Titanium dioxide (E 171) is authorised as a food additive in the EU according to Annex II of Regulation (EC) No 1333/2008.  

The skin of an adult person is, in most places, covered with a relatively thick (∼10 μm) barrier of keratinised dead cells. One of the main questions is still whether TiO₂ NPs are able to penetrate into the deeper layers of the skin. The majority of studies suggest that TiO₂ NPs, neither uncoated nor coated (SiO₂, Al₂O₃ and SiO₂/Al₂O₃) of different crystalline structures, penetrate normal animal or human skin. However, in most of these studies the exposures were short term (up to 48 h); only few long-term or repeated exposure studies have been published. Wu et al.83 have shown that dermal application of nano-TiO₂ of different crystal structures and sizes (4–90 nm) to pig ears for 30 days did not result in penetration of NPs beyond deep epidermis. On the other hand, in the same study the authors reported dermal penetration of TiO₂ NPs with subsequent appearance of lesions in multiple organs in hairless mice, that were dermal exposed to nano-TiO₂ for 60 days. However, the relevance of this study for human exposure is not conclusive because hairless mice skin has abnormal hair follicles, and mice stratum corneum has higher lipid content than human stratum corneum, which may contribute to different penetration. Recently Sadrieh et al. performed a 4 week dermal exposure to three different TiO₂ particles (uncoated submicron-sized, uncoated nano-sized and coated nano-sized) in 5 % sunscreen formulation with minipigs. They found elevated titanium levels in epidermis, dermis and in inguinal lymph nodes, but not in precapsular and submandibular lymph nodes and in liver. With the energy dispersive X-ray spectrometry and transmission electron microscopy (TEM) analysis the authors confirmed presence of few TiO₂ particles in dermis and calculated that uncoated nano-sized TiO₂ particles observed in dermis represented only 0.00008 % of the total applied amount of TiO₂ particles. Based on the same assumptions used by the authors in their calculations it can be calculated that the total number of particles applied was 1.8 × 10¹³ /cm² and of these 1.4 x10⁷/cm² penetrated. The surface area of skin in humans is around 1.8 m²  and for sun protection the cream is applied over whole body, which would mean that 4 week usage of such cream with 5 % TiO₂ would result in penetration of totally 2.6 × 10¹⁰ particles. Although Sadrieh et al.concluded that there was no significant penetration of TiO₂ NPs through intact normal epidermis, the results are not completely confirmative.

The future of TiO₂

A legal additive in the United States, titanium dioxide is used in everything from food to consumer goods and the U.S. Food and Drug Administration says regulated use of the product as a color additive in food is safe within certain restrictions.

Nano-sized P25TiO₂NPs were kindly donated by Dr. Scaiano, Ottawa University (Canada). Riboflavin (vitamin B2) was from Sigma and ascorbic acid (vitamin C) and KBr (for IR pills) were from Cicarelli. Base cream for the animal experiments was purchased from Todo Droga and the LED panel was built ad hoc.

This article discusses the discovery of phosphorescent lithopone on watercolor drawings by American artist John La Farge dated between 1890 and 1905 and the history of lithopone in the pigment industry in the late 19th and early 20th centuries. Despite having many desirable qualities for use in white watercolor or oil paints, the development of lithopone as an artists’ pigment was hampered by its tendency to darken in sunlight. Its availability to, and adoption by, artists remain unclear, as colormen's trade catalogs were generally not explicit in describing white pigments as containing lithopone. Further, lithopone may be mistaken for lead white during visual examination and its short-lived phosphorescence can be easily missed by the uninformed observer. Phosphorescent lithopone has been documented on only one other work-to-date: a watercolor by Van Gogh. In addition to the history of lithopone's manufacture, the article details the mechanism for its phosphorescence and its identification aided by Raman spectroscopy and spectrofluorimetry.

Introduction

Titanium dioxide can amplify and brighten white opacity because of its exceptional light-scattering properties. In food and drugs, these properties help to define colors clearly and can prevent products from UV degradation. 

Titanium dioxide (TiO₂) is by far the most suited white pigment to obtain whiteness and hiding power in coatings, inks and plastics. This is because it has an extremely high refractive index and it does not absorb visible light. TiO₂ is also readily available as particles with the right size (d ≈ 280 nm) and the right shape (more or less spherical) as well as with a variety of post-treatments.

However, the pigment is expensive, especially when the volume prices of systems are used. And, there always remains a need to develop a full-proof strategy to obtain the best results in terms of cost/performance ratio, scattering efficiency, dispersion… while using it in coating formulations. Are you searching for the same?

Explore the detailed knowledge of TiO₂ pigment, its scattering efficiency, optimization, selection, etc. to achieve the best possible white color strength and hiding power in your formulations.