Hygiene Fibres - Antimicrobial Polyester

1) – Introduction. Since the last part of the century an increasing improvement in qualitative standards of human lifestyles has brought to a greater sense of comfort, and cleanliness. People are more and more looking for fresh public living surroundings and a higher level of hygiene in home areas. A wide class of micro-organisms coexists in a natural equilibrium with human body and living environments, but a rapid and uncontrolled multiplication of even non pathogenic microbes can seriously compromise the hygienic and healthy personal standards. Because of their capillary spread in the human living spaces, the textiles have been involved in this research of a growing quality of hygienic living conditions. Actually, several combinations of temperature, humidity and other climate factors added to the presence of dust, soil and fat-stains on the textile surfaces can transform the textiles themselves in an optimal enrichment culture for a rapid multiplication of micro-organisms. In such a case two contemporary effects occur: the first is an uncontrolled proliferation from textile surfaces into the surrounding environment with a consequent increase of bio-burden level and potential health risks or, at least, of discomfort for the unpleasant odours produced by high concentrations of micro-organisms; the second one is the onset of degradation phenomena as colouring and discoloration of the textile fibres. Many efforts have been performed by textile industry with the aim to score two goals: the protection of the living environments and of the textile fibres from an uncontrolled proliferation of microorganisms like bacteria. 2) – Micro-organisms action on textile surfaces. In the broad spectrum of existing bacteria there are pathogenic and non-pathogenic organisms. Both of them can multiply abnormally on the textile surfaces with an accumulation that compromises the hygienic cleanliness. Tab.1 shows some examples of pathogenic and non pathogenic microorganism. Tab. 1 MICRO ORGANISM PATHOGENICIT Y EFFECTS Bacillus subtilis Generally non pathogenic Food spoiling occasionally conjunctivitis Escherichia coli Low pathogenic Food spoiling occasionally urinary bladder infection Klebsiella pnuemoniae Pathogenic Pneumonia, urinary bladder infection Pseudomonas aeuroginosa Pathogenic Multi-infections Proteus vulgaris Low pathogenic Infiammations Staphylococcus epidermidis Low pathogenic Surgical wound infections Staphylococcus aureus Pathogenic Toxic shock, purulence, abscess, fibrin coagulation, endocarditis The proliferation of pathogenic micro-organisms has to be fought for 3 the physiologic impact to the human health, while non pathogenic micro-organisms have to be controlled for the visual, olfactory and tactile effects produced by their metabolism. The textile materials, on which source of nutrients are present (food contamination, oil, fat, protein, sugar, skin secretions like sweat and sebum etc.) become a medium for a rapid multiplication of microorganisms. Many bacterial colonies produce, in their metabolism, coloured pigments that protect them against light and UV radiation. In fig. 1 some colouring pigments, synthesized by different bacteria, are reported: Fig. 1 These substances cause colouring of textiles through adhesion to the surface. The pigments attached to the fibre cannot be adequately 4 removed by normal washing and, as time passes, colour stains firmly bond to the textile with no possibility of removal, even after repetitive washings. In some cases, according to the type of fibre material and attached pigment, only bleaching agents can be helpful, but it is quite difficult remove the pigment even by the oxidation and reduction reactions of the bleaching process. In their growth on a fibre, micro-organisms can produce volatile compounds of unpleasant odour as decomposition by-products of their feeding. Spilled foods and drinks, dirt, dust, organic stains, secretions from the human body like sweat and sebum are decomposed from bacteria with a production of bad smelling components like : fatty acids (acetic, propionic, butyric, valerianic, caproic), n-methylamines, ammonia, aldehydes, sulfides, mercaptans, aromatics and lactones. Other micro-organisms transform the human steroid hormones in foul ketones and steroids with the same odour of urine. 3) – Bio-active fibres. A general term that is adopted to indicate the textile fibres with activity against micro-organisms growth is “bio-active fibres”. A distinction can be made according to the possible end-uses: hospital uses, home textiles, carpets, furnishing, mattress and pillows fillings, air-liquid filters, nonwovens, protective clothing, sportswear etc. Each of these application fields will demand a different bioactivity performance from the fibre. Man-made antibacterial fibres are manufactured by two basic methods: the first is kneading antibacterial additive during the spinning stage and the second is an after-treatment method in which an antibacterial agent solution is used. In the mixed spinning technology, the antibacterial agent is supplied 5 into the polymer stream before the spinneret or blended into the spinning polymer feeding. The additive characteristics have to be compatible with spinning conditions (e.g. particle diameter, heat and chemical stability, no degradation interactions with polymer, lack of adverse effects on fibre quality). A reserve of antibacterial additive is englobed into the fibre and, after migration to the surface, it can practise its bioactivity against micro-organisms. In the post-process finishing technology, the most common techniques to apply antibacterial agents are: spraying, immersion, padding and coating. The textile surfaces are often treated in the final dyeing and finishing stages of their manufacturing process. Antibacterial agent is linked to the surface through physical bonds or anchored by a crosslinking on the fibre. The most used additives are based on organic compounds like halogenated salicylic acid, anilides, organotin compounds, quaternary ammonium compounds, organosilicon quaternary ammonium salts, and quaternary ammonium sulphonamide derivatives . Since most of them are highly water soluble and weakly anchored to the fibre surface, they have to be constantly reapplied. According to the manufacture technology and the antimicrobial agent nature, the antibacterial fibres can exhibit two kinds of bioactivity mechanism: an elution mechanism and a non-elution mechanism. In the first the additive gradually migrates out from the fibre to the solvent external medium, while in the second mechanism it does not dissolve out. Although, sometimes, the two kinds of mechanism coexist in the antimicrobial activity of a bioactive fibre, generally, one of them is the predominant. 4) – Antibacterial activity tests . 6 Antibacterial activity of bioactive fibres is not immediately evident, but it can be evaluated by opportune test methods. Since the early appearance of bioactive fibres, several standard methods have been defined and, at the moment, there is not a unique test protocol that is suitable for all the sorts of the antibacterial fibres. Each of the existing methods has its own approach and application field, so that, if two of them are adopted to characterize the same antimicrobial textile, they often show opposite results. A first overall classification is carried out on the basis of the kind of the evaluation of the micro-organism population reduction: quantitative and qualitative. In the quantitative methods the number of bacteria, still living after an opportune contact time, is counted. Besides, the quantitative evaluation can be differentiated further in other two classes according to the main test conditions. For example, a small amount of liquid culture medium is used to cover a specimen in the static method ATCC 100, while the fibre specimen is immersed in a larger amount of liquid culture when the dynamic Shake Flask Test Method is carried out. In the qualitative methods the test specimen and an untreated control are pressed into intimate contact with an agar culture medium inoculated with the test bacteria solution. If antibacterial activity is present, it will be possible observe a clear zone around the treated sample comparing to the zone of bacterial growth around and over the untreated control sample after the same contact time. These qualitative methods provide a formula to measure the inhibition zone width, but this is a qualitative evaluation and it can not be considered as a quantitative indication of the antibacterial activity. The most important antibacterial activity test methods, with their main 7 features, are listed in Tab. 2 Tab. 2 Method Name Origin Evaluation Suitability AATCC 100/1988-98 USA Quantitative Textiles treated with antibacterial finishes. Hydrophilic fibres AATCC 147/1988-93 USA Qualitative Textiles treated with fast migrating/leaching rate agents SN 195924/1983 SWITZ. Quantitative Hydrophilic fibres SN 195920/1983 SWITZ. Qualitative Textiles treated with fast migrating/leaching rate agents AFNOR XP G 39010: 99 FRANC E Quantitative Textiles treated with migrating agents SHAKE FLASK TEST JAPAN USA Quantitative Textiles with antibacterial properties inherent to the structure Hydrophilic/Hydrophobic fibres JIS L 1902-8 (1998) JAPAN Quantitative and Qualitative Textiles treated with fast migrating/leaching rate agents The results that these methods can give depend strongly on the antibacterial additive mechanism of activity and on the hydrophobic or hydrophilic nature of the bioactive fibre. In each analysis, the measurement of the activity of a reference sample of nature similar to the antibacterial fibre but without additive must be carried out. After the time contact, three cases of bioactivity can present as result 8 of testing a textile: 1) a significant increase of the initial bacteria population 2) an inhibition of the bacteria growth comparing the antimicrobial product with the control sample for which there is a multiplication of test bacteria population inoculated at the beginning of the time contact. 3) a quantitative reduction of the number of test bacteria inoculated at the beginning of the time contact. The second and the third cases indicate an antibacterial activity from the bioactive fibre and the terms used to differentiate the two performances are biostatic and biocide.