The market for personal care and home care products is a very complex and saturated one in which efficacy claims, unique packaging or colour are some of the first elements influencing consumers in making purchasing decisions.
Consumers have a high level of expectation regarding all sensorial attributes of a product as they want to feel some pleasure when using it. In the consumer’s mind, the value of the product is not only reflected by its efficiency but also by its appealing look, feel and smell. Visual and sensorial aspects are key in mature, saturated markets. A challenge for manufacturers is to differentiate their products in the marketplace and battle for shelf space. A creative use of colour can attract consumers’ attention and differentiate a product from the competition of from counterfeit products. Products with vibrant colours in sophisticated clear packaging have been gaining a high degree of preference among consumers. However, these products are more susceptible to lightinduced degradation and have a whole set of stabilisation issues.
Impact of light
Once exposed to light, photodegradation of dyes and light sensitive ingredients may occur. The key wavelengths in which photo-induced degradation can occur are believed to be in the UVA/UVB range (280 – 400 nm). The light absorbed in this area causes cleavages and formation of radicals, which via photo-oxidation can further degrade the product. In the case of dyes, the UV light can cleave the chromophore and open the ring structure. This will result in loss of colour. Adding UV absorbency in the product can protect the colour of the product, avoiding fading and discoloration. Many different technical UV filters are used in personal care products and household cleaning products. Among them, benzophenones are the most commonly used UV filters for colour stabilisation. However, with recent concern about safety, formulators are finding new solutions to address this issue.
New blend of UV filters
To match today’s industry needs, a new colour protectant has been developed and patented – PARSOL Guard from DSM. This is an optimised blend of globally approved and safe UV filters such as octocrylene, homosalate, butyl methoxydibenzoylmethane, in combination with a natural antioxidant, tocopherol in sunflower oil (Helianthus annus). While the typical benzophenone filters are effective UVB filters with very limited UVA protection, PARSOL Guard provides broad spectrum protection against UVA and UVB (Fig. 1). Product performance was conducted on products such as fragrances, shampoo and hair gel formulations. Figure 2 shows a typical hair gel formulation with and without colour protection on 12 weeks exposure of daylight. As can be seen in Figure 3, the shampoo without colour protection has faded after 12 weeks exposure in daylight. Considering the cost, two additional UV absorbents priced at 50-70 USD/kg were selected and compared to PARSOL Guard in terms of colour protection efficacy.
Materials and methods
Reagents and equipments
• Benzophenone-4 (CA).
• Sodium benzotriazolyl butylphenol sulfate compound (CB).
• 2-ethylhexyl salicylate/homosalate/ butyl methoxydibenzoylmethane/ tocopherol/sunflower seed oil compound (PARSOL Guard).
• Red 33.
• Acid blue AE.
• 722S type spectrophotometer.
Test systems See formulations.
Test design Samples were prepared and poured into glass bottles for testing. For each test system a corresponding control was set. In the same system and a certain concentration range, the content of pigment has a linear relationship with its absorbance value, so the pigment retention can be calculated by measuring the absorbance values of samples. The samples were placed upright in daylight (8 hours a day in summer) and the content of remaining dye was regularly measured by spectrophotometry, taking the corresponding control sample as reference. The colour retention is calculated as follows: Pigment retention= CC0t x 100% Where Ct: pigment content in sample after t days/weeks of sunlight exposure; and C0: pigment content in sample before sunlight exposure. Three samples were prepared in parallel for each formula and the result given is the average measurement of the three.
Results and discussion
Application in transparent shampoo Figures 4 and 5 show the colour protection efficacy of three different compounds respectively for Acid blue AE and Red 33 in transparent shampoo. As seen from Figure 4, the UV absorbent 2-ethylhexyl salicylate/homosalate/butyl methoxydibenzoylmethane/tocopherol/ sunflower seed oil compound (PARSOL Guard) offers the best colour protection efficacy for Acid blue AE, while sodium benzotriazolyl butylphenol sulfate compound (CB) has the similar protection efficacy with benzophenone-4 (CA). The control, without UV absorbent shows the fastest fading with only 32.54% colour retention after one week. As seen from Figure 5, the colour protection of UV absorbent 2-ethylhexyl salicylate/ homosalate/butyl methoxydibenzoylmethane/ tocopherol/sunflower seed oil compound for Red 33 is slightly better than that of sodium benzotriazolyl butylphenol sulfate compound (CB). In this system benzophenone-4 (CA) shows the poorest protection. Application in perfume Figure 6 shows the colour protection efficacy of the three compounds for Acid blue AE in perfume. As shown on the graph, the samples containing benzophenone-4 (CA) did not perform better than the control: benzophenone-4 has almost no protective role to Acid blue AE. The UV absorbent 2-ethylhexyl salicylate/ homosalate/butyl methoxydibenzoylmethane/tocopherol/ sunflower seed oil imparts significantly better colour protection for Acid blue AE than the other two UV absorbents during the early 50 days of experiment. The perfume formulation containing Red 33 shows tremendous colour fading after 6 days. As shown in Figure 7, only the samples protected with UV absorbent 2-ethylhexyl salicylate/homosalate/butyl methoxydibenzoylmethane/tocopherol/ sunflower seed oil could still show some pigment retention after 6 weeks. The samples protected with sodium benzotriazolyl butylphenol sulfate (CB), with benzophenone-4 (CA) and the control samples completely faded out after 6 days of sunlight exposure. Application in gel formulation As seen in Figure 8, the gel formulation containing Acid blue AE protected by sodium benzotriazolyl butylphenol sulfate (CB), with benzophenone-4 (CA) almost faded out after 4 weeks. The same sample protected with 2-ethylhexyl salicylate/homosalate/butyl methoxydibenzoylmethane/tocopherol/ sunflower seed oil also faded out after 8 weeks. For this system the sequence of colour protection efficacy is 2-ethylhexyl salicylate/homosalate/butyl methoxydibenzoylmethane/tocopherol/ sunflower seed oil >benzophenone-4 (CA) >sodium benzotriazolyl butylphenol sulfate (CB).
Conclusion
In this study three colour protectors were evaluated for their colour protection efficacy on Red 33 and Acid blue AE in different systems. The results indicate that there are large differences between the different tested compounds regarding the colour protection efficacy of different dyes. The level of protection can vary from one specific system to another and there is no compound which can effectively protect all colours in all kind of systems. Overall, 2-ethylhexyl salicylate/homosalate/butyl methoxydibenzoylmethane/tocopherol/ sunflower seed oil compound (PARSOL Guard) could show better protection performance. With its safety profile and efficacy, this blend of globally approved UV filters offers a very good solution to safeguard colours and offer an appealing touch to personal care products in highly saturated markets.
Acknowledgements w Li Shi-zhong, Liu Hui-zhen, Hu Wei-hua (LAF International Daily Chemical Research Center, 515144, Shantou, Guangdong Province, China).
