WO2006040536A1

WO2006040536A1 - Method of processing a polymer coated substrate

Info

Publication number: WO2006040536A1
Application number: PCT/GB2005/003903
Authority: WO
Inventors: Peter Ridsdale Hornsby; Karnik Tarverdi
Original assignee: Brunel University
Priority date: 2004-10-14
Filing date: 2005-10-11
Publication date: 2006-04-20
Also published as: GB0422869D0

Abstract

A method of processing a polymer coated substrate (18) comprises the steps of providing a polymer coated substrate, forming fragments therefrom, melting at least some of the polymer, and mixing and compounding the fragments. The substrate may be paper such as wallpaper. Alternatively the method may be used to process other polymer coated papers such as those used in packaging. A plasticizes maybe added to the substrate being treated. Suitable plasticizers include those used in the plastics industry and in wallpaper manufacture.

Description

Method of Processing a Polymer Coated Substrate

The present invention relates to a method of processing a polymer coated substrate.

Vinyl wallpapers typically comprise a layer of cellulose fibre paper coated with a layer of polymer, such as polyvinylchloride. During the manufacturing process, a lot of material is wasted, for example wallpaper which is 'off-spec'. Typically, 16,000 tonnes of waste wallpaper is produced during manufacture in the UK each year. Most of this waste ends up in landfill sites. Manufacturers have to pay for landfill at a cost of about one million pounds sterling each year. In addition, the process generates liquid waste such as plastisol. Plastisol typically comprises about 24 to 28% plasticizer, about 40% polyvinyl chloride (PVC) typically in powder form, one or more fillers such as calcium carbonate and pigments. The plasticizer is usually a phthalate or organophosphate ester. Each wallpaper manufacturer makes its own blend. The plastisol cannot readily be reused in subsequent production runs due to the pigmentation, as dark pigments in particular are difficult to camouflage. Liquid waste is difficult to dispose of and manufacturers have to adhere to strict guidelines which is both time consuming and expensive.

Attempts have been made to recycle waste wallpaper by separating the polymer coating and the cellulose paper. However, these attempts have been largely unsuccessful. The process is very time consuming and laborious and requires large quantities of solvents which in turn generates waste. No effective methods have been established for re-using waste wallpaper.

The present invention seeks to overcome one or more of the above disadvantages.

According to an aspect of the present invention there is provided a method of processing a polymer coated substrate comprising the steps of providing a polymer coated substrate, forming fragments therefrom, melting at least some of the polymer, and mixing and compounding the fragments. Ideally the steps are carried out in an extruder, and preferably in a twin screw extruder. An advantage is that a twin screw extruder has a mixing capability. However, a single screw extruder could be used as some models have mixing capability. In one embodiment, the steps are carried out simultaneously. In an alternative embodiment, a batch internal mixer is used.

Advantageously, the polymer coated substrate comprises a layer of polymer and a layer of substrate.

Preferably, the substrate is paper. Advantageously the substrate is wall paper. Alternatively the method may be used to process other polymer coated papers such as those used in packaging.

The polymer may be polyvinyl chloride, polyester, polyethylene or a mixture thereof.

The method preferably includes the step of adding a plasticizer to the polymer coated substrate being treated. The plasticizer may be a phthalate ester. For example, the plasticizer may be DINP (Diisonoryl phthalate). The plasticizer may be an organophosphate ester. For example, the plasticizer may be TPP (triphenyl phosphate). An advantage of using these plasticizers is that they are commonly used in the plastics industry and in wallpaper manufacture. Thus waste plasticizer can be recycled. In an alternative embodiment, the plasticizer is glycerol. Typically, the plasticizer is added in the form of plastisol. The plastisol may be semi solid, semi liquid or liquid.

An advantage of adding plasticizer is that it softens the polymer. In addition, it improves the processability of the compound enabling it to pass through the apparatus more easily. Mixing is easier and additives can be more readily incorporated into the mixture. A further advantage is that waste plastisol can be used in the method thereby reducing the problem of its disposal. Moreover, the flexibility of the product can be altered by varying the amount of plasticizer added which extends the range of applications. The plastisol may be added at any stage although the plastisol is ideally added part way through, for example about halfway along the extruder.

Up to about 50% wt plastisol may be added, preferably up to about 30% wt plastisol, more preferably up to about 20 %wt plastisol, and most preferably up to about 10% wt plastisol is added. Typically, if more than 50% plastisol is added the material becomes too soft and the components begin to separate.

The method may include the step of adding a supercritical fluid. Preferably the supercritical fluid is carbon dioxide.

Use of supercritical carbon dioxide in material processing is described in our copending patent application PCT/GBOl/05489. The disclosure in patent application no. PCT/GBOl/05489 is incorporated herein by reference. Carbon dioxide, when introduced in a supercritical state, can plasticize thermoplastics during melt processing resulting in a significant reduction in viscosity resulting in easier flow through the machine. Under optimum conditions this effect can be achieved without the material foaming. In addition, the supercritical fluid effectively lowers the melt temperature in the apparatus, typically an extruder. This is important since the PVC used in wallpapers might not have heat stabilising agents. Heating the PVC for too long at too high a temperature causes the polymer to degrade. Accordingly, inclusion of the supercritical fluid reduces the risk of degradation. Moreover, heat stabilising agents do not have to be added to the mixture.

The method may further include the addition of one or more additives such as organic and/or inorganic fillers. Examples of fillers include flame retardants, calcium carbonate (which stiffens the material) and pigments.

The method may further include the addition of natural fibres. Examples of natural fibres include straw, hemp, flax, kenaf (elephant grass) and cellulose. This reinforces the end product which is particularly useful when the product is to be used in packaging. The method preferably includes the step of extruding the mixture through a die.

The method may include the step of further processing the mixture, for example by injection or compression moulding.

Preferred embodiments of the present invention are described with reference to the accompanying figures in which:

Figure 1 is a photograph of a first sample wallpaper crumbed and compounded by the preferred method,

Figure 2 is a photograph of a second sample wallpaper crumbed and compounded by the preferred method,

Figure 3 is a photograph of a third sample wallpaper crumbed and compounded by the preferred method,

Figure 4 is a photograph of a fourth sample wallpaper crumbed and compounded by the preferred method,

Figure 5 is a schematic diagram of an apparatus for carrying out the preferred method,

Figure 6 is a photograph of waste plastisol used for dosing and blending with wallpaper waste,

Figure 7 is a photograph of an apparatus for carrying out the preferred method,

Figure 8 comprises photographs of waste wallpaper samples processed in accordance with the preferred method, the samples comprising a mixture of samples 1 to 4 and 20% plastisol (A), and 30% plastisol (B) and 10% plastisol (D) or sample 1 and 10% plastisol (C). The products have been compression moulded (left hand side of each photo) or injection moulded (right hand side),

Figure 9 is a schematic diagram showing the addition of supercritical fluid to the extruder,

Figure 10 is a graph showing stress-strain curves for three end products, each comprising an equal mix of samples 1 to 4 obtained from a 40mm twin screw extruder and 10% plastisol (A), 20% plastisol (B) and 30% plastisol (C),

Figure 11 is a schematic diagram showing a polymer coated substrate before (top) and after (bottom) processing.

Figure 12 is a photograph of wallpaper samples and moulded products made therefrom, and

Figure 13 is a graph showing stress strain curves for samples obtained using a 57mm twin screw extruder, each sample comprising a mix of wallpapers and 15% wt plastisol (A) and 20% wt plastisol (B).

The processing stages are shown schematically in Figure 5, indicating feeding; twin-screw extrusion compounding; provision for liquid plastisol addition; secondary processing by injection moulding and single screw extrusion into a sheet.

Referring to Figure 5, the apparatus shown schematically includes a co-rotating twin screw extruder 10 with a feed port 12 located adjacent to an end of the extruder. The extruder has a further port 14 approximately halfway along its length for the addition of plastisol. At the opposite end, the extruder 10 is connected to a die 16.

Waste wall paper 18 is cut into strips and fed into the feed port 12 of the extruder 10. The operating temperature of the extruder is about 100 to 200°C. hi a first stage, the screws grind the wallpaper 18 into crumbs. The crumbs are then blended. Waste plastisol is added via port 14 about halfway along the extruder. The wallpaper crumbs and the plastisol are compounded and extruded through the die 16.

Vinyl wallpaper is effectively a laminated composite comprising a layer of paper with a layer of PVC thereon (Figure 12). The result of the above described process is to convert the laminated polymer composite into a short fibre-reinforced polymer composite. In the case of wallpaper, the short fibres are cellulose fibres.

The compound may be extruded as a profile or cooled and pelletised, using pelletisation or die face cutting techniques, into granules to be used for injection moulding or further processing.

Alternatively, a sheet extrusion line may be used to extrude the compound into a continuous sheet for commercial applications. The compound may be used in general injection moulded products, sheet, pipe, and other profiles. Figure 12 shows a range of moulded products. The end compound is a functional plastics product and can be used in a variety of applications. For example the compound may be used in the automotive industry, such as in door panels and air vents, in consumer products, such as flower pots, brush blocks, paint brush handles, tool handles, blinds, decking, storage crates, toilet seats, garment hangers, and in industrial products, such as pallets, chair supports and fencing. The compound may also be used with reinforcing natural fibres for example in door liners, trunk (boot) liners, parcel shelves, seat backs, sunroof sliders, sound insulation, furniture and in building and construction.

The compound may be blended with 'virgin' polymer resins. For example, instead of using 100% 'virgin' polymer resin in an application, a blend of 80% 'virgin' polymer and 20% of the compound may be used. This reduces costs since the compound is cheaper than 'virgin' polymer as it can be made from waste products. In addition, including the compound does not detract from the physical properties of the polymer.

Modifying additives may be added to the mixture in the extruder via the wallpaper feed port 12. Additives include organic and inorganic fillers such as calcium and magnesium carbonate, pigments, and flame retardants. Alternatively, the additives may be added via a separate feed port. Figure 7 is a photograph showing integrated extrusion compounding of waste wallpaper and plasticizer. The apparatus includes a twin screw extruder 100 having a wallpaper feed port 110, a secondary feed 120 for the inclusion of modifiers and a further feed 130 for plasticizer/plastisol injection. The end of the extruder 100 is connected to a die face cutter 140 for pellets.

Referring to Figure 9, supercritical fluid, such as carbon dioxide, may be added to the mixture in the extruder 200. A syringe pump 210 is located between a supply 220 of supercritical liquid carbon dioxide and single or twin screw extruder 200 to control the flow of fluid to the extruder. The extruder 200 includes an inlet 230 for the introduction of supercritical fluid. In addition, the extruder is connected to a measuring system including a data acquisition unit 240. Wallpaper waste is added to the extruder via feed port 260 and is crumbed and blended. Supercritical carbon dioxide is added to the mixture via inlet 230, reducing the viscosity of the mixture and aiding the flow of the mixture through the extruder and effectively lowering the melt temperature in the extruder.

The amount of wallpaper that can be processed at one time is in part limited by the volume of the feed port of the extruder. This is a particular problem with low bulk density material. The feed port may be adapted to receive more material at a given time. The port may include a device such as modified screws to assist in pulling the material into the extruder. Modified feed ports are generally used in the rubber industry although not typically in the synthetic polymer industry.

Other methods of feeding the wallpaper into the extruder can be used. For example, the wallpaper may be crushed and ground or shredded instead of cutting into neat small rolls.

Instead of wallpaper, other polymer coated substrates may be used such as polyethelene coated paper used in moisture resistant packaging. Thus the process can be used to recycle a variety of waste material. Instead of using an extruder, alternative strategies could involve the use of batch internal mixers. Polymer coated substrate could be added to the mixer, the polymer melted and the substrate ground up. The resulting compound could then be squeezed out of a die.

Example 1

To facilitate melt extrusion and compounding of the samples, a co-rotating twin-screw extruder was used, first to crumb the wallpaper without degrading the PVC or the cellulose. This was followed by a second extrusion cycle in which various levels of waste plasticizer were injected into the extruder. The waste wallpaper and the plasticizer were then extrusion compounded.

Sample 1

A light brown/orange wallpaper supplied by Graham & Brown (UK). The backing is a mechanically foamed cellulose fibre paper having a density of 90g/m². The facing is a coloured low foam plasticised PVC pad (density 160g/m²) and a light brown/orange coloured compact plasticized PVC (density 15g/m²).

Sample 2

A textured white wallpaper supplied by Graham & Brown (UK). The backing is nonwoven chemical cellulose fibre and polyester fibre mixture (density 70g/m²) and is manufactured by Ahlstrom Corporation. The facing is white textured medium foam plasticised PVC (density 150g/m²) Sample 3

A Blue and silver wallpaper supplied by Graham & Brown. The backing is nonwoven chemical cellulose and polyester fibres manufactured by Dresden Papier (density 75g/m²). The facing is a coloured compact plasticized PVC pad (100g/m²) and prints of a 'silver' (aluminium) compact plasticised PVC and coloured textured medium foam plasticized PVC (90g/m² )

Sample 4

A light brown and textured wallpaper supplied by Imperial Home Decor. The wallpaper comprises high-blown plastisol on paper with a paper iplastisol ratio of 120:110 g/m². The plastisol is roughly 45% PVC and 25% Plasticizer with 30% fillers including Magnesium Carbonate and Titanium dioxide.

The wallpaper was supplied in rolls which were 540mm wide and 120mm in diameter on average. These were cut into narrower rolls of 120mm to suit the feed port of the extruder (Figures 1-4). It was found that some wallpapers fed better than others, for instance sample 1 was more difficult than samples 2 or 3. This is due to the texture of the wallpaper and the amount of cellulose or wood fibre contained on the surface.

A Betol 40mm diameter co-rotating twin-screw extruder was used for grinding and blending of the wallpapers. A gentle screw profile was designed to grind and blend the materials, but avoiding very high shear and thus thermal degradation of the PVC. During this preliminary stage of grinding and mixing, the operations were carried out in two stages. The wallpaper was crumbed first and then the waste plastisol was added subsequently.

Extrusion Conditions used: A 21 :1 length to diameter ratio 40 mm twin-screw extruder was used. A gentle screw profile was designed with 25mm of kneading elements within 320mm of 12mm pitch screws. Venting was not applied, even though cellulose in the wallpaper could have absorbed moisture. However, since the compound was not extruded through a die, venting took place from the end of the screw tips.

Operating conditions:

Plastisol (Figure 6) was injected into the extruder at barrel zone 3, using a Bran & Luebbe positive dosing pump.

Barrel Number: 1 2 3 4 5

Temperature °C: 140 160 180 180 200

Screw speed: 240 rpm

Motor current: 5-10 amps

The samples were modified by injection of different concentrations of waste plasticizer/plastisol supplied by Graham & Brown, in order to modify mechanical properties and to improve processability during extrusion compounding. Samples 1 to 4 had 10%wt plastisol added. Sample consisting of an equal blend of samples 1 to 4, had either 10%wt, 20%wt or 30%wt plastisol added.

The extrudate was cooled in air at exit from the extruder, in the form of crumbs, (the extrudate may be cooled in water). In this set of experiments, a die was not attached to the extruder. However, trials using plasticized variants of the compound indicated that die forming was feasible. Part of the extrudate was compression moulded into tiles. Another part of the extrudate was injection moulded into tensile test bars, (Figure 8), using a Demag 110 tonne Ergotech injection-moulding machine. The barrel temperatures were set at 190 ⁰C₃ and the dwell time was 60 seconds. If the dwell time was increased to over 150 seconds in the barrel, thermal degradation was evident.

The tensile strength, modulus and strain at failure of all compounds prepared were determined on injection moulded test bars (Figure 8) at 23 ⁰C according to BS EN ISO 527-1: 1996. A strain rate of 5mm/min. was used. Mechanical property results are summarised in Table 2 and representative stress strain curves are shown in FigurelO. These results indicate that individual wallpaper types yield broadly similar mechanical behaviour, although sample 4 gave a slightly higher elastic modulus. This may be a result of lower plasticizer content in this material. The effect of increasing plasticizer addition was to reduce stiffness and strength, as anticipated, however significantly improved flow was observed during processing. Encouragingly, combinations of all four wallpapers had no adverse effect on properties, indicating that mixtures of these waste materials can be tolerated during processing and subsequent moulding.

Example 2

The experiments were scaled up and a 57 mm twin screw extruder used. A mixture of wallpaper samples was added to the extruder. The extruder was used to pulp and melt extrude the mixture. Following pulping, the mixture was blended with either 15% wt or 20% wt plastisol and re-extruded. Throughput rates of at least 25 kg/hour of resulting compound were obtained. It is envisaged that this could be increased substantially with suitable upstream and/or downstream ancillary equipment. The following results were achieved when the mixture was injection moulded into tensile test bars and plaques:

Sample: % wt plastisol Elastic Tensile

Modulus Strength

(GPa) (MPa)

A 15 0.60 17.34

B 20 0.76 17.29 These mechanic properties are improved with respect to the results using a 40mm twin screw extruder.

Representative stress strain curves are shown in Figure 13.

Extrusion compounded vinyl wallpaper was successfully injection moulded into tensile test bars, plaques and plant pegs.

It will be understood that the above description of the present invention is susceptible to various modification, changes and adaptations.

In summary, waste vinyl coated wallpaper can be converted into cellulose reinforced PVC pellets by modified twin-screw extrusion technology. Compounded pellets can be processed into extruded and injection moulded parts. Compound properties can be modified by addition of waste PVC plastisol.

The method and apparatus can be used to recycle any heat sensitive composite (including vinyl composites such as PVC) including modified starches used with and without synthetic polymers. The technology can also be used to recycle general polymeric composites including natural and/or synthetic fibres.

Table 1 Wallpaper pre-treatment and compounding, using twin-screw extruder techniques

Crumbed % plastisol addition 10 20 30

Wallpaper 1 X X

Wallpaper 2 X X

Wallpaper 3 X X

Wallpaper 4 X X

Combination of all 4 wallpapers X X X X

Table 2. Tensile properties of recycled wallpaper.

Material E (GPa) UTS (MPa)

1. Sample 5 +10% Plastisol 0.95 13.4

2. Sample 5 + 20% Plastisol 0.79 11.2

3. Sample 5 + 30% Plastisol 0.57 10.74

4. Samplel + 10% Plastisol 0.78 13.53

5. Sample 2 + 10% Plastisol 0.70 13.16

6. Sample 3 + 10% Plastisol 0.79 14.05

7. Sample 4 + 10% Plastisol 1.15 13.75

Materials 1-3 are equal blends of all 4 wallpaper wastes

Our results show that waste vinyl wallpaper from different manufacturing companies can be blended together to produce a processable compound.

Claims

1. A method of processing a polymer coated substrate (18) comprising the steps of providing a polymer coated substrate, forming fragments therefrom, melting at least some of the polymer, and mixing and compounding the fragments.

2. A method as claimed in claim 1 wherein at least some of the steps are carried out in an extruder.

3. A method as claimed in claim 2 wherein the extruder is a twin screw extruder (10).

4. A method as claimed in any preceding claim wherein the steps are carried out simultaneously.

5. A method as claimed in claim 1 wherein at least some of the steps are carried out in a batch internal mixer.

6. A method as claimed in any preceding claim wherein the polymer coated substrate (18) comprises a layer of polymer and a layer of substrate.

7. A method as claimed in any preceding claim wherein the substrate (18) is paper.

8. A method as claimed in any preceding claim wherein the substrate (18) is wall paper.

9. A method as claimed in any preceding claim wherein the polymer is polyvinyl chloride, polyester, polyethylene or a mixture thereof.

10. A method as claimed in any preceding claim including the step of adding a plasticizer to the polymer coated substrate being treated.

11. A method as claimed in claim 10 wherein the plasticizer is a phthalate ester.

12. A method as claimed in claim 10 or 11 wherein the plasticizer is Diisonoryl phthalate.

13. A method as claimed in claim 10 wherein the plasticizer is an organophosphate ester.

14. A method as claimed in claim 13 wherein the plasticizer is triphenyl phosphate.

15. A method as claimed in claim 10 wherein the plasticizer is glycerol.

16. A method as claimed in any of claims 10 to 15 wherein the plasticizer is added in the form of plastisol.

17. A method as claimed in claim 16 wherein the plastisol is semi solid, semi liquid or liquid.

18. A method as claimed in any of claims 10 to 17 wherein up to about 50% wt plastisol is added.

19. A method as claimed in any of claims 10 to 17 wherein up to about 30% wt plastisol, is added.

20. A method as claimed in any of claims 10 to 17 wherein up to about 20 %wt plastisol is added.

21. A method as claimed in any one of claims 10 to 17 wherein up to about 10% wt plastisol is added.

22. A method as claimed in any preceding claim including the step of adding a supercritical fluid.

23. A method as claimed in any preceding claim further including the addition of one or more organic and/or inorganic fillers.

24. A method as claimed in claim 23 wherein the filler is a flame retardant, calcium carbonate and/or a pigment.

25. A method as claimed in any preceding claim further including the addition of natural fibres.

26. A method as claimed in claim 25 wherein the natural fibres are straw, hemp, flax, kenaf and/or cellulose.

27. A method as claimed in any preceding claim including the step of extruding the mixture through a die (16).

28. A method as claimed in any preceding claim including the step of further processing the mixture by injection or compression moulding.