About Flexible Gel Packs
Flexible gel packs get their name from retaining flexibility upon being frozen. These packs are usually reusable and filled with a thickened aqueous gel. Gel packs can be used for applications ranging from shipping to cold food packaging to pain relief. All flexible gel packs contain mixes of three main ingredients: water, a freeze point depressant, and a thickener. The physical properties and quality of the end product are determined by the selection of these ingredients.
Freeze Point Depressants
While this article primarily focuses on thickeners, it is also important to mention freeze point depressants since they play a key role in formulation. Gel packs use water-soluble materials such as glycols, salts, and alcohols to allow gels to maintain flexibility below freezing temperatures. Determining the freeze point depressant depends on the end temperature and intended eutectic point for the gel pack.
Thickeners
A thickener must be added to increase the viscosity of the aqueous interior of a gel pack. The type and amount of thickener added determines a gel pack's consistency. Thick gels better conform to the shape of the gel pack.
Gel Pack Thickeners
Flexible gel packs use two main types of thickeners: superabsorbent polymers (SAPs) and cellulose ethers, such as carboxymethyl cellulose (CMC). Both thickener types have advantages and disadvantages in flexible gel pack manufacturing.
Superabsorbent Polymers
Due to their high affinity for water,
superabsorbent polymers (SAPs) are named for their ability to absorb large amounts of water, forming a gel. The most common chemistry for these polymers is sodium polyacrylate. The ionic concentration of the aqueous solution and the cross-linked density of the polyacrylate polymer determine the amount of water the SAP absorbs. Superabsorbent polymers are used when a thinner consistency (lower viscosity) is required.
TEXTURECEL™ Cellulose Ethers
TEXTURECEL™ cellulose ethers are a line of highly efficient sodium carboxymethyl cellulose polymers. The ideal TEXTURECEL™ thickeners for flexible gel packs are typically high in molecular weight.
Compared to SAPs, gels formed with TEXTURECEL™ CMC will have a firmer texture, preventing leakage when punctured. If a gel pack containing TEXTURECEL™ ruptures or is punctured, content disposed of down the drain will also not pose a problem as this chemistry is drain safe. This chemistry is nontoxic to the environment and animals. Additionally, TEXTURECEL™ GA, PA, and PPA grades are approved for food contact, making them ideal for gel packs in close contact with food products.
TEXTURECEL™ Grade Selection
The best grade of TEXTURECEL™ CMC to select depends on the intended physical properties of the gel pack. As a guideline for formulating, higher molecular weights of TEXTURECEL™ lead to higher solution viscosities. Choosing the highest–molecular weight grade available can even reduce the amount of thickener needed to achieve the desired gel consistency. TEXTURECEL™ sodium CMC granular grades are usually recommended over powder grades due to their easier hydration and gel formation.
TEXTURECEL™ Recommended Grades
Gel Pack Formulations
Depending on the desired consistency and physical properties, the amount of TEXTURECEL™ CMC required for gel pack formulation will vary. The typical use rates for most formulations range from 0.5% to 3%. It is recommended to fully disperse the TEXTURECEL™ CMC in the water-soluble freeze point depressant before hydrating with water. This will help ensure a lump-free gel. Other additives can be incorporated once the gel is formed. Below is a typical formulation for a cold or hot gel pack.
Summary
The most common thickening agent for gel packs is a form of superabsorbent polymer (SAP), but they are not safe for drains, are not environmentally conscious, and are not approved for food contact. TEXTURECEL™ carboxymethyl cellulose is an ideal alternative that requires fewer considerations when formulating, making manufacturing easier. Gel packs containing TEXTURECEL™ prevent leakage when punctured and will not cause clogging if poured down the drain. Additionally, this chemistry has food contact approvals and is nontoxic to animals and the environment.
Click the link below to talk to a product specialist about your next flexible gel pack project and request a sample of TEXTURECEL™.
