Materials Engineering Department
BS in Materials Engineering
Considering an increasing interest in renewable, biodegradable resources that exhibit excellent mechanical properties, 24 species of cactus spines were investigated using three-point bend testing, X-ray diffraction (XRD) for structural parameters, and scanning electron microscopy (SEM) to analyze fracture surfaces. Additionally, a density of about 1.3 g/cm3 was measured for each spine utilizing the displacement method, closely matching existing data from literature. The flexural modulus varied greatly between species, ranging from 1.22 GPa (Echinocactus polycephalus) to 43.58 GPa (Stenocereus thurberi). In addition, flexural strength and strain to failure was also measured for each spine. XRD analysis of the spines was used to find the degree of crystallinity and the multifibrillar angle (MFA). The degree of crystallinity for most species ranged from 20-60% with two species ranging above 65%. MFA, which is a measurement of the divergence of the fiber angle from the central axis of the spine, ranged from 1-2.5°; this showed a consistent high degree of alignment of the cellulose fibers, despite the wide range and relatively low values of crystallinity. Examining the trends between mechanical properties, degree of crystallinity, and MFA showed no significant correlation, but it is possible that the crystallinity and MFA have a combined effect on these properties rather than individual effects. It was seen, however, that there is a trend of decreasing resiliency in larger spines due to an increased number of defects. Comparisons were made with engineering materials, such as fiberglass, and it was found that the resiliency of most cactus spines was comparable or superior to those materials.