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WOOL 472-572: Wool Biology and Metrology

Revision Notes

WOOL-472-572 was originally issued in 2008. It was created with funding provided by the Sheep CRC supported by AWET.

A revised version, released in 2012, had been subject to a number of minor amendments, mostly related to formatting. The first 5 topics had some additional text added, but they are substantially the same as the 2008 version.

The 2014 version has been substantially edited. The total number of topics has been reduced from 18 to 16, by eliminating some duplications and also by merging some topics together. Moreover two new Topics have been introduced (Topics 14 & 15) and the previous topic on Developments in Wool Metrology has been updated.

Topic 1: Skin Structure and Function

This topic is titled skin structure and function because the main objective is to describe cellular aspects of the growth of wool. The description of the structure of the skin of the sheep and of its wool follicles not only draws on studies of sheep but also from our knowledge of the similar events in the skin of humans and mice that differ from that of sheep in only minor detail.

This topic should provide you with:

  • knowing some functions of the skin;
  • knowledge of development of wool follicles in the skin and some of the mechanisms involved in the formation of mature follicles growing wool; and
  • the ability to critically assess scientific and other professional literature on wool growth in relation to commercial implications.

Topic 2: Structure of the fibre

To understand the measurement (metrology) of the physical and chemical properties of wool fibres it is helpful to understand how fibres develop and the sources of variation of their shapes and composition. The skin of mammals is the largest of all the organs in the body and has many functions. Hair is found only in mammals. The skin acts as a barrier that protects the whole organism from the environment but it is also concerned with thermoregulation via sweat glands and hair. In sheep, the growth of the wool has been enormously influenced by selective breeding to increase the amount grown per animal and improving quality characters such as fineness and crimp.

On completion of this topic you should have:

  • an understanding of the structure of wool as a complex tissue containing dead cells filled with proteins that provide it with the mechanical properties that make it a textile fibre.
  • An overview of the properties of wool in relation to its structure

See an animated demonstration of the physical and chemical properties of wool fibres: CSIRO_Fibre_of_the Gods

Topic 3: Follicle Kinetics

The hair or wool of mammals is the fully keratinised product of events occurring within the hair (wool) follicle and once this differentiation event has taken place, the keratinised fibre is no longer metabolically active. The hair (or wool) follicle on the other hand is one of the most highly metabolically active structures in the mammalian body plan and undergoes some of the most dramatic physical changes, not only, during initiation and morphogenesis in embryonic skin, but also throughout the functional lifetime of the follicle as it rotates through the phases of the hair cycle (anagen, catagen and telogen). This morphological pattern of change is generally the same for all follicles with the major difference being the temporal pattern, which varies with species, age, gender, spatial distribution and metabolic status of the animal.

On completion of this topic, you should be able to:

  • describe the techniques that are routinely used to measure cell kinetics, wool growth rates and wool quality;
  • explain the application and limitations of each technique;
  • outline the basic biochemical and molecular mechanisms underpinning wool growth rates in the mature wool follicle; and
  • critically assess scientific papers and related professional literature on factors influencing wool growth and fleece quality and the methods used to quantify the responses.

Topic 4: Genetic Engineering

This aim of this topic is to explain what is currently known about genes that are active in the adult wool follicle and to discuss the way that the process of genetic engineering can be used to cause the wool follicle to produce new wool fibre types. A detailed example of the first work done to achieve this will be given along with a description of the results and the potential of this technology for the future.

On completion of this topic you should have an understanding of:

  • the opportunity that transgenesis presents for the modification of wool properties;
  • the method used to make transgenic sheep and results from early experiments;
  • the genes that can be used as transgenes;
  • the potential wool fibre modifications that could be made by transgenesis; and
  • the issues of biosafety, ethics and acceptance in relation to the use of transgenesis in sheep.

Topic 5: Wool Measurement Principles & Sampling Techniques

Put quite simply, metrology is the science of measurement. In broad terms metrologists are generally focussed upon developing (evaluating) technologies and systems for objectively measuring the quality attributes of raw materials and manufactured products. This general definition applies as much to wool as to any other material.

By the end of this topic, you should have:

  • an understanding of the essential technical requirements of wool measurement systems;
  • an understanding of the sources of variation within wool metrology systems;
  • knowledge of the procedures by which metrology standards are developed, including the role of IWTO;
  • knowledge of the procedures whereby the technical limitations of metrology systems is managed;
  • the meaning of common statistical terms used in wool metrology;
  • the development of standard test methods;
  • Describe the reason grab and core samples are taken from wool bales;
  • Describe the equipment used for grab and core sampling wool bales;and
  • Understand the sampling factors that influence the precision of wool test results.

Topic 6: Yield

This topic focuses on the determination of Yield as applied to the trading and processing of wool, and the considerations inherent in this determination, by progressing the reader through the following areas:

  • Purpose of Measurement;
  • Components of Yield;
  • Principles;
  • Equipment;
  • Procedures;
  • Standards;
  • Derived Yield Estimates; and
  • Yield Testing of Fleeces.

By the end of this topic, you should have:

  • an understanding of the importance of Yield to the textile manufacturer;
  • an understanding of the processes involved in producing an estimate for Yield;
  • knowledge of the components which lead to estimates of Yield;
  • knowledge of the different types of Yield estimates available, and the markets in which they most commonly apply; and
  • an understanding of the requirements in providing an estimate of Yield on an IWTO Test Certificate.

Topic 7: Fibre Diameter

This topic describes the measurement of fibre diameter of wool samples, slivers and tops and outlines the relevance of fibre diameter testing to determine wool value and to processing performance and quality of textile or apparel end product. Fibre diameter is arguably their most important property, because of the importance of fibre diameter in the efficient spinning of fine worsted yarns and in the manufacturing light, soft handling fabrics for apparel. The finer the fibres, and the fewer the number of fibres present in a cross section of a yarn produced from the fibres; the more flexible is the yarn. These factors are critical to the quality of wool fabrics.

On completion of this topic you should have an understanding of:

  • the relevance of Fibre Diameter to wool fibre value, processing performance and end product quality;
  • the difference between visual appraisal and measurement of Fibre Diameter • the sources of variation in Fibre Diameter measurement;
  • sampling and sample preparation for the four (4) Standard methods of Fibre Diameter measurement, viz. Projection Microscope, Airflow, Laserscan and OFDA 100;
  • Fibre Diameter testing of top, slivers, core and fleece samples (including On-farm Testing); and
  • compare the precision levels possible with the various instruments used for measuring mean fibre diameter.

Topic 8: Staple Length, Staple Strength and Position of Break

This topic describes the subjective assessment and objective measurement of Staple Length, Staple Strength and Position of Break. The principles of the measurements made on an ATLAS instrument are described as is the relationship between Staple and Fibre based measurements.

By the end of this topic, you should have:

  • an understanding of the limitations associated with subjective appraisal of Staple Length, Staple Strength and Position of Break;
  • an understanding of the relationship between Staple and Fibre properties e.g. Staple Length and Fibre Length, Staple Strength and Fibre Tenacity; and
  • an understanding of the principles of objective measurement on an ATLAS instrument including the requirements of the IWTO Test Method.

Topic 9: Wool Style and Wool Colour Measurement

Style is of particular importance in the superfine end of the market and becomes less important as fibre diameter increases.

This topic describes the visual characteristics used to appraise wool style and examines the relationship between subjective appraisal and objective measurement of wool style. Instruments developed to quantify components of style are described. The importance of components of wool style in processing are quantified and described.

Colour is one of the most important wool properties for processing because it provides the best indication of the ‘dyeing potential’ of a grower’s lot or an export consignment. Wool of poor colour cannot be used to produce a yarn with a light pastel shade, and extremely poor colour may be associated with microbial damage of the fibres.

By the end of this topic, you should have:

  • an understanding of the subjective nature of traditional wool style;
  • developed an understanding of the components of style and how these may be objectively measured, and
  • an understanding of the impact of style and components of style on early stage processing.
  • Explain the importance of colour measurement for wool and why there is a wide variation in wool colour;
  • Explain the specific requirements in wool colour measurement regarding sample preparation, its presentation to the instrument and the calibration procedure; and
  • Differentiate between the base colour and as-is colour of wool.

Topic 10: Contamination

This topic describes the main forms for “contamination” occurring in the Australian wool clip. Contamination, which is considered a major issue by early and late stage processors, includes man-made fibres, dark and medullated fibres, skin pieces through to chemical residues.

By the end of this topic you should have an understanding of:

  • the source of contamination:
    • contamination of wool origin; viz. urine-stained, pigmented and medullated fibres
    • contamination of non-wool origin, viz. wool packs, farm objects (including baling twine), mill packs and mill objects;
  • the problems created by each form of contamination;
  • methods to minimise the risk of contamination; and
  • future developments.

Topic 11: Fibre Curvature, Crimp Frequency, Resistance to Compression and Bulk

This topic describes the relationship between the four different measurements of fibre shape, and explores the relationship between these measurements. The four measurements to be covered in this topic are fibre curvature, crimp frequency, resistance to compression and bulk.

By the end of this topic, you should have:

  • an understanding of the measurements of fibre shape
  • an understanding of the principles of measurement of Bulk and Resistance to Compression
  • an understanding of the relationship between Bulk and Resistance to Compression
  • an appreciation of the measurement of Crimp Frequency, and
  • an understanding of the commercial measurement of Fibre Curvature.

Topic 12: Use of Measurement in Prediction Technology

This topic is in 3 parts:

  • Use of Measurement in Sheep Production
  • Use of Measurement in Greasy Wool Commerce, and
  • Commercial Use Of Prediction Technology.

The first two parts summarise details of the use of measurements and part three provides a more detailed tudy of processing prediction, how it originated, its development and its use in industry today in the purchasing of greasy wool, mill monitoring for quality control (QC) and in risk management.

At the completion of this topic the student will have and understanding of:

  • the commercial importance of objective measurement in topmaking and blend engineering and how prediction formulae are developed and used,
  • an insight into the flexibility of prediction and its benefits

Topic 13: Wool Top Measurement

This topic looks at the measurement of top length and length distributions. It discusses different technologies used in the measurement of this important commercial parameter and the effect these have on defining different top lengths.

This topic also provides a more in-depth understanding of the current base measurement system; the Almeter and its measuring principle – capacitance. This has a specific set of biases that require understanding in light of the development of new technologies based on different measuring principles.

Advances in technology have enabled the development of a new instrument, the OFDA4000. It uses different measuring systems, and introduces its own set of measurement biases.

By the end of this topic, you should have:

  • an understanding of the measurements of fibre shape;
  • have an understanding of top measurement principles, the differences that accompany different systems and the effect these have in respect to spinning and trading in tops;
  • understand the underlying basis of the current system along with the principles of calculating results; and
  • appreciate the importance of prediction technology to top length measurement.

Topic 14: Bundle Strength

This topic examines what is meant when we refer to the strength of a top. The average tenacity is usually expressed in terms of bundle strength. The measurement of bundle tenacity and intrinsic fibre strength are examined in terms of the methods and how they depend on and relate to the strength properties of individual fibres, to staple strength, and to variations within and between fibres. The test methods and instruments for measuring bundle strength are briefly examined with particular emphasis on Sirolan Tensor. Finally, the potential causes and implications of differences in fibre strength are examined in terms of their effects on yarn properties and spinning performance.

By the end of this topic, you should have:

  • an appreciation of the difference between bundle tenacity, staple strength and intrinsic fibre strength;
  • an understanding of the measurement methods for bundle strength and their limitations;
  • an appreciation of the key factors that affect bundle strength; and
  • an understanding of the impact of lowered fibre strength (bundle and staple) on processing.

Topic 15: Measurements of Yarn and Fabric

Fibre assemblies relevant to wool include slivers, tops, yarn and fabrics. The kinds of measurements relevant to these structures can be grouped as follows:

  • constituent properties – e.g. fibre diameter, fibre length;
  • construction – e.g. linear density, twist;
  • mechanical tests – e.g. strength, flexibility, bulk; and
  • contamination tests – e.g. residual grease, vegetable matter faults, neps, moisture content.

In this topic tests for wool fibre assemblies are considered, for yarns and fabrics.

At the completion of this topic the student will be able to:

  • explain how the constructional parameters, evenness and tensile properties of yarn are measured and interpreted;
  • describe the features of a software system for predicting the properties and spinning performance of worsted yarn;
  • outline the principles by which the tensile, dimensional stability, serviceability, drape and other mechanical properties of fabrics are determined; and
  • describe and compare the two instrument systems for objectively measuring the handle and related properties of fabrics.

Topic 16: Recent Developments in Wool Metrology

This topic briefly describes the framework in which future developments may occur in wool metrology and provides examples of possible developments.

By the end of this topic, you should have:

  • an appreciation of the factors which drive developments in wool metrology; and
  • a guide to possible future developments in wool metrology.