GB2253854A

GB2253854A - Recycling process for non-fibre-reinforced thermosetting plastics

Info

Publication number: GB2253854A
Application number: GB9206241A
Authority: GB
Inventors: Braun Ulrich; Sigrid Muehlhauser
Original assignee: Ruetgerswerke AG
Current assignee: Ruetgers Germany GmbH
Priority date: 1991-03-21
Filing date: 1992-03-23
Publication date: 1992-09-23
Anticipated expiration: 2012-03-23
Also published as: ITRM920183A1; ES2039190A1; ATA17192A; IT1258393B; DK10192A; BE1005057A3; AT402404B; GB2253854B; ES2039190B1; CH686352A5; FR2674175B1; FR2674175A1; PT100263A; GB9206241D0; ITRM920183A0; NL9200507A; PT100263B; DK10192D0

Abstract

A process for recycling waste thermoset plastics which are not fibre-reinforced comprises granulating the waste thermoset plastics material to a particle size of 0.2 mm or less, mixing the granulate with a phenol resin, a hardener, e.g. hexamethylene tetramine, and optionally, processing aids e.g. Me stearates where Me Al, Ca, Mg, Li and/or Zn, a lubricant e.g. wax, or fillers, e.g. chalk, and/or reinforcement materials, e.g. cut glass fibres, and subsequently homogenising the mixture, e.g. by action of strong shearing forces. The resulting compound after cooling may be ground to a granulated material of particle size less than 2 mm, and can be used as a moulding compound to form new plastic articles by injection- or compression-moulding processes. The waste plastics may be based on phenol, melamine, urea or unsaturated polyester resins.

Description

Recycling Process for non-fibre-reinforced Thermosettins Plastics The present invention relates to a recycling process for thermoset plastics which are not fibre-reinforced, to form new thermosetting moulding compounds which can be used in the injection-moulding or compressionmoulding processes.

In the processing of thermosetting plastic materials, about 10 to 15W of waste is usually produced, the disposal of which becomes increasingly more difficult and expensive as the capacities of the dumps become smaller, and the combustion of plastic materials for recovering heat energy meets with ever increasing public resistance. Environmental and economical pressures also have had an effect, and the motor car industry, for example, is expected to take back old cars, and parts which cannot be re-used are designated as separate waste.

While substances such as glass, metal, paper and thermoplastic materials are generally regarded as recyclable, thermosetting plastic materials have the reputation of being incapable, in principle, of being recycled.

Scientific investigations and tests by the plastics industry have shown that industrial re-utilisation of fibre-reinforced plastic parts is possible. Suitable, used moulded articles, or waste substances, are fragmented into particles of between approximately 0.5 and 3 mm, and mixed in a quantity of between 30 and 40% by weight with an unsaturated polyester resin and styrene as reactive diluents, as well as with calcium carbonate or chalk, to form a moulding compound, from which moulded plastic articles can be produced once more.On account of the particle size, the reinforcing effect of the glass fibres contained in the particles is retained to a limited degree but, on account of their rheological properties, moulding compounds obtained in this fashion can be made into new articles only by pressure-moulding In addition, the mechanical characteristics of such plastic materials containing recycled fillers is considerably lower than in the case of conventional pressed masses. Pressed masses filled exclusively with recycled material have a low bending strength and are extremely brittle. Although mechanical properties can be improved by additionally kneading glass fibres into the moulding compounds, this leads to a slightly corrugated surface on setting.

Processing of thermosetting plastic materials without fibre-reinforcement gives rise to waste material, and this is partly ground and used as a filler. However, the amount of waste which can be recycled in this manner has, hitherto, been limited to approximately 15% by weight of the moulding compound, so that this does not offer the possibility of recycling returned thermoset articles at the end of their service life, thereby returning them to the plastic cycle.

Thus, after fragmentation into small particles, thermoset moulded parts which are not fibre-reinforced cannot be re-utilised as reinforcement materials, only as fillers.

There is, therefore, a requirement to make available a process which will allow the recycling of thermoset plastics The object is attained by a recycling process according to Claims 1 to 9, by which granulated materials according to Claim 10, and moulding compounds according to Claim 12 are obtained, which can be moulded by compression moulding or injection moulding into articles as claimed in Claims 11 and 13.

Various advantages of the present invention are as follows. For example, thermoset moulding compounds consisting primarily of re-utilised thermosetting plastic material can be produced, and these may typically be processed in injection-moulding or compression-moulding processes to form moulded parts with the same, or better, electrical and mechanical properties as, or than, those produced from new material.

In accordance with the present invention, a granulated material with a particle size of less than 0.2 mm may be produced by grinding either the thermoset processing waste produced or the moulded parts to be re-used, and the granulated material processed by mixing with a phenol resin, a hardener and, where appropriate, with additional processing aids to form a mixture which can be homogenised by the action of, preferably strong, shearing forces, which product can then be processed to form a moulding compound.

This processing can be carried out, for example, by rolling, kneading or extrusion. After the moulding and setting, products formed from such compounds tend to have a better bond between the added resin, the fillers, any appropriate reinforcement materials, and the recycled thermosetting material, than can be attributed to the added resins.

Moulded parts produced in accordance with the present invention have a smooth surface and mechanical, thermal and electrical properties which correspond to those of moulded parts produced in accordance with conventional methods.

Moulded substances based on phenol, melamine, urea and unsaturated polyester resins are suitable for recycling according to the invention.

In order to perform the process, the thermosetting moulded parts and materials to be recycled are ground in a manner, generally as known per se, to a fine granulated material with a particle size of less than 0.2 mm.

In a preferred embodiment, between 40 and 60k by weight of such a ground plastic recycling material are then vigorously mixed with between 25 and 35% by weight of a low-viscosity phenol resin, in particular a low-viscosity phenol novolak, with a viscosity of between 200 and 600 mPa.s at 1750C, between 4 and 6% by weight of a hardener, preferably hexamethylene tetramine, and, where appropriate, between 0.5 and 1.2% by weight of lubricants and release agents, between 4 and 6% by weight of fillers and between 0 and 20% by weight of cut glass fibres.

The phenol resins used can be those resins which are generally used for producing moulding compounds. They may be, for example, both alkaline- and acid-condensed resins of phenol or its derivatives with formaldehyde, and resins obtained by the mixing condensation of formaldehyde, urea and phenols. Low-molecular phenol resins with viscosities of between 100 and 1500 mPas.s at 1750C are preferably used. Particularly preferred moulding compounds having advantageous properties are obtained using phenol novolaks with a viscosity of between 200 and 600 mPas.s at 1750C.

Preferred lubricants and release agents are the metal stearates (wherein the metals are preferably selected from Al, Ca, Mg, Li and Zn), in a quantity of between 0.1 and 0.8k by weight, and wax also in a quantity of between 0.1 and 0.8W by weight. Preferred waxes are amide wax, ester wax, mineral wax and/or paraffin wax. In order to improve the rolling behaviour of the thermosetting moulding compound, chalk is preferably mixed in as a filler.

After mixing the raw materials, the mixture obtained is suitably homogenised and compressed at a temperature of between 100 and 1300C by the action of strong shear forces such as may be supplied by heated rollers. After a rolling period of between approximately 2 and 4 minutes, a cohesive rolled sheet is formed which can be drawn off and, after cooling, ground again to a particle size of less than 2 mm.

The raw mixture may also be homogenised and compressed in a heatable extruder or kneader.

The granulated material obtained after the renewed grinding has, as a thermosetting moulding compound, a medium to soft flow adjustment and can be processed without difficulty in injection-moulding. The granulated material can optionally be additionally mixed with approximately 0.2 by weight of a metal stearate before inj ection-moulding.

If the moulding compound is to be used for producing compression-moulded parts, the recycled material may be mixed with a higher-viscosity phenol resin having a viscosity of between 600 and 1000 mPa.s at 1750C. It is also possible, however, for a hardening accelerator, such as for example magnesium oxide, suitably in a quantity of between 0.5 and 0.2k by weight, to be added to the moulding compound described above.

Plastic parts having approximately the same density and the same mechanical properties as corresponding parts of newly used raw materials can be produced from the moulding compounds obtained.

In addition, moulded parts, produced in accordance with the process according to the invention, have a very low water absorption and good thermal properties.

In order to improve impact and bending strength, up to 28% by weight of cut glass fibres with a fibre length of up to 4.5 mm can be added to the thermosetting moulding compound.

The following examples are to explain the invention, but without restricting the invention thereto.

Examples Example 1 30 kg of a standard phenol novolak (Bakelite [Registered Trade Mark]) with a dynamic viscosity of 300 mPa.s at 1750C is vigorously mixed in a high quality steel drum with 150 g of calcium stearate, 140 g of mineral wax and 500 g of amide wax, 4.7 kg of chalk, 4.5 kg of hexamethylene tetramine and 60 kg of finely ground thermosetting recycled material (grain size less than 0.2 mm) from the production of moulded parts from wood-metal- reinforced phenol-resin moulding compounds (Type 31 according to DIN [German Industrial Standard] 7708) for 20 minutes on a gyrowheel.

The thermosetting raw material obtained is supplied to rollers heated to between 100 and 1300C and is compressed and homogenised in a rolling period of approximately 2.5 minutes to form a cohesive rolling skin.

The rolled sheet produced is drawn off and after cooling is fragmented by a toothed-disc mill to granulated material with a particle size of approximately 2 mm.

The granulated material obtained is mixed with 0.2 by weight of calcium stearate and is moulded and hardened after pre-plasticisation in a barrel extruder in the compression process to form samples (DIN 53470).

In the investigation into the materials, these samples displayed the following properties: Bending strength (DIN 53452) 100 N/mm2 Impact strength (DIN 53453) 8 kJ/m2 Notch impact strength (DIN 53453) 1.8 kJ/m2 Surface resistance (DIN 53482) > 1O10 < 1O11 Heat deformation resistance (Martens DIN 53458) 1400C Water absorption (DIN 53495) 50 mg.

Example 2 30 kg of a standard phenol novolak (Bakelite [Registered Trade Mark]) with a dynamic viscosity of 300 mPa.s at 1750C is vigorously mixed in a high quality steel drum with 150 g of calcium stearate, 140 g of mineral wax and 500 g of amide wax, 4.7 kg of chalk, 4.5 kg of hexamethylene tetramine and 45 kg of finely ground thermosetting recycled material (grain size less than 0.2 mm) from the production of moulded parts from wood-metal- reinforced phenol-resin moulding compound, Type 31 (DIN 7708 and 15 kg of cut glass fibres with a fibre length of up to 4.5 mm for 20 minutes.

The thermosetting raw material obtained is supplied to rollers heated to between 100 and 1300C and is compressed and homogenised in a rolling period of approximately 2.5 minutes to form a cohesive rolled sheet. The rolled sheet produced is drawn off and-after cooling is fragmented by a toothed-disc mill to granulated material with a particle size of approximately 2 mm.

The granulated material obtained, which is somewhat more reactive than that obtained in Example 1, is likewise mixed with 0.2 by weight of calcium stearate and is processed after pre-plasticisation in a barrel extruder in the compression process to form samples (DIN 53470).

In the investigation into the materials, these samples displayed the following properties: Bending strength (DIN 53452) 110 N/mm2 Impact strength (DIN 53453) 9 kJ/m2 Notch impact strength (DIN 53453) 2.5 kJ/m2 Surface resistance (DIN 53482) > 1010 < 1011 Heat deformation resistance (Martens DIN 53458) 1540C Water absorption (DIN 53495) 50 mg.

Claims

1. A process for recycling thermoset plastics which are not fibre-reinforced, the resulting product being usable as a moulding compound, characterised in that the thermoset plastics material is granulated to a particle size of 0.2 mm or less, and the resulting granulate mixed with a phenol resin, a hardener and, where appropriate, additional processing aids and/or fillers and/or reinforcement materials, and subsequently homogenising the mixture.

2. A process according to any preceding claim, wherein the homogenisation is accomplished by action of strong shearing forces.

3. A recycling process according to Claim 1 or 2, wherein a low-viscosity phenol novolak is used as the phenol resin.

4. A recycling process according to any preceding claim, wherein the phenol resin is used in a quantity of between 25 and 35 by weight.

5. A recycling process according to any preceding claim, wherein hexamethylene tetramine is added as the hardener.

6. A recycling process according to any preceding Claim, wherein the hardener is added in a quantity of between 4 and 6 by weight.

7. A recycling process according to any preceding claim, wherein one or more Me stearates (wherein Me = Al, Ca, Mg, Li and/or Zn) are added as processing aids, and wax is added as a lubricant and release agent.

8. A recycling process according to any preceding claim, wherein processing aids are added in a quantity of between 0.1 and 0.8 by weight, and/or lubricants and/or release agents are added in a quantity of between 0.1 and 0.8 by weight.

9. A recycling process according to any preceding claim, wherein between 4 and 6% by weight of chalk is added as a filler.

10. A recycling process according to any preceding claim, wherein between 0 and 20% by weight of cut glass fibres or other fibres with a fibre length of up to 4.5 mm are added as a reinforcement material.

11. A recycling process according to any preceding claim, wherein a finely granulated thermosetting plastic recycling material in a quantity of between 40 and 60k by weight is used.

12. A recycling process according to Claim 11, wherein a finely granulated thermosetting plastic recycling material in a quantity of between 45 and 60k by weight is used.

13. A recycling process according to any preceding claim, wherein the resulting compound is, after cooling, again ground to a granulated material with a particle size of less than 2 mm.

14. Granulated material, produced from a mixture of finely granulated thermosetting recycling material with a grain size of less than 0.2 mm, between 25 and 35 by weight of a phenol resin, between 4 and 6% by weight of a hardener, and where appropriate additional adjuvants and reinforcement materials, with the application of strong shear forces at between 100 and 1300C.

15. Use of granulated material according to Claim 14, for producing compression-moulded articles or, after mixing with approximately 0.26 by weight of stearate, for producing injection-moulded articles.

16. A thermosetting moulding compound, produced according to any preceding claim.

17. A thermosetting moulding compound, produced from finely granulated thermosetting plastic recycling material with a grain size of less than 0.2 mm, between 25 and 35% by weight of a phenol resin, between 4 and 6% by weight of a hardener, and where appropriate Me stearates (Me = Al, Ca, Mg, Li, Zn) in a quantity of between 0.1 and 0.8k by weight and wax in a quantity of between 0.1 and 0.8k by weight as a lubricant and release agent, between 4 and 6W by weight of chalk as a filler, and from 0 to 20% by weight of cut glass fibres with a fibre length of up to 4.5 mm as a reinforcement material.

18. A process for recycling thermoset plastics which are not fibre-reinforced, substantially as described hereinbefore, especially with respect to the accompanying Examples.

19. Use of a thermosetting moulding compound according to any preceding claim, for producing compressionmoulded or injection-moulded articles.