**3. Other applications of gamma radiation to wood**

One of the interesting areas of application of gamma rays and X-rays is in non-destructive analysis of density and water content and their distribution in solid wood, and the woodbased materials, i.e. wood panels (Davis *et al.* 1993, Lu and Lam, 1999). Karsulovič *et al.* (2002) used gamma irradiation in their studies for non-destructive detection of decay and other defects in logs. In this way, the quality of the timber can be to some extent predicted prior to mechanical processing. Because of extremely high energy of gamma radiation, it penetrates through the entire cross section of wood. Consequently, gamma rays can be used as a catalyst for polymerization of monomers in monomer-impregnated wood as well as for chemical modification of wood to create wood-plastic composites – WPC (Chawla, 1985; Sheikh and Afshar Taromi, 1993; Bakraji *et al.* 2001; Bakraji *et al.*, 2002). Struszczyk *et al.* (2004) mentioned three possible uses of gamma radiation:


According to Kunstadt (1998), insects do not withstand doses between 0.7 and 1.3 kGy, while elimination of fungi requires significantly higher doses. Unger *et al.* (2001) mentioned doses between 0.25 and 3 kGy to be adequate for extermination of wood-destroying insects, depending on species and developmental stage. Extermination of wood decay fungi in wood usually requires higher doses, ranging from 2 to 18 kGy depending on the fungus species. Mycelium of the fungus *Serpula lacrymans* can be killed off with 2 – 3 kGy, but it can be reduced to 0.5 kGy if the temperature rises to 50 °C. Unger *et al.* (2001) also stated that the bacteria elimination requires doses of 3 – 15 kGy. Lester *et al.* (2000) sterilised New Zealand soft woods including radiata pine (*Pinus radiata*) against Huhu beetle larvae (*Prionoplus reticularis*) and concluded that doses between 2.5 and 3.7 kGy are enough to control wood destroying insects and that moisture content of wood during irradiation has an important role in radiation dose determination. Magaudda *et al.* (2001) stated that the dose of 10 kGy is sufficient for practical disinfestations of Whatman paper-destroying insects. Freitag and Morrell (1998) reported on gamma radiation doses around 15 kGy to be adequate to combat pests in wood (predominantly insects). They have also stated that the doses for extermination of *Xylophagous* microorganisms in wood are much higher than for sterilisation of other materials. Csupor *et al.* (2000) irradiated wood decayed by *Xylophagous* fungi in the range from 2 to 1400 kGy, and they concluded that 12 kGy is sufficient for safe sterilisation of wood against fungi. The European Standard EN 113 (CEN, 1996) requires doses between

The treatment time depends on the power of the irradiation source, and there is no significant difference if the wood was irradiated with a weaker source for a longer time or with a stronger source for a shorter time (Unger *et al.*, 2001; Hasan, 2006 mentioned Ražem, 2005). The important quantity is the absorbed dose (the amount of absorbed energy per mass unit) which irradiated substance receives (Fairand and Ražem, 2010). On the contrary Curling and Winandy (2008) reported that dose rate and total dose of gamma radiation differently affect both, bending strength and some chemical components in tested wood.

One of the interesting areas of application of gamma rays and X-rays is in non-destructive analysis of density and water content and their distribution in solid wood, and the woodbased materials, i.e. wood panels (Davis *et al.* 1993, Lu and Lam, 1999). Karsulovič *et al.* (2002) used gamma irradiation in their studies for non-destructive detection of decay and other defects in logs. In this way, the quality of the timber can be to some extent predicted prior to mechanical processing. Because of extremely high energy of gamma radiation, it penetrates through the entire cross section of wood. Consequently, gamma rays can be used as a catalyst for polymerization of monomers in monomer-impregnated wood as well as for chemical modification of wood to create wood-plastic composites – WPC (Chawla, 1985; Sheikh and Afshar Taromi, 1993; Bakraji *et al.* 2001; Bakraji *et al.*, 2002). Struszczyk *et al.*

b. as the initiator of the catalytic polymerization of monomers in the cellulose chain and c. as pre-treatment for further chemical processing of cellulose in order to improve its

**2.1 Doses of gamma radiation necessary for wood sterilisation** 

25 and 50 kGy for wood sterilisation in lab testing procedures.

**3. Other applications of gamma radiation to wood** 

(2004) mentioned three possible uses of gamma radiation:

solubility.

a. as pre-treatment in the chemical modification of cellulose;

Klimentov and Bysotskaia (1979); Chawla (1985) and Šimkovic *et al.* (1991) reported that gamma irradiation as a pre-treatment for the "softening" of wood prior to chemical processing, can significantly reduce the use of chemicals. Oldham *et al.* (1990) used gamma radiographic technique for analysing wood destruction by fire. They determined the efficiency of fire retardants by measuring the difference in absorbed gamma radiation energy in wood protected by these retardants before and after burning the wood. Bogner (1993) and Bogner *et al.* (1997) used different surface activators in order to achieve greater adhesion of adhesives to wood. Among other used activators, gamma radiation at different doses was also used. The results show that after treatment of wood by gamma radiation in doses range of 0 and 100 kGy, glue improves adhesion to wood and thus increases the strength of glued bonds. The first investigations of the influence of gamma radiation on lignocellulose materials, in terms of increasing the solubility of insoluble high-polymerized sugars such as cellulose, were performed by Klimentov and Bysotskaia (1979) and Klimentov *et al.* (1981).
