Mango peel is the major by-product of mango processing, and compromises 7–24% of the total mango weight. In this study, pectin was extracted from mango peel waste by using subcritical water extraction (SWE) in the absence of mineral acid. A highest yield of 18.34% was achieved from the Kesar variety and the pectin was characterised using ATR-IR spectroscopy, TGA and 13C solid-state NMR spectroscopy to confirm the structure. The degree of esterification (DE) of the pectin was analysed with both titrimetry and 13C solid-state NMR spectroscopy, and a high DE (>70%) was observed for all three varieties (Keitt, Sindhri and Kesar). This is the first report on acid-free subcritical water extraction of pectin from mango peel, which provides a green route for the valorisation of mango peel waste and contributes to a source of biobased materials and chemicals for a sustainable 21st century.

The hydrothermal microwave-assisted selective scissoring (Hy-MASS) of depectinated orange peel residues (OPR), produced via conventional acid hydrolysis and acid-free microwave processing, to yield (meso)porous nanocellulose fibrils and crystals simultaneously in the absence of additional auxiliary reagents and/or mechanical treatment is reported. In the stepwise microwave hydrothermal treatment (MHT) of OPR from 120 °C–200 °C at 20 °C intervals, release of residual pectins and hemicelluloses is observed up to 180 °C producing nanocellulose fibrils (3–15 × 500–2000 nm). Beyond 180 °C, selective leaching/hydrolysis of amorphous regions occur to yield nanocellulose crystals (200–400 × 40–50 nm) and crystallites (5–15 × 40–50 nm). This selective, step-wise scissoring process is termed Hy-MASS Concept. Structure, morphology and properties of (meso)porous nanocellulose are strongly influenced by pectin extraction methodology employed. With acid depectinated OPR, deconstruction of the lignocellulosic matrix via microwave is hastened by approx. 20 °C with respect to acid-free microwave depectinated OPR. Td of acid depectinated nanocelluloses (CMC) is ca. 350 °C compared to microwave depectinated nanocelluloses (MMC, Td, varies 342–361 °C). Nanocellulose produced via microwave pre-treatment is (meso)porous: BJH pore size 5–35 nm; BET surface area, 1.5–107 m2 g−1, and; BJH pore volume, 0.01–0.27 cm3 g−1, when compared to acid pre-treated counterparts. The crystallinity index of CMC and MMC increases in two stages, 120–140 °C (ca. 8%) and at 180–200 °C (5–9%). XRD revealed presence of calciuim salts, most likely calcium oxalate. The hydration capacities of nanocelluloses (12–23 g water per g sample) are much higher than their precursors or literature citrus nanocellulose.

Combating food waste is a vital 21st century global challenge befitting of green and sustainable chemistry. Prevention is the first and foremost route for reduction of food waste, but inevitably, there are unavoidable food losses as a result of primary and secondary processing that represents an interesting green and sustainable chemistry valorization opportunity. Herein, pea vine waste (Pisum sativum) as an unavoidable food supply chain waste is explored as the source for (bio)renewable chemicals and materials and as a potential bioenergy source. Through a cascade approach simulating a potential biorefinery, pea vine waste was subjected to pseudosubcritical water extraction as a green extraction methodology technique to extract potential platform molecules: 5-hydroxy furfural (HMF); ethanoic acid; sugars (levoglucosenone, rhamnose, xylose, fructose, glucose and sucrose); and a precipitated biopolymer showing pectinaceous and starch-like characteristics as evidenced by infrared spectroscopy, solid-state 13C NMR, and thermogravimetric analysis. The postextraction residues of pea vine waste were further subjected to microwave pyrolysis to produce a bio-oil and a biochar. The bio-oil is rich in phenolic compounds while the biochar has a gross calorific value of 26.6 MJ kg–1 and thus may be used as a potential source of bioenergy. While peas alone have been explored previously, the work within represents the first study of valorization of pea vine wastes, a real as-received industrial problematic waste source, using a cascade approach of pseudo-sub-critical water and microwave pyrolysis simulating a potential biorefinery.Keywords: Biorefinery; Microwave pyrolysis; Pea vine waste; Subcritical water extraction

In this study, the preparation and characterization of biobased thermosets comprising epoxidized linseed oil (ELO), adipic acid and/or glutaric anhydride, initiated by N,N-4-dimethylaminopyridine (DMAP) is reported. By changing the ratio of adipic acid to glutaric anhydride, the obtained resins changed from soft and flexible to hard and brittle materials. The Young’s modulus varied from 25 MPa to 1477 MPa, tensile strength varied from 10.3 MPa to 25.7 MPa, and the elongation at break varied from 2.7% to 67.5%. The maximum toughness was found with the sample containing 20% glutaric anhydride and 80% adipic acid. With the increase of glutaric anhydride content, the total heat released during the curing reaction and the glass transition temperature (Tg) increased. This is the first paper that reports the combination of glutaric anhydride and adipic acid as curing agents for epoxidized plant oils to produce thermosets ranging from flexible to hard.In this graph, it’s shown that the sample changed from hard rigid samples to ductile plastics and then to soft flexible polymers by gradually changing the ratio of glutaric anhydride to adipic acid.

The conversion of waste office paper (printed or photocopied) to bio-oil via low temperature (<200 °C) microwave-assisted pyrolysis, and its utilisation as an adhesive for aluminium–aluminium bonding are reported. The yields for the organic and aqueous phase bio-oil are 19% and 23%, respectively. The pyrolysis products were characterized by ICP-MS, ATR-IR, GC-MS and NMR to reveal broad categories of compounds indicative of sugars (carbohydrates), aromatics and carbonyl-containing moieties. Application of the organic phase bio-oil (70 mg) to Al plates (50 mm × 50 mm) followed by curing at different temperatures and time periods revealed that a maximum tensile strength of approximately 2300 N could be attained at 160 °C for 8 h cure. Also, at a fixed temperature, the tensile strength increased with increasing curing time. To gain an in-depth understanding of the adhesive properties of bio-oil, a liquid–liquid fractionation of the organic phase bio-oil was conducted. The ‘acidic’ fraction showed far better adhesion properties than the ‘neutral’ fraction with no bonding achieved for the aqueous fraction. A combination of the ‘acidic’ and ‘neutral’ fraction gave better adhesion, thus suggesting a possible synergistic or co-operative effect.

The effect of systematically increasing chain length of a series of linear α,ω-dicarboxylic acids (DCAs) from C6 to C18 diacids and a cyclic diacid, Pripol 1009F, on thermal and mechanical properties of the resultant epoxy thermosets derived from epoxidized linseed oil (ELO) are reported. Different techniques including differential scanning calorimetry (DSC), solvent extraction, FT-IR, NMR, dynamic mechanical analysis (DMA), tensile tests and thermogravimetric analysis (TGA) are used in this study. The results indicated that the obtained epoxy resins were highly crosslinked polymers with only a small fraction of low molecular weight soluble materials. The glass transition temperature (Tg), tensile strength, Young's modulus, elongation at break and toughness decreased while the thermal stability increased with respect to increasing chain length of DCAs. Interestingly, strain hardening was only observed for adipic acid (C6) sample for which the best mechanical properties observed.

Significant amounts of paper deinking residue (DIR) has been and is still being generated from paper deinking processes, representing both an economic and environmental burden for recycled paper mills. Our research on low-temperature (<200 °C) microwave-assisted (MW-assisted) pyrolysis of DIR allows for simultaneously efficient fast separation and recovery of the organic and inorganic content of DIR at relatively low temperature and within 15 min. Our study is the first highly detailed account of the use low-temperature MW-assisted pyrolysis to effect this change. The obtained liquid and solid products were characterized by a variety of analytical techniques (e.g., attenuated total reflection infrared, gas chromatography–mass spectrometry, liquid-state nuclear magnetic resonance (NMR), X-ray diffraction, solid-state cross-polarization/magic-angle spinning 13C NMR, and Bloch-decay 13C NMR). The results reveal that the process efficiently separates the inorganic minerals as microwave residue (mainly calcite and kaolinite) from organic matter, and hence the microwave residue could be reused to produce new paper/cardboard products. The organic fraction bio-oil generated is energy-densified and rich in carbohydrates and is a potential source for valuable aromatic compounds.

Making innovative use of low-value and underutilized biorenewable waste streams, and the unavoidable losses resulted from industrial practices, is crucial for transitioning from a petro- to a biobased economy in the 21st century. This study provides a holistic and comprehensive overview of the adhesive properties of bio-oils generated from microwave-assisted low-temperature (<200 °C) pyrolysis of three biorenewable wastes: spruce wood chips, waste paper, and paper deinking residue (DIR). The spruce wood chips and waste paper derived bio-oil could bond two Al plates with high tensile strengths generally. Highest tensile strengths around 2520 N were reached with the spruce wood chips derived bio-oil. The ATR-IR and solid-state CP/MAS 13C NMR characterization of the bio-oil polymer scrapings reveal that the bio-oil possibly undergoes homo- and/or cross-coupling reactions during curing. A model compound study using 5-hydroxymethylfurfural (HMF), levoglucosan, and catechol was conducted to study the role of different categories of compounds within bio-oil in terms of bonding. The adhesion properties of both single model compound, mixtures of each two and/or three of the model compounds with various molar ratios were explored. The results indicate that the presence of (hetero-) aromatic and furan compounds is crucial toward good adhesion.Keywords: Bio-oil; Lignocellulosic waste; Metal adhesives; Microwave-assisted pyrolysis;

The drive toward sustainable practices and principles across the supply chain has led to an upsurge in renewable materials. Epoxy resins are used in a wide range of applications in various fields, such as coatings, adhesives, castings, modeling compounds, impregnation materials, high-performance composites, insulating materials, and encapsulating and packaging materials for electronic devices. In order to achieve the desired properties, uncured epoxy resins must be converted to hard, infusible, thermoset networks in the presence of a variety of curing agents, also known as hardeners. This paper reviews recent advances in the development of curing agents from renewable materials. Attention is given to modified plant oils, biobased acids and anhydrides, amines and their derivatives, biobased phenols, rosin acids, and terpenes and lignin as biobased curing agents for primarily epoxy resin or biobased epoxy resin systems.Keywords: Biobased; Curing agents; Epoxy resins; Renewable materials

Adhesives are of pivotal importance in modern society as over 6 billion pounds of adhesives are used globally per annum. Among these, hot melt adhesives (HMAs) represent the most dynamically developing area, reaching 15–21% of the global volume of production and usage of adhesives. The application of expanded high amylose corn starch (HACS) and its propionate derivatives with differing degrees of substitution (DS) in a formulation comprising polyvinyl alcohol (PVOH) and glycerol to afford 100% biodegradable HMAs is reported. Esterification of expanded starch was conducted to increase the stability and hydrophobicity of starch. The effects of amounts of esterifying reagent and reaction time on DS of starch propionates were investigated. Native starch was expanded (BET surface area, 176 m2 g−1; DS = 0) and derived propionate esters were studied by ATR-IR, TGA, 13C CPMAS NMR, 1H NMR and titrimetric methods. The HMAs, irrespective of DS, displayed a Tg at approximately 0 °C, melting (Tpeak) at approximately 160 °C and crystallisation (on cooling) at approximately 115 °C. The adhesive properties (tensile strength) with respect to DS of expanded high amylose corn starch and its propionate esters show a distinct structure–property relationship. Expanded high amylose corn starch (DS = 0) gives the strongest adhesion, outperforming native (non-expanded) starch. The expansion process is beneficial in promoting adhesion which may be linked to the increased availability of hydroxyl moieties promoting better non-covalent interactions and mixing with PVOH and glycerol. Adhesion strengths decrease with increasing DS of base polymer and those of starch propionates with DS in the range 1.46–1.82 are comparable to that of non-expanded HACS based HMA. This is the first reported occurrence of the use of expanded starch and its propionate esters as HMAs.

Thermosetting resins were synthesised from epoxidised linseed oil (ELO) in combination with a bio-derived diacid cross linker (Pripol 1009) in the presence of amine catalysts (triethylamine (TEA), 1-methylimidazole (1-MeIm), 2-methylimidazole (2-MeIm), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP), yielding a 99.5% bio-derived, highly flexible transparent film, with significant water resistance. It was demonstrated that the mechanical and thermal properties of the resulting films were significantly influenced by the type of amine catalyst selected. The use of catalysts significantly enhanced the mechanical properties of the films; tensile strength improved by up to 545% (DMAP), Young's modulus improved by up to 422% (2-MeIm) and elongation at break improved by 14–84%. An infrared spectroscopic study coupled with simultaneous thermal analysis and modulated differential scanning calorimetry (MDSC) was undertaken in an attempt to elucidate the curing mechanism. Epoxide ring opening is clearly evidenced by infrared spectroscopy and the studies suggest that DMAP probably aids crosslinking between ELO and Pripol 1009 via epoxide ring opening, followed by etherification, due to its good nucleophilicity. The optimum DMAP catalyst loading giving the highest value of Young's modulus was determined at 1% with respect to the total resin weight. Higher concentrations of DMAP (5% wt) decreased the Young's modulus.