Overall Introduction of Fluorescent Brightener

What Is Fluorescent Brightener?

Optical brightener sometimes called optical brightening agents (OBAs), fluorescent brightening agents (FBAs) or fluorescent whitening agents (FWA) are colorless to weakly colored organic compounds. When present on a substrate, absorb primarily invisible ultraviolet light in the 300-400 nanometer (nm) range and re-emit in the visible violet-to-blue fluorescent light to yield a brighter, fresher appearance. They are designed to brighten colors or mask yellowing in plastics, lacquers, paints, inks, photo-processing solutions and fibers.

Fluorescent Brightener Synonyms

Here we listed the synonym names of optical brightener which we often see and all refers to optical brighteners in most cases

optical brightener agent
optical brightener
optical whitener
optical whitener agent
optical whitening
optical whitening agent
optical brightening
whitening agent
brightening agent
fluorescent whitener
fluorescent whitening
fluorescent whitening agent
fluorescent brightening
fluorescent brightening agent

Optical Brightener Classification

1)Classification by Application

  • Fluorescent brightener for detergent

include optical brightener CBS-X, DMS/AMS, CBS-155

  • Fluorescent brightener for paper

include Optical brightener PC, BBU/ BBU-L, VBL/VBL-L

  • Fluorescent brightener for fiber and textile

include optical brightener 4BK, ER-I/ER-I L, ER-II/ER-II L, EBF/EBF-L, PF / DT, BA, CXT, R4, MST-L, BAC, SWN / AW-L, WGS, NFW

  • Fluorescent brightener for plastic

include optical brightener OB, OBR, OB-1KSNKCB, KSBFP-127, CBS-127, PF

  • Fluorescent brightener for paint and ink

include optical brightener UVT-1, ST, OEF, RT


2) Classification by Chemical Structure.

1. Toluylene type, with blue fluorescent light, used in cotton fiber, synthesis fiber, paper, soap industries.

2. Vanilla type, with coumarone structure and strong blue fluorescent light, use in celluloid, PVC plastics.

3. Pyrazoline type, with green fluorescent light, used in wool, polyamide, acrylic fibers.

4. Benzo nitrogen type, with red fluorescent light, used in acrylic fiber, PVC, PS.

5. Phthalimide type, with blue fluorescent light, used in terylene, acrylic fiber, cotton fiber.

3) Plastic Fluorescent Brightener Classification

1. Bisbenzoxazole, the chemical structure as below, OB, OB-1, KSN, KCB all belong to this chemical structure

Bisbenzoxazole-optical-brighteners baoxu chemical info@additivesforpolymer.com




2. Phenyl coumarin, chemical structure as below

phenylcoumarin-optical-brighteners baoxu-chemical-info@additivesforpolymer.com




3. distyry-biphenyls, chemical structure as below, CBS-X is with this chemical structure

distyry-biphenyls-optical-brighteners baoxu chemical info@additivesforpolymer.com



How Does Optical Brightener Work? 

Optical brighteners or fluorescent whitening agents (FWA) are colorless to weakly colored organic compounds that, in solution or applied to a substrate, absorb ultraviolet light and re-emit most of the absorbed energy as blue fluorescent light between 400 and 500 nm.

Materials that evenly reflect most of the light at all wavelengths striking their surface appear white to the human eye. Natural fibers, for example, generally absorb more light in the blue region of the visible spectrum (‘blue defect’) than in others because of impurities (natural pigments) they contain. As a result, natural fibers take on an unwanted, yellowish cast. Synthetic fibers also have this yellowish cast, although not as pronounced.

Whiteness in substrates can be improved by (1) increasing reflection (reflectance) or (2) compensating the blue defect. Bleaching has both of these effects to some extent, but invariably leave behind part of the yellowish cast. Even the most thorough bleach cannot remove all traces of a yellowish cast. Before the advent of fluorescent whitening agents (FWA), the common practice was to apply small amounts of blue or violet dyes (called ‘bluing’) to boost the visual impression of whiteness. These dyes absorb light in the green-yellow region of the spectrum, thereby reducing lightness. But, since at the same time they shift the shade of the yellowish material towards blue, the human eye perceives an increase of whiteness.

Unlike dyes, FWAs offset the yellowish cast and at the same time improve lightness because their bluing effect is not based on subtracting yellow-green light, but rather on adding blue light. FWAs are virtually colorless compounds which, when present on a substrate, absorb primarily invisible ultraviolet light in the 300-400 nanometer (nm) range and re-emit in the visible violet-to-blue fluorescent light. This ability of FWAs to absorb invisible short wavelength radiation and re-emit in the visible blue light which imparts a brilliant whiteness to the light reflected by a substrate is the key to FWAs effectiveness.

Test Of Optical Brightener

Appearance, Volatile content, Max melting point, Content are typical testing items in Certification Of Analysis (COA) each mass production batch.
How to test optical brighteners in plastics?
1.Immigration and bleeding
it is better to observe immigration and bleeding of optical brightener in UV lamp, yellow and green spots could be scattered on the surface of plastics. The fluorescent light of spots is much higher than in other areas.
2.Whitening effect
The whitening effect of optical brightener agent could be estimated by the visual method which betters under the sunlight or measured by the colorimeter.
3.Light Fastness
There is no international standard for testing optical brightener lightfastness in plastics. most tests used DIN 54004 for reference. One may better and objective method is to test plastic whiteness movement with exposure time。

How To Choose Optical Brightener Agent?

General Guide

Here we could use optical brightener classification as a general guide which we could know if we choosing the right type of optical brightener for our application
  • Detergent optical brightener including  CBS-X,DMS/AMS, CBS-155.
  • Paper optical brightener includes PC, BBU / BBU-L, VBL/VBL-L.
  • Fiber / Textile optical brightener contains 4BK, ER-I/ER-I L, ER-II/ER-II L, EBF/EBF-L, PF / DT, BA, CXT, R4, MST-L, BAC, SWN / AW-L, WGS, NFW.
  • Plastic optical brightener includes OB, OBR, OB-1, KSN, KCB, KSB, FP-127, CBS-127, PF.
  • Paint / Ink optical brightener are UVT-1, ST, OEF, RT.

Things to Know When Choosing Brightener Agent For Plastics?

1.Whitening Effect
The whitening effect is related to the substrate to whitening, processing conditions and possible interactions with other components in the formulation.
OBAs should compatible with plastic in case of bleeding. Compared with textile, thermoplastic usage OBAs shall require higher heat resistance and lower volatility.
3.Light Resistance
Fluorescent optical brightener had a limited light resistance, much lower than pigments and most plastics. While in many cases, the photochemical degradation of fluorescent whitening agents shall not yellowing the plastics.
In most cases, people would prefer mid to blue to bluish green shade rather than red.
5.Processing condition
To maximize the whitening effect, OBAs should completely resolve or evenly dispensed into the product.
6.Other Components
Other components in systems, such as pigments, UV absorber, titanium dioxide pigments (TiO2 ) absorb light in the same UV wavelength range as fluorescent whiteners, thus reduce OBAs whitening effect. Anatase-type titanium dioxide pigments absorb approximately 40% of the incident radiation at 380nm, while rutile type titanium dioxide pigments absorb about 90%. UV absorber absorber the light as well while whitening effectiveness is less reduced.

Typical Optical Brighteners For Plastics, Detergent

As chart below, we listed the typical plastic and detergent applied optical brightener
OBAs Adding Form
Typical OBAs
Issue to mind
Dry powder mix
Immigration resistance
Dissolve or disperse in Plasticizer
Plasticizer+OBAs Masterbatch
OBAs+PVC Masterbatch
Dry powder mix before processing
Dry powder mix before processing
PC <300
Dry powder mix before processing
Heat stability; volatility
PC >300
Dry powder mix before processing
PU Film
Dry powder mix before process with granules or solution
Single component
Immigration resistance
PU Coating
Dry powder mix before process with a solution
PU Adhesive
Liquid or dispersion
PU form
Polyhydric alcohol soluble
Dry powder mix
KP 127
Immigration resistance
Dry powder mix
Dissolve FWA into UPR
Before curing
No side effect during curing
After treatment necessary
Water base coating

How to choose optical brightener for PVC

It is worth noting that same optical brightener gain different whitening effect in rigid PVC (RPVC)  and flexible PVC (FPVC). Bisbenzoxazole or phenyl coumarin group are often used in PVC. When PVC powder, heat stabilizer, fluorescent brightener agent dry mixed, optical brighteners were evenly dispensed. For flexible PVC, OBAs were dissolved or dispersed into plasticizer. It is better to add FWAs in masterbatch form. For transport PVC, optical brightener plus plasticizer masterbatch or OBAs plus PVC masterbatch were used.
normally,50 to 100 mg/kg is enough. To meet the requirement of extreme white with filler in, 500mg/kg optical brightener agent is added. For rutile titanium dioxide PVC system,1000mg/kg OBAs is suggested. in most cases the, plasticizer in PVC had little effect on OBAs, Processing temperature is normally 100 to 200 degree which means optical brightener heat stability shall meet. We shall pay attention to solubility and immigration which is important to flexible PVC

How to choose optical brightener for polyolefin, polyurethane, engineering plastic, fiber, styrenics, elastomer&rubber?

(this part to be updated)

How to add optical brighteners into plastics?

Optical brighteners are added during thermoplastic molding process, rather than added in liquid form afterward, that’s the word mass-whitening come from.Generally, OBAs were mixed with powder or granules plastic For flexible PVC, OBAs were added in solution form or dispense into plasticizer. OBAs were used in masterbatch form to gain a better dispense effect in plastic. For PET fiber, some OBAs could add during polymerization process which in monomer from. in this way, stable heat resistance and low volatility is required for OBAs
Sign Up for Our Newsletter!
We’ll provide useful product/market info.
[contact-form-7 id=”2272″ title=”Sign Up to Our Newsletter!”]