Design and characterization of poplar fiber based nonwoven structures for sustainable textile applications

Abstract

In recent years, the global textile industry has experienced a significant shift toward sustainability and environmentally responsible practices. Central to this transformation is the growing preference for natural fibers as an alternative to conventional synthetic materials. The integration of these renewable fibers into functional nonwovens that serve a wide range of applications has emerged as a prominent area of research and innovation. Natural fibers derived from plant or animal sources offer significant advantages, including biodegradability and a lower environmental footprint during production. As the industry progresses toward a more sustainable future, exploiting the potential of such fibers becomes increasingly critical. Within this framework, the efficient use of natural resources is crucial to minimize pollution and water consumption, which are significant concerns in textile production. This growing awareness has led researchers to investigate alternative raw materials and develop processing techniques that support their integration into the textile industry. In this context, poplar seed fibers, harvested from trees commonyl grown in the Northern Hemisphere, have been selected for this study as promising, underutilized alternatives. The goal of this doctoral study is to transform poplar fibers, a natural material with no prior application in fabric form in commercial textiles, into functional, high value-added nonwoven textiles. This transformation is achieved using three different fabrication techniques: needle punching, wet-laying and bio-composite production. Due to their porous structure and inherent hydrophobic, antibacterial and sustainable characteristics, poplar fibers present significant potential for advanced textile applications. These properties are being explored for the first time within the context of textile research. This thesis study consists of four chapters, carefully organized to maintain the coherence and integrity of the research scope. Each experimantal chapter presents original contributions and offers new insights that enrich the existing literature in the field of sustainable textile materials. Throughout the chapters, key findings related to the conversion of poplar fibers into functional nonwoven structures are explored in detail. The first introductory chapter provides a comprehensive literature review of the distinct physicochemical properties of poplar fibers, including their short length (~4mm), hollow morphology, hydrophobic surface and inherent antibacterial activity. The chapter also introduces the fundamentals of nonwoven textiles, their production methods and their importance in the context of sustainable development. The literature review highlights the environmental importance and industrial potential of converting agricultural waste (especially underutilized natural fibers, into high-performance textile products. In the second chapter, the needle-punching method was employed as the production method. Owing to their short length, poplar fibers were combined with longer hollow polyester fibers (64 mm) in weight ratios of 30% and 60% to facilitate carding. The blended nonwoven fabrics were extensively characterized to evaluate their physical, morphological, mechanical, thermal, acoustic and permeability properties. The results revealed a decrease in tensile strength due to reduced fiber cohesion as poplar content increased (from 1.78 MPa for pure PET to 0.58 MPa for PET-PO60). However, there were significant improvements in thermal insulation (maximum 0.1209 K·m²/W) and acoustic absorption (SAC=0.78 for PET-PO60), indicating that these fabrics are strongly suitable for building or automotive insulation and comfort applications. Higher poplar content also resulted in increased thickness and basis weight, lower density and air permeability, while properties related to water vapor permeability and general comfort features were largely maintained. The third chapter introduces an innovative bio-composite production strategy, in which poplar fibers were combined with PLA (polylactic acid) fibers using the wet-laying technique, followed by hot-pressing to form multilayer structures. This method allowed for poplar fiber content of up to 80%, offering a more sustainable alternative compared to the needle punching. The fabricated composites were subjected to mechanical (tensile, flexural, impact), thermal, acoustic and hydrophobic performance analyses. Results indicated that the multilayer structure singificantly improved the tensile strength (from 1.5 GPa in single-layer (WL1) to 5.1 GPa in five-layer (WL5) sample) and flexural properties, meeting the standards required for automotive dashboard components. However, increased layering was associated with a decrease in impact resistance, likely due to interfacial brittleness. Importantly, the lowest thermal conductivity was achieved in WL5 (0.028 W/m·K) and sound absorption performance was improved, confirming the potential of the composites in insulation applications. All samples exhibited strong hydrophobicity with an average water contact angle of ~130°, supporting their durability in humid environments, such as automotive interiors. The final experimental chapter examines the use of 100% poplar fiber nonwovens, produced by wet-laid method, in wastewater treatment applications.