Alumina Trihydrate in Paints and Coatings

Demand for Alumina Trihydrate used in paints and coatings is forecasted to drive market growth over the forecast period, due to increasing construction and automotive industries as well as stringent fire safety regulations driving this demand for Alumina Trihydrate.

Alumina trihydrate has low acute toxicity and bioavailability; however, chronic use can lead to hypercalcemia (Poisindex 1998).

Solubility

Alumina trihydrate is a white powder with low solubility in both water and ethanol, but an amphoteric property, meaning that it binds with both acids and alkalis. Dilute sulfuric acid and hydrochloric acid dissolve well while it remains insoluble in nitric acid; its melting point makes it suitable for high-temperature applications like ceramics and enamels, while aluminum metal production as well as being flame retardant filler in polymer composites use it extensively.

The global alumina trihydrate market is estimated to reach more than 100 million tons by 2019 and grow at an average compound annual compound growth rate of approximately 7%. It is divided into applications, product types, end-use industries and end-use applications with plastic end uses accounting for the largest market share due to increasing consumption in construction, automotive and electrical & electronics sectors – due largely in part to carbon emissions reduction requirements driving replacement of metal components with plastic ones in automobile components.

Alumina trihydrate is an extremely useful substance with numerous applications, from ink pigment and paper filler, adsorption, lubricant and refractory material applications, manufacturing of alumina metal manufacturing and as an analytical reagent. Produced through dissolving bauxite in sodium hydroxide using the Bayer process and subsequent separation from solids by heating; however this energy intensive procedure raises environmental concerns.

Inhalation exposure to alumina trihydrate has been linked with respiratory ailments in workers handling it (Ueda et al., 1958; Edling, 1961). Pulmonary fibrosis has also been reported following inhalation exposures involving finely ground pyrophosphate dust and other forms of aluminum (Park et al. 1996 cited in ATSDR 1999).

Precipitated Alumina Trihydrate was the market leader, comprising more than 40% of the global Alumina Trihydrate market in 2019. It offers numerous advantages over ground Alumina Trihydrate, including lower viscosity in polyester SMC applications and better flame retardancy properties. Furthermore, precipitate Alumina Trihydrate can be less costly to purchase because its physically absorbed moisture evaporates when heated compared with decomposing Alumina Trihydrate particles; making this form suitable for applications requiring rapid curing with increased impact resistance and rapid cure timeframes.

Toxicity

Alumina trihydrate is used in the production of aluminum compounds such as calcined alumina, polyaluminum chloride, aluminum sulfate, alumina nitrate and zeolite. Furthermore, it serves as a flame retardant material and smoke suppressant agent as well as thermal insulation material. Antimony has been banned by the European Union. Cadmium provides an effective alternative, offering superior fireproofing qualities and being compatible with many organic solvents. ATH can easily be added to polyurethane, latex and neoprene foam systems, vinyl wall coverings & flooring coverings and rubber wire & cable insulation as a white powder with excellent thermal conductivity and flame suppression abilities. Soluble in water, alcohol and petroleum products; can be washed off using soapy water or acidic solutions; very stable at high temperatures and abrasion-resistant.

Grounded aluminum can be excreted through urine with less than 10% being absorbed (Gorsky et al. 1979), with most being processed through liver metabolism and eliminated via hepatic secretion (Kaehny et al. 1977). Alumina trihydrate, in contrast, is quickly absorbed from the gut into urine via rapid absorption from its source (Lansdown 1973 cited by ATSDR 1999), with only minimal systemic absorption occurring (ATSDR 1999). Bioavailability depends upon both form of administration as well as presence of complexing substances such as calcium citrate which enhances absorption through complex formation (for instance). Calcium citrate can enhances absorption by creating absorbable complexes that increase absorption rates dramatically and thus increasing bioavailability dramatically; dietary calcium citrate enhances absorption through complexing.

Although chronic carcinogenicity data for other aluminum compounds is available, this does not provide enough data for human exposure assessments by dermal or inhalation exposure to Alumina Trihydrate. Therefore, an oral route hazard index of one was chosen.

Subcommittee members determined that Alumina Trihydrate was unlikely to pose a significant noncancer risk via dermal exposure route, based on its water permeability, highest expected application rate of 7.5 mg/cm2, Equation 1 from Chapter 3, and dermal RfD values as determined in Chapter 3. This led them to arrive at 1.5 mg/kg-day as their conclusion.

Bioavailability

Alumina trihydrate (Al3O4) is an inert white powder or granule with excellent thermal stability and low water content, making it suitable for use as an adhesive material in multiple industries. Asbestos can be used as a flame retardant, fire suppressant and smoke suppressant in plastics, rubber, textiles, wire and cable insulation, vinyl wall and flooring coverings and epoxy systems; additionally it may also serve as a whitening agent in paper industries. Production of flame retardant and smoke suppression material takes place via the Bayer process of digestion of bauxite, where constitution water over 180 degrees Celsius is removed to cool its surface and block oxygen entry, giving this material its flame retardant and smoke suppression properties. Flame retardant materials can be used in place of antimony for vinyl as low-smoke non toxic replacement, as well as an essential raw material in products like polyurethane foam systems, cable insulations and thermoplastics.

Abrasion resistant grades of alumina trihydrate are widely used as fillers and extenders in paints, adhesives, sealants and plastics to increase strength, durability and appearance. Alumina trihydrate is also an integral component of solid surface materials used in countertops and bathroom fixtures; its purity and precipitation conditions determine its morphologies – blocky particles with lower viscosity may yield to lower viscosity while platy grains increase viscosity.

Inhalation and ingestion of alumina trihydrate can have detrimental health effects. To address this risk, the Agency for Toxic Substances and Disease Registry has set an intermediate duration oral minimal risk level (MRL) of 2.0 mg aluminum/kg daily in its minimum risk level analysis; furthermore it has determined a lung minimum risk level (LMRL) of 15 mg/m3 aluminum dust dust as an MRL/LMRL combination threshold value.

Increased consumption of plastics by the automotive and construction industries is fuelling global alumina trihydrate market growth. Regulations designed to decrease vehicle weight to improve fuel efficiency and carbon emissions has further encouraged use of plastics as an alternative material to metal.

The market can be divided by end-use industry into plastics, building & construction, paints & coatings and other applications. Plastics currently hold the largest share in this market followed by building & construction and paints & coatings segments. Plastics is expected to experience the fastest growth due to rising consumer awareness and regulations that mandate car body weight reductions.

Siguranța

Annual production of Alumina Trihydrate (ATH) is predominantly used as a flame retardant. When integrated into polymer molecules, ATH creates a chemical barrier which delays fire propagation by emitting water vapor that dilutes into the atmosphere to help reduce combustion and stop its spread. Furthermore, rubbers often incorporate this substance to improve physical properties.

Alumina trihydrate may not be as absorbed by the body as easily due to limited solubility data; however, such information cannot be extrapolated quantitatively to bioavailability as there may be unknown influences such as diet which affect absorption.

When taken internally, Alumina Trihydrate (ATH) is excreted through the feces without being absorbed systemically. Although nonirritating when inhaled as fine dust particles, prolonged exposure may cause respiratory irritation and should be avoided to avoid adverse health outcomes.

Due to its low toxicity, alumina trihydrate does not pose a significant environmental hazard. While it does not pollute soil or water sources, improper handling procedures and disposal could release excessive dust particles which may irritate eyes, nose and throats.

Alumina trihydrate’s thermal stability makes it suitable for applications that demand higher temperatures, including use as an antacid to buffer stomach contents’ pH levels. Production occurs via the Bayer process which dissolves bauxite in sodium hydroxide under elevated temperatures.

The Agency of Toxic Substances and Disease Registry has set an oral reference dose (RfD) of 1.5 mg aluminum/kg daily for alumina trihydrate. This RfD was calculated assuming a child is exposed to alumina trihydrate by sucking on 50 cm2 of fabric coated with it over two years and one hour per day, for two years and one hour/day. Oral cancer risk was estimated using a combination of skin fibrosarcoma, lung and colon cancer risk estimates for rats and mice exposed to Alumina trihydrate. These estimates were then multiplied by a composite uncertainty factor of 300 (10 for interspecies extrapolations and 10 for intraspecies variability; see Table 6-3 in the Quantitative Toxicity Assessment section). The cancer hazard index generated from this process was then divided by RfD to obtain oral RfC values.