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    Desiccant Sachets: what they are, how they work and what they are used for

    A desiccant is basically a substance that either causes something to become dry or which keeps something in a state of dryness.

    The most commonly used form of desiccant sachet is the ubiquitous silica gel sachet which contains many granules of silica gel. The granules have a porous structure and an extremely large surface area relative to their size which enables them to absorb water efficiently. These granules literally attract water on the basis of vapour pressure, drawing it within their structure. Silica gel will not absorb water indefinitely but will stop at a given threshold. For this reason it is necessary to change silica gel sachets according to the conditions under which they are used and to vary the amount used depending on how much moisture a given environment contains.

    Some silica gels change colour when they have reached a certain degree of moisture which makes them an attractive prospect for those that want to make sure they are operating effectively. These so call self indicating gels are also a good way to ensure that they are being used effectively and in a way that reduces costs. These come in a variety of different colours that are visible through the breathable, porous membrane of the paper. This means that the indicating sachets are particularly useful for those using the gel in situations where prolonged moist conditions may require frequent changing of the sachets.

    It is also worth remembering that this gel will only work effectively in an enclosed or sealed environment because it relies on humidity and changes in pressure to operate. In lay terns this means that a greater area of space surrounding the material to be protected will require more silica gel to maintain the same rate of absorption. A large plastic container for example, may need more gel than a small one. If circulating air is added to the equation then more may be needed to maintain the action of the gel at optimum levels. This ability to regulate moisture in enclosed environments has led to its use in a variety of applications. It has been used in gas masks canisters, for protecting medicines and safeguarding a range of different types of sensitive equipment that could be damaged by moisture. They can be used to prevent mould, corrosion, mildew and odours in a variety of materials which means they have applications for perishable as well as non perishable items.
    It is possible to reuse silica gel if it is gently heated. This will cause it to lose its moisture and return to a usable state. It is also a lightweight material which means that large quantities of it can be stored and handled without too much effort. Relative to the weight of other desiccants it has a far greater absorption rate, so pound for pound there is much to recommend it above other similar materials.

    Silica gel is widely regarded as ‘nearly harmless’ although different types of sachet and silica gel have variable levels of toxicity. It is worth checking into this before deciding on the suitability of the product for the job in hand. Of course this is particularly important for silica gel that may come into contact with food. Silica gel has been used to prevent spoilage of items like dietary supplement pills for example. On the other hand it has also been used to protect sensitive equipment like cameras, mobile phones and laptops from moisture damage. They can be used to preserve cigars at the correct level of humidity inside their protective chamber and may also be used to help keep dehydrated foods at the right consistency. A less palatable use for silica gel (although not the sachets) is in cat litter, where it helps to absorb that which kitty has excreted.

    The basic white, non indicating silica gel is neither toxic nor flammable and is considered to be a neutral material.

    There are two forms of orange self indicating silica gels which are regarded as non toxic. One of these turns from orange to a dark green colour and the other, from orange to clear. There is a blue coloured silica gel sachet that is considered toxic because of the addition of cobalt colouring to the gel. It is nonetheless considered to be non-hazardous for transportation applications.
    Whatever your moisture beating requirements are make sure that you check with a supplier about the best silica sachet options for you. They should be able to advise on the appropriate quantities and types to ensure you get the most moisture out for the last cash in.  


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