Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1995-03-21
1997-07-01
Morgan, Kriellion S.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524343, 524399, 524400, 524151, 25240023, 25240024, 25240052, 25240053, 252403, C08K 509, C08K 5526
Patent
active
056439857
DESCRIPTION:
BRIEF SUMMARY
PROCESS FOR THE STABILIZATION OF AND STABILIZER MIXTURES FOR RECYCLED
PLASTICS
The invention relates to a process for the stabilization of recycled plastics, as predominantly produced in the household, in commerce or in industry and in useful material collections, and to the stabilizer mixtures which can be used for this purpose.
Recycling of waste is a problem of increasing importance for ecological reasons. The recycling of paper, textiles, glass or metals already takes place on a large scale, whether by separate collection or by sorting of the refuse. The recycling of plastic waste and used plastics is also an increasing aim. Thermoplastics are generally processed by re-melting.
However, the plastic waste produced in the household, in commerce or in industry or the plastic used for materials or used plastics obtained from collections or a return obligation, for example in specific sectors of industry, such as the automobile industry, electrical industry, agriculture or the packaging industry, predominantly comprises thermoplastics based on polyolefins, styrene polymers, polyvinyl chloride or polyethylene terephthalate.
Used plastics which are valuable raw materials can be obtained either as a single material or as a mixture. Single-material plastic waste can be produced directly in the production of plastic parts or obtained by separate collections.
On the other hand, the recycling of used plastics frequently means the use of a mixture of different types of plastic. Known industrial separation methods, for example hydrocyclone separation, mostly give only moderately clean fractions of various plastic mixes, for example a mixture of polyolefins.
The use of plastic mixtures is associated with technical problems, since individual types of plastic have only restricted miscibility with one another, or none at all. Although various types of thermoplastics can be processed by melting and moulding, the resultant mixtures (polyblends) of immiscible plastics are inhomogeneous when considered microscopically, i.e. on a microscopic level they Comprise different solid phases. This has a considerable adverse effect on the mechanical properties. Recyclates of this type can normally only be used for purposes where relatively low length requirements are made, for example as fillers or where thick-walled pans are used, for example noise protection dams.
Typical incompatible combinations which occur in domestic refuse are, for example, polyethylene and PVC or polyethylene and polystyrene or PET and polyolefins. In order to solve this problem, it has been proposed to add polymeric compatibilizers, also known as solid phase dispersants. Thus, for example, the addition of chlorinated polyethylene is capable of homogenizing mixtures of polyethylene and PVC. The addition of styrene-butadiene copolymers is capable of homogenizing mixtures of polyolefins and polystyrene. As a result of such a homogenization, the mechanical properties improve so much that these polyblends are also suitable for high-performance uses. A review of these developments is given by C. Sadrmohaghegh, G. Scott and E. Setudeh in Polym. Plast. Technol. Eng. 24 (1985), 149-185.
In an article which appeared in Polymer Eng. and Science, Vol. 17, pp. 700-705 (1977), the effect of small amounts of PVC and CPE on recycled polyethylene is studied, the authors observing that satisfactory stabilization of such recyclates is still not possible.
For the stabilization of recycled high-density polyethylene, P. Vink, R. T. Rotteveel and J. D. M. Wisse in Polymer Degr. and Stability, Issue 9, p. 133 (1984) studied various stabilizers from the classes of the phosphites, hindered phenols, benzotriazoles, hindered amines and phosphonites.
These authors also indicated that the recyclates must be re-stabilized. Although the plastics have mostly been treated originally with stabilizers against thermooxidative and in some cases also against photooxidative degradation, these stabilizers are lost during use of the plastics, during storage of the waste and during processing of the
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G. Scott, pp. 8/1-1 to 8/1-19, The Role Of Stabilizing Additives in Polymer Recycling (1993).
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Herbst Heinz
Hoffmann Kurt
Pfaendner Rudolf
Sander Hans-Jurgen
Sitek Franciszek
Ciba-Geigy Corporation
Kovaleski Michele A.
Morgan Kriellion S.
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