The Relationship Between Elongation, Shrinkage, and Break Strength in Polyester Yarns

How Drawing Affects Polyester Yarn Properties

Drawing is the process of stretching polyester yarn during production to align the molecular chains, increasing strength and reducing elongation. However, drawing also affects shrinkage and imposes trade-offs between these critical properties.

Key Properties of Polyester Yarns

1. Break Strength

   • Definition: Break strength is the maximum tensile force a polyester yarn can withstand before breaking.
   • Importance: High break strength is essential for industrial applications that require load-bearing capacity, such as tire cords and hose reinforcement.
   • Influence of Drawing: Polyester yarn's break strength depends largely on how much the yarn is drawn during production. Increased drawing aligns the molecular structure, enhancing strength but also impacting other properties like elongation and shrinkage.

2. Elongation

   • Definition: Elongation is the ability of polyester yarn to stretch under a tensile load, expressed as a percentage of its original length.
   • Importance: In industrial applications, elongation must be carefully controlled:
     • Too much elongation can lead to deformation under stress.
     • Too little elongation may result in brittleness, making the yarn less capable of absorbing dynamic or cyclic loads.
   • Influence of Drawing: The more the yarn is drawn, the lower the elongation, as stretching the fibers aligns the molecular chains and reduces flexibility.

3. Shrinkage

   • Definition: Shrinkage is the dimensional change (typically reduction in length) that occurs when polyester yarn is exposed to heat.
   • Importance: Low shrinkage polyester is crucial in applications requiring dimensional stability in high temperature manufacturing processes, such as polyesters used for binding fiber optic cable or reinforcement for rubber hoses. 
   • Influence of Drawing: Increased drawing enhances molecular alignment, which typically results in higher shrinkage. This is because the oriented molecular chains are more prone to thermal contraction when heat is applied.

In summary, elongation and shrinkage are inversely related—drawing polyester yarn more reduces elongation but increases shrinkage, while drawing it less results in lower shrinkage and higher elongation. Achieving the right balance between elongation, shrinkage, and break strength is crucial for meeting the unique demands of industrial applications. If you need assistance determining the right yarn for your industrial application, feel free to reach out—we're here to help!