506
T. Scherzer
prediction error of the external validation, which was sufficient for further processing
such as ink jet printing. Moreover, traces of size applied by arbitrary spraying of a
dilute solution to clean fabrics could be detected and quantified by this method as
well.
Aside from the treatment with such processing agents, which have to be removed
before subsequent processing, textile fabrics may be also finished with finishing
agents in order to provide them permanently with certain functional properties such
as flame retardancy, optical brightening, stiffening, hydrophilicity or hydrophobicity,
water repellence, biocide or stain resistance, anti-static behavior and other features.
Typically, such agents are applied by impregnation in aqueous solutions in a foulard,
which is often followed by heat setting to improve fixation to the textile fibers.
Depending on the special substrate, agent, and intended application finishes are
applied with application weights in the range from less than 1 g/m
2 and to several
tens of g/m
2 . The finishes have to be applied according to the specified value of the
application weight and with exceedingly homogenous spatial distribution across the
textile fabric, which is required for both further processing of the finished textiles as
well as for optimum application properties. However, similar to sizes and finishing
oils most of the finishing agents form colorless layers on the surface of the textile,
which usually prevents in-line detection by optical methods in the visible range.
Rather, quantification is mostly carried out off-line by extraction, gravimetry etc.
Recently, Scherzer et al. [49] have demonstrated the immense potential of hyperspectral imaging for both quantitative analysis of the applied amount and monitoring
of the spatial homogeneity of finishing layers on textiles fabrics. For example, it was
shown that the application weight of flame retardant layers (in the order of several
tens of g/m
2 ) applied to polyester fabric can be detected with a prediction error
(RMSEP) of 2.2 g/m
2 . The corresponding PLS calibration is given in Fig. 21.17.
Figure 21.18 shows spectral images of two finished polyester fabrics. In one of them,
a spot pattern resulting from several drops of finishing solution that were dripping
down to the already dried material, can be seen. The average application weight
obtained by integration over the individual values across the complete surface of
the spectral image of each finished sample proved a very close correlation with the
corresponding reference values obtained by gravimetry (i.e., differences < 2 g/m
2 ).
Moreover, local inhomogeneities of the density thickness were clearly detected. In
particular, the dotted pattern forming a rectangular frame close to the cut edges originates from pinning the fabric on a tentering frame for drying after impregnation and
squeezing.
Similar investigations were carried out with other textile materials such as PA
fabric and with other finishing systems such as stiffening agents, optical brighteners, adhesion promoters and hydrophilic layers. Depending on the specific material
combination, prediction errors were found to be in the order of 1–2 g/m
2 . However,
there is one exception of finishing layers that cannot be monitored by NIR imaging.
Water-repellent finishes are often based on fluorocarbon compounds, which cannot
be detected by NIR spectroscopy.
The next step in finishing of textiles by impregnation in aqueous solutions is
the drying process. Typically, this is a multistage process consisting of dewatering
T. Scherzer
prediction error of the external validation, which was sufficient for further processing
such as ink jet printing. Moreover, traces of size applied by arbitrary spraying of a
dilute solution to clean fabrics could be detected and quantified by this method as
well.
Aside from the treatment with such processing agents, which have to be removed
before subsequent processing, textile fabrics may be also finished with finishing
agents in order to provide them permanently with certain functional properties such
as flame retardancy, optical brightening, stiffening, hydrophilicity or hydrophobicity,
water repellence, biocide or stain resistance, anti-static behavior and other features.
Typically, such agents are applied by impregnation in aqueous solutions in a foulard,
which is often followed by heat setting to improve fixation to the textile fibers.
Depending on the special substrate, agent, and intended application finishes are
applied with application weights in the range from less than 1 g/m
2 and to several
tens of g/m
2 . The finishes have to be applied according to the specified value of the
application weight and with exceedingly homogenous spatial distribution across the
textile fabric, which is required for both further processing of the finished textiles as
well as for optimum application properties. However, similar to sizes and finishing
oils most of the finishing agents form colorless layers on the surface of the textile,
which usually prevents in-line detection by optical methods in the visible range.
Rather, quantification is mostly carried out off-line by extraction, gravimetry etc.
Recently, Scherzer et al. [49] have demonstrated the immense potential of hyperspectral imaging for both quantitative analysis of the applied amount and monitoring
of the spatial homogeneity of finishing layers on textiles fabrics. For example, it was
shown that the application weight of flame retardant layers (in the order of several
tens of g/m
2 ) applied to polyester fabric can be detected with a prediction error
(RMSEP) of 2.2 g/m
2 . The corresponding PLS calibration is given in Fig. 21.17.
Figure 21.18 shows spectral images of two finished polyester fabrics. In one of them,
a spot pattern resulting from several drops of finishing solution that were dripping
down to the already dried material, can be seen. The average application weight
obtained by integration over the individual values across the complete surface of
the spectral image of each finished sample proved a very close correlation with the
corresponding reference values obtained by gravimetry (i.e., differences < 2 g/m
2 ).
Moreover, local inhomogeneities of the density thickness were clearly detected. In
particular, the dotted pattern forming a rectangular frame close to the cut edges originates from pinning the fabric on a tentering frame for drying after impregnation and
squeezing.
Similar investigations were carried out with other textile materials such as PA
fabric and with other finishing systems such as stiffening agents, optical brighteners, adhesion promoters and hydrophilic layers. Depending on the specific material
combination, prediction errors were found to be in the order of 1–2 g/m
2 . However,
there is one exception of finishing layers that cannot be monitored by NIR imaging.
Water-repellent finishes are often based on fluorocarbon compounds, which cannot
be detected by NIR spectroscopy.
The next step in finishing of textiles by impregnation in aqueous solutions is
the drying process. Typically, this is a multistage process consisting of dewatering