Antioxidants & UV stabilizers: new forms, new chemistries.

The latest products bring higher performance with lower volatility, less dust, and even lower cost.

More efficient, less fugitive, easier to handle, and more economical to use - everything you ever wanted in an antioxidant or uv stabilizer is what suppliers are promising from their latest generation of products. A fertile period of R&D activity in the past year or two has led to the introduction of brand-new chemistries as well as new blends of stabilizers in free-flowing, non-dusting granule and pastille forms.

Most of the new antioxidants are geared to polyolefins. In primary antioxidants, the news includes hindered phenolics with low volatility and extractability, new blends, and phenol-free alternatives. Also new are antioxidants that boost performance of HIPS and PVC impact modifiers, plus some liquid alternatives to BHT for stabilizing urethane polyols. Secondary antioxidants include new phosphites and thioesters with improved hydrolytic stability and low volatility.

In uv stabilizers, there are new HALS and blends, primarily for polyolefins, that offer high activity and permanence and have lower interaction with pigments and halogens. There is also a new class of uv absorbers for polycarbonate, a photo-graftable uv absorber for PC, a low-melting benzophenone/benzotriazole for polyester fibers and engineering resins, and a benzotriazole for halogenated polyesters, PUR, and styrenics.

NEW PHENOLICS & BLENDS

Peroxy radicals formed during the very early stages of degradation of polyolefins and most other polymers are the targets of a new sterically hindered, high-molecular-weight phenolic antioxidant from Akcros Chemicals. Lankromark LE314 is said to be superior to conventional phenolics in PP fibers due to its hydrolytic stability. Low volatility, high extraction resistance, and good color retention in PP are also cited.

Both radical-trapping and peroxide-decomposing functions are said to be combined in one molecule with PMC Specialty Chemicals' new sulfur-bridged phenolic antioxidant, Prodox 46S. In most cases, it can be used without a secondary antioxidant, PMC says. Prodox 46S is reported to be especially effective in black LL/LDPE mulch film and wire or cable insulation.

Also new from PMC, through its 1996 acquisition of Germany's Raschig, is a HMW polymeric hindered phenolic, Ralox AC. This low-volatility product is recommended for ABS.

Great Lakes Chemical is entering the metal-deactivator market with the launch of Lowinox MD24, a hindered-phenolic-based product with metal-deactivating groups on it. Polyethylene cable is a key target.

Ciba Specialty Chemicals is in the early stages of commercializing a new antioxidant chemistry with its Irganox HP products for demanding polyolefin applications (see PT, March '97, p. 26). These are synergistic combinations of the firm's new HP-136 cyclic-ester processing stabilizer and Irganox B-Blends. The latter comprise a phenolic antioxidant plus Irgafos 168 hydrolytically stable phosphite. The new ester's lactone functionality is believed to react with polymer radicals before they combine with oxygen, thus stopping degradation at its earliest stage. Ciba is awaiting FDA approval.

Clariant, which acquired the specialty chemicals business of Hoechst Celanese earlier this year, is gearing up for more aggressive marketing of the acquired product lines in North America. Among them is Hostanox 03, a hindered phenolic said to be superior to Irganox 1010 types in imparting long-term heat stability. It also boasts very low migration from polyolefins and much lower water extraction than 1010 types, as well as lower adsorption onto fillers. It reportedly performs well in appliance parts, wire/cable insulation, and thin LL/LDPE films.

Meanwhile, Burlington Scientific recently expanded its Burlox line of antioxidants to include a BHT grade for plastics and rubber. Burlox BHT is said to be suitable for food-contact applications. Efficient production technology is said to make this product extremely cost competitive.

Two relatively new entrants in vitamin E antioxidants are BASF and Ciba (which took over plastics marketing from Hoffmann-LaRoche in 1996). Both firms now offer them in liquid and solid forms and are investigating new formulated systems with greater functionality. These products hold most potential in polyolefin food and medical packaging, where they are said to offer excellent melt flow and color retention and to minimize production of byproducts containing aldehydes and ketones.

Ciba also introduced two new stabilizers specifically for impact modifiers. Irganox 1520 LR is a non-staining, liquid hindered phenolic that can be used instead of TNPP to stabilize butadiene rubber used in HIPS. FDA sanctioned for food contact, it reportedly features high efficiency at low concentrations (0.1-0.2%) and superior stabilization in high-temperature processing.

Ciba has an experimental high-performance antioxidant for MBS modifiers in PVC. CGA AO-141 is a liquid substituted hindered phenolic that reportedly eliminates color development and potential for ignition associated with the usual powder products.

'PHENOL-FREE' ANTIOXIDANTS

For critical-color applications, interest is growing in so-called "phenol-free" stabilizers with low color development. Among them are Ciba's Full Spectrum (FS) systems (PT, July '96, p. 42), which combine a new hydroxylamine secondary stabilizer with a HMW-HALS. FS products are used in PP fibers as substitutes for traditional hindered-phenolic/phosphite systems. Excellent color retention, high thermal and uv stability, and high resistance to gas fading are reported benefits.

Ciba's latest developments in this line include Full Spectrum L (FSL), which utilizes a lactone as the secondary stabilizer and appears most promising for higher-temperature PP nonwovens. Also new is FS-812, a mixture of HMW and LMW HALS plus a benzotriazole uv absorber and hydroxylamine processing stabilizer. It reportedly offers a combination of uv stability and color retention for molded-in-color PP and TPOs.

North American processors will be hearing more about a new stabilizer category that Clariant calls "HATS" (hindered amine thermal stabilizer). Hostavin N-30 (formerly a Hoechst product) is said to fit this description. It's a low-basicity, polymeric, HMW HALS used in geomembranes, black film, and black wire and cable, where it can serve as both an antioxidant and uv stabilizer.

NEW SECONDARY ANTIOXIDANTS

Great Lakes Chemical recently launched two high-performance phosphites. Alkanox 24-44 is said to provide outstanding maintenance of molecular weight, color control, and hydrolytic stability in LDPE and LLDPE. Alkanox P24 reportedly gives excellent processing stability in all polyolefins as well as outstanding protection against color development both with and without phenolic antioxidants.

Witco Corp. has introduced a sulfur-containing secondary antioxidant that is said to provide stability superior to conventional thioesters such as DLTDP and DSTDP. In combination with a hindered phenolic, Seenox 412S reportedly achieves higher temperature stability in PP, PE, and engineering plastics for applications such as automotive under-hood parts.

Also new is Morstille 18, a pastille form of DSTDP from Morton Performance Chemicals.

CONTROLLING HALS MOBILITY

Permanence is one of the benefits claimed for two new polysiloxane-bound HALS products from Great Lakes Chemical. Both are supplied as dust-free mini-pellets. Uvasil 2006 is a blend of two HMW-HALS - polysiloxane-bound Uvasil 299HM plus Lowilite 62, a tertiary HALS with very low basicity. The blend is said to offer high activity and low color during processing and long-term storage or outdoor exposure. It's aimed at color-sensitive PP fiber and HDPE film, as well as thicker parts. Priced 30% lower than Uvasil 299HM alone, it competes with Ciba's Tinuvin 783 - a blend of a workhorse HALS (Chimassorb 944) and a tertiary HMW HALS (Tinuvin 622).

New Uvasil 2007 is a synergistic blend of LMW and HMW HALS said to result in a broad distribution of stabilizer mobility within a polyolefin matrix. Long-term permanence and high activity during outdoor exposure are claimed.

Clariant plans to introduce new photoreactive chemistry to broaden the line started with its Sanduvor PR 31 photoreactive HALS (PT, April, '97, p. 26). This LMW methylated, monomeric HALS remains mobile within the polymer, allowing it to migrate to the surface, where a photo-reaction with light causes it to graft onto the host polymer. In this way, the additive becomes anchored where it is needed most. Its effectiveness has been shown in polyolefins, PUR, ABS, and thermoplastic and thermoset polyesters.

Clariant is also introducing to North America Hostavin N-24, a monomeric LMW HALS for acrylic, PP, HDPE, PS, ABS, PC, polyesters, and nylon. This liquid product, which can be incorporated during polymerization or compounding, is said to have high solubility and compatibility. As a result it can be used where other LMW HALS are too migration-prone. Also unlike other LMW HALS, it has some antioxidant properties. In applications like greenhouses and solariums, Hostavin N-24 is said to ensure long-term transparency.

In the past year, Ciba launched the first in a new series of pesticide-resistant uv-stabilizer systems for agricultural films. They are designed to withstand even high concentrations of pesticides, insecticides, or soil disinfectants. Tinuvin 492 and 494, which are based on a low-reactivity, HMW HALS optimized with co-additives, are said to outperform traditional HALS or nickel quenchers without increasing costs.

Also new from Ciba is a free-flowing, non-dusting granule form of Tinuvin 123 S, an NOR hindered aminoether light stabilizer that was previously available only as a liquid. It's said to provide good gloss and color retention in molded PP and TPO. NOR HALS have low basicity, making them non-reactive with acid catalysts and pigments.

Mayzo, Inc. has introduced BLS-1944, a polymeric HALS equivalent to Ciba's Chimassorb 944.

NEW UV ABSORBERS

A new chemical class of uv absorbers for polycarbonate is being explored by a number of suppliers. The first commercial product in this family is Ciba's Tinuvin 1577 FF, a low-volatility hydroxy phenyltriazine said to offer better cost/performance than traditional benzotriazole systems. Its effectiveness has been demonstrated in PC sheet and films for outdoor glazing and signage.

Sanduvor PR 25 is a new non-staining, highly absorbtive, photo-graftable uv absorber from Clariant. It has the same backbone chemistry as Clariant's PR 31 but without the HALS (piperidine) functionality. It shows most promise in coatings and clear plastics like polycarbonate.

Mayzo has launched BLS-1328, a hydroxyphenyl benzotriazole equivalent to Ciba's Tinuvin 328. It is used in halogenated polyesters, polyurethanes, and styrenics.

Fairmount Chemical has a new heat-resistant, HMW uv absorber that combines a benzotriazole with a benzophenone. Mixxim PB-30 boasts exceptionally low volatility and intense uv absorption over a broad spectrum. It melts at 212 F and reportedly survives processing at up to 512 F, making it a candidate for engineering resins.

New Uses for Familiar Stabilizers

Besides all the new products discussed in the accompanying story, suppliers have identified wider utility for their existing stabilizers:

* BASF has found that TPUs can be stabilized with either an oligomeric HALS, Uvinul 5050, or a combination of a cinnamate uv absorber (Uvinul 3088) and a Vitamin E-based antioxidant (Uvinul 2003).

* BASF's Uvinul 3035 diphenyl acrylate uv absorber has been found effective in rigid PVC, where it imparts no color and does not plate out during calendering. A liquid version, Uvinul 3039, has recently found use in cast PVC and polycarbonate films.

* Uvinul 3050, a tetra-substituted benzophenone from BASF, shows potential in PET, although it can impart a slight color, depending on concentration. Extraction studies are under way.

* Clariant is looking to expand use of its Sandostab P-EPQ, an FDA-sanctioned phosphonite, beyond polyolefins and PS to include higher- temperature engineering resins from ABS and PC to PEI and PPS. Also, the additive recently has been found to be synergistic with all phenolic and thioester antioxidants and with lactones.

* A HMW pentaerythritol diphosphite launched two years ago by Dover Chemical has received the green light from FDA for food-contact use in PP, HDPE, and LLDPE. Structurally similar to Ultranox 626 from GE Specialty Chemicals, Doverphos S-9228 has higher molecular weight and is said to offer excellent hydrolytic stability without addition of inert fillers or tris-isopropanolamine (TIPA). It will soon be available in free-flowing, non-dusting granules.

* A few months ago, GE Specialty. Chemicals received FDA clearance for use of its Ultranox 641 phosphite in LLDPE, LDPE, HDPE, and PP for all types of food packaging, including fatty, aqueous, and aqueous acidic foods. The product is the first of a family of hydrolytically stable solid phosphites based on butyl ethyl propanediol chemistry in place of traditional pentaerythritol derivatives.

New Stabilizers for Urethane Polyols

Two companies have introduced easier-to-handle, non-volatile liquid antioxidant systems to replace BHT in stabilizing polyether polyols for flexible PUR foam slabstock. A third has launched a new antioxidant blend for semi-rigid PUR.

* New Irganox B3557 from Ciba is a combination of Irganox 1135, a low-volatility hindered phenolic, and Irganox 5057 diphenyl amine. This product is said to give better scorch resistance than BHT-based systems and causes less staining and yellowing. Ciba says it exhibits 50% weight loss at 500 F versus up to 50% weight loss for BHT at 284 F.

* PMC Specialty Chemicals offers new Prodox 316, a liquid hindered phenolic based on distyryl paracresol. Showing 50% weight loss at 600 F, it's much less volatile than BHT and eliminates yellowing problems. It costs slightly more than BHT.

* Also new from PMC is a liquid HMW hindered analog of BHT. Ralox 926 (introduced here after PMC's Raschig acquisition in Germany) is less volatile than conventional BHT and is currently being investigated for use in polyether polyols.

* BASF has a new proprietary stabilizer for semi-rigid PUR applications such as automotive window seals. This liquid system - a blend of HALS, uv absorbers, and an antioxidant - is said to be easily soluble in polyols and does not migrate from the PUR or cause fogging.