Charpy’s impact strength

In studies III and IV, Charpy’s impact strengths (unnotched) were determined according to ISO 179-1. The measurements were carried out using a Ray-ran advanced universal pendulum system (JD Instruments Inc., Houston, Texas, United States) as presented in Figure 12. The injection-molded samples were cut into pieces with dimensions of 4.1 mm × 10.1 mm × 80 mm.

Before the measurements, the test machine was calibrated to determine the frictional losses and to correct for any absorbed energy. In addition, the dimensions of one specimen from each material type were measured to ensure that the dimensions corresponded to the guidelines given in ISO 179-1. The samples were then placed edgewise between two supports (L^s= 62 mm).

The pendulum (m= 0.952 kg) was lifted up its prescribed height to achieve a pendulum velocity of 2.9 m/s. The pendulum was released and the result was recorded. For all material types, the impact resulted in a complete fracture of the specimen.

Figure 12. Ray-ran advanced universal pendulum system used in studies III and IV.

6.3 WATER ABSORPTION

In studies I, III, and IV, the water absorption of the WPCs was determined from the injection-molded samples as outlined in ISO 62. Sprues and runners were removed from the specimens to ensure that the specimens were similar in shape. A total of three samples of each material type was tested.

The specimens were first dried in a force-convection oven at 50 ± 2 °C for 24 hours. The specimens were then allowed to cool to room temperature in a desiccator before they were weighed using a Mettler Toledo AX205 –scale (Mettler-Toledo, LCC, Columbus (Ohio), United States). Immediately thereafter, the specimens were immersed in distilled water (T = 21.0 °C) for 24 and 48 hours. After the immersion, any excess water was removed from the surfaces of the specimens and they were reweighed within 1 minute of their removal from water. The specimens were weighed at least three times at each stage, with the results being reported as the means of the separate weighings.

6.4 VOC EMISSIONS

The VOC emissions from the WPC samples were measured using a high-resolution PTR-TOF-MS (PTR-TOF 8000, Ionicon Analytik, Innsbruck, Austria) as presented in Figure 13. The PTR-TOF-MS was operated under controlled conditions:

2.3 mbar drift tube pressure, 600 V drift tube voltage and 60 °C temperature.

Figure 13. PTR-TOF 8000 used in studies II, III, and IV.

In study II, the VOC emissions from seven different WPC deck boards were determined. One of the decks (LunaComp) was obtained from the manufacturer immediately after its production to investigate the changes in the VOC emissions during the first 41 days. Starting from the first day after the manufacture, the VOC emissions for this sample were characterized 11 times over a 41-day period to monitor the changes in the VOC emission rates. The sample was stored under laboratory conditions between the measurements. The ages of the six remaining decks were unknown, but they represented products that a consumer would use. As the WPC deck samples were prepared from different products, their shapes were irregular and dissimilar. Therefore, the VOC emission rates of these samples were determined with respect to their masses.

In studies III and IV, the VOC emission measurements were carried out using the injection-molded specimens as samples.

Five specimens of each material type were cut so that they had dimensions of 4.1 mm × 10.1 mm × 80 mm. The areas of the samples were determined so that it was possible to convert the obtained emissions into area-specific emissions rates.

The emissions were determined using 1.5 L glass vessels as the chambers. The glass vessels were prepared for the measurements by cleaning the inner surfaces with detergent and then rinsing them with distilled water. Furthermore, to ensure the purity of the chambers, the vessels were thermally cleaned by heating them in a force-convection oven at 120 °C for at least one hour. The tubes that introduce the air to the chamber and transport it to the PTR-TOF-MS system were installed on the metal lid that covered the glass vessels. The air (RH < 5%) that was introduced into the chamber with a flow rate of 0.3 L/min had been filtered with an active carbon/Purafil^®/HEPA filter. The air containing VOCs was then transported into the PTR drift tube via a polyether ether ketone (PEEK) tube at a total flow rate of 0.1–0.3 L/min.

Before the samples were analyzed, the emissions from empty chambers were measured and this background was subtracted from the data during the analysis. Once the samples were placed in the chamber, the system immediately started to collect the data. As the VOC emissions could be observed online, each measurement was continued until the emissions of the compounds of interest stabilized. This took approximately 15 minutes for each material. After each measurement, the chamber was carefully flushed with purified air.

The obtained data were analyzed using PTR-MS Viewer 3.1.0.27 software (Ionicon Analytik, Innsbruck, Austria). The concentrations were calculated by the program using a standard reaction rate constant of 2 × 10^-9 cm³ s^-1 molecule^-1. The trace gases were detected from the spectral peaks assuming that the molecules consisted only of hydrogen, carbon, and oxygen. The detection of gases was further supported by the literature data on the VOC emissions of wood materials and the matching of the isotope patterns, especially in cases where the detection was ambiguous. Table 4 lists the VOCs studied in each study.

Table 4. The VOCs studied in studies II, III and IV. Cyclohexene (m/z 83.0706 C6H11+)

Furan (m/z 69.034 C4H5O⁺)

The VOC emission values calculated by the software were expressed as parts per billion (ppb). In studies III and IV, these emission values were converted into emission rates (µg/m²h) according to the following equation:

E_voc = ^{0.0409 C}_A^vocFvocMvoc

sample , (6.1)

whereC^voc is the concentration of the VOC (ppb),F^voc is the flow rate (m³/h), and M^voc is the molar mass of the individual VOC molecule (g/mol). The unitless constant 0.0409 was obtained from the conversion of units using the ideal gas law at 1 atm pressure and 25 °C, andAsample is the area of the WPC sample. In study II, the emission rates were calculated with respect to the mass of the samples; the emission rates were expressed as µg/kgh, therefore.

The emission rates were further converted into real room air concentrations (µg/m³) using product loading factor (L^p), which is equal to the sample surface area divided by the chamber volume. By applying this conversion, it was possible to compare the VOC emissions of the material with the odor thresholds of VOCs, and thus one could estimate whether a certain VOC could be smelled. The real room air concentration is expressed as follows:

Creal room=^Evoc_n^Lp , (6.2)

whereE^voc is the emission rate of VOC (µg/m²h),L^p is the loading factor of the sample (m²/m³) andn is the air exchange rate (1/h) in the chamber. In studies III and IV, L^p was calculated with respect to the area of the samples, but in study II, sample mass was used to determineL^p. In study II, it was also assumed that the samples had similar compositions and shapes.