Recycling of Plastic Materials Part 11 potx

• the larger percentage drop in properties on addition of GRT to HDPE (70% decrease at 40 wt%) compared to LLDPE (50% decrease at 40 wt%) • the increased ductility afforded the HDPE composites on addition of the thermoplastic elastomers. As discussed in the section on the influence of the polymer matrix, it is the semi-brittle failure of HDPE which is believed to be responsible for its greater intolerance tothe large,poorly bondedGRT particles.The increasein theductil- ity of the HDPE matrix on addition of the thermoplastic elastomers, then, results in significant impact improvement through crack suppression, thus rendering the matrix more tolerant of the large GRT particles. The small increase on going from non-reactive to reactive SEBS may be an indication that 166 Ground Rubber Tire-Polymer Composites Figure 4. Properties of compatibilized GRT-PCPEPP composites: (a) unmodified RCPEPP, (b) 3:2 RCPEPP:GRT composite, (c) 14:10:1 RCPEPP:GRT:SEBS composite. for LLDPE composites are believed to be a result of : the adhesion,although increased, isstill below thelevel necessary to achieve additional improvements in the properties. GROUND RUBBER TIRE AND RECYCLED PLASTICS In order for GRT composites to find high volume applications they have to be a lower costreplacement forvirgin, commodity polymers. To achieve this, each as- pect of the composite fabrication process, from tire collection and grinding to compounding and final product manufacture, has to be optimized on a cost/per- formance basis. One very attractive approach to minimizing overall composite costs isto utilizerecycled polymers as the matrix phase in place of virgin materials. There are also a number of advantages in addition to cost that this method may provide. As GRT composites are already black (although they can be colored to some extent 29 ), the use of colored post-industrial or post-consumer waste is easily tolerated. Low levels of dirt or impurities, which may render scrap un- suitable for some applications, will probably be of secondary concern compared to the large GRT particles. comingled waste, where material properties are usu- ally very poor and require the addition of compatibilizing agents anyway, may provide for particularly interesting opportunities. As part of a larger study on compatibilizing a comingled waste stream of PE and PP, 33 Rajalingam and Baker have investigated composites of scrap PE/PP with GRT. The initial PE/PP mixed waste (RCPEPP) was found to have an impact energy of 4.7 J (See Table 2). Addition of a number of thermoplasticelastomers was found to provide significant increases in impact strength. For a particular SEBS copolymer, the addition of 6.7 wt% to the PE/PP blend increases the impact energy from 4.7 J to K. Oliphant, P. Rajalingam, and W. E. Baker 167 Table 2 Impact properties of RCPEPP/GRT composites Blend composition Impact energy (J) RCPEPP 4.7 RCPEPP:GRT (3:2) 4.4 RCPEPP:GRT:SEBS (14:10:1) 10.5 RCPEPP:GRT:SEBS (13.8:22.2:1) 11.2 pact energy similar to pure RCPEPP, about 5 J. The addition of the SEBS copolymer to produce a composite of 14:10:1 (RCPEPP-GRT-SEBS) increases the impact energy to 10.5 J. A composite of even higher GRT content (13.8:22.2:1) has an impact energy of 11.2 J. Impact curves for select composites are shown in Figure 4. These results were obtained with a Rheometrics drop-weight instrumented impact tester (described previously). Curve A repre- sents the impact failure of the unmodified RCPEPP blend, showing the highly brittle failure. Curve B shows the impact failure of the RCPEPP-GRT (3:2) composite, showing how the ductility is increased although the impact energy (inte- grated area under the curve) remains approximately constant. The large increase in ductility for the composite modified with SEBS (14:10:1) is shown in curve C. Clearly, the use of comingled waste as the matrix phase for GRT composites provides for interesting opportunities given that suitable compatibilizerscan be found. CONCLUSIONS In general it is seen that simple addition of GRT to most polymers results in significant decreases in mechanical properties due to the large particle size and poor adhesion. Although some of these materialsmay find limited application in low level usages, it is clearly necessary to improve on the properties of GRT-polymer composites for them to become a large volume material. Since lowering particle size results in only small improvements in material properties (and increased grinding costs) strategies for overcoming the deleterious effects of adding GRT to polymers have focused on methods of improving adhesion. In this area it is seen that judicious selection of a compatibilizing agent can lead to composites with quite reasonable mechanical properties at significant levels of GRT (as high as 50-60 wt%). As added compatibilizer levels are low (4-7 wt%) and no specialized processing steps are necessary, these higher value composites can be produced at little additional cost over simple GRT-polymer blends. Perhaps even more attractive is the use of recycled polymers as the matrix phase for GRT-polymer composites. Although only one example is presented in this review, this is an area that would seem to have great potential for increas- ing the recycling of both GRT and polymer wastes. 168 Ground Rubber Tire-Polymer Composites tential matrix material. A blend of RCPEPP with GRT in a 3:2 ratio has an im- 18.6 J, clearlyshowing a majorcompatibilizing and tougheningeffect for thispo- The studies of ductile LLDPE and semi-brittle HDPE indicate that mechanical properties of GRT filled thermoplastics can be better retained when GRT is added toa ductile matrix in which failure occurs with littleor nocrazing or crack formation. One issue that may seem neglected in this review is that of applications for GRT-polymer composites. It is theopinion of the authors thatif GRT composites can bedeveloped where 1) the mechanicalproperties are close to virgincommod- ity polymer properties, 2) rheological properties are retained, and 3) costly processing steps are not required, the applications will follow. This question, as to whether cost effective composites can be produced, depends, as with any recycling effort, on a number of factors, and is not easily answered. The potential, however, is evident. REFERENCES 1. J. A. Beckman, G. Crane, E. L. Kay, and J. R. Laman, Rubber Chem. Technol., 47, 597 (1974). 2. J. D. Snyder and R. F. Hickox, Rubber World, 161 (3), 49 (1962). 3. J. Winker, Chem. Eng. News, 49 (20), 29 (1971). 4. J. Paul, Encyclopedia of Polymer Science and Engineering, Vol. 14, 2nd ed., Ed. H. Mark, John Wiley & Sons, New York, 787 (1986). 5. R. J. Sperber and S. L. Rosen, Polym. Plast. Technol. Eng., 3 (2), 215 (1974). 6. J. R. M. Duhaime and W. E. Baker, Plast. Rubber Comp. Process. Appl., 15, 87 (1991). 7. K. Oliphant and W. E. Baker, Polym. Eng. Sci., in press 8. A. Ratcliffe, Chem. Eng., 79 (7), 62 (1972). 9. A. A. Hershaft, Environ. Sci. Technol., 6 (5), 412 (1972). 10. Cryogenic Size-Reduction Technology Provides Economical Recycling Method, Elastomerics, 109 (12), 39 (1977). 11. A. A. Phadke, Plast. Rubber Process. Appl., 6 (3), 273 (1986). 12. R. A. Swor, L. W. Jenson, and M. Budzol, Rubber Chem. Technol., 53, 1215 (1980). 13. G. Cheater, Eur. Rubber J., 161, 11 (1979). 14. D. Dempster, Eur. Rubber J.,159, 87 (1977). 15. D. Tuchman and S. L. Rosen, J. Elast. Plast, 10, 115 (1978). 16. E. L. Rodriguez, Polym. Eng. Sci., 28, 1455 (1988). 17. R. D. Deanin and S. M. Hashemielya, Polym. Mater. Sci. Eng., 57, 212 (1987). 18. A. A. Phadke and S. K. De, Polym. Eng. Sci., 26, 1079 (1986). 19. T. Liu and W. E. Baker, Polym. Eng. Sci., 31, 753 (1991). 20. P. Rajalingam and W. E. Baker, Report being prepared for the Ontario Ministry of the Environment. 21. S. Wu, Polymer Interface and Adhesion, M. Decker, New York, (1982). 22. S. Wu, Polymer, 26, 1855 (1985). 23. F. G. Smith and W. B. Klingensmity, Paper Presented at a Meeting of the Rubber K. Oliphant, P. Rajalingam, and W. E. Baker 169 Division, American Chemical Society, Washington, 9-12 October, 1990. 24. D. H. Chang, Multiphase Flow in Polymer Processing, Academic Press, New York (1981). 25. N. C. Liu and W. E. Baker, Polymer Eng. Sci., in press. 26. M. D. Ellul and A. N. Gent, J. Polym. Sci., Polym. Phy. Edn., 22, 1953 (1984). 27. H. C. Wang, R. H. Schatz, and E. N. Kresge, Encyclopedia of Polymer Science and Engineering, Vol. 8, 2nd ed., Ed. H. Mark, John Wiley & Sons, New York, 423 (1986). 28. G. Koski, Annual Technical Conference of the Soc. of Plastics Engineers, 1799 (1988). 29. F. J. Stark Jr. and A. Leigton, Rubber World, 12, 36 (1983). 30. K. Oliphant and W. E. Baker, unpublished results. 31. P. Rajalingam and W. E. Baker, Rubber Chem. Technol., submitted. 32. P. Rajalingam, K. Oliphant, and W. E. Baker, Paper presented at the IUPAC International Symposium on Recycling of Polymers - Science and Technology, Marbella, Spain, 18-20 September, 1991. 33. P. Rajalingam and W. E. Baker, Annual Technical Conference of the Society of Plastics Engineers, Detroit, May, 1992. 170 Ground Rubber Tire-Polymer Composites Quality Assurance in Plastics Recycling by the Example of Polypropylene Report on the experience gathered with a scrap battery recycling plant K. Heil and R. Pfaff Metallgesellschaft AG, Zentral-Laboratorium, Reuterweg 14, 6000 Frankfurt/Main 1, Germany RESOURCE RECYCLING Originally, industrial production relied on a linear material flow. Raw materials weremined and upgraded, premixes producedfor themanufacture of components and equipment which were then utilized and eventually dumped into landfills after their useful life had elapsed. As the proportion of synthetic products in the total production volume increased, landfilling became ever more of a problem. The consequences of this disposal practice became unforeseeable. The price of landfilling rose dramatically. The resulting bottlenecks called for a fun- damental change in our attitude towards disposal. Both industrial producers and consumers have since been looking for new concepts and solutions. As compared to the linear material flow, a cyclical concept offers the advantage of avoiding waste or at leastpostponing landfilling to a laterdate. Recycling of materials and products into the production processes soon became a commonly used phrase. Recycling can start in a production process itself or during or after the product’s life. Thus, the maintenance of goods can be viewed as productrecy- cling. Therefore the return of defective or partly renewed products should have the highest rank among the recycling priorities. Here, the product undergoes no changes in its form. If, on the other hand, the product is disassembled or decom- posed into itsbasic components orsubstances, thisisreferred toas a resourcere- cycling. Ideally, these materials or substances should be sorted and returned to the production route. A flow diagram of this cyclical material flow concept is shown in Figure 1. K. Heil and R. Pfaff 171 From the point of view of quality assurance, recycling of used materials into production poses its own special problems. The used material originates from different material streams varying in their impurity content and age. They bear the traces of their former service life. Their original properties have suffered, changed ordisappeared altogether. Another important factor to be considered is the material damage resulting fromthe stresses to which thematerials were ex- posed during their former service life. The impact of such damage is not known and cannot be predicted without comprehensive testing. Processing of recycled materials involves unknown risks. This applies to post-use of metal, plastics just as well as to minerals and textiles. When it comes to supply, recyclers face a problem of finding reliable sources of used materials, and organizing their collection and transportation. Supply may be a subject of considerable seasonal fluctuations as it is for example the case of used batteries. Continuous operation of the recycling process 172 Quality Assurance in Plastics Recycling Figure 1. Flow diagram of material recycling. therefore requires that a large volume of used materials are held in stock. Col- lection often requires the sophisticated organization and transportation, fre- quently not possiblewithout the useof specialmeansof transport.Thus logistics alone may jeopardize the profitability of a recycling process. This cost factor increases with decreasing value of the post-used materials to be collected and transported. From the point of view of quality assurance, pure post-use material streams rank highest on the value ladder while mixed or contaminated materials are grouped into an inferior category. 1 Metallgesellschaft AG as a process and raw material-oriented technology and services group has a long and successful track record in recycling of post-use metals. Ever since recycling of post-consumer goods and durables gained a foot- hold in industry, polymers recycling has been attracting growing attention. The first commercial-scale plastics recycling plants are currently in the planning phase. Several pilot plants are already in operation. BSB RECYCLING GmbH in Braubach, a subsidiary of Metallgesellschaft AG operates a secondary lead smelter for lead recovery from post-use lead-acid batteries. 7 They process some 60,000 tonsof batteries per annum whichaccounts for about half ofthe usedbat- tery volume to be disposed in the western states of the Federal Republic of Ger- many. BSB started to segregate the polypropylene from the battery casings and route it to a separate recycling process as far back as in 1984. For the recycling process, a quality assurance system geared to the specific requirements of the application has been developed and implemented. 3 USED BATTERY RECYCLING Lead-acid batteries from automotive applications normally have a shorter service life than the caritself. After their service lifehas elapsed, they are no longer suitable for use. Because of their high lead content, lead-acid batteries have always been eagerly snapped up by secondary lead smelters. Via the car dealer and garage network, lead-acid batteries are collected in large quantities and then transported to secondary lead smelters. The logistics system is geared to lead recycling. The first battery reprocessing step yields not only lead but also PP in a form of the casing fragments. Accordingly,the polymeris available without additional cost. As the casing makes up a substantial part of the total battery, the quantities of polypropylene obtained are sufficient to warrant the operation of a plastics recycling plant (Figure 2). The secondary lead smelter K. Heil and R. Pfaff 173 processes up to 60,000 tpa of used batteries corresponding to about 3000 tpa of polypropylene. For this material stream, a recycling plant was developed, built and put into operation in 1986. Crushing and separation In thefirst step,the batteriesare processedthrough acrushing andseparation system operating on the TONOLLI ® principle (Figure 3) which has been suc- cessfully employed in various battery recycling plants in Europe and North America. Next, the heavy fractions (lead, lattice metal) and Ebonite are separated from the light fractions (polypropylene and impurities). At this stage, the polypropylene has a purity of 97 %, which is still insufficient for its further processing. It is therefore routed to an upgrading stage, where it is further reduced in size in a wet-type rotary grinder and subsequently separated from water by sedimentation. After having passed through two series-connected driers and a cyclone separator, the polypropylene is available as so-called regrind with a purity of 99.5 %. The regrind consists of various types of polypropylene differing in their formulation, molecular composition and stabilizer content, having a broad spectrum of characteristics. Suitable mixing yields an intermediate product with a narrowed range of statistically uniform product characteristics. 174 Quality Assurance in Plastics Recycling Figure 2. Parts of an original 12V 44Ah lead-acid battery with a casing made of polypropylene. Further processing to polypropylene granulate As a next step, the regrind is routed to compounding (Figure 4). By controlled addition of additives, polymers and fillers, the feed mix can be adjusted to suit the specific customer requirements. This feed mix is then gravimetrically me- tered into a special twin-screw kneader where it is molten under the dual action of an external heater and internal shear forces to obtain a homogeneous com- pound. Volatile matter is extracted and impurities resulting from unmolten components are filtered out. Subsequently, the melt is pelletized in a melt granulator. The resulting granulate is quenched in a water bath, centrifuged and finally processed through a hammer mill to break up lumps. The end product is a packagable granulate suitable for injection molding. This granulate is a secondary raw material which not only meets customer specifications but is also manufactured under a quality assurance system. K. Heil and R. Pfaff 175 Figure 3. Process steps in preparation of polypropylene regrind. [...]... “telquel” From the quality assurance point of view, this means that a buyer accepts a processing risk without having an option of rejection If the recycling process is robust and flexible, this kind of used material application is of a low risk alternative If not, processing of the used materials is liable to lead to considerable problems In recycling of battery casing plastics, the battery crushing and separation... 8 Flow diagram of process control system market in large quantities However, even in such a case, controlled process conditions in terms of quality assurance can still be expected After crushing and upgrading, the regrind exhibits a purity of over 99.5 %, is color-mixed, and has a characteristic particle size distribution of 2 to 4 mm In this condition, it meets all the requirements of the subsequent... technological and economic requirements of the compounding process It is at this point where the process control element of quality 180 Quality Assurance in Plastics Recycling assurance is brought to bear The 5 M influencing factors (man, method, machine, milieu, material) have to be planned, organized and implemented to achieve a desired result (Figure 8) In plastics recycling, process control gains added... processing of many diverse formulations, computer administration of the formulation data makes for a great simplicity of handling The target-versus-actual comparison of the process parameters identifies deviations from the process target condition From this information, staged responses to the process are derived with the aim of reestablishing and maintaining the target conditions 182 Quality Assurance in Plastics... products, special processes, and the size of the plant Corresponding models are given in EN 29,001 to 29,003 However, the key elements are always the same, irrespective of the quality assurance system selected The quality cycle, illustrated in Figure 5, shows the interaction of the individual QA elements QA element - raw materials The raw material element is a key component of the quality assurance system Unlike...176 Quality Assurance in Plastics Recycling Figure 4 Flow diagram (according to DIN 28004) of the compounding plant QUALITY ASSURANCE TO EN 29,000 PP The EN 29,000 pp standards provide a selection of quality assurance elements 2 and a guideline for establishing quality assurance systems The selection of an optimum quality assurance system is governed by many diverse... quality of the end-product Accordingly, feedstock qualification testing only makes sense after materials have undergone the first processing steps Extensive tests and analyses conducted over many years were necessary to characterize the material - “polypropylene from used batteries” For this pur- 178 Quality Assurance in Plastics Recycling Figure 6 Impurities in regrind Figure 7 Improvement of product... repeatedly The examples of wood impurities (Figure 6) and flow properties of the melt (Figure 7) demonstrate that the characteristics are scattered at random Although, the used material stems from different sources and is delivered in batches, the parameter distribution is homogeneous Major variations in the parameters only occur when used batteries of a new design enter the recycling K Heil and R Pfaff... testing of the product Therefore, supervision of the process and maintaining the quality-relevant process parameters constant are imperative For this purpose, we have developed and implemented a process control concept which has for many years been employed with great success in a day-to-day operation even for plant startup, after process modifications and after the introduction of new formulations Out of. .. actual values of these process parameters are recorded and compared with given target values The target values were determined by previous trial runs A trial run is defined as a production phase in which a TO-SPEC product is produced under realistic conditions over a prolonged period Trial runs are performed to verify the process capability of production of a product, having a defined range of characteristics . possiblewithout the useof specialmeansof transport.Thus logistics alone may jeopardize the profitability of a recycling process. This cost factor increases with decreasing value of the post-used materials. be a subject of considerable seasonal fluctuations as it is for example the case of used batteries. Continuous operation of the recycling process 172 Quality Assurance in Plastics Recycling Figure. energy of 4.7 J (See Table 2). Addition of a number of thermoplasticelastomers was found to provide significant increases in impact strength. For a particular SEBS copolymer, the addition of 6.7

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