Recycling of Plastic Materials Part 7 ppsx

F.P. La Mantia, C. Perrone and E. Bellio 95 Figure 12. Modulus vs. PE content for blends having varying content of LDPE and CaCO 3 . Figure 13. Tensile strength vs. PE content for blends having varying content of LDPE and CaCO 3 . 96 Blends of Polyethylenes and Plastics Waste Figure 14. Elongation at break vs. PE content for blends having varying content of LDPE and CaCO 3 . Figure 15. Impact strength vs. PE content for blends having varying content of LDPE and CaCO 3 . could be the same as the above proposed to interpret the small sensitivity of these properties to the MPW concentration. Elongation at break and impact strength of blends with LDPE and RPE decrease slightly only by adding 10% CaCO 3 . A 20% addition of calcium carbonate significantly decreases elongation and impact strength of blends. The elongation at break and impact strength drastically deteriorate on addition of 10% CaCO 3 to HDPE blends. Blends containing LDPE On thebasis ofthe aboveresults, blendsmade fromLDPE withlarger amounts of MPW were prepared. It is worth noticing that all blends previously character- ized were composed of polyethylene matrix (PE > 50%) with dispersed PET and PVC particles. Blends with larger amounts of MPW show a PE content lower than 50%. The mechanical properties of LDPE/MPW blends with and without calcium carbonate are reported in Figures 12-15 as a function of the polyethylene content. The total amount of polyethylene was evaluated considering the polyethylene in the plastics waste (about 33%). The modulus increases with the MPW and is only slightly influenced by the CaCO 3 content. As already discussed, the tensile strength does not significantly change with decreasing the PEand CaCO 3 content. The elongation at breakrap- idly decreases even at a low content of plastics waste (for PE content lower than 70% theinfluence ofCaCO 3 is negligible).At highPE contents,CaCO 3 seems im- proving the elongation at break. It is however worth noticing that the compari- son is not made for the same MPW content. The data for PE = 80% (graph for 20% CaCO 3 ) refers to a blend without plastics waste showing that the effect of the heterogeneous plastics waste is more deleterious for the elongation at break of the polyethylene than that of the CaCO 3 addition. The impact strength, on the contrary, strongly depends on the presence of CaCO 3 . With increasing the CaCO 3 concentration, the amount of MPW at which the impact strength declines decreases. Whereas at CaCO 3 = 0%, impact strength diminishes at a PE content lower than 40%, at a concentration of CaCO 3 = 20%, impact strength is considerably reduced at a PE content lower than 70%. F.P. La Mantia, C. Perrone and E. Bellio 97 CONCLUSIONS • Blends of polyethylene with mixed plastics waste, up to 50-75%, can be extruded without significant difficulties and accelerated degradation of the PVC component. • The mechanical properties depend on the structure of the polyethylene matrix, but, in general, are very similar to those of the matrix up to a MPW content of about 25-50%. • The elongation at break rapidly decreases even at low MPW content; however, in many applications this characteristic is not very important and the values recorded for blends under the study can be considered adequate. • Considering polyethylenes tested in these blends, LDPE and polyethylene recycled from greenhouse films gave the best results. • The additionof CaCO 3 , upto 10% content, does not significantly change the processability and the mechanical properties of blends but the cost of the blends is reduced because of replacing a corresponding amount of polyethylene. ACKNOWLEDGMENT This work was financially supported by MURST and Enichem Polimeri. REFERENCES 1. Plastic Waste: Resource Recovery and Recycling in Japan. Plastic Waste Management Institute, Tokyo, Japan 1985. 2. F. P. La Mantia, Polym. Deg. Stab., 37, 145 (1992). 98 Blends of Polyethylenes and Plastics Waste Techniques for Selection and Recycle of Post-Consumer Bottles E. Sereni Tecoplast and Govoni, 44047 Casumaro, Ferrara, Italy INTRODUCTION Techniques for selection and recycling of post-consumer plastics are closely re- lated to the characteristics of plastic containers consumption, which are extremely diversified according to the geographical areas and the relevant law regulations governing activities in this sector. In each area, socio-economic and legislative features as a whole determine the first stage of the recycling process, that is collection. This, in turn, influences the layout of the recycling plant which aims at the re-use of plastic materials re- claimed in the most economical way. Hence theenactment of laws which bind municipalities to recycle containers in general, as is the case in Germany, or in a more restrictive sense, in Italy, where recycle is limited to containers for liquids only. On the other hand, consumption features play a major role in the choice of the materials to be recycled. So, in the United States materials chiefly recycled are PET bottles and PE containers; in France, on the contrary, they began to recycle PVC on account of the large quantity of such material used in the packaging of drinks. In Australia recycling includes PET and PE, whereas in Japan PET alone. In Italy plastics recycled are PET, PVC and PE. In short, the material to be recycled and the enforced legislation are determi- nants for the choice of the collection system. In the United States, Australia, France, Austria and Switzerland, different fractions of post-consumer plastics are collected in the most homogeneous way possible. In other countries, on the contrary, plastics are collected more heteroge- neously, that is to say, different types of plastics out of different types of manufactured articles, such as foil, containers, bottles, are collected together. E. Sereni 99 At any rate, collection must necessarily be a “differentiated” one, although the degree of differentiation may vary extremely. In Italy, collection, according to Law 475, is differentiated as far as recycle of plastic containers is concerned, whereas it is non-differentiated with regards to type of plastics, since liquids containers may be made of either PVC, or PET, or PE, or else. The outcome of the collection system, therefore, constitutes the raw material for the recycling process. Consequently, as we are taught by experience in this field, the more selective the collection, the higher the degree of purity from foreign bodies in the final product. In Italy, for instance, collection of liquid containers by means of plastic boxes, shows 15% to 20% contamination resulting from foreign bodies. Collection of drink containers carried out with the AZURE-Bottle-eater - an automatic machine installed inside supermarkets presents pollutants solely composed of other types of containers, and not exceeding 1%. Aim of this paper is to present the more recent technologies of automatic separation of plastic items. A brief paragraph on a typical recycling plant of homogeneous plastics is also presented. GENERAL CONSIDERATIONS The collection always yields a polluted product, and this fact poses the need for the first operation of the recycling process, namely the cleaning of foreign bodies. The machinery required at this stage may be of either manual or automatic type. Manual cleaning is simpler from the installation standpoint, nevertheless it equally requires a number of operating steps. Normally, the first operation is carried out by a machine called de-baler. The collected material, indeed, for transport cost reasons, is reduced into bales. There exist very efficient de-balers and the best brands have been equipped with specific devices designed in accor- dance to the composition of the bales to be loosed. Such factors as the proportion of PVC, PET or PE in the bales, the collection features, the container typology, and the share of foil plastics, determine the type of de-baler construction technique. After the first step, the following operations are determined by the type of recycling process to which the material is to be subjected. Basically there are two main recycling processes: • recycle of heterogeneous plastics • recycle of selected polymers. 100 Techniques for Selection and Recycle of Bottles The former technique consists of the manufacture of extruded or injected prod- ucts, whose main component is either PE or PVC, whereas other plastics act as fillers. Thelatter consistsof separationof the mix of collected plastics into homogeneous fractions, subjected to a recycling process which brings their characteristics and purity as near as possible to those of original polymers. The two techniques are not contrasting, in fact they can be regarded as complementary to each other. The polymers recycling process is the technique an industry is the most concerned with. Attention is called to the fact that the utmost degree of purity of the finished product should be aimed at, because reclaiming process requires various plant operations determinant for the final cost of the material. The difference in outcome - namely a product similar to the original one or a polluted product - does not entail such a difference in installation and operating costs as there may be between the price of an optimum product and that of a lower-quality product. If this is true for every type of plastics, it is the more so for the PET, which, if it is not recycled tothe utmostlevel of quality, has virtually nomarket. The cleaning of foreign bodies to obtain recycled plastics as polymers is fol- lowed by the selection by fractions which can be carried out as well with manual or automatic techniques. Cleaning and selection operations, in general, have the purpose to obtain a selected material to be “refined” by processing it through a recycling plant. The process of cleaning and selection has therefore the function to remove, during this stage, all materials that cannot be selected during the recycling process. It is therefore necessary to eliminate in advance metals and foreign bodies and sort out plastics presenting such physical affinity with the type of plasticto be recycled as to make it impossible to separate themby themethods employed in the recycling process. Typical is the case of PET and PVC, which contaminate each other mutually and have very similar specific weights. As a consequence, they cannot be separated through such ordinary physical processes as water flotation and, therefore, must be separated prior to recycling. The simplest method to perform the cleaning and selection operation consists of a selection platform where a number of trained sorters separate the different types of plastics on the basis of visual assessment. This is a hard and unpleasant job. Therefore, planning of works station according to ergonometric criteria is paramount in order to attain manpower’s maximum efficiency, the more soif the cost of labor is considered.To the advantage of manual selection is the fact that E. Sereni 101 not reach. On the other hand, manual selection is comprehensibly always liable to human error. For this reason, inItaly, selection platforms, which are being installed, are equipped with detectors to checkthe qualityof the selected material. The detectors employed in Italy are the clue to the automatic selection. These are electronic appliances capable of recognizing PET in a flux of PVC and vice versa. The checking equipment is further completed by detectors able to identify traces of metal overlooked during manual sorting, such as aluminum from caps and rings. The material manually selected and then electronically checked is therefore of best quality and can be sold at the maximum market price. The most serious inconvenience with manual platforms lies in the high cost of labor and in the complexity that the management of a large number of workers poses when considerable quantities of material are to be selected. Such draw- backs may be avoided by resorting to automatic platforms. Automation is intro- duced at the stage of de-baling. In order to obtain a product suitable for the recycling process, operations to remove undesired impurities must be carried out. The machines required are manifold and the necessity to employ them is re- lated to the quality of the collected material. Essential machines are: • Rotary screen, by which parts of the desired dimension are sorted out, sepa- rating them from smaller and larger ones. • Light-parts separation equipment. In this machine lighter parts, such as for example films, are separated from the plastic material to be recycled. The method of separation is by air blowing. • Heavy-parts separation equipment. Also this operation is carried out by means of air which shifts the material selectively, so that heavy particles are separated. • Aluminum rejection equipment. It normally consists of an electromagnetic drum placed in suitable location on the train of operations. All such machines are preliminary to the stage of selection into homogeneous plastics fractions. 102 Techniques for Selection and Recycle of Bottles sorters operate to such a degree of intelligence as the automatic equipment can- • Molecular separation • Microseparation • Macroseparation. MOLECULAR SEPARATION This type of selection is still inthe stage of study and there is no evidence of any industrial plant in operation so far. The technique is based on the dissolution of the various plastics in selective solvents with reclaim of the dissolved sub- stances. The system appears to be very promising, but no moredetailed informa- tion is currently available. MICROSEPARATION Microseparation is a method by which a suspension medium is used to separate plastics with density higher or lower than the suspension medium. For example, water can be used as medium to separate PE from PVC or PET. In this case special tanks are used in which various types of plastic flakes are mixed with water and then given a sufficient time to position themselves in the most suitable way according to their density. Materials are subsequently ex- tracted separately from the top or bottom. This method is not suitable for sepa- rating PVC from PET. Researchers at the Rutgers University 1 studied a method of PVC microseparation from PET, by which PVC is subjected to a process of selective bulking which causes it to float. Such method may perhaps be applied in the fu- ture to separate small quantities of PVC from large quantities of PET, as normally is the case in United States. In Italy, for example, PVC is a major component of the containers mix and, therefore, it is necessary not only to separate PET, but also to recycle PVC for re-use. For this reason the above method does not appear suitable. There are known experiments on separation in super critical fluids. Beckman 2 reported separation of PVC and PET, using carbon dioxide and sulphur esofluoride. The conditions under which experiment was conducted are objec- tively difficult and, at present, an application of this method is not practical. The electrostatic separation is presently arising great expectations. By ex- ploiting the characteristics of the triboelectrical charge, two mixed polymers obtain opposite charges. The particles, which are allowed to fall in electromagnetic E. Sereni 103 Selection can be carried out by different methods which fall mainly into three groups: field, are attracted by to the opposed pole. The equipment recently shown by Kali and Saltz 3 and Carpco 4 let us reasonably predict encouraging results. How- ever, prior to the industrial introduction of the method described above, it will be necessary to make an accurate assessment of the final cost of treatment and to evaluate whether the conditions under which the system is efficient are those actually encountered in the treatment of post-consumer plastics. One should also mention some other studies and experiments conducted by various institutes regarding techniques applicable to PVC and PET containers, previously reduced to flakes, namely: flotation with surface active agents and separation by thermal treatment, which enables to retain PVC by its softening on a belt having a suitable temperature. Decontamination is already applied in practice, the most frequently by micronization which takes advantage of a higher brittleness of PVC as compared to PET. Such grinding produces PVC particles of smaller size than those of PET. Consequently PVC can be separated by screening with a satisfactory degree of efficiency. The method is employed in Micronil, France and Cabot in Bel- gium. Low-temperature micronization techniques, used in Australia by Cryogrind, do not appear useful in Europe because of a high energy cost in- volved. MACROSEPARATION Separation of plastic fractions when waste materials are still in initial form continues to appear the most conveniently applicable system, considering the increasing possibilities of automation it offers. It is of little interest as long as separation is manual, but it becomes worth discussing when conducted by an automatic separation process which includes various systems employing detectors currently available in the market. The first detector was developed by Tecoplast in Casumaro, Ferrara-Italy, to separate PVC from PET. The application of this system resulted in the introduction of an automatic plant processing drink plastic bottles using the AZZURRA machine. A peculiar composition of the collected material made it possible to fully automate the operations of selection, thus totally excluding manual han- dling of bottles. The Tecoplast’s detector consists of an X-ray source and a receiver which mea- sures the bottle absorption while passing between the source and receiver. PVC has a higher absorption compared to the other plastics due to the presence of a 104 Techniques for Selection and Recycle of Bottles [...]... Denmark INTRODUCTION Recycling of pure plastics is not difficult from a technical point of view However, the majority of municipal solid wastes consists, however, of plastics waste which is often contaminated with significant amounts of paper This is not only the case with the plastics fraction of municipal solid waste (PFMW), but also with such industrial waste as used packaging materials, laminates,... the plastics fraction of municipal solid waste (PFMW) and a number of different 2-4 industrial plastic waste materials contaminated with paper 112 Hydrolytic Treatment of Plastic Waste Containing Paper The aim of this study is to demonstrate that the CUT-method, consisting of a pre-hydrolytic treatment of the paper component, is an industrially applicable method of reprocessing paper-contaminated plastics... the level of impurities within the limits required Returning to the previous example: with a mix in the proportion of 90% of PET and 10% of PVC, two detectors with 99,5% 106 Techniques for Selection and Recycle of Bottles Figure 1 Automatic platform for plastics selection efficiency placed in series enable to obtain a level of impurities of 2,5 ppm, whereas with efficiency of 99% the value of residue... centrifugal machines, normally used for water separation The installation of the above machinery according to a specific sequence is part of a know-how of various manufacturers In conclusion, in view of complex problems posed by post-consumer plastics installations, we deem it necessary to suggest that the design of a plastic recycling plant be inspired by one major principle: it is not possible to... repetition of the same operation in more than one phase E Sereni 109 REFERENCES 1 2 3 4 5 6 H Frankel, Proceedings of Recycle 92, Davos (Suisse), April 7- 10, 1992 E Beckman, M S Super, and R M Enick, Proceedings of Recycle 92, Davos (Suisse), April 7- 10, 1992 U Kleine-Kleffmann, Proceedings of Recycle 92, Davos (Suisse), April 7- 10, 1992 R T Gottesman, Proceedings of Recycle 92, Davos (Suisse), April 7- 10,... Kenny and R S Bruner, Proceedings of Recycle 92, Davos (Suisse), April 7- 10, 1992 AIC, Baltimore, USA, Technical Bulletin C Klason, J Kubát, and H.R Skov 111 Hydrolytic Treatment of Plastics Waste Containing Paper C Klason, J Kubát,* and H R Skov** Polymer Center, University of Lund, Box 118, S-22100 Lund, Sweden *Department of Polymeric Materials, Chalmers University of Technology, S-41296 Gothenburg,... check (Figure 1) The notion of “error reduction” in the execution of an operation by a way of repetition of the same step is adopted also in the phases of pre-cleaning of the parts to be passed onto electronic selection In conclusion, we believe that the described system allows one to achieve the aim of selection purity using an automatic equipment, having a sufficient degree of reliability RECYCLE INSTALLATIONS... machines are very useful for removal of parts of labels which were freed by grounding The purpose of this operation is the removal of a part - important with regard to volume and weight in the dry phase Process allows to avoid problems of dissolution in water and relevant contamination An extremely interesting and certainly unique application of this method is the separation of PVC labels from PET bottle... refer to liquid containers in general, these, beside the body made out of plastic, consist of additional components which are to be regarded as foreign bodies to be removed Such elements are: • caps made of: PE, PE with PVC gaskets, aluminum • labels of tacky paper with different types of glue, composed of PE or PVC • base cups of PEAD • residues and dirt which may have been added during waste collection... is generally devoted to the techniques of electronic selection of homogeneous fractions, while disregarding the phase of regeneration of selected plastic flakes This minor interest would be justified if bottles were manufactured following criteria of perfect recyclability However, such criteria are not yet universally accepted and complied with; therefore the recycling plant designer must give an accurate . Denmark INTRODUCTION Recycling of pure plastics is not difficult from a technical point of view. How- ever, the majority of municipal solid wastes consists, however, of plastics waste which is often contaminated. exceeding 1%. Aim of this paper is to present the more recent technologies of automatic separation of plastic items. A brief paragraph on a typical recycling plant of homogeneous plastics is also. proportion of 90% of PET and 10% of PVC, two detectors with 99,5% E. Sereni 105 efficiency placed in series enable to obtain a level of impurities of 2,5 ppm, whereas with efficiency of 99% the value of

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