GB2249989A

GB2249989A - Absorbent material from polyolefin film

Info

Publication number: GB2249989A
Application number: GB9025409A
Authority: GB
Inventors: Michael Hill
Original assignee: Filter Materials Ltd
Current assignee: Filter Materials Ltd
Priority date: 1990-11-22
Filing date: 1990-11-22
Publication date: 1992-05-27
Also published as: GB9025409D0

Abstract

Absorbent material is produced by fibrillating and then stretching polyolefin film. A material which may be used as an adsorbent for organic compounds such as oil. The material is buoyant in water and as such is able to be used to remove oil from the surface of contaminated water. The material is able to be reused after cleaning thereof. The material is preferably formed from polypropylene and is characterised by its primary and secondary longitudinally extending strands. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO ADSORBENT MATERIAL The present invention relates to adsorbent material and particularly, but not exclusively, to oil adsorbent material.

British patent specification number GB 1 442593 discloses a method of producing a material which is useful as a tobacco smoke filter material. The filter material of GB 1 442 593 has good filtration properties with regard to filtering out pyrolytic fragments contained in smoke aerosols and is accordingly useful in filtering out compounds such as nicotine and tar from tobacco smoke.

However, the material of GB 1 442593 is found to have a limited use in adsorbing large quantities of long chain carbon molecules and is accordingly of limited usefulness as an adsorbent for oil or grease compounds.

The problems generally encountered in producing an oil or grease adsorbent material are to create a material with a massive enough surface area to be practically useful, and to be able to cleanse the dirty surface of such a material, or remove adsorbed compounds from within the structure of the material, so that the material can be reused to adsorb further quantities of oil or grease, for example.

It is an object of the present invention to obviate the aforementioned problems.

The filter material of GB 1 442 593 is formed by fibrillating at least one polyolefin film. Polyolefins such as polypropylene are known to present a non-polar boundary surface structure of low surface energy and oleophilic in character. In this sense, it is not surprising that any polyolefin based material will adsorb semi or non-polar organic compounds. It has, however, surprisingly been found that by subjecting the material of GB 1 442 593 to at least a controlled stretching process there is produced a material of substantially increased surface area which has excellent adsorbtive properties with regard to long carbon chain molecules and thus comprises an excellent oil or grease adsorbent material.

Short carbon chain compounds are considered to include organic compounds whose constituent molecules have a carbon chain length between C1 and C22 and include organic compounds such as soot, nicotine and tar, for example. long carbon chain compounds are considered to include organic compounds whose constituent molecules have a carbon chain length substantially greater than C12, for example gear oil.

Accordingly, the- present invention provides a method of producing an adsorbent material which comprises fibrillating at least one polyolefin film to produce a fibrillated material having a plurality of longitudinally extending primary strands with generally interconnecting and free-ended lateral strands therebetween and subsequently subjecting said fibrillated material to at least a stretching process to produce at least secondary longitudinally extending strands formed from said primary strands.

The method of producing the adsorbent material may include an air blasting process comprising air jet means arranged to blast air on to the adsorbent material to entangle at least the primary and secondary longitudinally extending strands of the material, prior to collection thereof in or on collection devices.

The method of producing the adsorbent material may also include a crimping process to improve the structural integrity of the fibrillated material prior to the fibrillated material being subjected to the stretching process and thus enhance the structural integrity of the adsorbent material.

The crimping process to which the fibrillated material is subjected prior to being subjected to the stretching process may be stuffer box crimping.

Alternatively, the crimping process may be gear tooth crimping.

According to a second aspect of the invention there is provided an adsorbent material comprising a plurality of longitudinally extending primary strands with generally interconnecting and free-ended lateral strands therebetween characterised in that said material having undergone at least a stretching process also comprises at least secondary longitudinally extending strands formed from said primary strands.

Some of the interconnecting strands and laterally extending free-ends may peel away from the longitudinally extending primary strands during the stretching process thereby increasing the length of said interconnecting strands and laterally extending free ends but reducing their width and thus increasing the resultant surface area of the adsorbent material.

The polyolefin film from which the adsorbent material is subsequently formed may consist of polypropylene.

Alternatively the polyolefin film may consists of polyethylene or a mixture of polypropylene and polyethylene or a copolymer of propylene and ethylene.

The primary longitudinal strands of the adsorbent material may have a thickness in the range of 5 microns to 25 microns.

According to a third aspect of the invention there is provided apparatus for producing the adsorbent material comprising a primary roller having projecting pins thereon over which at least one polyolefin film is passed to produce a fibrillated material having a plurality of longitudinally extending primary strands with generally interconnecting and free-ended lateral strands therebetween; and first and second pairs of secondary rollers, the apparatus being arranged such that the fibrillated material passes through a first nip between the first pair of secondary rollers, and thereafter through a second nip between the second pair of secondary rollers, the material being stretched during its passage between the pairs of secondary rollers, to produce at least secondary longitudinally extending strands from said primary strands, the compression between at least the second pair of secondary rollers being such that the overall structural integrity of the adsorbent material so produced is not substantially impaired.

The apparatus for producing the adsorbent material may include at least one air jet means wherein the air jet means is arranged to direct a jet of air on to the adsorbent material prior to its collection in or on collection devices.

The apparatus to produce the adsorbent material may also include means to crimp the fibrillated material prior to its passage through the first nip between the first set of secondary rollers.

The crimping means may comprise a stuffer box crimper.

Alternatively, the crimping means comprises a gear tooth crimper.

The first and second pairs of secondary rollers may each comprise a non driven superior roller a#nd a driven inferior roller wherein each pair of superior and inferior rollers are urged together to form therebetween the first and second nips respectively.

The ratio of the peripheral velocity of the first inferior roller to the second inferior roller preferably lies in the range of 1.01: 1-2.5.

The superior rollers may have a smooth rubber coated surface.

The inferior rollers may be made of metal and may have castellated surfaces.

The foregoing and further features of the present invention may be more readily understood from the following description of a preferred embodiment, by way of example thereof, with reference to the accompanying drawings, of which: Figure 1 shows a portion of the adsorbent material according to the invention expanded laterally to show the network formation thereof; Figure 2 shows in enlarged scale a portion E of the adsorbent material of fig 1.

Figure 3 shows a side schematic view of a process apparatus for producing the adsorbent material of figure 1; Figure 4a & b show side schematic views of alternative stretching means utilised in the process apparatus of figure 3; Figures Sa, b and c show partial cross sectional views along the longitudinal axis of each of a number of alternative secondary rollers employed in the alternative stretching means of figures 4a & b.

Referring to the drawings, figure 1 shows a laterally expanded portion of an adsorbent material 10 showing the network formation of said material 10.

The adsorbent material 10 comprises a plurality of longitudinally extending primary strands-~12 with interconnecting strands 14 and free-ended lateral strands 16 extending therebetween. Some of the primary strands 12 and some of the interconnecting strands 14, having undergone a stretching process, have portions thereof consisting of at least secondary longitudinally extending strands 18.

Figure 2 shows an enlarged view of a portion E of the adsorbent material 10 of figure 1 showing in more detail some of said secondary strands 18 formed from a portion 20 of a primary strand 12a and also showing in detail a first interconnecting strand 14a which has been caused, under the action of the stretching process, to peel away at a junction 22 with a second interconnecting strand 14b. The first and second interconnecting strands 14a & b have become elongated in length and of reduced width thus increasing the resultant surface area of the adsorbent material 10.

The formation of secondary strands 18 from at least some primary strands 12 and the peeling of at least some interconnecting strands 14 away from junctions with other strands 12, 14, 16 greatly increases the resultant surface area of the adsorbent material 10.

Figure 3 shows a schematic illustration of a process apparatus 22 utilised in the production of the adsorbent material 10. The apparatus 22 comprises means 24 for fibrillating at least one polyolefin film 25 to produce a fibrillated material 26, means 28 for crimping said fibrillated material 26, means 30 for partially stretching said fibrillated material 26 to produce the adsorbent material 10, air jet means 32, and means 34 for collecting the processed adsorbent material 10.

Figure 4a & b show side schematic views of alternative stretching means 30 utilised in the process apparatus 22 to produce the adsorbent material 10, each of the alternative stretching means 30 comprising at least a first pair of secondary rollers 36 and a second pair of secondary rollers 38.

Each pair of secondary rollers 36, 38 is comprised of an upper superior roller 36a, 38a and a lower inferior roller 36b, 38b respectively wherein the superior roller 36a, 38b is, in each case, held against the inferior roller 36b, 38b-pneumatically, hydraulically or by other suitable means to form a nip between said rollers 36, 38 and through which, in use, the fibrillated/adsorbent material 26, 10 will be passed. The inferior rollers 36b, 38b are driven whereas the superior rollers 36a, 38b are free running.

The secondary rollers 36, 38 may be formed from various combinations of materials as indicated by the letters A, B and C in figures 4a & b, wherein A signifies a smooth surfaced (figure 5a) rubber coated metallic roller, B signifies a smooth surfaced (figures Sa) substantially metallic roller which may be made of aluminium, steel or iron and which may be chromium plated or ceramic coated and C signifies a metallic roller having a castellated surface, the surface may be square toothed in longitudinal cross-section or convex toothed in longitudinal cross-sections as shown in figures Sb & c.

The adsorbent material 10 is formed by firstly fibrillating at least one polyolefin film 25 to form the fibrillated material 26 and subjecting said fibrillated material 26 to at least a stretching process. The fibrillated material 26 is formed by passing said film 25 over the surface of a primary roller 40.

The primary roller 40 has a number of pins 42 projecting outwardly from the surface thereof and to produce the fibrillated material 26 the polyolefin film 25 is passed over the surface of the primary roller 40 at a linear speed greater or less than the peripheral speed of said roller 40. Several superposed polyolefin films 25 may be simultaneously passed over said roller 40 to form the said fibrillated material 26.

The fibrillated material 26 is then subjected to a stretching process by passing said material 26 through the nip formed between the first pair of secondary rollers 36 and thereafter through the nip formed between the second pair of secondary rollers 38. The fibrillated material 26 is stretched during its passage between the first and second pairs of secondary rollers 36, 38 such that at least some of the longitudinally extending strands 12 thereof are sufficiently stressed to form at least secondary longitudinally extending strands 18 therefrom.

The stretching of the fibrillated material 26 to form the adsorbent material 10 must be carefully controlled in order to maintain the structural integrity of the adsorbent material so formed. This is achieved by controlling the relative peripheral speeds of the inferior rollers 36b, 38b.

The preferred stretch ratio between the rollers 36 in position X and the rollers 38 in position Y lies in the range of 1.01:1-2.5, that is, the ratio of the peripheral speed of the inferior roller 38a in position Y to inferior roller 36a in position X. The separation of the pairs of rollers 36, 38 should be between 100 to 2000 mm rom centre to centre.

Figure 4b shows an alternative stretching means 30 including a pair of non-driven idler rollers 44 in a position indicated W as shown in figure 4b.

The diameter of the idler rollers 44 may range rom 50 to 200 mm and the separation of said rollers 44 from the rollers 36 in position X should be in the range of 200 to 2000 mm.

The use of a roller having a castellated surface as a driven inferior roller 36b, 38b is found to be beneficial in the formation of the adsorbent material 10 in that as the fibrillated material 26 is being stretched between the secondary rollers 36, 38, the castellated rollers 36b, 38b partially grip the fibrillated material 26 and thus, in effect, randomly stretch said material 26.

This has the desired effect of producing the adsorbent material 10 without impairing the overall structural integrity of the adsorbent material 10 so formed.

Air jet means 32 may be located at a point adjacent the exit of the stretching means 30 and may be arranged to air blast the adsorbent material 10 as it exits said means 30. The air blasting may cause the primary longitudinal strands 12 and secondary strands 18 to become intertwined and voluminous and as a result enhance the structural integrity of the adsorbent material 10 and allow easier structural penetration of the molecules to be adsorbed.

Preferred collection means 34 for the collection of the adsorbent material 10 formed by the aforedescribed method include winders and can coilers (not shown), such collection devices facilitating storage of the adsorbent material 10 on cardboard centres or in cans and also providing feed material for further processes such as weaving, for example.

Tests have been carried out to measure the oil adsorbtion qualities of the adsorbent material 10 compared with the filter material of GB Patent No 1 442 593.

Two tests were performed. In the first test, a sample of each of the two materials was immersed in oil for 15 minutes and allowed to "drip dry" for 24 hours before being weighed.

The second test comprised taking a sample of each of the materials and immersing each in oil for a period of 15 minutes, withdrawing each from the oil and allowing them to "drip dry" for 10 minutes before being weighed.

After weighing, the oily tow samples were "squeeze" dried by hand and using these same samples the procedure was repeated a further 3 times.

The type of oil used in the tests was a brand name gear oil called Castrol Hypoy EP90 Gear Oil.

The results of the tests are as listed in tables 1 and 2 hereto.

TABLE ONE MATERIAL TYPE A B (Adsorbent (GB 1 442593 Material 10) Filter Material) Weight of Tow (g) 3.14 7.69 Weight of Tow + Oil (g) 23.03 32.95 After 24 hours Weight of oil retained (g) 19.89 25.26 Adsorbtion of oil (g) per gram of material 633 3.28 TABLE TWO MATERIAL TYPE A B Weight of Tow (g) 3.21 7.30 FIRST IMMERSION Weight of Tow + remaining oil after 10 mins "drying" (g) 110.18 83.35 Oil retained by sample (g) 106.97 76.05 Weight of oil (g) retained per gram of tow material 33.32 10.42 SECOND IMMERSION Weight of oily sample "squeezed" dried 18.95 30.14 Weight of oily tow sample after immersion in oil for 15 mins and then drying for 10 mins (g) 96.53 134.59 Weight of oil retained by sample (g) 77.58 104.45 Weight of oil (g) retained per gram of tow material 24.17 14.31 The results of test two, hereinbefore described, are more easily understood from the comparison of results depicted in Graph 1 hereto. GRAPH 1

Consecutive immersion no.

X Adsorbent material 10 O GB 1447593 material The comparative tests clearly show that the adsorbent material 10 of the invention can adsorb more than twice the mass of gear oil per unit mass of material 10 than the filter material of GB 1 442 593 under identical test conditions.

The fibrillated material 26 from which the adsorbent material 10 is produced may be subjected to stuffer box crimping or gear tooth crimping in order to enhance the structural integrity thereof, prior to being subjected to the stretching process.

The polyolefin from which the adsorbent material 10 is formed is preferably polypropylene. However, the polyolefin might consist of polyethylene or a mixture of polyethylene and polypropylene or a copolymer of propylene and ethylene.

The adsorbent material 10 is primarily intended for use in adsorbing oil slicks and it would be envisaged that for large oil spills, the oil would be reclaimed by squeegee techniques, that is, the adsorbent material 10 would be allowed to remain afloat on the surface of oil contaminated water for a predetermined period of time before being lifted from the surface of the water and passed through a mangle. Having been passed through the mangle, the material 10 could be placed back on to the contaminated water. This could form the basis for a continuous process involving an endless "belt" of adsorbent material 10.

The adsorbent material 10, because of its formation and structure, has an affinity for oil and is buoyant in water.

For smaller spillages the adsorbent material 10 could be allowed to contact the oil/grease until such time as pick up was completed, then recovered and disposed of by incineration/land fill techniques, as appropriate.

The adsorbent material 10 may be applied in various formats to oil slicks at sea or on the shoreline as circumstances demand, as strand, carpet or rope, for example. The material 10 is less dense in water and will float irrespective of sea conditions, allowing for recovery of adsorbed slick material whilst offering the quintessential advantages of polypropylene of separating oil from water and yet being biologically inactive in the ecosphere, thus not presenting a pollution problem in the environment in the manor that oil dispersants, as are presently employed, do.

The adsorbent material 10 is less expensive to produce than known oil slick adsorbent materials or dispersant materials.

It is also envisaged that the adsorbent material 10 will be useful as an adsorbent for organic compounds other than oil and as such may be provided in any suitable format. In this regard, the adsorbent material 10 lends itself to weaving and other similar processes and can be handled and processed without requiring specialist machinery.

Claims

1. A method of producing an adsorbent material which comprises fibrillating at least one polyolefin film to produce a fibrillated material having a plurality of longitudinally extending primary strands with generally interconnecting and free-ended lateral strands therebetween and subsequently subjecting said fibrillated material to at least a stretching process to produce at least secondary longitudinally extending strands formed from said primary strands.

2. An adsorbent material comprising a plurality of longitudinally extending primary strands with generally interconnecting and free-ended lateral strands therebetween characterised in that said material having undergone at least a stretching process also comprises at least secondary longitudinally extending strands formed from said primary strands.

3. Apparatus for producing the material of claim 2 comprising a primary roller having projecting pins thereon over which at least one polyolefin film is passed to produce a fibrillated material having a plurality of longitudinally extending primary strands with generally interconnecting and free-ended lateral strands therebetween; and first and second pairs of secondary rollers, the apparatus being operated such that the fibrillated material is passed through a first nip between the first pair of secondary rollers at a predetermined speed and thereafter through a second nip between the second pair of secondary rollers to produce at least secondary longitudinally extending strands from said primary strands, the compression between at least the second pair of secondary rollers being such that the overall structural integrity of the adsorbent material so produced is not impaired.

4. A method of producing an adsorbent material as claimed in claim 1 wherein the adsorbent material is subjected to an air blasting process to entangle at least the primary and secondary longitudinally extending strands thereof, prior to collection of the adsorbent material in or on collection devices.

5. A method of producing an adsorbent material as claimed in claim 1 wherein the fibrillated material is subjected to a crimping process to improve the structural integrity thereof prior to being subjected to the. stretching process.

6. A method of producing an adsorbent material as claimed in claim 5 wherein the fibrillated material is subjected to a stuffer box crimping process prior to being subjected to the stretching process.

7. A method of producing an adsorbent material as claimed in claim 5 wherein the fibrillated material is subje-cted-to a gear tooth crimping process prior to being subjected to the stretching process.

8. An adsorbent material as claimed in claim 2 wherein some of the interconnecting strands and laterally extending free-ends have peeled away from the longitudinally extending primary strands thereby increasing their length but reducing their width and thus increasing the resultant surface area of the adsorbent material.

9. An adsorbent material as claimed in claims 2 or 8 wherein the polyolefin from which the polyolefin film is made is polypropylene.

10. An adsorbent material as claimed in claims 2 or 8 wherein the polyolefin from which the polyolefin film is made consists of polyethylene or a mixture of polypropylene and polyethylene or a copolymer of propylene and ethylene.

11. An adsorbent material as claimed in claims 2 or 8 wherein the primary longitudinal strands have a thickness in the range of 5 microns to 25 microns.

12. Apparatus as claimed in claim 3 including at least one air jet means wherein the air jet means is arranged to direct a jet of air on the adsorbent material prior to its collection in or on collection devices.

13. Apparatus as claimed in claim 3 including means to crimp the fibrillated material prior to its passage through the first nip between the first set of secondary rollers.

14. Apparatus as claimed in claims 3 or 13 wherein the crimping means comprises a stuffer box crimper.

15. Apparatus as claimed in claims 3 or 13 wherein the crimping means comprises a gear tooth crimper.

16. Apparatus as claimed in claims 3 or 13 wherein the first and second pairs of secondary rollers each comprise a non driven superior roller and a driven inferior roller wherein the rollers are urged together to form the first and second nips respectively.

17. Apparatus as claimed in claim 16 wherein the ratio of the peripheral velocity of the first inferior roller to the second inferior roller lies in the range of 1.01:1-2.5.

18. Apparatus as claimed in claim 16 wherein the superior rollers have a smooth rubber coated surface.

19. Apparatus as claimed in claim 16 wherein the inferior rollers are made of metal and have a castellated surface.

20. An adsorbent material substantially as hereinbefore described with reference to figures 1 and 2.

21. Apparatus substantially as hereinbefore described with reference to figures 3, 4 and 5.