WO2000063469A1

WO2000063469A1 - Polyolefin fibres

Info

Publication number: WO2000063469A1
Application number: PCT/GB1999/001147
Authority: WO
Inventors: Keith Bailey; David Geoffrey Ellis
Original assignee: Plasticisers Ltd
Current assignee: Plasticisers Ltd
Priority date: 1999-04-15
Filing date: 1999-04-15
Publication date: 2000-10-26
Anticipated expiration: 2001-10-15
Also published as: AU3436499A

Abstract

The present invention relates to polyolefin fibres which incorporates one or more cytotoxic additives in the body of the fibre. The fibres are able to prevent or reduce the growth of bacteria or other cellular micro organisms on or close to the surface of the fibre. The fibres find use in domestic applications for floor, bedding and wall coverings. The fibres of the present invention may be mixed in a woven or non-woven matrix with other untreated fibres to extend the cytotoxic properties to the material as a whole.

Description

Polyolefin Fibres

The present invention relates to polyolefin fibres which are able to prevent or reduce the growth of bacteria or other cellular micro organisms on or close to the surface of the fibre. More particularly, the present invention relates to fibres which are antibacterial and/or antifungal and which are suitable for incorporation into woven and non-woven products such as floor and wall coverings. The fibres of the present invention possess this activity because they contain one or more cytotoxic additives in small quantities. Amongst polyolefins, polypropylene fibres in particular are generally the material of choice in such domestic applications although other polyolefin are also suitable.

Polypropylene textile fibres have excellent stain resistance and chemical resistance, and a very low moisture regain. They are widely used in household textiles and in floor coverings because, amongst other things, they are easy to clean and maintain. They do not themselves support the growth of bacteria or fungi which could cause unpleasant smells or unacceptable appearance in the carpet . However where polyolefin fibres are used in blends with other fibres (e.g., wool) which do not have such advantageous properties, or where the cleanliness of the carpet is difficult to maintain to the required standards at all times (e.g., residential care homes, school class rooms and sports locker rooms) , it is important to ensure these other materials or contaminants adjacent to, or in contact with, the polypropylene, do not themselves support the growth of unpleasant bacteria or fungi. Furthermore, the household debris and stains frequently found in carpets can provide nutrients for house dust mites and there is concern that these may in turn be related to asthma attacks. Similar concerns are raised in bedding and upholstery applications.

Also, in domestic applications there is a growing awareness of unacceptable smells in the home .

Unacceptable smells may result from the bacteria or fungi growing on household debris or other stains (for example, residues of human sweat, skin or food stains) falling onto the carpet or bedding. Such materials may decompose providing an ideal medium for sustained growth of bacteria or fungi . The activity of the house dust mite is dependent on such nutrients and the elimination of the associated growth of bacteria and/or fungi helps to minimise or eliminate this problem. Attempts to inhibit or control the growth of such bacteria and fungi have in the past focused on aqueous chemical surface treatments of fibres or textile end products. However, such surface treatments can easily wash or wear off. Furthermore, great care has to be exercised in the production processes in which they are applied. The chemicals chosen for elimination of bacteria and fungi also can, if discharged in too high a concentration into water courses, have a disastrous impact on the environment. Frequently, such chemicals are hazardous to humans in higher concentrations.

Furthermore, it is difficult to apply any surface treatments to polyolefin fibres (and to polypropylene fibres in particular) and conventional surface treatments usually easily wash or wear off these types of fibres. The relative inertness of the polyolefin fibres is one reason why surface treatments of this type are not a serious practical option.

Despite the above disadvantages of polyolefin fibres, there are nevertheless many other advantages of using these types of fibres, and polypropylene in particular, in household textiles, including carpets, upholstery and bedding etc . These materials are readily available, fairly easy to manufacture in crude form and relatively inert and non-toxic. Hence, there is a need to provide polyolefin, and in particular polypropylene, fibres which possess all the advantages of conventional polyolefin fibres and which also have significant antibacterial and antifungal properties themselves. There is also a need for polyolefin fibres which can be incorporated into a woven or non-woven matrix containing other fibres which are able to impart antibacterial and antifungal properties to their surroundings. This is particularly important when the other fibres present are not otherwise easily protected. It is therefore an object of the present invention to provide polyolefin fibres which have a cytotoxic effect. In the context of the present invention, cytotoxic activity refers to the ability of the fibres to eliminate substantially all of, or at least a significant proportion of, submicroscopic cellular organisms including: bacteria, spores, fungi and algae present on or within about 15mm of the fibre .

It is an object of the present invention that the fibres should also have a good degree of resistance to staining.

It is a further object of the present invention that the polyolefin fibres should be easy and inexpensive to manufacture.

It is also intended that the fibres should be durable so as to provide a cytotoxic effect over a relatively long time, and ideally at least 3 years.

It is also an aim to provide fibres in which the cytotoxic agents are retained by the fibre so that the cytotoxic agents do not enter the local environment in any significant quantities; these types of agents are often harmful to human or animal life in higher concentrations . At the same time is also an aim to provide fibres which are able to make available just sufficient of the cytotoxic agents to allow the cytotoxic effect i.e. the antibacterial, antifungal, sporicidal, and/or anti algal effect to be imparted to adjacent concentrated fibres which may be present in a woven or non-woven matrix. In a related aim of the present invention, it is intended to provide fibres which permit a slow sustained supply of the cytotoxic agent so that the availability of the agent remains fairly constant over a relatively extended period of time, and ideally for at least 3 years.

In the context of the present invention, fibres which release all or a significant proportion of the cytotoxic agent in a period of less than 3 years would have limited use in domestic textiles because the cytotoxic activity would soon be lost . The product would thus have an unacceptably short useful life or shelf life. Thus, the purposes of the present invention "relatively long" and "extended period" both refer to a period of time of at least 3 years and may be as long as 15 years.

According to one aspect of the present invention, there is provided a polyolefin fibre incorporating from 0.01 to 0.5% by weight inclusive of at least one cytotoxic additive dispersed within the body of the fibre, the additive having a molecular weight of from 200 to 650 inclusive, wherein the fibre is capable of sustained and substantially uniform release of the additive from the interior of the fibre over an extended period of time.

According to another aspect of the present invention, there is provided a process for making polyolefin fibre incorporating at least one cytotoxic additive, the process comprising the steps of: (a) mixing one or more cytotoxic additives with a polyolefin under conditions of high shear to form a homogenous mixture, (b) extruding the homogenous mixture to produce a fibre, (c) cooling the extruded fibre at a rate of from 100 to 10,000 degrees per sec inclusive, and (d) stretching the fibre.

We have thus found that it is possible to incorporate one or more suitably chosen cytotoxic additives into the polymer structure during the process of extrusion. The cytotoxic additive may be a single compound or a mixture of several compounds each of which contributes in some way to the cytotoxic activity of the fibre.

The subsequent fibre processing is conducted to ensure that the antibacterial, antifungal, sporicidal, and/or antialgal properties of the fibre are available at the surface of individual fibres due to a small degree of mobility of the cytotoxic additives within the fibre.

At the same time, the cytotoxic additives are not so mobile that they are able to rapidly escape from the fibre. Hence the available surface concentration of the cytotoxic additive does not fall in an exponential- type manner with time but remains fairly constant over a period of in excess of 5 years and up to 15 years. Thus, the problem of rapid initial release followed by depletion of the additive is avoided and during the useful life of the fibre there is always a reservoir of additive available in the fibre.

These additives are also able to transfer their cytotoxic activity to other materials which come into contact with these special fibres i.e. to adjacent fibres in a woven or non-woven matrix. The additive molecules have just sufficient mobility to supply and replenish any of the cytotoxic molecules at the fibre surface which may have migrated to protect other adjacent materials. The polyolefin fibre may be any of the conventionally used olefin fibres including: polyethylene, polypropylene and polybutylene, or may be a copolymer derived from unsaturated feedstocks such as ethene, propene and butene. Preferably, the polyolefin is polypropylene on the basis of suitability for domestic uses.

The additives used in the present invention are molecules of low molecular weight (i.e. in the range 200 to 650 inclusive) which can be sufficiently well held within the body of the fibres i.e. within the crystalline structure of the fibres so that they are not readily extracted in use or on washing. The use of additives having a molecular weight in the range 200 to 650 inclusive ensures that there is sufficient agent available at the fibre surface to be useful in the early life of the product but not so rapid a migration that the additive are removed during washing or leaching out tests. If the molecular weight is less than 200 the molecules tend to be too mobile and it is difficult to control the mobility of the additive even when varying the processing conditions. If the additives have molecular weights in excess of 650 the additives tend to be immobile, and likewise it is difficult to influence the mobility sufficiently by varying the processing conditions.

It is therefore preferable that the molecular weight of the additive is within the range of 250 to 500 inclusive in order to provide optimum mobility. Suitable additives include conventional low molecular weight molecules which provide one or more of antibacterial, antifungal, sporicidal or antialgal effect. Particular examples of such agents are: Tri-butyl tin maleate (TBTM molecular weight 392) and 2, 4, 4 trichloro-2-Hydroxy diphenyl ether (molecular weight 290 - reference DP300) . Both these molecules are also available as proprietary additives for wet treating textiles.

Other additives may be chosen from those already conventionally used in connection with textile-based applications to impart suitable cytotoxic antibacterial and/or antifungal properties. The stability of these agents in the extrusion process, their ability to be dispersed throughout the polymer, and the antimicrobial or antifungal properties possible at the fibre surface, can easily be determined by measurement as described below.

As little as a few parts per million of the cytotoxic additive is sufficient to start inhibiting the growth of common bacteria (e.g., staphylococcus aureus) or fungi (e.g., aspergillus niger) . However, it is important that the agent is present in an amount of at least 0.01% by weight in order to provide sufficient activity to ensure substantial or complete eradication of bacteria. If, however, the amount of agent exceeds 0.5% little benefit is gained by the presence of the additional amount and the processing becomes more difficult and costly. Ideally, there is at least 0.03% by weight of the agent in the fibre because this guarantees that there is sufficient of the agent to support the required concentration of the agent at the fibre surface .

We also found that at sufficiently high concentrations of additive in the polypropylene fibre, (typically at least 0.05% by weight and preferably 0.1% by weight) the cytotoxic properties were transferrable to the other fibres present in a blend of fibres, and even when there was as little as 20% of the polyolefin fibres of the present invention. The extrusion process conditions are also important and these contribute to the mobility of the agent within the fibre body. Hence the processing conditions contribute to the effectiveness, or inutility, of the fibre product. Indeed, the crystallinity of the eventual fibre is an important determinant of the additive mobility. The crystallinity depends on the cooling rate, the stretching conditions of the cooled fibre, and to a lesser degree on the molecular weight of the polyolefin. The skilled person will, of course, appreciate that these factors can be used to tailor the mobility of a given additive in a given polyolefin and that the appropriate conditions can be determined by experimentation.

The extrusion conditions must be sufficiently vigorous (good mixing at high pressures and high shear rate in the extrusion process) to ensure good homogenous dispersion of the additive amongst the polyolefin during manufacture .

The cooling and subsequent stretching of the extruded fibres also must be sufficiently fast to ensure that there are sufficient amorphous regions in the polymer's crystalline structure through which the additive molecules may migrate to the fibre surface.

The fibres should thus be cooled at a rate of from 100 to 10,000°C per sec, inclusive to ensure the advantageous effects are achieved. A preferred range of cooling is from 300 to 4,500°C per sec, inclusive, and more preferably 500 to 4000°C per sec, inclusive.

When the fibres are cooled too slowly (i.e. less than 100°C per sec) they are consequently more crystalline and there is insufficient additive mobility. In this case we found that there is less opportunity for the additive molecules to move freely in the fibre cross-section, and consequently little or no cytotoxic activity at the fibre surface.

On the other hand, if the fibres are cooled too quickly (i.e. faster than 10,000°C per sec) the fibre structure is amorphous and the molecules are not easily retained in the body of the fibre and leach out rapidly. There is thus no possibility of sustained release and there may be problems with the initial sudden build up of high concentrations of cytotoxic agents .

The molecular weight of polypropylene (and other similar polyolefins) is very high (for example 50,000 upwards depending on the polymer type and grade) . Additives commonly used, for example, to provide stabilisation to ultra violet light in polypropylene fibres, typically have high molecular weight (about 2,000 upwards). Additives used for example for imparting resistance to thermal degradation have molecular weights of about 700 upwards. Compounds with molecular weights of about 700 upwards have been found to be adequate in use over many years of product life (e.g., 5 years upwards) without significant migration of the additives from the body of the fibres regardless of processing conditions.

However, it is known that additives having molecular weights of 700 or less can easily migrate out of the fibre structure in a short period of time . Typically such additives would be expected to concentrate at the surface over a period of not more than 1 or 2 years, and in some cases in a significantly shorter time period depending on the processing conditions. Consequently, additives having such low molecular weights (i.e. 700 or less) have not previously been considered for incorporation into polymeric materials such as those described herein. Additives having a high degree of mobility would, of course, be incompatible with the present invention since their duration of action would be too short. Consequently, there is both the risk of too high an initial release of the agent and the disadvantage of too short a useful life.

It is possible to disperse the additives in conventional extruding equipment such as a twin screw compounding extruder. The additives may be initially incorporated into the polyolefin using a polyolefin carrier which may be the same or different as the polyolefin material forming the bulk of the fibre; for example, in the case of a polypropylene fibre a polypropylene carrier might be used for ease of use in the subsequent polypropylene fibre extrusion process . In the following examples pellets of the additive dispersed in polypropylene were first prepared in this way. Thus pellets containing for example a combination of 1.25% active TBTM and 10% active DP300 as the cytotoxic agent, were used to extrude fibres which are used in some of the following examples.

The present invention will now be illustrated by means of examples of some cytotoxic fibres which we have tested. These examples demonstrate the effect that the extrusion process has on the finished fibre; the effect that the amount of additive has on the antibacterial and antifungal properties; the resistance of the fibres to leaching of the additives; and the ability of the fibres to impart resistance to bacteria and fungus when incorporated in a matrix of woven or non-woven fibres which have not been treated.

The cytotoxic properties of the fibres of the present invention were determined by the antibacterial and antifungal performance of the fibres in AATCC recognised tests (AATCC = American' Association of Textile Chemists and Colorists).

The AATCC tests employed were : a) Antibacterial AATCC Method 147 1993 using Staphylococcus aureus (ATCC No. 6538) . b) Antifungal AATCC Method 30 1993 using Aspergillus niger (ATCC No. 6275) .

The results quoted in the Examples given below are for % contact or surface inhibition (1%) . 100% is required to confirm that the sample provides optimum antibacterial activity.

The growth free zone (gfz) is an indication of the distance (in mm) around the sample in which there is also antibacterial or antifungal activity. In the case of samples with relatively high loadings (at least 0.05% by weight) of additive, this can be an indication of the amount of available additive molecules on the surface of the fibre which can migrate into the surrounding medium on which bacteria, fungus etc would otherwise grow.

In contrast, in the case of textiles having superficial surface treatments (i.e., not an integral additive system as in the present invention) , the size of the growth free zone can be an indication of the impermanence of the antibacterial/antifungal reagents and the ease with which they can transfer from the textile.

Example 1

15 denier filaments of polypropylene polymer of melt index 12 (Targor 1101 M) were produced on a 20mm diameter extruder having a L/D ratio of 25:1.

Polypropylene polymer of melt index 12 (Targor

1101M) used in this example without any additives as a control. In the subsequent experiments in which cytotoxic additives were incorporated, the additives were pre-mixed with the polypropylene polymer and then extruded and collected as filaments under the same conditions as described above. The results of the various experiments are summarised in Table 1.

The metering pump feeding the extruder had a back pressure 1000 psi and extrusion took place through 0.5mm diameter holes in a die block at 230°C. The extruded filaments were passed vertically down through an air cross draft at ambient temperature (20°C) and cooled from the extrusion temperature (230°C) to a temperature of 30°C in 4 sec. The cooling rate was 50°C per sec. The cooled extruded fibres were then passed at their ambient temperature over a first set of rollers at the rate of 15m/min then over heated rollers (75°C) also at the rate of 15m/min. The fibres were then passed over second stretch rollers at 46 m/min. Fibre filaments were then collected on a winder.

The filaments were passed over a lick roller to apply a small amount (0.4%) of a surfactant and wetting agent to aid processing.

The filaments were then subjected to the AATCC test methods .

TABLE 1

Although the active levels of TBTM were present in the fibre these active molecules were trapped in the crystalline structure of the orientated polypropylene fibres in this particular case as a consequence of the processing conditions. In this case, the cooling rate was too slow leading to too high a degree of crystallinity in the fibre.

This example illustrates that the resulting antibacterial effect is a combination of both the presence of a suitable additive and the processing conditions since either one alone is not sufficient to provide this effect. Indeed, the TBTM was actually- present in a sufficient quantity for an antibacterial effect to have otherwise been expected to be observed.

The DP300 had excellent antibacterial activity despite the apparent crystallinity of the fibre. This is consistent with its lower molecular weight than TBTM .

No antifungal activity was observed in either case on testing with Method 30. However, it is noted that even in the free state DP300 is not recognised as an antifungal agent at such low concentrations. Example 2

Polypropylene fibres having a denier of 4 denier per filament were produced in the same manner as for Example 1. TBTM was incorporated in the fibre alone, and also in combination with DP300 as indicated in Table 2.

TABLE 2

Again, antibacterial activity was observed in several cases. No antifungal activity was observed, despite the higher concentrations of TBTM tried.

Example 3

Polypropylene polymer of melt index 25 (Targor 1101R) was used in this example without any additives as a control. In the subsequent experiments in which cytotoxic additives were incorporated the additives were pre-mixed with the polymer and extruded as filaments under the same conditions. The compositions of these fibres and their properties are indicated in Table 3.

A 75mm diameter extruder having a L/D ratio of 25:1 was used. The filament production process was conducted at a higher speed so that there would be less opportunity for the filaments to crystallise. Thus the fibres contained a higher proportion of amorphous polymer sites in the filament structure so as to increase the additive mobility.

The metering pump feeding the extruder had a back pressure of 3000 psi and extrusion took place through 0.5mm diameter holes in the die block at 230°C. The extruded filaments were passed vertically down through an air cross draft at 20°C and cooled from the extrusion temperature (230°C) to a temperature of 45°C in 0.045 sec. The cooling rate was 4100°C per sec.

The cooled extruded fibre was then subsequently rolled at the following roller speeds and temperatures:

Top 80°C 674 m/min Middle 120°C 1502 m/min Bottom 120°C 1850 m/min

The filaments were then passed over lick roller to apply a small (0.8%) of surfactant and wetting agent and wound at 1650 m/min.

TABLE 3

In these test results good antifungal activity was achieved at the concentrations of additive used in the previous examples where there had been no such activity. This indicated a delicate balance between the additive chosen and the processing conditions. This also confirmed that the rate of cooling in particular is important in achieving the desired properties.

Sample numbers 3 and 5 were submitted to a leaching test in which the filaments were left 24 hours in a detergent solution. The antibacterial and antifungal properties were found to be retained after 24 hours immersion in the detergent solution.

A washing test was also performed on the fibres and it was demonstrated that 100% antibacterial activity was still present after 15 wash cycles.

Example 4

Yarns incorporating polypropylene fibres containing TBTM as the cytotoxic agent were woven into fabrics as the weft using polyester warps. The compositions of these polypropylene fibres is indicated in Table 4. This Example shows that the antifungal and antibacterial properties were transferable to the whole fabric at average levels of TBTM additive.

TABLE 4

Similar results were also obtained when weaving the polypropylene weft yarn onto cotton or spun rayon warps.

In a separate weaving exercise, the same types of polypropylene yarns were woven into fabrics with even less calculated average % TBTM in the whole fabric. Even in these cases we still observed 100% inhibition results .

Table 5 indicates fabrics which were tested using yarns in the weft with 0.125% TBTM content.

TABLE 5

All these results illustrate that with yarns containing 0.08 - 0.125% TBTM in fabrics with average content of 0.03 - 0.125% TBTM it was possible to achieve 100% inhibition of bacteria and fungi. Growth free zones of 0 - 15mm are also possible depending on the fibre and are indicative of the fact that the inhibition may extend into the fabric structure.

Example 5

This example relates to a staple fibre production plant having a 100mm diameter extruder with a L/D ratio of 25:1. The control fibre sample was extruded from 12 melt index polymer (e.g., Targor 1101M) . The various addition levels of the special additives were metered into the extruder as required and processed under the same conditions . The compositions and properties of thee fibres are indicated in Table 6.

The pressure before and after the metering pump was 1000 psi and extrusion was performed through 0.5mm diameter holes in die block at 235°C. The extruded filaments were passed vertically up through an air knife to air cool the fibre with air at 20°C. The rate of cooling of the fibre was 500°C per sec. Rollers pulled the cooled extruded fibres from the die at 15 m/min. The fibres were then passed through steam (100°C) a second set of stretch rollers (at 50 m/min) and relax rollers (at 44 m/min) and then passed through a turbo crimper, spin finish applicator (lick roller applying up to 0.4% surfactant and antistat) and cutting machine.

TABLE 6

In this process 100% inhibition and growth free zones were achieved at concentrations of TBTM for which such benefits were not achieved in the process employed in Example 1.

Example 6

The extrusion process of Example 5 was used to produce a variety of deniers and colours of fibre in the range 6 to 300 denier. Again 100% inhibition was achieved for concentrations of 0.05% TBTM and above.

In the case of thicker fibres which do not offer as much surface area for contact with the bacteria, another antibacterial test in which the inoculum of staphylococcus aureus was applied directly to the samples was employed. Good antibacterial activity was again demonstrated for these samples .

Fibres from blends of polypropylene, polyethylene (LDPE and LLDPE) were all shown to produce similar effects with cytotoxic additives. In each case, the optimum additive level in the fibre can be determined by simple experimentation.

Example 7

Fibres containing as little as 0.0375% TBTM in the fibre were blended into carpets to give as little as 0.018% TBTM on average in the pile of the carpet. This level of TBTM was sufficient to produce 100% inhibition in the antifungal test and excellent antibacterial activity in the direct contact test (i.e., 0% bacteria survival scores by quantitative analysis) .

Example 8

15 denier fibre containing 0.25% TBTM was blended with wool fibre in various proportions as indicated in Table 7 and the resulting yarns were spun and tested. Again, even at relatively low concentrations of TBTM the ability of the yarn in inhibiting growth of bacterial and fungus was excellent.

TABLE 7

Carpet was produced using the yarns containing subsequently tested. This performance was considered quite extraordinary in view of the low molecular weight, and hence expected mobility, of TBTM.

Example 9

6 denier polypropylene fibre containing 0.25% TBTM was blended with polyester fibre to make a carded fibre web suitable for fillings for pillows and duvets. With as little as 20% of the treated fibre in the blend (equivalent to 0.05% of TBTM), excellent antibacterial and antifungal results were obtained as follows.

The various examples confirm that fibres having TBTM levels of 0.05% upwards in polyolefin fibres enables fibres having excellent antibacterial and antifungal properties to be produced.

Claims

1. A polyolefin fibre incorporating 0.01 to 0.5% by weight inclusive of at least one cytotoxic additive dispersed within the body of the fibre, the additive having a molecular weight of from 200 to 650 inclusive, wherein the fibre is capable of sustained and substantially uniform release of the additive from the interior of the fibre over an extended period of time.

2. A fibre as claimed in claim 1, wherein the polyolefin is a homopolymer or copolymer derived from one or more of ethylene, propylene and butylene.

3. A fibre as claimed in claim 1 or 2, wherein the additive has a molecular weight of from 250 to 500 inclusive.

4. A fibre as claimed in claim 3 selected from tri-butyle tin maleate and 2, 4, 4 trichloro-2-hydroxy diphenyl ether.

5. A fibre as claimed in any preceding claim, wherein the fibre is capable of sustained and substantially uniform release of the cytotoxic additive over a period of from 3 to 15 years inclusive.

6. A floor covering or filling for bedding incorporating the fibre as claimed in claims 1 to 5.

7. Use of the fibre as claimed in any of claims 1 to 5 for the prevention of one or more of bacterial growth, fungal growth, and the growth of algi.

8. A process for making polyolefin fibre incorporating at least one cytotoxic additive, the process comprising the steps of :

(a) mixing one or more cytotoxic additives with a polyolefin under conditions of high shear to form a homogenous mixture,

(b) extruding the homogenous mixture to produce a fibre,

(c) cooling the extruded fibre at a rate of from 100 to 10,000 degrees per sec inclusive, and

(d) stretching the fibre.

9. A process as claimed in claim 8 wherein the rate of cooling is from 300 to 4,500 degrees per sec, inclusive, and preferably from 500 to 4000 degrees per sec, inclusive.