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Sustainable fabric finishing: the modern-day “Philosopher’s Stone”

Features | December 22, 2014 | By:

Photo: GreenTheme Technologies Inc.
Photo: GreenTheme Technologies Inc.

Before knowledge of elements, atoms, nanotechnology and environmental issues, alchemists sought to convert base metal to gold and silver. They believed this transmutation would happen through the magical use of a “Philosopher’s Stone.” Significantly, this ability would also transform the holder of the Stone into riches beyond their imagination. This motivation helped develop chemistry into a modern science—chemistry taught that such elemental change does not happen easily.

Today, the meaning of the Philosopher’s Stone has expanded to denote a search for truth and desirable change. Chemistry has brought us means for textile finishing, but it has also brought us PFOA (perfluorooctyl acid), a known carcinogen present in nearly all products finished with fluorocarbons, as well as environmental problems caused by the use of finishing baths containing non-biodegradable fluorochemicals and nanoparaticles. Today’s Philosophers Stone is the magical technology that is a drop-in replacement for C6 and C8 fluorocarbon finishing; it will transform the textile industry into one that is safe for the end-user, is environmentally benign—and it costs less.

Sustainable high performance

The textile industry offers finishes such as water and stain repellency, fire retardency and easy care for the end-user. Consumers demand these attributes and regulators require some. Sustainability has become a key concern for the textile industry, even as the demand for higher performance finishing has increased. Sustainability has come to represent the unattainable Philosophers Stone—a noble goal that can be envisioned, but not created. Certainly there are many who believe that sustainability costs more and performs less.

Sustainability has different meanings, so it is best to define what sustainability is. For some, sustainability means the preferential use of recycled materials or the production of biodegradable products. Many also include a goal of reduction of energy and water use. At Green Theme Technologies, we include the elimination of hazardous chemicals, solvents and volatile organic compounds (VOCs) from the finishing process to ensure a safe and sustainable end product. Beyond that, we focus on the use of natural products whenever possible, and the reduction of waste water and off-gases from the finishing technology. Nanoparticles, which offer some enticing process opportunities, may also threaten the environment and human health due to their passage through waste water remediation facilities, similar to nanoparticle passage through the skin.

With the above definition, it is now clear why the goal of sustainability for the textile industry is nearly as elusive as the alchemist’s Philosophers Stone: the industry reliance on “padding” or wet finishing is fundamentally at odds with the goals of sustainability. Furthermore, heavy use of fluorochemical polymers combined with wet finishing invariably results in a waste stream that cannot be easily remediated by standard water treatment methods. This effluent, which may also contain nanoparticles, ultimately threatens the quality of aquifers in surrounding communities. Even worse, the curing process for wet finishing boils off large quantities of water, thereby consuming another limited resource. On the financial side, there are real costs associated with the discharge of chemicals from expended wet baths for waste water treatment and for the energy required to dry wet fabric.

Dry finishing

Because wet finishing is identified as a leading detractor in the industry’s effort at sustainability, dry finishing has recently elicited much attention. As a minimal benefit, dry finishing eliminates the need for fabric drying—a step in the right direction. Plasma finishing has garnered the most attention as a promising dry finishing technique.

Plasma treatment may use vacuum-based or atmospheric–based plasma. Both plasma technologies use little or no water, generate very little waste stream, and are energy efficient. Several early stage companies offer plasma-based dry finishing, including one founded by this author. Unfortunately, the progress of plasma-based finishing has been limited to date and no plasma-based finishing is yet in production—even for companies at this effort for many years.

However, “sexy” and futuristic plasma finishing may seem, its high capital and operational cost seems to turn customers gold into base metal. The important lesson learned is that any sustainable technology must make financial sense in order to be adopted. Thus, a key question is whether the expense and effort of generating an ionized gas (i.e., a plasma) for finishing fabric actually provides a benefit that cannot be obtained by other means?

Thermal dry finishing

That question moved me from my comfort zone of 35 years of experience in plasma and led me to develop a new technology for sustainable fabric finishing. Plasma dry finishing works by creating free radicals needed for polymerization by the impact of electrons on gas molecules. But free radicals can also be produced by simple, thermal decomposition of certain chemical compounds, so the same polymerization process as plasma finishing can be thermally generated.

This new technology, thermal dry finishing (TDF), makes sense for the textile mill, the end-user and the entrepreneur. It simply costs less and works better. One clear difference is that heat is easier and less expensive to generate than an ionized gas.

TDF involves a bit of alchemy, because it uses a combination of chemical components found in nature combined with the safer alternatives provided by modern chemistry. The basic concept is to first apply a coating of various long-chain hydrocarbon monomers; polymerization cross-linkers and a thermally triggered free radical initiator onto the fabric. This is infused directly into the fibers by a proprietary combination of heat and pressure. In the second step, the treated fabric is exposed to a short, thermal pulse that triggers the free-radical polymerization process. Since the fabric is not wet, the thermal pulse can be as short as several seconds.

The TDF process has been shown to work better than plasma finishing because the resultant polymer is infused into the fibers, so, instead of a surface coating, it is strongly bonded to the fabric. Plasma does not penetrate a fabric, whereas heat does: the infused monomer is cured and cross-linked this way. Laundry durability of plasma-finished fabric has been mediocre, at best. By comparison, the durability of the TDF polymer far exceeds that of plasma curing. TDF even works better than the conventional wet finishing, yet is also a fully sustainable, environmentally-friendly technology. To understand why TDF works better than the current treatment, it is necessary to delve into the chemistry of the conventional wet finishing.

Comparing TDF and wet finishing

Wet finishing requires mixing polymers with water. Making hydrophobic polymers stay mixed with water for wet finishing is not easy. It is necessary to add emulsifiers and surfactants to make water-unfriendly polymers stay suspended in water. Unfortunately, these emulsifiers and surfactants remain in the fabric after drying and curing. They become the failure mechanism that leads to poor laundry durability; the wetting agents help pull the hydrophobic polymer coating off the fabric.

Laundry testing proves that the TDF process works far better than the incumbent wet finishing because the polymer is embedded into and fused to the fiber. The hydrophobic polymer does not contain emulsifiers and surfactants. The result is that the laundry durability of the TDF treatment exceeds conventional C6 and C8 hydrophobic finishing. (View a video comparing spray testing of TDF-treated fabric and fabric that was wet-finished with C6 or C8 fluorocarbons after multiple laundry cycles) For most synthetic fabrics, the treatment appears to remain optimal and undiminished the lifetime of the fabric—a result that is unheard of for wet finishing and is far better than plasma finishing.

The treatment is sustainable because hydrocarbon-based polymers are biodegradable. Also, no fluorocarbons, VOCs or solvents are used, and it is naturally PFOA-free. Because there is virtually no water used, there is no need to consume energy to dry the fabric. Like the alchemists of yesteryear, finding the right mix took many tries. From a sustainability viewpoint, we have the Philosopher’s Stone.

Gary S Selwyn, Ph.D., is founder and president of Green Theme Technologies LLC, a chemical formulator and technology developer for cost-effective, high-performance and environmentally-friendly finishing of textiles and nonwovens using either thermal or plasma curing methods.

GreenTheme Technologies LLC was awarded a 2014 R&D100 Award jointly with Under Armour for its ChemStik technology water-repellent treatment for performance outdoor apparel. The awards are given out annually by R&D Magazine.

Photo: GreenTheme Technologies Inc.
Photo: GreenTheme Technologies Inc.

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