Experimental characterisation and hyperelastic modelling of the mechanical behaviour of arenga pinnata – silicone biocomposite / Siti Humairah Kamarul Bahrain

The increasing awareness about global climate change issues has slowly led to the use of natural fibers in composite materials as an alternative to synthetic fibres since the latter produces harmful gases upon burning. This concern has motivated the study to produce a new soft biocomposite material by employing a natural fibre; Arenga pinnata fibre (AP) as a filler for silicone rubber. Silicone rubber is known to possess high flexibility and elasticity, nevertheless silicone rubber exhibits weak strength. To improve this, AP fibre which possess good seawater resistance was added into silicone rubber. The interfacial adhesion between the silicone rubber and the AP fibre were also investigated since both possessed hydrophobic and hydrophilic properties respectively. Therefore, the main aims of this study are to investigate the physical and mechanical properties of the Arenga pinnata – silicone biocomposite (APSil) and to model its deformation behaviour using hyperelastic constitutive model. The specimens were prepared with 0wt%, 4wt%, 8wt%, 12wt% and 16wt% of filler compositions. Physical tests: swelling test, moisture absorption test and density test were carried out to investigate its physical properties. Uniaxial tensile test, compression test, and dynamic mechanical analysis were also conducted to compare the mechanical properties of both soft (silicone) and hard (epoxy) biocomposites. Morphological analysis on the fractured specimens after tensile test was conducted using Scanning Electron Microscope (SEM). Since this material is soft, hyperelastic constitutive models; Mooney-Rivlin, Yeoh and Polynomial models were also adopted using Excel Solver and polynomial regression method (PRM). A new mathematical modelling; the Modified Polynomial model was also developed to accurately describe the tensile deformation behaviour of the soft materials. It was found that the density and moisture absorption intake showed a steady increment as the filler content increased. The highest water intake recorded was 3.26% (16wt%). Besides, result displayed the swelling properties of Arenga pinnata – silicone biocomposite was enhanced as the filler composition is increased. Pure silicone rubber (0wt%) shows the highest swelling rate (283.27%) in comparison to 16wt% specimen which possesses the lowest swelling rate (146.84%). Comparing both soft and hard materials, both materials demonstrated different mechanical behaviour. However, it is interesting to find from the tensile test that a gradual increment of filler content had improved its stiffness property. Results from compression tests and dynamic mechanical analyses also revealed that the increment of filler addition had enhanced both soft and hard biocomposite as its compressive strength and thermal properties increases. The SEM images also indicated that all specimens (soft and hard) possessed good filler-matrix bonding and the AP fillers were well distributed. Through numerical study, the new Modified Polynomial hyperelastic model showed the best performance (R2 up to 0.9998) to accurately curve fit the experimental data of all specimens as compared to Mooney-Rivlin, Yeoh and Polynomial models. Therefore, it can be concluded that this study has successfully achieved the aims to investigate the effect of the addition of Arenga pinnata fibres into silicone rubber mechanically and numerically. It could also be determined that the addition of AP filler has significantly improved the chemical, stiffness and thermal properties of the material. This has contributed significantly to the knowledge about Arenga pinnata – silicone biocomposite and soft materials as well. Its material constants have also been successfully quantified using the Modified Polynomial model accurately and the mechanical properties of hard (epoxy) and soft (silicone rubber) biocomposite have been well distinguished.