Desiccants are moisture-adsorbent (hygroscopic) substances that are used in packaging to protect a large number of products from corrosion, mold and other types of moisture-related damage and degradation. Desiccants are essential in maintaining the quality of products and their shelf life.
Two of the most prominent desiccants are silica gel and bentonite clay, which are used to protect a wide range of products including electronics, leather goods, textiles, metal components, foods, pharmaceuticals, nutraceuticals, and medical devices.
When it comes to sourcing the right desiccant for a given application, packaging engineers, responsible for ensuring the shelf life, and the quality of packaged products, face a range of considerations. In this article, various factors of both bentonite clay and silica gel are considered in a range of categories which are essential to making a well-informed sourcing decision: Performance, material composition, production, environmental impact, among other factors.
Bentonite clay is a naturally occurring mineral that forms as a result of the weathering and sedimentation of volcanic ash deposits. The principal ingredient of Bentonite clay is calcium montmorillonite, a chemically inert and non-corrosive substance that is highly absorbent.
After being mined from the ground, Bentonite clay is processed and dried into the form of free-flowing granules. In this form, it attracts and readily binds water vapor within its complex and highly layered structure, allowing it to function as a highly effective desiccant.
Silica gel is a synthetic material and is formed as a highly porous form of amorphous silicon dioxide. This compound is typically produced in the form of transparent beads, each around 2-3 mm in size. Silica gel adsorbs water vapor in an internal network of random, intersecting channels with a range of sizes. Silica gel is produced through a multi-stage chemical process on a huge scale, with the majority produced in China. As a result, silica gel desiccants are generally shipped worldwide in bulk or in the form of individual packages.
In terms of their performance as desiccants, the two materials possess numerous similarities. For example, both are highly adsorbent, meaning that even at full water vapor capacity, they both remain dry and free-flowing, with no apparent change in shape, size or texture. As well as this, both desiccants can be “reactivated” after being oven-dried to remove retained water vapor between uses.
In addition, they are both similar in terms of “unit” weight and relative adsorption performance. According to industry and military specifications including MIL-D-3464 (U.S), DIN 55473 (Germany) and AFNOR NF H00-321 (France), the performance of desiccants is measured in “units”. The DIN and MIL specifications define a unit as the quantity of desiccant that, at a temperature of 25° C, will adsorb 3 g of water vapor at 20% relative humidity and 6 g of water vapor at 40% relative humidity.
According to this standard, a single unit of bentonite clay desiccant weighs about 33 grams, compared to 26 grams for one unit of silica gel. Both will adsorb water vapor equivalent to somewhere in the range of 30-40 percent of their unit weight. (Note: in the AFNOR NF H00-321 specification, one desiccant unit is defined according to 100 g of moisture adsorption.)
While both bentonite clay and silica gel have comparable adsorption performance on a unit for-unit basis, tests have shown that bentonite clay can offer a higher adsorption capacity in some of the most common and industry relevant packaging conditions.
Substantial at low humidity levels, the adsorption capacity of bentonite is seen to further increase with increasing relative humidity. Silica gel is seen to behave similarly but becomes even more adsorbent at higher levels of relative humidity. At higher humidity levels, the very high rate of adsorption of silica gel can, at times, make it difficult to handle.
Figure 1. Comparing desiccant performance
Although bentonite clay is abundant and readily available, only the top grades of bentonite clay are selected by Clariant to meet demanding adsorption requirements. After locating top-grade mineral deposits, Clariant manages all aspects of mining and processing bentonite clay into desiccants at a number of sites worldwide.
In general, desiccant-quality bentonite clay is found in deposits located in the first 40 feet (approximately 10 m) of the earth’s crust. To obtain the mineral, surface mining operations are conducted that expose and allow extraction of the mineral. After the deposit is exhausted, Clariant manages the reclamation and re-cultivation of the mined site to high ecological and environmental sustainability standards.
After being mined, the bentonite clay is transported to a desiccant processing facility where it is processed into high-performance desiccant material. It is put through a mechanical extrusion process, dried to an appropriate moisture content and then graded into uniformly sized, finely granulated material, ready for packaging.
Silica gel desiccant production involves a significantly more complex, multi-step process. This process starts with a raw material, in this case sand, as well as sodium carbonate, a chemical feedstock. The two materials are combined in an energy intensive hydrothermal or furnace process, which is followed by additional processing as a means to produce an intermediate material — sodium silicate.
In a reaction vessel, the sodium silicate is then combined with sulfuric acid to produce sodium sulfate and amorphous silica gel. The sodium sulfate and process effluent are then removed, after which the amorphous silica gel is extensively washed, leaving it ready for processing into desiccant material. It is washed down with water to a level of desired conductivity, heat-dried so that it has a moisture content of below 3%, and then graded prior to packaging.
Figure 2. Comparing production complexity and environmental impact
Manufacturers of a wide range of products are increasingly concerned about the environmental impact of their products and packaging materials, and many are actively looking for alternatives that can offer excellent performance alongside greater sustainability, a reduced carbon footprint, low resource consumption, and a reduced environmental impact.
When environmental impact is considered, bentonite clay can offer an extremely positive package as a desiccant solution. It has many environmental and sustainability advantages when compared to silica gel:
- Bentonite Clay is abundant and naturally occurring.
- After being mined, its production and processing do not require chemical processing or the use of chemical additives or solvents.
- It has a small carbon footprint: only a modest amount of energy is used by the equipment needed to mine, extrude, dry, and sort bentonite clay for packaging. In addition, Clariant is working to further reduce the energy consumption in these processes, for example, through the use of sun drying.
- The significant global availability of bentonite clay ensures that there can be an uninterrupted supply, while the fact that it can be mined at numerous sites for regional production can help to reduce the carbon footprint from transporting this desiccant to markets across the world.
Clariant Desi Pak®: Superior Quality Bentonite Clay Desiccants
A complete line of bentonite clay desiccants, trade-named Desi Pak®, are now manufactured by Clariant. All of the ingredients used in Desi Pak products are sourced by Clariant. The process starts with exploration to identify and acquire top-grade deposits of bentonite clay, through to the mining (extraction) process, and even to the reclamation/restoration process for areas in which mining has been completed.
Clariant has a clear commitment to ecological sustainability: Clariant will restore and re-cultivate all bentonite mining areas to an equal or better state than when its operations began.
Trees planted at a former Clariant bentonite mine.
After its extraction at around 40 bentonite mining sites worldwide, bentonite clay is transported to one of three Clariant production facilities. These facilities produce Desi Pak desiccants to meet demanding global quality standards and are located in:
- Belen, New Mexico, USA;
- Balikesir, Turkey; and,
- Zhenjiang, China.
Clariant Desi Pak® bentonite clay desiccants
When it comes to making decisions about sourcing desiccants, there are numerous important issues that need to be considered. While there are many similarities in the performance of bentonite clay and silica gel, there are important differences, and their meaning to the success of your product, supply chain, customers, and the impact of your operations on the global environment need to be considered.
||Bentonite clay supplies are abundant and available worldwide.
Clariant mines bentonite clay and produces Desi Pak desiccants at 3 locations on 3 continents.
Production requires no chemical feedstocks or processes.
|Silica gel production currently is concentrated at a handful of large plants in China.
Production requires chemical feedstocks.
Production of Clariant Desi Pak bentonite clay desiccants involve:
- Low resource consumption
- Small carbon footprint for mining, processing
- No harsh chemicals
- Minimal water and energy consumption
|Silica gel production:
- Is more energy intensive
- Has a larger carbon footprint
- Consumes more chemicals and fresh water
- Produces significant process effluents/discharges
||Reclamation and replanting of mined areas is well understood, part of Clariant’s commitment to ecological sustainability.
||As a result of high pollution levels, Chinese regulators are placing increased restrictions on the creation and discharge of industrial pollutants in more than 80 industries. Highpolluting plants are subject to closure.
This information has been sourced, reviewed and adapted from materials provided by Clariant Corporation.
For more information on this source, please visit Clariant Corporation.