- Created on Saturday, 03 January 2004 04:08
- Written by Steven J. Tinker
Several key factors in the laundry industry have seen major changes in the last several years. Polyester fabrics have become more dominant vs. cotton. Today, 100 percent spun poly fabrics are replacing cotton/poly blends in many applications. Tunnel washers are becoming more prominent as smaller, less efficient plants are being consolidated and upgraded. Water and energy conservation and wastewater quality are a greater concern.The nature of detergents is being changed to meet the new challenges in the industry, with more emphasis on surfactant cleaning and a reduction in the use of harsh alkaline builders.
But one area in laundry chemistry has been left unexamined in light of all these changes, and that is: What bleach will work best for my operation?
Let’s look at the pros and cons of the two major bleaches, chlorine and oxygen. (We will limit this discussion to liquid bleaches.) There are several areas that we should consider: Bleaching efficiency, fabric safety, storage requirements and employee safety, and environmental concerns.
Bleaching efficiency: First, let’s review the function of bleach. In laundry applications bleach is primarily a stain removal agent. As such, bleaching is best done after the bulk of the soil is removed form the fabric and flushed away. Bleach cycles in traditional washers are usually done “in the clear” or in fresh water so that excessive amounts of dissolved soils won’t react with the bleach before it can react with the stains remaining on the fabric. Bleaches oxidize stain molecules, breaking them up into smaller, more soluble molecules that can be washed away. Or bleaches will react with colored stains making them colorless.
Liquid chlorine bleach chemically is a solution of sodium hypochlorite, usually about 12 percent active as chlorine. In a traditional wash application chlorine bleach is applied at a rate of 75-150 parts per million (ppm) of active chlorine, in a wash temperature of 140-150°F, at a pH of 10.2-10.8. Chlorine bleach will become more aggressive as the pH decreases and less aggressive as the temperature decreases. So some have recommended low temperature (90-120°F) bleaching be done at a lower pH, around 9.8-10.5, to maintain bleaching efficiency. The potential drawback with this bleaching method is creating an over-aggressive bleaching environment that may damage some fabrics.
Liquid oxygen bleach chemically is hydrogen peroxide, and can be as high as 35 percent, which calculates to about 16.5 percent active oxygen. Oxygen bleaches differ from chlorine bleaches in the most efficient application. Generally oxygen bleaches are used at a little higher level, about 100-200 ppm activity. And, they need higher temperature and higher pH to be activated. The recommended levels are temperatures of 160-180°F and pH of 10.8-11.8. Unlike chlorine, oxygen bleaches become less aggressive as the pH decreases. However, like chlorine, oxygen also becomes less aggressive as the temperature decreases. Since oxygen bleaches work well at high pHs, in many situations you can combine the detergent and bleach steps for a more efficient wash formula. And tunnel washers that may have a limited number of modules may benefit from oxygen bleach, as you can combine the detergent and bleach operations in one zone of the tunnel.
Fabric safety: Chlorine bleach is generally considered to have a greater potential to damage cotton-based fabrics. Cotton can easily be oxidized by chlorine when it is applied wrong, creating a weakness in the fiber that can lead to thin areas or to excessive linting. Cotton is especially vulnerable to damage when chlorine bleaches are not properly rinsed out of the fabric. And a residual of just a few part per million of chlorine in the fabric can be a major problem when a sour is added to the final rinse, dropping the pH to under 7.0. This activates the chlorine to its most aggressive chemical form, and can cause significant damage to cotton. So it is always a good idea to use an “anti-chlor” to neutralize residual chlorine before the sour step in the wash formula.
Chlorine bleach, when used at lower temperatures (90-120ºF) and increased chlorine concentrations (200 ppm) at the proper pH of 9.8 10.5 will give excellent results, with very little tensile strength loss. This method is used in tunnel washers for bleaching in the rinse zone with great success. It also applies to conventional washer bleaching as well. This low temperature chlorine bleaching method is often utilized in Europe. It is very important to use an anti-chlor with this method to avoid potential fabric damage caused by chlorine carryover into the sour operation.
Polyester fibers are generally unaffected by chlorine or by oxygen bleaches. However some permanent press finishes on fabrics can react with chlorine and possibly retain the chlorine in the fiber, causing a yellowing of the fabric.
Oxygen bleaches are sometimes referred to as ”color-safe” bleaches. However, oxygen bleaches can be as aggressive on fibers and dyes as chlorine bleaches, if applied in inappropriate methods. But, generally oxygen bleaches are safer on fabrics because they are “deactivated” by the low pH of the sour step. And when dried, oxygen bleaches degrade to water and oxygen, which will safely evaporate away without damaging the fabric.
Storage requirements and employee safety: Concentrated chlorine bleach solutions a very unstable. They actually begin to slowly degrade immediately after they are manufactured. The degradation can be accelerated by storing at high temperatures (over 90°F). Exposure to sunlight will also increases degradation. And contact with organic material or metals are also detrimental to stability. In the concentrated form, chlorine bleach can be very dangerous if accidentally mixed or contaminated with an acidic product, such as a laundry sour. This can cause rapid release of chlorine gas, which is toxic.
Oxygen bleach is much more stable than chlorine bleach. However, it is good practice to store in a cool place, out of direct sunlight. With proper storage, most oxygen bleaches can be stable, and not lose activity, for a year or more. Oxygen bleach can become rapidly unstable if it is contaminated with metals or organic materials. Concentrated hydrogen peroxide, when contaminated with incompatible materials can release oxygen and hydrogen gases, which can be an explosive combination.
Exposure to concentrated chlorine or oxygen bleaches can cause irritation, severe burns, or corrosion. Proper Personal Protective Equipment (PPE) should be used when handling concentrated bleaches. Rubber gloves, boots, goggles and/or face shields are recommended. It is best to refer to your chemical manufacturer’s Material Safety Data Sheet (MSDS) for proper precautions on storage, handling and spill clean-up procedures.
Environmental concerns: Chlorine bleach has come into scrutiny over the past few years due to environmental concerns. Some claim that chlorine in the water and wastewater streams can cause the formation of certain chlorinated organic materials that may have negative human health impacts. However, the science of these assertions is not fully developed. As a result, in some areas of the world there is pressure to reduce the use of chlorine compounds including chlorine bleaches.
In another aspect, however, chlorine is well known to have excellent anti-bacterial and anti-viral efficacy. In the laundering process, several factors assure us that the finished textiles are essentially bacteria-free. These factors include the effect of dilution from several exchanges of water, temperature, high pH followed by low pH, and the use of oxidizers such as chlorine bleach. Oxygen bleach is considered to be somewhat less aggressive on bacteria and viruses, however, when combined with the other cleaning factors in a laundry formula, oxygen bleach is effective in deactivating residual microbes.
How do you choose? So what do all these differences mean to you? Check what you need in a bleach. If you are running most of your operations at low temperature, chlorine bleach, at the right pH is probably your best choice. But, since chlorine is difficult to rinse at low temperature, it is essential that you use an anti-chlor to prevent cotton fabric damage.
If you have a tunnel washer your best choice is probably oxygen bleach, especially if it is shorter than 12 mods. The use of oxygen in shorter tunnels let’s you wash and bleach in the same zone. And oxygen bleach in this application is less aggressive on colors. And as an added benefit in the tunnel, oxygen bleach is less aggressive on the stainless steel when it evaporates, so you can minimize potential rusting issues that may be a problem with chlorine bleaches.
Or maybe you have heavy soiled textiles that need super stain removal performance. Then we would select chlorine bleach due to its rapid aggressive action on stains. Maybe you have a lot of light soil classifications, and you want to save water and time. Combining you wash and bleach steps and the use of oxygen bleach would serve you best. There are numerous scenarios that can be considered. The selection of the best bleach depends on your specific conditions and needs. Our recommendation is to check with your laundry chemical technician for his or her advice. Together you can make the best choice.
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