Biodegradable plastics degradation technology and its prospect!

  • 2022-08-07

Conventional plastic waste is usually disposed of by landfill, which produces leachate and greenhouse gases that not only pollute the soil but also contribute to the greenhouse effect. Biodegradable plastics have the possibility of biodegradation under different environmental conditions, such as compost, soil and aquatic systems. Compost and soil degradation have been widely used due to their microbial diversity.

First, compost degradation

Compost degradation technology is an effective method to recycle organic waste and treat organic solid waste. Biodegradable plastics are transformed into humus by bacteria, fungi and actinomycetes. This technique can directly reflect the degradation of plastics under natural conditions and has gradually become the main method to evaluate the biodegradability of plastics。


Using compost as a microbial community to biodegrade different biodegradable materials has been the subject of extensive research in recent years.


The degradation effect of biodegradable materials is usually shown by the weight loss rate of degradation. By adding degradable materials to pure bioplastics, blended biocomposites were prepared, which could improve biodegradability of bioplastics under composting conditions.


Anstey et al. used composting method to degrade polybutanediol succinate (PBS). The study showed that the compost degradation rate of pure PBS was 24% after 100 days. The soybean meal powder containing soluble sugar was added to PBS to obtain the blended biocomposite. Under the same conditions, the degradation rate of the composite could reach 60%.


Wu et al. blended polylactic acid (PLA)/ sisal fibers into thin films. Under the same conditions and buried for 14 weeks, the degradation rate was 50% higher than that of pure PLA. Ahn et al. made PLA/ starch/poultry feather fiber (PFF) blend material and pure PLA into plastic POTS, placed them at 58℃ and composted them for 60 days. The study found that the degradation rates of the two were 53% and 13%, respectively.

The analysis results showed that the biodegradation ability of pure PLA was lower, because the addition of starch in the blended biocomposite was easier to be degraded by microorganisms than pure PLA, and the processing operations such as molding and extrusion during the production of pure PLA could also lead to the low biodegradation ability.


Mostafa et al. used cellulose acetate (CA) to blend with flax and cotton wool, which are fibers with low cost. After 14 days of composting, the biodegradation rates of the two materials were 44% and 35%, respectively. Wu et al. found that the degradation rate of PHA composite containing rice husk (RH) was 45% higher than that of pure PHA after 60 days of composting under the same conditions. This is because, with the continuous increase of rice husk content, the performance of the blended biomaterial is significantly improved, and its water absorption performance is significantly reduced, which improves the degradation effect of the blended biomaterial in the process of composting.


Tabasi et al. blended PLA and polyβ-hydroxybutyric acid (PHB) with polyadipic acid/butylene terephthalate (PBAT) to make bioplastics under the same conditions. The degradation rate of the two blends was significantly lower than that of pure PLA and pure PHB by composting method under the same conditions. Fourier transform infrared spectroscopy (FTIR) was used to observe the composition changes of the two blends during the composting process. The results showed that the biodegradation rates of the two blends were basically the same at the beginning of degradation. Later, because PBAT formed a three-dimensional spatial network with PLA and PHB, the degradation rate of the bio-blend material was slowed down, and finally, the degradation effect was reduced.


Other studies have shown that some special blends of biocomposites need to be composted at high temperature and for a long time to fully degrade. Rudnik et al. studied the biodegradation of PLA under the conditions of natural composting and industrial composting at 40℃ and about 150℃ respectively. The results showed that the degradation rate of PLA under natural compost conditions was significantly lower than that of the latter. Therefore, temperature was the main factor affecting the degradation effect of PLA compost.


Although some bioplastics on the market are labeled as purely biodegradable, their composting potential is unproven. Vaverkova et al. conducted A 22-week compost biodegradation experiment on two sponge cloth bioplastic samples (sample A and sample B) used for surface cleaning under the conditions of pH=6.5 ~ 8.0, humidity of 30%~65% and temperature of 58℃. The results showed that the biodegradation rate of sample B could exceed 80%. The lowest biodegradation rate of sample A was only 12.8%. By adding some easily degradable materials to pure bioplastics, the blended biocomposites can not only change their mechanical properties, but also significantly improve the degradation effect of bioplastics under composting conditions. However, due to the complexity of compost degradation mechanism, long degradation time, and also affected by biological and abiotic factors, it is necessary to further study the biodegradation under compost conditions.


second soil degradation

Because plastic waste is widely distributed in soil environment, it is necessary to study the change and influence of plastic waste in this environment. The soil environment contains a large number of microorganisms and their diversity makes the biodegradation of plastics more feasible than in other environments.


In order to improve the degradation effect of bioplastics, researchers have studied the degradation of various biodegradable materials in soil. Wei et al. studied the biodegradability of potato peel waste residue fiber (PPW-FR)/PHB blended biocomposite in soil, and the results showed that, compared with pure PHB, when the PPW-FR in the blended biocomposite reached 50%, the blended biocomposite could be completely degraded in only 8 months. Further studies showed that PPW-FR reduced the crystallinity of PHB and increased the degradation rate of the material.


Harmaen et al. added empty fruit cluster (EFB) fiber to PLA, and degraded the obtained blend material in soil for 2 weeks. It was found that under the same conditions, the degradation rate of EFB fiber was increased by 15% compared with pure PLA. The higher the cellulose content of EFB fiber, the higher the water absorption, which has a synergistic effect on the biodegradation rate of the material.


Soil biodegradation of pure PLA and PLA/EFB blend biocomposites was studied simultaneously for 11 months in the Mediterranean region. The results showed that although PLA/EFB was completely degraded eventually, its biodegradation process was very slow. Therefore, the material needs a high temperature and a long time to be completely degraded.


Studies have shown that the pH of soil environment is different, the biodegradation effect of materials is also different. Boyandin et al. showed that the degradation rate of PHA film in the soil environment of Vietnam and Ho Le region was more than 98%, while the degradation rate of PHA film in the soil environment of Dam Bai region of Vietnam was only 47% during the same period. The pH values of soil in these two areas were 6.63 and 5.48, respectively, indicating that different soil pH values affected microbial activity and degradation enzymes secreted by microorganisms, thus affecting the degradation rate of PHA.


Some easily degraded materials are added to pure bioplastics to produce blended biocomposite plastics, which can improve the biodegradability of bioplastics under soil conditions. However, bioplastics require high degradation conditions. Moreover, pH value is also a factor that affects the biodegradation effect of biomaterials under soil conditions.

Degradation of aquatic systems

In aquatic systems, there is also a large accumulation of plastic waste. Plastic waste not only pollutes aquatic systems, but also adversely affects aquatic plants and animals. In recent years, a lot of research has been done on the biodegradation of bioplastics in aquatic systems.

Tosin et al. studied the degradation of bioplastics buried in six different habitats. The results showed that the degradation effect of bioplastics was more obvious in the middle and upper ocean than in the eutrophic environment. Moreover, at the water-sand interface, the bioplastic degradation rate is the highest, because the environmental conditions of the water-sand interface are conducive to the growth of plastic-degrading microorganisms.


Thellen et al. compared the degradation of 3-hydroxyvalerate copolymer (PHBV) and PHB in static and dynamic seawater. The results showed that the weight loss rates of PHBV and PHB under dynamic conditions were lower than those under static conditions. This is due to insufficient microbial nutrient supply in seawater and changes in seawater temperature under dynamic conditions. In addition, the effect of the addition of sediment on the degradation efficiency of plastic was also studied. The results showed that the sediment had a good promotion effect on the degradation of plastic.


Volova et al. studied the effect of seawater temperature on the biodegradation of plastic, and the results showed that the biodegradation rate of PHA films was different due to the change of climate temperature in different periods in 1999 and 2000. In addition, different microorganisms play an important role in the degradation of bioplastics in seawater.


Although the degradation mechanism of bioplastics is different due to environmental factors and bioplastic forms, both of them will affect the degradation effect of bioplastics in aquatic systems. For example, environmental factors affect bioplastic degradability mainly through bioplastic degrading enzymes produced by corresponding microorganisms; The shape of the bioplastic affects the degradability of the bioplastic by changing the number of microorganisms that the bioplastic adheres to in seawater.


Biodegradable bioplastic bag microorganisms

Under different environmental conditions, the microbial species that degrade plastic are also different. The study found that there are more than 90 kinds of microorganisms that can degrade plastic, and they are widely distributed. There are many ways to degrade biodegradable plastics, among which enzymatic degradation by microorganisms is one of the most effective methods.

These microorganisms, which can degrade biodegradable plastics, can use bioplastics for catabolism by producing corresponding intracellular enzymes or extracellular enzymes. For example, in the process of biodegradable PHB soil, microbial usually starts from the surface of PHB attack, then the bacteria will degradation enzyme secretion to in vitro, rely on the c-terminal and depolymerization of extracellular enzyme N the close function, the PHB degradation of low molecular weight products, such as acetyl acetate and a small amount of acetic acid, and then, the above material is through the cell membrane, microorganisms into the inside, Microbes can break down and reuse the ingested material, which is eventually metabolized into CO2 and H2O.


Wang Yan isolated and screened Pseudomonas strain DSWY0601 from microorganisms that degraded PHB. The extracellular enzyme produced by the strain could degrade PHB to small molecules soluble in water. These small molecules can enter the cell through the biofilm, thus participating in the microbial metabolic cycle, and finally can be completely degraded.


In addition, some microorganisms capable of degrading PLA produce extracellular depolymerase, but this enzyme cannot penetrate PLA. Therefore, the enzymatic degradation process secreted by microorganisms only occurs on the surface of PLA. Because depolymerase is selective, will first into a particular area of the PLA degradation (such as amorphous area), also began to degrade and PLA crystallization area, result in PLA molecular ester bond rupture, PLA is decomposed into small molecular products (such as oligomers, etc.), due to the degradation of small molecular products can through a semipermeable membrane bacteria, as a result, it can eventually be bacterial metabolism.


Yu Dan et al. used strain DS0901 to degrade the surface of PCL membrane and found that the membrane was decomposed first, and small pores appeared. With the prolongation of time, the pore radius increased continuously. With the deepening of degradation time and degree, the membrane surface degradation becomes more obvious. Further studies showed that the final degradation products were low amounts of PCL monomer and dimer, and the degradation process was gradually from the surface to the interior of the membrane. The above degradation process did not find the attachment of thalli, which indicated that the strain degraded PCL films through its own secreted extracellular depolymerase.


Bioplastics produced from renewable resources can be degraded by microorganisms in other environments. Sekiguchi et al. found that PCL-degrading bacteria isolated from deep-sea sediments could not degrade PLA, PHB, PBS, and other bioplastics such as butanediol succinate copolymer (PBSA), mainly due to the pressure difference between deep-sea conditions and other conditions. A variety of biodegrading bacteria such as Pseudomonas, Bacillus and Bacillus gracilis were isolated from this environment.


The co-culture of different microorganisms can promote the degradation of bioplastics. Other microorganisms can use the host microorganisms to degrade the intermediates obtained from the bioplastics and promote biodegradation.

Abe et al. found that oligotrophic monospora YB-6 could not degrade PBS alone, but when it was mixed with Fusarium vulcanis WF-6, it could promote the biodegradation of PBS.


Nishida et al. showed that co-culture of sphingosinomonas oligmomosis and hydrolase strains significantly improved the biodegradation performance of polyp-dioxacyclohexanone.


In the study of Nakasaki et al., when Bacillus HA1 was co-cultured with Streptomyces PDS-1, the biodegradation ability of PCL was significantly improved.


In soil, there are suitable temperature, pH, nutrition and other conditions for the growth of most microorganisms. Therefore, microorganisms can degrade bioplastics by producing corresponding enzymes themselves. In addition, we can screen a wider range of microorganisms from soil, and expect to obtain more microorganisms capable of degrading bioplastics, and apply them to the field of bioplastic degradation.


Under some extreme conditions, microorganisms can degrade a bioplastic, but not all bioplastics can be degraded by microorganisms under such conditions. Therefore, co-culture of different microorganisms provides a new idea for bioplastic degradation, and this method can be used to completely degrade bioplastics in an efficient and orderly manner.


conclusion

Bioplastics can be degraded by various microorganisms in different ecosystems (landfill, compost, seawater, river water, etc.). However, under different environmental conditions, the biodiversity of plastic-degrading microorganisms is also different. Under the conditions of soil and compost environment, the bioplastic degradability is higher, which is mainly due to the high diversity of microorganisms under the conditions. Large amounts of plastic enter water bodies and Marine systems, with unavoidable impacts on freshwater and Marine ecosystems. Based on the above problems, the future research and development of bioplastic degradation should focus on the following aspects.

1. The co-culture of different microorganisms can promote the biodegradation of bioplastics, but the related degradation mechanism has not been studied. Therefore, in future research, we can improve the degradability of biodegradable plastics by studying the related mechanism of co-culture of different microorganisms.

2. According to the properties of biodegradable plastics, it makes reasonable use of traditional methods such as molding, extrusion molding and blow molding to produce plastic products, and expands its application field combined with 3D printing technology, which has an important impact on solving environmental pollution and realizing green and sustainable development.

3. Traditional disposable non-degradable plastic products have been widely used in emerging industries such as takeout and e-commerce, but the subsequent treatment is complicated, which limits its development. Therefore, higher requirements are put forward for the development and innovation of biodegradable plastic production and processing technology. Biodegradable plastic products with low energy consumption, high energy and environmental friendliness are the key research directions in the future.

© Copyright: DONGGUAN SENGTOR PLASTICS PRODUCTS CO.,LTD. All Rights Reserved.     SiteMap.xml | SiteMap.html | Terms & Conditions | Privacy

top

Leave a Message

Leave a Message

    If you are interested in our products and want to know more details, please leave a message here and we will reply to you as soon as possible.

粤ICP备05035280号
x

Download product manual

Please fill in your email and we will send you the latest product manual