examples, o - tensile strength at break, E - elongation at break, E - Youngs' modulus
[0063] Polymers: PBAT-polybutylene adipate-co-terephthalate, PC-polycaprolactone, PLA - polylactic acid, PHB-polyhydroxybutyrate,
[0064] PHBl-polyhydroxybutyrate-co-valerate
[0065] Liquid rubbers, basic polymer: PI - polyisoprene PB - polybutadiene, functional groups on the chain: COOH - carboxylated, OH - hydroxyls end functional groups: -OH - hydroxyl, -SH - sulfonic, -COOH - carboxylic, -NCO, -isocyanate
Claims
CLAIMS1. A mixture for the preparation of a biodegradable polymer material suitable as a packaging material, characterized in that it contains:- 1 to 99 parts by weight of at least one biodegradable polymer, which in the basic chain contains at least 30% of carbons with secondary or tertiary hydrogens from the total number of carbons in the chain without carbons forming aromatic rings,- 99 to 1 part by weight of thermoplastic starch or native starch and plasticizer,- 0.02 to 12 parts by weight of a compatibilizer formed by oligomeric polymers of the type of liquid rubbers with a molar mass between 3,000 and 50,000, the skeleton of which is formed by an elastomer containing at least two different functional groups, one of which is polar and is able to form hydrogen bonds with hydroxyl groups on the macromolecule starch and the second functional group consists of double bonds capable of reacting with free radicals, especially of the oxyl radical type, created by thermal decomposition of organic peroxides,- 0.1 to 5 parts by weight of the initiator of radical processes consisting of an organic peroxide whose decomposition temperature is higher than the melting temperature of all the components of the mixture.
2. The mixture for the preparation of a biodegradable polymer material according to claim 1, characterized in that the compatibilizer is at least one substance selected from the group of liquid rubbers such as liquid carboxylated polyisoprenes or polybutadienes, liquid polybutadienes functionalized with hydroxyl groups, liquid polybutadienes terminated with -OH, -SH, -COOH, -NCO, -NH2 groups.
3. The mixture for the preparation of a biodegradable polymer material according to claim 1 or 2, characterized in that the biodegradable polymer is selected from the group comprising polybutylene adipate-co-terephthalate, poly hydroxy butyrate, polyhydroxybutyrate-co-valerate copolymer, polycaprolactone, or polylactic acid or mixtures thereof.
4. The mixture for the preparation of a biodegradable polymer material according to any of the preceding claims, characterized in that it contains one or more additional additives for adjusting strength, antistatic and antibacterial properties, resistance to fire, or gas permeability.
5. A biodegradable polymer material that can be prepared from the mixture according to claims 1 to 4 by the following steps:- homogenization by mixing the components of the mixture at a temperature higher than the melting temperature of the individual components of the mixture but lower than the decomposition temperature of the initiator of radical processes, and consequently,- with constant stirring, heating the mixture at least to the temperature of the decomposition of the initiator of radical processes and maintaining the temperature for at least 6 times the half-time of the decomposition of the initiator of radical processes at the given temperature;- subsequently, the material is shaped using a standard procedure.
6. A biodegradable polymer material that can be prepared from the mixture according to claims 1 to 4 by the following steps:- the compatibilizer is mixed with the plasticizer and native starch at a temperature higher than the melting temperature of the individual components of the mixture, and subsequently- this mixture is mixed with at least one biodegradable polymer and the initiator of radical processes at a temperature lower than the decomposition temperature of the initiator of radical processes,- subsequently, the material is shaped at a temperature higher than or equal to the decomposition temperature of the initiator of radical processes for at least 6 times the half-time of the decomposition of the initiator of radical processes at the given temperature.
7. An use of oligomeric polymers of the liquid rubber type with a molar mass between 3,000 and 50,000, the skeleton of which is formed by an elastomer containing atleast two different functional groups, one of which is polar and is capable of forming hydrogen bonds with the hydroxyl groups on the starch macromolecule, and the other functional group is formed by double bonds capable of reacting with free radicals, especially of the oxyl radical type, created by thermal decomposition of organic peroxides, as a compatibilizer for the production of biodegradable polymer material according to claim 5 or 6.
8. The use according to claim 7, where the oligomeric polymers are liquid carboxylated polyisoprenes or polybutadienes, liquid polybutadienes functionalized with hydroxyl groups, liquid polybutadienes terminated with -OH, -SH, -COOH, -NCO, -NH2 groups.