Processing of chemically modified cellulosic fibres

Abstract

A chemically modified cellulosic fibre or filament having a moisture content of at least 7% by weight obtained by a process comprising the steps of (i) obtaining cellulosic fibres or filament and chemically modifying the cellulose by substitution to increase its absorbency; (ii) washing the fibres after step (i) in a mixture comprising water and up to 99% by weight of water-miscible organic solvent; (iii) drying the fibres to a moisture content of at least 7% by weight.

Claims

1. A process for processing a cellulosic fibre or a cellulosic filament, the process comprising: chemically modifying the cellulose of the cellulosic fibre or the cellulosic filament by substitution to increase absorbency; washing the chemically modified cellulosic fibre or chemically modified cellulosic filament in a wash solution comprising up to 99% by weight of an organic solvent and at least 95% by weight of the organic solvent; and adjusting the washed fibre or washed filament to a moisture content of at least 7% by weight.

2. The process of claim 1, wherein the washed fibre or washed filament is dried to a moisture content from 11% to 18% by weight.

3. The process of claim 1, wherein the adjusting step comprises drying the washed fibre or washed filament.

4. The process of claim 3, further comprising carding the dried fibre or dried filament to make a nonwoven web of fibre.

5. The process of claim 4, further comprising needling the nonwoven web of fibre to form a wound dressing.

6. The process of claim 5, further comprising sealing the wound dressing in a pouch that maintains the moisture content of the wound dressing in a sterile environment.

7. The process of claim 1, wherein the adjusting step comprises conditioning the washed fibre or washed filament in an atmosphere having a relative humidity of at least 40%.

8. The process of claim 7, wherein the relative humidity is from 45% to 85%.

9. The process of claim 7, further comprising carding the conditioned fibre or filament to produce a non-woven web of chemically modified cellulosic fibre.

10. A process for producing a non-woven web of chemically modified cellulosic fibres, the process comprising: neutralizing chemically modified cellulosic fibres; finishing the chemically modified cellulosic fibres with a solution comprising less than 99% by weight of an organic solvent to produce finished chemically modified cellulosic fibres; adjusting the moisture content of the finished chemically modified cellulosic fibres to a moisture content from 11% to 20% by weight; processing the finished chemically modified cellulosic fibres into the non-woven web of chemically modified cellulosic fibres, and wherein the moisture content of the non-woven web of chemically modified cellulosic fibres is from 11% to 20% by weight; and packaging the non-woven web of chemically modified cellulosic fibres in a pouch that maintains the moisture content of the non-woven web of chemically modified cellulosic fibres in a sterile environment, and wherein the packaged non-woven web of chemically modified cellulosic fibres has a tensile strength of at least 3N per cm, wherein the solution comprises at least 95% by weight of the organic solvent.

11. The process of claim 10, wherein the solution comprises less than 95% by weight of an organic solvent.

12. The process of claim 10, wherein the adjusting step comprises drying the finished chemically modified cellulosic fibres to achieve the moisture content from 11% to 20% by weight.

13. The process of claim 10, wherein the adjusting step comprises conditioning the finished chemically modified cellulosic fibres in air having a relative humidity of at least 40% to achieve the moisture content from 11% to 20% by weight.

14. The process of claim 13, wherein the relative humidity is from 45% to 85%.

15. The process of claim 10, wherein the adjusting step comprises drying the finished chemically modified cellulosic fibres in air having a relative humidity of at least 40% to achieve the moisture content from 11% to 20% by weight.

16. A non-woven web of chemically modified cellulosic fibres produced by the process of claim 10.

17. The non-woven web of chemically modified cellulosic fibres of claim 16, wherein the non-woven web of chemically modified cellulosic fibres has a tensile strength from 3N/cm to 25N/cm.

18. The non-woven web of chemically modified cellulosic fibres of claim 16, wherein the non-woven web of chemically modified cellulosic fibres has a basis weight from 80 gsm to 120 gsm.

19. The non-woven web of chemically modified cellulosic fibres of claim 16, wherein the tensile strength is in a cross-direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the fiber moisture content vs. tensile strength of carded needled fabric in the transverse (cross) direction before and after moisture conditioning to increase moisture content.

(2) The invention will now be illustrated by the following examples.

EXAMPLE 1

(3) Comparison of the moisture content of fibres vs their tensile strengths once carded and needled was made by measuring the initial moisture content of dried modified cellulosic fibres produced using washes of varying alcohol content. That initial moisture content was then increased by conditioning the fibres in a moist atmosphere for 24 hours at a relative humidity of 55 to 60% and the tensile strength of the needled fabric measured again.

(4) FIG. 1 shows the fibre moisture content vs tensile strength of carded needled fabric in the transverse (cross) direction before and after moisture conditioning to increase the moisture content.

(5) The results show that the moisture content of the fibres influences the tensile strength of the resulting carded and needled web. The column headed IDA in the table of FIG. 1 refers to the percentage of IDA (industrial denatured alcohols) used in the wash liquor as part of the modification process. The columns headed % refer to the % moisture in the fibre and N/cm to the tensile strength of the resulting carded needled web in the transverse direction. It can be seen from FIG. 1 that decreasing the % of IDA in the wash liquor has a negative influence on tensile strength for carded and needled webs made from unconditioned fibres. It can also be seen that once the moisture content of those fibres is raised to more than 11%, such as 12.5 to 14% moisture those tensile strength values of the carded needled web increase.

EXAMPLE 2

(6) Effect of moisture content on the tensile strength of silver containing wound dressings.

(7) Dressings were prepared by modification of solvent spun cellulose tow to a degree of substitution of 0.3 to form carboxymethylcellulose, neutralising to a pH of 5.5 with an organic acid. Adding 1.2% cationic silver by an ion exchange process in a largely organic solvent such as by the process described in Ep1343510, washing in an aqueous organic solution containing sodium chloride and di-sodium EDTA for light stabilisation and to entrain approximately 0.4% EDTA. Followed by washing in organic solvent wash containing fibre finishing agents including tween 20 and benzethonium chloride (to give 0.135% wt/wt BeCl on the finished product) and subsequently warm air drying, cutting to staple and processing into a nonwoven felt by carding and a needle punching process. The dressings were cut to size from the web and packaged in a light, moisture and vapour impermeable heat sealed foil pouch.

(8) The dressings were removed from the packs and then subjected to various controlled environments.

(9) Controlled Environments Ambient as packed, tested without any preconditioning Zero humidity: Stored in a square desiccator with 3 perforated perspex shelves above a layer of silica gel desiccant, conditioned for a minimum of 5 days 25° C./60% RH, for a minimum of 6 days 30° C./65% RH, for a minimum of 6 days 40° C./75% RH, for a minimum of 6 days

(10) Samples (ambient as packed) were tested immediately after opening the packs. Samples removed from the other environments were sealed into plastic bags during removal, and then tested immediately. The plastic bags (also preconditioned in corresponding controlled environments) were used to maintain the humidity of the environment of the samples until the point of testing.

(11) Loss on Drying CLOD)

(12) LOD of the samples was determined using the Ohaus moisture balance MB23 operated in accordance with the instruction manual. A sample mass of greater than 1 gram was used. Samples were cut to fit within the weighing pan, ensuring there was adequate clearance from the heating element. A standardised method was used with a maximum temperature limit of 110° C. The endpoint was determined automatically when the sample mass stopped reducing and was stable. Under these conditions the fabric did not char. Typically, samples would be subjected to a 10 minute cycle.

(13) Fabric Thickness (Loft)

(14) Samples were tested using the Hampden Soft Materials Thickness Gauge, Model FMTml-4D, S/N 14082. Fabric thickness (sometimes referred to as loft) was determined for 6 dressings per batch.

(15) Fabric Dry Tensile Strength

(16) 2.5 cm×7.5 cm rectangular strips were cut from along the length (machine direction) and across the width (transverse direction) using a ribbon cutting die and press. Samples were conditioned as described Table 1. The peak force and the extension at which that force occurred were recorded when a 50 mm test length was stretched at a constant separation rate of 100 mm per minute.

Results

(17) TABLE-US-00001 TABLE 1 Relationship between absolute and relative humidity 25° C./ 30° C./ 40° C./ Conditioning Dry Ambient 60% RH 65% RH 75% RH Moisture 0.00 9.50 13.81 19.71 38.29 (g/m3) Thickness 0.170 0.190 0.198 0.183 0.202 (mm) LOD % 9.28 11.93 14.17 15.27 18.10 Tensile 3.10 5.19 5.80 5.36 7.75 Machine (N/cm) Tensile 5.15 6.53 11.12 10.23 14.28 Transverse (N/Cm) GSM 91 102 105 98 108 (g/m2)

(18) Loss on drying is the summation of all the volatile substances that can be removed by heating at 110° C. These include ethanol, water and to some degree acetic acid.

(19) For this particular fibre, for this example, textile trials have shown that fibres for use in wound dressings according to the invention can be successfully textiled between 42% and 50% RH at around 18 to 20° C. Trials suggest that fibres with 10.5% to 11.5% w/w moisture content can be carded efficiently.

(20) The results show that tensile strength, loft and LOD are all functions of equilibrium moisture content. The results suggest that fibres with a moisture content of greater than 9% will be able to be textiled to produce dressings suitable for use in the present invention.

EXAMPLE 3

(21) Materials

(22) Two gelling fibre types were used in this study; cellulose ethylsulphonate (CES) and carboxymethyl cellulose (CMC).

(23) TABLE-US-00002 TABLE 1 Surnmary of gelling fibres used Gelling Fibre CES fibre tow CMC fibre tow

(24) Methods

(25) Single fibres were mounted onto card windows as described in BS EN 5079:1996.

(26) In addition, tow bundles were prepared to assess the moisture content.

(27) Fibres were oven dried at 105° C. for one hour prior to being conditioned at the chosen relative humidity for a minimum of 16 hours. The mass of the oven dried tow bundles (W1) and the conditioned tow bundles (W2) was taken to assess the moisture content of the fibres, using Equation 1.

(28) $\begin{array}{cc}\mathrm{Moisture}\mathrm{Content}\left(\%\right)=\frac{W2-W1}{W2}\times 100& \mathrm{Equation}1\end{array}$

(29) Single fibre tensile strength of the conditioned samples was undertaken using the method described in BS EN 5079:1996.

(30) Fibres were tested at 45% RH, 65% RH, and 85% RH.

(31) Results

(32) Results found that a significantly higher (P≤0.05) tensile strength was seen in the samples conditioned at 65% RH than those conditioned at 45% RH and 85% RH as shown in Table 2.

(33) TABLE-US-00003 TABLE 2 Summary of results Relative Humidity of Atmosphere (%) Ambient 45 65 85 CES Moisture Content in fibre (%) w/w 9 15 22 Mean Fibre Breaking Strength (cN) 4.85 6.16 3.79 Standard Deviation (cN) 1.08 3.61 1.21 T-Test aganst 65% RH data P value 0.016 N/A 0.000 CMC Moisture Content in fibre (%) w/w 12 15 21 Mean Fibre Breaking Strength (cN) 6.04 3.24 4.16 Standard Deviation (cN) 2.65 6.06 1.55 T-Test against 65% RH data P value 0.029 N/A 0.000