The utility of dmso in wool textile treatments

The dyeing and the oxidation of wool at room temperature:

By Aldo Malara 

 

  • A characteristic of dmso together with others applications in textile field already explained is related to the dyeing of fibers, particularly to dyeing wool textiles manufacturing.
• We can point out that we have positively dyed a flat wool fabric without utilizing water. The new solvent used is dmso, dimethyl sulfoxide.
• To explain the interaction with dyes we have to remember others characteristic of this solvent. It is already employed for years as stripping agent for paint, and its affinity towards organic and inorganic dyes is well documented in the industry for this solvent. As we have seen also the wool dyed with non reactive dyes is well stripped at 60 degrees Celsius in a few seconds.
• As the water is a good solvent for textile dyes, the dmso has better characteristics of solvency.
• Moreover it is used as solvent in reactions of nucleophilic substitution to build up molecules also in the dyes industry.
• This kind of nucleophilic substitution reaction SN2 on polar aprotic solvents is known to be faster and accomplish better yields of products of reaction compared to water.
• A classical system of dyeing textile wool is about utilizing reactive dyes to be applied at the boil in discontinuous dye machine.
• This dyes are useful to accomplish better fastness, being fixed covalently to the fibers and at the state of the art they are the more successful and sustainable for the environment. Stakeholder organizations (ZDHC) and private PRSL (inditex, LVMH, Burberry, Armani, etc.), National and International rulers about textile are well informed about the importance of these dyes to accomplish their request of fastness.


• The goal :

• to use a green solvent different from water to saving a common good
• utilizing classical reactive dyes for wool or cellulosic applied to wool.
• recovering the solvent used closing the loop
• maximizing the yield of reaction.
• Minimizing energy consumption.


The reactions of wool with the solvent and dyes:


• The reaction used to fix the dyes on wool is the same reaction of nucleophilic substitution SN2 cited above, were the wool is rich of nucleophilic amino acids sites, the dyes are the electrophile agent and the solvent is the favorable aprotic polar solvent to conduct the reaction. But because the dmso give reaction with electrophile agents it react with the dyes forming an alkoxysulfonim salt of the dye. Especially with MCT reactive dyes the cianuric chloride residue react well with dmso (reaction between cyanuric chloride and DMSO are well documented in letterature, “Unusual behavior of dimethyl sulfoxide towards different alcohols in the presence of cyanuric chloride” Subrata, Kumar, Chaudhuri et all, J.Indian Chem. Soc., vol.90, October 2013 pp1773-1780). The formed alkoxy sulfonium dye intermediate will form a ketone group after the elimination reaction of the sulfinium byproduct. At this point the primary amino lysine and other nucleophilic amino group of the wool will react with keto group forming the relative imino functional group (nucleophilic addition, carbinol amine dehydrate to give substitute imines), fixing the dye covalently to the fiber. All these reactions are conducted at room temperature around 24 degrees Celsius.
• Analogy had be seen with Lanasol reactive dyes for wool (Archroma, formerly Huntsman, CGY) based on alfa-bromoacryloamido reactive group. Good yield of reaction was obtained with deep colors (study ongoing).

• The suggested apparatus machine where to conduct the dyeing is named cold pad batch cpb (continuous dyeing), this system of dyeing is well known for the dyeing of cellulosic fibers with reactive dyes. In the past others authors had tried to dyeing wool with cpb system {The Coloration of wool and other Keratin Fibres editors D.M.LewisJ.A.Rippon 2013 (D.M. Lewis and I. Seltzer, journal of Society of Dyers and Colourists, 1968)} with water solvent and a massive quantity of auxiliary chemicals (sodium bisulfite and urea) trying to wetting and swelling the wool (cleavage of sulfur bridge) with the scope of maximize the reaction but probably it wasn’t industrially successful. Differently from that the dmso solvent is a very good wetting a swelling agent without utilizing any auxiliary agent. The fabric is readily wetted from the solvent and the reaction start immediately. Study ongoing for others apparatus of dyeing machine (discontinuous dyeing machine)
• As already seen with the dissolution of the polyamide, Lycra, and others thermoplastics fibers, a characteristic of DMSO is to break the hydrogen bonding inside the polymeric chain decreasing the strength of cohesion of the fibres. Treating wool with solvent DMSO will start more some others reactions during the dyeing; primarily, the oxidation of cysteine amino acid, Analysis with ft-ir peaks at 1121, 1040cm-1 (cysteine dioxide and cysteic acid) to confirm the cleavage of cysteine sulfur bridge. This oxidation reaction (swelling of the fibres) permit together with the solvent, to dyeing the wool at room temperature.

• Briefs on “Oxidation of wool.”

Oxidation and super oxidation of wool (cleavage of sulfur bridge and descaling of the fibres) is normally performed in the finishing cycle of wool (shrink proofing) and in its preparation to printing, with different oxidative agents; just bisulfite of mono ethanol amine (angra) to minimize felting during dyeing cycle. Sodium hypochlorite +sulfuric acid (to develop ipoclorose acid) in the Kroy system. Potassium permonosulfuric acid+bisulfite in a similar way to Kroy but with less performance , or potassium dichloroisocyanuric acid DCCA,to develop ipoclorose acid (Basolan DC, BASF)and all these treatments involved wool to enhance printing resolution or super washing characteristics of non felting (domestic laundry). At the moment the system more used worldwide is the kroy system because is very effective, with good grade of descaling and non felting results.

• The solvent DMSO is to be considered a new oxidative process for wool treating.


• Microscopy analysis:

The microscope analysis show a light medium grade of oxidation of the wool fibres, the scales of the wool treated are more rounded but not removed from the surface, although the ftir analysis point out a relevant peak at 1040-1048 cm-1 analogue to that of Kroy system.


• Also others oxidation are visible at 1750 and 910 cm-1 probably due to ester/ether forming (methylation of carboxylic acid residue of glutamic acid and aspartic acid) study ongoing. “Autocatalytic methylthiomethylation of carboxylic acid/phenol involving the formation of dmso enolate: convenient synthesis of methylthiomethyl ester/ether. Hongshi Liu et all. RSC publishing, Issue 51, 2022”. This reaction of oxidation is to be considered not functional for the dyeing. We know for sure that MTM (methyl methylene sulfonium chloride ion is formed from alkoxysulfonium product of reaction between MTM residue of the reactive dye and DMSO solvent. It is not to be excluded the formation of the alkyl halide chloro methyl methyl sulfide, a reactive species for the thiomethylation of carboxylic acid.
• The sample dyed with Lanasol reactive red 116 shows similitude at the ftir analysis as I saw with the precedent dyeing with reactive red 120 (picture 2). Peaks at 1750, 1447, 1229, and 1048 cm-1. (Not at 910 cm -1). All these peaks showing strong oxidation of the solvent on the fibre, with the formation of cysteic acid, ester,ether of carboxylic acid without the presence of methyl methylene sulfonium chloride. With this dye based on Alfa bromo acryloamido the precedent cation can’t be formed, so quite all the oxidation we see on the fibre are to be attributed to the solvent and not with byproducts of reaction between the dye and the solvent, maybe just that peak at 910cm-1. We could have a simple sn2 reaction substitution on bromine maybe after the dye reaction with the solvent with oxidation of the vinyl group to aldehyde. We can have two reactions of the dye with the fibre, bromide substitution and imino reaction between the aldehyde and the amino group present on the fibre. This class of reactive dyes is preferable to the others. The morfologie of wool after dyeing quite doesn’t change. The scales appeared more rounded but any breaking of cuticole and any fibrillation are visible at the microscope 1000X picture 1). SEM-EDX microscope (study ongoing). SEM to better value the morphology of the scales. EDX to value an increase of the quantity of sulfur present, to confirm thioether functional group presence (thiomethylation). NMR analysis to confirm the presence of imino group.
• The presence of reactive dyes is quite negligible on the rate of oxidation and we can accomplish oxidative treatment together with dyeing, reducing time and energy consumption.
• At the end of the dyeing The solvent will be recovered from the fabric, distilled and reused with vacuum drying system at low temperatures. (Study ongoing)
• Studies of chemical and physical resistance of wool dyed with reactive dyes in DMSO solvent are to be considered.

• Conclusion:

• We have studied the possibility to create super wool treated garment without using dangerous halogen based products. The treatment is very easy to accomplish and could be performed alone or together with dyeing. Any others chemicals is to be used as to assistant of dyeing or oxidation process, minimizing waste water. We can observe Mild changes in the structure of wool when is treated with the solvent at room temperature also for several hours (24 hours). Industrial trials are needed to confirm these data.

NOTE :   CH20150000698 20150520