Antimicrobial functionalization of technical textiles for medical, aerospace and civil applications

Textiles, today, are no more just traditional textiles. With the advancements in nano and fiber technology, they find various technical applications and are known as technical textiles. Antimicrobial functionalization is an integral requirement for some of these applications that include medical textiles, aerospace textiles and textiles used in filtration. Various organic and inorganic antimicrobial agents are being explored for antimicrobial functionalization of textiles with the objective to obtain effective, durable and broad spectrum antimicrobial properties. However, these antimicrobial agents may have their own advantages and disadvantages. Some of them may lack broad spectrum antimicrobial properties as well as complex method of their synthesis and application which may not always be environmental friendly. Silver is well known inorganic antimicrobial agent with effective antimicrobial action against broad spectrum of microbes. Silver is being intensively studied in nano particle form for the functionalization of textiles. However, mostly the synthesis and application of silver nano particles to textiles is carried through wet routes. These may have environmental considerations due to possible use of toxic reducing and stabilizing agents. In addition their solution or colloidal based application to textiles is intense in water and energy consumption along with production of waste water and necessitating its treatment. This may not help reduce environmental burden of textile industry which is regarded as one of the most polluting industrial sector of the world. Therefore, along with providing antimicrobial protection, the process of obtaining antimicrobial textiles itself should not create adverse environmental impact. In this context, ecofriendly processes for textile industry have always been in focus of research. The objective of this thesis was to achieve “antimicrobial functionalization of technical textiles for medical, aerospace and civil applications” via a simple and single step environment friendly technique known as radio frequency “co-sputtering”. Sputtering is a plasma based process and is mostly used in automotive, tools and electronics industry. It is not yet fully explored in textile industry. This study aimed at obtaining antimicrobial textiles via co-sputtering and exploring some of the its key strengths and weaknesses for textiles. In the adopted co-sputtering technique, an antimicrobial silver nano clusters/silica composite coating was deposited on four different textile substrates. The deposition parameters of both silica and silver were controlled independently such that silica constituted the matrix of the composite coating and silver was deposited in the form of nano clusters embedded in the silica matrix. The four textile substrates used in this study were: cotton fabric intended for medical applications, high performance Kevlar® and Vectran® fabrics for aerospace applications and activated carbon fabric (ACF) to be used in air filtration. The morphology and composition of the deposited coating was investigated in detail using FESEM, EDX and XPS which showed that silver nano clusters (25-50 nm) were uniformly distributed and firmly embedded in the silica matrix. Total silver concentration in the composite coating was evaluated through ICP_MS and was found to be dependent on deposition time and thus on coating thickness. Silver ion release test in water and in artificial sweat showed a progressive and gradual release of silver ions, beneficial for prolonged antimicrobial activity. The nature of the fabric substrate was also found to influence the release of silver ions. The coating showed effective antimicrobial properties against Gram positive (S. aureus, S. epidermidis), Gram negative (E. coli) bacteria and fungus (C. albicans) with varying intensity of the action depending upon the microbe as well as silver ion release profiles. Water contact angle and sorption tests revealed hydrophilic nature of the coating. Moisture management properties evaluated by Moisture Management Tester showed that coating imparted fast absorbing and quick drying characteristic to the fabric. The coating was highly conformal and did not altered air permeability of the substrates which is a highly desirable characteristic to preserve thermo physiological comfort of the fabric as well as maintain filtration capacity of ACF. However, the washing stability of the coating was found not to be completely satisfactory. The work was carried with in the frame wok of an Italian regional project with several other project partners. Some results from these partners, duly acknowledged, are also discussed in this thesis and summarized in conclusion.