Preparing Polyester Fabrics: Saving Time Down the Line
We’ve talked before about how important it is to start with fresh, clean raw materials in the dyeing process. In the last article, we looked in-depth at cotton and basic practices to ensure you start with good raw materials. Now we’re going to look at knit polyester fabrics. The choice of processing steps depend on the construction of the polyester or Lycra fabric. The following steps will help you prepare these fabrics for dyeing.
Relax and Set the Fabric
Relaxing the fabric improves the final results if done before heat setting the fabric. This prevents shrinkage and ensures you have even tension throughout the fabric. You can use a steam box at the entry point of the stenter or hot water in the dyeing machine before the pre-scour.
Setting of polyester or Lycra knit fabrics before or after dyeing will also improve your end result. There are two options to consider. Pre-set fabrics are leaner, there are less crease marks, and better colorfastness. This setting needs to be around 185 – 195°C. Yet, post-set fabrics have better stretch recovery and a fuller hand. The choice will depend on what you’re looking for in your final product and department availability of machinery.
Pre-scouring Polyester to Release Oils
Scouring is a process to remove dirt and oil from fabric, while setting the fabric up for excellent dye uptake. One option is to pre-scour in the dyeing machine. This will also help to remove these impurities after the pre-set. Performing a pre-set in the machine while scouring will also work. This process helps pre-set the goods for dyeing and aids in removing the knitting oils and impurities. This will allow a clean base for dyeing and finishing later.
We recommend this general rule for the pre-scouring process:
An alkaline bath of 1 – 2 g/L of Soda Ash on 100% polyester
This will give you a good start for removing the knitting oils and impurities. However, fabrics with Lycra are a bit different. For these, we’ll look at a more acidic bath.
Prescouring Lycra Blend Fabric
Since fabrics containing 8% or more Lycra yarn have a higher oil content, they should be slit and preheat set before dyeing. This preheat setting volatilizes some of the silicone oils. Then you can continue with a pre-scour process.
If you pre-scour Lycra in an alkaline bath, you can damage its fibers. This will cause burnout and can tenderize the fabric, almost destroying it. Pre-scouring in a neutral bath will clean the fabric and save time and money on processing. There is no need to neutralize or rinse the fabric, which reduces water usage and the number of rinses needed after the scour.
Utilizing Sora Plus LDE in the Pre-Scour Process for Lycra
One hundred percent polyester fabrics and polyester and Lycra blend fabrics can be pre-scoured with Sora Plus LDE. This product will help remove knitting oil and act as a lubricant, while exhibiting excellent emulsifying properties.
First, pre-scour at a low temperature to help remove soluble oils. Then follow with a scour at a higher temperature with detergent. Using a neutral pH and running around 45°C will help remove impurities before dyeing.
Scouring with Sora Scour LF-MD
Sora Scour LF-MD is an excellent product for scouring polyester and Lycra blends. It has an emulsifying package and is low-foaming. In the bath, it will prevent crease marks and help remove impurities. We recommend you scour the fabric at 80°C.
Why It’s Important to Prepare the Fabric
The preparation stage of the process is critical. With preparation, you increase your chances of a quality end product by cleaning and setting the fabric so it’s ready for the rest of processing. This will improve quality and appearance of the fabric.
Failure to process fabrics can lead to many operational issues down the production line. Possible problems that can occur if not well-prepared include:
- Uneven, blotchy dyeings caused by residual knitting oils and impurity in the cloth
- Dye spots caused by residual oil spots in the fabric
- Dye stains will appear darker because of oil stains
- Colorfastness and crock fastness can fail because of poor preparation in the cloth
- Failure of repeatability lot to lot and right the first time tests
Remember, the preparation stage of the process is the start of what will follow. Take the time to check what procedure will give you the best final results.
Download the Technical Data Sheets for the products mentioned in this post here to sample them in your applications.