SILICA GEL OR ACTIVATED CLAY?
Both have the ability to absorb moisture vapour from the air and are desiccants.
At equilibrium, silica gel will remain “dry” to the touch. Depending on how well the sachet material tolerates heat, silica gel may occasionally be replenished by drying out in an oven. At equilibrium, activated clay will feel damp and is non-regenerating.
One Desiccant Unit (DU) of silica gel = 25grm
One Desiccant Unit (DU) of basic activated clay = 33grm
Therefore, more clay is needed to adsorb the same amount of moisture.
R-Tech offers a modified clay which includes a small percentage of calcium chloride blended with the modified clay. This overcomes the problem of dampness at equilibrium and enhances performance to the same level as silica gel, i.e. One Desiccant Unit = 25grm. It cannot be regenerated, but is a lower-cost alternative to silica gel for general packaging applications.
Small sachets, generally used in contact with pharmaceutical or food products, are almost 100% silica gel.
MOISTURE INDICATOR
R-Tech uses a silica gel impregnated with orange that changes to green when moisture adsorbed. These sachets are only offered in sizes up to 5grm. The material used is a food grade, high tensile strength filter paper which allows the colour change to be seen.
BRITISH STANDARDS
R-Tech Sachets and Desiccant Bags are supplied with a moisture content lower (i.e. better) than that specified by BS7554:1992. The standard for our modified clay products is BS7529:1991 and again, moisture content on despatch is lower than that required by the Standard. We produce sachets and bags for MOD Def.Stan 81-68/5 and MIL-D-3464E.
SHIPPING CONTAINER DESICCANTS
We supply an excellent shipping container desiccant in modern-style packaging, with a hook for hanging – quick and easy to install and safe to remove. Made in Europe using the latest technology, this desiccant has maximum adsorption (3 kilo liquid per pack) but goes solid as equilibrium is reached – no dangerous liquid to dispose of on removal. Supplied in cartons of 12 strips – enough for a 40ft container.
FREQUENTLY ASKED QUESTIONS
Desiccants containing calcium chloride cannot easily be regenerated, but good quality silica gel can be dried out and re-used several times over. It will lose some capacity each time and for best results regeneration should start before the desiccant has reached equilibrium. Be aware that the sachets/bags themselves are made by heat sealing and re-heating may therefore compromise the seal integrity of the bags.
Basic clay is cheaper but does not adsorb as much. This is usually overcome by adding 30% which does add weight and cost – so not all win win. At R-Tech we offer a modified clay which is a lot less dusty and also adsorbs the same amount of moisture vapour as silica gel. Silica gel stays dry to touch, even at equilibrium. Clay can be damp at equilibrium and relies on the encapsulation packaging to ensure that this is not a problem.
Historically Silica gel has been the number one choice of desiccant in the UK and sachets have always been described by weight. In Europe clays were always the predominant choice of desiccant and Germany produced a desiccant unit standard (DU), for clays primarily, which is a method of evaluating the amount of moisture vapour a sachet can adsorb. One DU of most clay products equals 33grm. One DU of R-Tech modified clay is equal to 25grm – the same as 1 DU of silica gel.
Both Silica gel and our Modified Clay desiccant will adsorb up to 30% their own weight in moisture. It is impossible for the product to arrive with you containing no moisture at all but R-Tech desiccants are top quality and will not contain a residual of more than 2% moisture on despatch.
Chemically, silica gel is inert. It would be extremely difficult to eat in any amount—similar to eating sand—but if you could, you should definitely drink lots of water to prevent dehydration. Although not provided by R-Tech, cobalt is an ingredient in blue silica gel sachets and bulk that are readily available. When moisture is absorbed, cobalt turns pink and is used as a “moisture indicator.” Since January 2000, cobalt has been classified as a poison and has to be labelled specifically in the UK and throughout Europe. Our indicator is non-toxic and ranges from orange to green. If in doubt, consult a medical professional or the MSDS.