1!

!• 1

.!

I

A\rA? L' if 1

I T, rI •,»r. ,w >•«i Vv-i1::

A futuredenim blueprint

4

iii;

;>,t

':

,

i i!I

With over 30 years in the denim sector, many of these at the cutting edgeof manufacturing technology,Miguel Sanchez speaks to John Mowbray

about what 'sustainable' denim production could actually look like.:

i

i i

other environmental challenges for thedenim sector that impinge on fibre type,yarn preparation, dyeing, finishing andespecially laundering. All theseproduction steps can have a significantimpact on the environment before asingle drop of liquor reaches thewastewater treatment plant - if there isone. Or if there is a wastewater treatmentplant, how often is it used correctly?

Yet water, along with its unnecessaryconsumption and waste, still remainsthe central area of concern when itcomes to denim's impact on theenvironment. It's been widely quotedthat it can take anything up to 1,800

gallons of water to make one singlepair of jeans. Although Levi Straussclaims an LCA it conducted on a pair ofits 501 jeans uses 3,781 litres of waterin its full lifecycle (830 gallons).

So, what will the denim mill of thefuture look like if the industry is to startimplementing some of the newtechnologies that are coming on stream?And what are these new technologies? •

What sort of blueprint should theindustry be looking to achieve from asustainability point of view? And is thiseven technically feasible?

The good news is that investment inbest available technology continues in

decent pair of jeans is anessential part of a modernwardrobe, but over recentyears consumers have

started to ask: "at what cost to theenvironment? "A question whichmultiplied after the release of theRiver Blue documentary back in 2016that looked specifically at textileeffluent pollutio.

Since then, and quite honestly beforethen, the denim industry has upped itsgame to develop new productiontechnologies to improve its environ-mental profile when it comes towastewater discharge. But there are still

A!I;!

/

!

8

I I:i r

. i

'mnyl Knvmiv!

which is necessary to turn the indigodye molecule bright blue. Commercialdenim fabrics are being dyed with thismethod at Tejidos Royo in Spain.

As with any new technology thereare also some downsides. Initially theseare usually related to cost beforeeconomies of scale are achieved. "Theconcept is in itself very interesting andhas a clear plus in terms of sustainabilityover the conventional dyeing with adyebath solution," said Sanchez. "Morepractical experience is required toconfirm important aspects such asdyeing levelness on different yarns,achievable range of depths, casts andshades, flexibility for ring/solid dyeingand variety of wash down looks."

It's likely that only practicalexperience will determine whether thistechnology is either a replacement orjust a complement of existing denimdyeing techniques.

He also notes there is more interestfrom denim mills for dyeing ranges withboxes that allow for pre-treatment,washing and after-treatment, or thatincrease the efficiency of the dyeingand washing-off of unfixed dyes.

the industry despite the fact there arealready signs of a denim over-capacityfor 2019. We also know that at theITMA event in Barcelona, there will bemore new environmental solutions dueto be released from the main suppliersof denim technology.

Nitrogen fixationMore recently, denim dyeing accessoriesthat use foam-blown nitrogen (asopposed to other foams) have beendeveloped to reduce dyebath volumeswhile increasing dye fixation.

The concept of using foam instead ofwater to deliver indigo dyes to yarns is aninteresting one from an environmentalpoint of view. Indigo yarn dyeing is notedfor using large amounts of water,whereas foam dyeing is a water-savingtechnique - albeit known for many years.Yet foam has been a problem for indigodyeing because the dye reacts with airtrapped inside the foam,which stops itpenetrating the cotton fibre.

The idea is that using foam blownwith nitrogen - instead of oxygen-ladenair - is said to overcome this problem.

New machines are now availablefrom the likes of US-based Gaston Millswhich uses a patented techniqueoriginally developed by Indigo MillDesigns. This technology is said tomaintain oxygen-free conditions untilyarns are ready for exposure to eitheropen air or to an oxidation chamber,

Technology trendsIn terms of indigo dyeing denim, brandswho stop by Planet Textiles 2019 andthe ITMA textile machinery show inBarcelona in June (see: p. 54) will beable to see the current 'best available'

machinery technology that nowincludes water saving technology, usingnitrogen and foam application of indigodyes, along with other new techniques.

Speaking to Ecotextile News, denimexpert Miguel Sanchez, who has beeninvolved in denim dyeing for over 30years says that modern denim millsinterested in investing in sustainabilityshould consider a number of keytechnical factors when looking at newdenim warp dyeing ranges.

"These include flexibility andsimplicity," he said. "Compact rangesthat can do the same work or evenbetter than traditional multi-box denimdyeing ranges, yet reduce complexityand improve quality. This also results inthe minimal use of resources - partic-ularly water - without compromisingon high quality dyed yarns."

Spray dyeingElsewhere there has been renewedinterest more recently in spray dyeingtechniques for denim yarns. Unlikefoam dyeing, RotaSpray in Germanyuses rotating atomisers to colour yarnsand in December installed its 'RotoDy-erTWIN' installation for denim warpyarn spray dyeing at Mou Fung Ltd inZhuhai, China.

Founded in 1970,Mou Fung was the ©

ecotextilenews | 29

Bums

DyStar

Combine the most sustainable indigo dyeing process withlatest garment finishing technology for the ultimate ecolo

i

processing of denim.The Cadira® Denim process using DyStar Indigo Vat 40% Solution andSera® Con C-RDA allows salt-free dyeing with strong effluent load reductioFor laundry applications DyStar offers Cadira Laundry, a complete range oiproducts designed for the latest generation of ultra low liquor ratio machii

|

www.DyStar.cCommitted to Sustainability* ,DyStar,econfidence,Cadira and Sera are registered trademarks of DyStar Colours Distribution

Denim weaving at Candiani, Italy -a firm well known for its environ- DENIM INDUSTRYmental approach.

first to introduce rope dyed denim intoHong Kong and is now one of the firstmills to use such a spray dyedtechnique in Asia, using warp yarnspraying for indigo, VAT, sulphur andreactive dyes. Commercial productionwill commence in June 2019.

Other units have already been sold todenim mills in Turkey, India and Pakistan,so it will be interesting to find out howthese machines have performed oncethey become established. It is somewhatdifferent to the foam dyeing, asRotaspray uses a dye solution as avehicle for colouring the dyed yarn butrequires much smaller volumes of waterthan other types of application."However, the same concerns aboutachievable levelness, depths, casts,shades are applicable to spray dyeing asmuch as foam dyeing," said Sanchez."The leading chemical companies andthe machine manufacturers should teamup to determine technical viability androbustness of a new equipment and fixthe application limits at differentconditions. Partnerships with companieslike Archroma or DyStar are usual andparticularly important in an ITMA year."

Secondly, Sanchez says there are stillconcerns about the presence ofbanned amines during themanufacture and application of indigo.Aniline being one potential problem."The volumes and handling ofwastewater containing heavy loads ofunfixed dye and hazardous chemicalspecies generated in production is alsoa worry," he added.

After being under the radar for awhile, the potential for aniline to findits way into wastewater has reared itshead again, after the launch of a new'aniline-free' indigo dye by Archromaback in May 2018.

Another potential solution to some ofthese problems has been to take thesulphur dye approach to denim dyeing.Although it's not quite as simple asthat, Sanchez - who until recentlyworked with Archroma on its sulphur-based 'Advanced Denim' dyeing -broadly agrees.

"The same equipment and basicsettings used for indigo dyeing can beused for sulphur dyes and are anothergood way to colour denim warp eitheras self-shade elements (e.g. blackdenim) or as complements of indigo inbottoming and topping processes," hesaid. "The continuous requirement fornew effects and looks increased the useof sulphur dyes to a level where inmany cases at least 50 per cent of thedenim articles in the stores are basedtotally or partially on these dyes."

Sulphur dyes (those with little or nosulphide content in their composition)have a good eco-toxological profile.Sanchez says these dyes are appliedusing '100 per cent biodegradablereducing agents' and leave no hazardous

chemical species either on the dyedmaterials or in the dyeing effluents.

Currently, the main drawback forthe further expansion of sulphurdyes in denim to replace indigo is thespecial on-tone (going brighter)fading of this dye in some wash downtreatments, especially those involvinghypochlorite bleaching.

"Yet sulphur dyes can offer a widepalette of blue shades to rival indigoand can be used advantageously for'rigid' or 'raw' denim articles," he said,"and also when the wash-downtreatment is of a mechanical character- for high/low contrasts. There is alsothe possibility of new looks and wash-downs not achievable with indigo."

Another interesting alternative isgoing down the biosynthetic route toproduce indigo. Around one-year ago,researchers from the University ofCalifornia published a paper in which itwas revealed they'd developed abiosynthetic indigo dye derived fromenzymes produced by bacteria.

Biosynthesis of indigo avoids theneed to use potentially hazardoussubstances during indigo dye synthesisand also the need for reducing agentsfor dye solubilisation. It works by usinggenetically modified E. coli bacteria tohelp stabilise an indigo precursormolecule called indoxyl by linking it toa sugar molecule. When added tobacteria, this enzyme then producesindican, which can then be easilyisolated and kept for long-termstorage. Later, at the time of dyeing, adifferent enzyme then turns indicaninto the familiar crystalline indigodirectly on cotton textiles.

One problem though, could be the 0

i

BATLooking ahead, new best availabletechnology for the denim sector is likelyto be built upon the need for flexibility,simplicity and minimal usage ofresources considering ultra-short liquorratio dye ranges for all the processsteps, but still using the full dyebathtechnologies known today.

"The efforts that exhaust dyeingmanufacturers are making to minimiseresources can be a good reference forcontinuous (and specifically denim)machine manufacturers," says Sanchez,who outlines what he thinks will be themain three technology developmentsgoing forward.

"In my view, there are three aspectsto be considered," he stated. "Firstly,we need to look at the manufacturingof indigo dye itself. The raw materialsrequired, the synthesis process andparticularly the generation andhandling of potentially hazardous by-products and residues."

ecotextilenews | 31

flggillMllflilll

use of live media to dye fabrics. To getany sort of consistency these dyebathswill need to be monitored extremelyclosely - a bit like in a modern brewery.The denim sector is not yet set up forthis. Perhaps it would be much moreuseful to synthesise these biologicaldyes in bio-reactors off-line and thenharvest the dyes and use them in anormal way.

Speaking to Ecotextile News last year,lead researcher John Dueber at theUniversity of California, Berkeley, notedthat although purifying indicant - as wesuggest - would be an option, "wewanted to demonstrate feasibility of thelowest cost option, one wheredownstream purification of indican isnot required. However, better controlover the dye concentrations may beachievable with purification - that iscertainly an option."

He did also note that their approachat the time was not yet practicalon an industrial scale, but in thelong-term it may provide a moresustainable and environmentallyfriendly alternative to the currentchemical-based denim dyeing process.It's something that the industry hastaken a keen interest in already.

on ultracompact dyeing ranges and thefull automation (at the level of ArtificialIntelligence) of dyeing ranges.

Other moves will includedevelopments of new dye types thatmeet the strictest eco-toxicologicalprofiles and MRSLs, with furtherrefinement of nitrogen type dyeing,new types of auxiliaries for denim andeven less reliance on hydrosulphite forthe direct reduction of indigo.

All these changes will ultimately leadto more advanced and environmentallypreferential ways to dye denim by theend of the next decade.

Rounding up, Sanchez expectsconsumers will drive denim innovationsaround customisation, speed to marketand greater sustainability "In tenyears', I guess we will see the on-linecustomised design of denim articles,using augmented reality tools, for theon-the-spot manufacturing ofgarments," said Sanchez. "This willmean that the fashion market willmove away from the concept of a'collection' towards the permanentpresentation of new styles."

But he sees that when it comes tomanufacturing of denim itself, hepredicts that there will be a wideradoption of man-made cellulosic fibressuch as lyocell as more capacity comeson stream. "The use of 'water less'technologies, and a move away fromwidely used hazardous chemicals for thewash down of garments will surelybecome standard. The future will alsobring us the adoption of digitaltechnologies in different parts of themanufacturing process of a pair of jeans,such as dyeing and the creation of newlooks and patterns," he concluded.

Throughout its history, evolution andchange has been an integral part of thedenim story, and although demand forthis 'king of fabrics' could see aslowdown in the coming season - it willno doubt adapt, change and continueto meet the challenges that a moresustainable denim sector will demand.*

which also save on resourcerequirements, a regular topic of conver-sation has been whether to replacerope dyeing, which has moreproduction steps than direct awarp/slasher system? But then there areproblems about ease of use - repairingbroken ends, dyeing fine yarns etc.

"This is a very good (and old) topicfor discussion," agrees Sanchez. "Whilethere was a clear limit between ropeand slasher a few years back in terms ofproductivity, type of yarns that could bedyed, flexibility and even the differentiallook and wash-down of indigo, there isa new trend for 'hybrid' ranges whererope dyeing gains greater flexibility onshades/effects and slashers improve onproductivity and handling of a widerrange of yarn counts."

The recommendation is that if adenim mill needs the flexibility to offera range of articles, it's worthwhileconsidering the 'third way' Looptextype range as an option. Looptex is atechnology from EFI Mezzera and is acontinuous indigo rope and warp dyerange and denim fabric finishing range.

This machine has sealed nitrogenreactors and is suitable for indigodyeing between 0.3 - 6.0 per centintensity and sulphur dyeing betweenpastel colours to the deepest blacks.Operating costs are said to be up to 30per cent due to the reduction of theindigo liquor bath and the machine'ssize is up to 20 per cent smaller thanconventional ranges.

"Thanks to the sealed nitrogenreactor there's up to 40 per centreduction in hydrosulphite reductionwith fast processing speeds up to 38metres per minutes," according to theItalian machine builder.

So, what's on the horizon? At PlanetTextiles 2019, located within the heartof ITMA on 22nd June this year, therewill be a special breakout session ondenim that will reveal the very newesttechnology in this area.

Expect to see new adaptations foradoption of other dye families for warpcoloration beyond their current verylimited usage at the moment, theimplementation of digital technologies

i

i ;

m«

!

;I;

il

j.

Production stepsWith denim mills always looking toincrease efficiencies for costs reasons -

f!

Denim Blueprinti*

Online customisationShape recovery fabricsReplacement of elastomersTruly compostableNitrogen-based foamsHybrid dyeing rangesToxic- free dyestuffsand auxiliariesMinimal wastewater

Digitally printed denimNo wash-downsArtificial intelligenceBiosynthetic dyesClean indigq raw materials

M

Miguel Sanchez is the managing director ofGavilan, Barcelona, Spain and an expertcorrespondent for Ecotextile News.

f

32 l ecotextilenews

I