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Control of Migration Profiles and Structural Evolution in Thin and Non-Compact Materials by Photothermal Methods


A few general conclusions of the network became clear: Much progress was achieved within the ETN to understand the behaviour of photothermal signals arising from complex and non-homogeneous samples and to retrieve a property's depth profile. The better signal understanding is based on more qualified models, which appropriately describe heat diffusion in no-homogeneous, multilayered or phase-mixed materials. Several new approaches of data inversion technique have been established. For measuring water content, the only way to get reliable measurements is to exploit unique spectroscopic properties of water using either a specific excitation, and/or a specific detection wavelength.

Food working group: Two lines of research were distinguished for the quality assessment in seeds. The first type of techniques (flash thermography, radiometry, opto-thermal transient emission radiometry (OTTER), enable non-contact and non-destructive inspection of individual seeds, while the second class of techniques (photoacoustic PA and reflectance spectroscopy, gas chromatography GC) is suitable for characterisation of seed lots. The industrial partner (Rijk Zwaan BV) is satisfied with what has been reached so far, a few meetings were already organised to discuss the possibilities and criteria concerning a more definite action towards the submission of new research proposals.

Results on TLC plates obtained using several methods (photoacoustics, radiometry, thermography, densitometry) are interesting, subsurface sampling to a depth as much as 250µm were performed and secondary chromatography effects observed.
Various methods were applied (UV spectroscopy, FTIR, Raman and IR absorption, DSC, refractometry, photoluminescesce, GC and HPLC chromatography) to determined the extent of oxidation in safflower oil. Thermal lens spectrometry (TLS) combined with HPLC seems the most sensitive approach.
As to the last two issues (lipids and TLC plates, Univ. Wageningen and SES, Nova Gorica are trying to establish contacts with manufacturers.

Packaging working group: Very promising results were obtained on water migration study in starch samples (provided by ESIEC) by using the non-contact PPE.
Several photothermal techniques have been applied to measure the varnish/coating thickness in paper and board packaging materials; it has been shown that these techniques can have 1µm resolution. A reference sample is required in most cases, and the on-line applicability seems very difficult.
For the water content in paper and board packaging materials, the techniques that have been used did not reach the required resolution.
Renault is interested in the water uptake of coated samples in a controlled atmosphere. The results obtained up to now are considered, by the industrial partner, interesting enough to elaborate a R&D project proposal on this issue.

Textile working group: For the knitted textiles the results were encouraging: two methods were able to give tomographic information on the water content of a sample: non-contact PPE method and photothermal radiometry, both using 1.94µm as excitation wavelength.
On the DTNW samples, several methods were sensitive either to the water content (photoacoustics, OTTER) or to distinguish between the treated/untreated sides (radiometry) but not to both aspects.

Living Tissues working group:
Both OTTER and non-contact PPE techniques are highly promising for hydration measurements. Other aspects of these two techniques (versatility and speed of OTTER and low cost of PPE) are complementary. These results were judged by the industrial partners to be sufficiently encouraging to underpin a follow-on programme.
An impressive theoretical model of blood sedimentation based on optical attenuation measurements was reported.
The work over the next period will focused on how these scientific opportunities can be translated into successful research proposals.
After the organisation of the four working groups (Food, Packaging, Textiles and Living Tissues) at the beginning of the network, the measurement campaign was prepared according to the contract. During the Workshop in Ostia (Italy): October 29-30, 1998 the final decisions were taken concerning the selected samples and the requirements imposed by the industrial partners. Each scientific partner has decided on which problem it would participate with what type of measurement technique. This research activity was not financially supported by EC, only the exchanges between partners and circulation and conditioning of samples.

Original research objectives:
Food working group focused its attention on three selected topics i.e. The quality assessment in seeds, depth profiling of thin layer chromatography (TLC) plates and the oxidative stability of lipids.
Packaging working group selected the following topics: water migration in starch used as packaging material (provided by ESIEC) or edible films (provided by TEI); varnish/coating thickness (the demand was for an on-line measurement with a resolution of 0.1µm and a measuring range of 0 to 10µm) and water content with a resolution of 1% in the RH range from 23% to 60% in paper and board packaging materials provided by Hueck Folien and PTS; migration of aroma compound in polymer samples; water uptake in Renault samples (cataphoresis films).
Textiles working group selected two categories of samples. ITF prepared samples (knitted textiles) with the aim of studying the water migration on macroscopic scale, e.g. over the thickness of a textile (0.5-2mm); DTNW prepared samples for the purpose migration study at microscopic level, e.g. the thickness of a fibre (10-20µm).
Living Tissues working group: Despite the strong emphasis on in-vivo human skin measurements, the campaign was planned on the basis of in-vitro samples and phantoms only. Blood sedimentation study was another topic.

Expected deliverables:
According to the network proposal document, the aim of the measurement campaign is to critically evaluate the potential and limitations of the envisaged methods in order to estimate the obstacles and eventually to select the most reasonable technologies before embarking on new R&D programmes to develop instrumentation capable of meeting all the requirements imposed be the various industrial sectors.

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Université de Reims Champagne - Ardenne
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Moulin de la Housse
51087 Reims

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