Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carbohydrate or derivative as a reactant
Reexamination Certificate
1997-09-17
2003-02-25
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carbohydrate or derivative as a reactant
C521S046500, C524S433000, C524S400000, C524S128000, C524S349000, C524S348000, C524S315000
Reexamination Certificate
active
06525158
ABSTRACT:
The invention relates to a process for the stabilization of recycled plastic mixtures, as predominantly produced in the household, in commerce and also 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 is already carried out 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 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.
These used plastics, which may constitute useful raw materials, can be obtained either as a single material or as a mixture.
The recycling of plastic waste 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 mixtures, for example a polyolefin mixture.
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 generally only be used for purposes where relatively low strength requirements are made, for example as fillers or where thick-walled parts 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 recyclates, in some cases due to migration, extraction or by degradation. In addition, a recycled plastic generally differs structurally and also chemically from a new plastic as a consequence of the prior use or due to storage and processing; for example, sites of attack for oxidative degradation may already have formed. A recycled plastic therefore requires, for example, a relatively large amount of stabilizers or alternatively stabilizers which take into account these particular circumstances. The difficulty of finding suitable stabilizers is due to the specific type of previous damage/impurities, which may have taken place over an extended period.
Stabilization of a plastic mixture is also a difficult task, since each type of polymer makes specific requirements of the stabilizers. Thus, for example, completely different stabilizers are used for vinyl chloride polymers than for polyolefins or styrene polymers.
It would therefore be necessary to add a mixture of various stabilizers in order to stabilize a plastic mixture. In the case of complex plastic mixtures, this is a complicated method. In addition, various stabilizers can have adverse effects on one another or a stabilizer for one component can be damaging for the other component.
This problem has also been studied in the abovementioned literature and in Europ. Polym. J. 18 (1982), 1007, and the authors come to the conclusion that certain nickel complexes, in particular nickel dialkyldithiocarbamates, effect the best stabilization both against thermooxidative and against photooxidative degradation of polyethylene/polystyrene and polyethylene/polypropylene blends which have been homogenized by means of a compatibilizer. There is no mention therein of the stabilization of recyclates also containing PVC or of complex recyclate mixtures.
From U.S. Pat. No. 4,443,572, JP-A-57-202,346, JP-A-01/020,249 and FR-A-2 528 056 it is known to use a mixture including a phenol, a pentaerythritol diphosphite and a selected inorganic compound in certain virgin plastics.
It has now been found that mixed recycled plastics can be stabilized in a simple and economical manner against thermooxidative degradation during processing and subsequent use by means of a mixture of stabilizers known per se.
The invention relates to a process for the stabilization of mixtures of recycled plastics, predominantly thermoplastics, obtained from domestic, commercial and industrial waste or from useful material collections, which comprises adding from 0.01 to 15% by weight of a mixture of a) at least one sterically hindered phenol, b) at least one organic phosphite or phosphonite and c) at least one inorganic compound from the series consisting of metal oxides, hydroxides and carbonates to these plastics.
The a:b weight ratio is preferably from 20:1 to 1:20, particularly preferably from 10:1 to 1:1:10, very particularly preferably from 4:1 to 1:4. The (a+b):c weight ratio is preferably from 10:1 to 1:20, particularly preferably from 5:1 to 1:10, very particularly preferably from 3:1 to 1:3.
The plastic mixtures to be stabilized are, for example, used plastics from households and commerce (for example supermarkets), which predominantly originate from packaging materials. These can be, for example, films, bags, bottles and other containers or foams. Other materials may also be present. However, it is also possible for mixtures of plastics which have been previously damaged by use, storage or processing to be stabilized. These materials originate, for example, from useful material collections or return obligations, for example from the automobile industry, electrical/electronic industry, construction, agriculture and the textile industry.
The invention therefore relates to the stabilization of recycled plastic mixtures of this type which comprise 25-100% by weight, in particular 35-99% by weight, of polyolefins, 0-25% by weight of polystyrene, 0-25% by weight of polyvinyl chloride and 0-25% by weight of other thermoplastics, it also being possible for mixtures to be present within these groups of thermoplastics. Non-thermoplastics may also be present in the mixture in small amounts.
In particular, the invention relates to the stabilization of recyc
Herbst Heinz
Hoffmann Kurt
Pfaendner Rudolf
Sander Hans-Jürgen
Sitek Franciszek
Ciba Specialty Chemicals Corporation
Crichton David R.
Hall Luther A. R.
Szekely Peter
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