Application of Polylactic Acid (PLA) in Packaging
PLA is one of the biodegradable materials that has received the most research attention at home and abroad. Medical, packaging and fibers are its three popular application fields. PLA uses lactic acid from natural sources as the main raw material, has good biodegradability and biocompatibility, and its life cycle load on the environment is significantly lower than that of petroleum-based materials, and is considered to be the most promising green packaging material.
Polylactic acid (PLA) can be completely decomposed into carbon dioxide and water under natural conditions after being discarded. It has good water resistance, mechanical properties, biocompatibility, can be absorbed by organisms, and has no pollution to the environment. At the same time, PLA also has good mechanical properties. It has high impact strength, good flexibility and thermal stability, plasticity, processability, no discoloration, good permeability to oxygen and water vapor, and good transparency, anti-mildew, antibacterial , the service life of 2 to 3 years.
Film food packaging
The most important performance index of packaging materials is air permeability, and the application field of this material in packaging can be determined according to the different air permeability of materials. Some packaging materials require oxygen permeability to supply enough oxygen to the product; some packaging materials require a barrier to oxygen in terms of materials, such as beverage packaging, which requires materials that can prevent oxygen from entering the package to inhibit mold. effect of growth. PLA has gas barrier, water barrier, transparency and good printability.
Transparency
PLA has good transparency and gloss, and its excellent performance is comparable to cellophane and PET, which is not available in other degradable plastics. The transparency and gloss of PLA are 2~3 times that of ordinary PP film and 10 times that of LDPE. Its high transparency makes the appearance of using PLA as a packaging material beautiful. For example, it is used for candy packaging. At present, many candy packagings on the market use PLA packaging films.
The appearance and performance of this packaging film are similar to traditional candy packaging films, with high transparency, excellent kink retention, printability and strength, as well as excellent barrier properties, which can better retain the flavor of candy . A Japanese company uses the "racea" grade PLA of the American Cargil Dow Polymer Company as the packaging material for new products, and the packaging has good transparency in appearance. Toray Industries has developed PLA functional films and slices using its proprietary nano-alloy technology. This film has the same heat and impact resistance as petroleum-based films, but also has excellent elasticity and transparency.
Barrier
PLA can be made into film products with high transparency, good barrier properties, excellent processability and mechanical properties, and can be used for flexible packaging of fruits and vegetables. It can create a suitable storage environment for fruits and vegetables, maintain the life activities of fruits and vegetables, delay aging, and maintain the color, aroma, taste and appearance of fruits and vegetables. However, when applied to actual food packaging materials, some modifications are required to adapt to the characteristics of the food itself, so as to achieve better packaging effects.
For example, in practice, it has been experimentally found that the hybrid film is better than the pure film. He Yiyao packaged broccoli with pure PLA film and PLA composite film respectively, and stored them at (22±3) ℃, and regularly tested the changes of various physiological and biochemical indexes of broccoli during storage. The results show that the PLA composite film has a better preservation effect on broccoli at room temperature, and can form a humidity level and an air-conditioned environment in the packaging bag that is conducive to regulating the respiratory metabolism of broccoli, and maintains the appearance quality of broccoli. The original flavor and taste are well preserved, thus extending the shelf life of broccoli at room temperature by 23 days.
Bacteriostatic
PLA can form a weakly acidic environment on the surface of the product, which has the basis of antibacterial and antifungal. If other antibacterial agents are used in addition, the antibacterial rate of more than 90% can be achieved, which can be used for antibacterial packaging of products. Yin Min took Agaricus bisporus and golden ear as examples to study the fresh-keeping effect of the new PLA nano-antibacterial composite film on edible fungi, so as to prolong the shelf life of edible fungi and keep them in good quality. The results show that: PLA/rosemary essential oil (REO)/AgO composite film can effectively delay the reduction of vitamin C content in golden ear. Compared with LDPE film, PLA film and PLA/REO/TiO2 film, the water permeability of PLA/REO/Ag composite film is significantly higher than that of other films. It is concluded from this that it can effectively prevent the formation of condensed water and achieve the effect of inhibiting the growth of microorganisms; at the same time, it also has excellent bacteriostatic effect, can effectively inhibit the reproduction of microorganisms during the storage of golden ear, and can significantly extend the shelf life to 16 sky.
At the same time, compared with ordinary PE plastic wrap, PLA has better effect
Per the study of the fresh-keeping effect of PE plastic wrap and PLA film on broccoli respectively, the results show that the use of PLA film packaging can inhibit the yellowing of broccoli and the falling off of curds, and effectively maintain the content of chlorophyll, vitamin C and soluble solids in broccoli. PLA film has excellent gas selective permeability, which helps to form a storage environment with low O2 and high CO2 in PLA packaging bags, which can inhibit the life activities of broccoli, reduce water loss and nutrient consumption. The results show that compared with PE plastic wrap, PLA film can prolong the shelf life of broccoli by 1-2 days at room temperature, and the preservation effect is obvious.
