Crease and Wrinkle Resistance
Introduction
Creases and wrinkles are often seen as an undesirable property of fabrics. The susceptibility of a fabric to creasing it determined by its resilience.
Creases and wrinkles are of greatest concern in the Sports and Leisure and Clothing market sectors, but also relevant to the Interiors market sector. Wrinkles and creases may be unsightly, and usually reduce the lifespan of a textile by making it more susceptible to abrasion.
In clothing, pleats, also known as pressed-in creases are sometimes applied deliberately, such as in trousers, skirts and suit jackets. It is important not only to understand how to inhibit creasing and wrinkling, but also how to make pleats effectively. The two points are inextricably linked.
Though it may seem a simple subject, the physics and mechanics behind wrinkles and creases are extremely complex and difficult to analyse. This is because textiles are inhomogeneous at several levels, from the fibre, to the yarn, to the final textile structure. Secondly, textile structures are extremely geometrically complex, and thirdly, the deformations involved are multi-dimensional and extremely difficult to mode
The market for easy care chemical finishes is huge, and it is known that almost all cellulosic fabrics have some sort of handle treatment added, and this often includes an easy care element.
Terms and definitions
Creases are a fold in a fabric introduced unintentionally. The definition of a wrinkle is less clear, however. Some define wrinkles as three-dimensional creases, whereas others define them as short and irregular creases. They form when fabrics undergo double curvature, which occurs when a flat material is bent in both of its planes. Sufficient force must be applied that the change is permanent to some degree. Some people use the terms ‘wrinkle’ and ‘crease’ interchangeably.
Wrinkles and creases are distinct to pleats, because pleats are introduced intentionally and over regular intervals. They are usually sharp folds, often running lengthways to give a decorative effect.
Crease marks are marks left in a fabric once the crease has been removed and are usually caused by mechanical damage.
Crease resistance is the ability of a material to resist, or recover from, creasing. Crease recovery is a specific measurement of crease resistance that determines the crease recovery angle. It is therefore a quantitative method of analysis.
Basic principles
There are numerous possible causes of creasing: application of pressure, a change in temperature, a change in Relative humidity?, poor garment construction, or a poorly fitting garment. The reason why some fabrics are affected by creasing more than others is partly chemical, which is determined by the fibre used, and partly mechanical, which is determined by the yarn and fabric construction.
The resistance of wool and silk to creasing is generally good; the resistance of cellulosic fabrics to creasing is usually poor. In cellulosic materials hydrogen bonding (see Oleophobicity) has a large influence on the fabric’s properties. If a cellulosic material is wetted and subsequently dries then the hydrogen bonds that were present will be broken and will realign in a different arrangement, leading to creasing. As hydrogen bonds are less prevalent in synthetic fibres, or in wool and silk, they tend not to crease as easily by this process. The major cause of creasing in synthetic fibres is a change in temperature that spans the glass transition temperature (Tg) of the polymer.Above Tg a polymer’s amorphous sections are rubbery and below it these sections are glassy and hard. As a result, if a polymer is heated above its Tg then is allowed to cool while under pressure, these creases may become semi-permanent.
There are numerous mechanical factors that influence crease resistance and recovery, described below:
Wrinkles cannot be defined by their height alone. Slope, wrinkle density and the isotropy (uniformity) index are all important factors in measuring wrinkling. There are numerous standard tests (described under Regulations) that detail the procedures used to define the degree of wrinkling and creasing in a fabric.
Ways to minimise wrinkling and creasing
There are some simple ways in which fabric creasing can be reduced. During construction, incorporation of thicker fibres into yarns that will reduce frictional moment can be beneficial. One must be careful to ensure that the fibres are not so thick as to cause excessive fibre strain. During processing, rapid changes in temperature and Relative humidity? must be avoided. Large temperature fluctuations are particularly bad for synthetic fibres, and Relative humidity? changes undesirable for cellulosic fibres. In addition, applications of pressure that distort the weave or knit must be avoided.
If two fabrics are to be joined together, either by stitching or bonding, then it must be ensured that the seam is flat and does not bunch one fabric, which will result in unavoidable creases.
Many fabrics are treated chemically during finishing, minimising their wrinkling and creasing. This is usually carried out on cellulosic fibres and cross-links the polymer so hydrogen bonding is less dominant. As a result, creases and wrinkles do not form as readily. These treatments do not stop creasing that results from bad garment construction.
Some after-sale products are available to solve the problem of wrinkling and creasing. ‘Fabric De-Crease is one of many such products.
Regulations
There are many standard tests for determining both the resistance of a fabric to creasing, and for determining the resilience of pleats.
Challenges and Innovation
Accurate measurement of creases and wrinkles is difficult. Many complex methods have been developed, one study even using lasers. Despite this, fabrics that crease with ill-defined angles or that curl easily are still difficult to measure. Also, the correlation between human perception of wrinkling and a machine’s measurement is seldom 100%. A simple and cheap method that could measure wrinkles accurately is, arguably, still not available.
The development of chemical easy-care treatments that do not reduce the lifespan of the product is important: even now, some anti-crease treatments lead to increased wear and abrasion in a garment. These treatments have improved significantly since the neat formaldehyde that was first used, but further progress could be made. In addition, most of these treatments still incorporate formaldehyde, which is environmentally damaging. More environmentally benign treatments, such as silicones, are still underused.
