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Three fluorescent dyes were used in this study: bis(2-benzoxazolyl) stilbene (BOS), perylene, and bis(2,5-tert-butylphenyl)-3,4,9,10-perylenedicarboximide (BTBP).
For the preparation of polyethylene doped with BTBP, a 5 kg batch of PE pellets was prepared by pouring a solution of dye (toluene solvent) over 25% of the pellets, allowing the solvent to evaporate, leaving behind BTBP coated pellets.
For BTBP, an air-cooled argon ion laser tuned to 488 nm (Melles Griot) was used, and for BOS and perylene, a xenon arc lamp, filtered with 10 nm bandpass filters centered at 365 nm and 405 nm, respectively, was used for excitation.
Measurements of fluorescence anisotropy of BTBP doped into polyethylene were carried out as a function of pressure drop (shear stress) during extrusion through the die.
7, we plot the results from extrusion of polyethylene doped with BTBP dye.
The value of anisotropy for BTBP in polyethylene at 180[degrees]C, 0.32, is lower than the possible maximum of 0.40 (see Eq 6) because the BTBP molecule has some rotational freedom during its fluorescence decay that causes depolarization.
For example, fluorescence temperature measurements of stretched polypropylene doped with BTBP can be made using the ratio of intensities at 544 nm and 577 nm, but another wavelength pair (535 nm and 550 nm) are used for measurements of an unoriented polypropylene matrix.