Reusable mat for removing liquid contaminants

This invention relates to a method for removing liquid contaminant from surfaces, especially for removing spilled oil from the surface of water. More particularly, this invention relates to a method for removing liquid contaminant from a surface by applying a mat which is a nonwoven fabric having a dried substantially continuous aqueous foam coating on at least one side of the nonwoven fabric, whereby the foam coating absorbs at least some of the liquid contaminant. This invention also relates to a reusable mat for removing liquid contaminants from surfaces and a method for reusing the mat.

This invention relates to a method for removing liquid contaminants from 
surfaces, especially for removing spilled oil from the surface of water. 
More particularly, this invention relates to a method for removing liquid 
contaminant from a surface by (a) forming a nonwoven fabric; (b) applying 
a substantially continuous aqueous foam coating composition having an air 
to liquid ratio from 5 to 1 to 20 to 1 by volume and incorporating an 
emulsion polymer binder, to at least one side of the nonwoven fabric; (c) 
drying the foam coating; and (d) placing the dried foam coating on the 
liquid contaminant, whereby the foam coating absorbs at least some of the 
liquid contaminant. This invention also relates to a reusable mat for 
removing liquid contaminants from surfaces and a method for reusing the 
mat. 
The present invention serves to provide a liquid sorbant mat in which a 
polymeric foam coating provides for absorption of the liquid contaminant 
and transport of the liquid contaminant to a nonwoven substrate which may 
serve as a reservoir for the contaminant. In the case of absorbing 
substantially water-insoluble liquid from the surface of water, the foam 
coating also functions as a selective barrier by substantially preventing 
the passage of water to the nonwoven and also serves a role in ensuring 
flotation of the mat, i.e., that the density of the foam-coated mat is and 
remains lower than the density of the water during the desired exposure 
time. The liquid sorbant mat is mechanically strengthened by its nonwoven 
component, strength which is required for handling, use and, especially, 
for reuse by mechanically expelling absorbed liquid from the mat. 
U.S. Pat. No. 4,031,839 discloses a reusable oil-absorbing pad in which the 
absorbent pad is contained in an inner and an outer bag. The reusable pad 
consists of a particulate mass of expanded open pore resin, particularly 
of alternating layers of large (10,000 to 5,000 microns) medium (5,000 to 
2,000 microns) and small (less than 2,000 microns) particles of expanded 
synthetic material such as rigid polyurethane foam. However, the assembly 
of the pads from separate components and the provision of particles of 
particular sizes adds production complexity and cost to the absorbent pad. 
GB 1,414,826 discloses an oil-capturing network structure formed from a 
foamed resin filled with an inorganic calcium compound such as a 
polyethylene and 30-80 wt. % calcium sulfate into which a liquefied gas 
has been introduced under pressure and released. The structure is 
disclosed to be readily disposable such as by incineration after use. 
However, additional reinforcement of the structure which would facilitate 
reuse was not disclosed. 
The problem faced by the inventors is the provision of an alternative 
method for removing liquid contaminant from a surface such as, for 
example, oil from the surface of ocean water with a reusable absorbent 
structure; a reusable absorbent mat suitable for removing liquid 
contaminant from a surface; and a method for reusing a mat suitable for 
removing liquid contaminant from a surface. 
In a first aspect of the present invention there is provided a method for 
removing liquid contaminant from a surface including: 
(a) forming a nonwoven fabric; 
(b) applying a substantially continuous aqueous foam coating composition 
having an air to liquid ratio from 5 to 1 to 20 to 1 by volume, the 
coating composition incorporating an emulsion polymer binder, to at least 
one side of the nonwoven fabric; 
(c) drying the foam coating; 
(d) contacting the liquid contaminant with the dried foam coating, whereby 
the foam coating absorbs at least some of the liquid contaminant. 
In a second aspect of the present invention there is provided for a 
reusable mat suitable for removing liquid contaminant from a surface 
including a nonwoven fabric bearing a substantially continuous dried foam 
coating, the coating including an emulsion polymer binder, and the dried 
foam coating having a density of from 0.02 to 0.10 grams per cubic 
centimeter, disposed on at least one side of the mat. 
In a third aspect of the present invention there is provided a method for 
reusing a mat suitable for removing liquid contaminant from a surface 
including: 
(a) contacting the liquid contaminant with a mat including a dried foam 
coating, the coating having a density of from 0.02 to 0.10 grams per cubic 
centimeter, the coating disposed on at least one side of a nonwoven 
fabric, whereby the foam coating absorbs at least some of the liquid 
contaminant; 
(b) removing the mat from any remaining liquid contaminant; 
(c) expelling at least some of the absorbed liquid contaminant; 
(d) placing the previously used foam coating on remaining liquid 
contaminant. 
The reusable mat suitable for removing liquid contaminant from a surface of 
this invention has at least two layers: a layer of nonwoven fabric bearing 
a layer of substantially open cell foam. Preferably, the nonwoven fabric 
is disposed between, and attached to, two layers of substantially 
continuous open cell foam. 
Preferred fibers constituting the nonwoven fabric are cotton, rayon 
polypropylene, nylon, and polyester. Polyester fibers are more preferred. 
Reclaimed soft drink bottles that have been made into a polyester fibers 
sold under the trade name Quline.TM. by Wellman Fibers, Inc. provide more 
preferred fibers for the nonwoven fabric. 
The nonwoven fabric is preferably between 0.1-5.0 cm. in thickness, more 
preferably between 0.15-2.5 cm. in thickness, and most preferably between 
0.25-1.3 cm. in thickness. The preferred nonwoven fabric is made by first 
carding polyester fibers, then, optionally, bonding the fibers, preferably 
by resin bonding or heat treatment, and, finally, needle punching the 
bonded non-woven fabric to give it added strength. Depending on the fiber 
used, the strength and other properties desired, any other method of 
manufacturing the substrate may be used. For example, nonwoven fabrics 
made from carded fibers, needle punched fibers, thermally bonded fibers, 
or resin bonded fibers may be used. 
In addition to the nonwoven fabric, the mat has at least one layer of 
open-cell foam coating attached to it. By "open-cell foam coating" herein 
is meant a coating containing, when dried, holes or pores or cells, the 
predominant number of which are connected to other pores, thereby 
providing channels available for liquid transport from the outer surface 
of the foam coating to the nonwoven to which it is attached. By "attached" 
to the nonwoven herein is meant that the foam coating, which is applied to 
the nonwoven as an aqueous coating and then dried, is sufficiently affixed 
to the nonwoven that the dried coating does not become substantially 
delaminated or separated from the nonwoven during the formation, use, or 
reuse of the reusable mat of this invention. The open cell foam is 
believed to act as a selective barrier. The foam layer substantially 
prevents the nonwoven fabric from absorbing water when the liquid 
contaminant to be removed is floating on water and may aid in retaining 
absorbed liquid contaminant by acting as a reservoir. The foam coating 
composition contains at least one emulsion polymer formed by the emulsion 
polymerization in predominantly aqueous medium by conventional techniques 
of at least one ethylenically-unsaturated monomer such as, for example, 
C.sub.1 -C.sub.22 alkyl (meth)acrylates, styrene, butadiene, vinyl 
acetate, vinylidene chloride, vinyl chloride, ethylene, 
(meth)acrylonitrile; or polyurethane emulsions; or mixtures thereof Low 
levels such as from 1-10% of functional monomers bearing carboxylic acid, 
hydroxyl, etc. groups may also be incorporated into the emulsion polymer. 
A preferred foam contains an emulsion polymer formed by the emulsion 
polymerization of a predominant amount of at least one C.sub.2 -C.sub.4 
alkyl acrylate. 
The foam coating composition contains the emulsion polymer. Prior to 
foaming, it is preferred to adjust the pH of the foam coating composition 
to between 8.0 and 10.0, preferably with ammonium hydroxide. The foam 
coating composition may also contain pigments and foaming aids, such as 
surfactants and foam stabilizers. In addition, colorants, thickeners, 
cross-linkers, anti-static agents, antimicrobial agents, silicones, 
fluorocarbons, and flame retardants, for example, may be added. Pigments 
which may be used include clays, titanium dioxide, talc, feldspar, 
pyrophyllite, alumina and calcium carbonate. In some cases no pigment is 
used. The pigment amount is typically from 0 to 400 parts by weight of dry 
pigment per hundred parts dry emulsion polymer. Preferred is a pigment 
amount of about 140 to about 170 parts by weight of dry pigment per 100 
parts dry emulsion polymer. 
In order to produce a foam coating composition having the desired 
properties, that is, a microporous cellular structure with interconnecting 
cells, the aqueous foam coating composition is foamed or aerated to a blow 
ratio of 5 to 1 to 20 to 1, lower blow ratios providing insufficient void 
volume for effective absorption and higher blow ratios providing a fragile 
dried foam, and preferably 8 to 1 to 10 to 1. "Blow ratio" is defined 
herein as the ratio of parts of air to parts of liquid by volume and is a 
measure of the foam density. Foaming may be accomplished using any 
conventional industrial or laboratory equipment, for example, an Oakes 
foamer, a "Super Foamer" from Latex Equipment Sales and Service Co., a 
Hobart mixer, a Kitchen-Aid mixer or a hand mixer. 
The aqueous foam coating composition having the desired density is then 
coated onto the nonwoven fabric, typically without any surface treatment 
of the nonwoven fabric. Coating may be accomplished using any suitable 
coating method which gives the desired coat weight or thickness. For 
example, a Gardner knife, rod coater, or similar means can be used for 
this purpose. Although the aqueous foam coating composition may be applied 
to only one side of the nonwoven fabric, the aqueous foam coating 
composition is preferably applied to both surfaces of the nonwoven fabric. 
For example, a mat used to clean up oil in a garage need not be coated on 
both sides since preventing contamination of the nonwoven fabric is not an 
issue. However, a mat used to remove liquid oil from a body of water must 
be coated on both sides to prevent excess water absorption by the nonwoven 
fabric. The amount of foam applied is between 10 and 340 grams per sq. 
meter, preferably between 34 and 102 grams per sq. meter. The foam coating 
should preferably uniformly and continuously cover the entire substrate 
surface. Preferably, both surfaces of the mat are coated with the same 
amount of foam. The mat with the foam may be dried at between 100 and 
400.degree. F. to dry the foam and concurrently to affix the foam to the 
nonwoven fabric. The dried foam coating typically has a density of 0.02 to 
0.10 grams per cubic centimeter. 
The mat of the present invention can be made in either discrete pieces or 
in continuous bolts of mat material. The size of discrete pieces of mat 
material may vary from about 1 cm. by 1 cm, for small cleanup jobs, for 
example cleaning oil from skin, to about 10 meters by 10 meters, for large 
jobs, such as cleaning oil-contaminated water from a ruptured bulk oil 
tanker. The width of a continuous bolts of mat material may vary from 
about 2 meters to about 20 meters. A continuous bolt of mat may be as long 
as it can be made, for example between 20 and 100 meters. The size of the 
equipment available for mat handling dictates the final size of the mat. 
The handling equipment must accommodate the size of the mat, especially in 
the case where the mat is recovered after liquid contaminant absorption 
and the excess liquid contaminant is expressed from the mat to permit mat 
reuse. If mats are to be placed and taken up by hand, then smaller sizes 
are preferred. Removing oil contaminant from rough water generally 
requires mats of smaller size. 
The mat, whether used on a solid surface or on water, has sufficient 
strength that once liquid contaminant has been absorbed by the mat, the 
mat may then be compressed to remove excess liquid contaminant. The liquid 
contaminant collected in such a manner can be refined or otherwise 
appropriately disposed of The mats of the invention absorb between 5 and 
50 times their weight in liquid contaminant, preferably between 10 and 25 
times their weight in liquid contaminant. The mat may be compressed by any 
conventional means, for example, by running an liquid contaminant-soaked 
mat through a wringer. Preferably the mats can be reused up to 10 times. 
In one embodiment the mats of this invention are used for absorbing oil 
spilled in coastal waters or the open ocean. In this embodiment larger 
pieces of the mat are preferred to obtain good coverage of as much of the 
affected area as possible. The mats are retrieved after absorbing oil and 
the oil is removed by squeezing the mat and the mat is replaced in the 
ocean to absorb more oil.

EXAMPLES 
Example 1 
A foam coating composition was prepared; it contained 87.3 g emulsion 
polymer, poly(butyl acrylate/ethyl acrylate/methyl 
acrylate/acrylonitrile/N-methoylacrylamide/itaconic acid/methacrylic acid) 
to which 1.4 g ammonium hydroxide, 3.0 g melamine resin crosslinking 
agent, 1.2 g foaming agent, 4.3 g ammonium sterate, 1.0 g ammonium 
nitrate, 1.0 g silicone fluid and 0.8 g thickener were added. A 183 
g./m..sup.2 needle-punched Quline.TM. polyester mat was foam coated with 
128.8 g./m..sup.2 (64.4 g./m..sup.2 on each side) of an open cell acrylic 
foam that had been mixed in a Kitchen Aid.TM. blender until a blow ratio 
of 8 to 1 had been achieved. 
The foam compound latex was coated on the substrate using a Gardner knife 
at a thickness of 50 mils. The foam coating was dried in an oven at 
149.degree. C. and then the other side was coated and dried. 
A 6.35 cm. by 6.35 cm. square of the mat was placed in a large beaker of 
water which had a layer of motor oil (10w30) placed on top. The mat which 
weighed 1.1 grams absorbed 13 times its weight in oil. The mat was 
squeezed with nip rollers and reused two more times. The mat absorbed 
between 11 and 13 times its weight in oil each time. 
This example describes the method of making, using, and reusing the liquid 
contaminant-sorbent mat of the invention.