Quarantine plays a critical role to ensure that Australia remains free from serious pests, weeds and diseases present in other parts of the world. Australia places great importance on quarantine and has among the strongest quarantine measures of any country in the world. Cotton is treated to ensure that consignments are free from live insects, soil and other debris. Depending on the samples the quarantine treatments used can be chemical (fumigation) by either methyl bromide or ethylene oxide or by gamma irradiation at either 50kGray or 25kGray (kGy).

Experience from within the industry suggests that these treatments affect the quality of the cotton, although there is little direct scientific information available on the magnitude of the damage to the cotton. Thus, in order to determine the affect of the various quarantine treatments on the physical properties of cotton lint standard Upland cotton, Long Staple Upland cotton and Extra Long Staple cotton was treated with the various quarantine treatments.

The fumigation treatments by either ethylene oxide or methyl bromide had little or no significant effect on the physical properties of the cotton fibre. However gamma irradiation did have an effect on the physical properties of the fibre.The fumigation treatments by either ethylene oxide or methyl bromide had little or no significant effect on the physical properties of the cotton fibre. However gamma irradiation did have an effect on the physical properties of the fibre.

The results clearly indicate that the physical fibre properties of the cotton such as; strength, elongation, length uniformity, short fibre and to a lesser extent colour is affected by gamma irradiation. The study has shown that gamma irradiation affects normal Upland, Long Staple Upland as well as Extra Long Staple cotton. In the case of the Upland and Long Staple Upland cotton the strength of the fibre reduced by between 3cN/tex and 9 cN/tex, depending on the dosage. This decrease in fibre strength corresponded with a gradual decrease in fibre elongation by 1.0 to 2.0%. The Extra Long Staple cotton was dramatically affected by gamma irradiation. The strength reduced by between 5 cN/tex and 18 cN/tex. This decrease in fibre strength also corresponded with a 2% decrease in fibre elongation.

Analysis by various microscopy methodsrevealed no noticeable surface damage. However chemical analysis revealed that the molecular weight of the cotton decreases at even the lower dosages and continues to decrease as dosages with gamma irradiation increased. These results suggest that a low irradiation dose provokes the breakage of cellulose chains at the most sensitive points, which probably represents domains of lower crystallinity in the structures. Higher doses then further decrease the size of cellulose chains from the more crystalline domains of the fibers. The decrease in molecular size is most likely responsible for the observed alteration of the mechanical properties of the cotton fibers upon irradiation.

The message from this preliminary investigation is quite clear, if any cotton material needs to be imported into Australia; one must insist on chemical (fumigation) by either ethylene oxide or methyl bromide as gamma irradiation, even at low dosages, severely damages the physical properties of cotton.