期刊
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS
卷 18, 期 2, 页码 258-266出版社
UNIV FED SAO CARLOS, DEPT ENGENHARIA MATERIALS
DOI: 10.1590/1516-1439.286114
关键词
PHB; stress cracking; mechanical properties; failure
资金
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq/Brazil)
- Fundacao de Amparo a Ciencia e Tecnologia do Estado de Pernambuco (FACEPE/Brazil)
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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