Morphological and micromechanical characterization of calcium oxalate (CaOx) crystals embedded in the pecan nutshell (Carya illinoinensis)

摘要

The morphology and micromechanical properties of the mineral crystals embedded in the pecan nutshell (Carya illinoinensis) were characterized. Qualitative and quantitative morphological analyses carried out revealed that the crystals were comprised of calcium oxalate (CaOx) and have a wide range of sizes, with prismatic shapes, distributed heterogeneously in the sclerenchyma tissue. From indentation tests, it was found that CaOx crystals are stiffer structures compared to stone cells (sclerenchyma tissue), showing hardness and elastic modulus values of 0.53 +/- 0.19 GPa and 9.4 +/- 1.80 GPa, respectively. Additionally, the values of fracture toughness (0.08 +/- 0.02 MPa m(0.5)) and the brittleness index (9336 m(-0.5)) revealed that these types of structures are extremely brittle. The results obtained suggest that the main function of the CaOx crystals is to provide structural support to tissue. The presented methodology demonstrates the potential of the instrumented indentation technique (IIT) for in situ micromechanical characterization of mineral crystals located in plant tissues.