Flexible Gel Packs
Flexible gel packs are re-usesable packs of aqueous gel that remain flexible when in the frozen state. These packs are used in a variety of applications ranging from food packaging to first aid. While the applications can differ greatly, all flexible gel packs contain three main ingredients: water, a freezing point depressant, and a thickener.
Freezing Point Depressants
Water soluble freezing point depressants like glycols, salts, or alcohols are used in gel pack formulations to allow for gels to be cooled well below the freezing temperature of water while remaining flexible. The type and amount of freezing point depressant added to the gel depends on the intended eutectic point and end use temperature for the flexible gel pack.
A thickener must be added that can increase the viscosity of the aqueous medium in the flexible gel pack. There are many types of thickeners that can be used to make water based gels. The type and amount of thickener used determines the viscosity and rheology of the gel pack.
Thickeners Used in Gel Packs
There are two main type of thickeners used to make gel for flexible gel packs; superabsorbent polymers and cellulose ethers. These two families of thickeners each have advantages and disadvantages when used in flexible gel pack applications.
(SAPs) have a high affinity for water and are used to absorb large quantities of water to form a gel. Most superabsorbent polymers are composed of sodium polyacrylate and commercially available in granular form. The amount of water absorbed by a SAP is dependent on the ionic concentration of the aqueous solution and the cross link density of the polyacrylate polymer. SAPs are used in gel packs when a gel with a more "runny" consistency is required.
- Highly efficient (absorbs up to 300 times its weight in water)
- Forms gels quickly
- Gels will leak if gel pack is punctured
- Sensitive to pH and ionic concentration
- Not biodegradable
As the name implies, cellulose ethers are thickeners that are based on cellulose. These polymers consist of a cellulose backbone with hydroxy groups that have been substituted with another functional group. Highly viscous solutions can be produced through the addition of cellulose ethers to water at 0.5-5% by weight. Cellulose ethers are used in gel packs when a gel with a "firmer" consistency are required.
- Gel will not leak if pack is punctured
- Cellulose is natural and will biodegrade
- Stable over a wide pH
- Less sensitive to salt concentration
- More expensive than SAPs
- Can be difficult to hydrate
TEXTURECEL™ Cellulose Ethers
TEXTURECEL™ Cellulose Ethers are sodium carboxymethyl cellulose polymers that are highly efficient thickeners. High molecular weight TEXTURECEL™ grades are ideal thickeners for flexible gel pack applications. Gels formed with TEXTURECEL™ have a firm texture and will not leak if a pack is punctured or ruptured. Additionally, TEXTURECEL™ polymers have food contact approvals making them perfect for gel pack applications that are in close contact with food products.
TEXTURECEL™ Grades for Gel Pack Applications
Selecting the appropriate grade of TEXTURECEL™ depends on the desired physical properties of the gel pack. As a guideline, as molecular weight of the TEXTURECEL™ polymer increases so does the viscosity of the corresponding solution. In some cases selecting the highest molecular weight grade available allows for a reduction in the amount of thickener required to achieve the desired gel consistency. Granular grades of TEXTURECEL™ are typically recommended over powder grades because they are easier to hydrate and form gels faster.
Formulating Gels with TEXTURECEL™
The amount of TEXTURECEL™ required to formulate a gel for flexible gel packs varies depending on the desired consistency of the gel, however, typical usage rates range from 0.5 - 3%. When using TEXTURECEL™ as a thickener it is recommended to first fully disperse it in the water soluble freezing point depressant prior to hydrating with water. This will allow for a smooth gel to be formed that is free from any lumps. Once the gel is formed any other additives can be incorporated. The formulation listed below is typical of a hot or cold gel pack.