BIOSURFACTANTS AND BIOPOLYMERS 469 undergo enzymatic or microbial degradation (28). Biodegradability studies on chitosan show that this biopolymer degrades by enzymatic degradation into nontoxic oligosac- charides. The rate of degradation depends on the molecular weight as well as the degree of deacetylation of chitosan. This biopolymer is also biocompatible to some extent within the human body, making it suitable for application in cosmoceuticals as well (29). Xanthan gum, although completely biodegradable, is an extremely stable biopolymer, and only a few strains of xanthan degrading enzymes have been reported in microbes. As a result, it fi nds widespread use in areas that involve high enzymatic activity as a stabilizer or thickener (30). Biopolyme rs have been shown to increase the susceptibility of nondegradable polymers to biodegradation by photo oxidation. Albertsson et al. (126) demonstrated that granular starch could improve the degradation rate of polyethylene by 10 times when compared with pure polyethylene. FORMULATI ON CONSIDERATIONS Cosmetic formulations should be able to satisfy not just the functional benefi ts but the aesthetic benefi ts required by the consumers as well. They need to achieve their main purpose which can be anything from forming a protective barrier on hair or skin to deliver- ing certain active ingredients. However, the product also needs to appeal to the consumer on application. It should have an ideal consistency (rheology). The cosmetic industry makes use of emulsions, especially oil-in-water emulsions, to formulate products with desirable sensory properties (127). Furthermore, the droplets in the emulsion work as a delivery agent for various antimicrobials, moisturizing agents, or fragrance which are usually entrapped within the emulsion droplets (128,129). Cosmetic products with a long shelf life and good physicochemical and functional properties require the oil-in-water emulsions to be stable. Because of their inherent thermodynamic insta- bility, they require additional emulsifi ers and stabilizers (130). Thus, while formulating cos- metic products, it is vital to take into account the stability and rheology of the fi nal product. FILM FORM ATION For a wid e range of cosmetic and personal care products such as mascara, lipstick, and hair fi xatives, the ability to form a continuous and fl exible fi lm on the required substrate forms an important criterion for adequate performance and functioning of the product. Polymers constitute the main group of fi lm formers in the cosmetic industry. On the application of the polymer solution onto the substrate, the solvent begins to evaporate. As the solvent evaporates, the polymer chains slowly start to entangle and interpenetrate to form a fi lm over the substrate (131). Because of the environmental and health hazards of the synthetic polymers used in cosmetic formulations, there have been many studies on the potential application of biopolymers as fi lm-forming agents in cosmetic products (132–136). Although biopolymers have excellent fi lm-forming properties, the mechanical properties of these fi lms are inferior to that of the synthetic, petroleum derived polymer fi lms (134). Thus, to completely substitute the conventional polymeric fi lm-forming agents used in the cosmetic industry, it is necessary to modify the properties of the bio-based fi lm form- ers. Blending various biopolymers is a good way of creating new materials with improved
JOURNAL OF COSMETIC SCIENCE 470 fi lm properties based on the molecular interactions between the biopolymers (133). Sev- eral researchers have tried to characterize and determine the properties of the fi lms formed by biopolymers such as chitosan, xanthan gum, alginate, and carboxymethyl cellulose for use in the cosmetic industry (132–134). The fi lm-forming properties of chitosan have been an important area of research (133–137). Chitosan fi lms were found to lack resis- tance to water transmission and have poor structural integrity (135). However, Miranda et al. (137) demonstrated that the incorporation of lipids and plasticizers enhanced the hydrophobic character and mechanical strength of the fi lm. Sionkowska et al. (136) re- ported that it was possible to engineer the mechanical parameters of the biopolymer fi lms by blending two or more polymers. The addition of up to 1 wt% of hyaluronic acid to a mixture of chitosan and collagen led to increased mechanical resistance of the fi lm. Fur- thermore, the application of this three-component polymer blend on hair tresses showed an improvement in the mechanical properties of hair by forming a fi lm on the hair fi bers. Thus, this system shows great potential for use in hair care formulations. The addition of xanthan gum can improve the mechanical parameters like the tensile strength of starch-based fi lms. These enhanced fi lm properties emerge as a result of the development of hydrogen bonds between the starch and gum polymer chains. Xanthan gum easily dissolves in cold or hot water without signifi cant effect on its viscosity because of temperature or pH, which is ideal for fi lm formation (132). Another study reported that the addition of 5 wt% cellulose nanocrystals increased the elastic modulus and ten- sile strength of a mixture of carboxymethyl cellulose and starch by 94.77% and 65.86%, respectively, due to strong interfacial interactions resulting from the formation of hydro- gen bonds between the three components (133). It is clear that although biopolymers have great potential as fi lm formers in the cosmetic and personal care industry, further research needs to be conducted to optimize the mechanical properties of these substances. STABILITY Currently, the emulsifi ers used to stabilize oil-in-water systems include petroleum-derived surfactants or animal-based polysaccharides (138). Manufacturers are however shifting to biosurfactants and plant-derived or microbial biopolymers to decrease the harsh ecologi- cal impact of chemically synthesized ingredients. Biopolymers such as xanthan gum and carboxymethyl cellulose have found widespread uses as emulsion stabilizers in the beauty and personal care industry (83). Most biopolymers act as emulsion stabilizers, and they are not good emulsifi ers as this requires them to be surface active. They are typically used in conjunction with biosurfactants to impart stability to systems on a long-term basis (139). They increase emulsion stability by means of electro- static interactions or steric hindrance. The biopolymer molecules adsorb onto the droplets and steric stabilizes the emulsion by forming a layer around the droplets (139). However, certain biopolymers like chitosan are hydrophobically modifi ed to make them good emulsi- fi ers. Desbrieres and Babak (140) showed that the attachment of hydrophobic moieties like alkyl chains to the polymer backbone makes it amphiphilic, thus enhancing its interfacial properties. Another widely used biopolymer in emulsions is xanthan gum. It stabilizes oil- in-water systems through rheology modifi cation. Xanthan gum improves the viscosity of the aqueous phases, thus stopping or decreasing the rate of creaming of the droplets (141).
Previous Page Next Page