HARD- AND SOFT-MODELLING STRATEGY APPLIED TO A CURING REACTION OF EPOXY RESINS MONITORED BY NEAR-INFRARED SPECTROSCOPY

M. GARRIDO; M. S. LARRECHI; F. X. RIUS

Lisboa

Congreso; IX CAC Chemometrics in Analytical Chemistry; 2004

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Spectroscopic data from monitoring of kinetic process can be analysed using different approaches. The hard-modelling approach consists of the fitting of parameters of a well-known chemical model, which describes the mechanism of the reaction. The soft-modelling approaches allow describing the process without using explicitly the associate chemical model, and only require a series of constraints that are inherent to the chemical knowledge of the system. The results are normally affected by the so-called ambiguities, which can be reduced if additional information of the system is known (selectivity regions, pure spectra of the reagents or final products). When this information is not available, the interaction between hard- and soft-modelling can help to minimize the ambiguities and provides the rate constants as additional output information. The soft-modelling characteristics allow modelling the contributions of the instrumental responses not related to the kinetic process, situation in which would fail hard-modelling approach. In this study the mixed approach is applied to near-infrared data from the monitoring of curing reaction between phenylglycidyl ether (PGE) and aniline (PGE/aniline molar ratio: 1.5:1). No selectivity regions are present and is not possible to obtain the spectrum of the final product, since the reaction does not reach its end. When a new constraint is introduced to force the concentration profiles to fulfill the kinetic model, the obtained profiles represent, in a suitable way, the expected behaviour of the species along the time. Also, the rate constants are obtained and their values are in agreement with those found in the bibliography.