21 Applications of NIR Techniques in Polymer Coatings …
505
more resistant to mechanical stress during those processes (e.g. weaving, knitting)
by reinforcement and improved filament cohesion and (2) to reduce electrostatic
charging as well as frictional wear and abrasion during passing them over machine
parts such as needles, rolls, guides etc. The specific treatment depends on the fiber
material and the intended use of the product.
Typically, very low amounts of finishing oils are deposited on the fibers (< 1 wt%).
In order to achieve maximum quality of the products and optimum manufacturing
conditions, the amount of finishing agents has to be controlled continuously. Conventional quantitative determination of the finishing oils is based on their removal by
chlorinated solvents and analysis of the solutions by FTIR spectroscopy, which is a
time-consuming and laborious procedure. Blanco et al. have shown [48] by investigations on acrylic fibers made up of a acetonitrile–vinyl acetate copolymer that
quantitative data on the amount of finishing agent can be obtained directly from the
fiber during the spinning process by NIR reflection spectroscopy. The weight content
of the finishing oil varied between 0.22 and 0.62 wt%. These low application weights
require an excellent sensitivity of the spectroscopic method. Moreover, the properties
of the acrylic fibers varied with respect to fineness, color, gloss and other possible
sources of variability. The first component of the PLS model accounted for 99.99%
of the spectral variance, which was related to spectral scattering due to variations in
fineness of the fibers used for calibration. Generally, black samples and those dyed
with dark colors were found to result in rather high absolute errors (up to 0.06 wt%).
For all other samples, relative prediction errors (RMSEP) between about 6 and 7%
were obtained, which roughly corresponds to the precision of data from the reference
method. Similar investigations on the quantitative determination of finishing oil on
the surface of PA 6.6 yarns have been reported as well [38]. Using a four-wavelength
multiple linear regression (MLR) model, the amount of oil could be predicted with
a SEP of 0.04 wt% for deposits of about 1 wt%.
After manufacturing of the textile fabric, the processing agents have to be
removed carefully before further processing steps such as finishing with functional
agents, coating, lamination, printing, etc., since the finishing oils and sizes are often
hydrophobic and hence strongly affect wettability and adhesion. In particular, it has
to be made sure that the oil or size is completely removed everywhere across the
surface in order to avoid local wetting or adhesion problems. However, due to the
invisibility of the very thin and colorless layers, the detection of local remains of the
processing agents is hardly possible. Recently, NIR spectral imaging has been shown
to be a powerful tool for this analytical task [49]. A size consisting of hydrocarbons
and fatty acid ethoxylates was applied to polyester fabric with application weights
between 0.4 and 5.5 g/m
2 in order to provide samples for calibration of a PLS model.
Using this model the amount of size was determined with a precision of about 0.2
wt% by averaging the predicted individual values across the surface of the fabric.
Monitoring of the distribution of the size across the textile web is of no technical
relevance since it is applied to the yarn before weaving. After washing-out of the
size and drying of the textile, the cleanness of the desized fabric was inspected by
spectral imaging with respect to both quantification of the residual amount of size and
its spatial distribution. The amount of remaining size was found to be at or below the
505
more resistant to mechanical stress during those processes (e.g. weaving, knitting)
by reinforcement and improved filament cohesion and (2) to reduce electrostatic
charging as well as frictional wear and abrasion during passing them over machine
parts such as needles, rolls, guides etc. The specific treatment depends on the fiber
material and the intended use of the product.
Typically, very low amounts of finishing oils are deposited on the fibers (< 1 wt%).
In order to achieve maximum quality of the products and optimum manufacturing
conditions, the amount of finishing agents has to be controlled continuously. Conventional quantitative determination of the finishing oils is based on their removal by
chlorinated solvents and analysis of the solutions by FTIR spectroscopy, which is a
time-consuming and laborious procedure. Blanco et al. have shown [48] by investigations on acrylic fibers made up of a acetonitrile–vinyl acetate copolymer that
quantitative data on the amount of finishing agent can be obtained directly from the
fiber during the spinning process by NIR reflection spectroscopy. The weight content
of the finishing oil varied between 0.22 and 0.62 wt%. These low application weights
require an excellent sensitivity of the spectroscopic method. Moreover, the properties
of the acrylic fibers varied with respect to fineness, color, gloss and other possible
sources of variability. The first component of the PLS model accounted for 99.99%
of the spectral variance, which was related to spectral scattering due to variations in
fineness of the fibers used for calibration. Generally, black samples and those dyed
with dark colors were found to result in rather high absolute errors (up to 0.06 wt%).
For all other samples, relative prediction errors (RMSEP) between about 6 and 7%
were obtained, which roughly corresponds to the precision of data from the reference
method. Similar investigations on the quantitative determination of finishing oil on
the surface of PA 6.6 yarns have been reported as well [38]. Using a four-wavelength
multiple linear regression (MLR) model, the amount of oil could be predicted with
a SEP of 0.04 wt% for deposits of about 1 wt%.
After manufacturing of the textile fabric, the processing agents have to be
removed carefully before further processing steps such as finishing with functional
agents, coating, lamination, printing, etc., since the finishing oils and sizes are often
hydrophobic and hence strongly affect wettability and adhesion. In particular, it has
to be made sure that the oil or size is completely removed everywhere across the
surface in order to avoid local wetting or adhesion problems. However, due to the
invisibility of the very thin and colorless layers, the detection of local remains of the
processing agents is hardly possible. Recently, NIR spectral imaging has been shown
to be a powerful tool for this analytical task [49]. A size consisting of hydrocarbons
and fatty acid ethoxylates was applied to polyester fabric with application weights
between 0.4 and 5.5 g/m
2 in order to provide samples for calibration of a PLS model.
Using this model the amount of size was determined with a precision of about 0.2
wt% by averaging the predicted individual values across the surface of the fabric.
Monitoring of the distribution of the size across the textile web is of no technical
relevance since it is applied to the yarn before weaving. After washing-out of the
size and drying of the textile, the cleanness of the desized fabric was inspected by
spectral imaging with respect to both quantification of the residual amount of size and
its spatial distribution. The amount of remaining size was found to be at or below the