Abstract Silica is a versatile material employed in different applications fields including aerospace, especially for rocket engines thermal protections. It is known that particles diameter causes variations in the material properties, and the best-known methods for diameter determination in general consist of several steps in sample preparation such as drying, sieving and the determination of the refractive index according different methods. On the other hand, Fourier transform infrared spectroscopy techniques (FT-IR), in reflectance mode, related to the particle size, are less used for this type of determination. Moreover, methodologies in the near infrared region (NIR) are even less explored. Therefore, the aim of this paper is to present a FTIR methodology for diffuse reflectance (DRIFT) in the middle infrared region (MIR) and reflectance analysis in near infrared region (NIRA) for the determination of the particle diameter on silica samples. Both methodologies showed good results. As proven by a test sample analysis, NIRA methodology indicated better precision. Furthermore, considering small and intermediated particle sizes, a tendency towards smaller errors for the absorbance measurements of the samples was found, consistently with the available literature results.

Adesivos poliuretânicos (AD-PU), contendo teor conhecido de isocianato (NCO), foram preparados, nos laboratórios da Rohm and Haas Química Ltda, e amostras foram usadas para a elaboração de uma curva analítica, visando à determinação do teor de NCO por espectroscopia no infravermelho médio (MIR) e próximo (NIR). Os valores de % NCO, obtidos pelo método analítico por via úmida para amostras retiradas durante o processo de fabricação, foram usados como referência. A banda FT-IR escolhida na região MIR foi: 2270 cm-1 (banda analítica). Na região NIR, foi usada uma banda relativa, A4063/A4348. Em ambos os métodos, MIR e NIR, a intensidade das bandas escolhidas e o teor de NCO, obtidos a partir da análise via úmida, foram utilizados para construção de curvas que apresentaram boas correlações lineares (MIR - R = 0,995 e NIR - R = 0,961), que possibilitarão a determinação dos teores de NCO em misturas de composição semelhante.

Polyurethane adhesives reference samples (AD-PU) with known contents of isocyanate (NCO) have been prepared in Rohm and Haas to elaborate analytical curves for determination of NCO content, using MIR and NIR analysis. Wet chemical values were used to determine the content of NCO in the AD-PU samples obtained during the process. The MIR analytical band used was 2270 cm-1 and the NIR relative band was A4063/A4348. Data of absorbance intensity and NCO contents obtained from wet chemical analysis were used to elaborate the analytical curves (MIR - R = 0.995 and NIR - R = 0.961) which should allow for the determination of NCO content in adhesive samples of similar composition.

Técnicas FT-IR de transmissão, reflexão atenuada (ATR), reflexão difusa (DRIFT), microscopia acoplada ao FT-IR (MIC/FT-IR) e detecção fotoacústica (PAS) foram utilizadas para a caracterização de filmes multicamadas. As técnicas ATR, MIC/FT-IR e PAS apresentaram os melhores resultados, provavelmente em função da possibilidade de análise somente da superfície das amostras com cristal (ATR), análise de cada camada da amostra separadamente (MIC/FT-IR) e possibilidade de variação da velocidade de obtenção do espectro (PAS). Dados de análises de microscopia ótica (MO) e calorimetria exploratória diferencial (DSC) foram usados, associados aos dados FT-IR, para a caracterização completa dos materiais.

The transmission, reflection, photoacoustic (PAS) and microscopy FT-IR techniques have been used for characterizing multilayer films. The ATR, microscopy FT-IR and PAS techniques showed better results, probably because it was possible to analyze only the sample surface by ATR, while with MIC/FT-IR each layer of the sample could be studied separately and in PAS the spectra could be obtained at different rates. A complete characterization for the films was achieved by combining with optical microscopy, DSC and FT-IR data.

Samples of epoxy resin (EP) based on the diglycidyl ether of bisphenol A (DGEBA), cured with nadic methyl anhydride (NMA) and mercaptan (CAPCURE 3-800), or amine-phenol (CAPCURE EH-30), respectively, SE 4 and SE 5, were prepared in the stoichiometric ratio determined by the supplier. The curing behaviour of the epoxy systems SE 4 and SE 5 was followed by DSC (Differential Scanning Calorimetry). These SE and their ingredients were analyzed using FTIR transmission techniques (KBr pellets, pyrolysis without control and controlled pyrolysis-FT-IR, the CONTROLPIR/FT-IR) for characterizing the curing agents (CA). The temperature range used for samples pyrolysis was found from TG (thermogravimetry). Thus, the FT-IR bands of liquid pyrolysate obtained by CONTROLPIR/FT-IR were evaluated, in comparison to the reference spectrum of CA. The characterization of CA was also possible, by the analysis of such SE with the TG/FT-IR technique.

Um método SEC com dupla detecção para determinação de distribuição de funcionalidade de resina polibutadiênica hidroxilada HTPB foi desenvolvido, verificando-se a influência desse parâmetro no comportamento mecânico de poliuretano utilizado em motor-foguete fabricado no Centro Técnico Aeroespacial (CTA). O método mostrou-se sensível a pequenas diferenças de funcionalidade e sua distribuição podendo ser utilizado para a caracterização mais completa da resina. Ensaios de tração realizados em amostras de PU sem carga refletiram pequenas diferenças de distribuição de funcionalidade existentes entre os lotes de polibutadieno hidroxilado.

A size exclusion chromatography (SEC) method, with double detection, was developed to determine the functionality distribution of hydroxyl polybutadiene (HTPB) resin, evaluating the influence of that parameter on the mechanical behavior of HTPB polyurethane used as binder in the rocket motors manufactured at Centro Técnico Aeroespacial (CTA). The method showed to be sensitive to small differences in the functionality distribution of the HTPB resin and, thus, can be used for a more complete characterization of the resin. Tensile tests performed on HTPB polyurethane reflected the small differences observed in the functionality distribution of three batches of HTPB.

Um estudo comparativo envolvendo técnicas de análise por espectroscopia no infravermelho com transformada de Fourier (FTIR) de transmissão, reflexão e fotoacústica é apresentado com análise de poliamida-6. O potencial e as limitações destes métodos são investigados para analisar as alterações espectrométricas que ocorrem no interior e na superfície da poliamida-6, reciclada, e irradiada na presença de oxigênio, com feixe de elétrons de 1,5 MeV, na dose de 500 kGy. As técnicas mostram-se sensíveis para detectar pequenas mudanças de estruturas que ocorrem na poliamida-6 reciclada e irradiada. Os espectros sugerem formação de grupos --OH, HOC=O-, e -C=O, e mudanças estruturais relacionadas com grupos NH e -CN-C=O. Basicamente, as mesmas alterações espectrométricas são observadas com o uso das técnicas, sendo mais evidenciadas no interior das amostras pela espectroscopia-FTIR de transmissão, e na sua superfície, pela microscopia-FTIR.

A comparative study involving transmission, reflection and photoacoustic FTIR techniques is presented with analysis of polyamide-6. The potential and limitations of these methods are investigated by analyzing structural variations that take place at the surface in the bulk in recycled and irradiated polyamide-6 with a 1.5 MeV electron beam with a 500kGY dose, in the presence of O2. FTIR techniques appear to be sensitive in detecting small structural changes that occur in recycled and irradiated polyamide-6. The analysis of samples indicated the formation of --OH, HOC=O-, - C=O groups. Also, small structural changes were detected which are characterisitic of NH and --CN-C=O groups. Transmission techniques show better the structural changes in the bulk, and microscopy-FTIR appears to be more sensitive in detecting what occurs at the sample surface.