In-depth Technical FAQsFluorescent Whitening Agent OB-1: Analysis of Core Questi
Time：2025-09-19Views：
Addressing the more in-depth technical pain points of OB-1 in practical applications, the following answers the core questions of greater concern in the industry by combining its chemical properties and process logic.
1. With the same amount of OB-1 added, why is the whitening effect significantly different across different materials (e.g., PP and PC)?
The core reason lies in the differences in "solubility" and "compatibility" of OB-1 in different polymers, rather than unstable performance of the whitening agent itself.
- The molecular structure of OB-1 is more compatible with non-polar/weakly polar polymers (e.g., PP, PE, PS). In such materials, it can dissolve and disperse evenly, fully absorb ultraviolet (UV) light and convert it into blue-violet light to offset the yellow base color, resulting in a direct whitening effect.
- However, for strongly polar polymers (e.g., PC, PET, nylon), OB-1 has poor compatibility: it either fails to dissolve properly (forming tiny particles that cause the product to appear gray and dim) or has weak interaction with the material molecules, making it unable to exert effective optical complementary color effects. In some cases, uneven dispersion may even lead to "local bright spots".
Key Solution: For polar materials like PC/PET, OB-1 must be compounded with polar whitening agents (e.g., OB-3), or a "polar-modified" dedicated OB-1 grade should be selected, instead of using the general-purpose OB-1 directly.
2. Why does "blooming" (white frost-like substance on the surface) still occur even after adding a dispersant to OB-1?
It is not that the dispersant is ineffective, but that two key variables—OB-1’s "migration threshold" and "processing cooling rate"—are overlooked.
- First, OB-1 has a fixed "saturation solubility" in polymers (e.g., approximately 0.03% saturation dosage in PP). Even with a dispersant, if the added amount exceeds the saturation value of the material, the excess OB-1 will slowly migrate to the surface during subsequent storage/use, causing "blooming".
- Second, excessively fast processing cooling rate (e.g., too low mold temperature during plastic injection molding) leaves OB-1 molecules insufficient time to disperse evenly inside the polymer. They will quickly accumulate on the melt surface and precipitate directly after cooling.
Key Solution: ① First, determine the "saturation dosage" of OB-1 in the target material through small-scale tests (it is better to use a slightly lower amount, as long as it is close to the saturation value). ② Appropriately increase the cooling temperature (e.g., raise the injection mold temperature by 10-20℃) to allow sufficient time for OB-1 dispersion.
3. Why does some OB-1 achieve good initial whitening, but turn yellow after high-temperature storage (e.g., in an oven at 60℃)?
This is triggered by the shortcoming of OB-1’s "thermo-oxidative aging stability", rather than a simple "temperature resistance" issue (OB-1’s melting point of 359℃ refers to the "melting temperature", not "long-term temperature stability").
- The "benzoxazole ring" in the OB-1 molecule undergoes slow oxidative degradation in a high-temperature environment (>50℃) with oxygen, generating small yellow molecular impurities.
- If the product also contains antioxidants (e.g., 1010, 168), free radicals from some antioxidants will react with OB-1 degradation products, accelerating the formation of yellow substances and leading to "increasing yellowing during storage".
Key Solution: ① For products requiring high-temperature storage/use (e.g., automotive interior plastics, high-temperature pipes), OB-1 must be compounded with "high-temperature resistant antioxidants" (e.g., 1098) to inhibit oxidative degradation. ② Control the OB-1 dosage (the less OB-1 used, the lower the total amount of oxidative degradation, and the slower the yellowing).
4. Why does white plastic whitened with OB-1 "first become brighter, then darken and turn yellow" under UV lamps (e.g., simulating sunlight exposure)?
This is a typical process of OB-1’s "photoexcitation-photoaging failure", exposing its core issue of insufficient weather resistance.
- In the initial stage of UV lamp irradiation, OB-1 absorbs UV light and converts it into blue-violet light, enhancing the complementary color effect—hence the "brighter" appearance.
- However, after continuous irradiation (usually >24 hours), the molecular structure of OB-1 is damaged by UV light (the "styrene double bond" breaks), losing its ability to absorb UV light and no longer providing complementary color effects. At the same time, the broken molecular fragments oxidize into yellow substances, causing the product to "darken and turn yellow" instead (this is also why OB-1 is rarely used alone in outdoor plastics).
Key Solution: For outdoor-use products (e.g., outdoor pipes, sunshades), OB-1 cannot be used alone. It must be compounded with "UV absorbers" (e.g., UV-531) + "hindered amine light stabilizers (HALS)" (e.g., 944). The former absorbs UV light to reduce OB-1’s photoaging, while the latter inhibits the yellowing of OB-1 degradation products.
5. For the same "OB-1", why do products from different suppliers vary greatly in whitening effect and stability?
The core lies in differences in "purity" and "impurity content", not whether it is "genuine OB-1".
- Low-purity OB-1 (e.g., purity <95%) contains residual "raw material impurities" from the production process (e.g., o-aminophenol, terephthalaldehyde). These impurities are inherently yellow, which directly offsets OB-1’s whitening effect and may even cause the product’s base color to turn yellow.
- To cut costs, some small manufacturers mix OB-1 with "cheap fillers" (e.g., barium sulfate, talc powder). These fillers cannot whiten and also affect OB-1’s dispersibility, leading to "sufficient dosage but poor effect".
Key Solution: When purchasing, require suppliers to provide a "High-Performance Liquid Chromatography (HPLC) purity test report". Prioritize OB-1 with a purity of ≥98%, and the fewer impurity peaks (especially those at a wavelength of 254nm), the better.
