Means of maximum temperatures and relative humidity of the surroundings:

A maximum mean temperature was observed in August and a minimum in January at Alexandria city while a maximum was observed in July and August and a minimum in January at Helwan city.

A maximum mean of relative humidity was observed in August and a minimum in February at Alexandria city while a maximum was observed in September and a minimum in December and April at Helwan city.

Mechanical and physical properties:

Effects of the exposure time in months on the tensile strength and elongation of fabric cotton at Alexandria and Helwan Cities (Year2002/2003)

The change in the mechanical properties as a result of exposure to the environmental conditions at Helwan and Alexandria cities was shown in table (2) and figs. (1,2). It is shown that, the level of degradation of all the examined fabrics varied cyclically with the season of the year. The monthly exposed samples showed maximum deterioration of tensile strength in June and a minimum in January at Alexandria city while at Helwan city the maximum was in August and the minimum were in February. For the four monthly removed samples, the deterioration of tensile strength was increasing progressively at a rapid rate with increasing exposure to environmental conditions to be 58.1 % and 78.4% after 4 and 8 months respectively but at a slower rate after that to be 81 % after 12 months of exposure at Alexandria city. The same thing is applied at Helwan city, where deteriorations of tensile strength of 62.2% and 80.5% are seen after 4 and 8 months of exposure respectively while a deterioration of 81.1 % after 12 months of exposure. As regards the loss of elongation %, for the monthly exposed samples, the maximum deterioration was seen in August and the minimum was in January and February at Alexandria city, while at Helwan city the maximum deterioration was in August and the minimum was in January. For the 4 monthly exposed samples, there was rapid rate of deterioration after 4 and 8 months 50.7%, 56% and 76.7%, 78.7% for Alexandria and Helwan respectively versus 80.7%, 83.3% for Alexandria and Helwan after 12 months respectively. The sun light is known to result in progressive molecular chain scission at the exposed surface, and hence serious reduction of mechanical properties may occur. Since the energies of photons in the near UV radiation of the incident solar energy falling on the earth's surface correspond to, or exceed the covalent bond energies of some chemical structures, hence some bond rupture is likely to result from their absorption. It may be also suggested that the cyclic degradation of the fabrics exposed to weathering conditions at Alexandria and Helwan cities is associated with the intensity of the UV radiation and the pollution occurring at these cities. This was attributed to the nature of the fabric, structure, thickness and strength of the bonds linking their molecules.

In spite of the fact that the UV radiation (J/Sq/m) falling on the earth's surface at Alexandria city was more than that falling at Helwan city through the whole year, the rate of degradation of exposed samples at Helwan city was more than that at Alexandria city. This may explain the role of pollution at Helwan city in increasing the rate of deterioration of physical and mechanical properties of the Egyptian cotton fabric.