What is a desiccant?
A desiccant is a substance that induces dryness in its environment. The word desiccant dates from the 17th century and derives from the Latin word desiccant, meaning making thoroughly dry’, which sums up the use of desiccants very well.
What is silica gel?
Silica gel is the most commonly used desiccant. Despite the name, silica is not actually a gel but a solid, usually found in the form of small round beads.
Silica is naturally occuring and found in quartz and sand. It is chemically inert, non-toxic, non-flammable and non-water soluble, whilst also being highly hygroscopic, meaning that it absorbs water very efficiently.
Silica gel has been produced synthetically since the early 20th century, and is now used widely. New shoes often come with a small silica gel packet in the box to avoid dampness, and many cat litters are at least partly composed of silica gel beads. There are many other applications of silica gel in chemistry, water filtration, packaging, storage and the food industry.
What is indicating silica gel?
Indicating silica gels gradually change colour as moisture is absorbed and relative humidity increases. This shows the user when the silica gel is working, and when it needs to be renewed. Indicating silica gels are simply silica gel beads with a chemical added, usually in permeable packets or sachets.
There are different chemical additives used in indicator silica gel sachets. The most common types until recently were cobalt(II) chloride and methyl violet. Cobalt(II) chloride transitions from blue when dry to pink when wet, but is toxic and carcinogenic. Methyl violet changes from orange to green, or orange to colourless, but is also toxic. Both these types of indicator still have uses, particularly in medicine and storage, but are unsuitable for food applications.
At Mylar Shop, we sell neither cobalt(II) chloride nor methyl violet.
The indicating additive in our silica gel sachets is iron salts. They turn from bright orange when dry to pale yellow when used and are non-toxic and non-carcinogenic, so suitable for food storage. They are also reusable.
What are the benefits of silica gel?
Like all desiccants, silica gel reduces the humidity or moisture within an enclosed environment. This prevents chemical reactions that may spoil the contents, whether you are stroring food, electronics, medical equipment, or collectibles.
Advantages of silica gel over other desiccants include:
- High water absorption – up to 35% greater absorption than clay dessicants
- Non-toxic, non-carcinogenic and non-chemically reactive
- Conveniently packaged in permeable sachets in different sizes/weights
- Self-indicating so easy to identify when used
- Robust and easy to use
- Very long shelf-life if stored in an airtight environment
- Can be reused and renewed repeatedly
How do I store silica gel desiccants?
Silica gel starts absorbing moisture as soon as exposed to humidity, so it’s important to store them in an airtight container. Suitable containers include plastic zipper bags, sealed Mylar bags, plastic Tupperware type containers with an airtight lid or an airtight jar such as a Kilner jar.
For best results use a container or bag that is just big enough to contain the sachets, so that there is as little spare air as possible.
If you do incorrectly store your silica gel sachets, or once they have been used and change colour from orange to pale yellow, they can always be restored. Please see the paragraph below for instructions on how to do this.
How do I restore silica gel desiccants for reuse?
The silica gel desiccant sachets we sell are suitable for repeated reuse and renewal.
Silica gel absorbs moisture over a long period, but once used can easily be restored to new again by drying out the beads within the sachet. Doing this is very simple.
All you need to do is heat the sachets to 100-120C until the original orange colour returns. You can do this in a normal domestic oven on a very low setting (Gas Mark 1/2 for gas ovens or 100-120C for electric ovens), or in a microwave, again on a very low setting.
It should take from a few minutes to up to an hour to restore silica gel sachets, depending on the temperature and size of the sachet.
Always keep an eye on the oven or microwave when restoring silica gel sachets, and ere on the side of caution in terms of heat and time. As soon as the original color returns, remove the desiccants and store as in the paragraph above. Be careful when removing from the oven or microwave, as the sachets will be hot, so use oven gloves or tongs.
You can also restore silica gel sachets by leaving in strong sunlight (on a clear, dry and bright day), under a strong lamp that produces heat, or on a radiator. These methods will take a lot longer than using an oven or microwave, and drying time is less easily estimated.
Heating to above 300C will destroy the hygroscopic (water holding) properties of silica gel, so do not heat above 150C.
Silica gel desiccants can be repeatedly used and restored in this way, but the colour change will gradually become less obvious the more times the silica gel is regenerated.
All silica desiccants we supply conform to EU and US FDA regulations for food safety. Please Contact Us if you require certification for silica gel desiccants or any of the products we sell.
If you have any questions about the use, storage or renewal of our silica gel desiccants, please do not hesitate to contact us with your questions using the Contact Us form.
