Abstract

The present work deals with the photodegradation of cottonfabric in Egypt produced by monthly and continuous one year exposure toenvironmental conditions at industrial areas e.g. Helwan city and urban arease.g. Alexandria city. Thus cotton fabric was exposed to environmentalconditions at Helwan and Alexandria cities in May 2002 at first and till theend of April 2003. The produced deterioration was assessed by differentmethods. Thus, physical and mechanical changes in tensile strength, elongationas well as whiteness, yellowness and brightness were studied and evaluated. Thevariation of acidity of cotton fabric was also illustrated.

Introduction:

The deterioration of textiles is largely chemical in nature.Both natural and atiificial light sources can cause photochemical degradation.The effect is cumulative and irreversible. The level of illumination and theduration of exposure determine the rate of deterioration. Limiting both factorswill reduce damage. The exposure of high polymers to the action of sunlight isknown to result in progressive break down of molecular chain at the exposedsurface ^{(I, 2)}.

Two kinds of reactions, photolysis and photosensitization,may be involved when cellulose is degraded by light, and a third reaction isheat, which involves light but is not photochemical, since no light is absorbed⁽¹⁾.

Photolysis is a true photochemical reaction. When sufficientlight of proper wavelength is absorbed by cellulose itself to cause disruptionof a chemical bond, the reaction is referred to as photolysis. Pure cellulosedoes not absorb light which exceeds that of extremely low wavelength far belowthe limiting 2700 of solar ultraviolet reaching the earth. Therefore, directdegradation of cellulose by light on earth takes place only in the laboratoryunder carefully controlled conditions of light source ^{(2, 3)}.Furthermore,in photosensitization which is a secondary photochemical reaction, cottonfabric itself does not absorb near the ultraviolet or visible light. Theprimary action (which is photochemical) is between the light and foreign matterpresent in the cellulose. An added substance either as an impurity or addedtreatment, can absorb light or shift the effective light range limits. Thissecond substance, the sensitizer, carries the absorbed energy to the reactingmolecules of the fibers. Sensitizer absorbs the light and causes a reactionchanging water or oxygen present to either hydrogen peroxide or ozone. Hence,in turn react with the cellulose in a straight chemical reaction to degrade it.Milligan⁽⁴⁾, suggested that possibly the cotton substrate acts as anactivator and oxygen is converted to ozone ( photosensitization of the oxygen )which then degrades the cellulose, or the ultraviolet radiation activateswithout degrading the cellulose which is thereafter susceptible to be attackedby gaseous oxygen. The effects of photosensitization will vary tremendously,depending on the amount of moisture and oxygen present ^{(5, 6)}

Light and oxygen convert the cellulose to oxycellulose whichis then degraded further to strongly colored low molecular weight compounds⁽⁷⁾.

Heat has a destructive effect on cellulose, and degrades itby increasing the rate of chemical reaction ⁽⁸⁾.

Higher templtratures accelerate the rate of chemicalreactions, speeding up the degradation of fibers, dyes; and contaminants ⁽⁹⁾.

Many studies have recommended that the effect of temperatureand relative humidity on the photodegradation of fibers is best studiedtogether, because a change in temperature almost invariably cusses a change inmoisture content ^(10-15). At dawn the temperature is lowest, therelative humidity of the air is greatest, and therefore the moisture content isin the maximum, during the day the temperature rises, the humidity of the airconsequently falls, and the moisture content of the pattern also falls reachinga minimum value. It is clear that these two factors work in opposition for whenthe temperature is highest; the moisture content is the lowest, and vice versa.^(16.17)

Conclusion

Egyptian cotton fabric were exposed at Alexandria and Helwan city in May 2002 at first and till the end of April 2003 at monthly, 4,8 and 12 months continuous exposure to environmental conditions at these cities. The produced deterioration was assessed by different methods. Thus physical and mechanical changes were studied and evaluated. The environment at Helwan is highly contaminated with a large amount of cement dust and other pollutants and that their effects are very pronounced during summer time and especially in August. Besides, acid mists were also detected there and they were more than in Alexandria city. The whiteness and brightness indices for the exposed fabric decreased continuously with exposure during the whole year. While the yellowness index increased. It is observed that the degradation of the samples exposed in Helwan is higher than that of the samples exposed in Alexandria. This degradation occur due to the high pollution in Helwan city.

There is much degradation in tensile strength and elongation of the samples that were exposed for successive eight months more than that for the samples, which were exposed for four months only. It was found that there is less rate of degradation in samples exposed for more than eight months. The samples exposed in Alexandria had better tensile strength and elongation than that of Helwan in spite of the increase in ultraviolet and total sun hours .This emphasize the effect of pollution in Helwan in degradation of samples.

References:

1)    Ranby B. and Rabek J. F, Photo degradation, Photo-oxidation and Photo stabilization of Polymers, Wiley- Interscience, London, Chap II (1985)

2)    Tera, F.M.. Shady, K. E., Hegazy, H. Kolorisztikai Ertesito, (4) p80-83 (1987)

3)    Carr C.M. and Leaver I. H., Jou. Of Appli. Poly. Scien., Vol. 33, 2087-2095 (1987)

4)    Miligan B., Holt L.A. Polym, Degrad. Stabil., 5, 339 (1983)

5)    Asahigoaka, and Kashiwara, Dyes and Pigments, 9, 66, p103-108 (2004)

6)    Robert M. Reinhardt and James A., Textile Res. Inst. (3) p 139-146 (1980)

7)    Lock M. V, Chem., Eng. News 35 (25) p 26 (1987)

8)    Sash, C. D. and Srinicasan, R., J. Textile Inst., 69 151 (1978)

9)    Reinhardt R. M and Arthur, J Appl. Polm. Sci 24, 147-151 (1979)

10)  Tera, F.M. El Din, Shady Kamal and Alfy, E.A. Kolorisztikai, 5, 162 (1981)

11)  Egerton, G.S. and Shah, K.M Textile Res. J. 38, 130 (1968)

12)  Hearle, JWS and Wong, B.S., J. Textile Inst 63, 127 (1977)

13)  Arthur C. Stern, Air Pollution, Second edition, Vol I, Air Pollution and its effects, Academic Press, New York, London( 1968)

14)  Annual Book of ASTM Standards, Atmospheric analysis: occupational health and safety, Vol 11.03, PA, USA: ASTM (1988)

15)  Lorsen, R.I. and Zimmer, OE J Air Pollution control Assoc., 15, 565 (1968)

16)  Allen N.S. and Chirnis A., Polym. Degrad. Stabil., 13, 31 ( 1985)

17)  ASTM Book of Standards, D 1455-64 T, 325-332 (1964)

About the Authors:

The authors are associated with Textile Department, Faculty of Education in Helwan University and Textile Research Division, National Research Center, Cairo, respectively.

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Aim of the Work

The present work was carried out to clarify the effect of various climatic conditions in urban areas e.g. Alexandria city and industrial areas e.g. Helwan city on some physical and mechanical properties (tensile strength, elongation, whiteness, yellowness and brightness as well as the variation of acidity of cotton fabric.) of Egyptian cotton fabric Giza 70.

Materials and Methods:

Materials:

Cotton fabric was made of extra long staple Egyptian cotton with the following specifications of the fabric:

• Warp and weft: (raw cotton ofGiza70)
• Fabric is plain weave 1/1.
• Weight of square meter: 103 gm.
• Number of threads per cm of: warp: 28, weft: 24
• Twist Factor: warp 4 , weft 3.5.

Methodology:

The samples under study were subjected to various weathering effects at urban and industrial sites in Egypt. The exposure started on May (2002) till April (2003). The exposed fabric samples were stretching on wooden frames (70x70) cm and racks at 45 degrees to the horizon facing south.

Thus, outdoor unprotected exposure for two sets of all the examined samples was performed at Alexandria and Helwan cities in Egypt. The first set, the samples were exposed at the start of the month and removed and examined at the end of the month with a total exposure of 30 days. The second set, was exposed at the start of the year and subsets were removed and examined after 4, 8 and 12 months successively. The previously exposed samples were removed simultaneously at Alexandria and Helwan from the exposure sites and conditioned in a room maintained at a temperature of (21-oC I) and 65% relative humidity for 24 hours before testing.

The examined samples were stripped to smaller samples of 25x5 cm. and a mean of 6 readings of tensile strength, elongation, pH value, brightness, yellowness and whiteness for each sample was recorded. The recorded values were compared to the values recorded from other samples of cotton fabric of the same kind of cotton, which were kept at room temperature of 21-oC I and 65% relative humidity, and they were not exposed to the previous environmental conditions.

Tensile Strength and Elongation:

Tensile strength and elongation for the exposed and unexposed strips were tested by using Shimadzu universal testing machine, type S-500, according to the standard method of testing .Tensile strength (TS in weft direction) was determined by the strip method according to ASTM procedure D 2256-66T ⁽¹⁸⁾.

Whiteness, Yellowness and Brightness Testing:

These tests were measured using spectrophotometer type LC.S. TEXICON Limited, England.

pH values:

The pH values of an aqueous extract of both exposed and unexposed samples were measured according to the standard method for pH testing. Thus a constant weight of each fabric was finely divided using an electric divider to which a constant volume of distilled water was added, stirred very well and allowed to stand for 24 hours, then filtered. The pH values were determined using a pH meter produced by (Italy). Mean value of six readings for each sample was evaluated.

Results and Discussion

Climatic conditions:

The data of the climatic conditions were recorded continuously at the nearest meteorological station to the exposure site by the aid of the" Egyptian Meteorological Association". The mean values of twenty-four hours readings of temperature of the surroundings, relative humidity, incident solar energy and total sun hours were recorded as shown in table (I):

Table (1) : Monthly data of climatic conditions in

Alexandria and Helwan cities (Year:2002/2003)

Alex. : Alexandria Helw. : Helwan Temp: temperature

UV : Ultraviolet radiation J/Sq m: Joule/square meter

Monthly total incident sun hours and ultraviolet radiation:

The monthly values of the total incident sun hours falling on the earth surface which were recorded at the nearest meteorological station to Helwan and Alexandria cities, are shown in table (I). The data showed considerable variations as follows:

A maximum was observed in July and a minimum in December (Alexandria) while a maximum was observed, in August and a minimum in January (Helwan). The monthly data of climatic conditions in Alexandria and Helwan cities, are shown in table (1) where a cyclic seasonal variation of the UV Radiation J/Sq m was observed, in which a maximum value was shown in July and a minimum in December at Alexandria city while a maximum was observed in July and a minimum in January at Helwan city.

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.

Table (2) : Monthly data of Mechanical Properties of fabrics cotton at Alexandria and Helwan cities (Year2002/2003) :

T.S. : Tensile Strength El. : ElongationFabr. : Fabric G. 70 : Giza 70

Alex. : Alexandria Helw. : Helwan

Fig. (1): Effect of Exposure time in months on tensile strength (Kg )of cotton Fabric Giza70 at Alexandria and Helwan cities (Year2002/2003)

.

Fig. (2): Effect of Exposure time in months on loss of tensile strength % of cotton Fabric Giza70 at Alexandria and Helwan cities (Year2002/2003)

Fig. (3): Effect of Exposure time in months on Elongation % of cotton Fabric Giza70 at Alexandria and Helwan cities (Year2002/2003)

Fig. (4): Effect of Exposure time in months on loss of Elongation % of cotton Fabric Giza70 at Alexandria and Helwan cities (Year2002/2003)

2. Effects of the exposure time in months and on changes in pH values of cotton fabric at Helwan and Alexandria Cities:

Table (3) and figs (5, 6) showed that the pH- values of the examined samples had decreased gradually for each exposure month and that a maximum was obtained in June and July and a minimum in January and February at Alexandria city. While a maximum in August and July and a minimum in December and January at Helwan city.

For the 4 monthly removed samples, the increase in the acidity of cotton fabric after exposure follows the order:

4 months < 8 months <I2 months.

It was found that there is less rate of degradation in samples exposed for more than eight months.

In addition, it is observed that the degradation of the samples exposed in Helwan is higher than the samples exposed in Alexandria. This emphasizes the effect of pollution in Helwan in degradation of samples. In other words, the atmosphere at Helwan site is highly polluted and affects considerably man's life.

These results call to the fact that. the exposed samples were seriously attacked after the monthly exposure during the summer time and that they were left considerably weak where they lost about 50% of their initial strength. Hence, when dealing with results of continuous exposure, they must be carefully examined, analyzed and evaluated.

Table (3): Monthly data of Chemical Degradation (pH values evaluation) of fabric cotton at Alexandria and Helwan Cities (Year2002/2003):

Fabr.: Fabric. G. 70 : Giza 70. Alex. : Alexandria. Helw. : Helwan

Fig.(5): Effect of exposure time in months on degradation (pH values evaluation) of fabrics cotton at Alexandria and Helwan Cities (Year2002/2003)

Fig.(6): Effect of exposure time in months on changes of pH values % of fabrics cotton at Alexandria and Helwan Cities (Year2002/2003)

3. Whiteness, Yellowness indices and Brightness:

Table (4) and figs (7-9) shows the spectrophotometer measurements of the indices of brightness, yellowness and whiteness of the examined samples, which were exposed at the urban, and industrial and weather at Alexandria as well as Helwan cities. It is observed that at the start of the exposure of the samples in Helwan and Alexandria the whiteness and brightness decrease with increasing the duration of exposure. While Yellowness index increases with increasing duration of exposure. Also, the degradation of the samples exposed in Helwan is higher than the samples exposed in Alexandria.

This may by attributed to the fact that a lot of cement particles from the surroundings atmosphere and which were emitted from the cement factories - were settled on the fabric surface giving it less white appearance on one hand, On the other hand an oxidation of the cotton fabric had occurred by action of the sunlight and the humidity of the atmosphere.

Table (4)) : Monthly data of Spectrophotometer Properties of fabrics cotton at Alexandria and Helwan Cities(Year2002/2003) :

Fabr. : Fabric G. 70 : Giza 70

Alex. : Alexandria Helw. : Helwan

Fig.(7):Effect of exposure time in months on brightness of Fabric cotton Giza70 at Alexandria and Helwan Cities(Year2002/2003)

Fig.(8):Effect of exposure time in months on Yellowness of Fabric cotton Giza70 at Alexandria and Helwan Cities(Year2002/2003)

Fig.(9):Effect of exposure time in months on Whiteness of Fabric cotton Giza70 at Alexandria and Helwan Cities(Year2002/2003)