Composite Nonwoven Materials

Structure, Properties and Applications

Dipayan Das, Behnam Pourdeyhimi

• Publisher: Woodhead Publishing
• Year: 2014
• ISBN:
  9780857097750
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Composite nonwoven materials are versatile materials with a variety of applications, including hygiene, medicine and filtration. This important book provides a technical resource for professionals and academics in the field. It explores these materials in terms of fiber types used, manufacturing processes, structure, and physical properties.

The first part of the book focuses on the use of natural and synthetic fibers in composite nonwovens, discusses their structure in terms of fiber packing and alignment, and their physical properties. Further chapters deal with the practical applications of composite nonwoven materials. Hygiene applications, such as diapers, female sanitary products, incontinence pads, and wipes are covered, as well as composite nonwoven-based medical products and filters.

Composite Nonwoven Materials is an ideal reference for R&D managers in the textile industry and academic researchers in textile science.

• Systematic and comprehensive information on composite nonwovens
• Critical review of progress in research and development on composite nonwovens
• Comment on future research direction and ideas for product development

1

Introduction to composite nonwovens

D. Das, Indian Institute of Technology Delhi, India

Abstract:

This chapter gives an introduction to composite nonwovens. It begins with the definitions of composites and nonwovens and continues to discuss how these definitions are used to define composite nonwovens. It then classifies composite nonwovens according to the materials used or manufacturing processes employed for the creation of composite nonwovens. Each class of composite nonwoven is described and discussed with numerous practical examples. The chapter then proceeds to discuss the scope, markets and applications of composite nonwovens. The final section highlights the challenges and promises of composite nonwovens.

Key words

composite

nonwoven

definition

classification

scope

market

application

1.1 Introduction

The term ‘composite nonwoven’ has an interesting etymology. Impressionistically, it appears to mean a category of nonwoven materials which is prepared by a combination of different nonwoven preforms or different nonwoven fabrics. In the past, the members of the nonwoven industry used the terms ‘composite nonwoven’ and ‘nonwoven composite’ sometimes synonymously and sometimes differently. Those who preferred to use them differently would mean composite nonwoven as a material combining nonwoven preforms or nonwoven fabrics with at least one other material such as yarn, cloth, knit, braid and film, and nonwoven composite as a material consisting of a resinous matrix reinforced by an embedded nonwoven fabric (Das et al., 2012). Though composite nonwovens prepared by various combinations of materials and processes are well established, the definition of composite nonwovens has been a topic of debate in the nonwoven and allied industries. In the following sections, the definitions of the term ‘composite’ and ‘nonwoven’ are given and how they are used to define the term ‘composite nonwovens’ is discussed.

1.1.1 Definitions of composite

The term ‘composite’ comes from the Latin word compositus, which means ‘put together’ indicating something made by putting together different parts or materials. Nevertheless, the definition of the term ‘composite’ has been continued to be confusing to the members of the nonwoven and allied industries. Holliday (1990) suggested a definition of composite for the nonwoven industry as a material comprising two or more different parts or elements in which each material has its own unique characteristics. These materials may include fibre, fabric, plastics, superabsorbents or other materials that effect and become a homogeneous part of, and are nonseparable from, the total structure.

Holliday made an attempt to differentiate composites from laminates by stating that a laminate is a material which is formed by uniting or bonding two or more distant layers that may be similar or different in composition, with heat, adhesive or pressure. These layers may include fabrics, foam, sheets, webs or films such that each layer retains a substantial portion of its original characteristics and therefore does not become homogeneous in the structure. Further, a laminate can be theoretically delaminated, i.e. the layers can be separated from one another.

The North American Association of the Nonwoven Fabrics Industry (INDA) and the European Disposables and Nonwovens Association (EDANA) (2005) jointly define a composite material as a macroscopic combination of two or more distinct materials, having a recognizable interface between them. This definition of composite has not been accepted by the allied industries, however. The textile industry, which is closely associated with the nonwoven industry, follows another definition of composite. As per the Textile Institute Textile Terms and Definitions, composite is defined as a product formed by intimately combining two or more discrete physical phases, usually a solid matrix and a fibrous material (McIntyre and Daniels, 1995). The textile industry therefore thinks of composites as fibre-reinforced-composites only.

The man-made fibre industry, which is closely associated with the nonwoven industry, follows a similar definition of composite. As per the dictionary of manmade fibres, composites are materials with plastics as matrix and high tenacity fibres or short fibres as reinforcement; without this reinforcement, plastics would be insufficiently rigid, solid and impact resistant (Koslowski, 1998). Thus the manmade fibre industry thinks about composites as fibre-reinforced and plasticmatrix composites only. The polymer industry however typically follows another definition of composite. The Encyclopaedia of Polymer Science and Technology (Mark, 1970) defines composites as combinations of materials differing in composition or form on a macroscopic scale in which all of the constituents in the composites retain their identities and do not dissolve or otherwise completely merge into each other.

The composite industry uses a different definition of composite. As per the ASTM (Committee D-30 on Composite Materials) standard D3878–07, a composite material is defined as a substance consisting of two or more materials, insoluble in one another, which are combined to form a useful engineering material possessing certain properties not possessed by the constituents. Further, a composite material is inherently inhomogeneous on a microscopic scale, but can often be assumed to be homogeneous on a macroscopic scale for certain engineering applications. The constituents of a composite retain their identities: they do not dissolve or otherwise merge completely into each other, although they act in concert.

Each industry thus follows its own definition of composites. It appears that each of these industries have different circumstances and motivations so it is no wonder that they have pushed their own criteria for defining composites.

1.1.2 Definitions of nonwoven

The definition of nonwoven has had an interesting history. A chronological description of the definitions of nonwoven has been given by Batra and Pourdeyhimi (2012). It can be observed that nonwoven has been defined differently from time to time by different authors, standardization agencies and industry associations. Nevertheless, the following definitions of nonwoven are generally found acceptable worldwide. As per ISO 9092, nonwoven is defined as:

a manufactured sheet, web or batt of directionally or randomly oriented fibres, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments or felted by wet-milling, whether or not additionally needled. The fibres may be of natural or man-made origin. They may be staple or continuous filaments or be formed in situ. Note that the wet-laid nonwovens are distinguished from the wet-l aid papers by a clause that a material shall be regarded as a nonwoven if more than 50% by mass of its fibrous content is made up of fibres (excluding chemically digested vegetable fibres) with a length to diameter ratio greater than 300; else if more than 30% by mass of its fibrous content is made up of fibres (excluding chemically digested vegetable fibres) with a length to diameter ratio greater than 300 and its density is less than 0.40 g/cm³.

This definition of nonwoven by ISO 9092 has been adapted by CEN (EN 29092) and consequently by DIN, AFNOR, and all standardization offices in the EU.

ASTM prefers to define nonwoven as ‘a textile structure produced by bonding or interlocking of fibres, or both, accomplished by mechanical, chemical, thermal, or solvent means, and combinations thereof. Note that the term does not include paper, or fabrics which are woven, knitted, tufted, or those made by wool or other felting processes.’ This definition is available in many ASTM standards including D 123, D 1117, D 2646, D 3786, D 3787, D 5684, D 5732, D 5733, D 5734, D 5735, and D 5736.

There are currently two leading associations of nonwovens producers in the world, namely EDANA (the European Disposables and Nonwovens Association) and INDA (the North American Association of the Nonwoven Fabrics Industry). They have been the voice of the nonwoven industries in Europe and North America, respectively. Nonwovens are defined by them as well. Though EDANA has adopted the definition of nonwoven given by ISO 9092 or CEN 29092, INDA prefers to define nonwovens in another way. According to INDA, ‘nonwoven fabrics are broadly defined as sheet or web structures bonded together by entangling fibre or filaments (and by perforating films) mechanically, thermally or chemically. They are flat and porous sheets that are made directly from separate fibres or from molten plastic or plastic film. They are not made by weaving or knitting and do not require converting the fibres to yarn.’ It is quite interesting to note that everybody has their own definition of nonwoven and there is no unique definition of nonwovens existing in the world.

1.1.3 Definitions of composite nonwoven

There are also definitions available for composite nonwovens. Bikales (1976) classified nonwoven fabrics into four categories:

1. fabrics produced by chemical and mechanical finish

2. fabrics produced by wet processes using modified papermaking techniques

3. spunbonded fabrics

4. composite fabrics produced from laminates of scrims, fibres, or foams with tissue, films, or other nonwoven fabrics.

An example of the fourth category of nonwoven fabric is as follows. Continuous-filament yarns were coated with a phenolic resin and converted into a cross-laid nonwoven scrim to which layers of tissue were applied to each side and finally the composite was exposed to heat to allow the adhesive to set. Holliday (1990) cited interesting examples of composite nonwovens as a combination of carded webs and other webs or fibrous materials by means of water jet entanglement, or a combination of webs, fabrics, yarns, scrims, foam and other materials, or a combination of a highloft of fibrefill nonwoven and a meltblown nonwoven such that the meltblown fibres are blown between...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Textiles
• Chapter 1: Introduction to composite nonwovens
• Chapter 2: Natural and synthetic fibres for composite nonwovens
• Chapter 3: Structure of composite nonwovens
• Chapter 4: Properties of composite nonwovens
• Chapter 5: Composite nonwovens in absorbent hygiene products
• Chapter 6: Composite nonwovens in wipes
• Chapter 7: Composite nonwovens in filters: theory
• Chapter 8: Composite nonwovens in filters: applications
• Chapter 9: Composite nonwovens in medical applications
• Index