MATERIAL AND METHODS Wood Flooring samples

Wood samples of industrially finished and unfinished flooring elements were supplied by seven Austrian producers with top layers of the wood species beech (Fagus sylvatica), oak (Quercus sp.) and larch (Larix sp.). The standard surfaces were planed and sanded but from larch and oak wood also brushed surfaces with rough surface structure were used. The industrial partners treated the flooring elements in their plants with different oil/wax systems (including initial care treatment) and in particular beech samples were also treated with UV-oils and UV-sealers. Other beech samples were treated manually by roller with a 1K water based acrylic sealer system for wooden floors.

A few other materials were selected as references to compare with the wood surfaces. For roughness assessment these were a metal ruler with an even

edge and two samples of high pressure laminate (HPL), one with smooth and one with rough surface. For assessing the temperature sensation a ceramic tile was used as reference.

Studies with test persons

All assessments with test persons were carried out in conditioined rooms at 23°C and 50% relative humidity. The test persons were chosen by gender and age to gain as good as possible a representative sample.

The first study on surface roughness included 20 test persons (10 female, 10 male). In sessions with single persons they had to touch the surfaces of the samples without seeing them and to give a rating for surface roughness on a scale from 1 (smooth) to 5 (rough). To calibrate this scale they received the smoothes and the roughest sample before the test started. During the test the samples were given in a random order that was changing from one to the other test person. Together with the roughness rating the test persons had to state if they consider the surfaces to be wood or plastic.

The study on temperature sensation included 64 test persons (32 female, 32 male) evenly distributed over 5 age classes starting at 20 years. Before starting the test the test persons washed their feet and hands in water at room temperature (23°C) and dried them. In individual sessions the persons judged temperature sensation by feet and hands always in direct comparison of two different samples stating which material feels warmer than the other. The samples were chosen in random order leading to 11 comparisons and 3 control comparisons for each test person. In these comparisons the test persons ranked the temperature sensation of the samples in 4 classes from warm (rating 1) to cool (rating 4). These tests were carried out first excluding and then including the visual impression.

High resolution profilometry

To obtain high resolution surface profiles pictures from cross sections of the samples in a Scanning Electron Microscope (SEM) that showed the real surface topography were processed. Cross sections of the surfaces of the wood flooring samples and reference materials were prepared for microscopic investigations. Non-conductive samples were sputter coated with Gold in 5 nm thickness. The cross sections were observed in a SEM (Jeol JSM-6100) and photographed with a digital imaging system at constant magnification, working distance and accelerating voltage. The pictures were calibrated to enable measurements of structure dimensions. On a length of 5.93 mm the surface profiles were traced by digital image processing as shown in

The 5th Conference on Hardwood Research and Utilisation in Europe 2012

Figure 1. The profile depth was measured on these lines as distance to a straight reference line with an increment of 2.3 µm leading to 2580 data points for each profile. Electron-optic distortion of the pictures was corrected mathematically in order to receive straight surface profiles for the samples using the surface profile of an even edge of a metal ruler that was generated in the same procedure. The profile depth was stated as the range of data points from P1 to P99, which excluded 2 percentiles of the data with the extreme values.

0 1000 2000 3000 4000 5000 6000

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Figure 1: Digital image processing of SEM-pictures of cross sections of samples

Active thermography

The principle of active thermography is to assess time series of thermographic pictures of an Infrared camera (IR-camera) from samples that were subjected to controlled heating. In the present study an IR-camera (Varioscan 3021 ST) was mounted on a stand in constant and parallel orientation to the test panel. This setup was placed in a conditioned room at 14°C and 50% relative humidity and covered by a cardboard box to avoid excessive air movement.

Four different samples were joined together to obtain an even surface and placed on the test panel as shown in

Figure 2. To correct differences in emissivity, one part of each sample was coated with a deep matt black laquer with known emissivity. A petri dish of glass with 93 mm diameter and an even bottom was filled with water to a height of 10 mm and heated on an electric heating mat to a temperature of approximately 55 °C. This petri dish

was placed on the sample surfaces for 30 s. After removing the petri dish the samples were photographed with the IR-camera in intervals of 4 s (

Figure 2). The thermographs were processed in order to obtain mean and maximum temperature in a defined area of 30 by 30 mm centred on the heated surface of each sample.

Figure 2: Four samples on test panel (left) and top view on four samples (right) with petri dish filled with water to heat the surface

RESULTS AND DISCUSSION