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This study aims to assess kinetic modelling of the solid–liquid extraction process of total polyphenolic compounds (TPC) from apple pomace (AP). In this regard, we investigated the effects of temperature and solvent (i.e. water, ethanol, and acetone) on TPC extraction over various periods. The highest TPC yield of 11.1 ± 0.49 mg gallic acid equivalent (GAE)/g db (dry basis) was achieved with a mixture of 65% acetone–35% water (v/v) at 60 °C. The kinetics of the solvent-based TPC extraction processes were assessed via first-order and second-order kinetic models, with an associated investigation of the kinetic parameters and rate constants, saturation concentrations, and activation energies. The second-order kinetic model was sufficient to describe the extraction mechanism of TPC from AP. This study provides an understanding of the mass transfer mechanism involved in the polyphenolic compound extraction process, thus facilitating future large-scale design, optimization, and process control to valorize pomace waste.

The degradation of acetal derivatives of the diethylester of galactarate (GalX) was investigated by electron paramagnetic resonance (EPR) spectroscopy in the context of solvent-free, high-temperature reactions like polycondensations. It was demonstrated that less substituted cyclic acetals are prone to undergo radical degradation at higher temperatures as a result of hydrogen abstraction. The EPR observations were supported by the synthesis of GalX based polyamides via ester-amide exchange-type polycondensations in solvent-free conditions at high temperatures in the presence and in the absence of radical inhibitors. The radical degradation can be offset by the addition of a radical inhibitor. The radical is probably formed on the methylene unit between the oxygen atoms and subsequently undergoes a rearrangement.

Methacrylamide-modified gelatin (Gel-MA) is currently one of the most frequently reported materials in the context of biomaterial development and tissue engineering, because of its excellent biocompatibility, biodegradability and cell interactivity. Gel-MA is also frequently combined with other natural or synthetic polymers to prepare hybrid hydrogels with characteristics improved towards their targeted use. Herein, the development of fully biobased photo-crosslinked hybrid hydrogels is presented through combination of Gel-MA with methacrylate-modified poly(aspartic acid) (pAsp-AEMA), a sustainable alternative for petroleum-based poly(acrylic acid). The hybrid materials showed tunable swelling properties and excellent cell interactivity. Furthermore, photocurable resins of the blends were developed through addition of a photo-initiator and the resins were optimized to be exploited in digital light processing (DLP). In parallel, indirect 3D printing was also pursued. Resins constituting 10 w/v% 75:25 Gel-MA:pAsp-AEMA containing 50 versus 5 mol% photo-initiator in phosphate buffered saline (PBS) were exploited to produce 3D hydrogel scaffolds via direct (DLP) and indirect printing, respectively. The scaffolds were compared via optical microscopy, showing superiority of the indirectly printed scaffolds when considering computer-aided design-computer-aided manufacturing mimicry. In addition, the mechanical properties of the scaffolds following swelling were determined, showing a Young’s modulus of 1.05 ± 0.11 kPa in PBS and swelling of 8.2 ± 0.8 g g−1. In summary, biocompatible Gel-MA:pAsp-AEMA hybrid scaffolds could be fabricated via (in)direct 3D printing showing potential for usage in biomedical applications, in particular for tissue engineering.

A bio-derived monomer called 2,3:4,5-di-O-isopropylidene-galactarate acid/ester (GalXMe) has great potential in polymer production. The unique properties of this molecule, such as its rigidity and bulkiness, contribute to the good thermal properties and appealing transparency of the material. The main problem, however, is that like other biobased materials, the polymers derived thereof are very brittle. In this study, we report on the melt blending of GalXMe polyamides (PAs) with different commercial PA grades using extrusion as well as blend characterization. Biobased PA blends showed limited to no miscibility with other polyamides. However, their incorporation resulted in strong materials with high Young moduli. The increase in modulus of the prepared GalXMe blends with commercial PAs ranged from up to 75% for blends with aliphatic polyamide composed of 1,6-diaminohexane and 1,12-dodecanedioic acid PA(6,12) to up to 82% for blends with cycloaliphatic polyamide composed of 4,4′-methylenebis(cyclohexylamine) and 1,12-dodecanedioic acid PA(PACM,12). Investigation into the mechanism of blending revealed that for some polyamides a transamidation reaction improved the blend compatibility. The thermal stability of the biobased PAs depended on which diamine was used. Polymers with aliphatic/aromatic or alicyclic diamines showed no degradation, whereas with fully aromatic diamines such as p-phenylenediamine, some degradation processes were observed under extrusion conditions (260/270 °C).