Because of the presence in the wastes of about 10% of inks, pigments, fillers and so on, their microstructure cannot be studied by polarized optical micros- copy. Thus, a microstructural study by scanning electronic microscopy, using the fracture surface of impact tested specimens, was carried out in order to con- firm the previous data. Figures 14 and 15 give SEM micrographs of the fracture surface of HDPE, LDPE, and wastes at a very low magnification level. A similarity between the fracture surfaces from impact tests of the wastes and LDPE in liquid nitrogen is found. A smooth surface is observed at a low magnification in the front of a semi-brittle fracture observed in the hollowed region of HDPE specimen. Also, a lower amount of the solid particles (pigments) in the micrographs of the wastes is seen. At higher magnification (Fig. 16), it is possible to observe a significant differ- ence between the fracture surface of blends with HDPE as a matrix and with LDPE as a matrix. Indeed, rounded features in the 85% HDPE blend fracture surface suggest a semi-brittle fracture around macroaggregates of crystals. At a 78 Management of Plastic Wastes Figure 18. SEM micrographs of wastes showing their brittle fracture. O. Laguna Castellanos et al. 79 Figure 19. Mass balance of the recycling plant designed for treatment of film plastic wastes from municipal origin. Figure 20. Air view of the plant from Figure 19. higher level of magnification this feature is clearly evident and can be compared with the micrographs in Figure 17, where the homopolymers show striking dif- ferences in their fracture mechanism due to their different microstructure in macroaggregates of crystals. Furthermore, we must keep in mind that the LDPE does not break at -30 o C and its fracture surface was obtained in liquid ni- trogen. In Figure 18, the fracture surface of the waste specimens also has numerous rounded features at the higher level of magnification. Probably solid particles from inks act in the wastes as nucleation agents. Also, a very small size of the rounded forms is observed. In any case, the higher level of stress concentrators present in the wastes makes them more brittle and explains their low impact strength value. The failuremodeof the wastes is similar tothatof the matrix. 80 Management of Plastic Wastes Figure 21. Results of the ROI for economic study of viability of the utilities in figures 19 and 20. The economical approach Based on preliminary results, the design of a plant for treatment of the film plastic wastes was completed in 1985. The facilities were designed to produce pellets from the film plastic wastes ready to run a production with substitution of the required percentage of LDPE virgin resin. The mass balance and imple- mentation of the plant design can be seen in Figures 19 and 20, respectively. The preliminary economic study was carried out according to Machinery and Engines Charge. 30 Satisfactory results were obtained 31,32 and these were chosen as a starting point for two economic projects with immediate release in the 1986-89 period, 33,34 and as a Final Master Project. A summary of one project 35 is given in Figure 21 based on the results of the ROI (Rent Over Investment). It is very remarkable that in the 1986-1988 period, 43 % of ROI was achieved. CONCLUSIONS The main conclusion of this paper is a real and practical possibility of recycling of thermoplastic materials using an integrated management scheme in which plastic wastes are subjected to sequential recycling from initial high perfor- mance and high cost applications to subsequently lower performance and lower cost applications. Thus, based on the technical conclusions regarding recyclability of plastic wastes, it is necessary to create laws regarding genera- tion, collection, and location of sites having economic aspects in mind. The clas- sic commodity - thermoplastics can be successfully recycled into a sequential scheme from the top applications to the lower performance articles. Additives can be found to improve performance, processing, mechanical properties, sur- face properties, etc. In future, and probably according to international stan- dards and regulations, recyclability will become the most economical way to manage the Earth’s resources, in good agreement with the expected perfor- mance of the recycled plastic materials and their fundamental properties. REFERENCES 1. M. J. Curry, Secondary Reclamation of Plastic Wastes, Vol. I and II, Technomic Pub., (1987). 2. Proceedings of the Melting, Recycling Plas I, Technomic Pub., (1986). 3. Ibid, Recycling Plas II, Technomic Pub., (1987). 4. Ibid, Recycling Plas III, Technomic Pub., (1988). 5. Ibid, Recycling Plas IV, Technomic Pub., (1989). 6. Ibid, Recycling Plas V, Technomic Pub., (1990). O. Laguna Castellanos et al. 81 7. R. Leaversuch, Modern Plast., 4 (1990). 8. Proceeding of the Meeting, Plastics Recycling-88, SPE Scandinavian, Copenhagen (1988). 9. Ibid, Plastics Recycling-91, SPE Scandinavian, Copenhagen (1991). 10. Proceeding of the Meeting, Recycle-87, Davos, Switzerland (1987). 11. Ibid, Recycle-89, Davos, Switzerland (1989). 12. Ibid, Recycle-91, Davos, Switzerland (1991). 13. Technical Bulletins, General Electric Plastics, Belgium (1991). 14. Technical Press Bulletins, Neste Chemicals, Belgium (1992). 15. Technical Bulletins, Opel, Germany (1992). 16. G. E. P. Box, W. G. Hunter, and J. S. Hunter, Statistics for Experimenters, John Wiley, New York (1978). 17. J. E. Goodrich and R. S. Porter, Polym. Eng. Sci., 7, 45 (1967). 18. L. L. Blyler and J. H. Daane, Polym. Eng. Sci., 7, 178 (1967). 19. S. Y. Hobbs, J. Macromol. Sci., Rev. Macromol. Chem., C19, 221 (1980). 20. B. B. Stafford, J. Appl. Polym. Sci., 9, 729 (1965). 21. E. P. Collar, J. Taranco, and O. Laguna, J. Appl. Polym. Sci., 38, 667 (1989). 22. C. D. Han, Rheology in Polymer Processing, Academic Press, New York (1976). 23. L. A. Utracki, Polym. Eng. Sci., 23, 602 (1983). 24. C. D. Han and Y. W. Kim, Trans. Sco. Rheol., 19, 245 (1975). 25. D. D. Patterson, Polym. Eng. Sci., 22, 64 (1982). 26. C. D. Han, J. J. Kim, H. Chuang, and T. H. Kwack, J. Appl. Polym. Sci., 28, 3435 (1983). 27. O. Laguna, E. P. Collar, J. Taranco, and J. P. Vigo, J. Polym. Mat., 4, 195 (1987). 28. D. R. Paul and S. Newman, Polymer Blends, Vols. I and II, Academic Press, New York (1978). 29. E. Martuscelli, Polym. Eng. Sci., 24, 563 (1984). 30. A. Vian, El Pronóstico Económico en Química Industrial, Alhambra, Madrid (1975). 31. E. P. Collar, Doctorate Project, U. Complutense, Madrid (1985). 32. O. Laguna, J. Tijero, E. P. Collar, J. A. Serrano, V. E. Ibañez, D. Blanco, and J. Taranco, Rev. Plást. Mod., 50, 451 (1985). 33. B. Cantabrana, M. J. San Pablo, V. Evangelio, T. G. Iglesias, and J. A. Serrano, End’s Project, Enterprises Direction Master, Escuela de Organizacion Industrial, E.O.I., Madrid (1986). 34. S. Niddam and A. Sanz, End’s Project, Enterprises Management Master, Instituto de Empresa, Madrid (1989). 35. T. G. Iglesias, J. A. Serrano, O. Laguna, E. P. Collar, and J. Taranco, Rev. Plást. Mod., 52, 209 (1986). 82 Management of Plastic Wastes Blends of Polyethylenes and Plastics Waste. Processing and Characterization F. P. La Mantia, C. Perrone*, and E. Bellio** Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Università di Palermo, Viale delle Scienze, 90128 Palermo, Italy *I.P.I. SpA, S. S. Passo del Giogo, 50038 Scarperia (FI), Italy **Centro Ricerche Riciclo Materie Plastiche, Enichem Polimeri, Ragusa, Italy INTRODUCTION Recycling of mixed plastics waste is not new. The first industrial applications in Japan date from 1973. 1 It is well known that it is possible to manufacture rods, stakes, bars, boards, plates, etc. from mixed plastics waste but the me- chanical properties of these products are inferior. The recycled products cannot compete withvirgin plastic materials, and thereforethey have to find theirmar- ket in areas dominated by cheap materials like wood and concrete. Moreover, the market of park benches, playgrounds, fences, etc. cannot absorb, in the long run, the massive amounts of plastic wastes that are produced every year. A possible route to recycle mixed plastics wastes to obtain secondary materials with acceptable mechanical properties could be to blend them with virgin poly- mers or, at least, with recycled homopolymers. In a previous paper, 2 processing and properties of blends of virgin low density polyethylene (LDPE) and mixed plastics waste (MPW), have been presented. The experimental results have shown that all the mechanical properties, with an exception of elongation at break, are very similar to those of the virgin material if the MPW content does not exceed 50%. F.P. La Mantia, C. Perrone and E. Bellio 83 Considering these first experimental results, we have investigated the possi- bility to use the mixed plastics waste as “filler” for three types of polymeric ma- trices, namely, low density polyethylene, high density polyethylene (HDPE), and recycled polyethylene (RPE). Such approach may offer two important advantages: • improvement of utilization of huge amounts of a mixed plastics waste which are generated by municipalities and industries • savings in non-renewable raw materials and energy, both associated with the manufacturing of the fraction of the virgin materials that can be re- placed by plastics waste. Even if the percentage of plastics waste used as a filler cannot be high, its com- mon usemay absorb sizable amounts ofwastes. As an example, inItaly, a blend- ing of 10% of mixed plastics waste with non-food thermoplastics, excluding those for film manufacturing, could utilize 172,000 t/years, that is about 75% of all the plastic bottles manufactured every year in our country. It should be thus possible to fully satisfy the recycling objectives of the Italian law that requires a 40% recycling in 1992. Aim of this work isto investigate theprocessing conditions andthe mechanical properties of blends made usingdifferent homopolymeric matrices and different amounts of heterogeneous plastics waste. EXPERIMENTAL The characteristics of materials used as a matrix in this work are reported in Table 1. The recycled polyethylene (RPE) was obtained from films for agricul- tural use and is, therefore, mostly composed of a low density polyethylene. The average composition of the mixed plastics waste was: PEs 33% (mainly HDPE from blow molded detergent bottles) PVC 39% (plain mineral water bottles) PET 28% (soft drink and carbonated mineral water bottles). Such composition is representative of the average composition of the plastic fraction obtained by separatecollectionof bottles, as required by theItalianlaw. The plastics waste was reduced to small flakes by a rotating knives mill. Polyethylenes and MPW were mixed by hand and fed to a laboratory sin- gle-screw extruder (D = 19 mm, and L/D = 25) fitted with a venting port. For all the extrusion runs, thedietemperature was 270 o C, and the screwspeed60 rpm. 84 Blends of Polyethylenes and Plastics Waste The extruded material was cooled in a water bath, granulated and extruded again in order to reach a good homogenization. The unblended polymers were also treated in the same way. Three compositions were investigated for each blend, namely, 10, 25, and 50% MPW. Blends with a higher content of plastics waste were prepared only with LDPE. Blends of the same composition were also prepared by adding 10 and 20% of calcium carbonate. Small amounts of com- mercial antioxidants and lubricants were added to each blend. The samples for the stress-strain tests were prepared by compression molding of the granules of the extruded materials in a Carver laboratory press. The bars for the impact tests were obtained by the injection molding in a labo- ratory molder (Mini Max molder CS 183, Custom Scientific, USA). In both cases the temperature was 270 o C. Stress-strain curves were obtained with an Instron model 1122. Impact tests were carried out in Izod mode, using a CEAST Fractoscope. The results were averages of, at least, seven measurements. RESULTS AND DISCUSSION Processing When mixedplastics waste is processed, oneof the main problems isto find the best compromise between homogenization and degradation. In the waste mate- rial, there are polymers with different melting points and different thermal sta- bility. Especially, PVC and PET are very difficult to process together, because the melting point of PETis over 250 o C, and at this temperaturePVC is easilyde- composed forming HCl and chary residues. Therefore, the optimal processing F.P. La Mantia, C. Perrone and E. Bellio 85 Table 1 Polyethylene used in blends Sample Supplier Commercial name MFI Density (g/cm 3 ) LDPE Enichem Polimeri ZF 2200 0.30* 0.922 HDPE Enichem Polimeri AF 5015 0.24** 0.953 RPE - - - - *ASTM D-1238 cond B **ASTM D-1238 cond E conditions must ensure a good dispersion of the materials with high melting point in a continuous phase of molten polymers, avoiding gas bubbles, low mo- lecular weight compounds, and crosslinked residues that are formed by thermal degradation. In the previous work, 2 it has been demonstrated that all mechanical properties reach a maximum or a plateau after two extrusions. As an example, Figure 1 gives the data on the elastic modulus and the impact strength of a blend with 75% of LDPE. The data indicate that a double extrusion gives the best balance between homogenization (which improves with a number of passages through the extruder), and the degradation which is increased by the severity of the thermomechanical treatment. Based on these results, two extrusion steps were used for the preparation of all samples. During processing, no significant evolution of HCl from the venting port of the extruder was found,onlyat the die lipssomeacid vapors were observed.Thisis a rather surprising fact,because the HCl evolutionfrom PVC isa very common oc- currence in the industrial operation of plastics recycling. One possible explana- tion could be the residence time in the screw, which is much longer for the industrial extruders than used in laboratory extruder. Additionally, it should also be considered that some antioxidants and lubricants were added. 86 Blends of Polyethylenes and Plastics Waste Figure 1. The modulus and impact strength of LDPE/MPW blend (MPW = 25%) vs. the number of extrusions. The stability of PVC, under the processing conditions of experiment, was con- firmed by X-ray analysis with an energy-dispersive Philips apparatus. Signifi- cant amounts of chlorine are present in all extruded blends. The only processing difficulty, found during extrusion, was due to the presence of non-polymeric ma- terials (paper, aluminum, etc.) in the MPW which required frequent changes of filter at the end of the screw. Mechanical Properties The mechanical properties of all the investigated materials are reported in Figures 2-5 as a function of the mixed plastics waste concentration. The experimental results are reported in dimensionless form, i.e., the value relative to each blend is divided by the corresponding value of the unblended matrix. These latter values are reported in Table 2 for three matrices. As ex- pected, all the mechanical properties, except for the elastic modulus, decay on increasing the MPW content. The extent of this deterioration, however, is strongly dependent on the investigated property and on the nature of the ma- trix. F.P. La Mantia, C. Perrone and E. Bellio 87 Figure 2. Dimesionless modulus vs MPW content. [...]... polymers For this reason (a significant reduction of the cost of these recycled materials) , PE/MPW blends with different amounts (10 and 20%) were prepared and characterized The mechanical properties of the blends with 50% of MPW are reported in Figures 8-11 as a function of the calcium carbonate content The blends with 10 and 25% of MPW and with the same amounts of CaCO3 were also prepared and tested The... decrease of the impact strength also at the low MPW concentrations These latter results are difficult to explain on the basis of the nature of the components of these blends Only a better adhesion between the LDPE continuous matrix and the different phases of the MPW can be considered This fact is, however, quite unexpected considering that the PE phase in the plastics waste is mostly HDPE 92 Blends of. .. Polyethylenes and Plastics Waste Figure 8 Modulus of blends containing 50% MPW vs CaCO3 content Figure 9 Tensile strength of blends containing 50% MPW vs CaCO3 content F.P La Mantia, C Perrone and E Bellio Figure 10 Elongation at break of blends containing 50% MPW vs CaCO3 content Figure 11 Impact strength of blends containing 50% MPW vs CaCO3 content 93 94 Blends of Polyethylenes and Plastics Waste... micrograph of LDPE/MPW blend (MPW = 75%) multiphase morphology of these materials and the poor adhesion among the different components The lack of adhesion gives rise to microdefects in the structure of these material inducing a significant fragility The blends containing HDPE have also poor properties Impact strength (Figure 5) is also significantly influenced by the presence of a heterophasic dispersed plastics... content 93 94 Blends of Polyethylenes and Plastics Waste Table 3 Mechanical properties of blends with CaCO3 CaCO3 = 10% MPW = 10% CaCO3 = 20% LDPE RPE HDPE LDPE RPE HDPE E (MPa) 270 260 62 0 280 300 62 0 TS (MPa) 9 10 22 9 9.5 20 EB (%) 150 110 50 25 20 20 IS (J/m) 500 480 200 300 290 70 E (MPa) 370 340 64 0 400 400 64 0 TS (MPa) 8.5 10 21 8 8.5 19 EB (%) 50 25 15 7 5 5 IS (J/m) 400 300 100 140 140 40 MPW...88 Blends of Polyethylenes and Plastics Waste Figure 3 Dimensionless tensile strength vs MPW content Figure 4 Dimensionless elongation at break vs MPW content F.P La Mantia, C Perrone and E Bellio 89 Table 2 Mechanical properties of the three matrices Sample E TS EB IS (MPa) (MPa) (%) (J/m) LDPE 180 9 .6 450 470 HDPE 580 23.2 66 0 750 RPE 500 10.1 350 450 Figure 5 Dimensionless... proximity of elongation at yield of the matrix when the stress reaches a plateau, extending almost up to the break point It is probably due to this reason that the tensile strength slightly depends on the MPW content The elongation at break (Figure 4) is low for all blends due to the incompatibility between the various phases formed in the blends In Figure 7, the SEM micrograph of a sample of a blend of LDPE... plastics waste content Moreover, the improvement is larger for the blends containing LDPE and recycled polyethylene as a matrix This behavior can be attributed to the high modulus of the polymers forming the MPW mixture The remarkable increase of the modulus found for blends containing LDPE and RPE can be explained by considering their relatively low moduli compared 90 Blends of Polyethylenes and Plastics... Waste Figure 6 Stress-strain curves for LDPE and its blends with 10 and 50% MPW with polymers of the MPW phase which have considerably higher moduli) On the contrary this improvement is less pronounced for the blends containing HDPE as a matrix, because of its higher elastic modulus, similar to that of the PE component in the MPW phase 2 As demonstrated in the previous work, the values of the modulus... expected on the basis of an additive rule It is due to the incompatibility among the different polymeric phases present in the blends Tensile strength (Figure 3) is only slightly influenced (especially for LDPE and RPE) by adding mixed plastics waste but an elongation at break decreases rapidly even at low MPW content (Figure 4) The stress-strain curves of some blends are reported in Figure 6 The blends with . remarkable that in the 19 86- 1988 period, 43 % of ROI was achieved. CONCLUSIONS The main conclusion of this paper is a real and practical possibility of recycling of thermoplastic materials using an. impact strength value. The failuremodeof the wastes is similar tothatof the matrix. 80 Management of Plastic Wastes Figure 21. Results of the ROI for economic study of viability of the utilities in figures. Management of Plastic Wastes Figure 18. SEM micrographs of wastes showing their brittle fracture. O. Laguna Castellanos et al. 79 Figure 19. Mass balance of the recycling plant designed for treatment of