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Statistical Design of Experiments: Study of Cross-Linking Process Through the Phase-Resolved Photoacoustic Method as a Multivariable Response

Volume 59, Number 2 (Feb. 2005) Page 173-180

Dias, D.T.; Medina, A.N.; Baesso, M.L.; Bento, A.C.


This work presents an add-on result of cross-linking using photoacoustic spectroscopy (PAS) phases in a multivariable process using the phase-resolved photoacoustic (PRPA) method. The method is tested to separate contributions from groupings -OH, -CH2-, -CH3, and Si-OH overtones in the range from 700 to 2600 nm. Samples of the copolymers ethylene vinyltrimethoxysilane (EVS) and grafted vinyltrimethoxysilane (VTS) on low-density polyethylene (LDPE) were prepared having concentrations (C) of 3, 5, and 7% of catalyst and temperatures (T) of 70, 80, and 90°C. By considering the condensation reaction, the reduction of -OH groups is monitored. The PRPA analysis was carried out using the surface response methodology and results indicated the optimum point for both answers (signal and phase-resolved) and for both factors of interest (C, T). For the copolymers, it was found that C ≈ (5.00 ± 1.14)% and T ≈ (82.4 ± 4.3)°C, while for grafted LDPE PEg it was found that C ≈ (4.92 ± 0.85)% and T ≈ (80.8 ± 2.5)°C. These results agreed with the chemical analysis for gel content, which showed as the optimum point 5% of catalyst and temperature of 80°C. Further, it is an advantage that the photoacoustic method allows one to per- form a nondestructive analysis.