Research on Recycling Technology of Plastic Packaging Materials (I)

Raw material recycling refers to recycling of plastic packaging materials. Materials using this raw material recycling technology and process only change the shape and structure of the recycled plastic package without changing its physical and chemical properties. For the raw material type recycling of plastic packaging, the final technology and process treatment result in a plastic raw material (recycled plastic particles) that can be reused to manufacture the same or similar packaging products.

1 Technical principles

The principle of plastic packaging material recycling technology refers to the waste plastic after the pre-processing crushing directly plasticized, and then molding or granulation, in some cases the need to add a certain amount of new resin, made of recycled plastic products process. It can use existing technology, equipment, both economic and efficient. In this process, appropriate additives (such as antioxidants, lubricants, stabilizers, plasticizers, colorants, etc.) must be added to improve the appearance and aging resistance and improve the processing performance, but the mechanical strength of the material and No effect on performance (does not increase but decreases intensity as much as possible). The technology can be divided into three methods depending on the source and purpose of waste plastics.

a. It is not necessary to carry out pre-processing such as sorting and cleaning, and crushing directly after plasticization. This method is mainly used for scrap and defective products in the production of packaging products. They can be sent directly to the hopper and used with new materials without any pre-treatment. This method can also be used for the recycling of some plastic containers and products that have been used but are very clean and free of any pollution.

b. Recycling of pre-processing such as sorting, washing, drying, crushing, etc. is required. This is mainly required for those plastic packaging materials and products containing a lot of pollution components and impurities. Firstly, rough washing is performed on the recycled materials to remove impurities such as sand, stones, and metal to prevent damage to the machine. After rough washing, the material is dewatered centrifugally and then sent to the crusher for crushing. After crushing, fine crushing is performed to remove the inside of the package. Impurities. After cleaning and then drying, plasticization or granulation can be performed directly. The object of this method is generally plastic packaging waste collected from different channels after commodity circulation, various uses and various shapes of packaging containers, packaging bags, film sheets and so on. It is characterized by a lot of impurities, and it is difficult to deal with serious contamination. In order to obtain better results and the best economic benefits, this method requires the classification of raw materials for waste.

c. Special pretreatment is required for recycling. For example, PS foam packaging products, which are inconvenient for transportation and storage, are not easy to input into the processing machinery in the process. Therefore, a preliminary deaeration and volume reduction treatment is required. Specific treatment may be used for special foam removal or extrusion equipment ( Such as compactors, etc.). For different recycled plastic packaging materials, after the above-mentioned three different pretreatments are performed according to the requirements, plasticization, homogenization and granulation can be performed (some tubes can be directly formed and other shaped products can be obtained). Table 1 shows the application of recycled plastics.

2 Process

Plastic packaging raw material recycling process route is:

Rough Washing - Breaking - Fine Washing - Drying - Plasticizing - Homogenization - Granulation

The plasticization process is to put the waste plastic in a plastic mixer or a plastic extruder. After the internal spiral roller rotates and extrudes, it is heated to become a molten billet. After a period of time, the waste plastic has a uniform plasticity. Plasticization is the prerequisite for getting new recycled products. One of the purposes of plasticization is to prepare recycled pellets, and the second is to shape directly after plasticization. The direct molding can be completed on the plastic mixer after the plasticization is completed, and the granulation process is omitted. This is a process for directly manufacturing the packaging product (container) from the waste plastic.

The homogenization process is a kind of plasticization in which the waste plastic packaging material is mixed with various auxiliary agents or modifiers (plasticizers, lubricants, stabilizers, anti-aging agents, etc.) and uniformly mixed. There are two ways to homogenize: First, the mixing and plasticization are completed synchronously, and the broken waste plastic and various additives (plasticizers, etc.) are kneaded and homogenized to obtain various products (containers, etc.) ); Another is after homogenization granulation, homogenization granulation can make the materials mix very evenly. This is also the key to improving the quality of raw materials in recycling.

Granulation is the use of a rapidly moving tool to cut waste plastic into fine, uniform particles as it is melt extruded. Granulation process cold granulation and hot granulation two. The cold cut is that the extruded melt is cooled by a cold water tank and cut into pellets by a pelletizer. The eagerness is directly after the melt extrusion is cut by a rotary knife, and is sprayed with a water spray to cool, in order to prevent the particles from sticking to each other and affecting the quality. Granulation can be done on granulators or pelletizers, respectively. The size of the material obtained by the granulation of the granulator is not uniform, and the granulator is a granulating apparatus for sheet-like plastics refining, which cuts the sheet-shaped extrudate into a rectangular or hexahedron by slitting and cross-cutting.

The plastic particles obtained by the granulation are raw materials used for remanufacturing plastic packaging obtained by using waste plastic packaging recycling technology. When it is used to make plastic packaging, it can be used entirely in this granular material or in part (added in proportion to the original material). If all of these materials are used, the quality of plastic packaging will be reduced.

(to be continued)