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Dyeing Printing & Finishing

Solving Wool Finishing Problems

Cimi S.p.A. has conducted research into the use of bisulfite vapor for the stabilization of woolen fabrics.<b><i>TW</i></b> Special Report

Cimi S.p.A. has conducted research into the use of bisulfite vapor for the stabilization of woolen fabrics.Stabilizing woolen fabrics in a reducing environment is a widely established procedure, although there are many doubts concerning certain side effects.Today, the commonly used reducing agent is sodium bisulfite or its derived and differently formulated products. According to a mechanism suggested by Angliss, Cook, Delmenico and other researchers at the Commonwealth Scientific and Industrial Research Organization, Australia, whose general principles are still valid today, the bisulfite ion reacts through the direct attack of the disulfide bridges in order to start the formation of thiosulfonate ions (Bunte salts). In the propagation reaction, the thiol ions break the stretched disulfide bridges to create new disulfide bridges in a non-stretched position: New thiol ions develop simultaneously and, theoretically, the reaction can continue using a chain mechanism as long as accessible stretched disulfide bridges are present or the thiol ions are removed for a terminal chain reaction or other secondary reaction.The terminal reaction occurs through the addition of thiol ions to residues of dehydroalanine or through the release of thiosulfate ions from Bunte salt by one thiol ion.Both reactions lead to the formation of lanthionine and are much slower than the reactions of propagation. As a result, proper fixation can be achieved in a short time with a very small quantity of reducing agent.
Cimis Multifix machine treats woolen fabrics using superheated bisulfite vapor, providing higher and more stable fixation than standard treatments.The formation of lanthionine has not always been confirmed with certainty in the reducing treatments, leading to the belief that its formation is exclusively linked to the terminal chain reaction that occurs after many propagation stages.Moreover, with excessive reducing agent, a useless and excessive amount of bisulfite and a release of thiosulfate ions develop, which, in the operating conditions of the autoclave, can create color changes and acid vapor that hydrolyze satins and corrode metal parts.Also, working with excessive reducing agent can change the original structure of wool and its capacity to regain humidity, thus enhancing the phenomena linked to hygroscopic expansion.Developing the action of the bisulfite in the vapor stage can enhance the advantages of chemical fixation and reduce the negative side effects caused by excessive reducing agent.Research into this alternate procedure has been conducted using the Multifix machine, manufactured by Cimi S.p.A., Italy, and designed to test woolen fabrics using bisulfite vapor.Standard TreatmentIn a standard 35-meter treatment tank for bisulfite in a water bath, water usually amounts to about 2,500 liters with a 20 grams-per-liter (g/l) bisulfite concentration and a product content of 50 liters. During the working stage, a reintegration of 40 grams per kilogram of fabric is made in order to keep the concentration equal to that of the initial bath. Treatment of 1,000 meters of fabric weighing 330 grams per meter (g/m), working at a speed of 20 meters per minute (m/min), will consume 14 liters of bisulfite.At the end of the treatment, the entire content of the treatment tank 2,500 liters of water and 50 liters of bisulfite is disposed of.Alternate MethodIf a wet saturated vapor tank set at 102°C is used to develop bisulfite, water and product consumption will be much lower.The development tank will have a constant volume level adjusted by a device that signals excessive and minimum levels. A constant concentration of product in the bath will be ensured by the dosing pumps. The tank content will be only 200 liters with a 30 g/l bisulfite concentration, which will require only 6 liters of product to obtain the solution of work start. Treating 1,000 meters at 20 m/min will consume 6.5 liters of bisulfite because the bath will have to be reintegrated with only 126 grams per minute (g/min) of bisulfite to keep the product concentration constant.At the end of the treatment, only the content of the saturation tank will be disposed of 200 liters of water and 6 liters of bisulfite thus leading to better materials management and greater purification savings.Moreover, the amount of product that has reached the fabric and the uniformity of product distribution can be measured precisely.
Machine DescriptionThe Multifix machine comprises three main parts: the inlet hydraulic head; the treatment tank; and the outlet hydraulic head. The two heads are made up of a series of cylinders that guide the fabric, and a suction bar with a liquid ring vacuum pump at the inlet of the following tank or at the outlet of the previous tank.In the treatment tank, the fabric goes through a heated impregnation tank that contains 100 liters of product. The product concentration on the fabric is optimized by an equalizing bar. The fabric reaches the development section which can either work with high bath for a natural crabbing or washing function, or develop chemical products previously deposited in the impregnation tank in an atmosphere of saturated vapor created by water in the tank bottom heated by a coil. This section has a fabric capacity of 48 meters.Tests And ResultsThe Multifix process is being tested at Botto Giuseppe e Figli S.p.A., Italy, with the cooperation of the Polytechnic of Turin, Italy. Mercandino Piero from Botto Giuseppe is managing the process experimentation.Measurement of the crease angle, expressed as a percentage, permits the quantification of the permanent stabilization given by a fixing procedure. One hundred percent represents complete stabilization this occurs in the procedures that crush the fabric.At a treatment speed of 20 m/min, water treatment at 90°C creates lower permanent fixation than other treatments.The difference between the treatments in vapor and in water is obvious during the different treatments carried out at a speed of 40 m/min. In this case, vapor treatments give a higher permanent fixation degree.At a fabric-feeding speed of 50 m/min, the treatment that gives the highest permanent fixation degree is the vapor-plus-Angra (a bisulfite product) treatment.
Research ResultsThese results conclude that the superheated vapor treatment leads to higher and more stable fixation values up to a speed of 40 m/min; the superheated bath treatment leads to high permanent fixation values provided that the permanence time of the fabric in the treatment area is high for a speed of 20 m/min; and at 50 m/min, the only treatment that keeps a high permanent fixation level is the vapor-plus-Angra treatment.Editors Note: This article, written by L. Gallotti and M. Zampieri, was provided by Cimi S.p.A., Italy.

November 2003