Description of used experimental methods

Since the wood used in CBPB production is particles, the surface quality is not perfectly smooth.

In case of wood, sanded surface is the best-processed wood quality [132]. Boards from Scots pine and poplar with three types of surfaces – sawn with a band saw, planed with a planer, and sanded with a belt sander (sand paper grit size 120) – were prepared by dimension (250x90x10) mm. The measurements have been conducted on poplar hybrid I214 (Populus cv. euramericana I 214) and Scots Pine (Pinus sylvestris) samples. In order to describe the status of the surfaces, wood surface roughness was also measured, using a stylus tip MAHR S2P perthometer instrument, with a tip diameter of 2 μm. Fifteen measurements on each differently machined wood species have been performed, with a difference of 50 μm between the consecutive measurements, on three samples resulting five measurements on each sample. The unfiltered primary profile has been evaluated by Ra, the mean roughness [133], Rz the mean roughness depth and Rmax the maximum roughness, according to the standard DIN EN ISO 4288 [134].

3.1.2.2 Wettability test

Sanded, sawn and planed radial cut surfaces have been prepared with dimension of (250x90x10) mm from poplar and Scots pine, tested with 6 different test liquids. 5 samples being grouped for each type of combination, and 10 measurements have been performed on each sample. Resulting 50 measurements on each type of sample group and 1800 contact angle measurements in total (Fig.3.1). Prior to testing, all samples have been conditioned at room temperature of 20^o C and RH of 65 % until reaching constant weight. The average MC of the samples was 6.1 %. In order to test wettability of the two wood species, machined in three different ways, PG-X Goniometer was used (Fig.3.2). The size of the testing droplet can be adjusted prior to measurements. The effect of droplet’s size on contact angle was always a question and it appears that when surface is rougher may cause significant effect [135], [136].

Figure 3. 1: Wettability test experimental setting.

As we could not find any literature data on tests performed with the fire retardants in scope as test liquids, small tests were conducted to decide which size of the droplet would be appropriate. Finally, a droplet of 5 μl has been chosen, the tests have been performed in dynamic mode, and the apparent contact angle was taken in the 0.5^th second [137].

Figure 3. 2: Schematic description of contact angle measurement by PGx goniometer.

3.1.2.3 Lindner test

To perform the Lindner test, six test species for each surface type and wood species were used with each of the fire retardants. In total, 126 specimens for each type of wood were tested, and 18 specimens were left untreated as control (see Fig.3.3). Specimens were kept at a room temperature of 20 °C with a relative humidity of 65 % for 24 hours. Subsequently, the surface of each of the species was treated by spreading 5 g of each fire retardant with a brush. Specimens were allowed to dry for 24 hours in an ambient room condition. The room conditions (RH = 52 %, T = 22 °C) were similar to the conditions initially used for the 24-hour period (RH = 65 %, T = 20 °C), only this time the specimens were left for seven days according to standard MSZ 9607/1-83 (Hungarian National Standard) [138]. In general, this test is igniting wood samples via stove fire, but rather than using gas, a 1g pill of hexamethylenetetramine was ignited instead, and the wood specimen was placed on an iron stand above the flame. The burning time was the total burning time of examethylenetetramine pill. Mass loss was calculating based on following equation:

M = M0 - M1 (3.1)

Where, M: Mass loss (g), M0: initial mass (g), M1: Mass after burning (g).

Figure 3. 3: Fire tests experimental setting.

3.1.2.4 The singe flame source test

The surface treatment and preparation for the Lindner test and the single flame source test were achieved in the same manner (see Fig.3.3). However, in case of the single flame source test, specimens with dimension of (250x90x10) mm were used. The single flame source test was accomplishedaccording to standard MSZ EN ISO 11925-2:2011 Reaction to fire tests. Ignitability of products subjected to direct impingement of flame. Part 2: Single-flame source test with Taurus Instruments [16]. The aim of this test was to measure the ignitability of a vertically-oriented test samples exposed to a small flame. The specimens can be exposed at three different spots, either at the surface, the side or at the edge (Fig.3.4). In our test, the face was used. The specimens for this test were prepared by marking two lines on the surface of each specimen. The first line was 40 mm above the bottom of the specimens and the second line was located 150 mm above that. This space marks the flame area according to the standard. The first line is where the flame should be started. If the flame exceeds the second line, the specimen is out of standard. The test duration is 30 s. During the first 15 s, the specimen is burned. In the second 15 s period, observations concerning the success or failure of ignition are noted.

Figure 3. 4: The single flame source test.

3.1.2.5 The bomb calorimeter test

The bomb calorimeter is a heat of combustion measuring device of materials. Specimen with mass range between 0.6-1.2 g is burned inside the apparatus under standardised conditions [139]. The heat of combustion is calculated based on the observed temperature rise while the heat loss was taken into consideration.

In preparation for the calorimeter test MSZ EN ISO 1716:2011, the poplar and Scot’s pine hammer-milled particle were then kept in a room climate with a relative humidity of 65% and a temperature of 20 °C for 24 h. Afterward, 8 g of the particles were soaked into each fire retardant for 1 min, before being drained and left to dry. The tests were performed with a Parr™ 6200 Compensated Calorimeter. For the test, a bucket was filled with 2000 g of water and 1g of particles was put inside a calorimeter bomb, which was filled with oxygen. After that, the calorimeter bomb was put in the water bucket. The total test time was around 15 min.

Figure 3. 5: Calorimeter test experimental setting.

3.1.2.6 Hydration test

For hydration test, mixture of Portland cement CEM I 42.5 N, Sodium Silicate (Na2Sio2) water glass (SS), mixing water and fire retardant was created. The amount of the added FR’s was calculated based on the wood and dry after 24 hours. The mixture was poured into small cups and thermocouples were inserted into the mixture to measure the temperature change during cement curing for 24 hours.The thermocouples were connected to an AHLBORN device that was linked to a laptop via special software that collected the temperature data directly into an excel sheet with a given sampling rate (Fig.3.6).

Table 3. 2: Hydration test experimental setting.

Variant Cement Additive Fire retardants Samples

1 CEM I 42.5 N Sodium Silicate No treatment 3 samples

2 CEM I 42.5 N Sodium Silicate Borax 3 samples

3 CEM I 42.5 N Sodium Silicate DSHP 25 g/l 3 samples

4 CEM I 42.5 N Sodium Silicate DSHP 77 g/l 3 samples

5 CEM I 42.5 N Sodium Silicate DAHP 25 g/l 3 samples

6 CEM I 42.5 N Sodium Silicate DAHP 300 g/l 3 samples

7 CEM I 42.5 N Sodium Silicate PEG 400 3 samples

Figure 3. 6: Schematic description for hydration test.