I. Introduction
Titanium dioxide (TiO₂) is an inorganic white pigment whose main component is titanium dioxide. According to its crystal structure, TiO₂ can be classified into anatase, brookite, and rutile types. Due to its high refractive index, strong tinting strength, excellent whiteness, non-toxicity, and good stability, titanium dioxide is widely used in coatings, plastics, papermaking, and inks, among which the coating industry represents the largest consumption-about 60%.
Whether in solvent-based or water-based coatings, TiO₂ provides not only hiding power and decorative effects but also significantly improves the physical and chemical properties of coatings. It enhances chemical stability, hiding power, tinting strength, corrosion resistance, lightfastness, and weatherability; increases film mechanical strength and adhesion; prevents cracking; and blocks UV radiation and moisture penetration-delaying aging and extending coating life. It can also reduce material consumption and support product diversification.
II. Influence of Titanium Dioxide Particle Size on Coating Hiding Power
Variations in TiO₂ particle shape and size greatly affect the degree of light scattering and are key factors influencing hiding power. Research shows that under identical conditions, when TiO₂ particle size is between 160–350 nm-about 0.4–0.5 times the wavelength of visible light-the scattering ability is strongest, directly improving the coating's hiding performance.
If film-forming materials fail to fully coat the TiO₂ particles, particle contact and agglomeration may occur, effectively increasing particle size and reducing hiding power.
III. Influence of Titanium Dioxide Dispersibility on Coating Hiding Power
In the coatings industry, the dispersion degree of powder particles largely determines product performance. During production, TiO₂ dispersion involves wetting, grinding, and dispersing.
A stable suspension of TiO₂ improves hiding power, but due to TiO₂'s activity and sensitivity to the formulation environment, issues such as flocculation, sedimentation, and instability can occur. Therefore, dispersion quality significantly affects hiding power.
IV. Influence of Dispersant Dosage on Coating Hiding Power
Because TiO₂ particles are smaller than most fillers and tend to aggregate, the choice and dosage of dispersants strongly affect TiO₂ dispersion and thus coating hiding power. Studies show that as dispersant dosage increases, pigment/filler dispersion improves, particle size distribution narrows, and effective particle size decreases-resulting in higher hiding power.
V. Sustainable Development Pathways for Titanium Dioxide in Coatings
As a highly efficient light-scattering pigment, TiO₂ offers excellent whiteness and hiding power. With the rapid growth of the automotive, construction, and water-based coating industries, global demand continues to rise.
However, challenges related to resource consumption, energy use, and environmental impact have intensified. Enhancing the sustainability of the TiO₂ industry has become urgent.
In addition to developing new production technologies, coating manufacturers must explore ways to improve TiO₂ utilization efficiency or identify substitutes to reduce consumption.
1. Improving Titanium Dioxide Utilization Efficiency
In practical applications, TiO₂ agglomeration and flocculation can prevent optimal hiding power even at high pigment content. Therefore, enhancing light scattering efficiency has become a key research focus.
Michael used Monte Carlo simulations to demonstrate that replacing coarse fillers with fine fillers increases spacing between TiO₂ particles, improving hiding through a "pigment spacing" or "pigment dilution" effect. Smaller fillers better separate TiO₂ particles, enhancing scattering efficiency and reducing the TiO₂ amount needed for equivalent hiding.
However, spaced TiO₂ particles still have a tendency to re-agglomerate.
In 2013, Dow Chemical received the U.S. Presidential Green Chemistry Challenge Award for developing EVOQUE™ pre-composite polymer technology. These polymers bind to TiO₂ surfaces, providing spacing that enhances particle distribution and scattering efficiency. This improves hiding power and lowers TiO₂ content by up to 20%, reducing cost while maintaining or improving performance. The technology also improves stain resistance, corrosion resistance, reduces energy consumption, and-according to independent LCA-reduces carbon emissions by over 22% and water usage by 30%.
In 1997, Virtanen introduced TiO₂ "pre-encapsulation" technology, creating core-shell pigments with TiO₂ cores and calcium carbonate shells. The shell provides spacing, enhancing scattering and reducing carbon footprint by about 70%. FP Pigments has commercialized this technology.
Similarly, Chemours developed a treated TiO₂ grade, TS-6300, which features enhanced surface treatment that increases particle spacing and reduces agglomeration. Its increased oil absorption lowers CPVC, allowing air voids in the film to further improve light scattering.
2. Introducing Air
Air in the coating film reduces the refractive index of the resin/air mixture, increasing refractive index contrast with TiO₂ and improving light scattering. Three types of air voids contribute to hiding power:
- Air within resin
- Air within filler particles
- Air at the pigment–resin interface
A classic example is hollow polymer microspheres, first developed in 1984 by Kowalski and commercialized by Rohm and Haas as ROPAQUE™. During drying, water inside the microspheres evaporates and is replaced by air, enhancing dry hiding.
When TiO₂ is partially replaced with hollow microspheres, initial wet hiding may decrease, but dry hiding improves to the level of TiO₂-only coatings. Microspheres also enhance stain resistance, washability, and exterior color retention.
Microporous calcined kaolin from Omya similarly contains enclosed air voids. Produced through rapid calcination, the particles expand internally due to steam pressure, forming closed pores that enhance both wet and dry hiding. Up to 20% TiO₂ reduction is achievable.
Comparisons show:
- Microporous kaolin and hollow microspheres both greatly increase hiding.
- Microporous kaolin tends to create matte effects.
- Microspheres increase gloss.
Above the CPVC, microporous kaolin performs even better, as both internal and external voids contribute to hiding while maintaining low oil absorption and good scrub resistance.
Nguyen et al. further developed polymer–TiO₂ "sandwich" nanostructures, combining TiO₂, air voids, and polymer spacing to provide multiple scattering pathways.
In summary, improving TiO₂ dispersion, minimizing agglomeration, and introducing air-based structures can significantly enhance hiding power, enable partial TiO₂ replacement, reduce carbon emissions, and support the sustainable development of TiO₂.
VI. Applications of Titanium Dioxide
TiO₂ is widely used in coatings, plastics, rubber, inks, paper, chemical fibers, ceramics, daily chemicals, pharmaceuticals, and food products.
Coatings
The coating industry is the largest end-user, particularly for rutile TiO₂. Coatings containing TiO₂ offer bright colors, strong hiding and tinting power, improved film strength and adhesion, UV and moisture resistance, and extended service life.
Plastics
The plastic industry is the second-largest consumer. TiO₂ enhances heat resistance, lightfastness, weatherability, mechanical strength, and lifetime of plastic products.
Papermaking
Papermaking is the third-largest application. TiO₂ improves whiteness, gloss, strength, smoothness, and opacity. Anatase TiO₂ is commonly used for its bluish undertone and brightening effect. Laminated papers require rutile TiO₂ for better heat and light resistance.
Inks
TiO₂ is an essential white pigment in high-grade inks, offering excellent durability, wetting, and dispersibility.
Fibers and Textiles
TiO₂ is used as a delustrant in chemical fibers, usually in anatase form due to its softness. Some grades require surface treatment to reduce photocatalytic degradation of the fibers.
Enamel Industry
High-purity enamel-grade TiO₂ provides strong opacity, uniform particle size, high refractive index, excellent whiteness, and good resistance to acids-producing smooth, thin, durable enamel coatings.
Ceramics
Ceramic-grade TiO₂ features uniform particle size, high refractive index, and excellent thermal stability (withstanding 1200°C for 1 hour without graying). It is widely used in ceramics, construction, and decorative materials.
China's TiO₂ industry began in the mid-1950s. Today, China accounts for 30% of global TiO₂ capacity and is both the world's largest producer and consumer. From 1999 to 2011, China's TiO₂ consumption grew from 248,000 tons to 1.65 million tons-a CAGR of 17.11%.
China currently has over 50 TiO₂ manufacturers, many in the eastern region despite limited raw material resources. Meanwhile, titanium ore resources are mainly located in the southwest. The industry remains relatively fragmented. China's TiO₂ production has shifted from predominantly sulfate-process anatase to mainly rutile grades, now representing over 70% of output. However, high-end TiO₂ still relies heavily on imports.
Domestic chlorinated TiO₂ production remains very limited at about 30,000 tons, though several companies plan to expand chlorination capacity to over 600,000 tons. This period represents a critical stage for upgrading product structure, improving technology, and adopting advanced processes.
VII. Conclusion
With increasing environmental pressures and rising awareness of sustainability, the TiO₂ industry-characterized by high pollution and high energy consumption-faces significant challenges. As an essential white pigment in coatings, enhancing TiO₂ utilization efficiency, reducing consumption, and developing alternative materials are crucial steps toward sustainable development.