GB2368342A - Lyocell fibre and its production - Google Patents

Abstract

Lyocell fibre includes domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers. The fibre contains from 0.1 to 30% by weight of the low-melting thermoplastic polymer and substantially all of the domains are not visible when viewed by electron microscopy at x9000 enlargement. The invention further provides a process for the manufacture of lyocell fibre which comprises the steps of: <SL> <LI>(1) extruding a lyocell fibre which contains domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers; <LI>(2) applying to the fibre in never-dried state a reagent having from two to six functional groups reactive with cellulose; <LI>(3) inducing reaction between the fibre and the reagent; and <LI>(4) drying the fibre, wherein substantially all of the domains of the low-melting thermoplastic polymer in the dried fibre cannot be seen by electron microscopy at x9000 enlargement; or wherein substantially all of the domains have a maximum dimension of no more than 50 nm. </SL>

Description

2368342 Title: Fibre and its Production

Field of the invention

This invention relates to modified lyocell fibre and to a process for the preparation of modified lyocell fibre "Fibre" is used in this specification to include continuous filament yarns, tows of yarn for cutting into staple fibre and also staple fibre formed from such a tow.

Background art

Lyocell fibre is produced by dissolving cellulose in a suitable solvent, for example a tertiary amine N-oxide such as N-methyl morpholine oxide mixed with water A suitable method of manufacture is described in US-A-4,416,698 The solution of cellulose in the amine oxide solvent, which is solid at ambient temperature, is extruded at a temperature of 95-125 C from a spinneret through an air gap into a precipitation bath of water or dilute aqueous amine oxide, and the amine oxide solvent leaches into the bath, producing cellulose fibre.

JP-A-8-170224 discloses a biconstituent fibre of the islands-in-the-sea type in which the continuous "sea" component is a cellulose-type polymer spun from an organic solvent system and the "islands" are composed of a polymer dyeable by a disperse dye and are 0 01-3 pm in size and form 2-45 % by weight of the fibre The disperse dyeable polymer is for example a polyester such as polyethylene terephthalate, sulphonic acid-modified polyethylene terephthalate or polybutylene terephthalate.

GB-A-2121069 discloses cellulose-based (viscose rayon) fibres for the production of nonwovens containing as mineral fillers barium sulphate, talcum, muskovite, or a mixture thereof, in an amount of from 15 to 60 %, preferably 40 to 50 %, of the total fibre mass, and, if desired, additionally hydrophobic, polymer or oligomer substances, such as polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyester, polytetrafluoroethylene or waxes, in an amount of from 1 to 60 %, preferably 25 to 50 %, of the total fibre mass GB-A- 2008126 discloses the use of polystyrene as a delustrant for viscose rayon fibres.

WO-A-98/46814 discloses lyocell fibre containing elongated domains of polyester, polyamide or an olefin copolymer, the domains having an aspect ratio of at least 1 5 and being aligned substantially parallel to the axis of the fibre The domains are 70-1000 nm in length and 30-400 nm in diameter.

Disclosure of the invention

According to the invention, there is provided lyocell fibre which includes domains of a low- melting thermoplastic polymer selected from the group consisting of polyesters, polyamides, and olefin polymers, characterised in that the fibre contains from 0 1 to 30 % by weight of the low-melting thermoplastic polymer and in that substantially all of the domains are not visible when viewed by electron microscopy at x 9000 enlargement In an alternative formulation, the maximum dimension of substantially all of the domains is no more than 50 nm.

The fibre of the invention can be made from a solution of cellulose in an aqueous tertiary amine N-oxide ("amine oxide"), e g N-methylnorpholine N-oxide, which solution contains a suitable thermoplastic low-melting polymer in molten form The solution is extruded through a spinnerette via an air-gap into an aqueous coagulating bath The extrusion temperature is typically in the range from 90 to 1250 C The thusly- extruded fibre is then washed and dried.

The thermoplastic low-melting polymer should generally be sufficiently compatible with the cellulose solution that the polymer when molten does not agglomerate as a separate phase from the cellulose solution, but it is preferably not soluble either in amine oxide or in the solution of cellulose or in water A polymer should be chosen which is essentially all retained in the fibre during the extrusion (spinning), washing and drying processes One type of preferred low-melting polymer is a polyester, carboxy-functional polyesters being particularly preferred.

In general, we have found that the presence of carboxylic acid groups in the low-melting polymer increases its compatibility with the cellulose solution, giving more thorough mixing of the cellulose and the low-melting polymer For most uses, the polymer preferably has an acid value of at least 10, up to for example 50 or 100 or even 150 We also believe that a branched polymer structure may be advantageous.

The melting point of the low-melting polymer is preferably at least 50 C and up to 150 C, most preferably in the range 80 to 130 C, as measured by differential thermal analysis The Tg of the polymer is preferably higher than 30 C, more preferably higher than 50 C.

Examples of polyesters of this type having the required low melting point are formed from a mixture of aromatic dicarboxylic acids selected from isophthalic acid, terephthalic acid, and phthalic acid or anhydride, optionally with an aliphatic dicarboxylic acid such as adipic, succinic or sebacic acid, and one or more aliphatic diols such as neopentyl glycol, ethylene glycol, propylene glycol, propane-1,3-diol, butane-1,4-diol, butylene glycol or diethylene glycol Branching can be introduced by a trifunctional reagent, for example trimellitic acid or anhydride or trimethylolpropane, glycerol or pentaerythritol The required acid value can be obtained by using an appropriate excess of carboxylic acid-functional reagent Such polyesters are sold for use in thermosetting powder coatings, for example under the Trade Marks "Alftalat","Uralac" or "Grilesta".

Alternative thermoplastic low-melting polymers are polyamides, for example polyamides formed from fatty acid dimers and aliphatic diamines or the copolyamide sold under the Trade Mark "Griltex", or olefin copolymers, for example ethylene/vinyl acetate or ethylenelbutylene/butyl acrylate copolymers, preferably containing a small amount of acrylic acid comonomer to give the preferred acid value A further alternative low- melting thermoplastic polymer is an olefinic polymer such as poly(vinyl alcohol).

The concentration of cellulose in the solution to be extruded (otherwise known as the spinning solution) is generally 10 to 20 % by weight, preferably at least 13 or 15 % up to 17 or 18 % by weight The spinning solution preferably contains water, usually in the range 5- % by weight, with the remainder, generally 65-83 % by weight, being amine oxide The extrusion temperature is generally 95 to 1251 C.

The low-melting polymer can be added to the cellulose solution at any of various points during its preparation The polymer can for example be premixed with cellulose pulp, the pulp then being mixed with amine oxide and water to form the spinning solution The polymer can alternatively be added, preferably in molten form, to a preformed cellulose solution In a further alternative, a relatively high proportion of low- melting polymer is premixed with a preformed cellulose solution, for example forming 10 to 50 % by weight of the mixture The premixture can then be used as a masterbatch to add the low-melting polymer to cellulose solution at the required level In a still further alternative, the polymer is added to the amine oxide solvent and the resulting mixture is used to dissolve the cellulose.

The cellulose solution containing a low-melting polymer can be extruded to form fibres using the same spinneret at the same temperature as is conventionally used for forming lyocell fibre.

The domains of low-melting polymer are believed to be distributed uniformly throughout the fibre as a separate phase.

In contrast to the fibres disclosed in WO-A-98/46814, almost the entire amount of the polyester phase cannot be seen either by optical microscopy or by electron microscopy at x 9000 enlargement.

The level of low-melting polymer present in the fibre is from 0 1 to 30 per cent by weight based on cellulose The presence of the domains of low-melting polymer gives rise to various effects depending on the concentration of low-melting polymer and on the type of low-melting polymer used More specifically, an amount of from 0 5 to 15, preferably from 1 to 5, percent by weight may be preferred if crimp effects (explained hereinafter) are desired, whereas an amount from 2 to 20, preferably from 5 to 15, percent by weight may be preferred if textile effects (explained hereinafter) are desired.

The desired small domains of the thermoplastic polymer can be obtained in various ways For example, the polymer may be synthesised as small particles Alternatively, large particles can be comminuted for example by milling or grinding, or, preferably, by subjecting the spinning solution to high-shear conditions.

Lyocell fibre is naturally uncrimped However, crimp is desirable, particularly in staple fibre.

Crimp can be generated in lyocell fibre by stuffer-box crimping with the aid of dry steam, as disclosed in EP-A 0703 997 Experience has shown that such a process can generate up to about 2 3 crimps/cm without damage in conventional lyocell fibre Surprisingly, we have found the same process can generate up to about 4 5 crimps/cm in fibre of the invention.

Furthermore, we have also surprisingly found that variation of stuffer box geometry and temperature has considerably more effect on fibre of the invention than it does on conventional lyocell fibre We have also found that crimped fibre of the invention may have a higher crimp intensity, and that it may be less susceptible to mechanical damage during crimping, than crimped conventional fibre.

The invention accordingly further provides lyocell fibre having from 1 to 5 crimps/cm, characterised in that it includes domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers, wherein the fibre contains from 0 1 to 30 % by weight of the low-melting thermoplastic polymer and wherein substantially all of the domains are not visible when viewed by electron microscopy at x 9000 enlargement In an alternative formulation, the maximum dimension of substantially all of the domains is no more than 50 nm.

We have also surprisingly found that fibre of the invention is considerably easier to dry than conventional lyocell fibre This permits useful energy savings.

It is known that lyocell can be reacted with polyfunctional reagents in order to reduce its fibrillation tendency See, for example, EP 0 538 977, EP 0 665 904 and EP 0 755 467, the contents of all of which are incorporated herein by this reference Such reactions can be performed either on never-dried or on previously-dried fibre Similar reactions can be performed on fibre of the invention.

We have found that fibre of the invention may react less readily with such polyfunctional reagents than does conventional fibre This can be counteracted by using more forcing conditions, for example a higher reagent concentration.

We have surprisingly found that yam spun from fibre of the invention advantageously has higher tenacity and extensibility and contains fewer irregularities (thick and thin spots and neps) and is less hairy then yarn spun from conventional fibre The differences are especially marked if the fibres being compared were reacted in never-dried state.

The invention accordingly further provides a process for the manufacture of lyocell fibre which comprises the steps of:

( 1) extruding a lyocell fibre which contains domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers; ( 2) applying to the fibre in never-dried state a reagent having from two to six functional groups reactive with cellulose; ( 3) inducing reaction between the fibre and the reagent; and ( 4) drying the fibre, wherein substantially all of the domains of the low-melting thermoplastic polymer in the dried fibre cannot be seen by electron microscopy at x 9000 enlargement; or wherein substantially all of the domains have a maximum dimension of no more than 50 nm.

Yarn spun from crimped fibre of the invention, and fabric formed therefrom, are desirably more bulky than yarn and fabric of conventional crimped lyocell fibre The higher crimp intensity has been found to result in a bulkier yarn with improved uniformity This means that fabrics having acceptable porosity to light can be produced from thinner yams, i e yarns having a lower decitex The fabric produced from these thinner yams is more uniform and drapes more fluidly.

Fibre of the invention may be continuous filament or staple fibre.

Fibre of the invention can be formed into woven, knitted or nonwoven (e g hydroentangled, needlepunched or meltbonded) fabrics Such fabrics can be subjected to conventional processing treatments, such as being given a crease-resistant finishing treatment We have found that fibre of the invention which contains a low-melting polyester should not be causticised, because sodium hydroxide tends to hydrolyse the ester linkages.

Fibre of the invention may be dyed with conventional dyes for cellulose, for example direct and reactive dyes We have found that in at least some cases fibre of the invention has a higher receptivity to reactive dyes than known lyocell fibre which contains domains of polyester Polyester is not receptive to reactive dyes, but since the fibre of the invention contains only small domains of polyester, reactive dyes can be used to dye the fibre of the invention.

The low-melting polymer is generally a hydrophobic polymer, and thus susceptible to dyeing with disperse dyes We have however found that fibre of the invention dyed with a disperse dye suffers from cross-staining on laundering Accordingly, the dyeing of fibre of the invention with disperse dyes is not recommended.

Crimp in lyocell fibre can be assessed as follows A sample of titre about 200 tex is taken from a dry tow and placed under sufficient tension to pull out the crimp Marks are made on the sample 10 cm apart, and the tension removed The number of crimps between the marks is then counted The ratio of tensioned to untensioned length gives the crimp intensity or crimp ratio.

The invention is illustrated by the following Examples in which parts, percentages and ratios are by weight.

Examples

Comparative Example 1 Fibre containing particles of a low-melting polyester was prepared generally according to Example 1 of WO-A-98/46814 The polyester was a carboxy-functional saturated polyester resin of the kind used in powder coatings, having acid value about 40, melting within the range 95 to 130 'C, and having a branched structure Mixing of polyester into the cellulose solution was performed under low-shear conditions using a Z-blade mixer with blade tip speed 0 33 m/sec and gap approximately 4 mm A fibre having a diameter of 10 x 10-6 m was produced A cross section of the fibre produced, photographed using electron microscopy at x 9000 enlargement is shown in Figure 1 of the accompanying Figures The large black cracks are a result of the sample preparation and do not indicate the presence of another material other than cellulose It can clearly be seen that there are polyester particles visible in the fibre at x 9000 enlargement.

Example 1

Polyester resin of the kind used in Comparative Example 1 was mixed with 77/23 N- methylmorpholine N-oxide (NMMO)/water in a ploughshare mixer at about 70 TC After about 2 minutes, shredded woodpulp was added, after which mixing was continued for a further 10 minutes The ratio of woodpulp to resin was 92 8:7 2.

The mixture was passed through a Buss 5 5 m 2 Filmtruder (Trade Mark) Unit H 50055 to remove excess water and thereby form the spinning solution During passage through the Filmtruder, the mixture was subjected to high-shear conditions in a layer about 2-2 5 mm thick with blade speed about 5 m/sec for about 10 minutes The spinning solution contained 13.5 % cellulose, 1 1 % polyester, 75 4 % NMMO and the balance water.

The solution was extruded at 105 'C through a spinnerette by way of an airgap into an aqueous coagulating bath to form a fibre tow in conventional manner The dried fibre was of titre 1 7 dtex, contained about 8 1 % polyester on cellulose, and had 8 % moisture content A fibre having a diameter of 10 x 106 m was produced A cross section of the fibre produced, photographed using electron microscopy at x 9000 enlargement is shown in Figure 2 of the accompanying Figures The large black cracks are a result of the sample preparation and do not indicate the presence of another material other than cellulose Traces of polyester domains were visible in the fibre at x 9000 enlargement (believed to correspond to a resolution of about 50 nm) but substantially all of the polyester domains are not visible Optical enlargement of the picture shown in Figure 2 does not reveal any additional traces of the polyester domains.

The fibre was crimped in the general manner disclosed in EP-A-0,703,997 The fibre had 2 6 crimps/cm and crimp intensity 1 3 In comparison, conventional lyocell fibre (containing no low-melting polymer) crimped under the same conditions had 2 3 crimps/cm and crimp intensity 1 23.

The fibre was cut to 38 mm staple and ring-spun to make 20 tex yam The results obtained are shown in the following table, in which:

C V % = Coefficient of Variance of yarn mass, expressed as a percentage Irregularity Index = Actual C V % divided by the Limiting C V %, where Limiting C.V % = 100/vn, where N is the number of fibres in crossection (yarn tex divided by fibre tex) An Irregularity Index of 1 is a perfect yam.

Thins (-40 %) = in a kilometre of yam, the number of places at which the thickness of the yam is less than 40 % of the nominal thickness, as determined by the Uster Tester 3 test Thicks (+ 50 %) = in a kilometre of yam, the number of places at which the thickness of the yarn is greater than 50 % of the nominal thickness, as determined by the Uster Tester 3 test Neps (+ 200 %) = in a kilometre of yam, the number of places at which the thickness of the yarn is greater than 200 % of the nominal thickness, as determined by the Uster Tester 3 test Hairs = indirect measure for the number and cumulative length of all fibres protruding from the yarn surface, as determined by the Uster Tester 3 test Yam Tenacity Extension Regularity Irregularit Thins Thicks Neps Hairs c N/tex % C V% y Index (-40 %) (+ 50 %) (+ 200 %) Control 25 7 3 13 3 1 44 87 10 15 5 85 Ofthe 27 8 5 12 3 1 34 41 7 7 5 52 invention Example 2

Example 1 was repeated, except that crimper conditions were varied Conventional fibre can be crimped as set out in EP-A-0,703,997 using a stuffer box pressure of 8 psi ( 55 k Pa) and steam pressure 20 psig ( 138 k Pa) Higher pressures can lead to uneven crimp, tow damage, and stuffer box blockage Fibre of the invention could be satisfactorily crimped using stuffer box pressures up to 15 psi ( 103 k Pa) and steam pressures up to 43 psig ( 296 k Pa), thus giving very even crimp levels of up to 4 0 crimps/cm and crimp intensities of up to 1 50 with no signs of fibre damage Lower pressures yielded fibre with similar crimp properties to crimped conventional fibre.

Example 3

Example 1 was repeated, except that the fibre was reacted in never-dried state with 1,3,5- triacryloylhexahydro-l,3,5-hexahydrotriazine (TAHT) as described in EP-A- 0,755,467 at an application level of 0 7 % by weight on the fibre as an anti-fibrillation treatment The following results were obtained on yamrns spun from treated fibres:

Yam Crimps Tenacity Extension Irregulanty Thins Thins Thlcks Neps Hairs per 10 cm c N/tex % Index (-30 %) (-40 %) (+ 50 %) (+ 200 %) Control 24 24 7 9 1 48 1049 72 62 48 6 37 Invention 24 25 8 2 1 32 595 29 23 31 5 30 Invention 30 26 8 5 1 32 590 25 12 19 5 05 Invention 40 26 8 8 1 27 443 14 13 13 5 09 Dyed single-jersey knitted fabrics made from yams spun from treated fibre of the invention showed no signs of fibrillation after 10 domestic wash/tumble cycles at 40 C.

Claims (8)

1 Lyocell fibre which includes domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers, characterised in that the fibre contains from 0 1 to 30 % by weight of the low-melting thermoplastic polymer and in that substantially all of the domains are not visible when viewed by electron microscopy at x 9000 enlargement.

2 Lyocell fibre which includes domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers, characterised in that the fibre contains from 0 1 to 30 % by weight of the low-melting thermoplastic polymer and in that the maximum dimension of substantially all of the domains is no more than 50 rnm.

3 Lyocell fibre according to claim 1 or claim 2 characterised in that the fibre contains from 0.5 to 10 % by weight of the low-melting thermoplastic polymer.

4 Lyocell fibre according to claim 3 characterised in that the fibre contains from 1 to

5 % by weight of the low-melting thermoplastic polymer.

Lyocell fibre having from 1 to 5 crimps/cm, characterised in that it includes domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers, wherein substantially all of the domains cannot be seen by electron microscopy at x 9000 enlargement; or, wherein substantially all of the domains have a maximum dimension of no more than 50 nim.

6 Lyocell fibre substantially as herein described and with reference to Examples 1 to 3.

7 A process for the manufacture of lyocell fibre which comprises the steps of:

( 1) extruding a lyocell fibre which contains domains of a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers; ( 2) applying to the fibre in never-dried state a reagent having from two to six functional groups reactive with cellulose; ( 3) inducing reaction between the fibre and the reagent; and ( 4) drying the fibre, wherein substantially all of the domains of the low-melting thermoplastic polymer in the dried fibre cannot be seen by electron microscopy at x 9000 enlargement; or wherein substantially all of the domains have a maximum dimension of no more than 50 nm.

8 A process for the manufacture of lyocell fibre substantially as herein described and with reference to Examples 1 to 3.