The structural evolution of poly(ethylene vanillate) (PEV) crystals, after isothermal crystallization at Tc = 180 oC, was explored by synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS) measurements. The WAXS/SAXS analyses proved that an additional more perfect crystal population starts to grow exactly in correspondence of the exotherm displayed by the specific heat capacity curve. The study ascertained that two different reorganization/recrystallization mechanisms occur upon heating: the more perfect crystals originate from a recrystallization process, whereas the original crystals undergo small and progressive perfection maybe without previous complete fusion. Deconvolution of the double Lorentz-corrected SAXS profiles was performed to calculate the temperature evolution of the lamellar thickness for the original and additional crystal populations. The two crystal populations appear to differ substantially in the temperature evolution of the lamellar and amorphous thicknesses. Hypotheses on the relative location of the two different crystal stacks as well as on the possible thermodynamic reason that triggers the formation of the more perfect crystal population have been formulated.

The study investigates the distribution of the plasticizers acetyl triethyl citrate (ATEC) and acetyl tributyl citrate (ATBC) in the mobile amorphous (MAF) and rigid amorphous (RAF) fractions of semi-crystalline plasticized poly(lactic acid) (PLA) containing 5 wt% of plasticizer. During crystallization, the ATEC and ATBC concentration in the MAF increases from 5 to about 8 wt%. At the end of crystallization, the plasticizers concentration in the RAF is lower than that in the MAF. The progressive decrease of the ATEC and ATBC concentration in the RAF region could be linked to the growth of subsidiary lamellae in more restricted amorphous areas. The study also introduces an estimation of the tensile elastic modulus of the RAF (ERAF) in semi-crystalline pure and plasticized PLA containing ?-crystals. The mechanical model with crystalline lamellae perpendicular to the stress direction turned out to be the most appropriate arrangement to represent the morphological organization in PLA samples prepared by injection-moulding processing at high pressure. The mathematical procedure led to a crystal elastic modulus (EC) of the ?-phase in excellent agreement with the theoretical value reported in the literature (EC = 14 GPa), and to an ERAF value around 5.5 GPa, for both pure and plasticized PLA, thus suggesting that both ATEC and ATBC do not exert plasticizing action on the RAF.

Vanillic acid represents a potentially interesting bio-based building block for the production of new aliphatic-aromatic polymers, characterized by thermal properties similar to those of the analogous terephthalic polyesters. However, poly(ethylene vanillate) proved to be a very brittle material, probably due to a very high degree of crystallinity, and, then, not suitable for melt processing. Therefore, the synthesis of copolymers, based on vanillic acid and pentadecalactone is considered as a strategy to obtain new polymeric materials with a low degree of crystallinity, tunable properties, and better performances. The synthesis of these fully bio-based random copolymers is successful. The thermal properties have been studied in order to correlate chemical structure and final performances. The polymers proved to be processable and films are obtained, suggesting possible applications of the copolymers in a new sustainable flexible packaging.

The structural evolution of poly(butylene succinate) (PBS) crystals after crystallization at 100 °C has been investigated by synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS) analysis. Isothermal crystallization of PBS leads to a single lamellar population. Temperature-dependent WAXS/SAXS analysis has proven that an additional crystal population, characterized by thicker lamellae, develops upon heating, resulting in a dual lamellar population. Deconvolution of the Lorentz-corrected double SAXS profiles has allowed deriving the temperature dependence of the lamellar thickness for the two different crystal populations. The structural information derived by WAXS/SAXS has allowed elucidating the multiple melting behavior of PBS, so that the separate endotherms of the overall melting behavior could be associated with specific thermal events. The first melting peak has been connected to the fusion of original crystals, only minimally reorganized upon heating, whereas the second melting peak has been ascribed to the overlapping of two different melting processes, one linked to the fusion of original crystals thickened at high temperatures, most likely in the solid state, and the other one to the fusion of markedly thicker crystals, developed via melting/recrystallization mechanism.

The temperature dependence of the constrained amorphous interphase or rigid amorphous fraction (RAF) in bio-based semi-crystalline poly(ethylene 2,5-furandicarboxylate) (PEF) was assessed. RAF, which is located in proximity of the basal crystal planes, was found to develop in parallel with the crystal phase during crystallization at the lowest investigated Ts, i.e. 130 and 140 °C, at which the less stable alpha'-crystal phase grows. At higher Ts, RAF does not vitrify during crystallization, but only upon the subsequent cooling down to Tg. The rigid amorphous fraction at Tg increases by decreasing the crystallization temperature, ranging approximately from 15 to 25%. This information is useful for the development of PEF products, since many RAF physical properties, for example mechanical and barrier properties, are different from those of the amorphous fraction far from the crystals. RAF decreases with increasing temperature, and becomes zero around 150 °C. The same temperature limit of 150 °C was found to influence the reversing crystallization/melting process at the lateral crystal surfaces, as well as the crystallization rate, which reaches its maximum at temperatures above 150 °C. In addition, singularly, the more ordered crystalline alpha-form was found to grow only at temperatures higher than 150 °C. The total absence of constraints on the amorphous segments mobility, identified at temperatures higher than 150 °C, also favors additional crystallization upon heating in the PEF samples crystallized at low Ts, with also alpha-crystals development. The densities of the RAF connected to alpha'- and alpha-crystals were estimated at room temperature.

This paper reports the thermal, morphological and mechanical properties of environmentally friendly poly(3-hydroxybutyrate) (PHB)/poly(butylene succinate) (PBS) and PHB/poly[(butylene succinate)-co-(butylene adipate)] (PBSA) blends, prepared by melt mixing. The blends are known to be immiscible, as also confirmed by the thermodynamic analysis here presented. A detailed quantification of the crystalline and amorphous fractions was performed, in order to interpret the mechanical properties of the blends. As expected, the ductility increased with increasing PBS or PBSA amount, but in parallel the decrease in the elastic modulus appeared limited. Surprisingly, the elastic modulus was found properly described by the rule of mixtures in the whole composition range, thus attesting mechanical compatibility between the two blend components. This unusual behavior has been explained as due to co-continuous morphology, present in a wide composition range, but also at the same time as the result of shrinkage occurring during sequential crystallization of the two components, which can lead to physical adhesion between matrix and dispersed phase. For the first time, the elastic moduli of the crystalline and mobile amorphous fractions of PBS and PBSA and of the mobile amorphous fraction of PHB at ambient temperature have been estimated through a mechanical modelling approach. © 2021 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Poly(lactic acid) (PLA) is the most widely produced biobased, biodegradable and biocompatible polyester. Despite many of its properties are similar to those of common petroleum-based polymers, some drawbacks limit its utilization, especially high brittleness and low toughness. To overcome these problems and improve the ductility and the impact resistance, PLA is often blended with other biobased and biodegradable polymers. For this purpose, poly(butylene adipate-co-butylene terephthalate) (PBAT) and poly(butylene succinate-co-butylene adipate) (PBSA) are very advantageous copolymers, because their toughness and elongation at break are complementary to those of PLA. Similar to PLA, both these copolymers are biodegradable and can be produced from annual renewable resources. This literature review aims to collect results on the mechanical, thermal and morphological properties of PLA/PBAT and PLA/PBSA blends, as binary blends with and without addition of coupling agents. The effect of different compatibilizers on the PLA/PBAT and PLA/PBSA blends properties is here elucidated, to highlight how the PLA toughness and ductility can be improved and tuned by using appropriate additives. In addition, the incorporation of solid nanoparticles to the PLA/PBAT and PLA/PBSA blends is discussed in detail, to demonstrate how the nanofillers can act as morphology stabilizers, and so improve the properties of these PLA-based formulations, especially mechanical performance, thermal stability and gas/vapor barrier properties. Key points about the biodegradation of the blends and the nanocomposites are presented, together with current applications of these novel green materials.

In this contribution the temperature evolution of the constrained or rigid amorphous fraction (RAF) of biodegradable and biocompatible poly(butylene succinate) (PBS) was quantified, after detailed thermodynamic characterization by differential scanning calorimetry and X-ray diffraction analysis. At the glass transition temperature, around -40 °C, the rigid amorphous fraction in PBS is about 0.25. It decreases with increasing temperature and becomes zero in proximity of 25 °C. Thus, at room temperature and at the human body temperature, all the amorphous fraction is mobile. This information is important for the development of PBS products for various applications, including biomedical applications, since physical properties of the rigid amorphous fraction, for example mechanical and permeability properties, are different from those of the mobile amorphous fraction.

The origin of "annealing peaks" in semicrystalline polymers, obtained with aging thermal protocols at temperatures between the glass transition and the melting temperature, and revealed by calorimetry as small endotherms preceding the main melting peak, has been recently debated in the literature. On the one side it is claimed that these small endotherms are related to the melting of defective/thinner crystals, on the other side it is proposed that they can be associated to the enthalpy relaxation of the rigid amorphous fraction (RAF), i.e., that part of the amorphous region directly coupled to the crystalline stems. With this work we aim to contribute to the debate, by exploiting the different thermal properties of the RAF coupled with different crystal modifications of polymorphic poly (butene-1) (PB-1). In this polymer the RAF mobilizes at largely different temperatures when it is coupled with crystals of trigonal Form I, or tetragonal Form II. By exploiting this peculiarity, we performed isochronous aging experiments with differential scanning calorimetry (DSC) on both crystalline phases, in a wide temperature range between the glass transition of the mobile (bulk) amorphous fraction and the onset of crystal melting. An endothermic peak above the aging temperature was typically observed. The trend of the enthalpy of this annealing peak with temperature can be described by a bell-shaped curve, approaching zero recovered enthalpy at temperatures of 100-110 °C, and 40-50 °C for Form I and Form II, respectively. These temperatures coincide with previous literature report about mobilization of PB-1 RAF and are thus identified as the upper limit of the RAF glass transition for the two polymorphs. Isothermal aging experiments as a function of time suggest that the enthalpy recovery of Form I RAF show the typical signature of glassy dynamics, similarly to what occurs for Form II RAF after short aging times. At longer times, the superposition of the polymorphic phase transition and RAF aging changes the kinetics of the recovered enthalpy for the latter polymorph, possibly due to the increased stress at the crystal-amorphous interface and creation of additional RAF in parallel with Form II to Form I transformation. Overall, our results demonstrate that for PB-1, at least within the investigated temperature range, the annealing peaks can be related to the RAF strive to attain thermodynamic equilibrium in its glassy state.

In this work, processability and mechanical performances of bio-composites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 5, 10, and 15 wt % of bran fibers, untreated and treated with natural carnauba and bee waxes were evaluated. Wheat bran, the main byproduct of flour milling, was used as filler to reduce the final cost of the PHBV-based composites and, in the same time, to find a potential valorization to this agro-food by-product, widely available at low cost. The results showed that the wheat bran powder did not act as reinforcement, but as filler for PHBV, due to an unfavorable aspect ratio of the particles and poor adhesion with the polymeric matrix, with consequent moderate loss in mechanical properties (tensile strength and elongation at break). The surface treatment of the wheat bran particles with waxes, and in particular with beeswax, was found to improve the mechanical performance in terms of tensile properties and impact resistance of the composites, enhancing the adhesion between the PHBV-based polymeric matrix and the bran fibers, as confirmed by predictive analytic models and dynamic mechanical analysis results.

The semicrystalline state of polymers implies the formation of a noncrystalline interphase beside lamellar crystals known as the rigid amorphous fraction (RAF). This devitrifies on heating at temperatures much higher than the one typical of the bulk-amorphous fraction. Its glass transition and physical aging in the glassy state have thus far remained elusive. Here, we study the RAF glassy dynamics in poly(L-lactic acid) (PLLA) applying recently developed aging thermal protocols based on fast scanning calorimetry (FSC). Specifically, semicrystalline samples are aged in different conditions between the glass transition of mobile amorphous fraction and the crystals' melting temperature (TM). A distinct endothermic peak at temperatures above that of aging develops with time. We provide compelling evidence that in the initial part of aging the origin of this peak is due to the enthalpy recovery of glassy RAF. At longer aging times, the aging peak is at least partly associated with secondary crystallization. Isochronous experiments at different aging temperatures enable to obtain a fair estimate of the RAF glass transition temperature, whose upper limit is about 135 °C. The proposed method holds the promise of gaining new insights into the elusive glassy dynamics of the RAF of semicrystalline polymers.

The mechanical properties of semicrystalline PLLA containing exclusively alpha'- or alpha-crystals have been investigated. The connection between experimental elastic moduli and phase composition has been analyzed as a function of the polymorphic crystalline form. For a complete interpretation of the mechanical properties, the contribution of the crystalline regions and the constrained amorphous interphase or rigid amorphous fraction (RAF) has been quantified by a three-phase mechanical model. The mathematical approach allowed the simultaneous quantification of the elastic moduli of (i) the alpha'- and alpha-phases (11.2 and 14.8 GPa, respectively, in excellent agreement with experimental and theoretical data reported in the literature) and (ii) the rigid amorphous fractions linked to the alpha'- and alpha-forms (5.4 and 6.1 GPa, respectively). In parallel, the densities of the RAF connected with alpha'- and alpha-crystals have been measured (1.17 and 1.11 g/cm(3), respectively). The slightly higher value of the elastic modulus of the RAF connected to the alpha-crystals and its lower density have been associated to a stronger chain coupling at the amorphous/crystal interface. Thus, the elastic moduli at T-room of the crystalline (E-C), mobile amorphous (E-MAF), and rigid amorphous (E-RAF) fractions of PLLA turned out to be quantitatively in the order of E-MAF < E-RAF <E-C, with the experimental E-MAF, value equal to 3.6 GPa. These findings can allow a better tailoring of the properties of PLLA materials in relation to specific applications.

Biocomposites with by-products of agro-industrial feedstock are raising industrial interest. Potato pulp, as residue of the starch industry, can be valorised in polylactide (PLA) or polyhydroxyalkanoates (PHA) systems to replace the biomass feedstock for biocomposite production. In this study, biocomposites with up to 20% by weight of potato pulp were successfully produced on industrial scale and proposed for application in pots and rigid packaging. In order to evaluate and optimize the sustainability of biocomposite supply chain, a hybrid life cycle assessment model was developed to evaluate the economic, social and environmental impacts of potato pulp valorisation in the biocomposite supply chains. The results suggested potato pulp valorisation can bring positive social-economic impacts with adverse environmental effect to both PLA and PHA biocomposite supply chains. Improving the thermal energy used in drying potato pulp has potential to achieve positive performance in GHG reduction, especially for PLA based biocomposite supply chain. Given potato pulp valorisation has other benefits, such as reduce agricultural waste and improve biodegradability. Valorising potato pulp in PLA based biocomposite supply chain can potentially facilitate the transition to a sustainable bioeconomy. It deserves further research and support from financial and political aspects. (C) 2020 Elsevier Ltd. All rights reserved.

Furandicarboxylate-based polyesters are considered an interesting class of bio-based polymers due to their improved properties with respect to the petrol-based terephthalate homologs. An in-depth analysis of the crystal structure of poly(propylene 2,5-furandicarboxylate) (PPF), after maximum possible removal of the catalyst, was carried out. The study disclosed that purified PPF presents two different crystalline phases after crystallization from the melt. Crystallizations at temperatures lower than 120 °C lead to growth of a single crystal form (?-form), whereas two different crystal forms (? and ?) were found to coexist at higher Tcs. This behavior is opposite to that previously observed for unpurified PPF. The possibility that the catalyst nucleates the ?-phase, which therefore becomes the kinetically favored modification at low crystallization temperatures in the presence of a higher amount of catalyst residue, has been considered as a feasible explanation. Two concomitantly different spherulitic morphologies were observed and connected to the ?- A nd ?-phase, respectively. The association between polymorphism and melting behavior was studied. The origin of the peaks that compose the multiple melting endotherm recorded at conventional heating rates was determined by combined wide-angle X-ray scattering, differential scanning calorimetry, fast scanning chip calorimetry, and polarized light optical microscopy measurements. The higher thermal stability of the ?-crystals in comparison with the ?-form was thus demonstrated.

The use of biopolyesters, as polymeric matrices, and natural fillers derived from wastes or by-products of food production to achieve biocomposites is nowadays a reality. The present paper aims to valorize mussel shells, 95% made of calcium carbonate (CaCO ), converting them into high-value added products. The objective of this work was to verify if CaCO, obtained from Mediterranean Sea mussel shells, can be used as filler for a compostable matrix made of Polylactic acid (PLA) and Poly(butylene adipate-co-terephthalate) (PBAT). Thermal, mechanical, morphological and physical properties of these biocomposites were evaluated, and the micromechanical mechanism controlling stiffness and strength was investigated by analytical predictive models. The performances of these biocomposites were comparable with those of biocomposites produced with standard calcium carbonate. Thus, the present study has proved that the utilization of a waste, such as mussel shell, can become a resource for biocomposites production, and can be an effective option for further industrial scale-up.

In the present study, for the first time the evolution of tensile mechanical properties of different poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers (PHBV8 and PHBV12, with 8 mol% and 12 mol% of HV co-units, respectively) as a function of the storage time at room temperature has been investigated in parallel with the quantification of the crystalline, mobile amorphous, and rigid amorphous fractions. A comparison with the evolution of the crystalline and amorphous fractions in the homopolymer poly(3-hydroxybutyrate) (PHB) was also performed. For all the samples, the crystallinity was found to slightly increase during storage. In parallel, the mobile amorphous fraction (MAF) decreased markedly, with the result that a relevant increase in the rigid amorphous fraction (RAF) was detected. The RAF content in the copolymers was lower than that of PHB. For all the samples, the RAF formation during aging was ascribed to the growth of secondary crystals in geometrically restricted areas. It was demonstrated that the storage at T-room leads in PHB, PHBV8, and PHBV12 to a progressive increase in the total solid fraction (crystal phase + rigid amorphous fraction) and to a simultaneous physical aging of the rigid amorphous fraction. The two different processes cannot be separated and distinguished, so that only the resulting effect on the mechanical properties was considered. The experimental elastic modulus of both PHBV8 and PHBV12 was found to increase regularly with the total solid fraction, as well as the tensile strength. Conversely, the elongation at break turned out to be an increasing function of the mobile amorphous fraction. The elastic moduli of the crystalline, mobile amorphous, and rigid amorphous fractions of PHBV8 and PHBV12 were estimated by means of a three-phase modified Takayanagi's model, to take into account also the contribution of the rigid amorphous fraction. The calculated values were found in agreement with theoretical expectations.

For the academic and industrial research that aims at substituting plastics derived from fossil feedstock with bio-based alternatives, the furandicarboxylate-based polyesters are a very promising family of materials, because they exhibit enhanced properties for advanced applications. In order to lay the foundation for the comprehension of the relationships between crystallization process and final properties for these materials, a detailed investigation on the crystal structure of poly(propylene 2,5-furandicarboxylate) (PPF) has been performed. The study has revealed that PPF exhibits polymorphism when crystallized from the melt. Three forms have been identified, as well as a crystal transformation from a defective to a more perfect crystal structure upon heating. The different crystal modifications coexist, depending on the crystallization temperature. The relationship between polymorphism and melting behavior has been investigated, and the peaks that constitute the multiple melting endotherm assigned. This is the first case of polymorphism involving three crystal forms that is observed for bulk crystallized furandicarboxylates-based polyesters.

The thermal, mechanical and viscoelastic properties of biocomposites of poly(lactic acid) (PLA) with 20 wt.% of potato pulp powder were investigated. The potato pulp powder utilized is a byproduct from the production and extraction of starch. The results showed that the potato pulp powder does not act as reinforcement, but as filler for PLA, due to an unfavorable aspect ratio and the irregular shape of the particles. In order to improve the mechanical response of the PLA/potato pulp powder biocomposites, surface treatment of the potato pulp particles with bio-based and petroleum-based waxes was investigated. This treatment was found to improve the properties of the biocomposites, enhancing the adhesion between the PLA based polymeric matrix and the potato pulp fibers. The best result is obtained with a petroleum-based wax, but also the bio-based waxes lead to good mechanical properties of the biocomposite. Thus, the addition to PLA of potato pulp powder, treated with waxes, appears a method able to (i) utilize and valorize an abundant agro-food biomass such as potato pulp, according to the principles of circular economy, (ii) favor the production of articles with properties valuable for practical applications, and (iii) reduce the cost of the final products, considering the relatively high cost of PLA.

For the first time in this study, the utilization of rice bran oil (RBO) as possible totally eco-friendly plasticizer for poly(lactic acid) (PLA) has been investigated. For comparison, the behavior of soybean oil (SO) has also been analyzed. Both oils are not completely miscible with PLA. However, certain compatibility exists between PLA and (i) RBO and (ii) SO, because demixing is not complete. Although not totally miscible, RBO and SO are able to reduce the viscosity of the PLA+RBO and PLA+SO mixtures, which attests that a small amount of RBO or SO can be successfully added to PLA to improve its processability. Additionally, the mechanical properties of the PLA+RBO and PLA+SO mixtures exhibit trends typical of plasticizer-polymer systems. More interestingly, RBO was found to accelerate the growth of PLA '-crystals at a low crystallization temperature. This feature is appealing, because the '-phase presents lower elastic modulus and higher permeability to water vapor in comparison to the -phase, which grows at high temperatures. Thus, this study demonstrates that the addition of RBO to PLA in small percentages is a useful solution for a faster preparation of PLA materials containing mainly the '-phase.

The thermal and mechanical properties of biocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 5 wt % of valerate units, with 20 wt % of potato pulp powder were investigated in order (i) to obtain information on possible miscibility/compatibility between the biopolymers and the potato pulp, and (ii) to quantify how the addition of this filler modifies the properties of the polymeric material. The potato pulp powder utilized is a residue of processing for the production and extraction of starch. The final aim of this study is the preparation of PHBV based materials with reduced cost, thanks to biomass valorization, in agreement with the circular economy policy, as result of the incorporation of agricultural organic waste. The results showed that the potato pulp powder does not act as reinforcement, but rather as filler for the PHBV polymeric matrix. A moderate loss in mechanical properties is detected (decrease in elastic modulus, tensile strength and elongation at break), which regardless still meets the technical requirements indicated for rigid packaging production. In order to improve the mechanical response of the PHBV/potato pulp powder biocomposites, surface treatment of the potato pulp powder with bio-based and petroleum-based waxes was investigated. Good enhancement of the mechanical properties was achieved with the natural carnauba and bee waxes.