Effect of Lemon Waste Natural Dye and Essential Oil Loaded into Laminar Nanoclays on Thermomechanical and Color Properties of Polyester Based Bionanocomposites

Halloysite and Laponite Hybrid Pigments Synthesis with Copper Chlorophyll

Sustainable and green materials have been studied in dye and pigment productions to reduce their environment impacts from being produced and applied. Although natural dyes are an excellent choice to move from agrowaste, some improvements must be made before they are applied given their poor fastness. One way of improving natural dye properties is their adsorption into nanoclay structures to give hybrid pigments. This work used tubular halloysite and laminar laponite to adsorb and stabilize natural copper chlorophyll. With a statistical design of experiments, we observed interactions between synthesis factors, such as pH, ionic strength, and surfactant or silane modification. Cool hybrid pigments with high TSR (%) values and a wide color range were obtained by using dispersions with only distilled water at room temperature. Successful chlorophyll adsorption on both nanoclay surfaces took place by XRD and DTA analyses. The maximum natural dye absorption for both nanoclay types took place under acid conditions, pH 3–4, and in the presence of mordant. The TSR (%) improved by the silane pH interaction, and halloysite hybrid pigments obtained higher TSR values than the laponite ones. Finally, a wide chromatic green color range was obtained with the surfactant modification in both nanoclays, and the color fastening was also improved in the hybrid pigments application. The samples generated with 10% of hybrid pigments from both nanoclays and an Epoxy bioresin, show higher colorfastness than the sample with the natural chlorophyll, due to the nanoclays–dye interaction and protection.

Anthocyanin Hybrid Nanopigments from Pomegranate Waste: Colour, Thermomechanical Stability and Environmental Impact of Polyester-Based Bionanocomposites

In the present work, anthocyanin (ACN) hybrid nanopigments were synthetized by using a natural pomegranate dye (PD) and calcined hydrotalcite (HT) and montmorillonite (MMT) nanoclays. A wide colour gamut was obtained with MMT-based nanopigments ranging from reddish to bluish hues caused by structural transformations of ACNs at different pH values. However, a buffer effect was observed with HT obtaining samples a similar final colour regardless of the synthesis conditions. Nanopigments added with a biomordant extracted from pomegranate peels showed a different colour compared to the incorporation of a commercial mordant due to the intrinsic colouring properties of the pomegranate bioadditive. The developed nanopigments were incorporated at 7 wt% loading to produce novel polyester-based bionanocomposites which were characterized in terms of thermal, mechanical and colour properties. The encapsulation of PD into the nanoclays improved its thermal stability, in particular for MMT-based nanopigments. The pH changes observed during the nanofillers synthesis affected the final colour of the MMT-based nanocomposites, inducing a general increase in ∆E* and a decrease in gloss values. Slight improvements were obtained in terms of elastic modulus for MMT-based polymer samples confirming the applicability of the developed bionanocomposites as colouring and reinforcement materials. A very similar environmental profile was obtained for MMT and HT-based nanofillers showing MMT-based nanopigments a slightly better general behaviour. The results of the LCA study evidenced the suitability of the processes used in this work to the circular bioeconomy approach through sustainable food waste management and the production of bioplastics using waste substrates.

Effect of Na- and Organo-Modified Montmorillonite/Essential Oil Nanohybrids on the Kinetics of the In Situ Radical Polymerization of Styrene

The great concern about the use of hazardous additives in food packaging materials has shown the way to new bio-based materials, such as nanoclays incorporating bioactive essential oils (EO). One of the still unresolved issues is the proper incorporation of these materials into a polymeric matrix. The in situ polymerization seems to be a promising technique, not requiring high temperatures or toxic solvents. Therefore, in this study, the bulk radical polymerization of styrene was investigated in the presence of sodium montmorillonite (NaMMT) and organo-modified montmorillonite (orgMMT) including thyme (TO), oregano (OO), and basil (BO) essential oil. It was found that the hydroxyl groups present in the main ingredients of TO and OO may participate in side retardation reactions leading to lower polymerization rates (measured gravimetrically by the variation of monomer conversion with time) accompanied by higher polymer average molecular weight (measured via GPC). The use of BO did not seem to affect significantly the polymerization kinetics and polymer MWD. These results were verified from independent experiments using model compounds, thymol, carvacrol and estragol instead of the clays. Partially intercalated structures were revealed from XRD scans. The glass transition temperature (from DSC) and the thermal stability (from TGA) of the nanocomposites formed were slightly increased from 95 to 98 °C and from 435 to 445 °C, respectively. Finally, better dispersion was observed when orgMMT was added instead of NaMMT.

Effect of Chlorophyll Hybrid Nanopigments from Broccoli Waste on Thermomechanical and Colour Behaviour of Polyester-Based Bionanocomposites

Natural dyes obtained from agro-food waste can be considered promising substitutes of synthetic dyes to be used in several applications. With this aim, in the present work, we studied the use of chlorophyll dye (CD) extracted from broccoli waste to obtain hybrid nanopigments based on calcined hydrotalcite (HT) and montmorillonite (MMT) nanoclays. The synthesized chlorophyll hybrid nanopigments (CDNPs), optimized by using statistical designed experiments, were melt-extruded with a polyester-based matrix (INZEA) at 7 wt% loading. Mechanical, thermal, structural, morphological and colour properties of the obtained bionanocomposites were evaluated. The obtained results evidenced that the maximum CD adsorption into HT was obtained when adding 5 wt% of surfactant (sodium dodecyl sulphate) without using any biomordant and coupling agent, while the optimal conditions for MMT were achieved without adding any of the studied modifiers. In both cases, an improvement in CD thermal stability was observed by its incorporation in the nanoclays, able to protect chlorophyll degradation. The addition of MMT to INZEA resulted in large ΔE* values compared to HT incorporation, showing bionanocomposite green/yellow tones as a consequence of the CDNPs addition. The results obtained by XRD and TEM revealed a partially intercalated/exfoliated structure for INZEA-based bionanocomposites, due to the presence of an inorganic filler in the formulation of the commercial product, which was also confirmed by TGA analysis. CDNPs showed a reinforcement effect due to the presence of the hybrid nanopigments and up to 26% improvement in Young's modulus compared to neat INZEA. Finally, the incorporation of CDNPs induced a decrease in thermal stability as well as limited effect in the melting/crystallization behaviour of the INZEA matrix. The obtained results showed the potential use of green natural dyes from broccoli wastes, adsorbed into nanoclays, for the development of naturally coloured bionanocomposites.

Optimisation of Sequential Microwave-Assisted Extraction of Essential Oil and Pigment from Lemon Peels Waste

In this work, a cascade approach to obtain different valuable fractions from lemon peels waste was optimised using microwave-assisted processes. Microwave-assisted hydrodistillation (MAHD) with a Clevenger apparatus was firstly used to obtain the lemon essential oil (LEO). The remaining residue was then submitted to microwave-assisted extraction (MAE) to extract the lemon pigment (LP). A Box-Behnken design was used to evaluate the influence of ethanol concentration, temperature and time in LP extraction in terms of extraction yield and colour intensity. Optimal extraction conditions for LP were 80% (v/v) ethanol, 80 °C and 50 min, with a liquid-to-solid ratio of 1:10. The obtained yields for LEO and LP were around 2 wt.% and 6 wt.%, respectively. The composition of LEO was analysed by gas chromatography with flame ionisation detection (GC-FID), and limonene (65.082 wt.%), β-pinene (14.517 wt.%) and γ-terpinene (9.743 wt.%) were mainly identified. LP was purified by using different Amberlite adsorption resins (XAD4, XAD7HP and XAD16N), showing XAD16N the best adsorption capacity. Enrichment factors of 4.3, 4.5 and 5.0 were found for eriocitrin, diosmin and hesperidin, respectively, which were detected as the main components in LP by ultra-high-performance liquid chromatography-diode array detector-tandem mass spectrometry (UPLC-DAD-MS) analysis, with final concentrations of 4.728 wt.%, 7.368 wt.% and 2.658 wt.%, respectively. Successful antimicrobial capacity against Escherichia coli and Staphylococcus aureus was obtained for LEO. The results from this work showed the potential of applying a cascading approach based on microwave-assisted processes to valorise lemon wastes, obtaining natural pigments and antimicrobials to be applied in food, cosmetic and polymer industries.