6 Materials and methods
6.5 Statistical analyses
In studies I, III, and IV, the statistical analyses were performed using Matlab R2013b (Mathworks, Natick, MA, US) and IBM SPSS Statistics 21 software (IBM Corp., Armonk, NY, US). Both parametric and non-parametric statistical tests were considered.
Mann-Whitney U test was found to be suitable for evaluating the statistical significance of the differences observed between the material types when the number of specimens was more than five. The limit for statistical significance was set at p � 0.05, and p < 0.01 was designated as high statistical significance.
The most important findings from studies I–IV are summarized in Table 5. The results will be presented in more detail in the following chapters.
Table 5. A summary of the main findings in this thesis.
Study subject Studies The main findings
Impregnation of WPC granules with the
distillates
I, III, and IV
The LG granules were successfully impregnated with the distillates.
Hardwood and softwood distillates enhanced the processability of the WPC
granules.
Mechanical properties I, III, and IV
A small (1 wt%) addition of hardwood distillate significantly increased the tensile modulus of the WPC. A higher
distillate content (2–8 wt%) reduced the mechanical properties of the WPC.
A minor (2 wt%) addition of softwood distillate significantly increased the tensile strength of the WPC. Strain and
bending increased significantly with a high distillate content (over 4 wt%)
whereas the strength of the WPC declined.
Water absorption I, III, and IV
The WPCs containing wood distillates absorbed less water than those without
distillates.
VOCs II, III, and IV
PTR-TOF-MS is an applicable method for determining VOCs from WPCs.
The VOC emissions from the WPCs change considerably as a function of
time.
7.1 MECHANICAL PROPERTIES
The effects of wood distillates on the mechanical properties of the WPCs were determined in studies I, III, and IV. In study I, the addition of hardwood distillate did not improve the mechanical properties of the WPCs studied. UF40 had the highest flexural and tensile strength whereas the highest flexural modulus was detected for UF50 and the highest tensile modulus for UF50 + LG50.
In studies III and IV, a minor addition (1–2 wt%) of wood distillates significantly improved the mechanical properties of the WPC studied. In study III, the LG granules were impregnated with a similar hardwood distillate as used in study I. The distillate content ranged from 1 to 8 wt%. In study IV, 1–20 wt% of softwood distillate was added to the WPC. The results from studies III and IV are summarized in Table 6.
Tensile modulus increased highly significantly with 1 wt% of hardwood distillate. Similar trends, although not statistically significant, were observed for tensile and flexural strength and modulus of elasticity.
The addition of softwood distillate had advantageous effects on the mechanical properties of the WPC in study IV. With 2 wt% of softwood distillate, a highly significant increase was observed in the tensile strength. Another finding emerging from study IV was that when the softwood distillate content exceeded 4 wt%, statistically significant or highly significant increases were observed in strain and bending.
Table 6. The mechanical properties of the WPCs in studies III and IV (mean ± standard deviation). The underlined values indicate at least significant (p � 0.05)
difference in comparison with the other WPCs in the same study.
Property LG LG + HWD1 LG + HWD2 LG + HWD4 LG + HWD8
* p � 0.05 (a significant difference compared with the unmodified WPC).
** p < 0.01 (a highly significant difference compared with the unmodified WPC).
LG = LunaGrain, HWD = Hardwood distillate, SWD = Softwood distillate, TS = tensile strength, TM = tensile modulus,� = strain, FS = flexural strength, MOE = modulus of elasticity, B = bending, CIS = Charpy’s impact strength.
7.2 WATER ABSORPTION
Water absorption of WPCs was determined in studies I, III, and IV. In study I, the addition of hardwood distillate did not have any consistent effects on the amount of water absorbed by the UFs; for example, when distillate-treated LG was added to UF20, a minor increase was observed in water absorption, but the opposite effect was detected for UF30 and UF50. However, when 4.2 wt% of distillate was added to LG, water absorption reduced by over 30%.
In study III, the addition of hardwood distillate considerably decreased water absorption of the WPCs (Figure 14). The major differences occurred during the first 24 hours of immersion as
less the same after 48 hours even though there was an increase in the values for all the materials. After 48 hours of immersion, LG containing 8 wt% of hardwood distillate had absorbed approximately 20% less water than unmodified LG.
Accordingly, the difference between the unmodified LG and LG with 1 wt% of hardwood distillate was about 10%.
The addition of softwood distillate did not decrease water absorption of the WPCs to the same extent as hardwood distillate even though water absorption decreased as a function of the distillate content (Figure 14). The difference between water absorption of LG and LG + SWD20 was approximately 16% whereas no difference was observed between LG and LG with 1 wt% of distillate.
Study IV also shows that the difference in the water absorption values between LG and distillate-treated LGs decreased after 48 hours of immersion. The WPCs containing softwood distillate absorbed more water between 24 and 48 hours of immersion than those containing hardwood distillate.
Figure 14. Moisture content of the WPCs after 24 and 48 hours of water immersion in studies III and IV. HWD = hardwood distillate, and SWD = softwood
distillate.
0.25 0.3 0.35 0.4 0.45 0.5 0.55
0 5 10 15 20
Moisturecontent(wt%)
Distillate content (wt%)
HWD, 24h HWD, 48h SWD, 24h SWD, 48h
7.3 VOC EMISSIONS
The VOC emission rates of a WPC deck determined in study II are presented in Figures 15 and 16. The compounds of interest were formaldehyde, acetaldehyde, acetic acid, cyclohexene, furan, furfural, guaiacol, and monoterpenes.
Decreasing trends of the emission rates were observed for acetaldehyde, furfural, and monoterpenes. Additionally, a minor decline was observed in the guaiacol emission rates.
Formaldehyde and furan emission rates remained relatively stable during the experiment, but acetic acid emission rates fluctuated, especially at the beginning of the trial. During the first 13 days of the experiment, cyclohexene emission rates remained relatively stable. However, starting from the day 16, the emission rates of cyclohexene nearly tripled compared with the values observed during the first 13 days.
The VOC emission rates of the seven different WPC decks determined in study II are presented in Figures 17 and 18. One of the decks (LunaComp 3) was also used in the 41-day trial.
Figure 15. The emission rates of formaldehyde, acetaldehyde, acetic acid, and cyclohexene from a WPC deck during a 41-day period.
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Formaldehyde Acetaldehyde Acetic acid Cyclohexene
Emissionrate(�g/kgh)
Days: 1 3 6 10 13 16 21 24 28 34 41
Figure 16. The emission rates of furan, furfural, guaiacol, and monoterpenes from a WPC deck during a 41-day period.
Figure 17. The emission rates of formaldehyde, acetaldehyde, acetic acid and cyclohexene from seven different WPC decks.
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Furan Furfural Guaiacol Monoterpenes
Emissionrate(�g/kgh)
Days: 1 3 6 10 13 16 21 24 28 34 41
0 0.5 1 1.5 2 2.5 3 3.5 4
Formaldehyde Acetaldehyde Acetic acid Cyclohexene
Emissionrate(�g/kgh)
Manufacturer 1 Manufacturer 2 UPM ProFi 1 UPM ProFi 2 LunaComp 1 LunaComp 2 LunaComp 3
Figure 18. The emission rates of furan, furfural, guaiacol, and monoterpenes from seven different WPC decks.
An overview of the results reveals that the deck from Manufacturer 2 had the highest emission rates for cyclohexene, furan, furfural, and guaiacol. The highest formaldehyde emission rates were observed for the deck from Manufacturer 1.
UPM ProFi had the highest acetic acid and acetaldehyde emission rates. Monoterpenes were most abundantly released from UPM ProFi 2. In general, LunaComp decks had the lowest VOC emission rates when compared with the other manufacturers.
The emission rates obtained from the comparative study were further converted into real room concentrations. This conversion revealed that acetaldehyde and guaiacol exceeded their odor thresholds and therefore, it was likely that they could be smelled from the decks. The values for other VOCs were low with respect to their odor thresholds.
In study III, the effects of hardwood distillate addition on the VOC characteristics of the WPCs were assessed by determining the emission rates of cyclohexene, furfural, guaiacol, monoterpenes, methanol, and benzene (Figures 19 and 20).
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Furan Furfural Guaiacol Monoterpenes
Emissionrate(�g/kgh)
Manufacturer 1 Manufacturer 2 UPM ProFi 1 UPM ProFi 2 LunaComp 1 LunaComp 2 LunaComp 3
Figure 19. The emission rates of cyclohexene, furfural, and guaiacol from the WPCs treated with hardwood distillate.
Figure 20. The emission rates of monoterpenes, methanol, and benzene from the WPCs treated with hardwood distillate.
0 1 2 3 4 5 6 7 8 9 10
Cyclohexene Furfural Guaiacol
Emissionrate(�g/m2h)
LG LG + HWD1 LG + HWD2 LG + HWD4 LG + HWD8
0 5 10 15 20 25 30 35
Monoterpenes Methanol Benzene
Emissionrate(�g/m2h)
LG LG + HWD1 LG + HWD2 LG + HWD4 LG + HWD8
The addition of hardwood distillate increased the emission rates of the studied compounds, especially for cyclohexene, furfural, monoterpenes, and methanol. Monoterpenes were most abundantly emitted whereas only trace amounts of guaiacol were detected. The emission rates of benzene were also low. The conversion of the emission rates into real room concentrations indicated that the odor threshold of guaiacol would be exceeded for all of these materials. The odor threshold for monoterpenes was also exceeded when 8 wt% of hardwood distillate was added to the WPC.
Similar evaluations were done in study IV where WPCs were modified with softwood distillate. The emission rates of cyclohexene, furfural, guaiacol, monoterpenes, acetaldehyde, and benzene were determined (Figures 21 and 22).
The addition of softwood distillate clearly increased the emission rates of cyclohexene, furfural, and monoterpenes. The emission rates of benzene and guaiacol, in turn, remained rather low although the odor threshold of guaiacol was exceeded in all of the materials. Acetaldehyde emission rates decreased below the odor threshold when softwood distillate content was increased from 1 wt% to 8 wt%. An increase in the distillate content from 8 wt% to 20 wt% resulted in a considerably higher emission rate of acetaldehyde, and as a consequence, the odor threshold of acetaldehyde was exceeded.
Figure 21. The emission rates of cyclohexene, furfural, and guaiacol from the WPCs treated with softwood distillate.
Figure 22. The emission rates of monoterpenes, acetaldehyde, and benzene from the WPCs treated with softwood distillate.
0 5 10 15 20 25
Cyclohexene Furfural Guaiacol
Emissionrate(�g/m2h)
LG LG + SWD1 LG + SWD2
LG + SWD4 LG + SWD8 LG + SWD20
0 2 4 6 8 10 12 14 16 18 20
Monoterpenes Acetaldehyde Benzene
Emissionrate(�g/m2h)
LG LG + SWD1 LG + SWD2
LG + SWD4 LG + SWD8 LG + SWD20
In the present thesis, the effects of hardwood and softwood