Research on Green Evaluation System of Polymer Materials (I)

With the continuous increase of modern polymer products, polymer waste has also become an important source of environmental pollution. The European Union's environmental protection directive RoHS is about to be implemented, and corresponding management measures in China will soon be introduced. For the polymer processing industry, how to deal with export trade barriers and meet environmental protection requirements has become one of the most important tasks. This requires that when evaluating and using polymer materials, not only performance, cost, etc., but also environmental impact factors must be considered.


With increasing production, polymers have become one of the major sources of waste and have had a tremendous impact on the environment. At present, many countries have successively formulated environmental directives and regulations for products, and require the producers to be responsible for 3R (reuse, recycle and reduce) disposal of waste products, of which polymers occupy a considerable proportion. Japan implemented the Household Appliances Recycling Act (HARL) in 2001. The EU implemented the WEEE directive in April 2005 and will implement the RoHS directive in July 2006. Similar directives in China are also under development and are expected to be implemented soon.

All of these directives and regulations require producers to achieve a higher rate of product recycling and reduce the amount of final product waste. Figure 1 shows the recycled reuse ratios of different materials that are currently used by European common electrical products. It can be clearly seen from the above that the recovery of polymer materials has become a bottleneck that restricts the overall environmental directive matching of products. This requires the full consideration of the recyclability and environmental impact of the material in addition to the performance and cost of the material itself in the development and production of the polymer. In this paper, the recyclability and environmental impact of materials are collectively referred to as greenness, but in many cases, the recyclability and environmental impact of materials are not exactly the same, which is particularly evident in metal materials. Metal materials have good recyclability, but in the process of processing and recycling will have a great impact on environmental pollution.

Figure 1 Status of recycling of different materials in European electrical products

Due to the important influence of polymer materials on the environment, the green evaluation system of polymer materials has also become one of the focuses of product life cycle research in recent years. KG Snowdon has established a polycarbonate/ABS aluminum-based panel product life cycle evaluation system based on the environmental impact of polycarbonate materials. H. Terho conducted an LCA (Life Cycle Assessment) analysis of the PBT/LDPE material's Nokia cable and compared the different environmental impacts of LDPE, LLDPE, and HDPE materials. G. Lewis et al. Photoelectric sensing components for United Solar Systems Corporation UPM-880 products, where the main materials are Tefzel (a polytetrafluoroethylene resin) and EVA for life cycle analysis and simulation. D. Pollock et al. conducted LCA studies on PE, PP, and polyester materials in inkjet print cartridge products. H. Tomita et al. conducted an LCA study on the recycling and recycling of compact audio cassettes and pocket disks (PS, polycarbonate, and PC). JA Stuart analyzed and summarized the material selection model in the product life cycle design. R. Kulkarni established an evaluation system for environmental impact of electronic components based on the Environmental Assessment (EIA) software system. These studies are aimed at a specific class of products and polymer materials, mainly for environmental impact analysis of the materials in the products. After the implementation of the product's environmental directives, it is necessary to use the polymer itself as the object of research and analysis. Through the life cycle analysis of polymer materials, the 3R status of simulated polymer materials is predicted and a green evaluation system reflecting the characteristics of polymers is established.

3R-based polymer life cycle

3R is expressed as increasing the ratio of Reuse and Recycle and reducing the final waste. For a product, reuse indicates that the product component is directly put into the production of a new product or the maintenance of an old product; the recycling indicates that the material is recycled; and the waste indicates that it cannot enter the part of the material produced in the next stage. From the point of view of polymer materials, this concept needs to be re-established: Reuse means that the material can be directly put into the next stage of production without adding other components; recovery means that the material is added after the other components are modified The next stage of production, while discarding means that the properties of the recovered polymer can no longer meet the needs of reproduction. In this phase, how to reduce the final solid waste is the key to reduce. The life cycle process of the polymer is shown in Figure 2(a). Figure 2(b) shows the performance change of the polymer during the life cycle. The time point Tm represents the time when the polymer enters the Recycle phase, and the time point Tn represents the time when the polymer enters the waste phase.

Figure 2 Polymer life cycle process

From the viewpoint of enhancing the environmental friendliness of the polymer, on the one hand, Tm and Tn are extended as much as possible to extend the time before the material enters the waste phase. On the other hand, it is to minimize the amount of material discarded and to reduce the impact of waste on the environment. According to the ASTM (American Society for Testing Material) D0883-92 standard, the final polymer treatment can be divided into: degradation, biodegradation, oxidative degradation, photodegradation, incineration and other methods. In the eventual processing of materials, re-energyization is avoided as much as possible by avoiding landfill disposal, which is a better way to reduce the adverse effects of the environment.

Key indicators for evaluation of polymer greenness

The greenness evaluation of polymers includes the following key indicators. These indicators are not isolated from each other, but are linked and interact with each other. Based on the analysis of these indicators, a framework can be established for the quantitative evaluation of the greenness of polymer materials.

The material itself contains additional dangerous substances

In order to enhance the application performance of polymers and to develop new materials, it is often necessary to modify the polymers with added materials. However, the implementation of RoHS and similar laws imposes restrictions on the addition of polymers. Manufacturers are required to limit the use of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers, and other harmful substances in the development and production of polymer materials. Even if the harmful substances are left behind due to raw materials or during the production process, the content must be strictly controlled within the specified percentage. From the viewpoint of increasing the recyclability of materials, not only the current dangerous material content but also the hazardous material content of the material should be taken into consideration in order to ensure that the material can meet the legal requirements and be put into reproduction.

Table 1 Performance comparison of PET, PVC and HCM recycled materials with new materials

Table 2 Performance Changes Due to Material Recovery from Residual Additives Recovered from PET and PE

The properties of recycled and recycled polymer materials will inevitably change. To control this change in a relatively small area is an effective means to extend the cycle life of materials. This is not only related to the material itself, but also has an important relationship with the processing method, use environment, and recycling method. Table 1 compares the performance of three polymer recycled materials with new materials. From the evaluation system, the performance of a material after recovery is smaller than that of the new material. The greater the possibility of recycling the material, the better the greenness.