Wood Powder as a New Natural Sunscreen Ingredient

Mechanistic insights and applications of lignin-based ultraviolet shielding composites: A comprehensive review

Lignin is a green aromatic polymer constructed from repeating phenylpropane units, incorporating features such as phenolic hydroxyl groups, carbonyl groups, and conjugated double bonds that serve as chromophores. These structural attributes enable it to absorb a wide spectrum of ultraviolet radiation within the 250-400 nm range. The resulting properties make lignin a material of considerable interest for its potential applications in polymers, packaging, architectural decoration, and beyond. By examining the structure of lignin, this research delves into the structural influence on its UV-shielding capabilities. Through a comparative analysis of lignin's use in various UV-shielding applications, the study explores the interplay between lignin's structure and its interactions with other materials. This investigation aims to elucidate the UV-shielding mechanism, thereby offering insights that could inform the development of high-value applications for lignin in UV-shielding composite materials.

UV Filters: Challenges and Prospects

The use of sunscreens is an established and recommended practice to protect skin from solar-induced damage. Around 30 UV filters can be used in sunscreen products in the European Union, which ought to follow the requirements of the regulation 1223/2009 to ensure their efficacy and safety for humans. Nevertheless, low photostability and putative toxicity for humans and environment have been reported for some UV filters. Particularly, the negative impact in marine organisms has recently raised concern on the scientific community. Therefore, it is important to develop new UV filters with improved safety profile and photostability. Over the last two decades, nearly 200 new compounds have revealed promising photoprotection properties. The explored compounds were obtained through different approaches, including exploration of natural sources, synthetic pathways, and nanotechnology. Almost 50 natural products and around 140 synthetic derivatives, such as benzimidazoles, benzotriazoles, hydroxycinnamic acids, xanthones, triazines, among others, have been studied aiming the discovery of novel, effective, and safer future photoprotective agents. Herein, we provide the reader with an overview about UV filters’ challenges and prospects, offering a forward-looking to the next-generation of UV filters.

Plant-Based Structures as an Opportunity to Engineer Optical Functions in Next-Generation Light Management

This review addresses the reconstruction of structural plant components (cellulose, lignin, and hemicelluloses) into materials displaying advanced optical properties. The strategies to isolate the main building blocks are discussed, and the effects of fibrillation, fibril alignment, densification, self-assembly, surface-patterning, and compositing are presented considering their role in engineering optical performance. Then, key elements that enable lignocellulosic to be translated into materials that present optical functionality, such as transparency, haze, reflectance, UV-blocking, luminescence, and structural colors, are described. Mapping the optical landscape that is accessible from lignocellulosics is shown as an essential step toward their utilization in smart devices. Advanced materials built from sustainable resources, including those obtained from industrial or agricultural side streams, demonstrate enormous promise in optoelectronics due to their potentially lower cost, while meeting or even exceeding current demands in performance. The requirements are summarized for the production and application of plant-based optically functional materials in different smart material applications and the review is concluded with a perspective about this active field of knowledge.

Optimization of Lutein Recovery from Tetraselmis suecica by Response Surface Methodology

Microalgae have been attracting attention as feedstock for biorefinery because they have various advantages, such as carbon fixation, high growth rate and high energy yield. The bioactive compounds and lutein contained in microalgae are known to be beneficial for human health, especially eye and brain health. In this study, in order to improve the recovery of bioactive extracts including lutein from Tetraselmis suecica with higher efficiency, an effective solvent was selected, and the extraction parameters such as temperature, time and solid loading were optimized by response surface methodology. The most effective solvent for lutein recovery was identified as 100% methanol, and the optimum condition was determined (42.4 °C, 4.0 h and 125 g/L biomass loading) by calculation of the multiple regression model. The maximum content of recovered lutein was found to be 2.79 mg/mL, and the ABTS radical scavenging activity (IC50) and ferric reducing antioxidant power (FRAP) value were about 3.36 mg/mL and 561.9 μmol/L, respectively. Finally, the maximum lutein recovery from T. suecica through statistical optimization was estimated to be 22.3 mg/g biomass, which was 3.1-fold improved compared to the control group.

Transparent Ultraviolet (UV)-Shielding Films Made from Waste Hemp Hurd and Polyvinyl Alcohol (PVA)

This work proposes a new approach to fabricate highly transparent and flexible composite films that exhibit enhanced UV-shielding properties. Lignin has innate UV-shielding properties. However, when purified lignin, which is conventionally extracted through chemical treatment, is mixed with polymeric materials, its presence negatively influences the transparency of the resulting composite. High transparency and UV-shielding are desirable properties for many applications. In this study, composites were made by mixing lignocellulose particles and polyvinyl alcohol (PVA), where lignocellulose particles were obtained from ball-milled waste hemp hurd without chemical treatments. The UV-shielding properties of the resulting composite film, as a function of hemp/PVA weight ratios, were investigated. The intermolecular interactions between the hemp particles and the PVA were characterized using infrared spectroscopy with the presence of -C=O group at 1655 cm-1, providing evidence that the chemical structure of lignin was preserved. The fabricated hemp/PVA films exhibit stronger UV-shielding, in the UVA-I range (340-400 nm) than TiO2/PVA films. The composite films also showed comparable water vapor permeability (WVP) with commercial packaging plastic film made of HDPE (high-density polyethylene). The optimization experiments were reported, with aim at understanding the balance between the UV-shielding and mechanical properties of the hemp/PVA films. The findings of this work can be applicable to the packaging, food and cosmetic industries where UV shielding is of utmost importance, hence adding value to hemp hurd waste.

Preparation and Application of Light-Colored Lignin Nanoparticles for Broad-Spectrum Sunscreens

Recently, natural sun blockers have been drawing considerable attention because synthetic UV filters could have adverse effects not only on humans but also on the environment. Even though lignin, the second most abundant renewable resource on earth, is a natural UV-absorbing polymer, its unfavorable dark color hampers its applications in sunscreens. In this work, we obtained light-colored lignin (CEL) from rice husks through cellulolytic enzyme treatment and subsequent solvent extraction under mild conditions and compared CEL to technical lignin from rice husks using the International Commission on Illumination L*a*b* (CIELAB) color space. Spherical nanoparticles of CEL (CEL-NP) were also prepared using a solvent shifting method and evaluated for broad-spectrum sunscreens. A moisturizing cream blended with CEL-NP exhibited higher sun protection factor (SPF) and UVA PF (protection factor) values than that with CEL. In addition, CEL-NP had synergistic effects when blended with an organic UV-filter sunscreen: CEL-NP enhanced the SPF and UVA PF values of the sunscreen greatly. However, there was no synergistic effect between CEL-NP and inorganic sunscreens. We expect nanoparticles of light-colored lignin to find high-value-added applications as a natural UV-blocking additive in sunscreens and cosmetics.