Structure and morphology of cladodes and spines of Opuntia ficus-indica. Cellulose extraction and characterisation

The morphology and structure of cladodes and spines from cactus Opuntia ficus-indica (OFI) were investigated by transmission and scanning electron microscopy together with electron and X-ray diffraction analysis. This paper focused also on the characterisation of cellulose from cladodes and spines of OFI. This cellulose can be found either as parenchyma cell cellulose (PCC) in cladodes, or as fibre in spines. Its localisation within the initial cladode was revealed by optical microscopy together with scanning electron microscopy (SEM). The surface of the cell wall is made of thin microfibrils easily observed by transmission electron microscopy (TEM) after shadowing. The purified preparations of cladodes PCC were mechanically homogenised leading to a stable and non flocculating suspension by microfibrils individualisation. The spines decorating the cladodes of OFI cactus consisted of a compact parallel arrangement of slender cellulosic fibres (0.4 mm long, 6–10 μm diameter) with very small lumens. The mechanical properties of these natural spines were investigated by tensile tests at various conditioning relative humidities. The morphology and structure account well for the high mechanical properties of these spines. It was observed that the tensile modulus decreases as the moisture content increases.