An aggregated understanding of physicochemical properties and surface functionalities of wheat straw node and internode

• Node has higher extractives, klason lignin and ash content than internode.
• Outer surface is more hydrophobic and the inner surface is hydrophilic.
• Pre-treatment reduced extractive and ash content of node and internode.

The variation of physicochemical characteristics across wheat straw node and internode with their surface functionalities was investigated. Node yielded slightly higher klason lignin, extractives and ash content than internode, which could be related to their morphology; specifically the higher ash and extractives content in the node are explained by thicker epidermis tissue. These properties make nodes defects in composite and bio-energy production, while internodes could be more favourable for aerobic digestion for biogas production. Surface chemical distribution examinations revealed, higher intensities of the hydrophobic aliphatic fraction of waxes on the outer surface, whereas the hydrophilic tendency of inner surface was reflected by the broad and more intense band in the 3200–3600 cm−1 region, due to OH stretching vibration of hydroxyl groups. This could translate into better interface when water-based resins are used for wheat straw composites. An environmentally friendly pre-treatment was employed to further investigate the effects on the physicochemical properties. The results showed: i) the reduction of waxes from the outer surface, ii) significantly lower (P < 0.05) extractives, along with iii) significant dissolution of Si (weight%) on the outer surface of both node and internode. These results could be beneficiary for composite production or for pulp and paper manufacturers.