Process for reprocessing plastic wastes

Details Process for reprocessing plastic wastes Process for reprocessing plastic wastes

1994-07-18

1995-12-05

Michl, Paul R.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

523326, 521 40, 521 405, 521 45, 525383, 525388, 525938, 526940, C08J 1106, C08J 1114, B29B 1700

Patent

active

054729971

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a process for reprocessing plastic wastes.


BACKGROUND OF THE INVENTION

Mixed-grade plastics from communal and/or industrial wastes cause considerable difficulties as regards possible reclamation because of the mixture of grades, on the one hand, and, on the other hand, because of the necessity of washing to remove impurities, especially since, even after washing, residues of impurities such as sand, foil fragments not made of plastic, wood pieces and the like, together with a corresponding residual moisture content are present.
Although it is known to compression mould flower pots, fence posts and the like from such plastic wastes under the effect of heat, these products are relatively inferior in quality, on the one hand, and, on the other hand, this does not result in an important product, but essentially only waste disposal, which otherwise does not lead to the processing of large amounts of wastes.
Nor are any of the pelletizing processes which are conventional in the plastics industry and used for pure-grade plastics suitable to allow large amounts of such plastic wastes, or even pure-grade plastic wastes, to be processed to form intermediate products which can be used forever. For example, a production of coarse-grained intermediate products, for example by means of a heated extruder, would be, because of the low power attainable, firstly uneconomical and secondly unsuitable with respect to the amounts produced. Difficulties are caused here by, inter alia, the poor thermal conductivity of the plastic wastes which impair the heating and cooling.


SUMMARY OF THE INVENTION

The object of the invention is to provide a process of the type mentioned at the outset which makes it possible to process plastic wastes economically in large amounts to form a product suitable for further use.
This object is achieved in that the plastic wastes filled into the vessel are autoclaved as coherent, porous bundles with a high water-absorption capacity in a steam atmosphere at approximately 150.degree. to 220.degree. C., preferably 165.degree. to 190.degree. C., and by this means melted, at the end of the autoclaving process, the resulting bodies of molten plastic are at least partly dried by re-evaporating the water content therein and are cooled.
This process is suitable in particular for mixed-grade plastics, such as occur especially in communal wastes, but also for pure-grade plastics. In addition, apart from meltable thermoplastics, thermosets, which do not melt but only decompose at a correspondingly high temperature, are tolerated in an amount up to less than approximately 50% by weight.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the sub-sieve fraction, as a %, plotted as a function of the test grain size.


DETAILED DESCRIPTION

A washing system for cleaning the plastic wastes is usually present and it is expedient to use the plastic wastes further in the moist state, in particular with a moisture content of up to approximately 30% by weight, excess moisture having only been removed by vibrating or the like, since this moisture has a positive effect on the heat transport into the interior of the bundle during autoclaving. Material of this kind generally has a bulk density of the order of magnitude of 200 kg/m.sup.3.
Since the plastic wastes from communal and/or industrial wastes are generally very inhomogeneous and, in the shredded state contain inter alia fibres, film scraps and lumpy particles, the plastic wastes are preferably first precomminuted. This may be carried out by means of cutting mills or the like and in particular with the aim of pregrinding the plastic wastes to form essentially particles which mat together, for example scraps or fibrous material with a greatest possible ratio of length to width and thickness.
The plastic wastes may be pressed and/or adhesively bonded to form coherent bundles, the pregrinding being intended to facilitate in particular the pressing.
The pressing may be carried out on refuse pressers or straw

REFERENCES:
patent: 23805 (1859-04-01), Baschnagel et al.
patent: 25160 (1859-08-01), Hall et al.
patent: 2873474 (1975-03-01), Ficker
patent: 3098046 (1983-07-01), Siggel et al.
patent: 5200432 (1993-04-01), Bopp et al.

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