Stress cracking e ataque químico do PET em diferentes agentes químicos

Teófilo, Edvânia Trajano; Melo, Rafaela N.; Silva, Suédina Maria de Lima; Rabello, Marcelo S.

doi:10.1590/s0104-14282009000300008

Cited by 7 publications

(15 citation statements)

References 26 publications

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“…In addition, a tensile relaxation test was conducted, in which a load (from 231 N to 1099 N) was pre-applied and its decay monitored as a function of time for up to 20 minutes. In both cases, tensile and relaxation conditions, the fluid was applied on the surface of the samples during testing, following a procedure described elsewhere 15 . After testing, the fracture and molded surfaces were photographed with an Olympus 10 MP digital camera and by scanning electron microscopy using a Shimadzu SSX 550 Superscan equipment.…”

Section: Methodsmentioning

confidence: 99%

“…Even though the effects of stress cracking on polymers is known for many decades 12,13 , very few investigations are reported in the scientific literature. One of the authors of this paper has some contribution in this field, with works on the combined effect of stress cracking and chemical degradation of poly(ethylene terephthalate) (PET) 14,15 , poly(methyl meta acrylate) (PMMA) 16,17 , polycarbonate (PC) 18 and polystyrene (PS) 19 . To the best of the authors knowledge, no work was done on the investigation of ESC behavior of PHB.…”

Section: Introductionmentioning

confidence: 99%

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Environmental Stress Cracking of Poly(3-hydroxibutyrate) Under Contact with Sodium Hydroxide

et al. 2015

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Environmental stress cracking (ESC) is one of the most important causes of polymer premature failure, occurring when a combination of mechanical load and an aggressive fluid is applied. The phenomenon is well know by polymer producers and product designers but its mechanisms are not very well understood. Although the ESC effects of many commercial polymers are well known, this type of failure in biopolymers were not studied yet. In the current work, the stress cracking behaviour of poly(3-hydroxybutyrate) (PHB) with 4,0 and 6,2% of hydroxyvalerate (HV) was investigated in injection-moulded bars under contact with sodium hydroxide (NaOH) solutions. The experiments were conducted using two different types of stress arrangements: (i) an ordinary tensile testing and (ii) a relaxation experiment. In both situations the injection-moulded bars were exposed to the NaOH solution and some testing conditions where varied, like the cross-head speed of the tensile test and the maximum load of the relaxation arrangement. The results showed that NaOH acted as a strong stress cracking agent for PHB, causing surface cracking and reducing significantly the mechanical properties. Catastrophic failure with an extensive surface damage was also observed by photographed and scanning electron microscopy (SEM) images. The magnitude of the effects increased with decreasing crosshead speed and increasing loading level.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Environmental Stress Cracking of Poly(3-hydroxibutyrate) Under Contact with Sodium Hydroxide

et al. 2015

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“…Outra técnica que os autores utilizam para avaliar os efeitos do stress cracking é a relaxação de tensão [18,27,28] . Neste procedimento, o corpo de prova é tensionado até uma determinada força e é mantido em deformação constante, sendo possível determinar a taxa de relaxação, definida como o decaimento da força aplicada com o tempo.…”

Section: Influência Da Morfologiaunclassified

“…Assim, a taxa de relaxação pode ser relacionada à falha por ESC, sendo dependente da quantidade e velocidade de propagação das trincas formadas. O que comumente se tem observado nos ensaios de ESC sob relaxação de tensão é que maiores graus de fissuramento e menores velocidades de propagação das trincas proporcionam maiores taxas de relaxação [18,27,28] . Na Tabela 1 tem-se as taxas de relaxação dos materiais em contato com concentrações de 0,25 e 1M de NaOH, sob as forças iniciais de 1300 e 1600N.…”

Section: Influência Da Morfologiaunclassified

“…Já foi verificado que durante os ensaios de ESC as soluções aquosas de hidróxido de sódio atacam quimicamente o PET, reduzindo significativamente sua massa molar [27,28] e que a quantidade e concentração da solução e a tensão mecânica exercem considerável influência nesse processo degradativo [18] . Anteriormente foi mostrado que a degradação depende do tempo de exposição e ficou evidenciado que pode ser favorecida pela presença de argila (Figura 7).…”

Section: Figuraunclassified

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Falha por stress cracking em híbridos PET/argila

Teófilo

Silva

et al. 2014

Polímeros

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Resumo: O presente estudo investiga a falha por stress cracking em polímeros contendo argila montmorilonítica. Ensaios de tração e de relaxação de tensão foram conduzidos para avaliar a resistência ao stress cracking do PET puro e dos híbridos PET/argila em contato com soluções aquosas de hidróxido de sódio. As análises por difratometria de raios-X evidenciaram que a argila adicionada não gerou uma estrutura esfoliada e sim a obtenção de microcompósitos. Os resultados mostraram que a presença de argila dispersa no PET causa concentração de tensão, o que exerce forte influência no comportamento de stress cracking, com os efeitos sendo afetados pela ordenação lamelar e ao teor de carga, resultando em maiores taxas de relaxação de tensão. A argila com menor regularidade no empilhamento lamelar, embora ocasione menor concentração de tensão, favorece mais o fissuramento superficial da matriz, sugerindo que o efeito de barreira ao fluido não foi efetivo. Medidas de massa molar evidenciaram que a argila acelera o ataque químico da matriz quando elevadas concentrações de solução são utilizadas, porém diminui o efeito da tensão mecânica na degradação.Palavras-chave: PET, argila, stress cracking, nanocompósitos. Stress Cracking Failure of PET/Clay CompositesAbstract: This study investigates stress-cracking failure of polymer/clay composites. Tensile and stress relaxation tests were conducted to evaluate the stress cracking resistance of PET and PET/clay in the presence of sodium hydroxide aqueous solution. The X-ray diffraction analyses showed that the clay formed a typical structure of a microcomposite, and not an exfoliated structure. The presence of clay causes stress concentration, with a strong consequence to the stress cracking behavior, but the effects depend on the lamellar ordering and the content of clay. When the clay lamellae are less ordered the rise in stress concentration is lower, but causes more surface cracks on the polymer, suggesting that the barrier effect was not very effective. Molar mass measurements showed that the clay accelerates the chemical attack of the matrix when higher concentrations of NaOH are used, but reduces the effect of mechanical stress on degradation. Keywords: PET, clay, stress-cracking, nanocomposites.Autor para correspondência: Marcelo Silveira Aabello, Unidade Acadêmica de Engenharia de Materiais, Rua Aprigio Veloso, 882, Campina Grande, PB, Brasil, IntroduçãoO poli (tereftalato de etileno) (PET) é um dos mais importantes plásticos de engenharia da atualidade, sendo um dos termoplásticos mais produzidos no mundo [1] . Apresenta uma excelente combinação de rigidez e tenacidade, alta resistência ao calor, estabilidade dimensional, capacidade de isolamento elétrico, além da possibilidade de se apresentar no estado amorfo (transparente), parcialmente cristalino e orientado (translúcido) e altamente cristalino (opaco) [2] . Entretanto, desvantagens tais como baixa taxa de cristalização e baixa temperatura de distorção térmica têm limitado suas aplicações como um plástico de engenh...

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The investigation of the stress cracking behavior of PBT by acoustic emission

Braz

Silva

Wellen

et al. 2021

Polymers for Advanced Techs

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Despite being a major cause of failure of polymer products under service, environmental stress cracking (ESC) is still a phenomenon poorly investigated and, as consequence, not fully understood. This article aims to contribute to this field in a study of the stress cracking behavior of polybutylene terephthalate (PBT) exposed to ethanol (a common fluid, used in several daily situations), by means of two types of mechanical tests (tensile and stress relaxation). During mechanical testing the technique of acoustic emission (AE) was applied to identify certain mechanisms of internal failure.As a non-destructive technique, AE is widely used with metals to monitor the integrity of components but it is very scarcely applied to polymers. The article, therefore, innovates by using AE as a tool to better understand the ESC behavior of an engineering polymer produced under different conditions. The PBT samples were prepared by injection molding, using different mold temperatures (20 C, 40 C, and 80 C), resulting in different crystallinities. The results showed that the tensile properties were highly dependent on the crosshead speed and that ethanol affected the mechanical performance of the materials, anticipating the necking, but its evaporation during the experiment reduced the actual temperature on the sample bar. This latter effect caused an unexpected behavior, with an increase in tensile strength and reduction of stress relaxation rate, the opposite trends that would be expected from a stress cracking agent. The crystallinity of PBT had some influence on the results, with the more crystalline samples being more resistant to ESC, as observed by both stress relaxation and AE analyses. The technique of AE showed to be a very useful tool to understand the mechanical behavior and to differentiate the various testing conditions, with the detection and quantification of hits and released energy, related to the several stages of deformation and failure, including the formation of shear bands, nucleation and growth of crazes and cracks, and so forth. The fracture surface analyses by scanning electron microscopy were very consistent with the AE experiments, in which rough topography were related to high acoustic activities.

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Stress cracking e ataque químico do PET em diferentes agentes químicos

Cited by 7 publications

References 26 publications

Environmental Stress Cracking of Poly(3-hydroxibutyrate) Under Contact with Sodium Hydroxide

Environmental Stress Cracking of Poly(3-hydroxibutyrate) Under Contact with Sodium Hydroxide

Falha por stress cracking em híbridos PET/argila

The investigation of the stress cracking behavior of PBT by acoustic emission

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