I. Development trend of composite flexible packaging materials at home and abroad 1. Development trend of domestic composite flexible packaging materials Develop environmentally friendly composite flexible packaging films . At present, the world recognizes PET as an environmentally friendly material, which can be recycled and reused. Due to the improvement of people's living standards, the shelf life of food in supermarkets will increase, the amount of BOPET will also continue to increase, and it will be conducive to recycling. Three-layer co-extruded heat-sealable BOPET films will soon enter the market to meet the storage life of flexible packaging. Requirements.
Flexible plastic packaging film is developing towards special functionalization. For example, high-barrier materials are becoming hot-spot flexible packaging materials. Commonly used are PVDC-based materials, nylon-based packaging materials, EVOH-based materials, and inorganic oxide coated films. The role of shelf life. High barrier composites will continue to increase market capacity. In the future, high barrier films with simple processing, strong oxygen barrier, water vapor performance, and improved shelf life will be the mainstream of flexible food packaging in supermarkets in the future. Multi-layer compounding, blending, copolymerization, and evaporation technology are also developing rapidly in the flexible packaging industry .
Through microporous or modified film formulation structure. Microporous materials can improve film properties and improve the atmosphere in the packaging bag . By using an oxygen scavenger and then selectively permeating the film combination, the purpose of keeping freshness can be achieved.
Flexible packaging materials are becoming thinner. The thinning of the film refers to reducing the thickness of the material and the various packaging performance indicators can still fully meet the packaging requirements. There are three main ways to achieve this goal: First, the development of new materials, using PEN as raw materials, the strength of PET produced can be increased by 3.5 times, the thickness of the film is reduced by 1/3 than BOPET, and the requirements of BOPET film can be met. The second is the use of nano-inorganic and polymer composite materials to produce flexible packaging films. Nano-inorganic and high polymer composite materials can simultaneously improve the strength and toughness of the film, and play an important role in reducing the thickness of flexible plastic packaging. Compared with films made of pure homopolymers, the strength and toughness of nano-inorganic and polymer composite films are increased by 50%. The third is to use multi-layer composite packaging materials to improve the comprehensive performance of flexible packaging materials, reduce the amount of plastic used in flexible packaging, reduce environmental pollution and save resources.
2. Development trend of foreign composite flexible packaging materials High barrier materials. The performance of aluminum-plastic composite packaging materials is superior, but it is opaque. Thin films made of inorganic materials (such as silicon oxide and titanium oxide) are deposited on the surface of plastic films, and their coating performance is stable, even after high temperature sterilization, the gas barrier performance is superior.
Antibacterial material. Food spoilage or deterioration caused by microorganisms places high demands on packaging materials. Antibacterial packaging usually adds a new type of inorganic antibacterial agent to the packaging material to achieve antibacterial effects on a variety of pathogenic bacteria. Currently widely used is antibacterial film, which is made by adding antibacterial agent and synergist to polyolefin film. This antibacterial packaging material has antibacterial effect on most common microorganisms such as E. coli and Staphylococcus aureus.
Functional packaging materials. Common are rust-proof, mold-proof, fresh-keeping, nano-type functional materials. Due to people's requirements for a high standard of living, fresh-keeping packaging has developed rapidly, and a series of fresh-keeping functional materials have been successfully developed, which are usually processed into bags or sheets for convenience.
Smart packaging materials. It is usually made of functional materials such as photoelectricity, temperature and humidity, and packaging materials. It can identify and indicate some important parameters such as temperature, humidity, pressure, degree of sealing, and time in the packaging space.
Deodorizing film. There are three main types of this type of film. One type is chemical deodorization type, which can remove nitrogen-based compounds and sulfur-based compounds, such as ammonia, dimethylamine, hydrogen sulfide and other odors. The second type is mainly used to remove odors such as hydrogen sulfide and formic acid, and is characterized by good deodorization effect on high concentration hydrogen sulfide. The third type is a physical deodorant type, which is made of an active deodorant and has a low deodorizing power. Deodorizing film is used for food packaging . In addition to keeping freshness, it is also mainly used for packaging of foods, agricultural products, and aquatic products with special odors. In addition, it is used for packaging of medical materials, sanitary materials, and miscellaneous goods. Progress has also been made. However, the deodorizing film is selective, so it must be selected according to odor components, concentration, environmental humidity and other factors when using it.
Low temperature sealing material. Packaging machinery requires simple and convenient, save energy, increase speed, increase efficiency to meet the needs of modern large-scale packaging, so the use of low-temperature sealing packaging materials is a necessary condition. The low-temperature sealing material does not have a thermal effect on the contents of the package, so it is particularly suitable for packaging heat-repellent articles. It can be applied to substrates that are difficult to heat-seal, simplify the packaging structure, reduce costs, save energy, and achieve high-speed packaging. The sealing has good cold resistance, and the sealing strength does not decrease even at -20 ° C.
High-speed sealing material. Common packaging materials are coated with low-temperature heat-sealing layer HSS, which can be sealed at high speed at low temperatures. It is superior to other materials such as EVA, acrylic resin, heat seal varnish, trace paraffin, etc. Therefore, it can be used for packaging that requires strict restrictions on odor effects. It is characterized by fast sealing speed and is suitable for high-speed machinery. For example, when using OPP / KOP / HSS packaging materials, the speed of the bag making machine can reach 500 pcs / min. The low-temperature layer HSS can not only be coated on the surface of paper and aluminum foil, but also on the surface of various plastic films such as OPP, KOP, PET, PVC, PE, etc. Generally, the thickness of the HSS coating is about several microns to meet the requirements.
New composite paper. It is a kind of high-strength composite paper with high whiteness, extremely thin and extremely soft. It can still be intact after repeated folding, and the price is low. Composite paper is made of rock powder as a raw material, made of fibers at high temperature, impregnated with phenolic resin and infiltrated into white clay powder to form. It will not be brittle, moldy, moth-eaten, etc. during long-term storage, and can be printed with colors. Dust-free paper, sterilized paper, anti-static paper, anti-electromagnetic interference paper, high transparent paper, etc.
Conductive packaging materials. This type of material is mainly used for static-sensitive products such as anti-static and anti-static packaging, as well as anti-electromagnetic packaging for precision instruments and missiles.
Second, the life cycle assessment of composite flexible packaging materials 1. Life cycle scope Life cycle assessment (LCA), as a technology used to evaluate the environmental factors and potential impacts of products, consists of four interconnected elements, namely goals and scope definition ( GSD), inventory analysis (LCI), impact assessment (LCIA), and interpretation of results. The life cycle scope is the most important factor that affects the definition of the scope. Generally, the following whole or part of the life cycle can be selected according to the purpose of LCA evaluation.
(1) Acquisition of raw materials. Before the product is manufactured, it is beyond the direct control of the manufacturer. It is generally difficult for enterprises to consider this stage when making environmental impact assessments of products, but it is also necessary to obtain some information necessary for the manufacturing stage.
(2) Product manufacturing stage. That is, from the entry of raw materials into the factory door to the product door, also known as the "door-to-door stage." Enterprises are mainly engaged in LCA at this stage, such as implementing clean production and environmental management.
(3) Product packaging and transportation stage. Packaging is closely related to the product, so the LCA for product evaluation should generally consider packaging, such as reduction, and selection of green materials. Packaging should be considered; the transportation stage involves petroleum consumption and exhaust gas and photochemical smog, so the product's LCA is also All need to consider this stage.
(4) Use or consumption stage of the product. This stage is often a stage where the product has a serious environmental pollution and resource consumption, but when evaluating the packaging materials, it chooses according to the situation.
(5) Product recycling and final disposal stages. Whether it is product recycling or final disposal, it consumes energy, resources and waste, so it must be included in the LCA evaluation.
2. Life cycle system boundary and inventory analysis Before data collection and evaluation, the functional unit and system boundary must be defined. In comparative evaluation, the same functional unit and system boundary definition can lead to fair and just results. If the content of the evaluation content in the production stage is small, the environmental load generated is also small and can be excluded from the evaluation scope.
Taking the paper-plastic aluminum composite Tetra Pak as an example, the evaluation content does not involve the use of packaging products. This is mainly because most milk packaging product production lines and milk filling lines are basically synchronized, and there is no off-site transportation. Finally, the recycling of the product after it is discarded is added to the life cycle, that is, the recycling of paper-plastic aluminum composite packaging. Therefore, the life cycle assessment of the Tetra Pak can be defined as raw material acquisition, packaging production, packaging transportation, and packaging disposal. At this stage, the aluminum-plastic waste part is represented by landfill disposal, as shown in Figure 1 (the dotted line indicates that it is not within the evaluation scope).
Figure 1 Tetra Pak life cycle assessment system boundary
Once the life cycle system boundaries are defined, inventory analysis can be performed. LCI is a qualitative description of the material flow and energy flow inside and outside the system. By registering the type and size of each process load in the product life cycle, the resource, energy input and waste of the system within the entire cycle of the product or service are registered. The process of quantitative analysis of emissions. The main procedures of LCI include data collection preparation, confirming the validity and completeness of data, connecting system boundaries, allocating inflows and outflows, and proposing restrictions on LCI.
3. Life cycle impact assessment and result analysis Life cycle impact assessment is a qualitative and quantitative analysis of environmental impacts based on the elements listed in the inventory analysis process. LCIA includes classification of the elements listed in the inventory analysis process, qualitative and quantitative analysis of the listed elements using environmental knowledge, identification of major environmental factors in each link of the system, and analysis and judgment of the identified environmental factors. The types of environmental impacts include directly harmful and toxic to organisms and humans; damage to the living environment; damage to the recycling system of renewable resources; and large consumption of non-renewable resources. LCIA classifies the results of inventory analysis into different types of environmental impacts, and then quantifies them based on the characteristic coefficients of different types of environmental impacts for analysis and judgment.
At present, the life cycle impact assessment mainly uses the "environmental problem method" and the "target distance method". The former mainly focuses on environmental impact factors and impact mechanisms, and uses the equivalent factor conversion method for standardization and comparative analysis of various environmental interference factors, such as the EPS method in Sweden, the ecological scarcity method in Switzerland and the Netherlands (ecological factors), and the Danish The EDIP method, etc .; the latter focuses on the consequences of the impact, using the distance between the current level of an environmental effect and the target level (standard or capacity) to characterize the severity of an environmental effect, which is represented by the Swiss critical volume method . In addition, the environmental index method (Eco-Indicator) is a new evaluation method. It establishes a new environmental impact model of resource consumption, land use, climate change, ion irradiation, acidification, eutrophication, and ecotoxicity. Commonly used is EI95. And EI99. The interpretation of results is the last stage of LCA, which combines the results of inventory analysis and impact assessment to make the results of inventory analysis consistent with the goals and scope determined in order to make correct conclusions and recommendations.
Xie Minghui and others used the life cycle assessment method to study milk Tetra Pak packaging and ordinary plastic bag packaging, and compared and evaluated their environmental impact. The results show that the full-life cycle environmental impact values of the paper-plastic-aluminum composite milk packaging and plastic milk packaging using the EI99 evaluation method are 5.225Pt and 4.670Pt, respectively, and the environmental impacts in the raw material acquisition stage account for the entire lifecycle stage. About 80%. The environmental impact of plastic packaging in terms of consumption of fossil resources accounts for 79% of the environmental impact of the entire life cycle, which is more than twice that of paper-plastic aluminum composite packaging. Paper-plastic aluminum composite packaging has a greater impact on the environment in terms of fossil resource consumption, inorganic emissions and land occupation, followed by climate change, acidification and eutrophication. Considering the non-renewability of fossil resources, from the perspective of sustainable development, the development of paper-plastic aluminum composite packaging is more superior than the development of plastic packaging. Improving the environmental impact of paper-plastic-aluminum composite packaging can be further separated into plastic and aluminum through the development of recycling technology and improved recovery rates. This will greatly reduce its environmental impact, and when its recovery rate exceeds 43% , The environmental impact of paper-plastic aluminum composite packaging is less than that of plastic packaging.
3. Concluding remarks Composite flexible packaging materials have penetrated into every part of the manufacturing field, and will be developed in the direction of high performance, multi-function, non-toxic and harmless, green and environmentally friendly , inexpensive and convenient to use. The life cycle assessment has made a quantitative assessment of the environmental impact of composite flexible packaging materials, and some new problems have arisen after the materials are used and discarded.