Recycling of Plastic Materials Part 7 ppsx

PE content for blends having varying content of LDPE and CaCO 3 .Figure 13.. PE content for blends having varying content of LDPE and CaCO 3... PE content for blends having varying conte

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% CaCO3 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% CaCO3to HDPE blends

Blends containing LDPE

On the basis of the above results, blends made from LDPE with larger 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 con-tent The total amount of polyethylene was evaluated considering the polyethyl-ene in the plastics waste (about 33%)

The modulus increases with the MPW and is only slightly influenced by the CaCO3content As already discussed, the tensile strength does not significantly change with decreasing the PE and CaCO3content The elongation at break rap-idly decreases even at a low content of plastics waste (for PE content lower than 70% the influence of CaCO3is negligible) At high PE contents, CaCO3seems 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% CaCO3) 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 CaCO3addition

The impact strength, on the contrary, strongly depends on the presence of CaCO3 With increasing the CaCO3concentration, the amount of MPW at which the impact strength declines decreases Whereas at CaCO3 = 0%, impact strength diminishes at a PE content lower than 40%, at a concentration of CaCO3= 20%, impact strength is considerably reduced at a PE content lower than 70%

• Blends of polyethylene with mixed plastics waste, up to 50-75%, can be ex-truded without significant difficulties and accelerated degradation of the PVC component

• The mechanical properties depend on the structure of the polyethylene ma-trix, 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; how-ever, 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 addition of CaCO3, up to 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 ex-tremely 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 use of plastic materials re-claimed in the most economical way

Hence the enactment 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 manu-factured articles, such as foil, containers, bottles, are collected together

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 for-eign 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 ma-chine 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 sepa-ration of plastic items A brief paragraph on a typical recycling plant of homoge-neous 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 bod-ies 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 recy-cling 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 The latter consists of separation of the mix of collected plastics into homo-geneous fractions, subjected to a recycling process which brings their character-istics 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 con-cerned 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 vari-ous plant operations determinant for the final cost of the material The differ-ence 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-qual-ity product If this is true for every type of plastics, it is the more so for the PET, which, if it is not recycled to the utmost level of quality, has virtually no market 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 re-cycling process It is therefore necessary to eliminate in advance metals and for-eign bodies and sort out plastics presenting such physical affinity with the type

of plastic to be recycled as to make it impossible to separate them by the methods 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 pro-cesses 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 so if the cost of labor is considered.To the advantage of manual selection is the fact that

not reach On the other hand, manual selection is comprehensibly always liable

to human error For this reason, in Italy, selection platforms, which are being in-stalled, are equipped with detectors to check the quality of 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

for example films, are separated from the plastic material to be recycled The method of separation is by air blowing

means of air which shifts the material selectively, so that heavy particles are separated

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

MOLECULAR SEPARATION

This type of selection is still in the 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 more detailed informa-tion is currently available

MICROSEPARATION

Microseparation is a method by which a suspension medium is used to sepa-rate plastics with density higher or lower than the suspension medium For ex-ample, 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

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 nor-mally 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 sepa-rate 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 Beckman2 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 ob-tain opposite charges The particles, which are allowed to fall in electromagnetic 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 Saltz3and Carpco4let 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 com-pared to PET Such grinding produces PVC particles of smaller size than those

of PET Consequently PVC can be separated by screening with a satisfactory de-gree 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 detec-tors 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 introduc-tion 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