Degradable bio-based plastics and their application in packaging
Degradable bio-based plastics refer to plastics whose raw materials are all or partly derived from biomass and (products and/or waste) can be degraded by microorganisms. This kind of material can degrade under the action of natural microorganisms (bacteria, fungi, actinomycetes, etc.) .
Degradable bio-based plastics are divided into 3 types, including ① natural synthetic plastics, such as starch, cellulose, lignin, protein, chitin and their various derivatives and mixtures as raw materials, or added in various molding processes A type of plastic processed with additives. ②Chemical synthesis such as polylactic acid (PLA), polybutylene succinate (PBS), etc. ③ Microbial synthesis is represented by polyhydroxyalkanoate polymers (PHA), including β-hydroxybutyrate (PHB), copolymers of 3-hydroxybutyric acid and 3-hydroxyvaleric acid (PHBV), etc. The following is an analysis of starch-based degradable plastics, PLA, and PHA, which are the most researched and the largest in the market.
1.1 Starch-based degradable plastics and their application in packaging Starch is a high-molecular carbohydrate, which is formed by the polymerization of glucose molecules. It is rich in sources and has a high content in plants such as corn, wheat, and potatoes. Renewable, low in price, with good biodegradability, after starch degradation, it will return to nature in the form of carbon dioxide and water, and is considered to be a natural renewable material that does not cause any pollution to the environment. At present, it is widely used in agriculture, packaging materials, medical treatment and so on.
Yang Yue et al found that cross-linked cassava starch plastic wrap has a better fresh-keeping effect on tangerines. Warner-Lamber Company of the United States has prepared a thermoplastic starch plastic, which is made of 100% starch, has properties similar to polystyrene, and can be used as a medical capsule. Lei Junhua et al. modified waxy rice by chemical modification to obtain modified starch, and applied the modified starch as excipient to ibuprofen agent to prepare a high-temperature-resistant ibuprofen tablet.
1.2 PLA and its application in packaging Polylactic acid (PLA), also known as polylactide, is one of the most widely studied bio-based and biodegradable materials. It is non-toxic, non-irritating, biodegradable, high strength, easy to process and shape, and low cost. Advantages, it is considered to be an ideal degradable biopolymer material.
PLA uses renewable resources such as starch as raw materials. First, glucose is obtained through saccharification, and then high-purity lactic acid is produced by fermentation of bacteria. Lactic acid undergoes dehydration and condensation reaction to finally obtain polylactic acid. PLA has excellent performance, has similar mechanical properties to polypropylene, has similar impermeability to polyester, and its gloss, clarity and processability are similar to polystyrene. Therefore, PLA has been widely used in food Packaging and disposable cutlery.
Nature Works packages its organic fruit juice drinks in PLA bottles, which guarantee a 60-day shelf life for the product. Wal-Mart uses the high-quality air permeability of PLA to use PLA packaging materials in the packaging of bread, fried rings and other foods, which better guarantees the taste of the food. Xiao Wei and others applied PLA plastic film to packaging broccoli. The experimental results showed that PLA plastic film can effectively inhibit the yellowing of broccoli and maintain the solid content and chlorophyll content of broccoli. The Danish Faerch Plastic Company uses PLA to package low-temperature pasta, meat, salad and other fresh foods, which can achieve a long shelf life. In addition to food, PLA packaging is also used in a variety of fields: as textile fibers or technical products (fabrics, filters, nonwoven materials) or in consumables (e.g. office supplies or technical components).
PLA materials can also be used for disinfection wraps, masks, diapers, civilian wipes, wet wipes, beauty products, sanitary napkins, sanitary pads, and disposable sanitary cloths, etc. PLA non-woven fabrics not only fully meet the safety and ease-of-use requirements of disposable protective products, but also endow the products with new green and environmental protection features.
Zhu Lei et al. used different solvents to spin PLA raw materials on spunlace non-woven fabrics and melt-blown non-woven fabrics respectively by electrospinning method, and the filtration efficiency of the composite materials was significantly improved. In addition, it is widely used in packaging materials and biomedical materials and other fields.
1.3 PHA and its application in packaging PHA is an aliphatic copolyester synthesized by microorganisms through fermentation of various carbon sources. Different fermentation conditions can produce different types of PHA. Different types of PHA have different monomer structures, so there are many types. The PHA that has been discovered so far The total number of polymers exceeds 150.
The diversity of PHA structure brings the diversity of its physical and chemical properties. Among them, good biocompatibility and biodegradability are the most prominent characteristics of PHA, and the barrier performance of PHA to water vapor and most gases in the air Similar to PET, it has broad application prospects in biomedicine, food and beverage packaging, industry and agriculture. PHB is a material with the simplest structure, the earliest discovery and the most research and application in the PHA family. It has high structural regularity, hard and brittle properties, and its mechanical properties and melting point are similar to polypropylene (PP).
In 2007, the absorbable suture (TephaFLEX®) made of P4HB was approved by the US FDA and became the first commercialized PHA medical product. The plastic film prepared by PHA through casting extrusion molding has good barrier properties, which can effectively prevent the leakage of liquid or the entry of gas, so it can be used for disposable diapers for babies, or some liquid leak-proof packaging, Shrink film for wrapping metal.
On May 3, 2022, Kemira and DanimerScientific Inc signed an exclusive collaboration agreement to introduce new barrier PHA coatings for the food and beverage industry in the coming years. In the field of logistics and transportation packaging, PHA materials can be made into packing boxes, containers, pallets and even express boxes made of paper composites. These various box types are not only environmentally friendly but also recyclable. The performance advantages of PHA materials are obvious, but the high production cost and complicated process route of PHA limit the wide application of PHA. As far as the current stage is concerned, simplifying the production process of raw materials and reducing production costs are the primary factors to promote the application of PHA.
