PBAT is the mainstream degradable material in China's environmental protection market. For example, the raw material on many degradable plastic bag says: PLA + PBAT. In the supermarket, many degradable preservative films covering the fruits says: PCL + PBAT.
The reason why PBAT is so popular is closely related to its good physical and chemical properties. Its processability is like LDPE, and it can be blown by similar process. Good elasticity, waterproof and tear resistant, suitable for food contact. Its mechanical properties are like PBT, with good ductility, heat resistance and impact resistance. It is often used to modify and blend with other biodegradable materials.
In addition, PBAT is flexible and often cooperates with PLA. PLA is hard with poor toughness, easy to bend and deform, poor in impact and tear resistance, but good in transparency and barrier. PBAT has good tensile property and excellent heat resistance, which complement each other by blending.
The three popular application areas of PBAT span from agricultural film, plastic bags, and preservative film.
The role of the film is to increase temperature and moisture, and improve crop yield. However, the traditional non degradable ultra-thin polyethylene film is often used in agricultural production, and the problem of "residual film" often appears. The residual membrane is difficult to recover. Most of them are mixed in the soil. The existence of residual membrane not only destroys the soil structure, but also reduces the seedling rate and crop yield. According to the relevant experts' experiment statistics, when the amount of soil residual membrane exceeds a certain level, the effect of the soil yield reduction on crops will even exceed the yield increase benefit of the use of the mulch, rather than the mulch.
The appearance of degradable plastic film provides a solution to the problem of agricultural production. When a wave of crop production is completed, the degradable film is completely degraded in the soil without subsequent recovery, which not only saves the effectiveness of plastic film, but also avoids soil pollution. At present, degradable plastic film can be divided into three categories: photodegradable film, photo / biodegradable film and biodegradable film. The photodegradable film stopped degradation after covering soil, and the degradation effect was poor. However, the cost of photo / biodegradable film is high and its application is difficult. At present, the research of plastic film is mainly biodegradable.
Due to its high production cost, low thermal physical properties and mechanical properties, PBAT usually needs to add low-cost fillers as reinforcers. The filler not only ensures the biodegradability, but also improves the performance of the material and reduces the production cost. However, there are still many difficulties in the application of PBAT.
1. Degradable plastic film can't be degraded too early or too long. The degradation effect of PBAT film showed that cracks appeared 30 days after mulching, and completely degraded 90 days later. However, in order to adapt to different soil conditions and different agricultural needs (machine picking cotton), PBAT film may be blended with different plastics. Some experimenters still have a large amount of film residue on the soil surface after 180 days because of adding PET blend.
2. Compared with ordinary plastic film, the soil temperature of biodegradable plastic film was 2 ~ 3 ℃ lower, and the soil moisture was also decreased. According to the analysis of experimenters, the reason for this result is closely related to the thickness of degradable plastic film.
Conclusion: from the perspective of economy and application effect, in practical application, the thinner completely biodegradable film has stronger popularization. Although the economic effect of completely biodegradable film is not as good as ordinary plastic film at present, the completely biodegradable film will not do harm to the environment. In the long run, it can replace ordinary plastic film and has broad application prospects.
As a fresh-keeping film for fruit and vegetable packaging, the key point is to maintain the moisture in the packaging and the dynamic balance of gas composition. The materials generally used for fruit and vegetable packaging have better CO2 / O2 permeabilities, but when the permeability is too high, the gas exchange capacity inside and outside the packaging is large, and when it reaches equilibrium, the atmosphere inside the packaging is close to the external air components, which can not have a good preservation effect; when the permeability is low, the oxygen inside the packaging is quickly consumed, resulting in too much CO2, and the packaging film can not be replenished in time The oxygen needed for metabolism emits a large amount of carbon dioxide, which can not reach the ideal atmosphere conditions for the preservation of fruits and vegetables.
PBAT film must be mixed with other materials, pure PBAT film bag will be bonded together because of its self-adhesive, and the surface of the film bag will be wrinkled. Some experimenters added PCL to pure PBAT, and the effect was good. The surface of mixed film packaging bag was smooth, and there was no adhesion between the two layers.
The results of Yun Xueyan et al. Showed that when PBAT / pcl20 film was used for packaging, the thickness of the film was further reduced, the concentration of carbon dioxide in the packaging quickly entered the equilibrium state from the second day, and the volume fraction of oxygen was maintained in the range of 2% - 3%, while the volume fraction of oxygen gradually decreased with the storage time, and finally reached the maximum value 6% ～ 7%, which can effectively control the atmosphere inside the packaging to achieve a more suitable atmosphere composition for strawberry preservation.
At the same time, PBAT / pcl20 can keep the strawberry in the bag in good sensory state for a long time (more than 20 days), and has good moisture permeability.
At the same time, PBAT / PCL20 can keep the strawberry in the bag in good sensory state for a long time (more than 20 days), and has good moisture permeability.
Degradable plastic bag
PBAT is a kind of polymer compound based on fossil fuel, which is almost biodegradable. It is an environment-friendly material with high fracture elongation and strong toughness. Because of its good ductility and toughness, it is suitable for film blowing process and is widely used in plastic bags and other film blowing fields.
However, due to its soft nature and poor fluidity, PBAT needs to be modified by adding PLA and filler. Pure PBAT film blowing effect is poor, the bubble is unstable, and the film is difficult to open. In addition, the degradable material is not resistant to high temperature and easy to carbonize in the screw rod, so black spots may appear on the film bag.
PBAT is suitable for mixing with other materials because of its high processing viscosity, high melt strength and good gas permeability. However, compared with non biodegradable degradable polyester, PBAT has higher production cost and lower thermophysical properties, which hinders the development and application of PBAT biodegradable polyester.
To improve and strengthen the mechanical properties of PBAT polymer, further optimize the production process of upstream raw materials and reduce the price of PBAT are effective ways to expand its application in commercial and higher fields.
Source: Institute of biodegradable materials