Measuring jute yarn shrinkage with ASTM D2259 Standard
The dimensional stability of textile materials is a critical quality factor, and for yarns, this property is often assessed by measuring shrinkage. For natural fibers like jute, understanding and controlling shrinkage is essential for ensuring the final product - from carpet backing to hessian cloth - maintains its desired size and shape. The universally recognized method for quantifying this characteristic is the ASTM D2259: Standard Test Method for Shrinkage of Yarns. This standard provides a reliable, repeatable procedure for determining how much a jute yarn, or any fiber yarn, will shorten when exposed to heat or moisture.
Principle of the ASTM D2259 Method
The core of the ASTM D2259 test is the measurement of a yarn specimen's length before and after a prescribed treatment. The procedure is applicable to yarns in skein form (a large coil of yarn) and can be carried out using different conditioning media, including boiling water, dry heat, saturated steam, or solvents. For jute, which is a natural cellulosic fiber susceptible to swelling and relaxation in moisture, the boiling water treatment is the most relevant for assessing maximum potential wet shrinkage.
The test quantifies the percentage change in length of the yarn, with the fundamental objective being to release any built-in stresses or strains from the spinning and winding processes.
Step-by-step procedure
The determination of jute yarn shrinkage using the boiling water method involves a precise sequence of steps:
- Specimen preparation (Skein winding)
A specific length of the jute yarn is carefully wound into a standard skein using a reel of a known perimeter. This skein typically consists of a specified number of wraps (e.g., 20 turns) to ensure a measurable length. The yarn's linear density (tex or denier) must be known to apply the correct tension later in the process.
- Initial length measurement (L0)
The prepared skein is placed on a specialized yarn length measurement device. A low, specified tension is applied to the skein - just enough to remove any slack or kinks without causing the yarn to stretch. This low tension is crucial for accurately determining the relaxed initial length. The length of the skein, L0, is recorded, often in millimeters or inches.
- Boiling water treatment
The skein is then carefully removed from the measurement device and placed into a boiling water bath (100∘C or 212∘F). The yarn must be allowed to treat in a relaxed state (without any external tension) for a fixed period, typically 30 minutes. This step simulates the severe wet-processing conditions that could lead to maximum shrinkage. For jute, this heat and moisture exposure causes the cellulose fibers to swell and relax residual tensions, resulting in a shortening of the yarn.
- Conditioning and final measurement (LS)
After the specified time, the skein is removed, blotted to remove excess moisture, and allowed to recondition to equilibrium in a standard textile testing atmosphere (e.g., 65% relative humidity and 21∘C). Once conditioned, the skein is placed back onto the length measurement device, and its final length, LS, is measured under the exact same low tension used in the initial measurement.
Calculation of shrinkage rate
The yarn shrinkage rate is calculated as a percentage change in length using the following formula:
Shrinkage Rate (%)=L0(L0−LS)×100
Where L0 is the initial length and LS is the final length.
Example: If a jute yarn skein has an initial length (L0) of 500 mm and a final length (LS) of 490 mm after boiling water treatment, the shrinkage rate is: Shrinkage Rate (%)=500 mm(500 mm−490 mm)×100=2.0%
Significance for jute processing
A measured shrinkage rate is a vital quality control parameter. For jute, a relatively high percentage of shrinkage (e.g., above 2 per cent to 3 per cent for typical carpet yarns) indicates excessive residual strain in the yarn, which could lead to dimensional instability in the final fabric or floor covering. Manufacturers use this data to adjust spinning tensions or pre-treat the yarn (such as through steam setting) to reduce potential shrinkage, ensuring the final textile product meets the buyer's specifications for size and performance. The ASTM D2259 test, therefore, serves as an indispensable tool for guaranteeing quality and predicting the end-use behavior of jute yarns.