The Science Of Sifting In Bulk Bags: Know Your Microns

By troy_lott With 0 Comments

Larger than 20 microns or smaller than 20 microns; know if your product will sift.

Commonly used as shorthand for micrometer, a micron is the measure of length universally used to describe tiny particle size. The official symbol is μm, although it’s acceptable to simplify as um. A micron is a unit of length equal to one-millionth of a meter, a little more than one twenty-five thousandth of an inch. The naked eye can generally see particles larger than 40 microns.

Making the complex understandable: A human hair is 70 microns in diameter. A white blood cell is 25. Milled flour and milled corn range from 1 to 100 microns, while paint pigments can range from 0.1 to 100. Beach sand is enormous in comparison, reaching anywhere from 100 to 10,000 microns in size. Common household crystal sugar is typically 400 microns, while the average powdered sugar particle is approximately 50.

Bulk bags are manufactured using woven polypropylene fabric and are more prone to sifting than solid containers. Sifting occurs when tiny particles displace, using the path of least resistance. The size of the individual polypropylene fabric and how tightly they are woven together can alter the amount the fabric can sift: the tighter the weave of the fabric, the more successful it is at reducing sifting. Flat woven fabrics typically have a tighter weave than circular woven fabrics.

Some particles are too fine and require the bulk bags be made with sift resistant construction. For better sift resistant construction, fabric edges can be wrapped over and sewn together, and a polypropylene coating of approximately 1 mil thick can be added to one side to further reduce the chance of sifting, thus enclosing very tiny products. Super Sack® containers manufactured with sift resistant construction can contain products of 19-20 microns. For particles smaller than 20 microns, the use of a bulk bag liner is recommended. It is important to note that due to the construction of an FIBC, a sift-proof design cannot be achieved unless an inner liner is used.

Besides creating a sift-proof feature for bulk bags, liners can additionally provide barrier properties to products susceptible to chemical reactions. Some products are hygroscopic, or water absorbent, and will agglomerate, or form a rounded mass, when exposed to moisture. For the packaging of such products, the Moisture Vapor Transmission Rate (MVTR) of the liner material should be considered. You can contact a BAG Corp sales representative to discuss your MVTR, OTR (Oxygen Transmission Rate), or to learn the propensity of your specific product to sift in a bulk bag.


About BAG Corp:

BAG Corp is a bulk bag handling and supply chain solutions provider with one mission in mind: Helping businesses manage 100% of their bulk bag needs from a single source. BAG Corp's manufacturing resources for the Super Sack® container and other related FIBC products include our manufacturing operation located in Mexico, in combination with our international manufacturing and warehousing partners. BAG Corp is committed to meeting customer requirements and delivering quality products on time.