28 SUN CARE
applications such as cosmetic products due to their sulfur contamination, heterogeneity, low efficacy, odour and black colour.22
Limitations of bulk lignin in cosmetic applications Due to the increased demand for bio-based ingredients and the increased strategic relevance of bio-based industries for many countries, new generation biorefineries are going into operation worldwide.23
In contrast to traditional pulp
and paper mills, they use different extraction processes that yield lignin in a close-to-native form without sulphur contamination, strong odour, or black colour. These new generation extraction processes also maintain the functions of the lignin molecule such as protection from UV radiation and oxidative stress. Nevertheless, even this new generation of lignin, in its raw or bulk form, still poses some critical challenges for its use in cosmetics applications,24
as its particles are usually larger
than 10 µm, irregularly shaped and feature a wide distribution of molecular masses and a highly heterogeneous molecular alignment.25,26 It is, therefore, necessary to refine bulk lignin to make it suitable for cosmetic applications.
Refining lignin into cosmetic-grade colloidal lignin particles To maximize the processability and performance of regular lignin particles, they can be transformed into colloidal lignin particles (CLP) with a regular and spherical shape, a narrow range of molecular weights, and tailored primary particle size even smaller than 1 µm. They offer enhanced processability, improved performance, and increased homogeneity, making them suitable for the use in cosmetic formulations. Scanning electron microscope (SEM) images of bulk lignin and CLP are shown in Figure 1.27,28 To demonstrate the general applicability
of CLP in cosmetic products a comparison of emulsions produced with bulk lignin and with CLP has been made. The microscope picture (Figure 1) shows that CLP can stabilize o/w emulsions, forming an even distribution of
Control Sunscreen
Figure 1: (left) SEM picture of bulk lignin and microscope picture of corresponding o/w emulsion with MCT oil; (right) SEM picture of CLP and microscope picture of corresponding o/w emulsion with MCT oil
particles and a very stable droplet network.
Benefits of using CLP in sun protection products CLP have several properties that are very useful for cosmetic applications, specifically sun protection products. The small size and even distribution of CLP in the sunscreen film leads to reflection and scattering of sunlight, which increases the light path length, giving the UV filters more opportunities to absorb or reflect UV radiation.29 Due to their mainly hydrophilic surface
properties, they can stabilize o/w emulsions by aligning at the interface of the oil and water phases and creating a strong droplet network.24 This leads to a better and even distribution of UV filters, further increasing their effectiveness (Figure 2). Additionally, their strong antioxidative behaviour stabilizes UV filters and helps to reduce the negative effects of UV exposure to the skin.30
Sunscreen with CLP Lignovations manufactures cosmetics-grade
CLP through physical processes, increasing the specific surface area without chemical modification. This innovation enhances the efficacy of lignin products by significantly reducing particle size, improving dispersibility, and allowing for the creation of stable suspensions in water. The resulting CLP, range from 100-200 nm in particle diameter and demonstrate superior dispersibility compared to bulk lignin (Figure 1). To proof the SPF boosting ability, an
empirical approach was employed to identify the appropriate formulation route for integrating aqueous CLP into oil-in-water (o/w) cosmetic formulations.
The importance of a stable colloidal system A stable colloidal system is necessary to ascertain the homogeneous distribution of the
Bulk Lignin Colloidal Lignin Particles
Figure 2: Microscope image of an o/w sunscreens containing coated zinc oxide; (left) control formulation without CLP; (right) formulation with 2.5% CLP
PERSONAL CARE February 2024
www.personalcaremagazine.com
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