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ContentsPLASTICS RECYCLING EXPERIMENTS TO IMPROVE UNDERGRADUATE MATERIALS EDUCATION
ABSTRACT
There are growing interests among engineers to concern about the effects of the products and processes they design upon the environment. Since plastics account for approximately 20 percent of the landfill volume in U. S., recycling plastics will play a significant role in reducing solid waste to the increasingly-scarce landfills. Students must be educated in the methods to recycle materials in order to reduce future waste and protect the environment.
This paper is a result of two projects supported by the National Science Foundation. It introduces a series of plastic recycling experiments into undergraduate materials laboratories in such course as "polymers and composites." With an integrative review for students at various stages, students participated in the entire recycling process, including collecting, granulating, extrusion-compounding, drying, injection molding, testing and structure analyzing.
This series of plastic recycling activities has a significant impact on students and curriculum improvement. Many students have been attracted with great environmental concerns from not only the major but also from non-science disciplines. With the exposure to the typical plastic recycling activities, students not only understood the principles of polymer structure, property and processing, but also learnt many practical techniques of materials recycling. They became much more conscious and more responsible for environmental protection.
INTRODUCTION
Reducing the volume of solid waste disposal in landfills has drawn considerable public attention due to the decreasing number and size of landfills in the nation. It is estimated that four pounds of trash are produced daily by every man, woman and child in the United States [1]. At this rate, major cities including New York and Los Angeles will exhaust landfill space in just a few years Philadelphia and other cities are already out of space [2]. Because of the nature and application of packaging materials, plastics occupy about 20 per cent in volume of the landfill space [3]. However, less than 1 percent of the plastics in the United States was recycled in 1990 [4, 5]. Thus, recycling and reusing plastics will play a significant role in reducing the amount of solid waste disposal to landfills. Researchers are attempting to find different ways to recycle plastics [6, 7] and more industrial companies are becoming involved in plastic recycling activities [8, 9]. There is an urgent need to expose undergraduate students to materials recycling for environmental protection.
A series of plastic recycling experiments was introduced to students in materials-related courses such as "polymer and composites." With the plastic recycling experiments, students not only learned the fundamentals of polymer structure, processing and properties as in conventional materials courses, but also dealt with the effects of materials life cycle and the impact on society and environment. Many students became more environmental conscious and more knowledgeable of environmental protection.
EXPERIMENTS
The series of plastics recycling experiments used a granulator, an extruder, a pelletizer, and an injection molding machine. Before the laboratory activities, students were introduced to the fundamentals of materials structure, processing and behavior.
1. Collecting and Cleaning Post-Consumer Plastic Products
The blending of various types of plastics will result in different properties of the final products made from recycled materials, which makes the control of product quality difficult. Therefore, separation of plastics has been a critical issue for plastic recycling and reuse. To facilitate the separation effort, the Society for Plastic Industries (SPI) has recommended a series of voluntary codes to be placed on plastic containers. For example, high density polyethylene (HDPE) is coded #2 on the bottom of plastic milk jugs. This is an excellent way to introduce students to the plastics codes for practical recycling.
2. Granulating Recycled Plastic Products into Flakes
Ideally, thermoplastics can be reprocessed into new products by various thermo-processing methods such as extrusion and injection molding. A granulator was used to cut the post consumer plastic containers into small flakes for processing. Flakes of recycled plastics obtained from grinding were used for subsequent extrusion processing.
3. Extruding Recycled Plastic Flakes into Strands
An extrusion machine was used to extrude the recycled plastic flakes into strands of 6.35 mm (1/4") diameter. In this experiment, students were introduced to the principle of extrusion, the effects of processing parameters on the material integrity and properties. The processing variables included heating temperature profile on the extrusion barrel, melt temperature, extrusion pressure, extrusion speed and cooling on the extruded rods.
4. Pelletizing Strands
A downstream pelletizer was employed to cut the extruded rods into small pellets. After the initial setup, the pelletizing can be synchronized with the output of the above extruder. The pellets can be processed in subsequent injection molding for new products.
5. Injection Molding of Test Specimens
An injection molding machine (Boy 50M) was used to process the HDPE pellets into molded products. In this experiment, a four-cavity ASTM specimen mold was selected for the injection molding process. Students can also use the molded specimen for testing mechanical properties of the recycled plastics.
In this section, students learned the fundamentals of injection molding using an industrial scale injection molding machine. The major benefit of using the injection molding machine is that students can see the end products they make with recycled plastics.
CONCLUSIONS
A series of plastic recycling experiments was introduced successfully to undergraduate materials laboratories in "polymer and composites" course. With an integrative review at various stages, students participated in the entire recycling process, including collecting, granulating, extrusion, pelletizing, and injection molding.
In the experiments, students were exposed to some practical issues of material life cycles including the impacts on environment. By conducting plastic recycling experiments in the laboratory, students can learn the basic techniques for recycling plastic materials and they can see the final products they made with the recycled plastics.
ACKNOWLEDGMENT
The material is based on work supported by the National Science Foundation under Grant No. DUE-9550857. Another part of the support was from Illinois Department of Energy and Natural Resources through Office of Solid Waste Research at University of Illinois at Urbana-Champaign.
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