WO1998009785A1

WO1998009785A1 - Unitary solid moulding

Info

Publication number: WO1998009785A1
Application number: PCT/GB1997/002346
Authority: WO
Inventors: Peter Thomas; Peter Leonard Jacobs
Original assignee: STRUMAT INTERNATIONAL Corp Ltd
Current assignee: STRUMAT INTERNATIONAL Corp Ltd
Priority date: 1996-09-03
Filing date: 1997-09-02
Publication date: 1998-03-12
Anticipated expiration: 1999-03-03
Also published as: GB9618326D0; ZA977858B; AU4123997A

Abstract

Unitary solid mouldings are prepared by adding finely divided waste material to a batch of exothermically thermosettable polyester resin in a receptacle, blending the waste material and the resin, and allowing the resin in the resultant blend to undergo exothermic cure substantially without the application of external heat whilst the blend is in a mould.

Description

unitary Solid Moulding

The present invention relates to the manufacture of unitary solid mouldings, and products made therefrom.

A large variety of building elements or structural materials are known which comprise industrial or domestic waste bonded together by means of adhesive. Amongst such building elements or structural materials are breeze blocks (ashes and coal or coke bonded together with cement) , chipboard (woodchips bonded together with an adhesive) and synthetic slates (slate dust bonded together by means of adhesive) .

A broad disclosure of structural materials comprising adhesive and industrial or domestic waste is given in GB-A- 2294926, published on 15^th May 1996.

In the thermoplastics processing industry, by-product material results from the production or processing of the thermoplastic materials. Providing an individual thermoplastic material can be kept free of contamination with other thermoplastics, it may be recycled for further processing and is therefore not waste material.

However, in view of the wide variety of thermoplastics currently used in industry, it is frequent for different types of thermoplastics waste to become mixed together; except for some special combinations there are generally significant problems in processing mixtures of different types of thermoplastics. For example, polyethylene has very different processing characteristics to those of polyethylene terephthalate (PET) , both of which are common in food packaging. Furthermore, the processing characteristics of unplasticised PVC, ABS, polyethylene and PET, and other commonly used thermoplastic materials, are substantially different. A method for improving the stiffness of such commingled plastics (mixed plastics waste) is disclosed in the Society of Plastic Engineering Annual Technical Conference 1995, Volume 53, Number 3, Pages 3752 to 3756. However, the process disclosed is a continuous process and requires the application of external heat in order to enable a moulded body to be produced. This gives rise to the disadvantage that the process cannot be carried out away from an industrial processing plant.

Therefore, the principal aim of the present invention is to provide a method of manufacturing a unitary solid moulding from waste material, using a batch process, which method can be easily carried out in the field.

According to the present invention, there is provided a method of manufacturing a unitary solid moulding, which method comprises :

(a) providing a batch of exothermicaily thermosettable polyester resin in a receptacle;

(b) providing a finely divided waste material comprising at least two thermoplastics;

(c) adding the waste material to the batch of resin in said receptacle in an amount such that the resin constitutes at least five percent by weight of the resulting mix;

(d) blending the waste material and the resin;

(e) permitting the resin to undergo exothermic cure in a mould, substantially without application of external heat whilst the blend is in the mould.

The term "waste" material as used herein denotes any material that would normally have no further economic use, or would be dumped, in for example, a landfill, if the material were not used in the method according to the present invention. The waste material may be industrial or domestic waste.

The resulting moulding is no longer thermoplastic in nature; it has the characteristics of a cured thermoset material. The properties of the resulting element may be tailored depending on the nature of the thermoplastics present; for example, if a significant quantity of flexible thermoplastics is present, then the resulting moulding may have a degree of flexibility. Typically, the resultant blend of step (d) is transferred to a mould prior to step (e) , preferably within thirty minutes of completion of blending in step (d) . However, it is envisaged that in some embodiments of the invention, the receptacle may also function as the mould.

The blending in step d) is typically carried out in the receptacle by a tumbling action, or by means of a high speed mixer. Advantageously, the high speed mixer comprises a blade, paddle or the like which is shaped to entrain air into the mix during the blending in step d) .

The introduction of air is advantageous when it is desirable to manufacture a lightweight moulding. Such lightweight mouldings may be suitable as, for example, pallets or the like.

The amount of polyester resin present typically does not exceed 50% by weight of the mix.

The waste material may be pulverised to a particle size of less than 10mm. The size of particles may be selected depending on the properties required; typically the waste material has an average particle size in the range of 1 to 3mm.

The thermoplastics preferably have respective softening temperatures typically not more than 250°C. The thermoplastics are typically two or more types of plastics selected from ABS, polystyrene (for example high impact polystyrene) , unplasticised PVC, one or more polyolefins (such as polyethylene or polypropylene) , polyethylene terephthalate or other polyester, or a relatively low melting polyamid^'e.

The thermosettable polyester resin used in the method according to the invention is selected so as to be capable of undergoing exothermic cure, preferably to generate a temperature up to approximately 250°C in the mould. Because a thermosettable polyester resin is used which undergoes exothermic cure, it is not necessary to apply external heating; the heat generated by the curing of the polyester resin is sufficient to soften the waste material and render the thermoplastics processable in the mould. Typically, at least the interior of the receptacle is of a material to which the blend is substantially non-adhesive. The receptacle may advantageously be a drum dimensioned to be received in a cement mixer, which removes the necessity to provide a completely purpose-designed machine. It is preferred that such a drum is lined with stainless steel or polypropylene.

The blend may be moulded in an open mould or, alternatively, under pressure (for example, with a weight acting on top of the blending mould, or under compression from a hydraulic ram or the like) .

It is preferred that the finely divided waste material should be substantially dry; if there is water present in the mixed thermoplastics, the amount may be minimised by size reduction. If necessary, further heating can be applied and/or a fan assisted dryer used in order to reduce the water content substantially below 10% by weight.

Curing accelerators, such as cobalt salts, may be added at step (c) . Other additives such as fire retardants, pigments or the like may also advantageously be added at step (c) .

The cured polyester is preferably present in a minor amount by weight of the final building element, with a major part of the weight being a matrix derived from the softened and subsequently hardened thermoplastics, such that the matrix is bonded together by the cured polyester. The amount of polyester therefore preferably does not exceed 20% by weight of the blend to be moulded, a preferred amount being in the range 8 to 15% by weight.

Although it is preferred that the moulding consists primarily of the thermoplastics and the resin, further materials may be present in some cases. Examples of such further materials are cured thermoset resins, glass, paper and/or cardboard, and rubber compounds (for example, from used vehicle tyres) .

It is, however, preferred that the waste material should be substantially free of biologically degradable material, or metals, such as aluminium, steel or the like, which may be recycled independently (and are therefore not "waste" as referred to above) . A large variety of structural or building elements can be produced as unitary solid mouldings according to the invention, such as bricks, blocks, roof tiles, pallets, boards (such as floors, skirtings or facings) , doors and joists.

The present invention will be illustrated in more detail with reference to the following examples, given by way of illustration only:

Example i

85 parts of mixed polyethylene and PVC waste were size reduced to between 1 and 3mm diameter and a water content of about 5% by weight. The waste was then added to a stainless steel lined drum containing 15 parts of unsaturated thermosetting polyester resin with a styrene content of 42% by weight and a viscosity of 370 MPa S at 23°C and blended by a tumbling action in the drum. The polyester resin, which was commercially available as Palatal (BASF) , contained 2% by weight benzoyl peroxide and 1% by weight cobalt octanoate.

The mixture was transferred to a mould and subjected to a compressive force via a 10kg weight placed on top of the material present in the mould.

The mix was then allowed to cure, without application of external heating, for five minutes.

The resulting moulding, in the shape of security fencing, could be drilled, planed, sanded etc in a manner similar to wood.

Example 2

85 parts of mixed ABS, high impact polystyrene, PVC (plasticised and unplasticised) and phenolic resin waste were ground to a particle size of less than 2mm diameter and a water content of about 3% by weight. The waste was then added to 15 parts of unsaturated thermosetting polyester resin with a styrene content of 36% by weight and a viscosity of 600 MPa S at 23°C in a drum which was lined with polypropylene. The mix was blended by tumbling in the drum. The polyester resin contained 2% by weight benzoyl peroxide and 1% cobalt octanoate. The mixture was transferred to a mould of roof tile shape and subjected to a compressive force via a 10kg weight placed on top of the mixture.

The mix was then allowed to cure, without application of external heating, for five minutes. The resulting moulded roof tiles were rigid and suitable for use as replacement for conventional slates.

Example 3

85 parts of mixed polypropylene, polyethylene terephthalate and PVC (plasticised and unplasticised) waste were ground to less than 3mm diameter and a water content of about 4% by weight. The waste was then added to 15 parts of unsaturated thermosetting polyester resin with a styrene content of 42% by weight and a viscosity of 370 MPa S at 23°C in a drum which was lined with polypropylene. The polyester resin contained 2% by weight benzoyl peroxide and 1% by weight cobalt octanoate. (The amount of benzoyl peroxide could if wished be increased or decreased depending on ambient temperature and rate of cure required, as would be known to one skilled in the art.)

The mix was tumbled in a drum, and the resulting blend transferred to a mould and subjected to a compressive force via a 10kg weight placed on top of the material present in the mould.

The resulting moulding, in the shape of joists, could be drilled, planed, sanded etc in a manner similar to wood.

Example 4

85 parts of mixed unplasticised PVC and nylon waste (together with pulverised grp) were ground to between 1 and 3mm diameter and a water content of about 5% by weight. The waste was then added to 15 parts of unsaturated thermosetting polyester resin with a styrene content of 42% by weight and a viscosity of 370 MPa S at 23°C in a drum which was lined with stainless steel. The polyester resin contained 2% by weight benzoyl peroxide and 1% cobalt octanoate. The mix was blended in a drum using a high speed mixer. The blade of the mixer was shaped to introduce air into the blend.

The resulting blend was transferred to a mould and subjected to a compressive force via a 10kg weight placed on top of the material present in the mould.

The resulting moulding, in the shape of pallets, could be drilled, planed, sanded etc in a manner similar to wood. The introduction of air to the blend prior to curing produced a durable yet lightweight pallet.

The flexibility of the resulting mouldings could be controlled by adding, when appropriate, additional flexible resin.

Claims

Claima :

1. A method of manufacturing a unitary solid moulding, which comprises: a) providing a batch of exothermicaily thermosettable polyester resin in a receptacle; b) providing a finely divided waste material comprising at least two thermoplastics; c) adding said waste material to said batch of resin in said receptacle in an amount such that said resin constitutes at least 5% by weight of the resulting mix; d) blending said waste material and said resin; and e) permitting said resin to undergo exothermic cure in a mould, substantially without application of external heat whilst said blend is in said mould.

2. A method according to claim l, wherein the resultant blend of step (d) is transferred to said mould prior to step (e) .

3. A method according to claim 2, wherein said transfer to said mould is within 30 minutes of completion of blending in step (d) .

4. A method according to any of claims 1 to 3, wherein said blending in step d) is by tumbling.

5. A method according to any of claims l to 3, wherein said blending in step d) is by means of a high speed mixer.

6. A method according to claim 5, wherein said high speed mixer comprises a blade which is shaped to entrain air into said mix during said blending in step d) .

7. A method according to any of claims 1 to 6, wherein said amount is not exceeding 50% by weight of said mix.

8. A method according to any of claims 1 to 7, wherein at least the interior of said receptacle is of material to which said blend is substantially non-adhesive.

9. A method according to any of claims 1 to 8, wherein said receptacle is a drum dimensioned to be received by a cement mixer.

10. A method according to claim 9, wherein said drum is lined with stainless steel.

11. A method according to claim 9, wherein said drum is lined with polypropylene.

12. A method according to any of claims 1 to 11, wherein said waste material has an average particle size in the range 1 to 3mm.

13. A method according to any of claims l to 12 , wherein a compressive force is applied to said blend in step e) .

14. A method according to any of claims 1 to 13 , wherein said thermoplastics have respective softening temperatures of not more than 250°C.

15. A method according to any of claims 1 to 14, wherein said waste material and said resin are substantially dry.

16. A method according to any of claims 1 to 15, wherein a pigment is added at step c) .

17. A method according to any of claims 1 to 16, wherein a fire retardant is added at step c) .

18. A method according to any of claims 1 to 17, wherein an accelerator is added at step c) .

19. A method according to any of claims l to 18, wherein said waste material is substantially free of biologically degradable material.

20. A method according to any of claims l to 19, wherein said waste material is substantially free of metal.