A method for recycling a mixture of engineering thermoplastics to obtain a tough thermoplastic material and a mixture of engineering materials.

Technical field

This invention refers to a method for recycling a mixture of engineering thermoplastics to obtain a tough thermoplastic material and a mixture of engineering materials.

Background of the invention

At the present time, engineering thermoplastics generated from production waste, e.g. car rear lights and other products which have reached the end of their service life, such as rear lights from scrapped cars, is commonly disposed of in landfills or is incinerated. However, these disposal processes are uneconomical and unfriendly to the environment, and they waste the material and energetic content of the disposed polymers. The most effective way to use the material and energetic input in the production of a virgin polymer is to recycle the material. Material recycling involves supplying mechanical energy and additives, i.e. stabilizers, colorants, fillers, etc., to upgrade the waste material to a new material with mechanical and esthetical properties which will be close to those of the virgin material .

Recycling of production waste plastics is mainly limited to well-separated mono-material wastes from the production of plastic components. The main restriction on broader utilization of recycling procedures for waste plastics is the fact that the waste components tend to be composed of several plastics that

are hard to dismantle. The individual parts are usually produced from PC - polycarbonate, ABS - acrylonitrile-butadiene-styrene, PMMA - poly (methyl methacrylate) , TPE - thermoplastic elastomer or blends of PC/ABS, ABS/PMMA, PC/PMMA, etc. Separating the mono- material waste demands high investment in machinery, and the operating costs are high in relation to relatively low productivity. Another problem with the separating procedures is their low efficiency: in practice, not more than 95% purity of the separated fraction is achieved.

The above-mentioned problems of separating mono-material plastic wastes are solved when the plastic waste is recycled as a multi-material mixture. Recycling a mixture of polycarbonate with polymers on the basis of styrene and with the addition of elastomer was studied, for example, in invention JP 2004352762. Recycling a ternary mixture is addressed in invention US 5,232,986, which focuses on a mixture of PMMA/ABS/PC with a major component of PMMA. Extrusion of thermoplastic mixtures in a closed loop recycling system, especially mixtures of PC/PMMA, with the addition of a compatibilizator on the basis of MBS - methylmethacrylate-butadiene-styrene or terpolymer consisting of butadiene - is described in invention US 5,569,713. Recycling quaternary mixtures of PET/ABS/PC/SBS or PET/ABS/PC/SEBS, where PET is a major component, is discussed in invention US 2004209985.

In the case of a multi-material engineering thermoplastics mixture, a primary condition for the economic practicability of the recycling process is that the recyclate should have a high level of final utilizable properties. When the material properties of mixtures of PC, ABS, PMMA and TPE were investigated, it was surprisingly found that these mixtures of a certain composition exhibit essentially higher toughness than their individual components. Furthermore, it was proved that

increased thermo-mechanical loading of these mixtures during melt processing, e.g. regranulation, leads to undesirable deterioration of the mechanical properties of the final product. These considerations are fundamental to the method for recycling a mixture of PC, ABS, PMMA and TPE according to the invention.

Summary of the invention

The above-mentioned deficiencies are eliminated to a large extent in the method according to this invention for recycling a mixture of engineering thermoplastics to obtain a tough thermoplastic material. The subject matter of the invention is that the input material is disintegrated to a size of 1 mm to 10 mm. Then, a mixture is created containing 40 to 80 weight percent of polycarbonate, 10 to 50 weight percent of terpolymer acrylonitrile-butadiene-styrene, a maximum of 10 weight percent of poly (methyl methacrylate) and a maximum of 10 weight percent of thermoplastic elastomer on the basis of styrene- ethylene/butylene-styrene block copolymer or styrene-butadiene- styrene block copolymer. In the last step, the mixture is processed into the final product .

Advantageous implementation involves magnetic and induction separation of metallic impurities from the disintegrated material .

The invention also refers to a mixture of engineering materials, which contains 40 to 80 weight percent of polycarbonate, 10 to 50 weight percent of terpolymer acrylonitrile-butadiene-styrene, a maximum of 10 weight percent of poly (methyl methacrylate) and a maximum of 10 weight percent of thermoplastic elastomer on the basis of styrene-

-A- ethylene/butylene-styrene block copolymer or styrene-butadiene- styrene block copolymer.

The input material can be technological scrap generated during plastics processing, especially the scrap generated during the production of car lighting components. The input material can also be end-of-life plastic products, especially car lighting components from scrapped cars.

Any of the components can be a virgin material .

The considerable advantage of this method for recycling a mixture of engineering thermoplastics according to the invention is that the toughness of the final recyclate is usually higher than the toughness of the virgin materials PC, ABS, PMMA, while a balanced complex of utilizable properties is retained.

Another advantage of the method for recycling a mixture of engineering thermoplastics according to the invention is that there is no regranulation of the grind, which guarantees low thermo-mechanical loading of the mixture melt and, as a consequence, retention of the physical properties of the thermoplastic mixture according to the invention, especially the toughness. In addition/ omitting the regranulation step saves power costs for processing the mixture.

The advantages of the method for recycling a mixture of engineering thermoplastics to obtain a tough thermoplastic material according to the invention are further clarified by the following examples.

Detailed description of the preferred embodiments

In the following invention implementation examples, materials were used (see Tab.l) which occur in the production of car rear light assemblies. The materials were mainly as follows:

Polycarbonate (Lexan LS2, GEPlastics) , acrylonitrile-butadiene- styrene (Cycolac X37, GEPlastics), poly(methyl methacrylate)

(Lucryl G88, BASF) and styrene-ethylene/butylene-styrene

(Bergaflex BFI K70A, Bergmann) .

The toughness of the mixtures was evaluated on the basis of fracture mechanics, mainly using the concept of the J-integral (Ji _d ) • The methodology, the preparation of the samples and the equipment for J-integral determination are described in the literature, e.g. W. Grellmann, S. Seidler: Deformation and Fracture Behaviour of Polymers. Springer Verlag, Berlin Heidelberg, 2001.

Example 1

A mixture was obtained by grinding scrap material of car rear lights. The mixture corresponds to the composition of A according to Tab.l.

Grinding was performed with the help of a PH TRIA 47-30/CN granulator with three rotating cutting knives . The average grind size was 5mm. The ground material was de-dusted using an Allgier dust separator, and the metal particles were detected using a Mesurtronic metal detector.

The ground mixture was dried for a minimum of 6 hours at a temperature of 105 ⁰ C in a hot-air drier.

The mixture was processed using a Battenfeld 500 injection molding machine with a screw diameter of 35 mm and a length-to- diameter ratio of 75. The melt was injected into a mold for the production of standard ISO 179 specimens. The injection molding unit temperature was set to 245°C, the screw speed reached 128 revolutions per minute, and the backpressure was set to 10 MPa. The mold temperature was 90 ⁰ C.

In comparison with virgin (original) materials 1, 2, 3 according to Tab.l, mixture A shows a higher value of toughness (see values of J-integral Ji _d ) •

Example 2

As in the case of example 1, except that the mixture corresponds to composition B according to Tab.l.

In comparison with virgin (original) materials 1, 2, 3 according to Tab.l, mixture B shows a higher value of toughness (see values of J-integral Jia) .

Example 3

As in the case of example 1, except that the mixture corresponds to composition C according to Tab.l.

In comparison with virgin (original) materials 1, 2, 3 according to Tab.l, mixture C shows a slightly higher value of toughness (see values of J-integral J _τd ) .

Example 4

As in the case of example 1, except that the mixture corresponds to composition D according to Tab.l.

In comparison with virgin (original) materials 1, 2, 3 according to Tab.l, mixture D shows a slightly higher value of toughness (see values of J-integral J _Id ) .

Table 1. Toughness of the investigated mixtures

Mixture 1 2 3 A B C D

PC [%] Too - ^~ 80 40 60 60

ABS [%] 100 10 50 20 20

PMMA [%] 100 10 10 10 10

SEBS [%] _ 1 100 _

SBS [%] 10 ~J^ [kJ/m ² ] 11.0 10.2 0~~8 14, 8 12, 6 11,6 11,5

Industrial applications

The method for recycling a mixture of engineering thermoplastics to obtain a tough thermoplastic material, and a mixture which is prepared in this way, will be applied in the disposal of waste engineering thermoplastics generated by the production, for example, of car rear lights, or products that have reached the end of their service life, for example, rear lights from scrapped cars.