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New inspection techniques

(New) inspection techniques in analysing a printed curtain

In this article we describe the appliances and methods Centexbel uses in determining and analysing quality related complaints. We do this by using the case of an analysis of a viscose curtain with a discoloured print.

Observation

A viscose curtain has a pattern of three prints. One of the prints is discoloured. The other one have kept their lustre (images made with Olympus DSX 100 optical-digital microscope). Certain areas, however, show a strong discolouration and degradation - including bursts.

Macro-images made with the DSX 100 by means of "image stitching", where partial images overlap to form one hole

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Figure 1: Curtain with slightly discoloured pattern (Olympus DSX 100)

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Figure 2 : Progressive yellowing

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Figure 3a : Progressive discolouring + hole formation - overview

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Figure 3b : Progressive discolouring + hole formation - detail

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Figure 4 : Semi-automatic selection of the optimal light exposure conditions on the Olympus DSX 100

From optical micropscopy to XRF micro images (Edax Orbis PC)

A semi-automatic technique allows us to select the optimal light exposure conditions in function of the article under observation. In this manner we are able to visualise the different prints, including overlaps.

The existing Orbis has been equipped with a SDD detector for very fast measurements. Thanks to this equipment we are able to make mappings with an excellent resolution in light elements!
One print mainly contains titanium. The presence of sulphur indicates that the fabric is made from viscose.

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Figure 5 : Stitched image (Olympus DSX 100) of a zone used for µXRF measurements (three prints)

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Figure 6 : Mapping on Orbis µXRF system (+/- 1 cm2 – measuring time < 30’)

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Figure 7: Spectra and estimation of the element ratios in the different zones

Identification of the print with FTIR spectroscopy – use of µATR

Detecting the presence of elements is one thing, the identification of the composition is another one, and takes place by means of the FTIR spectroscopy and with the help of the chemicals database we have developed. The profile of the yellowed print clearly contains titanium dioxide whereas the more glossy prints have a mica (lustre) or clay spectrum.

Common micas

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The unprinted fabric has a cellulose spectrum (viscose or cotton). The dull print on the basis of titanium contains several sharp peaks which spectrum can be identified as acrylate (1250-1170 cm1 double peak). The broad rim of 750-450 cm-1 that only steeps at 460 cm-1 refers to the anatase form of titanium dioxide. This crystal form is known to provoke photo catalysis.

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Figure 8 : Identification of the prints by using FTIR (µATR – silica crystal split pea)

SEM analysis of degradation completed with EDX measurement

The FEG SEM (field emission gun scanning electron microscope) makes electron images in which all colour information disappears. However, the images are completed with the measurement (EDX) of the X-rays emitted after interaction of the electrons with the matter.

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Figure 9 : SEM images of the degraded zone printed with anatase

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Figure 10 : EDX image of a yarn printed with anatase: presence of titanium in granulates

The EDX mapping of the titanium shows that the titanium dioxide is present as granulate. The electron image in figure 9 shows that the degradation occurs around the titanium dioxide parts. This is even more visible in figures 11 & 12.

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Figure 11 : Degradation of the fibres around the titanium dioxide granulates

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Figure 12 : Progressive degradation of the fibres around the titanium dioxide granulates

The mica print looks quite different (figure 13). The mica flakes contain the typical elements Al, Si, K (and also O) whereas carbon and oxygen are present in the viscose fibres.

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Figure 13 : SEM image of mica printed zone

Conclusion

The Olympus DSX 100 allows to visualise flaws in a viscose curtain. The images can be used to assure a coherent data acquisition on the XRF, FTIR en SEM.

With the new SDD (silicon drift) detector on the Orbis micro XRF system it is now possible to proceed to a quick mapping with excellent resolutions for lighter elements. The presence of elements can be completed by means of FTIR spectroscopy with the identification of anatase as a photo catalyst in the degradation of the fabric. In addition it was possible to identify the acrylate binder as well as the mica flakes in the other prints.
Finally, SEM microscopy enables us to sufficiently enlarge the image to see not only the degradation around the anatase granulates but also the element distribution in the mica flakes.

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Figure 14 : EDX analysis of the mica print