Properties of hemp fibre polymer composites -An optimisation of ...

Figure 7. Pectin and wax stained in transverse sections of hemp stem. A: Pectin stained
by Ruthenium Red (arrows = pectin rich compound middle lamellae). B: Wax stained by
Sudan IV (arrows = wax rich cuticle layer).
Structure of the single fibers determined with fungal defibration and decay
Lignin slows down degradation by soft rot fungi like P. mutabilis in wood fibers and the
middle lamella and the primary wall normally remain morphologically intact even after
severe degradation of the S2 layer (Khalili et al., 2000). In single fibers of hemp, this
fungus formed cavities that were restricted to individual layers in the polylaminate S2
layer. The middle lamella and primary wall were degraded slower than S2 due to the
higher lignin content (Figure 3A). The partial degradation of middle lamellae was
presumably due to its high pectin content. The cavities increased in diameter through
cellulose but were inhibited – at least partially – by the thin concentric lamellae acting as
a chemical and/or physical barrier. P. radiata Cel 26 degraded the middle lamellae
between the single fibers and only middle lamellae cell corners remained after advanced
stages of decay (Figure 3C). In combination with the chemical analysis (Table 2), this
gives evidence for degradation of lignin, which P. radiata carries out by oxidation using
peroxidases (e. g. Mn- and lignin peroxidases; Hofrichter et al., 2001). The thin layers
between the thick concentric layers in S2 appear to lack cellulose since they were
selectively removed by P. radiata Cel 26 (Figure 3C). Evidence for a different chemical
composition in the thin layers was also obtained with P. radiata wild, which were more
rapidly attacked (Figure 3, inset) in comparison with the thicker concentric layers.
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