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Successful ways of fully exploiting the excellent structural and multifunctional performance of graphene and related materials are of great scientific and technological interest. New opportunities are provided by the fabrication of a novel class of nanocomposites with a nanolaminate architecture. In this work, by using the iterative lift-off/float-on process combined with wet depositions, we incorporated cm-size graphene monolayers produced via Chemical Vapour Deposition into a poly (methyl methacrylate) (PMMA) matrix with a controlled, alternate-layered structure. The produced nanolaminate shows a significant improvement in mechanical properties, with enhanced stiffness, strength and toughness, with the addition of only 0.06 vol% of graphene. Furthermore, oxygen and carbon dioxide permeability measurements performed at different relative humidity levels, reveal that the addition of graphene leads to significant reduction of permeability, compared to neat PMMA. Overall, we demonstrate that the produced graphene–PMMA nanolaminate surpasses, in terms of gas barrier properties, the traditional discontinuous graphene–particle composites with a similar filler content. Moreover, we found that the gas permeability through the nanocomposites departs from a monotonic decrease as a function of relative humidity, which is instead evident in the case of the pure PMMA nanolaminate. This work suggests the possible use of Chemical Vapour Deposition graphene–polymer nanolaminates as a flexible gas barrier, thus enlarging the spectrum of applications for this novel material.

Highly promising fully biobased random copolyesters, poly(trimethylene 2,5-furandicarboxylate-co-trimethylene sebacate) (PTFcoPTSeb), were synthesized by using bio derived 1,3-propanediol, dimethyl ester of 2,5- furandicarboxylic acid, and sebacic acid, through eco-friendly polycondensation in the melt. Copolymers with high molecular weight containing 5, 15, 25 mol % of PTSeb were obtained, and their chemical structure confirmed by 1H NMR and FTIR spectroscopy. The thermal, tensile and gas barrier properties and composability were studied in relation to the copolymer supramolecular structure. As expected, introduction of PTSeb co-units results in lowering of glass transition temperature of copolymers and improves their flexibility. Besides, all copolymers showed outstanding gas barrier properties to O2 and CO2, with copolymer containing 15 mol % of PTSeb showing exceptional gas barrier properties, better than those of PTF and comparable to those of EVOH, currently used in multilayer packaging films. The same copolymer exhibited temperature induced shape memory behaviour. It was found that low amounts (15-25 mol %) of PTSeb in copolymer significantly modifies PTF thermal, mechanical and barrier properties and renders the final material compostable. Copolyesters containing 15 and 25 mol % of PTSeb can compete in some applications with commercially available compostable Ecoflex® polymer, but with markedly improved barrier properties.

In the present study, 100% bio-based polyesters of 2,5-thiophenedicarboxylic acid were synthesized via two-stage melt polycondensation using glycols containing 3 to 6 methylene groups. The so-prepared samples were characterised from the molecular point of view and processed into free-standing thin films. Afterward, both the purified powders and the films were subjected to structural and thermal characterisation. In the case of thin films, mechanical response and barrier properties to O2 and CO2 were also evaluated. From the results obtained, it emerged that the length of glycolic sub-units is an effective tool to modulate the chain mobility and, in turn, the kind and amount of ordered phases developed in the samples. In addition to the usual amorphous and 3D crystalline phases, in all the samples investigated it was possible to evidence a further phase characterised by a lower degree of order (mesophase) than the crystalline one, whose amount is strictly related to the glycol sub-unit length. The relative fraction of all these phases is responsible for the different mechanical and barrier performances. Last, but not least, a comparison between thiophene-based homopolymers and their furan-based homologues was carried out.

In recent decades, synthetic plastic polymers have been the most practical and economical solution for packaging applications due to their low cost, availability, excellent optical, mechanical and barrier properties and resistance against water. However, most of the plastics used for packaging are hardly biodegradable. With a view to a circular economy, the aim of this work focused on the development of a new material made of commercial cellulose derivatives (hydroxypropyl methyl cellulose or carboxymethyl cellulose) mixed with snail mucus extracted from Helix Aspersa Muller. Increasing in Snail Mucus content enhances films elongation and adhesion strength while decreasing water vapor permeability. The cellulose-snail mucus based films are highly transparent but, more interestingly, the mucus confers UV-screening effect. In addition, the composite films exhibit antimicrobial activity against both Gram-positive and Gram-negative bacteria. Furthermore, snail mucus addition to carboxymethyl cellulose strongly decreases films solubility in water. The biodegradation tests indicate that all the films degrade in soil between two and four weeks. The excellent results indicate that these biocomposite films are very good candidate for food packaging.

In the present work, the effect of ether oxygen atom introduction in a furan ring-containing polymer has been evaluated. Solvent-free polycondensation process permitted the preparation of high molecular weight poly(diethylene 2,5-furandicarboxylate) (PDEF), by reacting the dimethyl ester of 2,5-furandicarboxylic acid with diethylene glycol. After molecular and thermal characterization, PDEF mechanical response and gas barrier properties to O2 and CO2, measured at different temperatures and humidity, were studied and compared with those of poly(butylene 2,5-furandicarboxylate) (PBF) and poly(pentamethylene 2,5-furanoate) (PPeF) previously determined. Both PDEF and PPeF films were amorphous, differently from PBF one. Glass transition temperature of PDEF (24 °C) is between those of PBF (39 °C) and PPeF (13 °C). As concerns mechanical response, PDEF is more flexible (elastic modulus [E] = 673 MPa) than PBF (E = 1290 MPa) but stiffer than PPeF (E = 9 MPa). Moreover, PDEF is the most thermally stable (temperature of maximum degradation rate being 418 for PDEF, 407 for PBF and 414 °C for PPeF) and hydrophilic (water contact angle being 74° for PDEF, 90° for PBF and 93° for PPeF), with gas barrier performances very similar to those of PPeF (O2 and CO2 transmission rate being 0.0022 and 0.0018 for PDEF and, 0.0016 and 0.0014 cm3 cm/m2 d atm for PPeF). Lab scale composting experiments indicated that PDEF and PPeF were compostable, the former degrading faster, in just one day. The results obtained are explained on the basis of the high electronegativity of ether oxygen atom with respect to the carbon one, and the consequent increase of dipoles along the macromolecule.

Novel poly(lactic acid)-based chain extended triblock copolymers have been successfully synthesized in melt. The new polymers are characterized by a triblock ABA architecture, where A, is poly(lactic acid) and B is an ad hoc synthesized random biobased aliphatic copolyester poly(propylene/neopentyl glycol succinate). PLLA homopolymer has been also prepared for the sake of comparison. The samples under study were deeply characterized from the molecular, thermal and structural point of view. Mechanical and barrier properties and compostability were also investigated, in order to assess the potentiality of these materials in food packaging applications. The results obtained show that copolymerization leads to better mechanical response and barrier properties with respect to poly(lactic) acid homopolymer. Moreover, the presence of the central B block in the main polymer chain facilitates the process of compostability.

11 pags., 7 figs., 4 tabs., In the present paper, four fully biobased homopolyesters of 2,5-furandicarboxylic acid (2,5-FDCA) with a high molecular weight have been successfully synthesized by two-stage melt polycondensation, starting from the dimethyl ester of 2,5-FDCA and glycols of different lengths (the number of methylene groups ranged from 3 to 6). The synthesized polyesters have been first subjected to an accurate molecular characterization by NMR and gel-permeation chromatography. Afterward, the samples have been successfully processed into free-standing thin films (thickness comprised between 150 to 180 μm) by compression molding. Such films have been characterized from the structural (by wide-angle X-ray scattering and small-angle X-ray scattering), thermal (by differential scanning calorimetry and thermogravimetric analysis), mechanical (by tensile test), and gas barrier (by permeability measurements) point of view. The glycol subunit length was revealed to be the key parameter in determining the kind and fraction of ordered phases developed by the sample during compression molding and subsequent cooling. After storage at room temperature for one month, only the homopolymers containing the glycol subunit with an even number of-CH2-groups (poly(butylene 2,5-furanoate) (PBF) and poly(hexamethylene 2,5-furanoate) (PHF)) were able to develop a three-dimensional ordered crystalline phase in addition to the amorphous one, the other two appearing completely amorphous (poly(propylene 2,5-furanoate (PPF) and poly(pentamethylene 2,5-furanoate) (PPeF)). From X-ray scattering experiments using synchrotron radiation, it was possible to evidence a third phase characterized by a lower degree of order (one-or two-dimensional), called a mesophase, in all the samples under study, its fraction being strictly related to the glycol subunit length: PPeF was found to be the sample with the highest fraction of mesophase followed by PHF. Such a mesophase, together with the amorphous and the eventually present crystalline phase, significantly impacted the mechanical and barrier properties, these last being particularly outstanding for PPeF, the polyester with the highest fraction of mesophase among those synthesized in the present work., G.G., M.S., N.L., and A.M. acknowledge the Italian Ministry of University and Research. This publication is based upon work from COST Action FUR4Sustain, CA18220, supported by COST (European Cooperation in Science and Technology).

9 pags., 8 figs., 1 tab., 2 schs.-- sc9b04407_si_001.mp4 (75.48 MB) sc9b04407_si_002.mp4 (5.46 MB), Among the various factors that contribute to the transition from a linear to a circular economy, the identification of superpolymers with outstanding mechanical as well as barrier properties and zero environmental impact has become a mandatory issue. Such new supermaterials render recycling a concrete option for the efficient and ecofriendly management of plastic wastes. In this study, a 100% biobased polyester has been prepared by a one-pot and solvent-free synthesis, starting from 2,5-furandicarboxylic acid and 1,5-pentanediol. At first, a molecular and thermal characterization of the polymer has been conducted and then processed to prepare a compression molded film, despite its amorphous and rubbery nature at room temperature. The mechanical response was typical of elastomers, with a low elastic modulus and stress at break and high elongation at break. An instant shape recovery after breaking was observed, indicating the presence of net points. The barrier properties to O and CO were exceptional and similar to those of ethylene vinyl alcohol (EVOH) and of polymer liquid crystals. All of these unexpected and surprising properties were explained as being due to the presence of a 2D microstructure characterized by partially ordered furanic rings favored by intermolecular C-H···O bonds., Experiments at the ALBA Synchrotron have been funded by the Spanish Ministry of Science, Innovation and Universities (MSIU). This study was also partially supported by MSIU by the grant MAT2015-66443-C02-1-R.

Edible films and coatings gained renewed interest in the food packaging sector with polysaccharide and protein blending being explored as a promising strategy to improve properties of edible films. The present work studies composite edible films in different proportions of pectin (P), alginate (A) and whey Protein concentrate (WP) formulated with a simplex centroid mixture design and evaluated for physico-chemical characteristics to understand the effects of individual components on the final film performance. The studied matrices exhibited good film forming capacity, except for whey protein at a certain concentration, with thickness, elastic and optical properties correlated to the initial solution viscosity. A whey protein component in general lowered the viscosity of the initial solutions compared to that of alginate or pectin solutions. Subsequently, a whey protein component lowered the mechanical strength, as well as the affinity for water, as evidenced from an increasing contact angle. The effect of pectin was reflected in the yellowness index, whereas alginate and whey protein affected the opacity of film. Whey protein favored higher opacity, lower gas barrier values and dense structures, resulting from the polysaccharide-protein aggregates. All films displayed however good thermal stability, with degradation onset temperatures higher than 170 &deg, C.

Thermal, structural and physico-chemical properties of different composite edible films based on alginate and pectin with the addition of citral essential oil (citral EO) as an agent to improve barrier properties, were investigated. The obtained films were clear and transparent, with a yellow hue that increased with citral EO addition. All the films displayed good thermal stability up to 160 &deg, C, with a slight improvement observed by increasing the amount of citral EO in the composites. Gas transmission rate (GTR) strongly depended on the polymer structure, gas type and temperature, with improvement in barrier performance for composite samples. Also, citral EO did not exert any weakening action on the tensile behavior. On the contrary, an increase of the elastic modulus and of the tensile strength was observed. Lastly, water contact angle measurements demonstrated the dependence of the film wettability on the content of citral EO.

The present paper describes the synthesis of novel bio-based poly(butylene 1,4-cyclohexane dicarboxylate)-containing random copolymers for sustainable and flexible packaging applications. On one side, the linear butylene moiety has been substituted by glycol subunits with alkyl pendant groups of different length. On the other side, copolymers with different cis/trans isomer ratio of cyclohexane rings have been synthesized. The prepared samples were subjected to molecular, thermal, diffractometric, and mechanical characterization. The barrier performances to O2, CO2, and N2 gases were also evaluated. The presence of side alkyl groups did not alter the thermal stability, whereas it significantly influences the formation of ordered phases that deeply affect the functional properties, mainly in terms of mechanical response and barrier performance. In particular, the final materials present higher flexibility and significantly improved barrier properties with respect to the homopolymer and most polymers widely employed for flexible packaging. The improvement due to copolymerization was more pronounced in the case of higher co-unit-containing copolymers and for the samples with cyclohexane rings in the trans conformation.

In the last decade, there has been an increased interest from the food packaging industry toward the development and application of bioplastics, to contribute to the sustainable economy and to reduce the huge environmental problem afflicting the planet. In the present work, we focus on a new furan-based polyester, poly(neopentyl glycol 2,5-furanoate) (PNF) to be used for sustainable food packaging applications. The aromatic polyester was successfully synthesized with high molecular weight, through a solvent-free process, starting directly from 2,5-furandicarboxylic acid. PNF was revealed to be a material with good thermal stability, characterized by a higher Tg and Tm and a lower RAF fraction compared to poly(propylene 2,5-furanoate) (PPF), ascribable to the two methyl side groups present in PNF glycol-sub-unit. PNF’s mechanical characteristics, i.e., very high elastic modulus and brittle fracture, were found to be similar to those of PPF and PEF. Barrier properties to different gases, temperatures and relative humidity were evaluated. From the results obtained, PNF was showed to be a material with very smart barrier performances, significantly superior with respect to PEF’s ones. Lastly, PNF’s permeability behavior did not appreciably change after contact with food simulants, whereas it got worse with increasing RH, due to the polar nature of furan ring.

In the last decade, there has been an increased interest from the food packaging industry toward the development and application of biodegradable and biobased plastics, to contribute to the sustainable economy and to reduce the huge environmental problem afflicting the planet. In this framework, the present paper describes the synthesis of novel PBS (poly(butylene succinate))-based random copolymers with different composition containing glycol sub-units characterized by alkyl pendant groups of different length. The prepared samples were subjected to molecular, thermal, diffractometric and mechanical characterization. The barrier performances to O2, CO2 and N2 gases were also evaluated, envisioning for these new materials an application in food packaging. The presence of the side alkyl groups did not alter the thermal stability, whereas it significantly reduced the sample crystallinity degree, making these materials more flexible. The barrier properties were found to be worse than PBS; however, some of them were comparable to, or even better than, those of Low Density Polyethylene (LDPE), widely employed for flexible food packaging. The entity of variations in the final properties due to copolymerization were more modest in the case of the co-unit with short side methyl groups, which, when included in the PBS crystal lattice, causes a more modest decrement of crystallinity degree.

A class of multiblock fully-aliphatic copolyesters containing thio-ether linkages has been synthesized by reactive blending. Solid-state properties have been correlated to the chemical structure and the molecular architecture. With the aim of employing these polymers for food packaging, the permeability behavior to CO2 and O2 gas has been analysed. The decrease of the degree of crystallinity, due to the copolymerization, together with the flexibility given by the thio-ether containing sequences, deeply influenced the behavior of the copolymers. The length of the copolymer sequences played the major role in tailoring the polymer characteristics. A decrease in the block length caused a decrease in the crystallinity degree and in the flexibility effect. Finally, the copolyesters here presented have been compared to ether-oxygen containing samples of comparable molecular architecture, to evaluate the effect of the different heteroatom on the polymer properties.

Fully bio-based and biodegradable materials, such as polylactic acid (PLA) and microfibrillated cellulose (MFC), are considered in order to produce a completely renewable packaging solution for oxygen barrier applications, even at medium-high relative humidity (R.H.). Thin layers of MFC were coated on different PLA substrates by activating film surface with an atmospheric plasma treatment, leading to the fabrication of robust and transparent multilayer composite films, which were then characterized by different experimental techniques. UV transmission measurements confirmed the transparency of multilayer films (60% of UV transmission rate), while SEM micrographs showed the presence of a continuous, dense and defect free layer of MFC on PLA surface. Concerning the mechanical behavior of the samples, tensile tests revealed that the multilayer films significantly improved the stress at break value of neat PLA. Moreover, the oxygen barrier properties of the multilayer films were improved more than one order of magnitude compared to neat PLA film at 35 °C and 0% R.H. and the permeability values were maintained up to 60% R.H. The obtained materials therefore showed interesting properties for their possible use in barrier packaging applications as fully biodegradable solution, coupling two primarily incompatible matrices in a multilayer film with no need of any solvent or chemical.

Novel fully biobased aliphatic-aromatic poly(butylene 2,5-furanoate/diglycolate) random copolyesters were successfully synthesized from 2,5-furandicarboxylic acid, diglycolic acid and 1,4-butanediol through two-stage melt polycondensation using titanium tetrabutoxide and titanium tetraisopropoxide as catalysts. The synthesized polymers were characterized in terms of molecular and solid-state properties, among these, barrier properties to different gases. In addition, biodegradability studies in compost have been conducted. All the polymers showed a good thermal stability, even higher than that of the thermally stable homopolymer poly(butylene furanoate), and at room temperature appeared as semicrystalline materials. The main effect of copolymerization was a lowering, up to 60 °C, in Tm respect to the homopolymer. The dependence of Tm on composition for copolymers was well described by Baur’s equation. Diffractometric measurements indicated that only the poly(butylene furanoate) crystalline phase is present in the copolymers under investigation. Amorphous samples showed a monotonic decrement of Tg, up to 30 °C, as the content of butylene diglycolate units is increased and this can be explained on the basis of the higher flexibility induced in the polymer chain by the ether-oxygen atoms. A Wood-type equation was found to fit the Tg data of completely amorphous samples. Final properties and biodegradation rate of the materials under study were strictly dependent on the copolymer composition and the crystallinity degree. As a matter of fact, hydrophilicity regularly increased with the increasing of butylene diglycolate mol%, due to the highly electronegative ether-oxygen atoms present in the co-units (water contact angle decreased of almost 15°). The elastic modulus decreased till one order of magnitude and the elongation to break increased, up to 400%, as co-unit content was increased. Regarding the gas barrier properties, copolymerization did not imply a worsening with respect to the homopolymer. A slight increment of the gas transmission rate was recorded just for the copolymer containing the highest amount of butylene diglycolate units, as a consequence of the increasing flexibility of the macromolecular chain due to the ether-oxygen atoms. This behavior was more evident with CO2 gas test than with O2, N2 and C2H4 ones.

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Use of polymers from renewable sources for food packaging applications is steadily growing. However, as compared to thermoplastic synthetic polymers, they present problems when processed with traditional technologies and show inferior performances in terms of functional and structural properties. This review paper focuses, in its first part, on current issues related to processing, such as thermoplasticization of starch and proteins, extrusion of films and foams. In the second part, the strategies for the technological advancements aimed to improve barrier properties, to promote active antimicrobial functionality and to apply these materials also in demanding high pressure processing of packaged foodstuff are discussed.

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