Development of antimicrobial textile finishes from plant species

A new approach to make textiles antimicrobial is incorporating the active principle of plant extracts with fabric. In this paper Dr G Thilagavathi, K Rajendrakumar & R Rajendran discuss the possibilities of using extracts of neem, prickly chaff flower and pomegranate on fabrics

The population explosion and the environmental pollution in the recent years forced the researchers to find new health and hygiene related products for the well being of mankind. The nuisance caused by microbes is numerous and the problem is still aggravated in tropical and subtropical regions. Pathogenic microorganisms transfer infectious diseases, develop lung related disorders. Mold and fungi cause staining, discolouration and degradation of textile substrates.

Now, there is a good deal of demand for the fabrics having functional/speciality finishes in general but antimicrobial finishes in particular to protect human being against microbes. The application of antimicrobial textile finishes include a wide range of textile products for medical, technical, industrial, home furnishing and apparel sectors. Though a number of commercial antimicrobial agents have been introduced in the market, their compliance to the regulations imposed by International Bodies like EPU is still unclear. Recent developments on Chitosan (a naturally occurring biopolymer) have opened up new avenues in this area of research.

The present investigation aims at developing an eco friendly natural antimicrobial finish from plant extracts for textile application. Some selective species of plants were identified and screened for their activity and the extracts were applied to cotton fabrics. An extensive study was conducted to assess the antimicrobial effectiveness of the herbs by employing standard test methods and the findings are discussed in this paper.

Antimicrobial herbs

Neem (Azadirachta indica), pomegranate rind (Punica granatum) and prickly chaff flower (Acyranthes aspera) are the plant species chosen for the study. Fresh leaves of neem and prickly chaff flower were shadow dried and made into a fine powder. In the similar way, the fine powder of pomegranate rind was obtained. Extracts of respective herbal powder were obtained by treating with methanol at room temperature resulting in active substance being dissolved in methanol.

Finish application

Methanolic extracts of herbs were applied to cotton fabric by dipping in bath at M: L ratio 1:10. The fabric was then dried at 80°C for fifteen minutes to remove the moisture. Finally, the fabric samples were tested for antimicrobial activity as per the standard test methods.

Antimicrobial activity assessment

Antimicrobial activity was evaluated by both qualitative and quantitative test methods. The following are the descriptions of test methods eployed for this study.

Antibacterial activity assessment of textile materials-parallel streak method (AATCC Test Method 147-1988)

Specimens of test material, including corresponding untreated controls of the same material placed in intimate contact with AATCC Bacteriostasis agar, which has been previously streaked with an innoculam of test organisms. Two test organisms namely; Staphylococcus aureus and Esherichia coli were used for the study. After incubation, a streak of interrupted growth underneath and along the side of the test material indicates antibacterial effectiveness of the fabric. AATCC Bacteriostasis agar medium was used as a growth medium for evaluation.

Antibacterial activity assessment of textile materials-agar diffusion method

Treated and untreated control fabric samples placed in intimate contact with AATCC bacteriostasis agar, which has been previously inoculated (Mat culture) with an innoculam of test organisms. After incubation, a clear area of uninterrupted growth underneath and along the side of the test material indicates antibacterial effectiveness of the fabric.

Hohenstein modified test method - Challenge test

Specimens of the test material were shaken in a known concentration of bacterial suspension and the reduction in bacterial activity in standard time is measured. The efficiency of the antimicrobial treatment is determined by comparing the reduction in bacterial concentration of the treated sample with that of control sample expressed as a percentage reduction in standard time.

Digging in soil test

The finished and unfinished fabric samples were buried inside the microbial active soil at 1-3 cm. depth. After two weeks of incubation at room temperature the samples were removed and washed thoroughly of soil particles and examined for degradation.

Results and discussion

Antimicrobial activity of neem and pomegranate (Agar Diffusion Test)

The result of Agar Diffusion Test for antimicrobial effectiveness against standard test cultures viz., E-Coli (gram negative) and Staphylococcus aureus (gram positive) organisms shows that the activity of neem treated samples is stronger for S.aureus than E-coli. It is attributed that bacterial inhibition is due to the slow release of active substances from the fabric surface.

While comparing the activity of neem and pomegranate treated fabric samples (No.2) against both the test organisms from the zone of inhibition, it is indicated that the antimicrobial activity of neem treated sample is stronger than pomegranate treated sample for both test cultures. Neem samples exhibited a zone of 5.8 mm for S.aureus and 3.3 mm inhibition for E-coli. Pomegranate finished samples showed 3.6 mm and 2.2 mm zone of inhibition for S.aureus and E-coli respectively. It is evident that the antimicrobial activity of both samples is greater for S.aureus than E-coli.

Antibacterial activity - parallel streak method

While testing the antimicrobial activity of Neem, Pomegranate, Achyranthus aspera as tested by Parallel Streak method for S.aureus, a complete plate clearance was observed for neem treated fabric samples. The zone of inhibition is 4.4 mm for pomegranate and 3.0 mm for Achyranthus treated fabric samples.

In the case of the antimicrobial activity of Neem, Pomegranate and Achyranthus aspera as tested by Parallel Streak method for E-coli, the same trend is observed for neem treated fabric samples yielding a complete plate clearance whereas the activity is moderate for pomegranate (zone of inhibition of 2.9 mm) and mild in the case of Achyranthus aspera.

In the test against E-coli in AATCC bacteriostasis broth, the uninoculated control, inoculated control and inoculated finished samples were evaluated for percentage bacterial reduction by cell counting using templates. It was observed that neem has 100% bacterial reduction followed by pomegranate with 90% reduction and Achyranthus with 82% reduction. Tulsi (Ocimum sanctum), which showed no activity in the preliminary tests, exhibited a bacterial reduction of 73% in the challenge test.

Results of Digging in Soil test

Structural damages on the untreated fabric surface were noticed at different spots. All the finished fabric samples viz., Neem, Pomegranate and Achyranthus treated showed resistance to microbial attack.

Wash durability of finishes

The antimicrobial activity of the finished samples was evaluated for fastness to washing after different wash cycles. The finished samples were washed using a standard detergent (1% owf) and sodium carbonate (1%owf) at 40øC. The antimicrobial activity was assessed after 2, 4 and 6 washes by challenge test. It is observed that the activity diminished gradually as the number of wash frequencies increase. The entire test specimen retained 50% activity after 6 washes. From this it is clear that only hydrogen bonds and weak Vander Val's forces exist between the cellulose and active principle of extract and thus resulting in poor wash durability.

Conclusions

From the studies conducted, neem, Pomegranate, and prickly chaff flower are found to contain active antimicrobial substances that can control the growth of microbes. Neem exhibited maximum antimicrobial activity in all tests. However, further work on bonding the active substances on textile substrates would help resolve the issues like poor wash fastness and diminishing activity of the finishes. Since the active principles are of natural origin and thus can be suitable alternative for the harmful chemicals.

(Dr Thilagavathi & Mr Rajendrakumar are with the Department of Textile Technology, PSG College of Technology,Coimbatore while Mr Rajendran is with Department of Microbiology, PSG College of Arts and Science, Coimbatore).