ABSTRACT Polymers based on glycidyl azide polymer (GAP) and isocyanate present molecular structures dependent on NCO/OH molar ratio and diisocyanate reactivity. In this study, GAP polymers are obtained from a reaction with aromatic (toluene diisocyanate, TDI) or aliphatic (isophoranediisocyanate, IPDI) diisocyanates, varying the NCO/OH molar ratio from equimolar to 2.5. The increment in NCO/OH molar ratio increases the gel fraction in GAP/TDI polymers up to 90 wt%, along with a progressive growth in their glass transition temperature (Tg), which rises 10 °C from NCO/OH equimolar to 2.5. In opposition, in the GAP/IPDI polymers, the maximum gel fraction is 20 wt%, and the Tg value practically does not change in NCO excess. Infrared spectroscopy shows the predominant presence of urethane groups in polymers containing up to 2.0 NCO/OH molar ratio; however, at 2.5, urethane and allophanate characteristic bands are present in both polymers. That reactivity is controlled by chemical kinetics since the activation barrier of the reaction between the GAP and TDI is 10 kcal.mol-1 lower than in the corresponding reaction with the IPDI. This difference results from the sum of the higher hyperconjugative interactions, approximately 65%, and the lower steric hindrance, about 35%, in the activated complex containing the TDI. (GAP NCOOH OH study toluene isophoranediisocyanate, isophoranediisocyanate (isophoranediisocyanate IPDI diisocyanates 25 2 5 2.5 GAPTDI 9 wt wt% Tg, , (Tg) 1 C opposition GAPIPDI excess 0 2. however kcal.mol1 kcalmol1 kcalmol kcal.mol kcal mol kcal.mol- interactions 65 65% hindrance 35 35% (Tg mol1 6 3

Abstract Composites are relevant to high-performance materials in the aerospace sector and have attracted the attention of the scientific and technological communities. Bentonites present very fine granulometry which enables their use in composites. This study showed the development of water absorbent composite based on sodium polyacrylate, bentonite coated by epoxy resin. Since there are gaps in the quantification of composite materials by near-infrared spectroscopy, especially by reflectance analysis (NIRA), this paper shows a quantification methodology (A7200/A5202) of sodium polyacrylate and bentonite. The methodology error found was 1.45% (95% of coefficient of determination). The effectiveness of the developed infrared methodology was verified showing that values are close to the nominal, especially for lower bentonite content. Besides, scanning electron microscopy (SEM) and universal attenuated total reflection (UATR) analysis evidenced the coating with the epoxy resin. Such development ensures rapid and precise methodologies that can be applied to the quality control of composite materials. highperformance high performance communities composites resin nearinfrared near spectroscopy NIRA, NIRA , (NIRA) A7200/A5202 A7200A5202 AA A7200 A5202 A (A7200/A5202 145 1 45 1.45 95% 95 (95 determination. determination . determination) nominal content Besides SEM (SEM UATR (UATR (NIRA A7200/A520 A7200A520 A720 A520 (A7200/A520 14 4 1.4 9 (9 A7200/A52 A7200A52 A72 A52 (A7200/A52 1. ( A7200/A5 A7200A5 A7 A5 (A7200/A5 A7200/A A7200A (A7200/A

ABSTRACT Ethylene-propylene-diene elastomer (EPDM) is employed as thermal insulation for rocket motors, as well as EPDM blends with ethylene vinyl acetate (EVA) have been used in the aerospace industry. The quantification of these blends is more common using Fourier Transform Infrared Spectrometry (FT-IR) by transmission mode, but without discussing sample preparation and methodology error. Considering this fact, a methodology was developed for determining EVA content in binary blend with EPDM samples, by Universal Attenuated Total Reflection (UATR) technique, associated to thermogravimetric analysis (TGA). This last one, it was applied to determine Vinyl Acetate (VA) content in EVA and to identify differences between EPDM/EVA blends. Samples of the analyzed blends showed two VA contents and five proportions of EPDM/EVA: 90/10, 70/30, 50/50, 30/70, and 10/90. The carbonyl stretching vibration band C=O at 1740 cm-1 was used as analytical band in FT-IR quantification. Finally, the results presented excellent accuracy with a good linear correlation coefficient (R > 0.940) and with relative error values lower than 2%, respecting the precision limits of the FT-IR spectrometer.

Abstract Epoxy resins (EP) usually cure in autoclave to minimize resin voids and to achieve the desired resin/fiber ratio. Cure parameters such as temperature, vacuum and pressure levels are controlled and monitored. Aiming time and cost optimization, new out-of-autoclave (OOA) cure processes have been developed lately. This study evaluated the cure cycle and the effect of non-programmed interruptions in an OOA process. Fourier Transform Infrared spectroscopy (FT-IR) results show similarities between the resin used and diglycidyl ether of bisphenol A (DGEBA) and also that the curing system is composed of cyan and sulfur hardeners, codified in industry, as Components of #2511 Resin System. The cure cycle and its interruptions were simulated by dynamic-mechanical analysis (DMA). The samples obtained were evaluated by FT-IR and differential scanning calorimetry (DSC), whose results show that the degree of cure varying between 0.8 to 0.85 was achieved at 120 °C.

Resumo A vulcanização é um importante fator que determina as propriedades mecânicas da borracha, mas a influência do método de vulcanização nas propriedades mecânicas do material, ainda é um assunto pouco explorado na literatura. Neste artigo, uma formulação à base de poli-cis-isopreno ou borracha natural (NR), denominada NR4010-A, foi vulcanizada em prensa e autoclave, com o objetivo de avaliar a influência do método de vulcanização na formação das ligações cruzadas e, consequentemente, nas propriedades mecânicas do material. Amostras do material vulcanizado, pelos dois métodos, foram caracterizadas por meio de análise reométrica, ensaio de inchamento e testes mecânicos, onde foi avaliada a resistência ao rasgo e à tração. Os resultados mostraram que para essa formulação, nas mesmas condições de temperatura, o método de vulcanização por autoclave se mostrou mais eficiente em relação às propriedades estudadas.

Abstract Vulcanization is an important factor on rubber mechanical properties determination. The influence of vulcanization method on mechanical properties is still an ongoing issue. Thus, a composition based in natural rubber (NR), named NR4010-A, was vulcanized by autoclave and press, on purpose to evaluated the vulcanization method influence on crosslink formation and thereafter on the mechanical properties of this material. Samples of vulcanized material in both conditions were characterized through swelling, rheometer tests, tear strength, strain strength and hardness. The mechanical properties studied and crosslink density were increased when the material was vulcanized by autoclave. Therefore, autoclave vulcanization method showed be more effective than press at the same conditions of temperature.

<title>Abstract</title><p>Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG/FT-IR) is a very popular technique for rubbers characterization. It involves analyses of the base polymer and additives. Ethylene–propylene–diene (EPDM) rubbers are frequently investigated by TG/FT-IR; however, the focus has been the degradation temperature range of the polymer. In this study, unvulcanized and vulcanized EPDM rubber and its additives were investigated by TG/FT-IR, without solvent extraction, and in a wide temperature range. Initially, the additives were individually characterized. TG/FT-IR identified the characteristic groups of all the additives analyzed and distinguished them from each other. Afterwards, unvulcanized and vulcanized EPDM rubbers were investigated without prior extraction.TG/FT-IR detected absorptions due to the additives tetramethylthiuram monosulfide and 2-mercaptobenzothiazole. Both of these sulfur-containing additives were present in the EPDM formulation at concentrations of 0.7 phr (0.63 wt %). The TG/FT-IR technique had some limitations, because not all the additives in EPDM rubber were detected. Paraffin oil, stearic acid and 2,2,4-trimethyl-1,2-dihydroquinoline functional groups were not observed in either the unvulcanized or vulcanized EPDM. Nevertheless, in addition to the ability of this method to detect sulfur-containing groups, the lack of a pre-extraction reduces the time and effort required for additive analysis in rubbers.</p>

ABSTRACT: It is very important to control the characteristics of a polymer used in rubber compositions and paints in aerospace applications. Hence, the development of simple and fast methodologies that allow the identification of these compositions becomes attractive to researches carried out in this area. This study has evaluated infrared (IR) techniques, such as transmission, universal attenuated total reflection (UATR), and attenuated total reflection (ATR), for the characterization of elastomers and paints. It takes into consideration the characteristics of surface techniques, such as the depth of penetration of the IR beam into the sample. The presence of additives in low concentrations on paints was only detected by UATR after grinding the components. Results show that it is possible to differentiate rubber mixtures with similar IR spectra and to detect small amounts of additives in the surface of coatings.

Abstract: Poly(epichlorohydrin) was synthesized using anhydrous and hydrate stannic chloride, separately, as initiator. Reactions were conducted in the presence of a diolat 70°C. Polymers were characterized by Fourier Transform Infrared I Spectroscopy (FT-IR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and hydroxyl value determination. It was observed that water has influence in growing chain, but not in its structural backbone. Besides, the monomer/initiator relationship has a higher influence in overall poly(epichlorohydrin) properties.

The aggregation behavior of the non-ionic surfactant Renex-100 in aqueous solutions and mesophases was evaluated by SAXS in a wide range of concentrations, between 20 and 30 °C. Complementary, water interactions were defined by DSC curves around 0°C. SAXS showed that the system undergoes the following phase transitions, from diluted to concentrated aqueous solutions: 1) isotropic solution of Renex aggregates; 2) hexagonal mesophase; 3) lamellar mesophase; and 4) isotropic solution. DSC analysis indicated the presence of interfacial water above 70wt%, which agreed with the segregation of free water to form the structural mesophases observed by SAXS bellow this concentration.

Dynamic mechanical analysis (DMA) is widely used in materials characterization. In this work, we briefly introduce the main concepts related to this technique such as, linear and non-linear viscoelasticity, relaxation time, response of material when it is submitted to a sinusoidal or other periodic stress. Moreover, the main applications of this technique in polymers and polymer blends are also presented. The discussion includes: phase behavior, crystallization; spectrum of relaxation as a function of frequency or temperature; correlation between the material damping and its acoustic and mechanical properties.