GB2069361A - Mopping up oil - Google Patents

Abstract

A method of removing oil from water or solid surfaces comprises contacting the oil with a pad consisting of a plurality of layers of polyolefin net joined together, until the oil is absorbed and thereafter removing the pad. The pad may comprise up to 36 layers of net alone or at least four layers of net sandwiching a layer of polyester fibre. Layers may be joined by quilting.

Description

SPECIFICATION Improvements to absorbent pad and use The present invention relates to the use of an absorbent pad, which is capable of taking up oil or like pollutants, to certain novel absorbent pads and to their preparation.

Oils are a common pollutant. At present oils are often removed from the environment by mopping them up with paper, fine polypropylene or the like.

Paper absorbents are cheap and have proved effective in a dry environment. However, in a moist environment such paper absorbents lack sufficient strength for convenient use. Known polypropylene absorbents are bulky and have proved somewhat expensive and also have a rather low mechanical strength. Clearly it would be desirable to provide an absorbent pad that can take up oil from a wet environment, has acceptable mechanical strength, is compact and is not prohibitively expensive.

Such a desirable pad has now been found to be useful in removing oil.

The present invention provides a method of removing oil from the environment which comprises contacting the oil with an oil absorbent pad which comprises polyolefin net constrained in contiguous configuration until oil is absorbed and thereafter removing the pad.

When used herein the term "polyolefin" includes polyethylene and polypropylene. A favoured polyolefin for use in the absorbent pad is high density polyethylene.

Nets suitable for use in this invention will aptly have a weight of 5 to 50 g/m2, will more suitably have a weight of 7 to 30 g/m2 and will preferably have a weight of from 10 to 15 g/m2. Normally the nets will have a hole area of 20 to 80%, more suitably 30 to 70% and preferably about 35 to 60%, for example about 35, 40, 45, 50, 55 to 60%. When used herein the percentage hole area is the ratio expressed in percentage terms between void spaces in the sheet surface and that part of the sheet surface occupied by polyolefin.

Normally the oil absorbent pad used in this invention will contain at least 4 sheets, favourably 6 to 50 sheets of net, more favourably 10 to 36 sheets and preferably 12 to 1 8 sheets. Aptly the present invention provides an oil absorbing pad which comprises 10 to 36 sheets of polyethylene net constrained in contiguous configuration. For very large scale oil ciearance a greater number of sheets may be employed, however the previously defined upper limit is sufficient for most domestic and factory oil pollution removal. The lower limit of the number of sheets is that below which the amount of oil taken up is too low for convenient use. When pads containing low numbers of sheets of net are used the pads will usually also comprise an absorption aid such as an interspacing net or polyester layer as hereinafter described.

The sheets in the absorbent pad are most suitably arranged in substantially overlapping form. Favoured pads will be rectangular with sides of 250 mm to 800 mm and a depth of 1 mm to 1 5 mm. Particularly suitable pads will be square with sides of 30 cm to 50 cm and a depth of 2 mm to 10 mm. However since oil pollution can occur on a very large scale much larger scale use of pads of oil absorbing materials are also envisaged, for example in the form of elongate booms which may be many metres long and up to about two metres wide.

Other suitable constructions for the oil absorbing pad are as described in British Patents Specification No. 1 276,300 the disclosures of which are included herein by cross-reference.

Nets for use in this invention will most suitably be those with integral junctions, for example those produced by biaxially stretching embossed sheets of polyolefin.

The nets that are favoured for use in the present invention will be non-woven, non-knotted, openwork structures comprising a plurality of bosses arranged in a plurality of rows extending substantially uniformly through the structure, substantially all of which bosses are integrally joined to at least two other such bosses by bands of polyolefin.

Suitable nets of the aforementioned types include those described in British Patent Specifications Nos. 1,055,963, 1 ,075,487, 1,261,515, 1,496,786 and 1,548,865. Nets of this type are presently available from Smith and Nephew Plastics Ltd., P.O. Box 202, English Street, Hull, HU3 2BN, England. Specific nets presently available from Smith and Nephew Plastics Ltd. which may be used in this invention includes those under their code nos. X540, X530, X240, X230, X220, D2 18, D2 11, P2 15, 0225, A7, H6, KS325A and GS110 (of which the iast two are polypropylene and the remainder polyethylene nets).

A favoured net for use in this invention is X540.

This net is of the type described in British Patent Specification No. 1 ,055,963 and is a net made by biaxially stretching by about 2.5 X in both longitudinal and transverse directions. X540 net has a boss count of 16 to 20 in the machine direction and 20 to 25 in the transverse direction.

Each boss is connected to six thin strands. The net has an overall thickness of 5 to 6 thou., a weight of 11.6 to 1 6.6 g/m2, a tensile strength of 600 to 800 g/cm in the machine direction and 300 to 600 g/cm in the transverse direction.

In addition to the nets hereinbefore described the oil absorbing pad of the invention may advantageously comprise an additional inner absorption sheet, for example of oil abosrbing fibres.

A favoured oil absorbing pad of this type contains at least 4 sheets of net and an additional absorption sheet comprised of an oil absorbing fibre.

Suitable oil absorbing fibres include fibres of polypropylene, polyethylene and polyester. A preferred oil absorbing fibre is polyester fibre.

A favoured oil absorption sheet comprises a needled sheet of undrawn polyester fibres.

The absorption sheet will usually have a weight of 50-500 g/m2 and preferably of 200-300 g/m2. The absorption sheet will usually have a thickness of 2 mm to 10 mm and preferably of 4 mm to 6 mm.

Preferably the absorption sheet is slightly smaller than the net sheets so that the net sheets enclose the absorption sheet in the soil absorbing pad.

A preferred oil absorbing pad comprises a needled sheet of undrawn polyester fibres between two pairs of net such as X540 net. Such a preferred oil absorbing pad of the invention can generally absorb at least of twenty five times its own weight of oil.

In addition to the nets previously described, it may be advantageous for the oil absorbing pad to include layers of an interspacing net. Suitable interspacing nets will have hole areas of at least 85% and generally at least 90%, for example 95 to 98%. Suitable open nets include square nets in which the holes are 2 x 2 mm to 8 x 8 mm and preferably about 5 x 5 mm. Such open nets will generally have a weight of 10 to 20 g/m2, aptly 12 to 16 g7m2 and favourably about 14 g/m2.

If desired, the ratio of sheets of interspacing net to sheets of embossed nets may be as high as 1:1 but in general a ratio of 1:2 to 1:12 is more apt and a ratio of 1:4 to 1:12 particularly suitable.

These internal layers of interspacing net are normally regularly spaced, for example 6 layers of embossed net, one layer of interspacing net and 6 layers of embossed or the like. In addition to the internal layers the absorbent pad may also be faced with such an open net. The presence of the interspacing net improves yet further the good flotation characteristics of the oil absorbing pad of this invention and improves yet further the good oil uptake characteristics of the oil absorbing pad of this invention.

The means of constraint for the oil absorbing pad may comprise any convenient method of fixing the sheets in place. An apt method comprises sowing the sheets together, for example along one or both pairs of opposing edges for rectangular pads. An alternative method is to weld the layers together. Such welding may advantageously take place along one or both pairs of opposing edges for rectangular pads and may be intermittent or continuous. Heat welding of the layers may be used. Ultrasonic welding of the layers is also envisaged.

One method of fabrication of the pads is to form a stack of the individual layers and then Intermittently spot weld them along their edges.

An alternative method would be to produce an elongate pad, weld along its long edge and then cut the welded elongate pad into the desired lengths. British Patent Specification No. 1,276,300 may be consulted for methods of preparing pads.

A preferred method of constraining the sheets in a continuous configuration is by quilting. In a further aspect the present invention provides an oil absorbing pad which comprises at least 4 sheets of polyolefin net constrained in contiguous configuration by quilting.

The term "quilting" as used in this specification means fastening sheets together by stitches or lines of stitching or equivalent means which includes welding and adhesive bonding. Suitable methods of quilting are described in British Patent No. 1,162,978.

The quilting lines can intersect to give an overall pattern of shaped areas such as triangles, squares, rectangles, parallelograms and other geometric shapes. Such quilting patterns can subdivide the oil absorbent pad of the invention into separate absorbent areas which has the advantage of restricting the flow of the absorbed oil between the areas and thus restricting the absorbed oil draining from the edges of the pad.

It is an advantage of this invention that the liquid oil to be removed may be taken up from contaminated solid or liquid surfaces.

After use, the oil soaked pad may be disposed of thereafter in convenient manner. Some oil may, r if desired, be recovered by squeezing the pad to liberate the oil from the interstices thereof.

The preferred pads for use in this invention are novel. Hence the present invention also provides an oil absorbent pad which comprises a plurality of sheets of polyolefin net constrained in contiguous configuration and at least one sheet of interspacing net as hereinbefore described.

The use of crimping layers of the type disclosed in the aforementioned Specification No. 1,276,300 has the advantage of providing good oil retention after uptake. This may be due at least in part to the provision of portions of net oriented at a different plane to the main surface of the oil absorbent pad. The presence of net at an angle to the main oil absorbing surface is thus believed desirable.

A favoured method for removing oil according to this invention will thus comprise contacting the oil with an oil absorbent pad which comprises a polyolefin net constrained in contiguous configuration until oil is absorbed and thereafter removing the pad and is further characterised in that the pad is applied with at least part of the net matrix perpendicular to the oil surface.

A suitable form of the pad for use in this aspect of the invention comprises a disc of net in which the net matrix is perpendicular to the major surface of the disc.

Such a disc may be prepared by forming a roll of net and then slitting the roll into thin widths which are suitable for laying on an oil impregnated surface. A disc of 20 cm diameter and 1 cm thickness would be appropriate. Alternatively a net tape could be produced and wound around a former to form a disc. Such discs may be sealed to prevent displacement of configuration if desired.

The preceeding discs may be constrained between layers of net which lie parallel to their major surfaces.

In another form small rolls of net may be constrained between two facing net layers.

The various preceeding embodiments may be used in combination, for example a construction may be employed comprising four layers of net, a disc of net and a further four layers of net or the like.

Another convenient method of ensuring that the pad presents at least part of its matrix at right angles to the oil surface is to use folded layers. A suitable form of this embodiment would comprise a single length of net, for example 2 m long and 20 cm wide loosely folded into ten lengths of about 20 cms so that the final pad would be approximately 1 8 cm x 20 cm in area. The pad could be constrained to this form by stitching along the edges or the like.

The invention is illustrated by the following examples.

EXAMPLE 1 A pad may be prepared by stacking 8 layers of X540 net, one layer of interspacing net and a further 8 layers of X540 net. The net layers employed may be square having 400 mm sides.

The open net employed may have a weight of 14 g/m2 with voids 5 x 5 mm which account for 95 to 98% of surface area. The 17 layers may be held together by stitching along their margins.

A pad as described may be used to remove spilled oil from a flat surface by placing the pad on the oil, leaving for about a half minute and then removing the pad with the absorbed oil.

A pad as described may be used to remove oil from a water surface by presenting the pad to the surface in a parallel plane. The pad may be presented to the surface by hand or by machine such as a boom being drawn across the surface.

When the oil is taken up, or it appears no more oil is being taken up, the pad and the absorbed oil is removed.

EXAMPLE 2 An oil absorbing pad was made from a 50 cm wide X540 net folded into 1 5 layers to form a 50 cm square pad. The pad layers were fixed by quilting using stitching. The stitching extended in lines across and around the periphery of pad to give a quilting pattern of approximately 1 2 cm squares. The pad had a weight of 263 grams.

The pad was floated onto the surface of a 10 W 30 multigrade oil (Alexander Duckham and Co. Ltd.) in a tray. The pad became fully saturated in 30 to 40 seconds. The pad was carefully removed from the tray of oil and weighed where it was found to have absorbed 2314 g of oil. The pad was vertically suspended for approximately 5 minutes to allow oil to drain out by dripping. The pad was again weighed and found to have retained 144 g of oil. The pad was then squeezed by hand. On weighing it was found that the squeezed pad had retained 894 g of oil.

EXAMPLE 3 An oil absorbing pad of the invention was made by placing a 50 cm square needled sheet of undrawn polyester fibres (250 g) between four 50 cm square sheets of X540 net (two sheets on either side) and the sheets fixed by quilting using stitching. The stitching extended in lines, across and around the periphery of the pad to give a quilting pattern of approximately 12 cm squares.

The pad had a weight of 260 g.

The oil absorption and retention properties of the pad were measured in the same manner as example 2. The pad became fully saturated in 60 seconds and absorbed 6552 g of oil. After being vertically suspended the pad retained 5720 g of oil. After squeezing by hand the pad retained 5200 g of oil.

Claims (12)

1. A mathod of removing oil from the environment which comprises contacting the oil with an oil absorbent pad which comprises polyolefin net constrained in contiguous configuration until oil is absorbed and thereafter removing the pad.

2. A method as claimed in claim 1 wherein the net is a polyethylene net which has a weight of 7 to 30 g/m2 and a hole area of 30 to 70%.

3. A method as claimed in claims 1 or 2 wherein the pad contains 10 to 36 sheets of polyolefin net.

4. A method as claimed in claims 1 or 2 wherein the pad contains at least 4 sheets of net and an additional inner absorption sheet comprised of oil absorbing fibre.

5. A method as claimed in claim 4 wherein the oil absorbing fibre is polyester.

6. A method as claimed in any of claims 1 to 5 wherein the sheets are constrained in contiguous configuration by quilting.

7. An oil absorbing pad which comprises 10 to 36 sheets of polyethylene net constrained in contiguous configuration.

8. A pad as claimed in claim 7 wherein the net has a weight of 7 to 30 g/m2 and a hole area of 30 to 70%.

9. An oil absorbing pad which comprises a.

least 4 sheets of polyolefin net constrained in contiguous configuration by quilting.

10. A pad as claimed in claim 9 which consists essentially of 10 to 36 sheets of net.

11. A pad as claimed in claim 9 which also comprises an additional absorption sheet comprised of oil absorbing fibre.

12. A pad as claimed in claim 11 wherein the oil absorbing fibre is polyester.