What's New

Plastic flexible packaging materials have a history of approximately 100 years since their inception. Along with the development of various material technologies, they have gradually evolved from simple process protection functions to comprehensive functional materials that combine visual, hygiene, protection, and the extension of food shelf life. Due to the diverse functional requirements of the industry for plastic packaging materials, plastic packaging has also gradually evolved from simple single-layer or double-layer structures to multi-layer material composite structures. However, the non-biodegradable nature of plastic undoubtedly poses a huge challenge to the recycling and disposal of plastic packaging after it is discarded.

China began to implement the plastic restriction order on June 1, 2008. On January 1, 2018, it banned the import of four major categories of 24 types of solid waste. On July 1, 2019, mandatory garbage sorting was implemented in Shanghai. The implementation pace of these regulations has accelerated, indicating the current country's high attention to the problem of plastic waste pollution and the huge challenges faced by the development of environmental protection.

Internationally, during the "Our Oceans Conference" held in Bali in October 2018, 250 producers, retailers, packaging recyclers, governments and non-governmental organizations, including Veolia, signed the "Global Commitment to Eliminate Plastic Pollution at Source" initiative, aiming to eliminate plastic pollution at its source. Its main goals are: (1) Eliminate problematic or unnecessary plastic packaging and shift to a reusable packaging model from one-time use; (2) Through innovation, ensure that 10% of plastic packaging can be conveniently, safely reused, recycled or composted by 2025; (3) Recycle the produced plastic, significantly increase the amount of plastic reused or recycled, and turn it into new packaging or products.

Under the close attention of both domestic and international communities to plastic pollution, the development of environmentally friendly plastics and the handling of discarded plastics have become important environmental factors for the current plastic packaging industry.

Analysis of the Current Situation and Problems of Flexible Packaging Materials

Depending on the application scenarios of flexible packaging, different materials are usually used as the composite base. The typical structure, materials and corresponding functions of flexible packaging are as follows:

1. Outer layer

Paper, BOPP, BOPA, BOPET, PVDC coated film, alumina-silicon oxide coating, EVOH or MKD-6 biaxially oriented film. The main function of the outer structure is to serve as the printing layer, heat-resistant layer and barrier layer, and a small part of it can also perform the role of a barrier layer.

2. Middle Layer

They are generally made of aluminum foil, aluminum-coated BOPET/BOPP, and PVDC coated films, etc. Their main function is to act as a barrier material, preventing the entry of external oxygen and water vapor into the interior of the flexible packaging, thereby affecting the shelf life of the contents (such as food, medicine, etc.); materials with excellent barrier properties also have good preservation of fragrance, which can prevent the aroma of the contents from escaping outside the packaging bag, and have a more significant improvement effect on maintaining the freshness period of the product.

3. Inner layer

PE film, PP film, heat sealing adhesive, sealing adhesive, etc. These are mainly used for sealing the contents after filling in soft packaging, requiring the material to have a lower softening point and be able to withstand tight heat bonding under rapid production conditions.

The complexity of the materials used in soft packaging also poses significant challenges for its recycling after disposal. In the current context of greater emphasis on environmental protection, soft packaging manufacturers have taken on their own responsibilities and have actively adopted measures to reduce waste, make materials uniform, and use degradable materials instead of the multi-layer and multi-type plastic film composite structures. That is:

(1) Replace two or more layers of composite substrates with high-performance materials;

(2) Replace the composite structure of various materials with the same type of materials such as PP and PE;

(3) Replace the non-degradable components in the current composite structure, such as BOPET, BOPP, PET film materials, and composite adhesives, with degradable materials.

The production technology of the new green flexible packaging material enables 100% environmental recycling of plastic films

1. Fully biodegradable and biobased materials

Biodegradable plastics refer to those that can be decomposed by the biological metabolic process in the natural environment through the composting process, converting into water, carbon dioxide and other small molecules that are harmless to the environment. According to their sources, they can be classified as natural compounds, microbial synthesis type and artificial synthesis type. The main products include PHA, PLA, PBS, PBAT and PCL, etc. Biobased materials utilize renewable materials, such as starch, crops, and trees, as raw materials, and are mixed with general plastics through a series of processing procedures to form plastic processing raw materials with high efficiency and high added value.

Taking bio-based materials as an example, the current national approach to handling waste is mainly through waste incineration for power generation. By adding 30% to 50% of starch to PE materials, soft packaging can reduce the equivalent amount of PE materials used, and during the waste incineration process, 5g of carbon dioxide can be reduced for every 10g of materials. Corresponding amounts of petrochemical products can also be reduced. However, fully degradable materials and bio-based materials have deficiencies in barrier properties and tear strength. Currently, their applications are mainly in the civilian industries such as shopping bags, garbage bags, and express delivery bags. This is mainly because the compatibility issues of PLA and PBAT have not been resolved, and more development efforts need to be invested in compatibilizers.

In the market, at present, the implementation of domestic waste sorting has been strengthened. The packaging industry has begun to pay attention to environmental protection and plastic reduction. However, the expansion speed of domestic incineration plants is faster than that of composting plants. For fully degradable plastics that require composting degradation and have higher production costs than bio-based materials, this does not conform to the current development direction. Therefore, the competitiveness of bio-based materials that can be directly incinerated is basically the same as that of fully degradable materials.

2. PVA High-barrier Coatings/Gum Adhesives

Polyvinyl alcohol (PVA) material, as an environmentally friendly and degradable material, has the advantage that compared with ordinary barrier layers, vapor deposition materials and PVDC coatings can generally only be applied to printing substrates such as BOPP, BOPET, and PA. However, PVA coatings can be applied to the inner layer of heat-sealing materials, which can structurally reduce the possibility of secondary pollution of trace small molecules from the outside, the surface layer, the middle layer, and the adhesive between the surface and the middle layer. The traditional composite structure cannot block the small molecule substances produced by the middle layer and the surface layer - middle layer adhesive. By applying PVA high barrier material on the heat-sealing material, the food safety is significantly improved.

In addition, PVA high-barrier coatings/gum adhesives provide a feasible solution for currently available fully degradable materials and bio-based materials that fail to meet the packaging requirements for food and medicine: when the usage of PVA material is 0.4 - 0.5 g/m2, it has extremely excellent oxygen barrier properties, strengthening the barrier performance of environmentally friendly materials and breaking the limitations of their application. Even in homogeneous packaging structures, the proportion of different materials does not exceed 5%, opening up a new development path for the green packaging industry.

3. Fully PP/PE packaging materials

In the context where the soft packaging produced by enterprises is required to be 100% recyclable, the homogeneous green plastic packaging structure has become a popular research direction. Generally speaking, the structures composed of different materials make up for each other's deficiencies in aspects such as heat sealing, printability, heat resistance, and mechanical strength. Therefore, homogeneous soft packaging places higher demands on material production technology.

The first step in producing homogeneous packaging is to abandon the traditional composite structure that cannot be decomposed at high temperatures and the PET film materials with a relatively high melting point (about 265℃), and instead use low-melting-point PP or PE film materials as substitutes. This will reduce the energy consumption required for subsequent recycling and heating. However, the resulting insufficient barrier properties of the flexible packaging is a problem that needs to be addressed in the next step. Generally, this is achieved by vapor depositing inorganic materials such as aluminum oxide, silicon oxide, and even aluminum on the PP or PE film materials. Currently, there is an emerging MDOPE technology in the international community, where the film is blown or extruded and then subjected to longitudinal stretching to significantly improve the mechanical strength of the PE film. Finally, after vapor depositing inorganic materials, surface coating treatment, printing, and compounding with heat-sealable PE materials, 100% recyclable homogeneous packaging materials can be produced.

Conclusion

Because plastic packaging materials can meet the performance requirements for various situations and have low costs, even though there are serious environmental pollution problems, we still cannot prohibit the use of plastic packaging materials at this stage. Therefore, seeking new materials, new processes, and new solutions to the problems of non-biodegradability, non-recyclability, or non-reusability of plastic packaging is the current development trend of new plastic packaging materials. However, we must also clearly recognize that the development of environmental-friendly plastic packaging technology cannot be achieved by a single enterprise alone. It requires international collaboration, support from national policies, mutual cooperation among upstream and downstream industries, and investment in technical strength within enterprises to promote the development of flexible packaging materials.