The specific interest for the use of bark in materials, instead than for energy recovery, is owed to circular economy considerations, since bark fibers are normally byproducts or even waste from other sectors, and therefore their use would globally reduce the amount of refuse by replacing other materials in the production of composites. For the purpose of promoting their application in polymer composites, mainly under a geometry of short random fibers, bark fibers are extracted and treated, normally chemically by alkali. Following this, investigations are increasingly carried out on their chemical composition. More specifically, this includes measuring cellulose, hemicellulose, and lignin content and their modification with treatment on their thermal properties and degradation profile, and on the mechanical performance of the fibers and of the tentatively obtained composites. This work aims at reviewing the current state of studies, trying to elicit which bark fibers might be most promising among the potentially enormous number of these, clarifying which of these have received some attention in literature and trying to elicit the reason for this specific interest. These can be more thoroughly characterized for the purpose of further use, also in competition with other fibers not from bark, but from bast, leaves, etc., and pertaining to developed production systems (cotton, hemp, flax, jute, etc.). The latter are already widely employed in the production of composites, a possibility scantly explored so far for bark fibers. However, some initial works on bark fiber composites and both thermoplastic and thermosetting are indicated and the importance of some parameters (aspect ratio, chemical treatment) is discussed.
This study aims to reuse the waste of uncured composite prepreg scraps from the ply cutting manufacturing process in the aerospace industry, avoiding the resin loss, waste disposal and expenses with its incineration.Carbon fiber/F155-epoxy resin laminates were produced by randomly positioned scraps, with different sizes and shapes, and characterized by tensile, compression, interlaminar shear (ILSS), and flexural tests. Tensile, compression, and flexural strengths of produced laminates decreased 13, 23, and 56%, respectively, compared to the same prepreg references. The ILSS test showed results 34% higher compared to the references. Higher specific strength (compression and tensile) was found in relation to a typical aircraft aluminum alloy. Therefore, the results opens a potential path to reuse uncured prepreg composite scraps to produce artifacts, as mold structures used in composites manufacturing, reducing the waste disposal in nature and contributing to sustainability.
Resumo Este trabalho apresenta um estudo comparativo dos comportamentos térmicos de três famílias de laminados de fibra de carbono/resina epóxi, submetidas a múltiplos ciclos térmicos, via análises termogravimétricas e dinâmico-mecânicas. Este estudo procura aliar a possibilidade de utilização de retalhos de pré-impregnados de fibra de carbono com resina epóxi - um material nobre na indústria aeronáutica, por meio da comparação do comportamento térmico de um laminado preparado com retalhos de pré-impregnados (laminado R), com outros dois laminados, sendo um manufaturado com prepreg comercial (laminado A) e um terceiro obtido por impregnação manual de reforço seco de fibra de carbono com resina epóxi (laminado B). Os laminados curados a 180 °C foram submetidos a múltiplos ciclos térmicos, totalizando 40, 100 e 300 h de exposição na temperatura máxima de 180 °C. As análises termogravimétricas mostram que os laminados submetidos às múltiplas ciclagens apresentam estabilidade térmica na temperatura de 180 °C, com perda de massa relativa à umidade absorvida pelos laminados. As análises dinâmico-mecânicas evidenciam que as múltiplas ciclagens térmicas afetam pouco ou até aumentam as temperaturas de transição vítrea dos sistemas de resinas epóxis estudados. A partir dos resultados obtidos pode-se afirmar que os laminados submetidos às múltiplas ciclagens térmicas apresentam estabilidade térmica suficiente para serem utilizados, por exemplo, em ferramentais de cura de componentes aeronáuticos.
The interest for models on a polymerization plant of acrylonitrile is (a) to predict the maximum capacity of an industrial reactor, (b) to increase the robustness of the process by defining stable operational conditions, and (c) to help the development of new copolymers. Using design of experiments (DOE), the copolymerization and terpolymerization of acrylonitrile with vinyl acetate and methyl-2 propene-1 sodium sulfonate were studied in aqueous suspension initiated by the redox system KClO 3 /NaHSO 3 /Fe 2þ . The molar fraction of the copolymers and terpolymers produced ranged from 93.0 to 98.2% for acrylonitrile, from 1.7 to 7.0% for vinyl acetate, and from 0.0 to 0.5% for sodium sulfonate. The mass molecular weight ranged from 76 000 to 419 000 g/gmol. Experiments were done in a pilot plant, consisting of 227 L of continuously stirred tank reactor, stripping and recycle systems, drum filter, and band dryer. The experiments were conducted according to a fractioned factorial 2 823 matrix with five central points. A statistic kinetic model was built, which explains well the copolymerization and terpolymerization of acrylonitrile. This model was applied with success on an industrial polymerization reactor, showing the potential of production increase, confirming the robustness of the process, and supporting the development of new copolymers of acrylonitrile. The focus of this paper is the development of a kinetic statistical polymerization model, the criteria to interrupt the regression analysis, and its application in the understanding of the polymerization phenomena.
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