Waste biomass as a resource represents an interesting opportunity that imbues the principles of green chemistry within the context of sustainability. Herein, potential routes for valorisation of currently low-value and/or underutilised biorenewable waste streams, namely: spruce wood chips; waste office paper; paper deinking residue (DIR), and; waste starch, using green chemical technologies are reported.
Microwave-assisted low-temperature (<200 oC) pyrolysis was conducted on spruce wood chips, waste office paper and paper deinking residue (DIR) to afford three product lines: bio-oil (organic and aqueous phase); bio-char (microwave residue), and; gas. The application of the crude organic phase bio-oils as adhesives for aluminium to aluminium bonding was explored. Maximum tensile strengths, from approximately 2520 N (spruce wood chips) to 2300 N (waste paper) to 400 N (DIR), were observed. A synergistic and/or co-operative effect between various components of waste paper derived bio-oil on adhesive properties is postulated based on evaluation the results from liquid-liquid fractionation. This is the first reported application of bio-oils derived via low-temperature microwave processing for use as adhesives for metal-metal bonding.
The first complete holistic characterization of low-temperature microwave-processed DIR is reported. The residue (78 wt.%) was characterized by solid-state 13C CP/MAS NMR and XRD, showing it was free from organic matter and primarily comprises calcite and kaolinite. The DIR-derived bio-oil gave the lowest adhesion properties (400 N) compared to paper and wood-derived bio-oil.
The incorporation of expanded high amylose corn starch (HACS) and its propionates, with differing degree of substitution (DS), into potentially biodegradable hot melt adhesives (HMAs) comprising polyvinyl alcohol (PVOH) and glycerol was studied. The expansion process to form HMAs, surface area of HACS was increased from around 5 m2 g-1 to 176 m2 g-1, is beneficial towards Al adhesion (ca. 2.0 MPa) as compared to non-expanded HACS (ca. 1.1 MPa).
