504
T. Scherzer
called “dope.” Extrusion of this solution through a spinneret into cold water leads
to precipitation of the copolymer and the formation of fibers, which may be drawn
to the desired thickness. For optimum process conditions, the actual ratio of thiocyanate and copolymer in the dope needs to be controlled continuously. NIR reflection spectroscopy was used for in-line monitoring of this ratio [47]. Difficulties in
PLS modeling resulted from the fact that a variation of the NaSCN concentration
led to a shift of the O-H bands of water, since the electrolyte prevents the formation
of hydrogen bonds. Individual PLS1 models for NaSCN and the copolymer were
developed resulting in RMSEP values of 1.6% (NaSCN) and 2.6% (copolymer),
respectively. Similar results were also obtained with a PLS 2 model for simultaneous
prediction of both concentration values.
Physical parameters of textiles may be determined as well. PA flocks with different
degrees of fineness are used for the production of upholstery fabrics, which are
indistinguishable by the human eye. Nevertheless, flocks with different degrees of
fineness lead to different appearances of the final product. NIR spectroscopy was
found to be an efficient tool for their discrimination [39].
Another parameter that influences the properties of textiles is the heat setting
temperature applied during the production process. Heat has a significant effect on
the molecular structure and the morphology of yarns. Heat setting is typically applied
in order to improve textile properties with respect to shrinkage, warping, relaxation of
internal stress, dye or finish fixation etc. When applied under tension, it may increase
the tensile strength of fibers or fabrics and improve the behavior of the material during
further manufacturing steps. For some applications (e.g. carpet manufacturing), very
low variation and a high spatial homogeneity of the heat set temperature are required
for the intended properties of the final products. NIR spectroscopy has been shown
to be able to reveal the thermal history of the polymers in synthetic fibers [38]. In
case of carpets based on PA, heat treatment is carried out at about 190–220 °C or
occasionally at even higher temperatures depending on the specific method. PLS
models could predict the heat set temperature of PA yarns from their NIR spectra
with a precision (SEP) of about 1–2 °C for greige yarns and 2..3 °C for dyed yarns.
Below 185 °C some deviation from linearity was observed, which was attributed
to the Brill transition. The Brill transition in PA 6.6 occurs at about 160–180 °C
and is due to the gradual transformation of the crystalline state from one triclinic
structure existent at room temperature into a different triclinic structure stable at
higher temperatures.
21.3.3 Finishing of Yarns and Textiles and Subsequent
Drying
It is common practice in textile industry to provide fibers and yarns with special
agents such as sizes (e.g. fatty acid ethoxylates, waxes, polyethylene) or lubricants
(finishing oils) before processing them to textile fabrics in order (1) to make them
T. Scherzer
called “dope.” Extrusion of this solution through a spinneret into cold water leads
to precipitation of the copolymer and the formation of fibers, which may be drawn
to the desired thickness. For optimum process conditions, the actual ratio of thiocyanate and copolymer in the dope needs to be controlled continuously. NIR reflection spectroscopy was used for in-line monitoring of this ratio [47]. Difficulties in
PLS modeling resulted from the fact that a variation of the NaSCN concentration
led to a shift of the O-H bands of water, since the electrolyte prevents the formation
of hydrogen bonds. Individual PLS1 models for NaSCN and the copolymer were
developed resulting in RMSEP values of 1.6% (NaSCN) and 2.6% (copolymer),
respectively. Similar results were also obtained with a PLS 2 model for simultaneous
prediction of both concentration values.
Physical parameters of textiles may be determined as well. PA flocks with different
degrees of fineness are used for the production of upholstery fabrics, which are
indistinguishable by the human eye. Nevertheless, flocks with different degrees of
fineness lead to different appearances of the final product. NIR spectroscopy was
found to be an efficient tool for their discrimination [39].
Another parameter that influences the properties of textiles is the heat setting
temperature applied during the production process. Heat has a significant effect on
the molecular structure and the morphology of yarns. Heat setting is typically applied
in order to improve textile properties with respect to shrinkage, warping, relaxation of
internal stress, dye or finish fixation etc. When applied under tension, it may increase
the tensile strength of fibers or fabrics and improve the behavior of the material during
further manufacturing steps. For some applications (e.g. carpet manufacturing), very
low variation and a high spatial homogeneity of the heat set temperature are required
for the intended properties of the final products. NIR spectroscopy has been shown
to be able to reveal the thermal history of the polymers in synthetic fibers [38]. In
case of carpets based on PA, heat treatment is carried out at about 190–220 °C or
occasionally at even higher temperatures depending on the specific method. PLS
models could predict the heat set temperature of PA yarns from their NIR spectra
with a precision (SEP) of about 1–2 °C for greige yarns and 2..3 °C for dyed yarns.
Below 185 °C some deviation from linearity was observed, which was attributed
to the Brill transition. The Brill transition in PA 6.6 occurs at about 160–180 °C
and is due to the gradual transformation of the crystalline state from one triclinic
structure existent at room temperature into a different triclinic structure stable at
higher temperatures.
21.3.3 Finishing of Yarns and Textiles and Subsequent
Drying
It is common practice in textile industry to provide fibers and yarns with special
agents such as sizes (e.g. fatty acid ethoxylates, waxes, polyethylene) or lubricants
(finishing oils) before processing them to textile fabrics in order (1) to make them