Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2000-08-30
2002-04-16
Medley, Margaret (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S046500, C521S047000, C524S502000, C524S515000
Reexamination Certificate
active
06372807
ABSTRACT:
The invention relates to a process for the conversion of mixed plastic waste to a homogeneous product which can be utilized in industry.
It is known that from end-products manufactured in large amounts, only a small proportion of plastics are recycled after use. The regeneration comprises mainly such plastic articles (e.g. bottles, cans etc.), which are easily recognized and thus easily separated from the waste to either re-utilize directly or to process them in the form of a re-granulated material after washing.
The re-utilization of mixed plastic waste is for the most part an unsolved problem. The main reason is that four or five types of plastics in general use that are prevalent in the waste that is selectively collected by the population, are available in many forms. Consequently they cannot be separated from the waste by a simple method and hence the appearance of the products is very diverse according to their type even before utilization and this becomes more complicated after wear.
The regeneration of simple packaging materials widely used in the trade is a relatively well-solved task. However, it is costly and an improvement in quality would be difficult to solve under market conditions.
Another problem seen during regeneration and re-utilization of plastic articles (products) is the result of aging during the period of their wear. Their physical-chemical state changes because of mechanical, thermal or other stresses and therefore, in comparison to the original ones, their color, mechanical and chemical properties are significantly changed depending on the amount of degradation.
An essential problem of the regeneration comprises that first during the wear and later during the waste processing, the plastics become contaminated by other materials (foreign materials) which are either incorporated into the waste or they remain adhered to the waste surface. The spectrum of these contaminants is extremely broad and extends from the remains of foods to oily and chemical residues, powder, metal residues etc., i.e. it is of organic or inorganic nature.
The main bulk of plastics alone or together with other waste is disposed or burnt.
A relatively simple manner of utilizing mixed plastic waste consists of granulating it after cleaning, and without a separation step, shaping it by melting together using known plastic processing techniques. In some fields the processed products are employed for the substitution of wood (fences, benches and the like), however, they can only be produced with a strong color and can be sold only within a limited scope. The quality of the regenerated product significantly depends on the composition of the raw material and therefore, the utilization of mixtures with a defined composition is not possible. Considering the heterogeneous state of such raw materials, the mechanical properties of the products cannot be foreseen or standardized. Thus, the production of “artificial wood” is only marginally important, and it cannot be considered to possibly play a large role in the utilization of plastic wastes.
DOS 2 311 797 describes a process for preparing solid articles, coatings, etc. based on heat resistant filling material and thermoplastic bounding material, which process comprises heating the heat resistant filling material to have a suitable particle size, at a temperature lower than the decomposition temperature of the thermoplasts, mechanically mixing additional thermoplasts with the heated filling materials, and if desired, a plasticizer is added, and finally shaping the mass in a hot state. This process relates to the production of second generation plastic articles which are suitable only for limited purposes.
In addition to the above difficulties, the re-granulation of plastic wastes without separation or moulding of final products directly from the melt is also problematic as it is known that the major part of the plastics do not constitute a compatible homogeneous mixture even in the molten state, and subsequently, the mechanical properties of the manufactured products are randomly formed. In order to solve this problem, EP 0 578 500 describes that high density polyethylene particles are suspended in a low density polyethylene matrix which are then moulded into plates. In spite of the considerable differences in apparent densities, the addition of mineral oil to the composite product prepared by moulding and other treatment does not become decomposed. This method is suitable only for processing of a mixture of two sorts of polyethylene and both the moulding as well as cooling should be carried out with the highest care for maintaining the cohesion.
It is desired to eliminate the heterogeneous state of the mixed plastic wastes containing similar plastic sorts mainly by a specific type of mechanical processing thereby making the product useful. For example, according to patent U.S. Pat. No. 5,468,431, the mingled mixture is divided into two parts in such a way that each part is homogeneous; then the specific surface of one material group is increased and then incorporated into the other material group used as a medium. The composite prepared in this way is quasi-homogeneous. However, this method is very sensitive towards the composition of the raw material and contaminants, and as such, it cannot be used without a previous selection step or pretreatment of the virgin material. Due to this circumstance the process is uneconomical.
U.S. Pat. No. 5,030,662 tried to solve the problem of the heterogeneous state of the mixture by means of reactive additives, however, the quality of products becomes much poorer than that of the virgin material. Hungarian patent HU 204,461, attempted to solve this problem by combining two steps. During the first operation, the mixed plastic waste is activated by a shear force of 500 to 5000 N within the range of softening temperature. The reactive sites formed at the molecular ends (broken by the decomposition) are polymerized by using a Ziegler type catalyst. The disadvantage of this process consists in that the organoaluminum compound is pyrophoric thereby making the process expensive. In addition, the catalyst is decomposed and made ineffective by contaminants, mainly through moisture of the mixed wastes.
A number of other known techniques for processing of plastics are disclosed in the introductory part of the Hungarian patent HU 204,461. The regeneration of mixed plastic waste for the original purpose is expensive and is substantially unsolved without a separation step of high selectivity.
A different way of utilizing mixed plastic wastes is to further modify a product of the mineral oil industry, i.e., prepare a raw material for the chemical industry or power industry from the raw material originally desired for the preparation of mineral oil. According to DE 4,311,034 a liquid fuel or basic material of the chemical industry is prepared from the plastic waste. The main point of this process is that depolymerization products in the gas and liquid phase are prepared in oil as a reaction medium and these products are processed separately. The coke-tar like residue is further utilized by partial hydrogenation. In this process, it is necessary to use a temperature between 250° C. and 450° C. and at a suitable pressure for a reaction time of 0.55 hour. It is evident that, although by means of a process used in the mineral oil processing, a product can be prepared which can be used more easily and generally than the secondary plastic product of low quality described above, however, when adapted to a waste having a broad range of different compositions, neither the composition nor the quantitative ratio of the product fractions become stable. The efficacy of this complicated process is poor, since the amount of products are an order lower than the power and investment costs of the process. Another difficulty is that the ratio of mineral oil used as the reaction medium to the waste is approximately 1:1 and therefore, a very significant quantity of oil should be maintained.
The process according to DE 3,037,829 has a simi
Medley Margaret
TVK Ecocenter KFT.
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