When Lafayette South America textile
manufacturer in Bogota, Colombia, couldn’t find the little blue paper strips it
had previously used to test for the presence of sodium hydrosulfite in its post
reduction dyebath, it went looking for an alternative.
Hyman Abadi, Lafayette’s co-founder, found a better testing
solution and new automatic methods of monitoring and controlling chemical feeds
in Myron L Company water quality instrumentation: the Ultrameter II™ 6
Parameter handheld digital meter; the 720II™ in-line ORP Monitor/controller;
the 720II™ pH Monitor/controller; and the TechPro™ PH1.
Hyman’s technicians use the Ultrameter II 6P to instantly test
for ORP in the textile dyeing process and continuous reduction washing of printed
and dyed fabrics. Lafayette also uses the Ultrameter II to spot check ORP
against the performance of automatic in-line monitor/controllers now in use.
The 720II Series ORP Monitor/controllers allow Lafayette to
automatically control the amount of sodium hydrosulfite added to reduce the
remaining solution in the textile bath. Before Myron L in-line
Monitor/controllers were used, chemical had to constantly be added by hand to
ensure product quality. Now, if the concentration is low, the
monitor/controller opens a valve that releases the reducing solution into the
bath. If it’s high, the valve remains closed. To ensure the process stays in
control, spot checks on the reduction bath are conducted twice daily using the
handheld Ultrameter IIs.
Myron L 720II Series pH Monitor/controllers are used to balance
the bath by controlling the amount of caustic soda added to maintain the
appropriate pH level. Accurately maintaining the pH ensures the effectiveness
of the reducing agent, thereby decreasing chemical consumption. With sodium
hydrosulfite, the pH must be maintained at around 10. If the pH drops below
that level, it decomposes rapidly and loses its reduction efficiency.
In dyeing, the pH is kept
at 5.5-6 because the dyes themselves are susceptible to color changes outside
of this pH range, until they diffuse into the fiber and become “fixed.” Once
properly applied in the fiber, they are protected from these variations in pH.
However, the unfixed dye remaining on the surface of the fiber must be removed
in order to ensure subsequent proper wash fastness and color “bleeding.” This
unfixed dye is removed by raising the pH along with the use of sodium
hydrosulfite. Careful control of this reductive process removes the unfixed
surface dye, without affecting the properly applied fixed dye.
Maintaining the pH not
only assists in the dyeing process, it also ensures reproducibility of color
between the lab and the dyebath and from batch to batch by ensuring that the
dyes are always applied in their optimum pH range of color stability. The
solubility of dyes is dependent on pH and varies from dye to dye. If the pH of
the dyebath is out of range for the dye type, the color will be off shade or
incorrect altogether. Lafayette uses TechPro PH1 meters to measure grab samples
as a confidence check against the equipment installation and functioning. PH1s
are also in use throughout the factory for other solution quality control.
Due to Hyman’s
implementation of basic water quality control in dyebath solutions, Lafayette
is now generally able to use half of the chemicals it had previously used for
this same process. Lafayette has drastically reduced costs, noxious fumes in
the factory, and the amount of harmful chemicals that must be removed before
effluent is discharged into local rivers, creating a win-win situation for the
company, its employees and the environment.