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FROM THE LAB - Current Issues
Choose from the following list for more information. Check regularly for new items.
Abrasion tests - Martindale and Wyzenbeek methods
PVC and PU Upholstery Fabrics - Are they different?
Waterproof mattress protectors
ABRASION TESTS - MARTINDALE AND WYZENBEEK METHODS
There are many different abrasion resistance tests to measure the durability or wear resistance of fabrics. For upholstery fabrics, two widely used methods are known as the Martindale test and the Wyzenbeek (or oscillatory cylinder) test. Both methods are referenced in the Australian Standard for Upholstery Fabrics (AS2687-1997).
The Martindale test rubs specimens of the test fabric against a standard crossbred worsted fabric ("the abradant") under a standard pressure of 12kPa. The rubbing pattern is complex but it causes the test fabric to rubbed in all directions. The Wyzenbeek test uses a stainless steel mesh as the abradant and the test fabric is rubbed back and forward in one direction under a standard pressure. The Wyzenbeek test is conducted on both the warp and weft specimens. For both tests, the result is the average of a number of test specimens. For the Wyzenbeek test, the direction with the lower number of cycles to endpoint determines the abrasion resistance.
There is no general correlation between the Martindale and Wyzenbeek tests. You cannot predict one result from the other. According to the Australian Standard, not less than 30 000 Martindale cycles are required before a fabric is rated as Heavy Commercial. For the Wyzenbeek test, not less than 15 000 cycles are required for the same rating. This does not mean that the Wyzenbeek test is twice as severe as the Martindale test. Nor does it mean that it is always more severe. The requirements for the Martindale test in the current Australian Standard reflect the long-term use of this test in Australia. The requirements for the Wyzenbeek test were adopted without amendment from the American standard (ASTM D3597). These requirements reflect the historical use of the test in America. Experiments conducted by this laboratory have shown some fabrics may achieve more cycles on the Martindale test while others may achieve more cycles on the Wyzenbeek test.
It should be noted that the Wyzenbeek test is also commonly conducted using a cotton duck as the abradant. This practice is used by a number of American companies. The results of these tests cannot be directly compared with those obtained using the stainless steel mesh. When discussing Wyzenbeek results, always make sure that you know what abradant was used.
November 2021
Since we first raised the issue of bamboo fibre in 2008, the term has been in constant use. This fibre is, seemingly, the answer to most of the problems besetting the textile and fashion industries. The terms "environmentally sustainable" and glowing statements of the fibres attributes are found in most of the promotional literature.
This article was prompted by an article in one of the newsletters that came my way. The particular clause that caught my eye was "...garments made with bamboo....are an eco-friendly alternative to man-made-fibre...". While textile technologists and chemists will well understand the basic facts about "bamboo fibre", many consumers and retailers are in danger of having the fibre misrepresented to them. The essential facts are:
1. There is no such fibre as "bamboo fibre". It is really a regenerated cellulosic fibre made by the viscose process. The Australian Standard AS/NZS 2450:1994 would require "bamboo fibre" to be labelled as "viscose". At best, it could be called "bamboo viscose" or "bamboo viscose rayon".
2. While the bamboo plant is certainly a fast-growing plant that is easy to cultivate, the cellulose obtained from the plant still needs to be regenerated into fibre form by the industrial viscose process. Thus, "bamboo fibre" is a man-made fibre..
3. Consumers and retailers should be told that "bamboo fibre" has the qualities that we associate with viscose. It is a good fibre for particular purposes - it is not a wonder fibre.
4. Promotional material that encourages consumers and retailers to believe that "bamboo fibre" is a new type of fibre or that the fibre is obtained directly from the bamboo plant should be discouraged.
November 2021
Formaldehyde is a widely-used chemical in many different products, including pressed-wood panels, plastics, adhesives, cosmetics and textiles. It is also produced by combustion processes, including motor vehicles, cooking, household heating and bush fires.
For many years, it has been recognised that exposure to formaldehyde can cause irritation to the eye, nose and throat and can cause allergies affecting the skin and the lungs. Formaldehyde is classified by the Australian National Occupational Health and Safety Commission as a potential carcinogen when inhaled.
Most formaldehyde in the environment is in the air where it decomposes relatively rapidly (generally within 24 hours). It does not bio-accumulate in plants and animals.
Along with many other industries, the textile industry has sought to minimise the emission of formaldehyde from fabrics that have been subject to formaldehyde-based treatments. These treatments have various purposes, including resins for wrinkle resistance and dimensional stability as well as some dyeing processes. Because formaldehyde is used in some adhesives, flocked textiles and textiles that have been adhesively bonded to a secondary backing may also contain formaldehyde.
Not all textiles release formaldehyde.
Some consumers and suppliers would like to eliminate free formaldehyde in textiles altogether. While this could be done, it would restrict the type of textiles available to consumers. Many consumers value the properties of textiles that have had a formaldehyde-based treatment. Further, the elimination of free formaldehyde in some of the textiles purchased by consumers will not eliminate the exposure of consumers to formaldehyde. To date, no country has set a zero limit on the maximum residue of free formaldehyde in textiles.
Along with many other countries, Australia does not have any regulations that limit the amount of free formaldehyde in textile products. However, following some work by the ACCC (Australian Competition & Consumer Commission). Product Safety Austalia issued guidelines on the acceptable levels of free and hydrolysed formaldehyde: 30ppm (parts per million) (max) for infant's products, 100ppm (max) for fabrics that contact the skin (this includes upholstery fabrics) and 300ppm (max) for other textiles. Reference is sometimes made to the limits in Japan but care is needed because the Japanese test method is different and produces results that are lower than those produced by the ISO method. The appropriate test method ISO 14184.1:1998.
Many people will recall PVC coated fabrics used for upholstery fabric, often with a simulated leather grain embossed on the PVC coating. In recent years, PU coated fabrics have become popular.
PVC is polyvinyl chloride and PU is polyurethane. They are just two different types of plastic. It is a little like the difference between wool and cotton or between polyester and nylon.
PVC and PU are both used to coat fabrics to produce a layer of the plastic on the surface of a basecloth (which may be woven or knitted). While they appear similar in a number of ways, they are not the same and have difference properties.
PU coated fabrics generally have a more pleasant handle and have better comfort characteristics when compared with PVC coated fabrics. Not all PVC or PU coated fabrics are suitable for upholstery.
If a PVC fabric was described as a PU fabric (or vise versa), this would breach the Competition and Consumer Act 2010 and the Fair Trading Acts in the Australian States.
The following notes are intended to provide some guidance to the understanding of the thermal resistance of continental quilts.
Thermal resistance - a measure of ‘warmth’
Any discussion of continental quilts or sleeping bags will invariably include a reference to the ‘warmth’ of the product. Thermal resistance is a measure of the resistance of a material to heat flow. A product that has a high thermal resistance will provide better insulation between a sleeping body and the environment in which they sleep. A person who describes themselves as a ‘cold’ person generally means that they prefer a continental quilt with a high thermal resistance if they are to remain comfortably warm through the night. A person who sleeps ‘hot’ requires a continental quilt with a lower thermal resistance to be equally comfortable.
The thermal resistance of a continental quilt or sleeping bag is measured in togs. One tog equals 0.1 Cm2/W. The name ‘tog’ is derived from the old English slang for clothing. It is not an acronym as is commonly thought. The tog is the unit for thermal resistance just as the kilogram is the unit for mass.
Thermal resistance - typical values
Continental quilts of various types in the Australian market would generally fall within the range of 4-12 tog. Typically, a lightweight polyester quilt would represent the lower end of this range while high-down content quilts would be found at the top end of the thermal resistance range. It should be noted that any filling can be used to deliver any desired thermal resistance value. By adjusting the amount of the filling in a quilt the thermal resistance will be altered. Thus, a continental quilt filled with shredded paper could be made to have a thermal resistance of 15 tog. In other words, the thermal resistance should be understood as a performance characteristic and not as a quality characteristic.
The most common thermal resistance values for double and queen sized continental quilts in the southern states of Australia would fall in the range 7-9 tog.
Individual requirements for thermal insulation
It should be understood that each person has their own individual requirements for thermal insulation. It is a common experience that children sleep ‘warmer’ than adults. Men often report needing less bed covering (i.e. less insulation) than women. The thermal insulation depends on many factors including age, sex, state of health, level of activity and the time since the last food intake. Thus, a person requires an appropriate level of thermal insulation to maintain thermal comfort. For one person this may mean much less insulation than required by another. It is inappropriate to select bedding because it has the highest thermal resistance.
Warmth to weight ratio
The warmth to weight ratio provides a measure of the weight required to produce a particular thermal resistance. Blankets have a relatively low warmth to weight ratio. Continental quilts produce more warmth for the same weight. Typically, wool filled quilts have warmth to weight ratios ranging from 90-120. Polyester filled quilts (carded batt type) fall within the range of 110-140. Feather and down filled quilts generally range from 120-160. A high warmth to weight ratio indicates that the quilt is relatively light for the particular thermal resistance.
Some people like the security associated with relatively heavy bed covering. They should look for lower warmth to weight ratios. Others may require a high thermal resistance but feel tired if they sleep under a heavy quilt. They should look for a high warmth to weight ratio.
Again, it is inappropriate to take the simplistic view that a high warmth to weight ratio is desirable for all consumers..
Other factors
The selection of a continental quilt should take into account factors other than thermal resistance. As indicated above, the warmth to weight ratio is an important factor. Comfort is also influenced by the absorbency of the fillings and factors such as the drape and price are important.
Measuring Thermal Resistance
The thermal resistance of a continental quilt is measured by comparing the temperature drop across the quilt with the temperature drop across a reference material of known thermal resistance that is placed in series with the quilt. The thermal resistance of the reference standard must be known with accuracy and the experimental techniques required for the measurement demand care and expertise.
Waterproof Mattress Protectors
The development of waterproof mattress protectors for infants, young children and other people who need to protect their mattress from wetness has seen a wide variety of products offered in retail outlets. It is not sufficient for these products to be waterproof at the time of purchase. It is essential for the protectors to be washable in hot water and to withstand many such washes. Delamination of the waterproof laminate or leaking of the laminate after a relatively few washes have been observed in some products. Excessive shrinkage of these products can produce an unsightly "crinkle" effect.
Mattress protectors intended for nursing homes and other institutional use require even higher standards of performance.
Apart from waterproofness, mattress protectors require good adhesion between the face fabric and the waterproof laminate, good pilling resistance of the face fabric and satisfactory dimensional stability (i.e. limited shrinkage). Noise levels and sleeper comfort should also be considered.
Laboratory reports are technical documents and can be difficult to understand unless you understand the particular test codes and test conditions. We often see reports that have been provided by a supplier in answer to their customer's question. We can help clients to understand what the report means and how relevant it is to their needs. In many cases, we can suggest further questions to be raised with the supplier before final approval is given. Even if the result is relevant and satisfactory, the cost of this service provides peace of mind.
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