Fabrication of Microcrystalline cellulose and nano-titanium dioxide composites with broad-spectrum UV protection

As a popular physical sunscreen, nano-titanium dioxide (nano-TiO2) can provide protection against UV radiation penetration into the skin and to avoid health problems caused by UVB and UVA irradiation. However, it was found that nano-TiO2 can penetrate the stratum corneum to induce health problems. To address concerns about the safety of nano-TiO2, a micro-sized core-shell microcrystalline cellulose (MCC) and nano-TiO2 composite (MCC@nano-TiO2) was fabricated by low-temperature hydrolysis under strong acidic conditions. The nano-TiO2 was loaded onto MCC, and obtained excellent UV protection performance with a lower dosage of nano-TiO2. First, an MCC suspension with a particle size distribution of 4-20 mu m was prepared with good suspension stability by direct acid hydrolysis and ultrasonic-assisted acid hydrolysis, which could be used as an ideal carrier of nanoTiO2. Furthermore, MCC@nano-TiO2 was fabricated via low-temperature hydrolysis at different pH values. The structures and properties of the MCC@nano-TiO2 were determined. The results showed that nano-TiO2 and MCC were closely connected through Ti-O-C bonds to form a core-shell structure. MCC@nano-TiO2 exhibited exceptional UV protection performance. In particular, MCC@nano-TiO2 with a mixed-crystal phase prepared at pH = 0.4 showed the potential for broad-spectrum UV protection. The relative content of rutile (WR) was 73.1%, the critical wavelength (lambda c) of the UV absorption of the powder was greater than 370 nm, the in vitro SPF value (SPFin vitro) of the cream with 5% addition was 7.99, and the ratio of initial UVA protection index to SPFin vitro (UVAPF0/SPFin vitro) was 0.61. The results could bring new insight into UV protection.