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Keys to Yarn Strength

In the textile industry, yarn strength is a key factor that determines the durability and quality of the textile products we use every day. When we talk about yarn strength, we refer to the yarn's breaking strength, i.e. the maximum force it can withstand before breaking.

In this article, we explore the main factors that influence this strength, from the properties of the fibre to the spinning process and the environmental conditions that can affect it.

1. Fibre properties

Let's review the main properties of the fibre that affect yarn strength:

Fibre length

Longer fibres, such as continuous filaments, offer more contact points, improving the cohesion and consequently the strength of the yarn. In contrast, short or staple fibres require a more careful alignment and twisting process to achieve higher strength.

Linear density

Thinner fibres allow more fibres to be included in the yarn cross-section, increasing its strength, provided good cohesion exists between the fibres.

Fibre strength

The inherent strength of each fibre is the property that really determines the overall strength of the yarn. In other words, a yarn will never be stronger than its component fibres.

Synthetic fibres such as polyester and nylon often offer superior strength compared to natural fibres, thanks to their more uniform molecular structure.

Fibre surface friction properties

Friction between the fibres is essential to achieve yarn cohesion. Irregularities on the surface of each fibre, such as flakes in wool, for example, allow the fibres to "hold" each other, preventing slippage.

Smooth fibres, such as certain types of viscose or synthetic microfibres, require specific treatments to improve this friction.

2. Structure of the thread

The way the fibres are arranged within the yarn influences its strength. These are the factors in the yarn structure that determine how the tension is distributed and how strong a fabric can be.

Torsion

By interlacing the fibres together, friction is increased and cohesion is improved. A yarn with insufficient twist will be weak and fray easily, while a yarn with excessive twist can become stiff and brittle, so it is ideal to work with an optimum twist point.

Furthermore, although the direction of twist (S or Z) does not directly influence the strength, it does affect the behaviour of the yarn during weaving and needs to be taken into account.

The impact of joint actions

The strength of the yarn also depends on how the fibres interact with each other. An even distribution of stress between the fibres helps the yarn to withstand higher loads. This synergy is highly dependent on the uniformity of fibre alignment and the absence of internal defects.

The arrangement of the fibre in staple yarns

The greater the parallelism between fibres, the greater the contribution of each fibre to the overall strength of the yarn. Processes such as carding and drawing help to orient the fibres in a common direction, which improves their ability to share the load.

Examples of thread structures

Bulk yarns

Bulk yarns, designed for bulk and softness, have a more open and less compact structure. This makes them ideal for applications where feel and aesthetics are a priority, but generally compromise on strength.

Texturised and elastic yarns

Texturised or warp yarns, as well as yarns containing elastomers such as spandex, are designed to offer specific properties such as elasticity and resilience. However, to achieve these properties, strength is often sacrificed.

3. Spinning method

The spinning process directly influences the arrangement and alignment of the fibres within the yarn.

Ring spinning is a method that achieves stronger yarns due to better twist and alignment, while techniques such as open-end spinning may be faster and cheaper, but tend to produce less strong yarns.

4. Mixing ratio

Combining different types of fibre in a yarn allows you to get the best out of each one. A blend such as cotton/polyester improves the strength of cotton and gives stability to polyester.

However, to achieve a functional yarn, it is necessary to consider the physical and chemical compatibility of the fibres, as well as their behaviour during spinning.

The proportions of the blend must also be adapted to the purpose of the yarn: higher synthetic content for strength, higher natural content for comfort or texture.

5. High temperature and humidity

Environmental conditions can also affect yarn strength. In humid environments, some textile fibres, such as cotton or rayon, gain strength through water absorption, which improves their flexibility.

In contrast, other fibres such as wool, silk or nylon tend to weaken as they absorb moisture.

In terms of temperature, synthetic fibres can lose strength if exposed to high temperatures or aggressive thermal finishing processes, especially if they are not designed to withstand heat.

Yarn strength is the result of the interaction of fibre characteristics, yarn structure and external conditions. Understanding this interaction allows textile professionals to design and select yarns that are more suitable for the application, resulting in more durable and functional end products.

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