Preparation, Bleaching, Dyeing and Finishing of Linen

FREDERICK R. W.SLOAN crease-resist treatments; embrittlement at and, moreover, the economics at present
the nodes, however, is a limiting factor. prices for fibre are not encouraging.
Kirkpatrick of Ballyclare Ltd Recently Neenan [3] has investigated
Co. Antrim Retting the feasibility of producing linen by the
N. Ireland Linen fibre is obtained from the flax dew-retted route in Eire. His work indi-
plant Linium Usitatissimurn by a compli- cated that in certain areas the correct
Linen has gradually been losing its posi- cated process of chemical or biochemical combination of moisture and heat pro-
tion as an apparel fabric since the 1950s and mechanical treatments to separate duced a similar fungus suitable for dew
and as a consequence has become an the fibre from the woody core. The older retting to that obtained in Northern
insignificant commercial target for dye method of water retting is now almost France, the most important of which is
manufacturers. There have thus been no extinct owing t o its high cost. The Chdosporiurn .
worthwhile studies of dyeing kinetics and method currently in widespread use is
dyeing behaviour in this field. Too often ‘dew retting’, i.e. allowing the straw to lie Fabric Preparation and Bleaching
the comment, ‘linen dyes like cotton’, is on the ground until the combined action The conventional method of preparing
heard and, although this is true to some of weather and fungus degrades the and bleaching linen involves a plurality of
extent, the large difference in morphol- woody core. A further objective of rett- treatments: a lime boil followed by
ogy between these two fibres‘affects the ing is to partially break down the lignin hydrochloric acid sour, alkaline boils
dyeing kinetics, not to mention the or binding material which is approx- (soda ash), acid chemic (hypochlorite at
effects of linen preparation. imately 2% of the total fibre assembly. pH 4-5), a further alkaline boil (soda
The emergence of linen as a compo- This enables the primary fibres to ash) which removes the chlorinated sprit
nent of blends has stimulated consider- separate so that they are free to draft (remnants of the woody core of the flax
able interest in preparation, bleaching and when drawn during preparation and wet stem), and, finally, a hypochlorite bleach
finishing as evidenced by the number of spinning. (pH 9- 10). T h s complicated sequence
papers published in the last few years. It Because of the non-uniform nature of has been streamlined over the years. The
is of interest to note that the first ‘dew retting’ along the stem of the plant lime boil has been replaced by a caustic
reference to blending is in the Bible - from root to tip and the difficulty of soda-soda ash boil. Sodium chlorite,
Deut. 22-11 [ l ] refers to the blending gathering the straw at precisely the right hydrogen peroxide and sodium hypochlo-
of wool and linen. The Jewish Laws were moment, there has been a tendency to rite are used as bleaching agents; niorc
often functional as well as religious and it under-rett. Consequently, the requisite often the first two are used in sequence.
is possible that the advantages of using amount of fibre separation is then Linen can be bleached white from the
both fibres in a blend without the dis- obtained by chemical treatment at the grey state without any prior boiling treat-
advantages of either alone were rec- spinning stage. Suitable methods have ment by using higher concentrations of
ognised. However, the method then of been developed by linen research estab- sodium chlorite (20-30 gl-’ at 85°C and
preparing, etc., linen cloth was to beat it lishments in France and Northern Ireland pH 3.5-4); the impurities in grey flax
with stones in the river, followed by [2]. The difficulty, however, is to obtain activate sodium chlorite. A novel method
treatment with sour milk; this would have a standard formula applicable to all types of activating this bleaching agent using
felted the wool - hence the law. of flax. The technique is relatively simple; water-soluble polyesters has been des-
Linen is a unique fibre, although an roving is prepared in the usual way, but cribed [4]. When sodium chlorite alone is
apparent paradox in that it is both wound on to stainless steel or plastic used it is essential to follow with a good
inextensible and flexible. Its structure is bobbins. The bobbins are then treated emulsifying boil to obtain a stable white.
essentially a highly crystalline arrange- with mild alkali on equipment identical The influence of retting on chlorite or
ment of anhydroglucose units, which to that used for bleaching yarn; bleaching peroxide bleaching of linen has been
accounts for its inextensibility. The flex- can also be carried out at this stage. studied by Boute [S]. He has shown that
ing or bending takes place at the nodes, Dew-retted flax is more difficult to changes in colour and chemical constitu-
which are natural bending points distrib- bleach and in some instances, when the tion during dew retting account for dif-
uted 0.03 mm apart along the fibre to fibre is very dark in colour, bleaching is ferences in behaviour on subsequent
enable the flax plant to bend under the extremely difficult and costly. The dark bleaching. Ruiker [6] has considered the
forces exerted by wind and rain. These colour is associated with a fungus called morphology of linen and the nature and
nodes are also areas of weakness, account- Altanaria, which must be avoided. It amount of impurities in relation to
ing for the relatively poor abrasion resist- appears under damp conditions and when modern trends in scouring and bleaching.
ance of the fibre and its propensity to the retting process is well advanced. Over Van Lancker [ 7 ] has studied the effect of
crease. They also account for the very the past ten years continuous efforts have different fabric treatments on the
rapid absorption and desorption of water, been made to obviate the retting process moisture absorption of linen. Lambrinou
providing the unique cool handle of linen. by scutching the flax green. Problems [8] has examined the effect of 14 dif-
It is of interest to note that linen has the associated with predictability and repro- ferent bleaching sequences on the struc-
highest measured response to chemical ducibility have so far not been solved ture of the fibre by photoniicrography.

12 REV. PROG. COLORATION VOL. 5 1974

 She observed that optimum results were there is a significant increase in abrasion not be said of the catalyst, which
obtained with a mixture (3: 1) of soda ash resistance. It is also used to disembrittle migrates freely, resulting in a concentra-
and caustic soda, followed by a chlorite linen finished with crease-resist resins or tion of acid at the crowns (high spots in
and peroxide bleaching sequence. chemical crosslinking agents. Mercerising the fabric) of the yarns. A water-soluble
The mechanism of bleaching with of linen fabrics is beneficial in the follow- polyester catalyst produced from tri-
sodium hypochlorite and sodium chlorite ing ways: ethylene glycol and citric acid was uti-
is not yet fully understood, notwithstand- lised by Sloan [I41 to overcome this
ing long association with usage under 1. It significantly improves abrasion problem with some degree of success. The
varying conditions. The formation of resistance. best results were obtained using a carba-
labile ions or free radicals is a likely 2. It covers the reediness in cloth associ- mate type resin. An advantage of this
mechanism. Peters [9] has examined the ated with yarn unlevelness - a feature method is that it does not require a
various theories from consideration of the of linen yarn. subsequent mercerising treatment. How-
kinetics involved. 3. It improves colour yield. ever, on using . t h e process in bulk
T h e modern, more streamlined, improvements were marginal. It remains
methods result in a lower weight loss The use of liquid ammonia as an alterna- difficult, therefore, to improve signifi-
(around 15%) than with the older tive to caustic soda solution of mercer- cantly upon the original Tootal, Broad-
methods (about 25%). This is due to only king strength has been investigated at hurst Lee process for producing a crease-
partial removal of the hemicelluloses, L.I.R.A. [ 121. Behaviour was similar to resist linen. The author has found that
which are low-molecular-weight poly- that observed with caustic soda, but the optimum results are obtained by omitting
saccharides and polyuronides. These are maximum shrinkage was somewhat less. the pre-mercerising stage and allowing all
sensitive to alkaline treatments and are T h e appearance, however, of the of the shrinkage to take place at the
present in the linen fibre to the extent of ammonia-treated dyed fabric was cleaner, subsequent mercerising stage; use of
about 18%. The absence, or otherwise, of and dye penetration superior. carbamate resins with the citric acid-
hemicellulose would appear to have little It is of interest to note that, if yarn is polyester catalyst gave the best overall
effect on dyeing behaviour. From studies treated with liquid ammonia by the Pro- result. It has long been recognised from
carried out by Sloan [ 101 there is grade process (J. & P. Coats), subse- studies at L.I.R.A. that the type of flax,
evidence that removal of hemicellulose quently woven into a cloth and finished degree of fineness and retting procedure
leaves the fibre more vulnerable to with a reactant resin, no worthwhile all have an important influence on the
damage by subsequent exposure to acid improvement in abrasion resistance is final result.
o r oxidising conditions, particularly obtained. The same considerations apply Demand for durable-press properties
during resin treatment and chemical to yarn treated with caustic soda. Investi- in linen tablecloths resulted in an investi-
crosslinking under anhydrous acid condi- gations of the effects obtained with liquid gation by L.I.R.A. [15]. The results
tions. Nothing is known of the distribu- ammonia at very low temperatures may indicated that linen was unacceptably
tion of the hemicellulose; it is probable prove rewarding. embrittled at the level of durable-press
that it is concentrated in the nodal Recently Kane [13] examined the rating required, e.g. 3-4. Notwithstand-
regions. application of various dyes to different ing the limitations indicated, considerable
A problem that may arise when chlo- fibres from anhydrous ammonia at yardages of 100% linen have been pro-
rite or peroxide (or both) is used as the -40°F. The results obtained were com- duced using a simple bifunctional cross-
bleaching agent is that of the presence of parable to those obtained by the conven- linking agent together with a stiffening
‘sprit’. This term is commonly used to tional route. This could prove of interest agent. The results, however, at best could
describe remnants of the woody core of where c o n s e r v a t i o n of water is only be described as marginally accept-
the flax stem present in small amounts. It mandatory. able. The use of blends of cellulose and
contains some short fibres and has a man-made fibres, however, enabled
higher lignin content than the rest of the Finishing materials to be made which gave reasona-
fibre. The dyeing properties of sprit [ 1 I ] In finishing the high measured response ble performance.
may differ from those of the linen fibre; of linen fabric to crease-resist and The finishing performance of linen in
it dyes more heavily (Alcian Blue 8GX), durable-press finishes continues to stimu- relation to fabric construction, bleaching
lighter (some vat and reactive dyes) or late research. Clearly, if the problem of treatment and absorbency has been
equally (selected vat dyes) compared with severe embrittlement could be minimised investigated by Lambrinou [ 161. She also
linen. When fibre is obtained by the sufficiently, linen would have outstanding studied the influence of fibre type,
turbine-scutched route and is well performance as a crease-resist fabric. It is bleaching methods and finishing processes
machined there is less possibility of sprit believed, however, that most of the resin on abrasion resistance and, finally,
being present (it is a common hazard, or chemical reactant is concentrated in showed the relation between crease-resist
however, with tow-type scutching). The the nodal regions. Moreover, because of level and loss in tensile strength and
only effective way to remove it is by the ease with which moisture can enter changes in water regain [ 171. Aluminium
treatment with acid hypochlorite. and leave this area, migration of reactant chlorohydroxide [ 181 is a useful chenu-
during drying is a much more acute cal for broad applications of various types
Mercerising problem as compared with cotton. of crease-resist treatment under moist-
Mercerising is an important part of linen Clearly, the reactant is limited in its cure, mild-cure and hard-cure conditions,
preparation and it is a matter of concern migration by either reaction with the and is particularly useful for producing a
that it is not more widely used. Swelling cellulose or increase in molecular size by low-temperature durable-press finish on
takes place at the nodes and as a result polymerisation. The same, however, can- linen tablecloths. ln recent years there

REV. PROG. COLORATION VOL. 5 1974 13

has been considerable interest in vapour- take place under the forces of dynamic remove sprit, would degrade the acrylic
phase crosslinking using formaldehyde and static friction such as occur in component and seriously destroy the
and gaseous hydrochloric acid; this route varying degrees on all spinning systems. wool component. Recommendations for
offers possibilities for linen since it avoids Thus it was possible to break down the finishing polyester-Linron blends are
anhydrous conditions*. Very few methyl- compound fibres by a dry-spun route in available from Kirkpatrick [22].
ene crosslinks are required to produce a much the same way as occurs on wet
substantial increase in crease resistance. spinning. Hence, for the first time a Dyeing
Recent research in the use of diepoxides bleached and purified linen fibre was The lack of published work or detailed
from organic solvents for imparting crease presented to the spinner which was not studies of the dyeing of linen and blends
resistance to cotton is worthy of exami- unlike a synthetic-polymer fibre and had has already been mentioned. Much practi-
nation in relation to linen and undoubt- a reproducible and predictable behavioui-. cal information has been gathered over
edly work along these lines will take The fibre assembly in a linen yarn is the years and is available in the form of
place. Grafting a thermoplastic polymer essentially a high-density packing. This pattern cards and technical information
by irradiation produced negative results presents difficulties with liquor penetra- manuals from various dye manufacturers.
on linen [ 191 . t i o n and uniformity of treatment It is essential that linen or linen-blend
throughout the cross-section of the yarns, material is well prepared and free from
Blends which in turn produces problems in dye- creases before dyeing. Continuous (pad-
The emergence of linen as a component ing and finishing. These are overcome by steam) and discontinuous (pad-batch)
of blends represents perhaps a turning the use of Linron. vat dyeing of linen fabrics is still standard
point in the decline of the industry. The greatest success for Linron has practice. The discontinuous method,
Terylene (IC1)-linen blends (50:50) were been in blends with wool and it has however, is the one in most general use
the first to appear. The blend yarns were enabled wool to be acceptable in spring- because of the lack of long runs per
spun on both the wet and the dry and summer-wear. It is interesting to note colour owing to the decline of linen as an
systems. With wet spinning the polyester that in such blends (up to a 40:60 ratio) apparel fabric. Phillips [23] has given an
was stretch-broken at the reach on the there is no apparent decrease in crease- account of the method from the practical
frame, with the result that it migrated to resist angle as compared with 100% wool. dyer’s point of view. Generally, it is
the core of the yarn. With dry-spun yarns Apart from the coolness and crispness of necessary to select dyes of low strike and
there was no stretch-breaking; resulting this blend, the emotional and prestige high rates of diffusion if well-penetrated
from alkaline treatments of the cloth appeal associated with these two fibres is dyeings are required, particularly when
formed from the yarns, the linen migra- undoubtedly a factor in its commerciai solublised vat dyes are employed. Dark
ted to the core on shrinking. The dry- acceptance. Clearly, as spinning costs colours such as navy and black can be
spun yarns had different dyeing and increase it may not be economic to spin dyed economically with sulphur dyes.
finishing properties and difficulties arose grey flax, when up to 25% of the weight Reactive dyes, e.g. Procion (ICI), are
if they were inadvertently mixed. is subsequently to be removed; nor can it particularly suitable for dyeing liner:
Generally, dry-spun blends could only be economical to bleach, say, a poly- because of their high rates of diffusion. A
be spun to relatively coarse counts (18s ester-Linron (67:33) blend yarn in cloth number of techniques are used in
metric) limited by the denier of the linen form when only approximately one-third practice:
compound fibres. of it requires the treatment.
Empirical methods of dyeing and The technical advantages, however, of 1. Pad-develop (beam or jig)
finishing new blends were developed by using Linron cannot be achieved by any 2. Pad-batch
ICI and L.I.R.A. Recently, Opitz [20] other route. Thus, for example, the 3. Continuous dyeing
studied the effect of weft tension in quality control and larger surface area 4. Beamdyeing
blends during dyeing and finishing, partic- produce higher abrasion resistance. In
ularly with crosslinking agents, and indi- addition, because the fibre is stabilised Because of the lack of long runs per
cated that improvements in weft tear there is little or no migration during colour techniques 1 and 2 are most
strength could be obtained by careful subsequent wet treatment, although treat- commonly employed. Reactive dyes give
control of tension throughout. The devel- ment with alkali of mercerising strength well-penetrated dyeings of excellent
opment of a bleached, peptonised, chemi- will cause the Linron to move towards quality. The skittery effect sometimes
cally pure linen fibre (Linron) by the core of the yarn. Naturally such associated with vat dyeings is notably
Kirkpatrick of Ballyclare [21] opened up treatment cannot be used in blends with absent.
completely new vistas for linen as a blend wool. Fine yarns up to 45s metric count Fox [24] has compared the dyeing
component. The precise chemical route have been produced on the cotton system behaviour of unmercerised linen using
of producing Linron has not been pub- of spinning in a blend of polyester- Procion M dyes with other fibres, e.g.
lished, but essentially it is a treatment Linron (67:33). So far it has not been cotton, rayon, Vincel 28 (Courtaulds)
that does not use alkali and allows fibril- possible to obtain similar results utilising and jute. The highest rate of dyeing is
lation of the compound fibre strands to green flax (unretted), so it must be shown by cotton and the lowest by
assumed that the retting process, particu- rayon. Linen was intermediate between
*It has recently been drawn to my attention larly by fungus, plays an important part. cotton and rayon on the one hand and
( C h e m . i n Britain, 9 (Sept 1973) 424) that With wool- and acrylic-linen blends Vincel 28 and jute on the other. Measure-
bis-chloromethyl ether, a highly toxic carcinog- this is the only route possible, since the ment of substantivity showed also that
enic compond, may be formed whenever
formaldehyde and hydrochloric acid come into normal method of preparing and bleach- linen was intermediate between cotton
contact. ing the linen component, expecially to and rayon. The rate of levelling, using C.I.

14 REV. PROG. COLORATION VOL. 5 1974

Reactive Red 8, was much lower on linen solubilised vat dyes wdl cover both com- Linen as a component of blends has
than cotton and considerably lower than ponents in light and pastel colours. Vat or much to offer. Traditionally it is consi-
on 1.5-den rayon. Measurement of strike reactive dyes in conjunction with disperse dered to be the most comfortable fabric
again showed that it was much lower on dyes can be used over a wide range of to wear under hot, humid conditions and
linen than on cotton and low-denier colours. Informa tion o n dyeing these the properties that make it so can be
rayon. blends is available [31]. transferred to blends. Spencer-Smith
Theoretical and practical aspects of Wool-Linron blends can be dyed [35] has investigated these properties -
batchwise dyeing with reactives have been using Procion dyes [32] (under condi- the high density, allowing relatively heavy
discussed by Marshall [25]. The influ- tions that do not damage the wool) for material to be constructed which has low
ences of finishing using bifunctional the cellulosic component and, subse- heat and water-vapour resistance, the high
amine reactants or resins have to be taken quently, acid or reactive wool dyes for rate of moisture absorption and the total
into consideration. The latter can effect the wool. Solid contrasting or tone-in- amount of moisture absorbed without
changes in light fastness and promote tone effects can be obtained. imparting a feeling of dampness. These
unexpected colour changes associated Acrylic-Linron blends are used three factors, together with high thermal
with photoreduction of certain dyes. mostly in knitted fabrics. The combina- reflectance, were found to be important.
Pfoff [26] has studied the effects of tion of a shrink-stable fibre such as He also observed a buffering action which
different resin catalysts on a range of vat, Linron with a high-shrink fibre such as a allows a large temporary increase in heat
direct and reactive dyes. He has shown bulked acrylic fibre enables the Linron loss, providing increased comfort under
that changes in light fastness and photo- component to move to the outside of the tropical conditions [36].
tropy are predictable from considerations yarn, thereby producing a maximum Solvent scouring and dyeing are
of resin structure, but changes in colour linen affect without the disadvantage of unlikely to prove of much value except
are not so related. The ‘after mercerising’ slubs, etc., which would present knitting where water is scarce; organic solvents
process can have a profound effect on problems, particularly on the finer-gauge will not remove lignin. Application of
colour, particularly with vat dyes; most machines. The usual blend level is 70:30 crosslinking agents from solvents is likely
of these, however, are noted in dyestuff acrylic-Linron, but because of fibre to prove of interest.
manufacturers’ pattern cards. migration the appearance of the yarn is Vacuum-impregnation techniques
With polyester-linen blends the pad- more linen-like. Reactive dyes in conjunc- [37] are likely to be of value, because
thermofix method employing vat or tion with disperse dyes are recommended linen and linen-blend fabrics lend them-
solubilised vat dyes and disperse dyes is WI. selves to padding techniques; penetration
commonly in use, although the mecha- Considerable quantities of natural and wetting problems are not infrequent
nism of dyeing is complicated. The dis- grey flax are used in blends with poly- in conventional dip-nip systems of
perse dye is first adsorbed by the cellu- ester and acrylic fibres to obtain coloured impregnation.
losic component and then transferred by effects. This is a dangerous practice The possibility of applying crease-
vapour-phase migration [27] to the poly- because of the poor fastness to light and and flame-resist finishes t o the fibre
ester. Practical aspects have been consi- bleachmg of the natural linen component. before spinning is worthy of investiga-
dered by Fox. et el. [28]. The partition A joint investigation by ICI and tion.
coefficients in the dyeing of linen- Kirkpatrick has shown that Linron can be Although linen is used t o obtain
polyester blends have been investigated dyed a natural colour, e.g. ecru, at the surface appeal on cloths, it is of interest
by Kruglov et el. [29]. They found a fibre stage using Soledon dyes [34]. The to note that polyester-Linron blends for
relationship between pH over the range presence of alkali promoted intense fibril- double-knit fabrics are now well estab-
2-9 and the partition coefficients of vat lation, so normal vat dyes could not be lished in the U.S.A., in spite of the lack
dyes. A useful practical summary of the used for this work. of interest of American producers in
preparation, dyeing and finishing of poly- surface effects. The cool, comfortable
ester-linen (50:50) blends has been given The Way Ahead handle given to the cloth is the prime
by Bruggeman [30]. The Linron concept has opened up possi- factor.
With Linron-polyester blends more bilities and outlets for linen in a plurality It remains to be seen whether the
uniform colouring of the Linron com- of blends and blend levels never before interest now shown in linen will promote
ponent is achieved with better penetra- thought possible. Today, blends with more detailed research. Linen, which is as
tion. This is undoubtedly due to the more cotton, wool, polyester and acrylic fibres old as the hills, is now as modern as the
uniform preparation of the fibre and the are well established over the complete hour - a factor that must promote its
greater surface area resulting from break- range of spinning systems. acceptability and use.
down of the fibre bundles. Soledon (ICI)

References 5 . Boute, Bull. Inst. Text. France, No. 9. Peters, ‘Textile Chemistry’ Vol. I1
24 (July-Aug 1970) 637. (Amsterdam: Elsevier, 1967).
1. Dr Moffat’s translation. 6. Riiiker, Melliand Textilber., 51 10. Sloan, unpublished work.
2. Lambeg Industrial Research Associa- (1970) 1085. 11. Fox, private communication.
tion. 7. Van Lancker, lndustrie Textil Balge, 12. L.I.R.A. Memo No. 2069 private
3. ATPUL and Neenan, Sci. Proc. Royal 13 No. 5 (1972) 41. reports.
Dublin SOC.,3 (14 Dec 1973) 201. 8. Lambrinou, Melliand Textilber., 52 13. Kane, Amer. Dyestuff Rep., 64 (May
4. Sloan, BP 821,168 (1958). (1971) 1184. 1973) 27.

REV. PROG. COLORATION VOL. 5 1974 15

14. Sloan, BP 877,582 (1958). 23. Phillips, J.S.D.C., 74 (1958) 180. 30. Bruggeman, Bull. Inst. T k t . France,
15. L.I.R.A. Memo No. 1848 private 24. Fox, private communication. No. 25 (1971) 161.
reports. 25. Marshall, Textilveredlung, 4 (Sept 3 1. Kirkpatrick of Ballyclare, Tech. Bull.
16. Lambrinou, Melliand Textilber., 51 1969) 19; Amer. Dyestuff Rep., 58 No. 4.
(1970) 930. (Aug 1969) 19. 32. Idem, Tech. Bull. No. 1.
17.Idem, ibid., 51 (1970) 815; 1241; 26. Pfoff, Z. Fur die ges. Textilind., 71 33. Idem, Tech. Bull. No. 2.
930. (1969) 616. 34. Idem, Tech. Bull. No. 6.
18. Thonig and Schmidt Textil Praxis, 27 27. Bent, Flynn and Sumner, J.S.D.C., 85 35. Spencer-Smith, Shirley International
(1972) 616. (1969) 606. Seminar, Textiles for Comfort (June
19. Spencer-Smith, L.I.R.A. private 28. Fox, Glover and Hughes, ibid., 85 1 97 1).
reports. (1969) 614. 36. Idem, private communication, Text.
20. Opitz, Textil Praxis, 27 (1972) 166. 29.Kruglov, Eruknimovitch and Research J., 36 (1966) 855.
21. Chem and Ind., (1 1 Mar 1967) 378. Kopelman, Tekstil. Prom., No. 6 37. Fox, Amer. Dyestuff Rep., 61 (Mar
22. Kirkpatrick of Ballyclare, Tech. Bull. (June 1971) 50. 1972) 48; J.S.D.C., 89 ( 1 973) 474.
No. 3.

16 REV. PROG. COLORATION VOL. 5 1974