WO1996028292A1

WO1996028292A1 - A process for reclaiming (meth)acrylate materials

Info

Publication number: WO1996028292A1
Application number: PCT/GB1996/000409
Authority: WO
Inventors: Philip Norton-Berry
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1995-03-09
Filing date: 1996-02-22
Publication date: 1996-09-19
Anticipated expiration: 1997-09-09
Also published as: TW325489B; GB9504719D0; AU4728096A; EP0873228A1

Abstract

A process for reclaiming a reinforced acrylic article comprising a GRP layer bonded to an acrylic layer in which a portion of the acrylic article is subjected to a shear cutting action of such force that the acrylic layer is substantially detached from the GRP layer so as to produce a crude product comprising a mixture of particulate acrylic polymer which is substantially free of GRP, glass fibre which is substantially free of polyester, polyester which is substantially free of glass fibre and residual GRP which is substantially free from acrylic polymer. The mixture of glass fibre, polyester and residual GRP forms a useful new material which may be reused as a reinforcement material for other articles.

Description

A Process for Reclaiming (Meth)acrylate Materials

The present invention relates to a process for reclaiming (meth)acrylate based materials, in particular glass fibre reinforced acrylic articles such as acrylic baths backed by a glass reinforced polyester Glass fibre reinforcement is commonly used to provide additional stiffness and rigidity to articles moulded from poly( methyl methacrylate), PMMA Usually the glass fibre is applied to the reverse side of the moulded article as a mat, either woven or random, or as chopped fibres The glass fibre is held in position by a suitable resin, most commonly a polyester resin, which on curing provides a firm bond to the PMMA Traditionally, the separation of the glass fibre and cured polyester resin, collectively known as GRP, from the moulded PMMA is regarded as a difficult separation due to the tenacity of the GRP to remain adhered to the PMMA The separation is so problematic that it is preferred to consign defective or redundant articles containing GRP to landfill rather than attempt to reclaim either the GRP or PMMA The rising environmental concerns regarding the use of landfill and the fact that

PMMA is able to be depolymeπsed back to the original monomeπc methyl methacrylate at high efficiencies make it desirable to provide a facile process for the separation of the GRP reinforcement from PMMA articles

In WO 93/05883 there is disclosed a process for the reclaiming of fibre reinforcement from sheet moulded compound, SMC, in which the fibre is intimately associated with a thermosetting resin The disclosed process requires an initial shredding of the SMC with the subsequent sequential and repeated pulverisation and classification of the shredded material

In the present process there is required an initial shearing action on the GRP reinforced PMMA such that the relatively brittle PMMA is detached from the GRP and which is then subsequently separated from the GRP such that a large proportion of the by now loose glass fibres are in a form which is readily separated from the PMMA thereby providing a relatively GRP-free PMMA product which can be depolymeπsed and a relatively PMMA-free GRP product which may be further classified and at least in part be reused as reinforcement material

Accordingly, in a first aspect, the present invention provides a process for reclaiming a reinforced acrylic article comprising a GRP layer, containing glass fibre reinforcement and a polyester, which is directly bonded to an acrylic layer containing an acrylic polymer which process comprises subjecting a portion of the acrylic article to a shear cutting action of such force that the acrylic layer is substantially detached from the GRP layer so as to produce a crude product comprising a mixture of particulate acrylic polymer which is substantially free of GRP, glass fibre which is substantially free of polyester, polyester which is substantially free of glass fibre and residual GRP which is substantially free from acrylic polymer Where appropriate, the reinforced acrylic article may undergo an initial comminution stage in order to produce pieces of material of a suitable size for the equipment in which the shear cutting is performed Typically, an acrylic bath is reduced to pieces of approximately 30 cm by 30 cm prior to shear cutting

The shear cutting action may be differentiated from the pulverisation action of the prior art in that in shear cutting the blades or other suitable cutting surfaces pass each other in a scissor like action (or for instance the action used in a cylinder lawn mower) between which the material which is to be cut is trapped whereas in a pulverisation action an accelerating force is provided to the material which causes it to impact on some other surface with such a percussive force that the material loses its structural integrity The material undergoing shear cutting may be thought of having a portion which is being cut off from the remainder of the material This portion may be referred to as the bite of the shear cutting device For a given material and cutting device it is possible to determine by simple experimentation the particular combination of shear force and range of bite size which causes the acrylic layer to be detached from the GRP layer If insufficient shear force is applied for a given bite size then the acrylic layer will not be sufficiently detached from the GRP whereas if too much shear force is applied for a given bite size then the acrylic layer tends to fall into such fine pieces that subsequent separation of the acrylic pieces from the pieces of GRP and residues of polyester resin and fibres is difficult

The crude product may be classified using known techniques of air classification and sieving so as to separate a substantial proportion of the acrylic polymer flakes from the glass fibre, polyester and residual GRP However, such a separation may be more readily accomplished by utilising a preferred feature of the present invention which comprises a table separator which is longitudinally and transversally inclined and which table separator is oscillated in an approximately circular motion in the general plane of the table Various outlets may be positioned around the perimeter of the table so as to receive appropriate fractions of the crude product which is fed to the table, preferably continuously, at a desired feed position The denser material, principally acrylic polymer will tend to move further up the length of the table whereas the lighter glass fibre, polyester and residual GRP will tend to accumulate lower down the table and by suitable transversal tilting of the table can be removed along the lower side of the table Fortuitously the oscillatory motion of the table has a tendency to cause at least some of the glass fibre to ball together Furthermore, by exposing the balled glass fibre, the polyester and the residual GRP to a fluidising air stream, for example by providing perforations in the table through which sufficient a volume of air is blown so as to achieve a suitable superficial air velocity, at least some of the balls of glass fibre may be fluidised and carried off from the table at lower air velocities than those required to remove the individual glass fibres. The volumetric rate of the fluidising air, and hence the superficial air velocity, used to remove the balls of glass fibre from the table may also be chosen so as to remove at least some of the polyester and GRP from the table thereby leaving a relatively pure fraction of acrylic polymer to be collected which may be depolymeπsed without significant further treatment and providing an eluted stream containing the eluted glass fibre, polyester, GRP and preferably a relatively small amount of or no acrylic.

Accordingly, in a second aspect the present invention provides a reclaimed mixture obtainable from such an eluted stream which reclaimed mixture comprises glass fibre, polyester, and residual GRP having the following size distribution (as expressed by the % by weight of the reclaimed mixture retained on a sieve having a mesh of the appropriate size)

(A) greater than 2 mm - from 5 to 20 % by weight

(B) greater than 0 3 mm to 2 mm - from 35 to 45 % by weight

(C) 0.3 mm and less - from 35 to 60 % by weight and wherein in fraction (B) a significant proportion of the glass fibre is present in the form of balls

Fraction (A) may more typically represent from 8 to 16 % by weight of the reclaimed mixture Within fraction (A), from 0 1 to 5 %, more typically from 0 3 to 1 5 % (by weight of the reclaimed mixture) may be greater than 4 mm. Fraction (B) may more typically represent from 38 to 42 % by weight of the reclaimed mixture. Within fraction (B), from 5 to 20 %, more typically from 8 to 14 % (by weight of the reclaimed mixture) may be greater than 1 mm to 2 mm

Fraction (C) may more typically represent from 40 to 45 % by weight of the reclaimed mixture Within fraction (C), from 10 to 20 %, more typically from 12 to 16% (by weight of the reclaimed mixture) is 0.1 mm and less

The individual fractions may be separated from each other using conventional separating techniques

The reclaimed mixture, preferably one or more of fractions (B), (C) and that part of fraction (A) having a size of up to 4 mm, may be reused as a reinforcing agent, particularly in combination with polyester or acrylic resins, for strengthening moulded acrylic articles such as acrylic baths and the like Fractions (B) and (C) have particular utility as reinforcement material, either alone, together or when supplemented by fresh glass fibre, in such moulded articles or other GRP strengthened systems Typically, a handlable GRP system containing 65 % or less, preferably 60 % or less, and particularly from 15 to 45 % by weight of the respective fraction may be formed As fraction (C) generally contains a significant amount of polyester powder, also known as dust, it is usual that a GRP system using fraction (C) can contain a higher proportion of it, e g from 30 to 45 % by weight, than a comparable system using fraction (B)

It is preferred that the fractions of the reclaimed material which contain the glass fibre balls are reused as reinforcement material once the balls are disentangled Surprisingly, the balls of glass fibre are relatively easily disentangled

Conveniently the reclaimed material may be applied as reinforcement by the use of a conventional GRP spray gun Such a spray gun typically comprises a glass fibre delivery system which feeds glass fibre tow to an air driven chopper The chopper cuts the glass fibre tow into an appropriate size and directs the chopped tow using the exhaust gas from the chopper into the fan of resin issuing from the nozzle of the spray gun The chopped tow is wetted by the resin and is carried by the resin towards the face of the article to be reinforced The reinforced material may be conveniently conveyed to the fan of resin by pneumatic means which also serves to disentangle the balls of glass fibre The reclaimed material is then applied to the face of the article in a manner similar to that used for the glass fibre tow and may also be supplemented by the application of fresh tow at the same time

Using the combination of shear cutting and table separator typically 90 %, more preferably from 95 to 98 % and particularly about 96 % of the acrylic in the reinforced acrylic article may be recovered for depolymeπsation or otherwise reused Typically, a GRP reinforced acrylic bath comprises an acrylic layer of about 3 mm depth and a GRP layer of comparable thickness Often, the bath is further strengthened by the use of a wooden baseboard which is incorporated into the reverse side of the acrylic bath It is preferred that such a baseboard is removed prior to the reclaiming of the bath as some of the denser material may remain with the reclaimed acrylic polymer Nevertheless, it is possible to perform the comminution of the bath with the baseboard in place However, the definition of the reclaimed mixture above is on the basis that the reclaimed mixture is free from contaminants such as comminuted baseboard

The present invention is further described by reference to the following figures, in which Figure 1 is a plan view of a table separator capable of separating the crude product into various fractions,

Figure 2a is a photograph of a sample of fraction (A) having a size greater than 4 mm,

Figure 2b is a photograph of a sample of fraction (A) having a size greater than 2 mm to 4 mm,

Figure 3a is a photograph of a sample of fraction (B) having a size greater than 1 mm to 2 mm,

Figure 3b is a photograph of a sample of fraction (B) having a size greater than 0 3 mm to 1 mm, and Figure 4 is a photograph of a sample of fraction (C) having a size greater than 0 1 mm to 03 mm

Figure (1 ) shows a table separator (1 ) having a feed zone (2) into which is introduced a crude product comprising acrylic polymer flakes, glass fibre, polyester and residual GRP The table separator (1) has off-takes (3, 4, 5, 6, 7, and 8) for various fractions of material The table separator (1 ) is inclined along direction B such that the feed zone (2) is generally higher than off-takes (3, 4, 5, 6, 7 and 8) and along direction A such that off-take (3) is generally lower than off take (8) A clockwise rotational motion may be applied to the table separator (1 ) in the general plane of the table so as to promote the separation of the material on the table into fractions according to their respective densities This rotational motion may also promote the formation of balls of glass fibre In use acrylic polymer tends to be migrate towards off-takes (7 and 8) whereas the lighter glass fibre, polyester and GRP tend to migrate to off-takes (3, 4, 5 and 6) from where the material may be collected, returned to the separator or recycled to a previous comminution stage The table separator (1 ) may be perforated with perforations (9) through which air may be blown at such a rate that the superficial velocity of the air above the table is able to preferentially fluidise and elute at least some of the glass fibre balls, and preferably at least some of the polyester and the residual GRP

Figures 2a and 2b show that fraction (A) mainly contains relatively large bundles of glass fibre with few balls of glass fibre being evident

Figures 3a and 3b show that fraction (B) contains a significant number of relatively large balls of glass fibre

Figure 4 shows that fraction (C) may still contain balls of glass fibre but that the predominant component is polyester dust

The present invention is further illustrated by reference to the following Examples

In the Examples, a proprietary cutter and separator system commonly used for the separation of metal wire from its sheathing of plastic material was employed The system known under the trade name "Firefox" and obtainable from Retech Recycling Technology AB, comprises a comminutor, also known as a granulator, which accepts material for shear cutting The cutting is performed by the action of five cylindncally mounted rotating knives against two co-operating stationery knives The cylindncally rotating knives are each 0 5 m in length, have a 5° cut angle and are driven by a 37 kW motor

The reinforced acrylic material used in the Examples was prepared by pre-cutting a standard GRP reinforced acrylic bath with baseboard removed into pieces of approximately 30 cm by 30 cm The crude product obtained from the comminutor was then conveyed by vibratory feeder and belt conveyer to a table separator The table separator had an overall length of 1 2 m and was perforated to allow the use of fluidising air up to a maximum rate of 3000 m³ hr¹ In the Examples the table was inclined to the horizontal by 6° along direction A (as defined in Figure 1 ) and by 3° along direction B (as defined in Figure 1 ) Six off-takes were positioned along the length of the table of which the two furthest from the inlet zone were usually used to collect acrylic polymer [Example 1

Over a period of 20 minutes 140 kg of GRP reinforced acrylic bath were fed to the comminutor and reduced to a size that allowed the crude product to pass through a mesh screen having apertures of diameter 10 mm on the exit from the comminutor The crude product from the comminutor was then fed to the table separator 71 kg of material was fluidised and eluted from the table separator and 69 kg of acrylic polymer was reclaimed The eluted material, which represents the reclaimed mixture of the present invention, had the following size distribution (expressed as % weight of the reclaimed mixture) (i) greater than 4 mm 1 2 %

(ii) greater than 2 mm to 4 mm 14 6 % (in) greater than 1 mm to 2 mm 13 6 %

(iv) greater than 0 3 mm to 1 mm 26 8 %

(v) greater than 0 1 mm to 0 3 mm 31 6 %

(vi) 0 1 mm and less 12 4 %

Fractions (in) and (iv), which when combined form fraction (B), contained a significant number of relatively large balls of glass fibre EΞxample 2

Example 1 was repeated except that the apertures were of 8 mm diameter and 261 kg of material was processed of which 126 kg was eluted from the table separator

The eluted material which represents the reclaimed mixture of the present invention, had the following size distribution (expressed as % weight of the reclaimed mixture) (i) greater than 4 mm 0.4 %

(ii) greater than 2 mm to 4 mm 7.6 %

(iii) greater than 1 mm to 2 mm 8.8 %

(iv) greater than 0.3 mm to 1 mm 30.8 % (v) greater than 0.1 mm to 0.3 mm 35.0 %

(vi) 0.1 mm and less 16.2 %

Again, fractions (iii) and (iv) contained a significant number of relatively large balls of glass fibre.

Example 3 Example 1 was again repeated except that a total of 1040 kg of material was processed over a period of approximately 50 minutes. 538 kg of the material was eluted from the table separator.

Claims

1 A process for reclaiming a reinforced acrylic article comprising a GRP layer, containing glass fibre reinforcement and a polyester, which is directly bonded to an acrylic layer containing an acrylic polymer which process comprises subjecting a portion of the acrylic article to a shear cutting action of such force that the acrylic layer is substantially detached from the GRP layer so as to produce a crude product comprising a mixture of particulate acrylic polymer which is substantially free of GRP, glass fibre which is substantially free of polyester, polyester which is substantially free of glass fibre and residual

GRP which is substantially free from acrylic polymer 2 A process as claimed in claim 1 wherein the crude product is subjected to a classification process such that a substantial proportion of the acrylic polymer flakes is separated out from the glass fibre, polyester and residual GRP

3 A process as claimed in claim 2 wherein the classification process causes at least some of the glass fibre to ball together 4 A process as claimed in claim 3 wherein the balls of glass fibre, the polyester and the residual GRP are exposed to a fluidising air stream so as to form an eluted stream of material comprising at least some of the balls of glass fibre and optionally at least some of the polyester and the residual GRP

5 A reclaimed mixture obtainable from an eluted stream as defined in claim 4, which reclaimed mixture comprises glass fibre, polyester and residual GRP having the following size distribution (as expressed by the % by weight of the mixture retained on a sieve having a mesh of the appropriate size)

(A) greater than 2 mm - from 5 to 20 % by weight

(B) greater than 0 3 mm to 2 mm - from 35 to 45 % by weight (C) 0 3 mm and less - from 35 to 60 % by weight and wherein in fraction (B) a significant proportion of the glass fibre is present in the form of balls