The application of PBAT in the field of packaging
PBAT is one of the few materials that is recognized as "biodegradable" today. It has good flexibility and is often teamed up with PLA, another popular player in the field of biodegradation. PLA is hard and has poor toughness, easy to bend and deform, and has poor impact and tear resistance, but has good transparency and barrier properties. PBAT has good stretchability and excellent heat resistance, and the two are produced by blending and complementing each other.
The following is a brief analysis of the three popular application areas of PBAT from agricultural mulch, plastic bags, and plastic wrap.
The function of mulch is to increase temperature and moisture and increase crop yield. When the traditional non-degradable ultra-thin polyethylene mulch film is used in agricultural production, the problem of "residual film" often occurs. Residual film is difficult to recover, and most of it is mixed in the soil. The existence of residual film not only destroys the soil structure, but also reduces the emergence rate of crops and crop yield. According to the experimental statistics of relevant experts, when the amount of residual film in the soil exceeds a certain level, its effect on crop yield reduction will even exceed the yield increase benefit of the use of plastic film, so it is better not to use plastic film.
The emergence of degradable plastic film provides a solution to this agricultural production problem. After a wave of crop production is completed, the degradable film is completely degraded in the soil, and subsequent recycling is not required, which not only preserves the effectiveness of the plastic film, but also avoids soil pollution. At present, degradable mulch films can be divided into three categories, photodegradable films, photo/biodegradable films, and biodegradable films. The photodegradable film stopped degrading after being covered with soil, and the degradation effect was poor. However, the implementation cost of the photo/biodegradable film is high and the application is difficult. The current research on plastic film is mainly biodegradable.
However, due to its higher production cost, lower thermophysical properties and mechanical properties, PBAT usually needs to add low-cost fillers as reinforcing agents. The filler improves the performance of the material while ensuring the biodegradability and reduces the production cost. However, there are still many difficulties in the application of PBAT in the field of thin film application.
First, the degradable mulch film can neither degrade prematurely nor degrade too long. The degradation effect of PBAT mulch film, some tests show that cracks appear after 30 days of mulching, and it is completely degraded after 90 days. However, since PBAT plastic film is suitable for different soil conditions (such as Xinjiang and other regions with large changes in climate and environment, the plastic film needs to have a certain thickness) and different agricultural needs (machine cotton picking), it may be blended with different plastics. After 180 days of blending with PET, there is still a large amount of plastic film remaining on the soil surface.
Second, the application of biodegradable plastic film is on average 2~3 °C lower than that of ordinary plastic film, and the soil moisture also decreases. According to the analysis of the experimenter, the reason for this result is closely related to the thickness of the degradable plastic film.
The focus of plastic wrap used for fruit and vegetable packaging is to maintain the moisture in the packaging and maintain a dynamic balance of gas components. The materials generally used for fruit and vegetable packaging have good carbon dioxide/oxygen selective permeability, but when the air permeability is too large, the gas exchange volume inside and outside the package is large. Good fresh-keeping effect; when the air permeability is low, the oxygen inside the package is quickly consumed, resulting in too much carbon dioxide, and the packaging film cannot supply the oxygen needed for metabolism in time and emit a large amount of carbon dioxide, which cannot achieve the ideal atmosphere conditions for fruit and vegetable preservation.
PBAT used for cling film must be mixed with other materials. Pure PBAT film bags will stick together because of their self-adhesion, and wrinkles will appear on the surface of the film bags. Some experimenters added PCL to pure PBAT, and the effect was good. The surface of the mixed-film packaging bag was smooth, and the double layer had no adhesion.
The research results show that when using PBAT/PCL20 film packaging, the thickness of the film is further reduced, the carbon dioxide concentration inside the package quickly enters an equilibrium state from the 2nd day, the volume fraction is maintained in the range of 2% to 3%, and the oxygen volume fraction increases with As the storage time gradually decreases, it finally reaches 6% to 7%, which effectively regulates the atmosphere inside the package and achieves a more suitable atmosphere composition for strawberry preservation.
At the same time, PBAT/PCL20 can keep the strawberries in the bag in a good sensory state for a long time (more than 20 days), and the moisture permeability is good.
PBAT is a polymer compound synthesized based on fossil fuels, which is almost completely biodegradable and is an environmentally friendly material with high fracture elongation and strong toughness. Due to its good ductility and toughness, it is suitable for the blown film process, and is currently widely used in blown film fields such as plastic bags.
However, due to its soft nature and poor fluidity, PBAT needs to be modified by adding PLA and fillers. Pure PBAT film blowing effect is poor, the film bubble is unstable, and the film is difficult to open. In addition, the degraded material is not resistant to high temperature, and is easily carbonized in the screw rod, and black spots may appear on the produced film bag.
Because PBAT has the characteristics of high processing viscosity, high melt strength, and good gas permeability, which makes PBAT suitable for mixing with other materials. However, compared with non-biodegradable polyester, PBAT has higher production cost and lower thermophysical properties, which hinders the development and application of PBAT biodegradable polyester materials.
