The Effect of Conditioning Time on Mean Fibre Diameter Results

Abstract

 At the 1999 IWTO meeting in Nice a working group was formed to investigate the gravimetric and fibre diameter conditioning profiles of core samples. It was recommended that, for the sake of simplicity, only one fine and one coarse core sample be used at this stage. This report investigated both the gravimetric and fibre diameter conditioning profiles for scoured logs and Shirley Analysed webs, as well as overnight and rapid conditioning of the samples. The two core samples used for this evaluation had nominal fibre diameters of 17.5 µm and 28.0 µm (AF) respectively.

The gravimetric analysis yielded the following results :

1. When samples are conditioned afternoon and overnight (>16 hours), Shirley Analysed samples conditioned faster than scoured logs. The fine wool samples also conditioned marginally faster than the coarse wool samples for both scoured logs and Shirley Analysed webs. All samples reached 99 % of their equilibrium mass after eight hours of normal conditioning.
2. When large volumes of conditioned air is drawn over or through the sample (i.e. rapid conditioning), there is virtually no difference between the conditioning profiles for Shirley Analysed or scoured logs, irrespective of fibre diameter. The sample equilibrium mass is reached after only one hour of rapid conditioning.

The fibre diameter (Airflow only) analysis yielded the following results :

1. The fibre diameter for both the fine and coarse wool samples stabilised after eight hours of normal conditioning. The fine wool fibre diameter was 17.63 µm after eight hours of conditioning compared to 17.59 µm at equilibrium. For coarse wool the corresponding values were 28.10 µm compared to 28.01 µm at equilibrium.
2. Both the fine and coarse wool samples yielded stable fibre diameter results after only one hour of rapid conditioning. The fine wool sample fibre diameter was 17.55 µm after one hour compared to 17.60 µm after eight hours of rapid conditioning. For coarse wool the corresponding values were 27.55 µm compared to 27.50 µm after eight hours. The slightly lower fibre diameter for the coarse wool samples can be ascribed to the additional Shirley Analysing step used prior to the rapid conditioning part of the investigation.

The above results indicate that eight or more hours of normal conditioning, of Shirley Analysed webs, should be sufficient to produce stable fibre diameter results using the Airflow instrument. It is also evident that rapid conditioning Shirley Analysed samples for as little as one hour may be sufficient to produce stable fibre diameter results using the Airflow instrument.

Citation

"The Effect of Conditioning Time on Mean Fibre Diameter Results", B. van Rensburg, Sliver Group, Report 06, IWTO Christchurch Meeting, April 2000.