Abstract
A near-infrared spectroscopic method and measurement
system for moisture depth profiling is presented in this
thesis. The measurement system is based on a fibre-optic
light source and probes, and a hyperspectral imaging
spectrograph. The probes feature six different
measurement geometries, including a specular reflection
measurement, and diffuse reflection and transmission
measurements, all of which are measured in seven
positions simultaneously. A theoretical analysis of the
depth profiling capabilities of the system is presented,
as well as laboratory tests of the system performance.
Based on these, the analysis depth of the reflection
moisture measurement in a 75 µm thick uncoated paper is
estimated to be about 40 µm. It is also shown that the
depth profiling properties depend on the average moisture
content of the paper, and that the inclusion of a coating
layer complicates the depth profiling. The use of the
theoretical analysis results in the interpretation of the
measurement results is also discussed.
As the main application, the measurement system was
installed on a pilot-scale paper coating machine. The
feasibility of semi-quantitative moisture depth profiling
during the coating process is shown. The determination of
the first and second critical concentrations of the
coating colour consolidation process is also discussed.
Detailed results from the extensive programme of trial
runs are presented, along with discussion of the physics
behind the measurements. It is found that the water
transport characteristics measured during the coating
process are not in accordance with mass and heat transfer
theories in some respects. Also, the specular reflection
measurement results do not behave as expected, making the
determination of the first critical concentration
impossible in some cases. Instead, the second critical
concentration is easily detected, but does not always
behave as expected. Reasons for the unexpected behaviour
of the measurements are discussed, and conclusions drawn
about the water transport during the coating process.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 14 Dec 2007 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 978-951-38-7063-8 |
Electronic ISBNs | 978-951-38-7064-5 |
Publication status | Published - 2007 |
MoE publication type | G4 Doctoral dissertation (monograph) |
Keywords
- moisture content
- depth profiling
- paper coating
- optical properties
- near-infrared spectroscopy
- NIR
- fibre-optic light sources
- fibre-optic probes
- multichannel spectroscopy
- water transport characteristics
- on-line measurement
- Monte Carlo modelling