Comments on: Denim Pollution – Solutions To Sulphur Dyeing Wastes

By: Dhruv

Dhruv — Wed, 19 Sep 2018 16:22:59 +0000

Hi Mercer.

You mentioned Reductor RDT is dextrin. Then is the Reductor poweder offered by them named as Reductor D Powder same as RDT? If not what is the difference.

Also you mentioned that Dextrin is not suitable othet than black. Then which are the other eco friendly reducing agents available for Colours other than black for Sulphur dyes?

By: Harry Mercer

Harry Mercer — Tue, 29 Mar 2011 15:57:24 +0000

Hi Alpha:
There are at least 10 different ways to reduce sulfur dyes. The method depends on costs, quality, colorfastness requirements. Sodim hydrosulfite will reduce sulfur dyes, but it is unstable and can present dyeing porblems when used by itself, especially on continuous dyeing where the consistancy of shade is hard to control at normal dyeing temperatures. I have developed a method using a special buffer with hydrosulfite that allows perfect sulfur dyeing with all colors on Indigo machinery.
That is one of my consulting secrets. It works best on loop machines and I have set up these procedures for 5 denim companies in the last 15 years.
Dextrin-type reducers are used widely because of lower pollution than sulfides or hydrosulfite and I have used reducing sugars to dye Indigo. The dextrins do not result in the best sulfur dyeing, especially for colors other than black.
Sulfides are used widwly in Asia because they are cheap. They have their best use for batch dyeing like package or jigs, but should not be used for continuous dyeing because they have low solubility which is important for continuous dyeing where the dye has only seconds to be applied as opposed to an hour or so in batch. The millivolt level of sulfide is only about -580 and continuous dyeing of sulfurs should be conducted at a minimum of -630, which requires other reducing agents.

Regards,

Harry Mercer
Hme3065805@aol.com

@Alpha –

By: Alpha

Alpha — Sun, 27 Mar 2011 07:57:54 +0000

sir can i use sodium hrdrosulfite in sulfer dyeing and if yes than why we prefer sodium sulfide in sulfer dyeing

By: Niraj

Niraj — Tue, 01 Jun 2010 06:24:12 +0000

@Harry Mercer - Thanks Herry, Let me try checking Redox of SHS blended with Sodium Sulfide as well as SHS with Sod. Thiosulfite

By: Harry Mercer

Harry Mercer — Mon, 31 May 2010 15:33:41 +0000

Hi Niraj:
The fundamental problem is that hydrosulfite is unstable and breaks down into sodium bisulfite and sodium sulfite. A lot of hydrosulfite breaks down in the mixing tank because of exposure to air, excessive agitation or concentration. There are 2 types of hydro loss in the mixing tanks: aerobic, which is caused by exposure to air and anerobic which is a result of excessive concentrations, greater than 80 g/l. Additional hydro losses occur in the dye boxes because of air exposure at the surface, oxygen carried in by yarn and by high recirculation pressures. More boxes mean more hydro loss. Also the size of the box has an effect. Small Indigo boxes have a higher ratio of surface area to volume and as much as 50% of total hydro that arrives to the machine are lost in small boxes, but in the large boxes of most rope ranges the loss is as low as 15%. Those losses are in addition to losses in mixing, so 70-90% of the hydro is not made available for dyeing. The losses at the dye box surface is the reason that some machinery companies recommend using nitrogen to protect the surface of the boxes. Many years ago a company in Taiwan put ping-pong balls on the surface of the dye boxes. High Indigo foam on the boxes also reduces the hydro loss, but results in more crocking. In cases where powder feeders are used to deliver additional hydro, there are losses there as well since the hydro breaks down into something like meta-bisulfite. Therefore practices are important. The hydro is more stable with higher concentrations of sodium hydroxide.
Sodium sulfide added at about 10 grams per liter to the mix will also stabilize. Sodium thiosulfite
has been also used in the past. The best stabilizer is available from the Bozzetto company.

Regards,

Harry Mercer

By: Niraj

Niraj — Fri, 28 May 2010 07:35:29 +0000

Hi Herry,

Thanks for your message.

Denim Manufacturers wanted to achieve max Redox with SHS to get better shade and stability. I do agree with you that SHS (hydrosulphite) is not the only one about stability but of course We can offer a solution to them as you advised.

Is there any additive to be added in / alongwith SHS which can help them to enhance the performance of this product against standard SHS.

Please suggest suitable additive to offer better solution to denim manufacturers.

By: Harry Mercer

Harry Mercer — Fri, 21 May 2010 19:54:21 +0000

@Niraj Sandesara –
Hi Niraj:
You can achieve Redox of around -950 with hydrosulfite. There must be a serious stability problem with your process. Send me the details of the machine type, number of boxes, speeds, abieny temperature, immersion time, % caustic(2-endpoint titration with formaldehyde and 0.1N HCl
stock mix formula and mixing procedure and supplemental hydro feed. There is a buffer that can be added for extreme stability. The only source I know of currently is made in Indonesia by an Italian chemical company called Bozzetto. I think that the name is Isopon. E-mail me at Hme3065805@aol.com and I will do an analysis.

Regards,

Harry Mercer

By: Niraj Sandesara

Niraj Sandesara — Fri, 21 May 2010 05:29:53 +0000

Dear Harry,

Thanks for your below feedback.

I understand from your message that for Indigo Dyeing on Denim with Powder Indigo and to get better & consistent shade the preferred REDOX Range is between (-800/830).

Using available Sodium Hydrosulphite we are getting REDOX in the range of (-710/750). What other additives can be added into Sodium Hydrosulphite to increase Redox upto -800

Please Advise.

Best Regards,

Niraj Sandesara

By: Harry Mercer

Harry Mercer — Wed, 19 May 2010 21:08:13 +0000

Hi Niraj:
There are definitely some additives that will improve Indigo dyeing, but they vary depending on the type of Indigo dyeing. With powder Indigo, there are some additives that will improve shade consistancy and greatly reduce hydro use.There are some that will allow the use of much less Indigo for a dark shade. The pre-reduced Indigo is a bigger problem, but that depends on whether the supplemental hydro feed is as a liquid or powder.
The reduction potential is critical for anthraquinoid vats, since different general structures require different reduction potentials for good dyeing. The reduction potential also determines the general colorfastness. With Indigo, low redction potential (-720/750) produces a darker, redder shade with lower amounts of Indigo, but it washes easily and the consistancy is not as good. At higher levels (-800/830) the shade is lighter with the same amount of Indigo, greener, but more colorfast and consistant.

Regards,

Harry Mercer

By: Harry Mercer

Harry Mercer — Wed, 19 May 2010 15:03:36 +0000

Hi Amitabh:
I take it that you are speaking of batch dyeing in package machines, jiggers etc. Dextrins have been used for many years in dyeing sulfurs and is especially easy in batch dyeing. Companies like Clariant have been selling dextrins like Reducer RDT for decades and they recommend it in order to reduce pollution that is caused by sulfur-containing reducers. Around pH 11 and at 85 degrees they produce reduction. I have been in some countries where dextrins are the only reducer used for sulfurs.
Sulfur dyes have long been known for excellent wetfastness when the dyeing conditions are correct, which is not ususally the case in the last 20 years or so.
I have presented many lectures around the world on dye chemistry and practice and if you are interested in dyeing theory, try to find a copy of “The Physical Chemistry of Dyeing” by Thomas Vickerstaff. It is a classic, but long out of print.
I have used these procedures in production over many years,in the U.S. Brazil, Indonesia,Ecuador- but only a limited number of companies have taken advantage. Dyers are very difficult to change procedures. Actually, one of them, cold dyeing of sulfur black, I picked up from craft dyers in India who made these wonderfully dark and colorfast borders for saris. They understood more about sulfur dyeing than any dyeing manager I have seen. They did not waste dye.
I learned the most valuable lessons about sulfur dyes as a dyeing superviser and researcher. I did conduct at least 1000 experiments in sulfur dyeing in the laboratory and proved that much of the guidande offered by dye companies is highly defective.

Regards,

Harry Mercer