Forensic Textile Science

Debra Carr

• Publisher: Woodhead Publishing
• Year: 2017
• ISBN:
  9780081018736
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Forensic Textile Science provides an introduction to textile science, emphasizing the terminology of the discipline and offering detailed coverage of the ways textile damage analysis can be used in forensics. Part One introduces textiles and their role in forensics, including chapters on fibers, yarns and fabrics, garment types and construction, and household textiles.

Part Two covers analysis of textile damage in a forensic context. Key topics include textile degradation and natural damage, weapon and impact damage, textile ripping, and ballistic damage.

This book is an important reference point for all those interested in textile damage and the role of textiles in forensics, including academics, post-graduate students, and forensic scientists.

• Offers various perspectives on forensic textile science from an international team of contributors
• Provides wide-ranging coverage of textile damage analysis in the context of forensic investigations
• Includes chapters on fibers, yarns and fabrics, garment types and construction, and household textiles

Part One

Introduction to Textiles and Their Role in Forensics

Chapter One

Fibres, Yarns and Fabrics

D.J. Carr Cranfield University, Shrivenham, United Kingdom

Abstract

Forensic textile science is a relatively young discipline; fibre identification is the most established component of this discipline. Textile products of interest to the forensic scientist include individual fibres, yarns, fabrics, apparel household textiles and furnishings and are hierarchical structures; fibres are used to manufacture yarns which are used to manufacture fabrics which are in turn used to manufacture products such as apparel, curtains, sheets, etc. Such products are often potential evidence in criminal investigations; typically supporting in nature. Of particular interest is damage caused to apparel during an alleged incident, fibre identification with respect to trace evidence and how blood interacts with fabrics. The correct and full description of a textile product using the appropriate discipline's terminology is critical and therefore this Chapter provides a brief introduction to textile science terminology.

Keywords

Natural; Man-made; Woven; Knitted; Nonwoven

1.1 Introduction

Forensic textile science is a relatively young discipline; fibre identification is the most established component of this discipline. Within the European Union a textile product is defined as “… any raw, semiworked, worked, semimanufactured, manufactured, semimade-up or made-up product which is exclusively composed of textile fibres, regardless of the mixing or assembly process employed.” and

• “Products containing at least 80% by weight of textile fibres.

• Furniture, umbrella, and sunshade coverings containing at least 80% by weight of textile fibres;

• The textile components (provided such textile components constitute at least 80% by weight of such upper layers or coverings) of:

(a) the upper layer of multilayer floor coverings;

(b) Mattress coverings;

(c) Coverings of camping goods

• Products incorporating textile components and which form an integral part of the product, where the compositions should be specified” (The European Parliament and the Council of the European Union, 2011).

Textile products of interest to forensic scientists include individual fibres, yarns, fabrics, apparel, household textiles and furnishings. These products are hierarchical structures—fibres are used to manufacture yarns, which are used to construct fabrics, which are in turn used to manufacture products such as apparel, curtains, sheets, etc. (Fig. 1.1). These products are often potential evidence in criminal investigations; albeit typically supporting in nature. Of particular interest is damage caused to apparel during an alleged incident, fibre identification with respect to trace evidence and blood staining and/or patterns on fabrics. The physical and mechanical properties of fabrics can affect such sources of evidence. Therefore potential evidence in textile products can be affected by poor handling and storage (further information on handling and storage is provided in Chapter 3) (e.g. Adolf and Hearle, 1998; Taupin et al., 1999; Taupin and Cwiklik, 2010). Textile products should be examined from the macro-level through to the micro-level (e.g. Pelton and Ukpabi, 1995; Taupin et al., 1999; Boland et al., 2006; Taupin and Cwiklik, 2010).

Fig. 1.1 Hierarchical structure of textile products. (Copyright: CDS Learning Services, Cranfield University 2015).

Of key importance is the correct and full description of a textile product using the appropriate discipline's terminology. Therefore, this Chapter provides a brief introduction to textile science and terminology. The reader is directed to publications by The International Organization for Standardization (ISO) and Textile Terms and Definitions (Denton and Daniels, 2002) for textile terminology, to standard textile science textbooks (e.g. Taylor, 1990; Tortora and Collier, 2000) for further information and to other text books written for forensic scientists (e.g. Robertson and Grieve, 1999).

1.2 Fibres

A fibre is defined as “Textile raw material, generally characterised by flexibility, fineness and high ratio of length to thickness.” (Denton and Daniels, 2002). In textile science, fibres are classified as being natural or man-made. Natural fibres are further subdivided into animal (referred to as protein fibres in older text books, e.g. wool, silk), vegetable (referred to as cellulose fibres in older text books, e.g. cotton, flax) and mineral (e.g. asbestos) (British Standards Institution, 2014). Man-made fibres are subdivided into synthetic-polymer (e.g. polyester, nylon, polypropylene), natural-polymer (e.g. viscose, acetate) and other (e.g. carbon, glass) (British Standards Institution, 2013). Generic names for fibres are provided in two ISO publications (British Standards Institution, 2013, 2014).

Fibre production figures are published each year in Textile Outlook International (https://www.textilesintelligence.com/tistoi/); these are useful as they provide information regarding the most commonly available fibres (e.g. polyester, cotton; Table 1.1). Textile Outlook International also provides international information on textile products.

Table 1.1

Fibre Production Data (Simpson, 2015)

Fibre Type	Amount (mn tonnes)
Polyester	49
Cotton	26
Nylon	5
Cellulosic	5
Acrylic	2
Wool	1

Fibres can be described by their length (i) staple (short and of distinct length, e.g. cotton, wool) or (ii) filament (sometime referred to as continuous fibres, e.g. silk, polyester, acrylic, nylon). Fibre length can assist with fibre identification; however it is important to remember that filament fibres can be cut in to staple lengths, e.g. acrylic filament fibre might be cut to staple length to be used in knitting yarn. Fibre trade-names, rather than generic names, are often referred to, e.g. Spandex or LYCRA® instead of elastane, CORDURA® instead of nylon 6,6 and Kevlar® instead of para-aramid. EU approved fibre names are included in the appropriate EU Regulation and ISO publications (The European Parliament and the Council of the European Union, 2011; British Standards Institution, 2013, 2014). In the United Kingdom the fibre content of textile products is usually provided on the care label in accordance with the Guidance on the Textile Products (Labelling and Fibre Composition) Regulations (2012) (Department for Business Innovation and Skills, 2012). If a product is identified on a care label as containing a fibre by its trade-name, then clearly that trade-name should be used in any report, otherwise the generic name should be used (British Standards Institution, 2013, 2014). Note even if a product is labelled as containing only one fibre type (e.g. 100% cotton), it might contain up to 2% other fibres (due to impurities) or if the fibres have been carded before spinning up to 5% (by mass) of the final product (Department for Business Innovation and Skills, 2012).

Fibre identification is the subject of many standard textbooks and articles published within textile science, forensic science and other disciplines such as conservation science (e.g. Luniak, 1953; The Textile Institute, 1975; Hearle et al., 1998; Robertson and Grieve, 1999; Carr et al., 2008, 2009; Houck, 2009). Whilst most forensic scientists would use an optical microscope to assist with fibre identification, low-magnification scanning electron microscopy (≤200×) is also useful as it provides improved depth of field (e.g. Fig. 1.2). Fibre identification should always start at the macro-level by considering the length, crimp (waviness), colour, thickness and consistency of a group of fibres. If variation is visible then it is likely that the fibres are natural in origin; identification of the most common fibre types (cotton, wool) is then relatively easily achieved using an optical microscope. In longitudinal view, cotton appears as a flat twisted ribbon and the scales on wool are usually clearly visible (e.g. Fig. 1.2). Identification of rarer, speciality or luxury fibres is more difficult. If a group of fibres appear consistent then they are likely to be man-made. Although many texts suggest visible features (under magnification) can assist in identifying man-made fibres, it is important to remember that they can be made to any form and thus other identification methods are required such as the use of chemical analytical equipment, or a combination of flammability and chemical solubility tests (e.g. Luniak, 1953; Taylor, 1990; Robertson and Grieve, 1999).

Fig. 1.2 Typical low-magnification SEM images of (A) cotton and (B) wool. (A) Twisted ribbon appearance of cotton fibre. (B) Scale appearance of wool fibre. (Images: Ms E. Girvan, University of Otago).

The chemical and molecular structures of fibres affect their physical and mechanical properties, including their interaction with liquids and this can be important, for example when considering the appearance of bloodstains on textile products. More crystall...