According to different classification standards, cold chain logistics can be divided into various types. For example, only from the operation mode, it mainly includes two modes:
The first is to use the method of “foam box + cold bag”, generally called “package cold chain”, which is characterized by using the package itself to create a small environment suitable for short-term storage of fresh products. The advantage of this method is that the packaged products can be distributed using the normal temperature logistics system, and the total logistics cost is lower.
The second mode is to use the real cold chain logistics system, that is, from the cold storage at the origin to the delivery of the final customer, all logistics links are in a low temperature environment to ensure the continuous chain of the cold chain. In this mode, the temperature of the whole cold chain should be controlled, which is generally called “environmental cold chain”. However, the requirements for the entire cold chain logistics system are very high, it is difficult to use the ordinary logistics system to operate, and the overall operating cost is relatively high.
But no matter which of the above cold chain models is used, foam materials that can keep warm, heat insulating, shock absorbing and buffering can be regarded as ideal materials.
At present, the most widely used in cold chain logistics and transportation are polyurethane foam, polypropylene foam and polystyrene foam. Trailers, refrigerated containers and cold storage are also found everywhere.
Polystyrene foam (EPS)
EPS is a lightweight polymer. Because of its low price, it is also the most widely used foam material in the entire packaging field, accounting for nearly 60%. The polystyrene resin is made by adding a foaming agent through the processes of pre-expansion, curing, molding, drying and cutting. The closed cavity structure of EPS determines that it has good thermal insulation, and the thermal conductivity is very low. The thermal conductivity of EPS boards of various specifications is between 0.024W/m.K~0.041W/m.K. It has good heat preservation and cold preservation effect in logistics.
However, as a thermoplastic material, EPS will melt when heated and become solid when cooled, and its thermal deformation temperature is around 70°C, which means that EPS incubators processed into foam packaging need to be used below 70°C. If the temperature is too high At 70°C, the strength of the box will be reduced, and toxic substances will be produced due to the volatilization of styrene. Therefore, EPS waste cannot be naturally weathered and cannot be incinerated.
In addition, the toughness of EPS incubators is not very good, the buffering performance is also average, and it is easy to be damaged during transportation, so it is mostly one-time use, used for short-term, short-distance cold chain transportation, and food industry such as meat and poultry. Trays and packaging materials for fast food. The service life of these products is usually short, about 50% of the polystyrene foam products have a service life of only 2 years, and 97% of the polystyrene foam products have a service life of less than 10 years, resulting in an increase in the amount of EPS foam waste year by year, but EPS foam is not easy to decompose and recycle, so it is currently the main culprit of white pollution: EPS accounts for more than 60% of the white garbage polluted in the ocean! And as a packaging material for EPS, most of the HCFC foaming agents are used in the foaming process, and most of the products will have an odor. The ozone depletion potential of HCFCs is 1,000 times that of carbon dioxide. Therefore, since the 2010s, the United Nations, the United States, the European Union, China, South Korea, Japan, and other relevant countries (organizations) and regions have legislated to prohibit or restrict the use of single-use plastics including polystyrene foam, and Humans forced a “correction roadmap”.
Polyurethane rigid foam (PU Foam)
PU Foam is a high molecular polymer made of isocyanate and polyether as the main raw materials, under the action of various additives such as foaming agents, catalysts, flame retardants, etc., mixed by special equipment, and foamed on-site by high-pressure spraying. It has both thermal insulation and waterproof functions, and has the lowest thermal conductivity among all organic thermal insulation materials at present.
However, the hardness of PU is not enough. The structure of commercially available PU incubators is mostly: food-grade PE material shell, and the middle filling layer is polyurethane (PU) foam. This composite structure is also not easy to recycle.
In fact, PU is often used in freezers and refrigerators as insulation fillers. According to statistics, more than 95% of refrigerators or refrigeration equipment in the world use polyurethane rigid foam as insulation material. In the future, with the expansion of the cold chain industry, the development of polyurethane thermal insulation materials will have two priorities, one is to control carbon emissions, and the other is to improve flame retardant properties. In this regard, many polyurethane insulation material manufacturers and cold chain insulation engineering suppliers are actively developing innovative solutions:
In addition, new foam materials such as polyisocyanurate foam material PIR, phenolic foam material (PF), foamed cement board and foamed glass board are also building environmentally friendly and energy-saving cold storage and cold chain logistics. applied on the system.
Polypropylene foam (EPP)
EPP is a highly crystalline polymer material with excellent performance, and it is also the fastest growing new type of environmentally friendly compressive buffer insulation material. Using PP as the main raw material, the foamed beads are made by physical foaming technology. The product is non-toxic and tasteless, and heating will not produce any toxic substances, and it can be directly contacted with food. Good thermal insulation, thermal conductivity is about 0.039W/m·k, its mechanical strength is also significantly better than EPS and PU, and there is basically no dust in friction or impact; and it has good heat and cold resistance stability, and can be used in the environment of -30°C to 110°C. use below. In addition, for EPS and PU, its weight is lighter, which can greatly reduce the weight of the item, thereby reducing the transportation cost.
In fact, in cold chain transportation, EPP packaging boxes are mostly used as turnover boxes, which are easy to clean and durable, and can be used repeatedly, reducing the cost of use. After it is no longer used, it is easier to recycle and reuse, and it will not cause white pollution. At present, most of the fresh food delivery industries, including Ele.me, Meituan, and Hema Xiansheng, basically choose to use EPP incubators.
In the future, as the country and the public attach great importance to environmental protection, the green road of cold chain packaging will be further accelerated. There are two main directions, one of which is the recycling of packaging. From this point of view, the future of polypropylene foaming will be accelerated. The material is expected to replace more foam materials of polyurethane and polystyrene, and has a bright future.
Biodegradable foam material
Expanding the use of degradable materials in cold chain logistics packaging is also another important direction for the greening of cold chain logistics packaging. At present, there are three main types of biodegradable materials that have been developed: polylactic acid PLA series (including PLA, PGA, PLAGA, etc.), polybutylene succinate PBS series (including PBS, PBAT, PBSA, PBST, PBIAT etc.), polyhydroxyalkanoate PHA series (including PHA, PHB, PHBV). However, the melt strength of these materials is usually relatively poor and cannot be produced on traditional continuous sheet foaming equipment, and the foaming ratio should not be too high, otherwise the physical properties of the foamed products are too poor to be used.
To this end, many innovative foaming methods have also emerged in the industry. For example, Synbra in the Netherlands has developed the world’s first polylactic acid foaming material, BioFoam, using patented in-mold foaming technology, and has achieved mass production; leading domestically The equipment manufacturer USEON has successfully developed the production technology of the multi-layer structure PLA foam board. The shift adopts the foam center layer, which has better thermal insulation performance, and the solid surface body on both sides can greatly improve the mechanical strength.
fiber foam
Fiber foam material is also a green degradable packaging material in cold chain transportation logistics. However, in appearance, the incubator made of fiber foam material cannot be compared with plastic, and the bulk density is high, which will also increase the transportation cost. In the future, it is more suitable to develop franchisees in each city in the form of franchises, using local straw resources to serve the local market at the lowest cost.
According to the data disclosed by the Cold Chain Committee of the China Federation of Things and the Prospective Industry Research Institute, the total demand for cold chain logistics in my country in 2019 reached 261 million tons, of which the demand for food cold chain logistics reached 235 million tons. The industry still maintained a high-speed growth trend in half a year. This has brought a once-in-a-lifetime market opportunity to the foaming material industry. In the future, foaming enterprises related to cold chain logistics need to grasp the general trend of green, energy-saving and safe industry in order to seize the market opportunities and find relative advantages in the ever-changing market. The constant competitive strategy makes the enterprise in an invincible position.
Post time: Aug-22-2022