Cross Polymers: Natural Surfactants for Personal Care Products
What is a cross polymer, and how can a polymer be natural?
Although many cosmetic raw materials being marketed today utilize polymer technology, ancient cultures were known to use natural polymers in combination with other materials to enhance appearance. Gum Arabic (a mixture of natural polysaccharides and glycoproteins from the Acacia Tree) was used for this purpose and it was considered a valued trade commodity during ancient times. Today, the use of natural polymers or polymers derived from natural sources is considered advantageous due to the enhanced biodegradability, low irritation and ability to satisfy market demand for “green” products.
Cross polymers are substances which have an interconnecting covalent bond between polymer chains. This increases the overall molecular weight of the substance and if multiple cross-links are introduced, a gel or network may form. Cross polymers can be made from synthetic monomers such as the acrylate and silicone cross polymers traditionally used in cosmetic formulations, or they can be made using natural bio-based materials. Even though there are no studies confirming health or environmental issues regarding synthetic cross polymers in cosmetic applications, some companies avoid the use of any material identified as a cross polymer simply due to the connotation of synthetic origin.
However, it is entirely possible to create cross polymers that are 100% bio-based. Polymer is a term meaning “many parts” and is used to describe large molecules or macromolecules where repeated subunits form the basic molecule. Polymers and cross polymers are prevalent in nature. For example, a vegetable starch shown here is one example of a natural polymer.
In this structure the repeating unit is alpha-D-glucose. An example of a highly branched natural polymer is glycogen used in liver and muscle tissue to store energy.
A defining characteristic of cross polymers is a covalent bond formed between and among polymer chains. The number and type of cross-links found within the structure will greatly influence the final properties of the material. Proteins are another example of natural cross polymers which utilize crosslinks in their structure.
Chemists today have a wide variety of options when choosing ingredients for cosmetic applications. Many raw materials can be harvested directly from nature or generated from natural resources. (Commonly, a calculation is performed for each ingredient to identify the percentage of natural carbon.) To provide the benefits found when using polymeric ingredients, cross-linking reactions can be introduced using 100% bio-based starting materials. These structures are produced utilizing a cross polymer structure and therefore have “cross polymer” in the INCI name, but the final ingredient can still be 100% bio-based, unlike acrylate and silicone cross polymers in use today.
100% Bio-based Cross Polymer
One example of a 100% bio-based cross polymer is Poly Suga®Mulse D9. The INCI name for this ingredient is Sorbitan Oleate Decylglucoside Crosspolymer. Poly Suga®Mulse D9 is an excellent fragrance solubilizer with an HLB of 12-14 and no eye or skin irritation potential. The structure shown below is linear, but due to the number of potential functional groups which could crosslink, the INCI name contains “cross polymer.”
As a formulator or marketing professional, understanding the basics of what is behind each INCI naming convention and recognizing that not all cross polymers are synthetic is important. If natural ingredients are important to your formula, consider using the percentage of natural carbon for the formulation, marketing, and promotion of products. In order to satisfy informed and demanding consumers, 100% bio-based cross polymers offer a way to bring natural and innovative products to market.