From food waste to eco-friendly functionalized polymer composites: Investigation of orange peels as active filler.

The development of eco-friendly polymer composites with multifunctional properties aligns with the goals of the circular economy agenda, which aims to minimize waste and promote the sustainable use of resources by closing the loop of product life cycles. Eco-friendly polymer composites play a crucial role in achieving these objectives. The present work focuses on the preparation of fully biobased blends obtained by melt mixing a bio-polyester, poly(butylene succinate-co-adipate) (PBSA), with orange peels up to 20 wt%, to yield active polymer composites. Orange peels, employed here as natural filler, are largely available from food wastes, they are rich in phenolic compounds and possess antioxidant activity as shown by the experimental tests carried out. The thermal stability of the formulated composites is almost unchanged by the filler addition, showing only a slight decrease of the crystallization temperatures and crystalline fraction within the composites. The mechanical properties of the compounds evidence an increase in the elastic modulus together with a decrease in the tensile strength, while the elongation at break remains almost constant. The incorporation of the natural filler enabled the integration of antioxidant and antibacterial properties, which were absent in the original pristine polymer.

Alkali-Activated Mortars Reinforced with Arundo donax: Properties and Durability to Environmental Stresses.

Natural fibers were used to modify alkali-activated fly-ash mortars. Arundo donax is a common, fast-growing, widespread plant with interesting mechanical properties. Short fibers of different lengths (from 5 to 15 mm) were added at a 3 wt% ratio to the binder amount to the alkali-activated fly-ash matrix. The possible effects on the fresh and cured properties of the mortars deriving from the different lengths of the reinforcing phase were investigated. The flexural strength of the mortars increased by up to 30% at the longest fiber dimensions, while the compressive strength remained almost unchanged in all of the compositions. The dimensional stability was increased slightly upon the addition of the fibers, depending on the fiber length, while the porosity of the mortars was reduced. Moreover, contrary to what was expected, the water permeability was not increased by the fibers' addition, irrespective of their length. The durability of the obtained mortars was tested through freeze-thaw and thermo-hygrometric cycles. The results obtained so far underline a fair resistance to the changes in temperature and moisture and a better resistance to the freeze-thaw stresses of the reinforced mortars.

Natural deep eutectic solvents as thermostabilizer for Humicola insolens cutinase.

As a new generation of green solvents, deep eutectic solvents (DESs) are considered a promising alternative to current harsh organic solvents and find application in many chemical processing methods such as extraction and synthesis. DESs, normally formed by two or more components via various hydrogen bond interactions, offer high potential as medium for biocatalysis reactions where they can improve efficiency by enhancing substrate solubility and the activity and stability of the enzymes. In the current study, the stabilization of Humicola insolens cutinase (HiC) in natural deep eutectic solvents (NADESs) was assessed. The best hydrogen bond donor among sorbitol, xylitol, erythritol, glycerol and ethylene glycol, and the best acceptor among betaine, choline chloride, choline acetate, choline dihydrogen citrate and tetramethylammonium chloride, were selected, evaluating binding energies and molecular orientations through molecular docking simulations, and finally used to prepare NADES aqueous solutions. The effects of component ratio and NADES concentration on HiC thermostability at 90 °C were also investigated. The choline dihydrogen citrate:xylitol, in a 1:1 ratio with a 20 wt% concentration, was selected as the best combination in stabilizing HiC, increasing its half-life three-fold.

Valorization of coffee wastes as plant growth promoter in mulching film production: A contribution to a circular economy.

Food waste valorization, considered as energy and/or chemicals source, via biorefinery or biotechnology, gained great attention in recent years, because of the fast depletion of primary resources, increased waste generation and landfilling worldwide. Coffee by-products for example (i.e. coffee pulp, coffee husks, silver skin, spent coffee, etc.) have been investigated in different forms either as a source of antioxidant and valuable chemicals and as a filler in composites. A new valorization route for coffee silver skin (CSS), up to now just sent to damping, is here investigated: particulate bio-composites based on poly(butylene succinate-co-adipate) (PBSA), an aliphatic biodegradable polyester commercially available, have been formulated with up to a 30 wt% of CSS, in order to prepare mulching films for agriculture. The bacterial analysis of the filler indeed, has underlined the presence of potential Plant Growth-Promoting Bacteria species, mainly ascribed to the Bacillus genus, which can survive both the roasting and the compounding processes. The obtained composites have been characterized mechanically and thermally and their hydrophilic nature has been investigated by measuring their contact angle. Eventually, the bacteria release from the composite films has been examined by means of in-vitro tests. The plant growth promoting capability of the films was preliminarily evaluated in pot experiments using lettuce as a model crop. The composite films were able to release the endogenous bacteria in the soil and to stimulate plant and root growth of the assayed crop. The possibility to produce functionalized biodegradable mulching films by recycling agricultural wastes can thus be forecast, highlighting potential multiple advantages in terms of soil preservation/fertilization, decrease of polymeric materials in mulching products, exploitation of a waste.

Triggering of Polymer-Degrading Enzymes from Layered Double Hydroxides for Recycling Strategies.

The use of degrading enzymes in polymer formulation is a very attractive strategy to manage the end-of-life of plastics. However, high temperatures cause the denaturation of enzymes and the loss of their catalytic activity; therefore, protection strategies are necessary. Once protected, the enzyme needs to be released in appropriate media to exert its catalytic activity. A successful protection strategy involves the use of layered double hydroxides: cutinase, selected as a highly degrading polyester hydrolytic enzyme, is thermally protected by immobilization in Mg/Al layered double hydroxide structures. Different triggering media are here evaluated in order to find the best releasing conditions of cutinase from LDH. In detail, phosphate and citrate-phosphate buffers, potassium carbonate, sodium chloride, and sodium sulfate solutions are studied. After the comparison of all media in terms of protein release and activity retained, phosphate buffer is selected as the best candidate for the release of cutinase from LDH, and the effect of pH and concentration is also evaluated. The amount of the enzyme released is determined with the Lowry method. Activity tests are performed via spectrophotometry.

Enzymatic Degradation of the Most Common Aliphatic Bio-Polyesters and Evaluation of the Mechanisms Involved: An Extended Study.

Commercial hydrolytic enzymes belonging to different subclasses (several lipases, proteinase k, cutinase) were investigated for their ability to degrade different aliphatic polyesters, i.e., poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA), two poly(caprolactone), having two different molecular weights, poly(lactic acid) (PLA) and poly(propylene carbonate) (PPC). The enzyme screening was first carried out by investigating the capacity of fully degrading the target polymers in 24 h, then weight loss measurements of selected polyesters and target enzymes were performed. Solid residues after enzyme degradation were characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetry (TGA). Liquid fractions were studied via GPC, 1H NMR and high-performance liquid chromatography (HPLC). PCL and PBSA were found to be the most biodegradable polyesters, under the conditions used in this study. PBS was fully degraded only by cutinase, whereas none of the tested enzymes were able to completely degrade PLA and PPC, in the conditions assessed here. Cutinase exhibited the highest hydrolytic activity on PBSA, while lipase from Candida sp. (CALB) on low molecular weight PCL. Chemical analyses on residual solids showed that the enzymatic degradation occurred homogeneously from the surface through an erosion mechanism and did not significantly affect the macromolecular structure and thermal stability. Cleaving action mode for each enzyme (endo- and/or exo-type) on the different polyesters were also proposed based on the evaluation of the degradation products in the liquid fraction.

Current Advances in the Sustainable Conversion of 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid.

2,5-Furandicarboxylic acid (FDCA) is currently considered one of the most relevant bio-sourced building blocks, representing a fully sustainable competitor for terephthalic acid as well as the main component in green polymers such as poly(ethylene 2,5-furandicarboxylate) (PEF). The oxidation of biobased 5-hydroxymethylfurfural (HMF) represents the most straightforward approach to obtain FDCA, thus attracting the attention of both academia and industries, as testified by Avantium with the creation of a new plant expected to produce 5000 tons per year. Several approaches allow the oxidation of HMF to FDCA. Metal-mediated homogeneous and heterogeneous catalysis, metal-free catalysis, electrochemical approaches, light-mediated procedures, as well as biocatalytic processes share the target to achieve FDCA in high yield and mild conditions. This Review aims to give an up-to-date overview of the current developments in the main synthetic pathways to obtain FDCA from HMF, with a specific focus on process sustainability.

End of Life of Biodegradable Plastics: Composting versus Re/Upcycling.

Nowadays the issues related to the end of life of traditional plastics are very urgent due to the important pollution problems that plastics have caused. Biodegradable plastics can help to try to mitigate these problems, but even bioplastics need much attention to carefully evaluate the different options for plastic waste disposal. In this Minireview, three different end-of-life scenarios (composting, recycling, and upcycling) were evaluated in terms of literature review. As a result, the ability of bioplastics to be biodegraded by composting has been related to physical variables and materials characteristics. Hence, it is possible to deduce that the process is mature enough to be a good way to minimize bioplastic waste and valorize it for the production of a fertilizer. Recycling and upcycling options, which could open up many interesting new scenarios for the production of high-value materials, are less studied. Research in this area can be strongly encouraged.

Bio-Based Furan-Polyesters/Graphene Nanocomposites Prepared by In Situ Polymerization.

In situ intercalative polymerization has been investigated as a strategic way to obtain poly(propylene 2,5-furandicarboxylate) (PPF) and poly(hexamethylene 2,5-furandicarboxylate) (PHF) nanocomposites with different graphene types and amounts. Graphene (G) has been dispersed in surfactant stabilized water suspensions. The loading range in composites was 0.25-0.75 wt %. For the highest composition, a different type of graphene (XT500) dispersed in 1,3 propanediol, containing a 6% of oxidized graphene and without surfactant has been also tested. The results showed that the amorphous PPF is able to crystallize during heating scan in DSC and graphene seems to affect such capability: G hinders the polymer chains in reaching an ordered state, showing even more depressed cold crystallization and melting. On the contrary, such hindering effect is absent with XT500, which rather induces the opposite. Concerning the thermal stability, no improvement has been induced by graphene, even if the onset degradation temperatures remain high for all the materials. A moderate enhancement in mechanical properties is observed in PPF composite with XT500, and especially in PHF composite, where a significative increase of 10-20% in storage modulus E' is maintained in almost all the temperature range. Such an increase is also reflected in a slightly higher heat distortion temperature. These preliminary results can be useful in order to further address the field of application of furan-based polyesters; in particular, they could be promising as packaging materials.

Olive Mill Wastewater Valorization in Multifunctional Biopolymer Composites for Antibacterial Packaging Application.

Olive mill wastewater (OMW) is the aqueous waste derived from the production of virgin olive oil. OMW typically contains a wide range of phenol-type molecules, which are natural antioxidants and/or antibacterials. In order to exploit the bioactive molecules and simultaneously decrease the environmental impact of such a food waste stream, OMW has been intercalated into the host structure of ZnAl layered double hydroxide (LDH) and employed as an integrative filler for the preparation of poly(butylene succinate) (PBS) composites by in situ polymerization. From the view point of the polymer continuous phase as well as from the side of the hybrid filler, an investigation was performed in terms of molecular and morphological characteristics by gel permeation chromatography (GPC) and X-ray diffraction (XRD); also, the thermal and mechanical properties were evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic thermomechanical analysis (DMTA). Antibacterial properties have been assessed against a Gram-positive and a Gram-negative bacterium, Staphylococcus aureus and Escherichia coli, respectively, as representatives of potential agents of foodborne illnesses.

Outstanding chain-extension effect and high UV resistance of polybutylene succinate containing amino-acid-modified layered double hydroxides.

Polybutylene succinate (PBS) nanocomposite materials were prepared using a melt compounding process. The Mg2Al-based PBS nanocomposites, dispersed with inorganic-organic hybrid materials (layered double hydroxides, LDHs), were functionalized with the amino acids L-histidine (HIS) and L-phenylalanine (PHE). The rheological and anti-ultraviolet (anti-UV) properties were investigated and compared to filler-free PBS as well as LDH Mg2Al/nitrate as references. Both organo-modified LDHs exhibited a remarkable chain-extension effect for PBS with an outstanding increase in the zero-shear viscosity η0 for PBS-Mg2Al/PHE (two order of magnitude increase as compared to filler-free PBS). These results were compared to data found in the literature. Moreover, HIS and PHE anions embedded into the LDH structure can successfully prevent the chain scission reactions that usually occur during photo-ageing of PBS under UV radiation exposure. This highlights the outstanding performance of the LDH hybrid materials, and in particular, their application as a polymer chain extender and UV stabilizer for PBS, which can likely be extended to other biodegradable polymers.

Bio-Based PA11/Graphene Nanocomposites Prepared by In Situ Polymerization.

Bio-based polyamide 11 (PA11)-graphene nanocomposites with different filler concentrations (0.25, 0.5, 0.75, 1.5 and 3 wt%) were prepared by In Situ polymerization starting from a water dispersed suspension of graphene nanoplatelets. The effects of the incorporation of the filler were studied in terms of molecular, morphological, thermal and dynamic mechanical properties of the final materials. During the crystallization process from the melt, the filler induces a notable nucleating effect even if the crystal growth rate tends to decrease. The glass transition temperature tends to shift to higher temperatures indicating a decrement of the molecular mobility. Thermal stability is enhanced confirming a good filler dispersion into the matrix. Mechanical reinforcement, investigated by means of a dynamic mechanical thermal analyzer was also highlighted. It was observed that a graphene concentration of 0.75 wt% induces the highest final performances.

Dual chain extension effect and antibacterial properties of biomolecules interleaved within LDH dispersed into PBS by in situ polymerization.

Nanocomposites based on poly(butylene succinate) (PBS) and hydrotalcite-type anionic clays (HTs) organo-modified with biomolecules characterized by antibacterial and/or antioxidant activities, such as l-ascorbic acid (ASA), phloretic acid (HPP), l-tyrosine (TYR) and l-tryptophan (TRP), have been prepared by in situ polymerization. From XRD analysis and rheology experiments in a molten polymer state, intercalated HT hybrid platelets acting here as a hybrid filler are found to be well dispersed into polymers while providing a chain extension effect on PBS. Moreover, the molecules, when hosted within a HT interlayer gap, do preserve their pristine antibacterial activity, both in HT and in the resulting PBS composites. In particular, under the experimental conditions tested, HT/ASA and HT/TYR present the best combination of both properties (chain extension effect and antibacterial), especially versus E. coli as high as 90 and 97% of inhibition, respectively, using 2.5 wt% hybrid filler only. These findings open future applications for PBS associated with the hybrid HT filler as multifunctional materials in active packaging applications.

Marinobacter sp. from marine sediments produce highly stable surface-active agents for combatting marine oil spills.

BACKGROUND: The application of chemical dispersants as a response to marine oil spills is raising concerns related to their potential toxicity also towards microbes involved in oil biodegradation. Hence, oil spills occurring under marine environments necessitate the application of biodispersants that are highly active, stable and effective under marine environment context. Biosurfactants from marine bacteria could be good candidates for the development of biodispersant formulations effective in marine environment. This study aimed at establishing a collection of marine bacteria able to produce surface-active compounds and evaluating the activity and stability of the produced compounds under conditions mimicking those found under marine environment context. RESULTS: A total of 43 different isolates were obtained from harbor sediments. Twenty-six of them produced mainly bioemulsifiers when glucose was used as carbon source and 16 were biosurfactant/bioemulsifiers producers after growth in the presence of soybean oil. Sequencing of 16S rRNA gene classified most isolates into the genus Marinobacter. The produced emulsions were shown to be stable up to 30 months monitoring period, in the presence of 300 g/l NaCl, at 4 °C and after high temperature treatment (120 °C for 20 min). The partially purified compounds obtained after growth on soybean oil-based media exhibited low toxicity towards V. fischeri and high capability to disperse crude oil on synthetic marine water. CONCLUSIONS: To the best of our knowledge, stability characterization of bioemulsifiers/biosurfactants from the non-pathogenic marine bacterium Marinobacter has not been previously reported. The produced compounds were shown to have potential for different applications including the environmental sector. Indeed, their high stability in the presence of high salt concentration and low temperature, conditions characterizing the marine environment, the capability to disperse crude oil and the low ecotoxicity makes them interesting for the development of biodispersants to be used in combatting marine oil spills.

Biowaste biorefinery in Europe: opportunities and research & development needs.

This review aims to explore the needs and opportunities of research & development in the field of biowaste biorefinery in Europe. Modern industry in recent years is giving its close attention on organic waste as a new precious bioresource. Specific biowaste valorisation pathways are focusing on food processing waste, being food sector the first manufacture in Europe. Anyway they need to be further tested and validated and then transferred at the larger scale. In particular, they also need to become integrated, combining biomass pretreatments and recovery of biogenic chemicals with bioconversion processes in order to obtain a large class of chemicals. This will help to (a) use the whole biowaste, by avoiding producing residues and providing to the approach the required environmental sustainability, and (b) producing different biobased products that enter different markets, to get the possible economical sustainability of the whole biorefinery. However, the costs of the developed integrated processes might be high, mostly for the fact that the industry dealing with such issues is still underdeveloped and therefore dominated by high processing costs. Such costs can be significantly reduced by intensifying research & development on process integration and intensification. The low or no cost of starting material along with the environmental benefits coming from the concomitant biowaste disposal would offset the high capital costs for initiating such a biorefinery. As long as the oil prices tend to increase (and they will) this strategy will become even more attractive.