Development and characterisation of thermal responsive shape memory natural rubberTools Kow, Yu Yang (2023) Development and characterisation of thermal responsive shape memory natural rubber. PhD thesis, University of Nottingham.
AbstractCompared to the last century, research and development of smart materials are receiving more attention due to their ability to change shape in response to specific environmental conditions. Although the development of shape memory natural rubber is motivated by the higher recovery strain, low trigger temperature leads to poor shape memory performance typically when the surrounding temperature is increased. A new shape memory natural rubber fabrication method, prevulcanisation is proposed to maintain the crystalline structure of the rubber molecule at elevated temperature. The low molar fatty acid which is palmitic acid involves in the prevulcanisation process to increase the trigger temperature of shape memory natural rubber. The prevulcanised rubber is fabricated with various amount of palmitic acid and sulphur to evaluate its shape memory capability under different temperature conditions (various programming temperatures and recovery temperatures). A custom-made stretching apparatus is developed to measure the shape memory parameters (shape fixity and shape recovery) under strain-control mode. The shape memory experimental settings (200% deformation strain for the shape memory natural rubber with less than 60% palmitic acid loading) are determined from the swollen shape memory natural rubber experiment. According to the shape memory experiment of prevulcanised rubber, the outstanding shape fixity and shape recovery are found when the temperature is closer to the melting temperature of the palmitic acid during the programming and recovery process. A similar trend is observed when palmitic acid content is increased. However, the sulphur content (>1.0pphr) has a reverse effect, causing the prevulcanised rubber to behave like elastic rubber and immediately recover its shape after unloading. Apart from the shape memory experiment, other material properties such as rubber strength and stress relaxation are also investigated. Furthermore, a shape memory behaviours prediction model is adopted to model the shape memory responses by using a standard linear solid model with Kelvin-Voigt element and a thermal strain model. The prediction model captured the shape memory behaviours appropriately and provided some insights on the stress-strain response of the respective segment phases for the shape memory process.
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