**4.1.1 Total amount of water-soluble carbohydrates, (TSC)**

Hasan (2006) and Despot *et al.* (2007; 2008) measured the total amount of water-soluble carbohydrates (TSC) according to Rapp *et al.* (2003). They used the following procedure: Five oven-dried specimens of each group were milled together for 60 s in a heavy vibratory disc mill (Herzog Maschinenfabrik, Osnabrück, Germany). 400 mg of wood powder were mixed up with one drop of detergent and 20 ml distilled water in 50 ml flasks. Afterwards, the flasks were shaken at 20 ºC for 60 min with a vibration of 120 min-1 and filtered through glass filter paper. The filtrates were diluted with distilled water in proportion 1:5.

The reagent for optical spectrophotometry was prepared by dissolving 2 g of dihydroxytoluol (Orcin) in 1l of 97 % sulphuric acid. For analysing the carbohydrate content 1 ml of dilution was mixed with 2 ml reagent in a test-tube and heated for 15 min at 100 ºC in a Thermo-block (Merck TR205). After cooling to room temperature, the dilution was analysed at 540 nm with a Merck SQ 115 filter-photometer. The TSC was calculated after calibration with a glucose standard between 20 and 200 ppm leading to extinction between 0.12 and 1.32.

Hasan (2006) and Despot *et al.* (2007; 2008) found a strong influence of gamma irradiation on TSC. As gamma radiation causes destruction of cellulose chains and the resulting smaller cellulose fragments are easily soluble, increasing of TSC with increasing radiation dose was expected. They found no significant influence of time after gamma treatment on TSC (Figures 2 and 3).

The sensitiveness of the TSC content to reveal changes in the carbohydrate structure of wooden materials was shown in earlier studies with thermally modified timber (TMT) where TSC was significantly reduced with ascending heat treatment temperature and increasing heat-induced loss of mass (Welzbacher *et al.,* 2004; 2009). Thus, the extraction of soluble carbohydrates appeared to be a sensitive method to display degradation of carbohydrates (Hasan, 2006; Despot *et al.*, 2007; 2008) and is therefore also considered as a suitable tool to characterize the treatment intensity of gamma radiation.

According to Fengel and Wegener (1989) and Tišler and Medved (1997), the highest TSC should be observed 150 days after gamma radiation. In contrast to mass loss by leaching, TSC did not decrease over time. Accordingly, the radical recombination is probably limited to higher mol mass fragments but not to lower fragments, which appear as TSC.

Changes in Selected Properties of Wood Caused by Gamma Radiation 287

All these studies lead to the conclusion that due to breaking the chains of cellulose in wood cell wall, there must be some changes in physical and mechanical properties of gammairradiated wood. These changes should mostly influence the hygroscopicity (Fengel and Wegener, 1989) and tension strength of gamma-irradiated wood, because it becomes more brittle (Divos and Bejo, 2005). Furthermore, gamma irradiated wood is more susceptible to chemical and enzymatic degradation (Seifert, 1964; Klimentov and Bysotskaia, 1979; Klimentov *et al.*, 1981; Ardica *et al.*, 1984; Šimkovic *et al.*, 1991; Magaudda *et al.*, 2001;

Gamma radiation lead to significant colour changes of wood. With increasing radiation dose

Fig. 4. Colour change of specimens used for mass loss determination, **3AA** – control group, **3AB** – group irradiated with 30 kGy, **3AC** – group irradiated with 90 kGy and **3AD** – group

On the question whether there is any loss of mass or density of the wood due to gamma radiation, Loos (1962) in his studies noted no significant changes in the density of wood. Seifert (1964) stated the possibility of negligible loss of CO2 from wood due to radiation induced chemical reactions. However, wood irradiated in the presence of air might absorb atmospheric nitrogen in small quantities (Seifert, 1964). Tsutomu *et al.* (1977) reported on a a very small effect of gamma radiation on specific gravity of wood and cellulose. Curling and Winandy (2008) reported that density of southern pine sapwood stayed unchanged by any tested level of irradiation dose or dose rate of gamma radiation. Hasan (2006) and Despot *et al.* (2007) measured oven dry mass of Scots pine (*Pinus sylvestris*) specimens. They determined no statistically significant changes in mass before and after irradiation at a confidence interval of 95 % although

specimens were gamma irradiated in plastic bags with the presence of air (Figure 5).

Struszczyk *et al.*, 2004; Despot *et al.*, 2006; Hasan, 2006 and Hasan *et al.*, 2006a; 2008).

the darkening of the specimens increased as can be seen from Figure 4.

**4.2 Physical properties of gamma irradiated wood** 

of specimens irradiated with 150 kGy.

**4.2.1 Decrease in mass caused by gamma irradiation** 

Fig. 2. Total amount of water-soluble carbohydrates (TSC) of leached and non-leached specimens irradiated with different gamma doses for different time intervals after gamma irradiation; n = 3 (Despot *et al.*, 2007).

After leaching, irradiated specimens still had significantly greater TSC than non-irradiated and non-leached controls. The TSC relative to the controls (TSCr) was calculated for each radiation dose as a ratio of mean TSC of gamma irradiated specimens and the mean TSC of non-irradiated and non-leached controls. TSCr of non-leached and leached specimens showed linear correlation with the radiation dose (Figure 3).

Fig. 3. Correlation between total amount of water-soluble carbohydrates relative to controls (TSCr) and gamma radiation dose (G) for non-leached and leached specimens (Despot *et al.*, 2007).

 0 0 30 90 150 30 90 150 30 90 150 30 90 150 30 90 150 Gamma radiation dosage, G [kGy]

Fig. 2. Total amount of water-soluble carbohydrates (TSC) of leached and non-leached specimens irradiated with different gamma doses for different time intervals after gamma

After leaching, irradiated specimens still had significantly greater TSC than non-irradiated and non-leached controls. The TSC relative to the controls (TSCr) was calculated for each radiation dose as a ratio of mean TSC of gamma irradiated specimens and the mean TSC of non-irradiated and non-leached controls. TSCr of non-leached and leached specimens

0 20 40 60 80 100 120 140 160

G [kGy]

Fig. 3. Correlation between total amount of water-soluble carbohydrates relative to controls

(TSCr) and gamma radiation dose (G) for non-leached and leached specimens

Leached 5 d 10 d 30 d 150 d

10 d (leached)


> **TSCr = 0.0106×G + 1.0301 R2 = 0.9962**

Non-leached Leached

0

0,0

(Despot *et al.*, 2007).

0,5

1,0

1,5

TSC relative to the control, TSCr

2,0

2,5

3,0

3,5

10

20

30

TSC [mg/g]

40

50

60

Control

Control

irradiation; n = 3 (Despot *et al.*, 2007).

showed linear correlation with the radiation dose (Figure 3).

**TSCr = 0.0136×G + 1.0281 R2 = 0.9991**

All these studies lead to the conclusion that due to breaking the chains of cellulose in wood cell wall, there must be some changes in physical and mechanical properties of gammairradiated wood. These changes should mostly influence the hygroscopicity (Fengel and Wegener, 1989) and tension strength of gamma-irradiated wood, because it becomes more brittle (Divos and Bejo, 2005). Furthermore, gamma irradiated wood is more susceptible to chemical and enzymatic degradation (Seifert, 1964; Klimentov and Bysotskaia, 1979; Klimentov *et al.*, 1981; Ardica *et al.*, 1984; Šimkovic *et al.*, 1991; Magaudda *et al.*, 2001; Struszczyk *et al.*, 2004; Despot *et al.*, 2006; Hasan, 2006 and Hasan *et al.*, 2006a; 2008).
