additives feature | Titanium dioxide
titanium dioxide performance, dialling those param- eters into consideration for a system approach to opacity effi cacy. Full comprehension of the impact of processing conditions, formulation design and end-use requirements are factors that can calculate an optimum opacity solution for the plastic end use.” DuPont’s
Performance Chemicals segment, including the TiO2 business, is expected to complete its spin-off from DuPont by mid-2015, but innovation and new product development continues, notes Niedenzu. Multi-functional TiO2
grades that provide more than
opacity, brightness, and tint strength will continue to be a trend in the coming years, agrees William Lashway, principal engineer for plastics at Cristal. “TiO2
brings a
UV absorbing capability used with durable grades, but there may be more options possible. Also the heat management aspects of TiO2
are fi nding a strong fi t in
the current market and will continue to grow and expand,” he notes. In addition, Cristal is developing a next-generation high-performance masterbatch grade and continues to work on extending durability.
Coatings for specifi c applications Although standard TiO2
pigments are available from
many suppliers, a limited number of suppliers offer treated grades designed to be fi t for a specifi c purpose, adds Kronos’s Scharf. Advanced, coated TiO2
pigments
have the thermal stability and dispersion required for increasingly thinner multilayer fi lms, for example.
Agricultural fi lms for wrapped-bale silage, which are typically multilayer, are a growing area, according to Kronos. White fi lms refl ect thermal radiation better than dark fi lms and thus create more favourable conditions for wrapped silage, Kronos points out. For this application, Kronos 2225 provides durability in outdoor use, is silicone-free, and generates low dust and low volatile compounds during fi lm processing, says the company. At AMI’s Thermoplastic Concentrates conference in January 2014, Richard Bordeleau, technical support
manager at Huntsman Pigments, explained that TiO2 particles can be coated with various types of inorganic coating and with an organic treatment to improve properties such as dispersibility and durability (see box story). To select the best pigment for an application, he
noted, it is important to know whether an application will have outdoor exposure and what level of durability will be required. In addition, identifying the dominant mechanism of degradation (photochemical or photo- catalytic) is important. TiO2
can provide an additional
protection against photochemical degradation of the polymer because TiO2
possesses an intrinsic UV blocking function. However, TiO2 particles can also be a
cause of photocatalytic degradation, because of their strong interaction with UV light. It is therefore important to select the right product based on its inorganic surface treatment. Dense silica and zirconia treated
Types of surface treatments for particles
Speaking at AMI’s Thermoplastic Concen- trates conference in January 2014, Huntsman’s pigments division’s Richard Bordeleau explained the types of
treatments that can be applied to TiO2 pigments. Inorganic coatings (about 1-15% by
weight), include oxides of silica, alumina, zirconia, and phosphate, and hydrous TiO2
. Alumina improves dispersibility and
aids dispersion stability, but provides minimal durability increase. Fluffy silica improves dispersibility and signifi cantly increases opacity in high PVC systems. Dense silica improves dispersibility and signifi cantly increases durability. Zirconia signifi cantly increases durability. Phosphate, added prior to wet milling, improves dispersibility.
18 COMPOUNDING WORLD | October 2014
In addition, organic treatments can be added, typically at less than 1%. Polyols aid milling during TiO2
production and
improve dispersibility. Silicone deriva- tives create a hydrophobic surface. Other patented organic treatments (such as silanes and phosphonated organics)
improve compatibility with resins and can act as a lubricant to improve processability. Huntsman offers a range of titanium
dioxide pigments with various combina- tions of inorganic and organic treatments.
www.huntsman.com
www.compoundingworld.com
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