Optical Brighteners for Plastics: 3 Chemical Classes, Dosage and Food-Contact Limits

Optical brighteners are colourless fluorescent additives that absorb ultraviolet light at about 340 to 370 nm and re-emit it as blue light at about 420 to 470 nm, so a plastic part with a yellow cast looks white at levels between 5 and 1,000 ppm. They add no colour of their own and remove no colour either, which is why a brightener is not a bleach: so which brightener belongs in which polymer, and how much is allowed in food contact?

Among the plastic additives used for appearance, optical brighteners sit in the colorant group even though they are colourless. They work alongside pigments, dyes and titanium dioxide, but unlike those, a brightener adds no reflected or absorbed colour of its own; it only adds fluorescence on top of whatever colour the part already reflects.

This page sets out the fluorescence mechanism behind that whitening effect, the 3 chemical classes used in plastics (bis(benzoxazolyl)stilbenes such as OB-1, bis(benzoxazolyl)thiophenes such as optical brightener OB, and the smaller group of stilbene-biphenyl and coumarin grades), the polymer-by-polymer dosage range, how a brightener competes with UV absorbers and titanium dioxide in the same formulation, how whiteness and yellowness are measured, which grades are listed for food contact in the EU and the US, and who manufactures them.

• 340-370 nm ultraviolet light absorbed, 420-470 nm blue light re-emitted
• 3 chemical classes used in plastics: benzoxazole stilbenes, benzoxazole thiophenes, and stilbene-biphenyl/coumarin types
• 5-10 ppm in unpigmented polyolefins, 50-1,000 ppm in polyester, polyamide, PVC and engineering plastics
• EU specific migration limit: 0.05 mg/kg for OB-1 (FCM 422), 0.6 mg/kg for optical brightener OB (FCM 500)

What Is an Optical Brightener?#

An optical brightener, also called a fluorescent whitening agent, is a colourless organic compound that makes a plastic look whiter by converting invisible ultraviolet light into visible blue light. The Colour Index lists about 400 brightener types under its Fluorescent Brightener series, but fewer than 90 of them are produced commercially, spread across detergents, paper, textiles and plastics.

Optical brighteners are grouped with the colorants for plastics because both change how a part looks, but a brightener adds no pigment. The US Food and Drug Administration codifies the same logic: 21 CFR 178.3297 defines a colorant to include optical brighteners and fluorescent whiteners explicitly, while noting that they "may not themselves be colored". Industry uses the terms optical brightening agent (OBA), fluorescent whitening agent (FWA) and fluorescent brightening agent (FBA) interchangeably for the same class.

How do optical brighteners work in a polymer?#

Optical brighteners work by fluorescence: the molecule absorbs ultraviolet light between about 340 and 370 nm, loses part of the energy as heat, and re-emits the rest as blue light between about 420 and 470 nm, which cancels the yellow tint of the polymer. Brightening runs in 4 steps, and each step is carried by a different acting species.

1. A UV photon between 340 and 370 nm strikes the brightener molecule dissolved in the polymer and is absorbed.
2. The brightener molecule jumps to an excited electronic state and loses part of the absorbed energy as heat within picoseconds.
3. The excited molecule relaxes back to its ground state and re-emits the remaining energy as a blue photon between 420 and 470 nm.
4. The eye sees more visible blue light leaving the surface than fell on it, which offsets the yellow the polymer otherwise reflects.

The two workhorse chromophores in plastics are a bis(benzoxazolyl)stilbene and a bis(benzoxazolyl)thiophene, and both fluoresce by the same 4-step process. Stilbene-type brighteners can fade under prolonged UV exposure through cis-isomerisation of the central double bond, which converts the fluorescent trans form into a non-fluorescent cis form.

Optical brightener vs bleach and blue toner#

An optical brightener is not a bleach: it destroys nothing in the polymer and removes no yellow chromophore, it only adds blue light on top of the reflected spectrum, whereas a blue toner cancels yellow by absorbing the complementary wavelengths and makes the part darker. A bleach or an antioxidant, by contrast, removes or prevents the chromophore that causes the discolouration in the first place; the mechanisms behind that discolouration are set out under why plastics turn yellow or pink.

Do optical brighteners make plastic permanently whiter?#

Only while the brightener survives: because it is dissolved in the polymer and not deposited on the surface, it cannot be washed off, but stilbene-type brighteners can lose effect under prolonged ultraviolet exposure through cis-isomerisation. Our source library holds no service-life figure, in hours or years, for any plastics brightener grade, so no retention percentage is stated here.

What Are the 3 Chemical Classes of Optical Brighteners Used in Plastics?#

The 3 chemical classes of optical brighteners used in plastics are bis(benzoxazolyl)stilbenes such as OB-1, bis(benzoxazolyl)thiophenes such as optical brightener OB, and the stilbene-biphenyl and coumarin types, and the two benzoxazoles carry nearly all of the volume in thermoplastics. Every commercial grade in the class also carries a separate identity in the Colour Index (C.I.) names and numbers system, alongside pigments and dyes.

Melting points and molecular data are given only where a primary source is on record. C.I. Fluorescent Brightener numbers are omitted until they are verified against the Colour Index.

1. Bis(benzoxazolyl)stilbenes: optical brightener OB-1#

Optical brightener OB-1 (CAS 1533-45-5, EC 216-245-3) is a bis(benzoxazolyl)stilbene with a melting point above 359 °C, which is why it survives polyester and polyamide melt processing and dominates fibre and engineering-plastic brightening. Its formula is C28H18N2O2 at a molecular weight of 414.5 g/mol, and it is also known by the synonym 4,4'-bis(2-benzoxazolyl)stilbene. Suppliers recommend OB-1 at 50 to 1,000 ppm (0.005 to 0.1 %) in polyester and polyamide fibres and in polycarbonate and polyester engineering plastics, with the higher end of the range needed when a UV absorber is also in the formulation.

The high melting point is the reason OB-1, rather than the lower-melting BBOT, covers every polymer with a hot melt window. OB-1 is REACH-registered at 100 to 1,000 t/y, is not a Substance of Very High Concern, sits on neither Annex XIV nor Annex XVII of REACH, and is not listed under the Stockholm Convention on persistent organic pollutants. Full identity, physical data and the regulatory matrix for Optical Brightener OB-1 sit on its substance page.

2. Bis(benzoxazolyl)thiophenes: optical brightener OB (BBOT)#

Optical brightener OB (BBOT, CAS 7128-64-5, EC 230-426-4) is a bis(benzoxazolyl)thiophene that melts at 192 to 208 °C and is the standard brightener for PVC and for unpigmented polyolefins, where 5 to 10 ppm is already enough. Its formula is C26H26N2O2S at a molecular weight of 430.6 g/mol, and it is sold under the trade names Tinopal OB (BASF), Benetex OB and Benetex OB Plus (Mayzo). "Tinopal OB" always carries CAS 7128-64-5 on first use; "Tinopal CBS-X" is a different, non-plastics product and is not an equivalent.

BBOT's lower melting point is also its limit: it suits PVC and polyolefin processing windows, while OB-1 is the choice where the melt runs hotter. In PVC and other thermoplastics, BBOT is dosed at 50 to 1,000 ppm (0.005 to 0.1 %), the same range as OB-1 in engineering plastics. BBOT is also used outside its brightening role as a coverage tracer, checked under black light to confirm even application in a coating or adhesive layer. It is REACH-registered at 100 to 1,000 t/y, self-classified by a minority of GHS notifiers as H413, and is not a Substance of Very High Concern. Full identity, physical data and the regulatory matrix for Optical Brightener OB (BBOT) sit on its substance page.

3. Stilbene-biphenyls and coumarin brighteners#

The stilbene-biphenyl brightener with CAS 40470-68-6 is dosed at 50 to 2,000 ppm and is recommended for indoor articles only, because its light stability does not carry outdoor exposure, and it is not cleared for US food contact. This chemistry is distinct from the FDA-listed mixed methylated and unmethylated bis(benzoxazolyl)stilbenes (CAS 5242-49-9 and related), which are a separate entry cleared for rigid PVC at up to 0.05 % and for other polymers at up to 0.03 %.

The coumarin brightener 7-(2H-naphtho[1,2-d]triazol-2-yl)-3-phenylcoumarin (CAS 3333-62-8) is listed in 21 CFR 178.3297 with an unusual thickness-dependent limit: the product of the brightener level in ppm and the article thickness in mils may not exceed 500, and the level itself may not exceed 20 ppm in olefin polymers. In PET fibre, the same coumarin is allowed at up to 0.035 % by weight.

Which Optical Brightener Suits Which Polymer?#

The right optical brightener for a polymer is decided by melt temperature, by whether the part is pigmented and by the food-contact status required: OB-1 for polyester, polyamide and engineering plastics, optical brightener OB for PVC and polyolefins, and a stilbene-biphenyl only for indoor articles. The table below is the master reference for grade, CAS number and typical level by polymer or application.

Supplier ranges are starting points; trials on the actual resin and pigment package decide the final level. The food-contact rows are legal maxima, not recommended dosages.

Request quotes for optical brighteners: send the grade or CAS number, polymer, volume, food-contact requirement and country to the plastic additive supplier finder and get matched to brightener suppliers.

PET bottles, film and polyester fibres#

Polyester takes optical brightener OB-1 at 50 to 1,000 ppm, which is why OB-1 is the default brightener for PET fibre, film and bottle grades. The brightener sits next to acetaldehyde scavengers, reheat additives and toners in the additive package described under additives for PET resin, alongside delustrants such as titanium dioxide in fibre grades.

In fibre applications specifically, the coumarin brightener 7-(2H-naphtho[1,2-d]triazol-2-yl)-3-phenylcoumarin is separately listed in 21 CFR 178.3297 at up to 0.035 % for food-contact PET fibre, a different chemistry and a different limit from OB-1.

Spin-finish, delustrant and other fibre-specific formulation questions are covered under additives for synthetic fibres, which places the brightener in the context of the full fibre additive package.

Polyamide (nylon)#

Polyamide fibres use the same OB-1 at 50 to 1,000 ppm, because a brightener for nylon has to survive both a high melt temperature and a reducing melt. The melting point above 359 °C is the property that lets OB-1 pass through polyamide processing without decomposing, the same property that qualifies it for polyester and polycarbonate. The full PA6 and PA66 additive package is on additives for nylon (polyamide).

Polyolefins: PE and PP#

Unpigmented polyethylene and polypropylene need only 5 to 10 ppm of optical brightener OB, one of the lowest use levels of any plastic additive. A brightener masks a yellow cast; it does not stop the chemistry that causes it. White PE and PP can pink or yellow from over-oxidised phenolic antioxidants together with low-treated titanium dioxide and nitrogen-oxide gas fading, and a brightener dosed at 5 to 10 ppm covers none of those underlying causes.

Because the use level is so low, brighteners for unpigmented polyolefins are almost always introduced through a masterbatch rather than dosed as neat powder, which keeps the metering accurate at single-digit ppm.

PVC#

Rigid and flexible PVC use optical brightener OB at 50 to 1,000 ppm, and its melting point of 192 to 208 °C fits the PVC processing window without the sublimation risk of a lower-melting additive. Where the food-contact status matters, the relevant chemistry changes: US food-contact rigid PVC uses the mixed methylated bis(benzoxazolyl)stilbenes (CAS 5242-49-9 and related), capped at 0.05 % under 21 CFR 178.3297, rather than BBOT itself. Where the brightener fits between stabiliser and lubricant in a full formulation is shown on additives for PVC.

Polycarbonate, ABS and styrenics#

Polycarbonate and polyester engineering plastics use OB-1 at 50 to 1,000 ppm, the same range as polyester fibre, because both need a brightener that does not decompose in a hot melt. Optical brightener OB (BBOT) covers "other thermoplastics" at the equivalent 50 to 1,000 ppm range where the melt window allows it. Transparent and lightly tinted polycarbonate grades are covered in full on additives for polycarbonate.

Our source library holds no brightener dosage specific to ABS, SAN or polystyrene. Styrenic grades and their yellowing behaviour, including where a brightener would fit relative to impact modifiers and antioxidants, are on additives for ABS, SAN and ASA.

Recycled plastics and white masterbatch#

Recyclers use optical brighteners as one of three tools against the grey cast of post-consumer resin, next to carbon-black masking and colour-correction masterbatch. Grey and black post-consumer recyclate varies from batch to batch, and the additive package described under additives for recycled plastics addresses that variability with all three tools together rather than a brightener alone.

Our source library holds no sourced brightener loading specific to a recyclate stream, so this page gives the tool, not a number; a compounder trials the actual let-down against the incoming resin.

OB-1 is a standard component of white masterbatch alongside titanium dioxide, which carries the brightener into the application at a fixed carrier ratio.

How Much Optical Brightener Does Plastic Need?#

Plastics need between 5 and 1,000 ppm of optical brightener, with unpigmented polyolefins at the bottom of the range and polyester, polyamide and PVC at the top. Colorants as a whole make up only 0.01 to 5 wt% of a finished plastic product, and optical brighteners, measured in single-digit to low-hundreds of ppm, sit at the very bottom of that colorant range. Four factors drive where a formulation lands within the 5 to 1,000 ppm span.

• The polymer and its starting yellowness set the baseline dose a brightener has to overcome.
• Whether the part is pigmented matters, because unpigmented polyolefins need the least brightener of any application.
• Whether a UV absorber is present in the same formulation raises the required brightener level, because the two additives compete for the same ultraviolet light.
• The food-contact limit that applies can sit below the supplier-recommended range and becomes the governing ceiling once it does.

A worked example shows the arithmetic: a 1 wt% optical brightener masterbatch let down at a 2 % addition rate delivers 200 ppm of active brightener in the finished part (0.01 x 0.02 = 0.0002 = 200 ppm). Check the arithmetic for other let-down ratios in the let-down ratio calculator.

How Do Optical Brighteners Interact with Other Additives?#

Optical brighteners work inside a package: a UV absorber steals the same ultraviolet light the brightener needs, titanium dioxide sets the whiteness the brightener builds on, and an over-oxidised phenolic antioxidant produces the very yellow cast the brightener is asked to hide. A UV absorbers grade in the same formulation is the single most common reason a brightener needs a higher loading than the supplier's base recommendation.

Beyond the UV absorber competition, an over-oxidised phenolic antioxidants for plastics system is the usual source of the yellow or pink cast that a brightener is then asked to hide, and the phenolic antioxidant converts to a quinone under heat, oxygen and NOx exposure. Zinc stearate remedies that pinking by forming colourless zinc-quinone complexes, which addresses the cause rather than masking the symptom the way a brightener does.

Synergy and antagonism across every additive family, not only brighteners, are mapped under additive interactions, and the same competition-for-light logic that governs UV absorbers and brighteners repeats across several other additive pairs in that reference.

How Is the Effect of an Optical Brightener Measured?#

The effect of an optical brightener is measured as whiteness index and yellowness index to ASTM E313-20 (reapproved 2025), and as colour difference to ASTM D2244-25. Three metrics cover the measurement in practice.

• Whiteness index (WI) to ASTM E313-20 (R2025), valid only where the CIE Y tristimulus value of the specimen is above 65.
• Yellowness index (YI) to the same ASTM E313-20 (R2025), valid only for specimens with a dominant wavelength of 570 to 580 nm.
• Colour difference (Delta E) to ASTM D2244-25, calculated under CIELAB, CMC, CIE94, DIN99o or CIEDE2000 formulas.

A fluorescent brightened sample behaves differently from a non-fluorescent one under different illuminants and instrument geometries, so ASTM E313 restricts comparison to specimens of the same material and appearance; a brightened white plaque is compared only against another specimen of that same material and appearance, never across different resins or finishes. ASTM D1925, an older yellowness index method, was withdrawn in 1995 and must never be cited as a current standard.

Instrument geometry and illuminant choice for fluorescent and non-fluorescent samples alike are explained under colour measurement and matching of plastics.

The yellowness index is the specific metric a brightener is meant to move toward zero or below.

Which Optical Brighteners Are Allowed in Food-Contact Plastics?#

Food-contact plastics may contain only optical brighteners that are listed by name: in the EU, OB-1 (FCM 422), optical brightener OB (FCM 500) and the bis(benzoxazolyl)stilbene mixture (FCM 65) of Regulation (EU) No 10/2011, each within its specific migration limit; in the US, the brighteners named in 21 CFR 178.3297, each within its weight limit for the polymer. No brightener is "FDA approved"; the correct terms are "listed", "authorised" or "cleared under 21 CFR 178.3297".

EU: Regulation (EU) No 10/2011 entries FCM 422, 500 and 65#

OB-1 carries the tightest specific migration limit of the three EU-listed brighteners: 0.05 mg/kg of food under FCM 422, with an Annex I note recording the risk that this limit can be exceeded in fatty food simulants. Optical brightener OB (BBOT) carries FCM 500 (Ref 38560) at a specific migration limit of 0.6 mg/kg, twelve times looser than OB-1. The third entry, FCM 65 (Ref 67155), covers a mixture of methylated and unmethylated 4,4'-bis(2-benzoxazolyl)stilbenes in a ratio of 58-62 : 23-27 : 13-17 %, restricted to a maximum of 0.05 % w/w in the formulation.

US limits are maximum use levels, not recommended dosages. Check the food type and the condition of use in 21 CFR 178.3297 for the specific article.

Alongside the specific migration limits above, the generic overall migration limit of EU 10/2011 applies: 10 mg/dm² for all substances combined, on top of any individual SML. Fatty-food simulant testing, which is the condition flagged for OB-1, is described under migration testing of plastics for food contact.

US: 21 CFR 178.3297 limits#

In the United States, optical brighteners are regulated as colorants: 21 CFR 178.3297 defines a colorant to include optical brighteners and fluorescent whiteners, which may not themselves be coloured, and each listed brightener carries its own weight limit. The regulation requires use under good manufacturing practice, at levels not in excess of those reasonably required to accomplish the intended effect.

The page's most useful comparison sits in the gap between the supplier-recommended range and the legal ceiling: OB-1 is recommended by its supplier up to 1,000 ppm but capped at 0.025 % (250 ppm) in food-contact polymers under 21 CFR 178.3297, and BBOT is recommended up to 1,000 ppm but capped at 0.015 % (150 ppm) under conditions of use A-H, or 0.05 % (500 ppm) for a narrower list of food types and conditions. A formulator working from the supplier datasheet alone can therefore land above the legal food-contact maximum without checking the eCFR entry directly. The 275°F (135°C) condition on OB-1 describes the temperature of the finished food-contact article in use, not a processing-temperature ceiling; OB-1's melting point stays above 359°C, so it is not a limit on extrusion or moulding temperature.

Its food-type and condition-of-use codes are decoded in full on 21 CFR 178.3297. The complete food-packaging additive package, including barrier and scavenger additives alongside colorants, is on additives for food packaging.

Colorant purity rules: Resolution AP(89)1 and national lists#

Pigments and dyes have no FCM number in the EU, so their purity is judged against Council of Europe Resolution AP(89)1 and national references such as the German BfR Recommendation IX, while optical brighteners are the exception: the three EU-listed brighteners are authorised additives with their own FCM entry and specific migration limit. Colorants as a class sit outside the Union list of Regulation (EU) No 10/2011, and Resolution AP(89)1 plus national lists (including the Swiss and Italian references) fill that gap for pigments and dyes in the EU market.

The numeric purity limits commonly associated with AP(89)1, such as heavy-metal or primary-aromatic-amine ceilings, are not established in our source library against a primary source and are not stated on this page. Purity thresholds for colorants generally are explained on Resolution AP(89)1.

Who Supplies Optical Brighteners for Plastics?#

Optical brighteners for plastics come from BASF (Tinopal), Clariant (Hostalux) and Mayzo (Benetex), alongside a group of Chinese producers, and the same two CAS numbers are sold under all of these names. Buyers should compare brighteners by CAS number and food-contact status, not by trade name, because trade-name equivalence does not guarantee the same particle size, purity or dispersion quality.

Trade-name equivalence means the same CAS number, not the same particle size, purity or dispersion quality.

Plants and grades by company are listed in the directory of pigment manufacturers and suppliers for plastics. Request quotes for optical brighteners: send grade or CAS number, polymer, volume, food-contact requirement and country to the plastic additive supplier finder.

What Else Makes Plastic Look Whiter?#

A white plastic part is the result of three separate tools: titanium dioxide scatters light and delivers opacity, a blue toner subtracts yellow, and an optical brightener adds blue light that was never there. Opacity comes from titanium dioxide (TiO2, Pigment White 6), not from the brightener, which explains why a brightener alone cannot make a transparent part opaque.

Titanium dioxide, blue toners and yellowing control#

Titanium dioxide gives the whiteness a brightener builds on, and a part that pinks in the warehouse needs a formulation fix rather than more brightener. Titanium dioxide (Pigment White 6, CAS 13463-67-7) works by refraction rather than absorption, with an optimal crystal size of about 220 nm for scattering visible light, and it is listed in the EU under FCM 610 without a specific migration limit. The pinking mechanism, driven by over-oxidised phenolic antioxidants together with low-treated titanium dioxide and NOx gas fading, is a formulation problem that a brightener masks but never removes; zinc stearate addresses the cause instead.

Daylight-fluorescent colour, distinct from an optical brightener, comes from fluorescent pigments for plastics, which are coloured, while brighteners are colourless and add no hue of their own.

Optical brighteners outside plastics: detergents, paper and textiles#

Most optical brighteners on the market never see a polymer melt: they are made for laundry detergents, paper and textile finishing, which is a different chemistry set from the benzoxazoles used in plastics. The Colour Index lists about 400 brightener types across all of those applications combined, and fewer than 90 are commercial, a spread that covers detergents, paper, textiles and the plastics chemistry described on this page. This page covers only the plastics-relevant grades; detergent, paper and textile brighteners fall outside plasticadditives.net's scope and are not named here.

Is OB-1 the same as optical brightener OB?#

No: OB-1 (CAS 1533-45-5) is a bis(benzoxazolyl)stilbene melting above 359°C, while optical brightener OB (BBOT, CAS 7128-64-5) is a bis(benzoxazolyl)thiophene melting at 192 to 208°C, and they are used in different polymers at different levels. OB-1 covers hot-melt polymers such as polyester, polyamide and polycarbonate; BBOT covers PVC and unpigmented polyolefins.

Are optical brighteners safe?#

Neither of the two brighteners used in plastics is on the REACH Candidate List, on Annex XIV or on Annex XVII, and neither is listed under the Stockholm Convention. OB-1 is REACH-registered at 100 to 1,000 t/y and self-classified by a minority of GHS notifiers with the hazard statements H315, H319, H335 and H411; BBOT is REACH-registered at the same tonnage band and self-classified by a minority of notifiers as H413. Both classifications are notified, not harmonised. Neither brightener appears on the list of chemicals of concern in plastics.

Do optical brighteners lose their effect outdoors?#

Stilbene-based brighteners lose effect under prolonged ultraviolet exposure through cis-isomerisation, which is why the stilbene-biphenyl grade is recommended for indoor articles only. No outdoor service-life figure, in hours or years, exists in our source library for any plastics brightener grade.

Do optical brighteners wash out of plastic?#

No: in a plastic the brightener is dissolved in the polymer rather than deposited on a fibre surface, so it cannot be rinsed off, although it can migrate out of the polymer over time, which is exactly what the food-contact migration limits control. The EU specific migration limits of 0.05 mg/kg for OB-1 and 0.6 mg/kg for BBOT exist precisely to cap that slow migration out of a food-contact article.