Smart textiles with Tuneable Architectures for Multifunctional Applications

Abstract

Innovations in electronics and the rapid developments in communication systems have been unprecedented and made life easier. One such advancement is wireless electronics, where gadgets operate in gigahertz frequencies – transmitting and receiving signals in the form of EM waves during their operation. The increased presence of EM waves in the atmosphere has led to electromagnetic (EM) pollution. With the miniaturization of devices, there is an increased volume of complex circuitry in a limited space – causing interference between them during operation, termed “electromagnetic interference” (EMI). EMI concerns are rising as they are considered severe threats to devices and their functioning. Different shielding materials were developed to combat this issue, from metals and ferrites to polymer-based nanocomposites. As the filler loading in a polymer-based nanocomposite is limited by processing and the accompanying stiffness, textiles have emerged as alternative materials with a broad design scope. This thesis entitled, “Smart textiles with tuneable architectures for multifunctional applications,” attempts to develop novel multilayer-like architectures based on coatings to target EMI shielding primarily. Different materials and processes were adopted to maximize EMI shielding effectiveness, UV blocking, and fire protection. The thesis consists of 7 chapters. Chapter 1 is an introductory note on EMI shielding and textile-based EMI shielding materials. It discusses the terminologies used in EMI shielding, the fundamental shielding mechanisms, and the different phenomena causing attenuation. It presents a comprehensive overview of the evolution of textile-based EMI shields with time and explains the inherent advantages of using textiles as EMI shields over other materials. Chapter 2 is the roadmap of the thesis. It delves into the rationale behind selecting the materials and processes adopted. It explains the advancements in the different chapters, highlighting the critical aspects of each. In Chapter 3, thermoplastic polyurethane (TPU)-based coatings containing iron titanate (FT) and multiwalled carbon nanotubes (CNT) were coated onto cotton fabrics by a dip coating process. The coated fabrics showed an EMI SE of -12 dB at a thickness of 1.1 mm, working on an absorption-driven mechanism amounting to around ca. 92% of the total attenuation. They also demonstrated a 99.9% UV blocking and a limiting oxygen index (LOI) of 20%. In Chapter 4, water-borne coatings were used on pretreated cotton fabrics. Here, water-borne polyurethane (WPU) was used as the matrix for dispersing chemically coupled CNT and FT. The coating was subsequently coated onto polyaniline-coated cotton fabric (PANi-CF) prepared by an in-situ polymerization route. The coated fabrics exhibited an EMI SE of -40 dB at a thickness of 2.4 mm, with the absorption contribution being 83%. They also demonstrated a 99.99% UV blocking and an LOI of 23%. Further, in Chapter 5, an attempt was made to study the effect of different conducting polymer pretreatments on cotton fabric on EMI shielding. Using a facile in-situ polymerization technique, two different conducting polymers, polyaniline and polypyrrole, were coated onto cotton fabrics to give PANi-CF and PPy-CF, respectively. A carbonaceous layer containing graphene nanoplatelets (GNP) and carbon nanofibers (CNF) dispersed in WPU was coated on both the pretreated cotton fabrics. PPy-CF showed better EMI SE (-22 dB), UV blocking (99.99%), and LOI (25%) than PANi-CF. The plausible reasons for the enhancement in properties are explained in this chapter. Chapter 6 adopted a facile mussel-inspired electroless deposition to deposit metallic silver on cotton fabric (giving Ag-CF). The deposition process was optimized by varying the seeding time to enhance the silver loading on the fabric surface. The Ag-CF was coated with the same carbonaceous layer mentioned above (GNP and CNF dispersed in WPU) to give a ‘hybrid textile.’ The hybrid textile showed an EMI SE of -50 dB, the maximum obtained in this thesis, due to ‘absorption-reflection-absorption’ with absorption percentages going as high as 94%. The UV blocking and LOI values also reached 99.999% and 27%, respectively. Chapter 7 presents a consolidated summary of the results obtained from the different chapters. It also suggests a possible extension of the work that could be done to enhance the multifunctional aspects of the coated fabric.