The last few years have seen tremendous growth in the use of silver to provide odor control and antibacterial activity to textiles and nonwovens. However, this growth has not been without its issues.
Textile mills and garment manufacturers are constantly looking at ways to streamline the antimicrobial application process. Their goals include reducing both time and temperatures required during typical pad applications, as well as reducing concentrations of active ingredient and the amount of auxiliary chemicals used in the process without sacrificing performance.
In addition, many antimicrobial products on the market are difficult to handle in the textile mill, require extensive pre and post-treatment processes, change other functional attributes of the apparel and textiles, and require additional agents that work as chemical binders or surfactants.
Drawbacks in Traditional Antimicrobial Systems
Traditional silver-based antimicrobial systems focus on three approaches, with each having several drawbacks.
The first encapsulates the silver in an inert matrix and completely depends on the silver leaching to control bacteria. The release of silver from the matrix is diffusion controlled. As a result, over time there will be a buildup of a high level of silver ions in the matrix, ultimately resulting in discoloration.
Another approach incorporates the silver into a zeolite matrix by ion exchange. In this approach, the release of the silver is controlled by the concentration of ions and humidity level, which does not necessarily correlate to bacterial contamination levels.
The third approach has been to use insoluble silver salts, relying on the solubility constant to release the silver. All the products that rely on this approach are solid materials with limited applicability due to formulation difficulty. An overarching factor in these solid delivery systems is particle size. At smaller silver carrier particle size, higher levels of silver ions are available on the surface, resulting in higher antibacterial activity. However, these high levels of free silver ions cause discoloration and reduced activity over time. In addition, the particulate nature of these products results in a non-uniform antimicrobial finish, which results in higher cost-to-treat.
Multi-Year New Product Development Effort
After extensive discussions about these drawbacks in solid systems with fiber producers, textile and apparel manufacturers and brand owners around the world, researchers at Dow Microbial Control embarked on a multi-year project to develop a new microbial control product that would:
Not discolor apparel and textiles when exposed to light and heat Control the release of the silver based on demand Be water-based and easily diluted in anionic, cationic or nonionic matrices Improve the efficiency and effectiveness of the antimicrobial application process
The result of their efforts is SILVADUR™ Antimicrobial, which was introduced by Dow Microbial Control in September 2012. It addresses all the shortcomings of current antimicrobial products, creating a new threshold for microbial performance.
SILVADUR Antimicrobial is a silver-based technology that provides light and heat-stable antimicrobial performance and durable protection of up to 50 washings for a wide range of textiles and nonwoven materials. It is completely soluble in textile treatment baths, but forms an insoluble interpenetrating polymer network with silver ions when applied to a fabric.
The product uses a patented polymer-silver complexation technology to deliver silver ions via an “intelligent control” mechanism. When organisms land on the surface of the treated fabric, the free silver ions interact with them, resulting in cell death. As the initial silver is consumed by this interaction, more silver is released from the complex and the process continues.
Unlike other products on the market today, SILVADUR Antimicrobial is a liquid delivery system, completely particle free and readily water-dilutable, forming phase stable and solids-free finishing bath solutions for easy and rapid processing of fabric. The material can be applied by both pad and exhaustion processes.
SILVADUR Antimicrobial has been assessed as harmless to human health and added to the list of active chemical products by the International Oeko-Tex® Association. It is registered with the U.S. EPA and its active ingredient is notified and supported under the EU BPD. SILVADUR technology is registered to meet REACH requirements in the EU.
Exhaustive Pre-Introduction Testing
Extensive independent testing was initiated to examine the antimicrobial activity and durability of fabrics treated with SILVADUR technology and compare and contrast how its performance compares to other silver, zinc pyrithione and quaternary ammonium-silane antimicrobial technologies currently on the market. These test results:
Detected significant antimicrobial activity using the latest internationally recognized test methods for determining the antimicrobial activity of treated apparel and textiles. This high level of antimicrobial activity was detected even after 50 simulated launderings of sample products using washing standards common to the industry. These tests demonstrated that all untreated fabric samples tested were susceptible to microbial growth under the test conditions, and all antimicrobial activity of SILVADUR-treated fabrics was compared to the identical untreated control fabric.
Demonstrated that SILVADUR Antimicrobial can control odor-causing microorganisms that have been directly applied to the textile surface. This type of laboratory odor study further substantiates the biocidal activity demonstrated on these treated articles.
Demonstrated that SILVADUR Antimicrobial did not significantly alter the color of white fabrics.
Demonstrated that moisture management properties are not affected on goods treated with SILVADUR Antimicrobial.
Measured the durability of silver on fabrics, an important feature of SILVADUR Antimicrobial. While biocidal activity of silver-containing fabrics has everything to do with the release rate of the ionic silver, measuring total concentrations of silver can assist in determining the durability of the carrier system (polymer versus particle). Tests showed that the first five washes removed up to 50 percent of the initial silver levels, likely due to polymer abrasion or fabric degradation rather than leaching of the active ingredient. After the first five washes, the antimicrobial levels remained relatively stable over the next 45 washes.
Confirmed that the SILVADUR technology performed as well or better than other common industrial biocides used to protect apparel and textiles. Other silver antimicrobial agents demonstrated limited durable antimicrobial activity under these treatment and testing conditions. The zinc pyrithione demonstrated similar performance levels to SILVADUR Antimicrobial. However, the zinc also demonstrated a large “zone of inhibition,” which could imply that these treated samples create significant environmental concerns. Each of the antimicrobial agents were used at levels consistent with its manufacturer’s suggestions, but were applied using the most basic and economical means of treatment (pad dry).
Indicate that, with the new and novel property of the SILVADUR Antimicrobial proprietary polymer binding system, clear solutions of active silver ingredient can be delivered using standard textile industry techniques that can produce uniform polymers of silver ligand attached to the surface. As a result, the antimicrobial activity exerted by Dow’s unique polymer system remains excellent after 50 simulated home launderings.
Collaboration Yields Results
With the recent introduction of SILVADUR Antimicrobial, Dow Microbial Control is aggressively seeking manufacturing and distribution partners around the world. Product samples are readily available so potential partners can see first-hand how the product can add value to apparel and textiles and improve the efficiency and effectiveness of their operations.
Importantly, the development of SILVADUR antimicrobial speaks to the value created from a continuing dialogue and collaboration between science and technology innovators such as Dow Microbial Control and fiber producers, apparel and textile manufacturers, and brand owners. That is the key to the development of cutting-edge products that address pressing marketplace needs.