PLA is one of the biodegradable materials that have received the most attention from domestic and foreign research. Medical, packaging and fiber are its three popular application fields. PLA uses natural source lactic acid as the main raw material and has good biodegradability and biocompatibility. Its life cycle load on the environment is significantly lower than that of petroleum-based materials. It 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 does not pollute the environment. At the same time, PLA also has good mechanical properties. It has high impact strength, good flexibility and thermal stability, plasticity, processing formability, no color change, and good permeability to oxygen and water vapor. At the same time, it has good transparency, anti-mildew, antibacterial and other characteristics, and its service life can reach 2 to 3 years.
1. Film food packaging
The more 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 the material. Some packaging materials require oxygen permeability to supply enough oxygen for the product; Some packaging materials require oxygen barrier properties in terms of materials. For example, packaging materials such as beverages require materials that can prevent oxygen from entering the packaging to achieve the effect of inhibiting the growth of mold. 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 a performance that other degradable plastics do not have. The transparency and gloss of PLA is 2 to 3 times that of ordinary PP film and 10 times that of LDPE. Its high transparency makes PLA as a packaging material beautiful in appearance. For example, it is used for candy packaging. At present, many candy packaging on the market use PLA packaging film.
The appearance and performance of this packaging film are similar to those of traditional candy packaging films. It has high transparency, excellent kink retention, printability and strength. It also has excellent barrier properties and can better retain the fragrance of the candy. A Japanese company uses the "racea" brand of PLA from the American Cargill Dowgold Co., Ltd. as the packaging material for its new product. The packaging has a very good appearance and transparency.
PLA film has good 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, fragrance, taste and appearance of fruits and vegetables. However, when applied to actual food packaging materials, some modifications are needed to adapt to the characteristics of the food itself, so as to achieve a better packaging effect.
For example, in specific practice, experiments have found that hybrid films are better than pure films. The researchers used pure PLA film and PLA composite film to package broccoli, and stored them at (22±3)℃. They regularly tested the changes in various physiological and biochemical indexes of broccoli during storage. The results show that: PLA composite film has a better preservation effect on broccoli storage at room temperature, and can form a humidity level and a modified atmosphere environment that is conducive to regulating the respiratory metabolism of broccoli in the packaging bag, and maintains the appearance quality of broccoli better. The original flavor and taste are well preserved, which extends the shelf life of broccoli at room temperature by 23 days.
PLA film is used for food preservation
Antibacterial
PLA can form a weakly acidic environment on the surface of the product. It has a basis for antibacterial and antifungal. If other antibacterial agents are used in addition, it can achieve an antibacterial rate of more than 90%, and can be used for antibacterial packaging of products. Researchers took Agaricus bisporus and Golden Ears as examples to study the fresh-keeping effect of the new PLA nano antibacterial composite film on edible fungi, thereby prolonging the shelf life of edible fungi and maintaining good quality status. The results show that: PLA/rosemary essential oil (REO)/AgO composite film can effectively delay the decrease of vitamin C content in golden ears.
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 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 an excellent antibacterial effect, which can effectively inhibit the reproduction of microorganisms during storage of golden ears, and can significantly extend the shelf life to 16 days.
At the same time, compared with ordinary PE cling film, PLA has a better effect
Researchers separately studied the fresh-keeping effect of PE cling film and PLA film on broccoli. The results show that the use of PLA film packaging can inhibit broccoli's yellowing and curd shedding, and effectively maintain the broccoli's chlorophyll, vitamin C and soluble solid content. PLA film has excellent gas selective permeability, which helps to form a low O2 and high CO2 storage environment in the PLA packaging bag, thereby inhibiting the life activities of broccoli, reducing water loss and nutrient consumption. The results showed that: compared with PE plastic wrap, PLA film packaging can extend the shelf life of broccoli at room temperature by 1 to 2 days, and the freshness preservation effect is obvious.
2. Disposable tableware with straws
The degradation products of PLA can assist plants to become the raw material of PLA through photosynthesis. Therefore, PLA is a "cradle to cradle" green material. PLA is currently the raw material for the mainstream disposable tableware on the market. PLA is relatively stable at normal temperature, but is easily degraded quickly in a slightly high temperature environment, acid-base environment or microbial environment, and has poor impact resistance, which often cannot meet the requirements of circulation in harsh environments.
3. Medical materials
PLA is widely used in sutures, bone fixation, repair materials, sustained and controlled release drug carriers, tissue engineering cell growth scaffold materials and other fields, and has become one of the important biomaterials in the medical field. The suture made of PLA can meet the requirements of suture in strength. As the wound heals, it will be slowly broken down and disappeared in the body. Compared with conventional sutures, there is no need to remove the sutures. It is especially suitable for the suture of deep tissue wounds.
PLA fiber that can be used as medical spinning
PLA can be used as a bone fixation material. With the growth of bones, the bone fixation material made of PLA is slowly decomposed, without the need for a second operation to take out, so as to avoid the physical injury and surgical cost caused by the second operation. PLA can be used as a carrier for sustained and controlled release drugs. It has the advantages of low toxicity, high efficiency, sustained release and long action time. It has good compatibility with organisms and has a long residence time. It can also be copolymerized with other monomers to adjust the drug release rate, so as to improve the activity of the drug and reduce the toxicity and side effects brought to the body.
Heart stent
PLA can be used as a tissue engineering scaffold material. By culturing cells on the PLA scaffold, the cells slowly grow and differentiate into tissues and organs. At the same time, the PLA scaffold material slowly degrades. This technology has made progress in the research of skin and blood vessels.
Summarizing the main applications of PLA mentioned above in the packaging field, we will find that PLA as a new type of pure bio-based material has great market application prospects. Its good physical properties and the environmental protection of the material itself will inevitably make PLA be more widely used in the future.
