Yaa Whitening Agent: Properties, Function, Machinery Together With Usages (Part-3)

Whitening Agent: Properties, Function, Mechanism in addition to Usages (Part-3)

Authors: Md. Mosharaf Hossain
Kiriti Kingkar Mondal
Tawhidul Islam
Dept. of Textile Engineering
Primeasia University, Dhaka

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Properties of Whitening Agent

Whiteness & Brightness
To the trained observer, fifty-fifty bleached are whit textile fabric has a slight yellowish tinge. This small-scale sum of yellowish tin laissez passer on the impression of slight soiling in addition to may detract from their aesthetic appeal the presence of slight sum of blueish gives the impression that the textile fabric is whiter. Before advent of OBAs. Improved whiteness was obtained using a laundry blue, which is a blueish pigment.

The evolution of OBAs had meant that this slight improver of blueish tin live on obtained through the calorie-free reflected past times the OBAs inwards the presence of ultraviolet radiation. This makes white textile whiter in addition to brighter. Colored textile materials tend to look brighter. OBAs are acquaint inwards most domestic but these are ordinarily entirely suitable for cellulosic textile material.

Light Fastness
There is large variation inwards the light fastness rating of these compounds when applied to cellulosic in addition to poly peptide fibers their calorie-free fastness gain 1 to 2, in addition to inwards unopen to instance may achieve 3. It should live on pointed out that this piteous calorie-free fastness is non also of import inwards the drive of cellulosic’s, since whatsoever loss of OBAs consequence due to sunlight volition live on replaced inwards subsequent laundering amongst domestic detergent. Fluorescent brighteners on xylon tin achieve a calorie-free fastness rating four amongst selected OBAs, a rating every bit high every bit vii for polyesters, in addition to inwards this shape of acrylic fibers a calorie-free fastness of nigh four – 5.

Figure : Light-sheet interactions

Figure: Specular reflectance, B: Semi glossy-paper in addition to C: Diffused reflectance (Re-drawn from Pauler 2002)

The piteous overall calorie-free fastness of fluorescent brighteners is due to their continuous absorption & emission of calorie-free which final result inwards their chemic degradation.

Washing Fastness
The washing fastness rating of fluorescent brighteners if nigh 3. The fair washing fastness of fluorescent brighteners is due to partly to their lack of substantively of textile fabric in addition to their gradual degradation past times exposure to sunlight. The fair washing fastness may non live on noticeable inwards cellulose because of the presence OBAs inwards domestic detergents when fluorescent are used on other fibers they are applied inwards the manufacturing province of affairs in addition to brighteners are chosen which volition concluding the expected life of the textile article.

Metameric Effect of OBA
Metamerism is a normal phenomenon relating to how the human oculus perceives color. It occurs when “two dissimilar color object accept the same color appearance to normal human viewer nether i calorie-free beginning ( metameric fit ) but aspect dissimilar nether unopen to other calorie-free source( metameric mismatch )” To a impress marker, this way that the painstakingly precise color data applied to each impress volition live on compromised whenever that impress inwards viewed nether a dissimilar calorie-free source. Thus, i principal finish of whatsoever impress marking should live on to avoid metamerism inwards gild to validate the fourth dimension spent on color administration in addition to to uphold the integrity of the reproduction. After all, what proficient is reproduction if it does? Now that nosotros empathise metamerism in addition to why it should live on avoided, how practice OBAs fit into the picture? When OBAs are exposed to UV light, the treated newspaper appears brighter in addition to whiter. When OBAs are non exposed to UV calorie-free (in the evening), the OBAs “lose activity” causing your oculus to genuinely meet the newspaper color without OBAs. This volition aspect creamy or somewhat yellowed. This sum of “OBAs activity loss” volition vary constantly depending upon how much exposure the newspaper has to UV light. Picture the lightening status within of an fine art gallery in addition to how they volition modify depending upon the fourth dimension of day. This volition accept subsequent consequence on the fine art itself; your impress could live on illuminating the print. It a illustration similar this, where in that location is a high UV component, inkjet papers that comprise OBAs volition strongly fluoresce in addition to volition look vivid white. However, inwards the eve when the same impress is displayed amongst depression or non – existent UV element (or incandescent tungsten illumination), the OBAs volition non fluoresce, making the newspaper look yellow, hence causing your eyes to meet the paradigm color differently.

Fluorescence
The might of a meat to absorb calorie-free at a specific wavelength in addition to emit it at a higher wavelength is called fluorescence. Optical brighteners or fluorescent whitening agents are added to amend the appearance properties (brightness, whiteness etc.) of printing in addition to writing papers (Heikkilä et al. 1998). When calorie-free strikes a fluorescent material, unopen to of the electrons larn unloose energy in addition to a part of unloose energy is converted into heat. Thus, the emitted calorie-free has lower unloose energy every bit compared to the incident light, which results inwards longer wavelengths (Hubbe et al. 2008). In contrast, non-fluorescent fabric either completely absorbs in addition to converts such unloose energy to heat, or straight off releases the unloose energy past times emitting calorie-free at a wavelength equal to the incident calorie-free (Hubbe et al. 2008).

Figure 1.3 Energy diagram of fluorescent materials illustrating the unloose energy transitions taking house within electronic orbitals (Re-drawn from Hubbe et al. 2008)

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