Demand for polyester-cellulosic fiber is growing worldwide. The blend combines the power of polyester and the comfort of cellulose to satisfy consumers who want apparel and home furnishings that perform better and look and feel good for longer.
The polyester fiber in the blend provides excellent crease recovery and shape retention, as well as easy care and durability. The cellulosic fiber offers absorbency, comfort and good heat conduction for winter warmth and summer cooling.
Unfortunately, there is a catch: producing polyester-cellulosic blends is challenging.
Each fiber type has its own dyeing process, so the overall dyeing cycle is much longer. This drives up costs, as you need more dye, more chemicals, and more energy and water.
Using more energy and water also carries a high environmental cost, especially in an age of stricter government regulations and higher consumer expectations. Furthermore, the standard way to dye polyester-cellulosic blends uses hydrosulphite, which is harmful to the environment and makes wastewater more difficult to treat.
Many leading brands today have a clean, green image that means their suppliers must avoid pollutants and minimize the water and energy they use during production.
Adding to the challenge, polyester-cellulosic blends command a lower price in the market than pure cellulosic fibers because polyester costs less than cotton or other cellulosic. Despite this, blends require longer to process, consume more utilities and create fastness and reproducibility issues.
All of these factors mean that textile mills are constantly making difficult choices as they strive to balance profitability and performance.
The selection of disperse and reactive dyes is fundamental to achieving good wet-fastness results and a shorter and most cost-effective dyeing process for polyester-cellulosic blends.
To dye polyester-cellulosic blends, you need a reactive dye for the cellulosic fibers and a disperse dye for the polyester. There are three main criteria to consider:
- Thermo-migration and cellulose staining
Conventional polyester dyes stain cellulosic fibers. This staining can occur in the washing bath, or during post-bath heat treatment, for example, or during the finishing process or wash-fastness testing (when it is known as thermo-migration).
- Reduction sensitivity
Reduction leads to loss of color yield and poor reproducibility when dyeing polyester-cellulosic blends. Bluish-red, blue and navy chromophores carry the most risk of reduction. And this risk is further raised in the absence of air, as in a fully flooded dyeing machine.
Reductive chemicals can be carried into the dye bath by fibers such as wool, viscose, bleached and neutralized cotton, and greige cotton. Some economical dispersants (such as sulphonated lignin) can also have a reduction effect.
- Substrate suitability
Some disperse dyes offer good wash fastness or wet fastness on 100-percent polyester, but fail to do so on a polyester-cellulosic blend. That’s why it is important to select dyes that are known to have high fastness properties for polyester-cellulosic blends.
Huntsman Textile Effects believes that it has created the best solution available today for dyeing polyester-cellulosic blends. Combining TERASIL® W/WW disperse dyes and AVITERA® SE reactive dyes in a new SE Fast process provides the shortest possible processing time and the lowest environmental impact, along with robust dyeing behavior for all shade depths.
A key factor in this process is that the TERASIL® W/WW dyes are alkali-clearable and less sensitive to reduction, even under extreme conditions. These dyes are washed off during the fixation phase of cellulosic dyeing and in the alkaline washing bath. This means that the TERASIL® W/WW dyes will not stain cotton or other cellulosic fibers, delivering outstanding fastness.
With TERASIL® W/WW dyes allowing alkaline clearing and AVITERA® SE delivering high-speed, low-temperature wash-off, the time required to dye polyester-cellulosic blends is reduced from around nine hours to just six hours. The process uses around 50 percent less water and energy and produces around 50 percent less carbon dioxide emissions.
To illustrate, let’s consider the case of a plant with a production capacity of 100 tons per day, of which 40 percent is polyester-cellulosic. Switching to the AVITERA® Fast SE process with TERASIL® W/WW, this plant can save more than 150,000 cubic meters of water per year, along with more than 16,000 tons of steam. What’s more, it will be able to produce an additional 2,700 tons of fabric each year, without making any other production changes. This is the equivalent of an extra month of production annually.
In short, this combination of innovative TERASIL® W/WW and AVITERA® SE dyes help mills overcome the challenges of dyeing polyester-cellulosic blends. It helps achieve the best possible production efficiency, operational excellence, and sustainability – all with reliable fastness results, even on difficult shades like Dark Navy and Dark Red.
Ultimately, this improved productivity and resource saving bring the textile sector closer to environmental and economic sustainability.