UNIVERSITY OF WISCONSIN SYSTEM SOLID WASTE RESEARCH PROGRAM. Processing Solutions and Market Applications for Mixed ABS.

Transcription

1 UNIVERSITY OF WISCONSIN SYSTEM SOLID WASTE RESEARCH PROGRAM Processing Solutions and Market Applications for Mixed ABS 2006 Final Report Tim A Osswald Michael W. Dattner Polymer Engineering Center University of Wisconsin-Madison

2 Abstract Electronics reclaimers are generating rising volumes of mixed ABS plastics from the processing of computer equipment and televisions. This flow represents a large market opportunity. Within our research we are investigating the processability of this scrap material and the properties of the resulting material. We found that the mechanical behavior of the reclaimed material was fairly repeatable, with the exception of impact properties. However, better compounding will result in even more consistent properties. We are also focusing on potential processing solutions and market applications for this mixed ABS scrap. Introduction Typical electronic housing retirement companies such as Cascade Asset Management Inc., in Madison, WI, see plastic housings as one of their two top problem areas, next to transportation [1]. These companies take computers, monitors, and printers, as well as TVs and other electronic devices, and recycle them. They have processes to remove the lead from monitor screens, and the hazardous metals from computer cards. They also specialize in destroying data from hard drives and tapes for security measures. In the process of separating materials, Cascade comes into the possession of over 30,000 lbs of plastic a month. They have computer and monitor housings, TV shells, and other odd pieces. These pieces are often made of high-end plastics, such as ABS and HIPS. Currently Cascade takes all of the plastic housings and places them in a bailer. The bailer flattens and crushes the material into bundles that are then placed in shipping containers and sent off to China. The company in China takes these materials, grinds the housings, and processes them to make the protective inside corners of suitcases. It results in a net profit to Cascade of about 2-3 cents a pound. The purpose of this experimental study is to find better and ultimately more profitable solutions. There are several questions that need to be answered. What materials are being dealt with here? What percentage of ABS, PS, HIPS, PC, and so on are in these housings? How do these materials interact with each other? Do the materials need to be separated or can they be run together as a blended material? How repeatable are the measurements of properties of the materials? Did processing affect the repeatability of the material s mechanical behaviors? What kinds of additives are in these materials? Certain additives, which are hazardous, have been outlawed and can no longer be used. Which parts have these additives? Should they be avoided? Can the material be used for higher end applications and therefore be sold to other companies for more money? All these questions lead to the ultimate question about a better, more profitable use for these plastics.

3 Experimental Procedure The first step taken was to identify the process of the scrapping and survey what materials were involved. A tour of Cascade gave some answers these questions. Several workers bring in the computers and other electronics to their workstations to scrap. The plastic parts are then placed in a bin to be rolled to the bailer at a later time. Once the items are bailed, they are tied up, and placed into a large shipping container bound for China when full. The survey of the materials would have to be done before the bailing. After bailing the pieces can break and spread throughout the bail. To get an accurate weight of each piece, the material of the item would have to be recognized before the bailing. The survey of the materials would also have to be done over a long time period. Cascade scraps the pieces as they come into the warehouse. Some days nothing but one brand of monitor may be scraped, while the next day they could scrap several different brands of computer towers. Because of these irregularities, it is hard to do the survey over a single bin of plastic, or any short period of time. After the part s materials were identified (usually by molded-in identifiers), they were weighed, and photographed. They were broken down into small enough pieces to fit into a grinder. Some of the ground materials were then injection molded into standard testing specimens depicted in Fig. 1. The remaining material was compounded using a thermal-kinetic mixer, or K-mixer, depicted in Fig. 2. A Kmixer consists of a small drum containing rotating blades, with a capacity of about 180 grams of the material. The blades spin at a speed set by the user, which in our case was 6,500 rpm. The material heats up from the friction and after reaching a desired temperature, also set by the user, a door opens and the material is ejected in a clump, which is ground down. We chose a K-mixer over a single or twin-screw extruder, because it only needs a small amount of material, and is quite fast. To heat our material to 205 degrees Celsius took approximately 20 seconds. Within this project we studied three different groupings of materials. The first material, which we denote as ground housings, was comprised primarily of computer housings as well as a small number of monitors, and a small number of printer pieces. The material was about 70% ABS, by weight, based on the labels molded on the housings. The second material, compounded housings, was the same as the first, but it was also run through the K-mixer. The third material, monitor housings, consisted almost entirely of monitor housings and was about 90% ABS by weight. These materials were then run through a Melt Flow Indexer to see the consistency of the material. The material was then molded into the test specimens depicted in Fig.1. Results and Discussion The results of the melt flow test were very promising. The numbers were quite consistent. The first material, the ground housings, gave a melt flow of 0.6 grams in 10 minutes with only 15% variability. The second material, the compounded housings, gave a value also around 0.6 with variability down to 11%. The ground housings injection molding samples were tested, and reground to see the melt flow index of the material after a further compounding from the screw. This material gave a melt flow of around 1.5 with variability down to 8.5%. The intense compounding needs to be studied further to fully understand this significant rise in melt flow index. A graph of these results can be seen in Fig. 3. Next, the three materials, ground housings, compounded housings and ground monitors, were molded into test specimens using a 22 ton BOY injection molder. The ground housings samples varied between 9.10 and 9.41 grams, with runners and gates, for a 3.3% variation. The compounded material weighed between 9.29 and 9.35 grams, with only a 0.6% variation. The three mechanical tests were then run on Instron machines at the USDA Forest Products Laboratory test facility in Madison, Wisconsin.

4 The izod samples were notched and tested in a controlled humidity environment. The ground housing and compounded housing materials both had impact strengths around 3.5(kJ/m2), and the ground monitors had a strength value around 1.1(kJ/m2). The first two materials had more HIPS, which could have accounted for the higher numbers between them. These results can be seen in Fig. 4. The fact that these materials provided somewhat low impact strengths is not surprising since they are comprised of materials that are not normally mixed together. The tension and bending tests provided fairly equal results for all three materials. This is promising for these materials. The maximum tensile load was ~1,400 kn, the modulus of elasticity was ~2.5 Gpa, and the maximum tensile strength was ~35,500 kpa. The bending max load was ~120 kn, the modulus ~0.17 GPa, and MOR (bending modulus) was ~17,000 kpa. All of these results can be seen more clearly in Figures These promising numbers showed that this project could be viable and profitable for Cascade far beyond the two cents per pound profit they were currently earning. The next step was to add a compounder to our project. During this project, a compounder, Pro Ex Extrusion, was contacted and brought into the project to further study the material. After studying the results of the material, they believe that they could purchase the bailed material for as high as 12 cents per pound, or ground material as high as 18 cents per pound, run it through their extruder and sell the material for 30 to 34 cents per pound. These numbers were quite promising to Cascade and future work will need to be conducted to maximize this project. Future Work There is still much work to be done to fully understand this material. A full survey needs to be done to better know what percentage each material is being used by the electronic manufactures. We need to determine what additives, such as flame-retardants, are being used, and where they are being used. In addition, we will study the benefits that might be gained by splitting up the different materials for reprocessing. In addition, current trends that exist in electronic housing manufacturing need to be incorporate in planning the future of electronic housing recycling companies. On the mechanical side, the materials blended by professional compounder need to be studied. Additives, such as rubber modifiers should be introduced to improve impact resistant, where necessary. Dimensional stability needs to be looked at in realistic parts to see if one of the main attributes of ABS is retained. Lastly, a plan to combine the recycled material with virgin resin using coinjection molding will be studied within our laboratories. Conclusions These computer and monitor housings present a high quality material that can be reprocessed without great loss in properties. They provide consistent melt flow and mechanical properties crucial to making a viable molding material. The high availability and low cost of the housings make them perfect candidates for parts such as general utility applications, such as, lighting fixtures, coinjection pieces, and maybe even electronics housings. Acknowledgements This work was done with funding by the UW Solid Waste Research Council. Materials and assistance provided by Cascade Asset Management, and Pro-Ex Extrusions INC. The USDA Forest Products Lab provided lab equipment and assistance in process and testing. References 1. Peters-Michaud, Neil. Cascade Asset Management, LLC. Personal Conversation. 24 April 2005

5