GB2053944A - Utilisation of expanded polymer scrap - Google Patents

Abstract

Polyurethane and other foam scrap is incorporated in new foam after comminution to sub-cellular size, conveniently under cryogenic cooling in a "turbine" grinder as shown. <IMAGE>

Description

SPECIFICATION Utilisation of expanded polymer scrap The invention relates to the utilisation of expanded polymer scrap.

In the conversion to finished products of materials such as foam rubber and synthetic polymer foams of all kinds, for example flexible polyurethane foam, a considerable quantity of waste or scrap offcuts is produced. This scrap is at present used in low value products and represents a considerable economic loss of raw materials as well as a troublesome handling and storage problem.

To make use of the scrap one approach is to granulate it into particles about 5-10 mm diameter and bond them together with a suitable adhesive to give a large block of, for example, reconstituted polyurethane foam. Thie product, known in the trade as "Chipfoam" is easily recognised as a reconstituted product and does not command such a high price as "virgin" foam. Moreover, its physical properties are variable throughout its bulk, due to the variety of scrap foam types and densities that are used in its manufacture.

Another approach, in which the present invention lies, is to incorporate the scrap in fresh batches of expanded polymer, as a filler.

The broad concept of adding fillers to materials such as polyurethane foam is of course not new.

Inorganic fillers such as whiting (calcium carbonate), barytes (barium sulphate) or aluminium hydrate (aluminium hydroxide) have been used to reduce cost, increase density or confer some degree of fire retardancy. In all cases, however, the addition of inorganic fillers tends to reduce physical properties such as elongation at break and tear strength.

In order both to recycle waste foam off-cuts and to retain physical properties of the finished product, it wouid be desirable to incorporate the waste foam, in a convenient form.

We have found however that attempts to incorporate, for example, polyurethane foam in the form of granulated particles of the size used for "chipfoam", into new foam batches, result in a nonhomogeneous product and a high viscosity of the reaction mixture, making it difficult to mix and reducing flow.

We have realised, and this is the essential of one aspect of the present invention, that if the expanded polymer is broken down until it is no longer of cellular structure, it may be incorporated in new material, generally but not essentially of the same polymer, without difficulty and in particular without unacceptable effects on viscosity of the mixture. It can act as a fully compatible filler, with chemical bonding to the raw material in suitable cases.

According to requirements, one can obtain a product of greater density than would be given by the same volume of mix without recycled material or, by simple modification of the mix, a greater volume of product of the same density. As expanded polymers are generally sold by volume the advantage is clear.

The physical properties of the product are unimpaired by reasonable levels of addition, limits being readily set by trial. Less than 1% by weight of the foam product is hardly worth incorporating, while 50% can in practice not be exceeded. Levels of 5 to 30% will ordinarily be used. For example, seven per cent by weight of flexible polyurethane scrap incorporated in a flexible polyurethane foam mix gives a product essentially indistinguishable from the "virgin" foam without recycled product.

Reduction of the expanded polymer scrap to non-cellular powder, which is a novel product in itself and constitutes a further aspect of the invention, may most readily be achieved at temperatures at which the polymer is embrittled, for example at cryogenic temperatures given by liquid nitrogen or other liquefied gases. Cooling is however not essential, rigid polyurethane foams for example being capable of suitable comminution at ordinary ambient temperatures.

A "turbine" type grinder as sketched in the accompanying drawing may for example be used, allowing convenient flow of the cooling gas and collection of the product. It is constructed of stainless steel for low-temperature strength and is run for example at 8000 r.p.m. for grinding flexible polyurethane foam scrap. A screw feed 1 passes the chopped scrap together with a liquid nitrogen feed and recycled cold gaseous nitrogen to the interior of a rotor 2. Projections 3 on the rotor run at 2-3 mm clearance from sets of projections 4 on a static drum 5 to carry out the grinding. The ground material emerges from sieves 6 alternating with the sets of projections 4, and falls into a bag 7.The feed of liquid nitrogen, in contact with the polymer either as such or as a generated gas, rather than simple external cooling of the machine, is found desirable to obtain full cooling, given the poor head conductivity of such materials.

There is no restriction to any one cooling medium, nitrogen simply being convenient and inexpensive. Operating costs are for example about 10% of the raw material value represented by recycled flexible polyurethane foam.

The invention is further illustrated in the following examples relating to polyurethane foams, without restriction to such materials.

EXAMPLE 1 Foam of the type known as "high-resilient" polyurethane foam was powdered by the "freezegrinding" technique above to a mean particle size of approximately 50 microns. Examination of the particles under a microscope showed that there were no complete cells remaining i.e. the particles were sub-cell in size. The particles were irregular in shape, slightly elongated and in some cases, slightly branched.

The powdered foam was used as a filler in a high-resilience urethane foam mix as follows: 1A 1B Weight in Grams Propylan M 1 (Trade Mark) proprietary polyoxyalkylene triol 500 500 Water 12 12 Proprietary cross linking agent '74' 20 20 Triethanolamine 10 10 Dabco 33 LV (Trade Mark) proprietary catalyst 2.5 2.5 Trichloroethyl phosphate fire retardant 10 10 Glycerol 10 10 Foam scrap powder 50 Desmodur MT 58 (Trade Mark) proprietary isocyanate 285 285 The ingredients except for foam scrap powder and Desmodur MT58 were mixed together in a bucket by means of an electric stirrer. The foam scrap powder was then added directly to the premix and mixed in with the stirrer. The Desmodur MT58 was then added, the complete mix stirred for 10 seconds and then poured into a rectangular, paper-lined mould.

The foam mix expanded in the mould and after 20 minutes the finished foam block was removed and mechanically crushed to remove closed cells. The block was then allowed to cure for 24 hours.

Sample 1 B was produced in exactly the same manner as Sample 1 A, except that no scrap foam powder was added.

After the blocks had cured they were cut into 2" thick slices and examined.

The physical appearance of the foam samples 1 A and 1 B was very similar, there being no obvious indication that Sample 1 A was not a completely "virgin" mix.

A density measurement on the samples gave 37 kg/m3 for Sample 1 A and 34.5 kg/m3 for Sample 1B.

EXAMPLE 2 Foam of the type known as "polyether" slabstock polyurethane foam was powdered by the "freeze-grinding" technique to a mean particle size of approximately 20 microns.

The powdered foam was used as a filler in the same foam formulation as used in Example 1, at an addition level of 20 parts per 100 parts of Propylan M 1.

Again, a foam of normal appearance was obtained.

EXAMPLE 3 A foam powder of the type described in Example 2 was used as a filler in the following "polyethe? formation: Weight in Grams Desmophen 7000 (Trade Mark) proprietary polyoxyalkylene triol 500 Water 20 Proprietary silicone stabiliser 'OS20' 4 Desmorapid PS207 (Trade Mark) proprietary catalyst 0.6 Stannous octoate (catalyst) 1 Powdered foam scrap (polyether) 150 80:20 toluene diisocyanate 45 The powdered foam scrap was blended with all ingredients except the stannous octoate and the isocyanate. The stannous octoate was then added and mixed in. The isocyanate was then immediately added, the composition mixed for 10 seconds and then poured into a paper-lined rectangular mould.

Again, a foam of normal appearance was obtained.

EXAMPLE 4 A polyether foam powder of the type described in Examples 2 and 3 was added to a proprietary two part flexible cold-cure foam moulding mix (type RB 511 supplied by Lankro Chemicals).

The powder was added in a similar manner to that already described at a level so as to give a finished addition level of 20% by weight. The completed mix was poured into a cushion shaped mould, giving a product of normal appearance and properties.

EXAMPLE 5 A rigid polyurethane foam of density 30 kg/m3 was powdered by the same type of turbine grinder used in examples 14, but without the introduction of a cooling gas.

The powdered foam was added to a proprietary two part rigid foam mix (Lankro Rigid System Propacon MR93 (Trade Mark) consisting of part A - polyol blend, and part B - crude diphenylmethane diisocyanate) in the ratio 30 parts of powdered foam to 70 parts of foam chemicals, by weight. An increase in viscosity was noticed on addition of the powdered filler, but an acceptable foam was produced.

Claims (11)

1. Expanded polymer foam containing, as a filler, preformed expanded polymer foam of the same or different kind comminuted until no longer of cellular structure.

2. Foam according to claim 1, the filler in which has been made by cooling the preformed foam until brittle then comminuting it.

3. Foam according to claim 2, the cooling being cryogenic cooling by liquid nitrogen or other liquefied gas or gas generated therefrom, brought into direct contact with the preformed foam.

4. Foam according to any preceding claim, the comminution being in a turbine grinder.

5. Foam according to any preceding claim, being a polyurethane foam and with the filler prepared from a polyurethane foam.

6. Foam according to any preceding claim, containing 1 to 50% by weight of the filler.

7. Foam according to any preceding claim, containing 5 to 30% by weight of the filler.

8. A filler for polyurethane or other polymer foam, consisting of preformed polyurethane or other polymer foam broken down until no longer of cellular structure.

9. Filler according to claim 8, comminuted as set out in claim 2, 3, or 4.

1 0. Expanded polymer foam according to claim 1, substantially as herein described in any one of the Examples.

11. A filler according to claim 8, substantially as herein described in any one of the Examples.