Advantages and disadvantages of PLA and its application in packaging industry
The application of PLA in the market is mainly concentrated in the three fields of packaging, medicine and textile (fiber), especially in the packaging industry.
Compared with traditional PE and PP materials, PLA has a higher melting point (about 180 ℃) and better processability. The hardness and mechanical properties of PLA are similar to those of traditional resins (such as PS), with good transparency and excellent gloss, which are more suitable for packaging materials. However, its shortcomings are also prominent. Compared with the commonly used high barrier nylon and polyvinylidene chloride (PVDC), PLA has insufficient oxygen and water vapor barrier and insufficient protection for greasy food.
In addition, PLA has poor toughness, low Tg and poor impact resistance, which means that PLA is not suitable for the packaging field with high durability for the time being. In addition, the degradation cycle of PLA is not easy to control, and it is easy to degrade or hydrolyze to varying degrees in use, and its performance will decline. The material cost is more than 2.5 times that of traditional PE and PP, which can not be ignored.
The application of PLA in the packaging industry is mainly benchmarking modified PP, PE and pet. In addition, cushioning materials are benchmarking EPS, EPE and EPU. In view of the advantages of PLA, as a packaging material, it can be made into films, foaming materials and containers, such as flexible packaging bags, plastic bottles, cushioning materials, disposable tableware, etc. in terms of morphology, it is mainly films, followed by containers and sheets.
The degradability, barrier property, mechanical property, optical property, antibacterial property, conductivity and piezoelectricity of PLA are mostly related to crystallinity. If the crystallinity of PLA is increased, its barrier property and mechanical property will generally be improved, but the processability, degradability and transparency will usually be reduced. Therefore, when modified PLA is used as packaging material, the key is to control its crystallization behavior and optimize all aspects of performance.
PLA films mainly include highly transparent films, heat shrinkable films, granular blend blown film bags and PLA based composite films. PLA film can replace the traditional film material as a new packaging material. For example, Wal Mart requires the use of fully degradable PLA film bags to replace the traditional non degradable PE bags, and Japanese electronic products have also begun to use PLA nanocomposite film packaging.
(2) PLA container
Due to the degradability of PLA, it is used to produce water and juice bottles, but the market is limited. Injection stretch blow molding is a typical production method of PLA bottles, which is mostly used in food packaging on short-term shelves. The transparency and oxygen resistance of PLA bottles are better than PE bottles. Due to the insufficient creep behavior of PLA and its low barrier to CO2, the application of PLA bottles is limited to non carbonated beverages.
NatureWorks uses PLA bottles to package organic fruit juice drinks, which can ensure a shelf life of 60 days. Faerch plastic company in Denmark uses PLA to pack low-temperature fresh foods such as pasta, meat and salad, which can reach a long shelf life. The European market has launched PLA yogurt cups and beverage packaging bottles, which can meet the relevant EU standards for food containers. Some companies have issued high transparency and heat-resistant PLA water bottles, which can meet the application conditions of both transparency and heat resistance (heat-resistant temperature ≥ 100 ℃). In the domestic market, PLA is coated on paper to make coated paper cups, which are used for various waterproof and oil-proof food packaging.
(3) PLA foaming material
PLA foaming material is biodegradable and can be used to produce disposable tableware (such as fast food boxes, instant noodles bowls, etc.) and cushion packaging liners. It will not produce white pollution, especially PLA heat-resistant tableware will become more practical. The "grave" series disposable tableware is made of PLA foam material and designed to have a realistic shape of fruits and vegetables, which is both environmentally friendly and beautiful. It is worth noting that foaming is an effective method for low-cost use of PLA. Pure PLA melt has low strength and its viscosity is not obvious to shear, which is not suitable for extrusion coating, foaming and other processing methods, but its melt strength can be improved by changing the molecular chain topology, such as long-chain branching.
