The aim of this work is to evaluate the effect of several types of plasticizers on the glass–rubber transition temperatures (Tg) of polyester-based polyurethane binders, using dynamic mechanical analysis (DMA). The polyester polyol commercially named Desmophen® 2200 (D2200®) has been investigated for use as binder for composite propellant applications due to its good ballistic properties and also due to its potential glass–rubber transition temperature when mixed with polar energetic plasticizers. Therefore, it is important to evaluate the behavior of D2200® with different energetic plasticizers. In the present work, this inert polar binder was mixed individually with several different plasticizers and cured with a polyisocyanate commercially named Desmodur® N3400. The plasticizers used were: nitrate ester methyl trimethylol ethane trinitrate (TMETN), N-(n-butyl)-N-(2-nitroxyethyl) nitramine (Bu-NENA), bis-(2,2-dinitropropyl) formal and bis-(2,2-dinitropropyl) acetal mix 1:1 (BDNPF-A), nearly monodispersed low molar mass azido-terminated glycidyl azide polymer (GAP-A), ethylene glycol bis-(azidoacetate) (EGBAA) and 1,2-bis-(2-azidoethoxy) ethane (TEGDA) or BATEG, bis-azido-triethylene glycol, in an amount of 35 mass/%. The cured elastomers were characterized using torsion DMA at several frequencies, and the loss factor curves were described with exponentially modified Gaussian (EMG) distribution functions. Increasing deformation frequency in DMA increases Tg, and an apparent activation energy was correlated with plasticizer performance. The plasticizer ability to decrease Tg follows the order: TEGDA > butyl-NENA > GAP-A > EGBAA > BDNPF-A > TMETN. The ability of each energetic plasticizer could be related to its molecular structure, as well as to its molar mass and interaction possibilities with the polymer chains
Kenaf (Hibiscus cannabinus L.) is one of the most investigated and industrially applied natural fibers for polymer composite reinforcement. However, relatively limited information is available regarding its epoxy composites. In this work, both thermal and chemical properties were, for the first time, determined in kenaf fiber reinforced epoxy matrix composites. Through XRD analysis, a microfibrillar angle of 7.1° and crystallinity index of 44.3% was obtained. The FTIR analysis showed the functional groups normally found for natural lignocellulosic fibers. TMA analysis of the composites with 10 vol% and 20 vol% of kenaf fibers disclosed a higher coefficient of thermal expansion. The TG/DTG results of the epoxy composites revealed enhanced thermal stability when compared to plain epoxy. The DSC results corroborated the results obtained by TGA, which indicated a higher mass loss in the first stage for kenaf when compared to its composites. These results might contribute to kenaf fiber composite applications requiring superior performance.
Titica vine (Heteropsis flexuosa) is a typical plant of the Amazon region commonly used for making baskets, bags, brooms and furniture, owing to its stiff fibers. In spite of its interesting properties, there is so far no reported information regarding the use of titica vine fibers (TVFs) in engineering composite materials. In this work, the TVF and its epoxy composites were for the first time physically, thermally and mechanically characterized. Additionally, the effect of two kinds of chemical treatments, one with sodium carbonate and one with calcium lignosulfonate, as well as different volume fractions, 10, 20, 30 and 40 vol%, of TVF-reinforced composites were assessed for corresponding basic properties. The thermogravimetric results of the composites reveal enhanced thermal stability for higher TVF content. In addition, the composite incorporated with 40 vol% of TVFs treated with sodium carbonate absorbed 19% more water than the composites with untreated fibers. By contrast, the calcium lignosulfonate treatment decreased water absorption by 8%. The Charpy and Izod impact tests showed that the composites, incorporated with the highest investigated volume fraction (40 vol%) of TVF, significantly increased the absorbed energy by 18% and 28%, respectively, compared to neat epoxy. ANOVA and Tukey statistical analyses displayed no direct influence of the chemical treatments on the energy absorption of the composites for either impact tests. SEM images revealed the main fracture mechanisms responsible for the performance of TVF composites.
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