NL8002149A - Recovering synthetic material from domestic waste - by addn. of heat stabiliser and melt filtration - Google Patents

Abstract

Synthetic material is recovered from synthetic waste sepd. from domestic waste material, by adding a heat stabiliser, opt. after removal of impurities, and filtering the material as a melt. Impurities include sand, metal and pieces of crockery. The synthetic is mainly (80-95 wt.%) low density polyethylene, with small amts. of high density polyethylene and/or polypropylene and possibly traces of polyamides. Phenolic stabiliser is pref. 2,6-di-tert.butyl-4-methylphenol (I). Stabilisers contg. S or P can also be used. The amt. is pref. not less than 0.01 (0.02-1) wt.%. Used esp. for processing of filtered material to a blown film. The film is esp. used for domestic waste sacks. The filtration sieve can be used for a longer time without blockage.

Description

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Inventors: Leonard L.C. COOKING CHOICES in Amstenrade Gijsbert A. Larue in Schinnen 1 3178

METHOD FOR RECOVERING PLASTIC FROM PLASTIC WASTE REACTIONS SEPARATED

The invention relates to a method for recovering plastic from plastic waste fractions separated from household waste.

It is known to separate a plastic waste fraction when processing household waste. The separation of the plastic waste is particularly important if one wants to process the household waste into compost, since the plastic waste is not compostable. The plastic waste fraction usually exists for the most part, e.g. 80 to 95% by weight of low density polyethylene, and usually also contains smaller proportions, e.g. 1 to 15% by weight, high density polyethylene and / or polypropylene, and sometimes traces of polyamide.

Attempts have already been made to make use of the separated plastic waste fraction by melting it down and extruding it, e.g. to granulate. The recovered plastic could then be reused.

An important potential application of the extrudate is the manufacture of blown film. In the manufacture of blown film, but also in a number of other interesting potential applications of recovered plastic, it is already necessary to filter the plastic in the melt when using fresh, non-recovered plastic. This is all the more necessary with the use of recovered plastic, since otherwise usable products cannot be obtained. In practice, however, the sieve or the sieve packet to be used thereby proves to be particularly dirty, so that only a very short sieve packet service life of e.g. several hours is reached. Attempts to improve this by removing further injustices, such as sand, metal, shards of earthenware, etc., still go further than this. In addition, the mechanical properties of the recovered plastic leave much to be desired.

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The object of the invention is to provide a solution to this problem of an economically completely insufficient sieve packet service life.

According to the invention, a plastic waste fraction separated from household waste is worked up by adding a heat stabilizer to the plastic waste fraction, after removal of the impurities, if necessary, and then filtering the fraction in the melt.

After the melt filtration, the recovered plastic can be extruded and granulated, or otherwise further processed.

Due to the processing according to the invention, the sieve package is extended for a long time, so that the reprocessing of the plastic waste is economically justified. Apparently, the contamination of the sieve package is not determined by residues of injustices. Surprisingly, however, the measure according to the invention has an effect.

As a heat stabilizer, any known heat stabilizer for polyolefins can be used, e.g. the preferred phenolic stabilizers, e.g. especially suitable 2,6-di-t-butyl-4-methylphenol, but also stearylr2- (4-hydroxy-3,5-di-t-butylphenyl) propionate, pentaerythrityl-tetrakis-2- (3.5 -di-t-butyl-4-hydroxyphenol) propionate-20,1,1,3-tris- (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-tri-methyl -2,4,6-tris- (3,5-di-t.butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t.butyl-4-hydroxybenzyl) isocyanurate, or 1,1- bis- (2-methyl-4-hydroxy-5-t-butylphenyl) butane; sulfur-containing stabilizers, e.g. dilauryl thlodipropionate or thio-bis-4,4 '- (2-t-butyl-5-methylphenol); or phosphorus-containing stabilizers, e.g. tris (nonylphenyl) phosphite or pentaerythrityl distearyl bisphosphite.

The stabilizers are already active at a low concentration, e.g. 0.01 wt.% Or more. Preferably, the concentration is 0.02-1% by weight, based on the plastic waste. They can e.g. are added in the hopper of the extruder or during the shredding of the plastic waste before it is melted.

The mesh size of the screen used is e.g. 50-250 μπι.

The filtration of the molten plastic waste can suitably be through a screen built into an extruder upstream of the extrusion opening. After passage through the screen, the recovered plastic can then be extruded directly, e.g. in bar form for granulation, or as flat or tubular film.

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The plastic recovered by the method according to the invention can e.g. are well used for the manufacture of blown film, in particular for use in household refuse bags. The recovered plastic is of such a quality that the garbage bags meet the requirements with regard to the mechanical properties, such as toughness and tear strength.

If desired, the recovered plastic can be mixed with fresh plastic or with clean plastic waste from another source, e.g. from a plastic processing factory, and use this mixture as plastic material. The plastic to be added may in particular be low density polyethylene. The fresh plastic or the clean plastic waste can e.g. in an amount of 1-400 wt%, in particular 1-50 wt%, calculated with respect to the recovered plastic, are used.

The invention is further illustrated by the following non-limiting examples and comparative experiments.

Examples and Comparative Experiments

The particle size of a plastic waste fraction separated from household waste is reduced until the particles can pass through a sieve with a mesh width of 10 mm. The reduced plastic waste, after tumbling a heat stabilizer if applicable, is fed to the hopper of an extruder. The extruder is equipped with a sieve package with a mesh size of approx. 150 μη. The molten plastic waste is filtered through the sieve package at a melting temperature of 468-475 K, then extruded and the plastic is granulated, if necessary. The pressure rise across the screen pack is measured as a function of the screened amount of polymer melt. The measured values are expressed in bar pressure rise per kg throughput.

In Comparative Experiment A, the plastic waste is fed to the extruder without additives. The pressure rise is 7.5 bar 30 per kg throughput. The extrudate is granulated. The obtained granulate is used in Preference Experiment B as pre-filtered plastic waste.

In Comparative Experiment B, pre-filtered plastic waste is fed to the extruder without additives. The pressure rise 35 is 6.1 bar per kg throughput. Pre-filtration therefore has little effect to reduce the unwanted pressure rise.

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In Example I ult of plastic waste with a pressure rise of 8.2 bar per kg is continued. After pre-filtration, as described in Comparative Experiment A, 0.05 wt%, 2,6-di-t-butyl-4-methylphenol is added to the plastic waste granulate by tumbling and the resulting mixture is added to the extruder. . The pressure rise is 3.4 bar per kg throughput.

In Example II, plastic waste with a pressure rise of 8.7 bar per kg throughput is assumed. After pre-filtration, as described in Comparative Experiment A, 0.30 wt.% 2,6-di-t, butyl-4-methylphenol is added to the plastic waste granulate by tumbling and the resulting mixture is fed to the extruder, The pressure rise is 3.4 bar per kg throughput.

The results are summarized in the accompanying table. Herein is As. the difference in pressure rise between the blank test and the measurement, i.e. a measure of the effectiveness of the measures taken.

Table

Ex. / Cf. Exp. Δ s (bar / kg) remarks A 0 blank B 1.4 pre-filtration 20 I 4.8 addition 0.05 wt.% II 5.3 addition 0.30 wt.%

The pressure rise in the examples according to the invention is considerably smaller than in the blank. As a result, the service life of the sieve package is considerably longer.

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Claims (8)

2. Process according to claim 1, characterized in that a phenolic stabilizer is used. Process according to claim 2, characterized in that the stabilizer used is 2,6-di-t-butyl-4-methylphenol. 4. Process according to any one of claims 1-3, characterized in that 0.02-1% by weight of the heat stabilizer is added, calculated on the plastic waste. 5. Process according to any one of claims 1-4, characterized in that the filtration in the melt takes place by means of a screen which is built into an extruder and, after passage through the screen, the recovered plastic is extruded with this extruder. . 6. Method according to claim 5, characterized in that the plastic is processed into blown film. 7. A method according to any one of claims 1-6, characterized in that the mesh size of the screen used is 50-250 μηι. A method according to claim 1, as substantially described in the description and / or the examples. Recovered plastic obtained by using the method according to any one of claims 1-8. 8002149