Probiotic agent for anaerobic biodegradable plastic, production method of probiotic agent and anaerobic biodegradable plastic

Abstract

The invention discloses a probiotic agent for anaerobic biodegradable plastics, a preparation method of the probiotic agent and biodegradable plastics, the probiotic agent takes PBAT as a carrier material and nano starch, PLA, nano calcium carbonate, carbamide and nano fumed silica as probiotic materials, and probiotic particles are formed through multiple mixing and plasticizing granulation. According to the invention, anaerobic degradation can be regulated and controlled. More importantly, anaerobic degradation also realizes normal use of the degradable plastic, the plastic cannot accelerate degradation in light and oxygen environments, the aging property of the plastic is equivalent to that of a resin matrix of the plastic, and the physical and mechanical properties are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of biodegradable plastics, and particularly relates to a probiotic agent for anaerobic biodegradable plastics, which can improve the biodegradation efficiency of plastics. Background Art

[0002] Petroleum-based synthetic resins mainly include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyurethane (PUR), as well as petroleum-based plastics such as PA (polyamide, nylon), ABS (acrylonitrile–butadiene–styrene copolymer) engineering plastics, and EPS expanded polystyrene plastics. Plastics with different properties are made by adding some additives and have been widely used in all aspects of life. Common synthetic plastics are difficult to degrade under natural conditions because of their large molecular weight and hydrophobicity, and monomers in plastics are often combined by very strong and stable covalent bonds such as C-C bonds, with high crystallinity. With the rapid development of the petroleum industry and the extensive application of synthetic plastics, the "white pollution" caused by a large number of discarded synthetic plastics has become a global problem.

[0003] To solve the problem of white pollution, the development of degradable plastics has become the development direction of the plastics industry. The first generation of degradable plastics is starch-modified plastics, in which additives such as modified starch are added during the monomer polymerization process. Utilizing the biodegradable property of starch, the modified plastics are cracked into tiny plastic fragments in the environment. However, since polymers such as PE are still very difficult to degrade, starch-modified plastics are also called "biologically destructive plastics" (incompletely degradable). The second generation of degradable plastics is photo-oxidative degradable plastics, in which photosensitive groups are constructed in the main chain of plastic molecules to absorb light energy (mainly ultraviolet light) and initiate photo-oxidation to degrade high-molecular polymers into low-molecular-weight compounds. The photosensitive groups are usually carbonyl-type photosensitive groups. Industrially available ones include ethylene-CO copolymers (such as ECO) and ethylene-vinyl ketone copolymers. Photo-oxidative degradation has very strict requirements for degradation conditions such as temperature and light intensity and develops slowly. More importantly, the first-generation starch-modified plastics and the second-generation photo-thermal degradable plastics actually crack the plastics into tiny fragments, i.e., microplastics, under composting conditions. These tiny fragments are macromolecules with difficult-to-degrade C-C chains and are not completely degraded. Scientists' research shows that the presence of microplastics in the environment is even more harmful to humans than white pollution, and a lot of evidence reveals that the occurrence of many diseases is related to microplastics.

[0004] The third-generation degradable plastics, namely fully biodegradable plastics, are formed by the dehydration polymerization of organic acids and alcohols. Their common feature is the introduction of ester groups into the molecular chain. Through various enzymes released by microorganisms, such as esterase, depolymerase, and dehydratase, they bind to specific receptors on the plastic surface and hydrolyze or oxidize the ester groups contained in the polymer, breaking down the macromolecules into fatty acids or lipids with a molecular weight less than 500. These oligomers or their degradation products will enter the microorganisms and ultimately be metabolized and decomposed by the microorganisms into water and carbon dioxide. Currently, such fully biodegradable plastics include polylactic acid (PLA), polyhydroxyalkanoates (PHA), poly-3-hydroxybutyrate (PHB), polybutylene succinate (PBS), poly(butylene adipate-co-terephthalate) (PBAT), etc. However, due to cost and performance limitations (such as poor water resistance), the proportion of such degradable plastics in practical applications is only very small.

[0005] Using third-generation degradable plastics such as PLA and PBAT in combination with PE, PP, etc. has also become an option. For example, in the preparation method of a degradable polyethylene mulch film material disclosed in CN109824962A, modified polyethylene, modified meat and bone meal, modified polylactic acid, and modified straw are mixed in a mass ratio of 45:32-50:28-35:29-37, and then extruded and pelletized through high-speed mixing to form the mulch film. Modified polylactic acid is the main component that endows the mulch film with degradability, and meat and bone meal, potassium silicate, urea, and ammonium lignosulfonate form an organic-inorganic composite nutrient component to improve the degradation performance. However, the content of modified polyethylene is below 33%. According to the ISO846 standard (a method for measuring the deterioration of plastics by measuring the mass change of specimens, whose purpose is not to determine the biodegradability of plastics), the degradation rate in Example 1 can reach 83.1%. An environmentally friendly ECO biodegradable plasticizer for eating plastics and its production method disclosed in CN111138760A uses 30-50 parts of polypropylene, 20-30 parts of biodegradable material polycaprolactone, 10-15 parts of photo-degradable material stearic acid amide, 5-10 parts of erucic acid amide, and stearic acid and palmitic acid. Among them, stearic acid and palmitic acid promote the growth of microorganisms. It is a degradable plastic that combines photo-degradation and biodegradation. When this ECO biodegradable plasticizer for eating plastics is added to the product at an addition amount of 1-5%, it is claimed that it can be completely degraded within 6-12 months under natural environmental conditions, but the literature does not provide detection methods and data. The degradable plastic disclosed in CN102875853A is prepared by mixing 25-33% of ultra-fine starch, 10-18% of ultra-fine plant powder, 15-45% of synthetic degradable resins such as polylactic acid, 10-22% of synthetic resin, and various additives, and then extruding to form degradable particles. Among them, the modified ultra-fine starch and ultra-fine plant powder are used as the main biodegradable components, and polylactic acid is also a biodegradable plastic. The biodegradable components are up to more than 45%. It is claimed that the mass loss rate is ≥20% after being buried in the soil for 30 days under natural conditions, and it can be degraded into powder after being discarded outdoors for 90 days, but the detection method is not disclosed. The common feature of these degradable plastics is that the content of polyethylene or polypropylene only accounts for 10-33%, and they are still mainly composed of degradable materials. Therefore, the cost is still relatively high, and the comprehensive performance is difficult to reach the same level as that of polyethylene and polypropylene plastics, resulting in limited use.

[0006] In addition, in order to ensure that during normal use in the environment, the performance of plastic products will not deteriorate due to the natural degradation of degradable plastics, the controllability of degradation must be considered. Otherwise, while solving white pollution, it will lead to a shortening of the product service life, which will inevitably increase the consumption of plastic products, and thus have a negative impact on the harm of microplastics that have not been truly degraded to the environment and biological health.

[0007] As a plastic products processing enterprise, in order to solve the problem of white pollution, the applicant has cooperated with East China University of Science and Technology, China University of Petroleum, Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences, Nanyang Technological University of Singapore and other institutions in the past 15 years, and has been committed to the research on the microbial degradation conditions and environment of PE, PP, etc. in the soil environment, industrial research and the drafting of industry standards, and has achieved certain results, thus obtaining the present invention. Summary of the Invention

[0008] Aiming at the problem that it is difficult for high molecular polymer plastics such as PE and PP to degrade in the soil environment, the purpose of the present invention is to provide a beneficial bacteria agent for biodegradable plastics, which can improve the anaerobic degradation performance of plastics in the natural environment by changing the ecological environment for degrading plastics in the natural environment, and the addition amount is small so that the cost and performance advantages of the biodegradable plastic base material can be maintained.

[0009] A beneficial bacteria agent for anaerobic biodegradable plastics uses PBAT as a carrier material and also contains nano starch, PLA, nano calcium carbonate, and carbonamide beneficial bacteria material. The mass percentage content of each component is as follows:

[0010]

[0011] Furthermore, the beneficial bacteria agent also contains 7-12% of nano fumed silica, and by utilizing its high specific surface area and adsorption performance, an aggregation nucleus of active centers is formed.

[0012] Preferably, the mass percentage content of each component is as follows:

[0013]

[0014]

[0015] In this application, the role of nano starch is different from that of modified starch in starch-based biodegradable plastics. The starch used in starch-based biodegradable plastics is modified. Through modification, one is to lower the glass transition temperature of starch to achieve the transition from crystalline state to amorphous state to achieve thermoplasticity, and the other is to modify hydrophilic starch into hydrophobic starch to enhance the compatibility with resins such as PLA. Both the starch and PLA in this application are used as attractants for anaerobic microorganisms and become nutrients and adsorption centers for microorganisms in nature (soil, water). It is necessary to maintain the hydrophilicity and high specific surface area of nano starch. Therefore, the nano starch in this application without the qualifier "modified" refers to starch that has not undergone conventional hydrophobic modification and plasticization modification to distinguish it from the modified starch in starch-based biodegradable plastics in the prior art.

[0016] Preferably, the nano-starch is mung bean starch modified by a weak acid or a weak alkaline sodium chloride (2-5% wt) solution. Specifically, it is soaked in a weak acid (pH 6-7) or a weak alkaline (pH 7-8) sodium chloride (2-5% wt) solution for 3-5 days and then dried to modify the mung beans. The modification here is to balance the balanced development of anaerobic microorganisms, rather than the traditional modification concept.

[0017] PLA is modified with absolute ethanol + titanate. PLA and titanate are ground into powders at low temperature for 3-5 minutes, and then absolute ethanol is added in an amount of 1.5 (wt)% and grinding is continued to weaken the van der Waals forces between PLA molecules and increase the binding (affinity) performance with other polar materials.

[0018] In the present invention, the carbamide provides a nitrogen source and energy for the growth of microorganisms. Importantly, the decomposed ammonia can adjust the environmental pH value to maintain the diversity of microorganisms.

[0019] Nano-calcium carbonate is used as an inorganic nano-filler in plastics to increase the physical and mechanical properties and processing properties of plastics. Similarly, due to the functional groups and charges on the surface of nano-calcium carbonate, it is not only easy to agglomerate, but also difficult to disperse when mixed with resin due to strong hydrophilicity. Therefore, nano-calcium carbonate used as a filler in conventional plastics needs to be modified first, such as treatment with a coupling agent, polymer coating treatment, and organic surface treatment. In this application, mainly by utilizing the hydrophilicity and high specific surface area of nano-calcium carbonate, in the soil and water environment, the dissolved calcium ions provide essential elements for the life activities of microorganisms, and promote the growth and metabolism of microorganisms during the initial implantation and enrichment stages of microorganisms. Since calcium carbonate is insoluble, and due to the control of the dosage and the isolation effect of the resin, the ion release is slow and there is no effective inhibitory effect on anaerobic microorganisms.

[0020] Since the beneficial bacteria agent of this application is pre-made into particles and added to the degradable plastic in an amount not exceeding 5% (wt), in order to form a microbial-induced active center, the nano-starch and nano-calcium carbonate are not subjected to hydrophobic modification treatment to maintain their hydrophilicity and a certain degree of agglomeration. However, in order not to affect the processability and physical and mechanical properties of the degradable plastic, this "active center" still needs to be dispersed into the degradable plastic. Therefore, a certain amount and type of dispersant and compatibilizer are still required, and the carrier also uses the degradable resin PBAT.

[0021] The anaerobic degradation beneficial bacteria agent of this application is produced by the following method to form a masterbatch for adding to plastics to improve the degradation speed and degradation rate of plastics. The method includes the following steps:

[0022] (1) First, modify PLA;

[0023] (2) Add carbamide to the modified PLA and mix evenly;

[0024] (3) Then add nano calcium carbonate to the modified PLA and carbamide mixture, stir evenly, and then add starch and stir evenly;

[0025] (4) Finally, add white oil and PBAT for mixing, and then perform plasticizing granulation to form beneficial bacteria particles.

[0026] Preferably, in the scheme containing fumed silica, before adding nano calcium carbonate in step (3), nano fumed silica is also added to the modified PLA and carbamide mixture and stirred evenly.

[0027] Furthermore, in the step of modifying PLA, PLA and titanate are ground into powder at low temperature for (3 - 5) minutes, and then anhydrous ethanol is added for continuous grinding according to a mass content of 1.5%. The present invention also provides a degradable plastic, in which the beneficial bacteria agent is added with a mass content of 1 - 5%. The low temperature is -10 to 0 °C, and it is easy to grind into fine powder at low temperature.

[0028] The present invention also provides an anaerobic biodegradable plastic, in which the aforementioned beneficial bacteria agent is added to the synthetic resin substrate with a mass content of 1 - 5%.

[0029] The synthetic resin substrate is one or more of PE, PP, PVC, PUR, PET, PLA, PHA, PHB, PBAT, PBS, PA, ABS, PS, EPS resins.

[0030] By this method, microparticles with PLA, nano-starch, nano-calcium carbonate, urea, and fumed silica as active centers are dispersed on a PBAT carrier and co-extruded with PE, PP, PVC, PUR, PET, PLA, PHA, PHB, PBAT, PBS, PA, ABS, PS, EPS, etc. to produce plastics, and further processed into different types of plastic products through different processes such as blow molding, film pressing, spinning, die casting, and stretching. After the plastic products are discarded, in the environment of soil, water body, or landfill, for the waste degradable plastics, the probiotic agents dispersed in the degradable plastics, due to the better hydrophilicity of nano-starch, nano-calcium carbonate, and fumed silica than that of organic resins and their high specific surface area, will first adsorb microorganisms in the environment and create active centers conducive to the reproduction and metabolism of microorganisms, providing nutrition and energy for the growth and metabolism of microorganisms, and first degrading the starch, PLA, and PBAT at the active centers. The degradation further enables the reproduction and amplification of microorganisms and the production of various enzymes, further degrading organic resins such as PP and PE to improve the degradation performance. Moreover, the probiotic agents are made into masterbatches, which are easy to control the addition amount according to the required degradation cycle length, thereby realizing adjustable anaerobic degradation. More importantly, anaerobic degradation also enables the degradable plastics of the present invention to be in normal use conditions. Under the light and oxygen environment, the plastics will not accelerate degradation, and their aging performance is equivalent to that of the resin matrix of the plastics, ensuring the physical and mechanical properties. Detailed implementation manners

[0031] The following further describes the present invention in detail with reference to embodiments.

[0032] The following further illustrates the present invention with specific embodiments to help understand the content of the present invention.

[0033] 1. Probiotic agent particles

[0034] For Examples 1-6, the materials are prepared according to the components and ratios shown in Table 1.

[0035] Table 1 Components and mass percentage contents (%) of different examples

[0036]

[0037] The production methods of the probiotic agents in Examples 1-6 are as follows:

[0038] (1) Grind PLA and titanate evenly at low temperature (-5°C) for (3-5) minutes into fine powder, and then continue to grind with anhydrous ethanol added at a mass content of 1.5% to modify PLA;

[0039] (2) Add urea to the modified PLA and mix evenly;

[0040] (3) Then add fumed silica to the mixture of modified PLA and carbamide, and stir evenly; then add nano calcium carbonate and stir evenly to form active particles with fumed silica as the adsorption center;

[0041] (4) Then add starch and stir evenly to make the particle surface wrapped with a hydrophilic starch coating;

[0042] (5) Finally, add white oil and PBAT for mixing and plasticizing granulation to form beneficial bacteria particles.

[0043] 2. Degradable plastics

[0044] Raw materials: Add the beneficial bacteria particles of Examples 1-6 to PE resin, and melt-extrude together with additives such as antioxidant 1010, N,N'-ethylenebisstearamide, and stearic acid, and blow-mold into a polyethylene degradable plastic film. The content of beneficial bacteria particles in the film is 3% (wt).

[0045] 3. Anaerobic degradation detection

[0046] Control: According to 72.2 g of PBAT, 6.8 g of PLA, 6.5 g of nano corn starch modified with polyol and long-chain fatty acid, and 4.5 g of modified nano calcium carbonate, add white oil for mixing and granulation to make a control masterbatch. Then add the control masterbatch to PE resin, and melt-extrude together with additives such as antioxidant 1010, N,N'-ethylenebisstearamide, and stearic acid, and blow-mold into a polyethylene degradable plastic film. The content of the control masterbatch in the film is 3% (wt).

[0047] According to "Determination of the ultimate anaerobic biodegradability of plastics under high-solids composting conditions - Method by analysis of evolved biogas" (GBT 33797-2017), detect the degradation rates of the degradable plastic films of Examples 1-6 and the control. This method is used to determine the decomposition rate of anaerobic decomposition, that is, the percentage of the carbon content in the test material and the carbon dioxide and methane converted after its degradation is used as the degradation rate. The measurement results are shown in Table 2 below:

[0048] Table 2 Anaerobic degradation rates of different materials

[0049]

[0050]

[0051] As can be seen from the above table, the anaerobic absolute degradation rate of the plastic in Example 1 reached 4.8% in 90 days, with the best degradation effect. Compared with the degradation rate of 3.9% in Example 2, it proves that nano mung bean starch indeed shows a better effect in promoting degradation than nano corn starch. The comparison between Example 1 and Example 2 proves the promoting effect of the addition of fumed silica on anaerobic degradation. The degradation rate of Example 4 is the lowest among the 6 examples, indicating that it is not the case that the higher the content of mung bean starch, nano calcium carbonate and carbamide, the more conducive to degradation. The comparison between Example 5 and Example 4 and Example 6 shows that the PLA content is highly sensitive. The inventor speculates that PLA may be used as the starting component for microbial degradation. The comparison between Examples 1-6 and the comparative example shows that the comparative example has a degradation rate of only 0.1% in 90 days, proving that the nano starch and nano calcium carbonate treated by hydrophobic compatibilization modification do not play a role in promoting degradation. The inventor speculates that it may be related to their hydrophobicity after modification.

[0052] 4. Aerobic Degradation Detection

[0053] The anaerobic degradation plastic film of Example 1 was tested for the degradation rate under aerobic conditions according to GB / T 19277.1-2011 Determination of the ultimate aerobic biodegradability of materials under controlled composting conditions - Method by measuring the evolved carbon dioxide. Obviously, the degradation rate in 90 days was 2.3%, which was significantly lower than the anaerobic degradation rate, proving that under aerobic conditions, only PBAT and PLA, which are inherently biodegradable materials, degraded, and PE did not degrade. Such an effect is conducive to maintaining the durability of the performance of degradable plastics under normal use.

[0054] Those of ordinary skill in the art can understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A probiotic agent for anaerobic biodegradable plastics, characterized in that: Using PBAT as the carrier material, it also contains nano-starch, PLA, nano-calcium carbonate, and carbonamide probiotic material, and the mass percentage content of each component is as follows:

2. The probiotic agent according to claim 1, characterized in that It also contains 7-12% by mass of nano-fumed silica.

3. The probiotic agent according to claim 2, characterized in that, The mass percentage content of each component is as follows:

4. The probiotic agent according to claim 1 or 2, characterized in that, The nano-starch described is mung bean starch modified by soaking in a weak acid or weak alkaline sodium chloride solution and then drying.

5. The probiotic agent according to claim 1 or 2, characterized in that, The PLA is PLA powder modified by anhydrous ethanol.

6. A production method of the probiotic agent for anaerobic biodegradable plastics according to claim 1 or 2 or 3, the steps are as follows: (1) First, modify PLA; (2) Add carbamide to the modified PLA and mix evenly; (3) Then add nano-calcium carbonate to the mixture of modified PLA and carbamide, stir evenly, and then add starch and stir evenly; (4) Finally, add white oil and PBAT and mix, plasticize and granulate to form probiotic granules.

7. The production method according to claim 6, characterized in that: Before adding nano-calcium carbonate in step (3), nano-fumed silica is also added to the modified PLA and carbonamide mixture and stirred evenly.

8. The production method according to claim 6, characterized in that: The step of modifying PLA is to grind PLA and titanate into powder at low temperature for 3-5 minutes, and then continue to grind with anhydrous ethanol added at a mass content of 1.5%.

9. An anaerobic biodegradable plastic, characterized in that a probiotic agent according to claim 1 or 2 or 3 is added in a synthetic resin substrate in a mass content of 1-5%.

10. The anaerobic biodegradable plastic according to claim 9, characterized in that: The synthetic resin substrate is one or more of PE, PP, PVC, PUR, PET, PLA, PHA, PHB, PBAT, PBS, PA, ABS, PS, EPS resins.

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