Yield & Diameter

The first step in determing Yield, Vegetable Matter Base and Mean Fibre diameter is to obtain a representative sample of the lot. Each bale weight is measured and recorded and a core sample is extracted, either manually or by machine, The number of core samples per bale depends upon the size of the lot, and the coring schedule is designed to ensure the required precision in the Yield is obtained. The samples are aggregated and carefully sealed in plastic bags to ensure no weight change occurs while they are in transit to the laboratory.

Upon receipt in the laboratory the core samples are weighed and blended. Then subsamples are taken for subsequent testing while the sample residue is stored should any additional testing be required.

The greasy subsamples are each individually washed with hot water and detergent. This removes most of the grease and wax, all the suint and most of the dirt. The washing machines (scours) are designed so that all of the vegetable matter is retained.

After washing, the subsamples are placed in a centrifuge (spin dryer) to remove most of the water. Air, preheatd to 105 degrees Celsius, is forced through the subsamples until each is thoroughly dry. At this point the subsamples are weighed and the Oven Dry Weight (ODW) recorded.

The Oven Dry subsamples are then further subsampled so that the residual grease, dirt, vegetable matter remaining after washing can be determined. An additional subsample is taken for determining the Mean Fibre Diameter. The residual grease is determined by dissolving it in hot alcohol and then removing the alchohol and weighing the remaining grease. The residual dirt is determined by burning the wool subsample and then measuring the weight of remaining ash. The vegetable matter is separated from the wool subsample by dissolving the wool in hot caustic soda. The vegetable matter is then dried and weighed. The percentage of grease, dirt and vegetable matter is subtracted from the ODW, the result being the percentage of clean wool in the initial greasy subsample. This is the Wool Base. The processing yields reported on IWTO Yield and Micron Certificates are derived from the Wool Base or from the Wool Base and the Vegetable Matter Base.

The Airflow instrument has served the industry well for many years. Specimens are prepared by carding the scoured subsample using a mechanical card (Shirley Analyser) and then conditioning the carded specimen to a constant regain, before measurement of MFD. The newer LASERSCAN technology uses fibre snippets obtained by minicoring the carded and conditioned specimen.

AWTA was established with the specific purpose of providing an independent testing service to the measure the Moisture Content of Scoured & Carbonised Wool for the Australian wool industry. This was a major step forward, but it created a need for an objective test for the Yield of clean fibre in Greasy Wool. This was achieved in the early 1960's when AWTA and other interested organisations:

• Developed an IWTO Test Method for Wool Base, which measured the amount of clean wool, free of all contaminants, and the amount of Vegetable Matter in Greasy Wool.
• Initiated processing trials, which resulted in the derivation of conversion factors that are used to calculate the various commercial yields used in trading from the test house data.

Subsequently:

• An IWTO Test Method for the determination of Mean Fibre Diameter by the Airflow Meter was developed in the late 1960's and early 1970's, giving wool exporters access to objective measurement data for the commercially most important Greasy Wool parameter.
• Demand from wool buyers and processors for both Yield & Fibre Diameter testing services grew rapidly and contracts increasingly included requirements for Greasy Wool to be tested prior to shipment. Approximately one third of the Australian clip was being tested by 1972.

All such testing was conducted Post Sale after the buyer had finalised his purchases and batching. Processing consignments to be tested comprised many sale lots distributed over different brokers within selling centres and between selling centres across the country. Brokers took the individual lots down from stacks, they were core sampled (using manual sampling equipment) and weighed by AWTA staff. The component samples for each consignment were amalgamated at the laboratory and tested.

As Post Sale testing grew during the 1960's, AWTA became aware that if wool could be tested before, rather than after, sale there was an opportunity to avoid the costly additional handling of bales and the information could be made available to all wool buyers - not just the purchaser of the wool.

The first Presale tests were conducted by AWTA in the late 1960s and Presale testing became an integral part of the auction system in July, 1972, as it moved towards Sale by Sample following implementation the recommendations from the Australian Objective Measurement Program (AOMP).

AWTA commenced a rapid expansion of laboratory space to accommodate the expected (and actual) increase in testing. The adoption of Presale testing was rapid, as most brokers offered lower warehousing rates for wool sold by sample and actively promoted its use.

By 1980:

• Most classed grower lots, interlots and bulk classed wools were being tested for Yield, Vegetable Matter Base and Mean Fibre Diameter as failure to provide test results in the catalogue invariably resulted in discounts which exceeded the cost of testing.
• Most privately purchased wools were also bought on the basis of test results, the wool being tested on arrival in the private treaty merchant's store.

During the 1980s:

• Presale testing continued to grow, partly because wool production was increasing and partly because growers were demonstrating a desire to test and sell their small lots in their own right, rather than include them in traditional subjectively matched interlots, which were known to attract discounts.
• The statutory AWTA was privatised and the new AWTA Ltd was formed.
• AWTA Ltd developed a new service known as Objective Lot Matching to enable brokers to match individually tested small lots into larger sale lots on the basis of uniform test results as well as similar visual characteristics. Objectively Matched Lots provide buyers with more uniform lots than can be obtained with traditional interlotting procedures.
• The TEAM trials were concluded and AWTA Ltd commenced a new commercial service certifying Staple Length & Strength.

By the end of the 1980's virtually all Australian wool was being Presale tested, whether sold through the traditional auction system, privately or direct to a processor. The test results played a major part in price determination and in the prediction of processing performance.

The Airflow instrument was a major development for the wool industry. It provided a rapid, and inexpensive means for determing Mean Fibre Diameter (MFD). However, it could not provide information about the distribution in diameter (CVD). Two new technologies emerged that were capable of providing this additional information.

The first of these, the LASERSCAN, developed by CSIRO, was based upon laser optics and high speed electronics that measured the diameter of short snippets of fibre as they were carried in suspension in an iso-propanol/water mixture through a coherent laser beam.  The second, the Optical Fibre Diameter Analyser or OFDA, used computer algorithms to analyse digital images of fibre snippets mounted on a glass slide, viewed by a microscope fitted with a digital camera.

The LASERSCAN commenced its development in 1975, whilst the development of the OFDA commenced in 1982.

During the 1990's:

• CSIRO completed development of the LASERSCAN instrument and the OFDA instrument also became available. Both technologies provided CVD as well as MFD.
• AWTA Ltd commenced a major metrology study to evaluate both the LASERSCAN and the OFDA.
• IWTO Test Methods for both the LASERSCAN and the OFDA were developed and approved.
• AWTA Ltd selected the LASERSCAN as its preferred technology and made representations to the International Wool Textile Organisation (IWTO) to allow the Company to replace Airflow with LASERSCAN for certifying the diameter characteristics of Australian wool
• AWTA Ltd negotiated the rights to manufacture the LASERSCAN instrument

On the 1st July 2000, AWTA Ltd replaced the Airflow with LASERSCAN, although an Airflow service was maintained, in order to facilitate the transition. The Company also introduced a commercial service for providing certificates based on OFDA.

In 2001 the Company replaced the alcohol extraction system for determining residual grease with Near Infra Red (NIR) technology. The IWTO Test Method had been modified to permit this change more than a decade previously, but the technology only became competitive with solvent extraction towards the end of the 1990's.

NIR has since been incorporated into the Test Method for measuring residual ash. However, for Australian wool a suitable method of preparing and presenting the specimens for measurement was required, and in 2007 AWTA Ltd succeeded in developing one. Consequently NIR has replaced the traditional ashing method for determination of residual mineral matter.