Understanding Yarn Shrinkage

Shown below is a typical yarn shrinkage curve:

Once an unsupported yarn is exposed to a temperature (T) greater than initiation set point, shrinkage will occur and the yarn memory will then be reset to the exposed temperature (T).

For example, the tufted carpet is exposed to 75°C during the secondary backing process. The resulting face yarn shrinkage is 7% (ref. curve above). The yarn memory is then reset to 75°C, meaning:

1. Any further temperature exposure below 75°C will result in 0% shrinkage.
2. Exposure to temperature above 75°C, will then result in additional shrinkage following the shrinkage curve but at the rates showing on the newly reset axis. Re-heated to 88°C, the face yarn will shrink around 3% (ref. curve above) and the new memory is reset to 88°C.

 

A newly installed carpet will gradually adjust itself to the hottest temperature of the region. This is a normal process that will not affect the carpet performance and appearance, as long as the shrinkage adjustment is occurring in a uniform manner. However, localized or non-uniform heating of small areas will result in uneven pile height with in turn affects the carpet appearance.

Do’s and Don’ts

A few examples of localized heating to avoid:

1. During installation, DO NOT leave uncovered roll in direct sunlight. The black secondary backing will absorb heat and temperature of the first layer may be in excess of 90°C, resulting in severe localized uneven shrinkage. White plastic wrapping or a shaded area must be used for outside roll storage.

 

Temperature inside top layer of carpet roll left in the sun at 90°F ambient for a few hours.

2. For installation facing south at sun incidences from 11:30AM to 2:00PM, care must be taken to avoid sunlight reflection from highly reflective surfaces (windows, glass doors, white smooth surfaces, etc.) from reaching the turf as a narrow band (3″ to 10″) of reflected heat may reach temperatures in excess of the melting point of most plastics used in the artificial turf industry.

 

3. Avoid leaving any source of heat absorbent material on the turf during daylight hours. For example: clear or dark plastic sheets or metal, garden hoses, pool floats, toys, etc. will absorb heat at a higher rate than the turf and may caused localized shrinkage as the temperature may exceed the turf stabilization temperature.