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Study of antimicrobial behavior of socks from bamboo fibers
by C. Gomathi

Microbial infestation poses danger to both living and nonliving matters. Obnoxious smell from the inner garments such as socks, spread of diseases, staining and degradation of textiles are some of the detrimental effects of bad microbes. Bamboo fiber clothes have actually been showing up in department stores and womens boutiques. Bamboo is now being made into a fiber that has wonderful characteristics. Bamboo fibers are the newest thing to hit the textile arena. An exclusive manufacturing process makes it possible to create heavily breathable, absorbent samples entirely from bamboo fiber.

Bamboo fiber has particular and natural functions of anti-bacteria, bacteriostasis and deodorization. It is validated by Japan Textile Inspection Association that, even after fifty times of washing, bamboo fiber samples still possesses excellent function of anti-bacteria, bacteriostasis. Its test result shows over 70% death rate after bacteria being incubated on bamboo fiber samples. Bamboo fibers natural anti-bacteria function differs greatly from that of chemical anti-microbial. The latter often tend to cause skin allergy when added to apparel.

This paper deals with the anti-microbial behavior of bamboo fibers with the use of socks.

This report deals with a study to assess the anti-bacterial and anti-fungal properties of socks made out of bamboo fibers compared with the socks those made from 100% cotton, 100% viscose and 50/50% bamboo/cotton (before and after wear of socks)

SOCKS CONSTRUCTION DETAILS

Yarn count	30s
Knit Structure	Flat Knit (Single Jersey)
Size	9 to 11
Cylinder	Double Cylinder
Diameter	4
Needles	168
Weight (Socks)	0.015gms

PROCEDURE (knitted into socks)

100% Bamboo yarn
100% Cotton yarn
50/50% Bamboo/Cotton yarn
100% Viscose yarn

Grey knitted socks were given pretreatment by using appropriate recipes. After bleaching microbial testing were conducted. Then microbial growth of bamboo socks was compared with the socks those made from 100% cotton, 100% viscose & 50/50% bamboo/cotton.

Methodology & Results

Test 1 - Survivability of Bacteria

To find out how the samples are able to resist the survivability of bacteria, a sample swatch survival test was carried out using two test organisms (Escherichia coli and Staphylococcus aureus). Starting from 24 hours to 120 hours of incubation at 37⁰C, the survival of known test bacterial concentration in all the four samples was assayed over time, every 24 hours. Survival test was also carried out using worn socks. The results of test indicate that the survivability of bacteria on cotton was more lasting compared to rayon and bamboo. The survivability of bacteria on 50/50% Bam/co is similar to bamboo.

The general survivability of the test organism E. coli, was less compared to S. aureus. This analysis indicated that bamboo potentially resists the colonization of both E. coli and S. aureus from the second day of incubation, which is an indication of bamboos antimicrobial resistance characteristic.

Table -1 Survival of bacteria - Escherichia coli (Before wear of socks)

* 10⁵ cfu/ml

Table -2 Survival of bacteria - Staphylococcus aureus (Before wear of socks)

* 10⁵ cfu/ml

TNTC - Too Numerous To Count

Survival of Bacteria (After Wear of Socks)

Table-3 Survival of bacteria - Escherichia coli (after wear of socks)

TNTC - Too Numerous To Count

Table-4 Survival of bacteria - Staphylococcus aureus (after wear of socks)

TNTC - Too Numerous To Count

Test 2 Survivability of Fungi

To find out how the samples are able to resist the survivability of fungi, a sample swatch survival test was carried out using two test organisms (Aspergillus niger and Trichoderma viridae. Starting from 48 hours to 260 hours of incubation at 27⁰C, the survival of the known fungi in all the 4 samples was assayed over a constant period of time, every 24 hours. Results indicate that the survivability of fungi was more or less the same on all the four test samples.

From this test, it can be concluded that the antifungal resistance of bamboo, cotton and 50/50% bam/cot are equally efficient, when compared with rayon. Generally, all the four samples supported the growth of T. Viridae and resisted the growth of A. niger.

Table - 5 Survival of fungi - Aspergillus niger (Before wear of socks)

* 10² cfu/ml

Table -6 Survival of fungi - Trichoderma viridae (Before wear of socks)

* 10² cfu/ml

Test 3 - Determination Of Rate Of Growth And Comparison Between Four Samples

The growth rate of bacteria (E. coli and S. aureus) and fungi (T. Viridae and A. niger) were compared when grown on the four test samples as substrates. The results are presented in Table.7. This test proves that the growth rate of organisms on bamboo as a substrate is less, when compared with cotton and rayon. The natural antimicrobial effect of bamboo does not allow the multiplication of bacteria and fungi and ultimately proves to be both bacteria static and fungi static. The growth rate of microorganisms on 100% cotton is same as rayon. On 50/50% bam/cot, the growth rate of organism is less when compared with cotton.

Table -7 Comparison of the growth rate of bacteria and fungi

Note
+ - Moderate Growth Rate
++ - High Growth Rate
+++ - Very High Growth Rate

Test 4 -Time Course Analysis

To study the inhibitory effect of bamboo, rayon and cotton & 50/50% bamboo/cotton samples towards microorganism

The inhibitory effect of bamboo, cotton, rayon and 50/50% bam/cot samples towards bacteria (E. coli and S. aureus) and fungi (T. viridae and A. niger) were compared based on a time course analysis and it was observed that E. coli was able to survive, only up to 24 hours on bamboo and 50/50% bamboo/cotton whereas on rayon it was able to survive for up to 120 hours. It was also observed that E.coli was able to survive for up to 72 hours on 100% cotton. It was also observed that S. aureus was able to survive on bamboo up to 48 hours and 50/50% bam/cot whereas on 100% cotton it was able to survive for up to 72 hours. It was also observed that S. aureus was able to survive on rayon up to 120 hours.

Test 5 - Other Normal Validation Tests

AATCC standard tests such as AATCC 100, AATCC 147, AATCC 30 and soil burial test, were carried out. All the above tests confirmed that the antimicrobial effect was highest in the case of bamboo followed by 50/50% bam/cot, rayon and cotton. Odour evaluation test was also carried out.

Soil Burial Test

The samples were buried in the microbial active soil at 1-3cm depth. After incubation at room temperature, the samples were removed and washed thoroughly of soil particles and examined for degradation.

Table 8 Soil burial test of different samples

Odour Inhibition Test

Tests for odour inhibition are done with a bottle incubation method using an artificial perspiration consisting of sodium chloride (2.5%), urea (1.2%) and lactic acid 85% (3.4%), potassium hydroxide (1.4%) and pH adjusted to 7.0 with ammonium hydroxide. This solution is incubated with soil suspension (1gm garden soil to 10ml water, 1 ml suspension to 100ml artificial perspiration). The sample is incubated in 500ml stoppered jar at 30^oC. The odour is judged subjectively by assessers after 1, 4, 8 and 11 days.

Table -9 Assessment of odour property

Conclusion

Based on the above in-depth analysis, it was observed that bamboo has GOOD antimicrobial properties followed by 50/50% bam/cot, cotton and rayon. The various tests carried out namely, rate of growth, survivability of bacteria and fungi, time course analysis of the inhibitory effect against microbes, normal AATCC procedures like AATCC 30, AATCC 100, AATCC 147 and Soil burial test confirm that the antimicrobial effect of bamboo samples is comparatively of an higher order than 50/50% bam/cot, cotton and rayon. Results also show that there is no appreciable level of antimicrobial activity for cotton samples and it supports the growth of micro-organisms on it. In the highlight of above in-depth study and its findings, it is evident that bamboo samples have got indigenous antimicrobial effect. This indigenous anti microbial property of bamboo makes it more suitable for clothings such as inner wears & foot wears such as socks as compared to cotton.

References:

1)    AATCC Technical manual 2006, Antifungal activity, Assessment on textile materials: Mildew & Rot Resistance of textile materials, AATCC.

2)    Journal of textile association Jan-Feb-2007.

3)    Vol.84. Feb.2004. IE Journal TX.

4)    SITRA Research Report, Studies on spinning behavior, antifungal and thermal properties of bamboo fiber s. vol. 51 June 2006.

5)    SITRA Research Report Development of bandages using bamboo fiber s. vol. 52. August 2007.

6)    Colourage, September 2005.

7)    Colourage, May 2006.

The article is prepared under the guidance of Prof. M. Manoharan, Head of Department of Textile Chemistry, S. S. M College of Engineering, Komarapalayam.

About the Author

The author is the student of Final Year M.Tech., Textile Technology (Textile Chemistry), S. S. M College of Engineering.