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Poly(ethylene terephthalate) (PET) is a thermoplastic polyester with excellent thermal and mechanical properties, widely used in a variety of industrial fields. It is a semicrystalline polymer, and most of the industrial success of PET derives from its easily tunable crystallization kinetics, which allow users to produce the polymer with a high crystal fraction for applications that demand high thermomechanical resistance and barrier properties, or a fully amorphous polymer when high transparency of the product is needed. The main properties of the polymer are presented and discussed in this contribution, together with the literature data on the crystal structure and morphology of PET. This is followed by an in-depth analysis of its crystallization kinetics, including both primary crystal nucleation and crystal growth, as well as secondary crystallization. The effect of molar mass, catalyst residues, chain composition, and thermo-mechanical treatments on the crystallization kinetics, structure, and morphology of PET are also reviewed in this contribution. [ABSTRACT FROM AUTHOR]

A novel bio-based and compostable cellulose film (NF) was studied for the packaging of fresh baby spinach, with results compared to a petroleum-derived non-biodegradable polypropylene (PP) film, currently used to market the same product. Baby spinach is a leafy vegetable with high metabolic activity. A preliminary analysis of the product respiration rate was conducted to select the cellulose film grade. The chosen NF film ensures the optimal O2 and CO2 concentration in the headspace, performing even better than the conventional PP film. In fact, when the leafy vegetable is packed within PP, after 15 days of storage, no equilibrium value of gas concentration was reached, which, upon longer storage, might cause anaerobic conditions and off-odor development. Baby spinach leaves packed with NF film showed a slower decrement in texture properties and total antioxidant capacity during storage with respect to control samples, but also a larger weight loss, mostly due to the high-water permeability of the cellulose. However, water condensation upon storage was noted for both packaging materials. Analysis of mechanical, thermal, and barrier properties of the NF film before, during, and after use probed no deterioration of material properties, confirming the potentiality of this polymer for sustainable packaging of fresh leafy vegetables. [ABSTRACT FROM AUTHOR]

Linear low‐density polyethylene (PE) containing an inclusion complex composed of β‐cyclodextrin and d‐limonene (CD‐lim) is proposed as an innovative food wrapping material with antimicrobial features. PE/CD‐lim composites are prepared by conventional, high‐volume processing, and the optical and mechanical properties of the developed formulations appear suitable for their use as food packaging materials. Compared to plain PE, the PE/CD‐lim films have improved haze and UV–vis outcomes, but also decreased gloss values. Addition of CD‐lim slightly increases water uptake, up to levels suitable for the foreseen application. It also allows to improve performance of PE as food packaging material, since the PE/CD‐lim composites provide barrier to ultraviolet light, an added value for packaging of fatty acids‐containing food items, whose shelf life is often limited by oxidation caused by UV light. Most importantly, PE/CD‐lim composites exhibit significant antimicrobial properties against a wide range of microorganisms, including fungi and bacteria. Hence, PE films containing CD‐lim display suitable properties to play a role as active food packaging films. Highlights: Development of polyethylene‐based composites containing a natural fillerComposite films with enhanced antimicrobial and antifungal efficiencyImproved transparency to visible light and barrier to UV of the composites [ABSTRACT FROM AUTHOR]

Composites made of linear low-density polyethylene (LLDPE) and β-cyclodextrin/d-limonene inclusion complex (CD-lim) were prepared by melt extrusion to develop a novel food packaging material. Scanning electron microscopy evidenced a fairly good dispersion of the filler within the polymeric matrix. Infrared spectroscopy coupled with thermogravimetric analysis confirmed the presence of CD-lim in the composites, proving that the applied technology of including the essential oil within β-CD cages allows for preventing a sizable loss of d-limonene despite a high temperature and shear applied upon extrusion processing. Moreover, the influence of the filler on the thermal properties of PE was assessed. It was found that the cyclodextrin-based inclusion complex significantly fastens the crystallization path of the polyethylene matrix with an improved crystallization rate of the PE/CD-lim composites compared to the neat polymer. [ABSTRACT FROM AUTHOR]

Composites made of poly(l‐lactic acid) (PLLA) and β‐cyclodextrin/D‐limonene inclusion complex (CD‐Lim) are prepared to develop novel food packaging material with antibacterial properties. The composites are formulated with bio‐based materials that are also biodegradable. The addition of CD‐Lim to PLLA results in enhanced permeability and water uptake. Optical properties of PLLA/CD‐Lim composites also significantly vary compared to plain PLLA, with partial loss of transparency and gloss, but sizably increased barrier to UV light, which imparts protection from oxidation to lipid‐containing food. The mechanical properties of the composite films are also affected by composition. Most notably, PLLA films containing CD‐Lim display significant antibacterial and antifungal properties, proving their potential as active food packaging films. [ABSTRACT FROM AUTHOR]

A novel method to enhance and control bubble nucleation in poly(l‐lactic acid) (PLLA) foaming, not relying on external nucleating agents, is presented. Amorphous PLLA is annealed at temperatures close to its glass transition, to allow local alignment of polymer chains in the form of nanosized aggregates, called homogeneous crystal nuclei (HCN). PLLA containing HCN is then foamed after sorption of CO2 at 120 °C and 10 MPa. Under the chosen experimental conditions, HCN can promote growth of PLLA spherulites that can be controlled by thermal‐pressure history. Foam morphology is strongly affected by the presence of HCN, which act as heterogeneous nucleation sites for bubbles. Resulting foams are characterized by a bimodal morphology, with bubbles of about 50–70 µm in diameter developed in the bulk, and much smaller cells of few µm, grown upon pre‐existing crystal aggregates. The method detailed here to attain PLLA foams with tailored morphology can be exploited also for other semicrystalline polymers. [ABSTRACT FROM AUTHOR]

Shear-induced formation of crystal nuclei in polyamide 11 (PA 11) was studied using a conventional parallel-plate rheometer. Crystallization of PA 11 after shearing the melt at different rates for 60 s was followed by the evolution of the complex viscosity. The sheared samples showed in an optical microscope a gradient structure along the radius, due to the increasing shear rate from the center to the edge. The critical shear rate for shear-induced formation of nuclei was identified at the position where a distinct change of the semicrystalline superstructure is observed, being at around 1 to 2 s−1. Below this threshold, a space-filled spherulitic superstructure developed as in quiescent-melt crystallization. Above this value, after shearing at rates between 1 and 5 s−1, an increased number of point-like nuclei was detected, connected with formation of randomly oriented crystals. Shearing the melt at even higher rates led to a further increase of the nuclei number and growth of crystals oriented such that the chain axis is in parallel to the direction of flow. In addition, optical microscopy confirmed formation of long fibrillar structures after shearing at such condition. The critical specific work of flow of PA 11 was calculated to allow a comparison with that of polyamide 66 (PA 66). This comparison showed that in the case of PA 11 more work for shear-induced formation of nuclei is needed than in the case of PA 66, discussed in terms of the chemical structure of the repeat unit in the chains. [ABSTRACT FROM AUTHOR]

Poly(l‐lactic acid) (PLLA) is a biodegradable and biocompatible thermoplastic polyester produced from renewable sources, widely used for biomedical devices, in food packaging and in agriculture. It is a semicrystalline polymer, and as such its properties are strongly affected by the developed semicrystalline morphology. As a function of the crystallization temperature, PLLA can form different crystal modifications, namely α′‐crystals below about 120 °C and α‐crystals at higher temperatures. The α′ modification is therefore of special importance as it may be the preferred polymorph developing at processing‐relevant conditions. It is a metastable modification which typically transforms into the more stable α‐crystals on annealing at elevated temperature. The structure, kinetics of formation and thermodynamics of α′‐ and α‐crystals of PLLA are reviewed in this contribution, together with the effect of α′‐/α‐crystal polymorphism on the properties of PLLA. © 2018 Society of Chemical Industry The structure, kinetics of formation and thermodynamics of the two main crystal modifications of PLLA are reviewed, together with the effect of crystal polymorphism on material properties. [ABSTRACT FROM AUTHOR]

Poly[(R)-3-hydroxybutyrate] (PHB) is the first produced and most studied polyhydroxyalkanoate (PHA), a class of polymers that can be synthesized by a variety of bacteria through fermentation. PHB, and with it most PHAs, is produced in vivo, contrarily to all other types of bio-based and biodegradable polymers that are attained by chemical reactions, like polycondensation or ring-opening polymerization. The in vivo polymerization leads to a number of special features, like the absence of catalyst residues and other impurities typically present in synthetic polymers, which can promote crystal nucleation. Moreover, PHB has a perfectly isotactic structure with all chiral carbon atoms in (R)-configuration. These peculiarities make PHB a model compound for the study of polymer crystallization; hence its crystallization behavior has received considerable attention over the years. The main properties of the polymer are presented and discussed, together with literature data on crystal structure and morphology of PHB. This is followed by in-depth analysis of the crystallization kinetics, including both the primary crystal nucleation and crystal growth. Secondary crystallization is also discussed, as it largely affects timedependent properties of molded PHB products, which progressively becomes brittle upon storage: the glass transition of PHB is around 0°C; hence at room temperature PHB amorphous chains have sufficient mobility to continue to crystallize, which in turn implies also vitrification of part of the amorphous chains coupled with the crystals, the rigid amorphous fraction (RAF). The influence of the RAF on crystallization of PHB is also discussed, since its vitrification during crystallization can hinder or even stop further crystal growth. The analysis of the crystallization behavior of PHB is completed by a thorough discussion of melting of PHB crystals, which also presents a number of notable features. [ABSTRACT FROM AUTHOR]

Abstract: Polarized‐light optical microscopy (POM) is applied for investigation of homogeneous crystal nucleation in polymers, using the advantage of precise control of the nucleation pathway by application of fast scanning chip calorimetry (FSC). In the first part of this paper, homogeneous crystal nucleation in glassy poly ( l‐lactic acid) (PLLA) employing Tammann's two‐stage crystal nuclei‐development method is highlighted. PLLA samples of different nucleation history are prepared in an FSC, and then POM micrographs are studied regarding the effect of time and temperature of annealing the glass on the number of spherulites, which developed in the growth‐stage at higher temperature. The obtained images provide ultimate evidence about the validity of Tammann's approach for obtaining information about the kinetics of homogeneous crystal nucleation using calorimetry, when quantifying the number of nuclei by the enthalpy of crystallization during their growth to crystals in the development stage. In the second part of this study, information about the semicrystalline morphology of samples of poly(butylene terephthalate) and polyamide 66 crystallized at different supercooling using FSC is presented. POM analysis confirms the origin of the frequently observed bimodal temperature‐dependence of the crystallization rate as being caused by different mechanisms of crystal nucleation, resulting in qualitatively different structures. [ABSTRACT FROM AUTHOR]

Prediction of the supermolecular structure and properties of poly(L-lactic acid) requires in-depth knowledge of the relation between the conditions of melt solidification and the crystallization process. Crystallization involves primary crystal nucleation, which then is followed by crystal growth. Both processes require chain segment mobility at different length scales, and exhibit different temperature and cooling-rate dependencies, as described in this review. Following an introduction to polymer crystallization and general information about crystallization of poly (L-lactic acid), data are presented on the kinetics of primary crystal nucleation, covering a wide range of temperatures. Crystal nuclei formation in the glassy state requires completion of the glass relaxation process, as shown by enthalpy relaxation experiments. Discussion of the nucleation behavior is then followed by information about crystal growth rates, which reveal a bimodal temperature dependence as a result of the specific a0/a-crystal polymorphism. Throughout this review, the effects of molar mass and optical purity on the kinetics of nucleation and growth of crystals are discussed. [ABSTRACT FROM AUTHOR]

The isotropic melt of poly(L-lactic acid) (PLLA) and random L/D-lactide copolymers with 2% and 4% D-isomer co-units in the chain has been crystallized at 90 °C, which leads to growth of α'-crystals. The maximum melting temperature of the α'-crystals is around 150 °C in case of the homopolymer, and decreases by about 10 and 15 K in the random copolymers containing 2% and 4% D-isomer co-units, respectively. Analysis of the stability of the α'-crystals requires suppression of formation of α-structure, which is achieved by fast heating using a fast scanning chip calorimeter. For the PLLA homopolymer, the critical heating rate above which the α'/α-transition is completely suppressed is around 30 K s-1, which significantly decreases in the copolymers due to the presence of D-isomer co-units. The slower kinetics of the melting-recrystallization process in such random L/D-lactide copolymers is explained by the required segregation of the chain defects. [ABSTRACT FROM AUTHOR]

ABSTRACT Composites based on isotactic polypropylene (iPP) modified with a sorbitol derivative (NX8000) and siloxane-silsesquioxane resin containing reactive phenyl groups (SiOPh) were prepared by melt extrusion. These iPP-based formulations were investigated to evaluate the influence of such additives on the crystallization behavior and morphology, as well as on thermal and mechanical properties. The addition of sorbitol fastens crystallization kinetics of iPP and leads to higher transparency of iPP films. Upon the incorporation of siloxane-silsesquioxane resin, no further effect on iPP crystallization kinetics is evidenced by calorimetry, optical microscopy, and X-ray diffraction analysis. Transparency of iPP-based composites is improved upon the addition of sorbitol, but decreased when SiOPh is added to the formulation. The composites are also stiffer, compared to neat polypropylene with a decreased elongation at break and increased Young's modulus values, with increasing amounts of fillers. The effect of the siloxane-silsesquioxane resin on properties of iPP/NX8000/SiOPh composites was explained taking into account compatibility of the components and morphology of the composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43476. [ABSTRACT FROM AUTHOR]

Binary blends of poly(lactic acid) (PLA) and poly(propylene carbonate) (PPC) were found to display a peculiar crystallization kinetics. The two biodegradable polymers were blended by melt mixing, to obtain binary blends at various compositions. Temperature-modulated calorimetry and dynamic-mechanical analysis indicated that the blend components are partially miscible, and display two separate glass transitions, at temperatures intermediate to those of the plain polymers. Electron microscopy analysis disclosed the morphology of PLA/PPC blends, made of PPC-rich particles finely dispersed within the PLA-rich matrix. The possible establishment of interactions between the functional groups of the two polymers upon melt mixing has been hypothesized as the reason for partial miscibility and compatibility of the two biodegradable polymers. The PLA/PPC blends display good mechanical properties, with enhanced performance at rupture compared with plain PLA. Most importantly, the addition of PPC affects also the crystallization kinetics of PLA, since the more mobile PPC chains favor diffusion of the stiffer PLA chain segments towards the growing crystals, which fastens the spherulite growth rate of PLA. Such positive influence of an amorphous polymer on crystal growth rate has been demonstrated here for the first time in blends that display phase-separation in the melt. [ABSTRACT FROM AUTHOR]

Melting and reorganization of conformationally disordered crystals (α′-phase) of poly( l-lactic acid) (PLLA) are analyzed as a function of the rate of heating in a wide range between about 10−1 and 103 K s−1. It is found for the first time that the reorganization of conformationally disordered α′-crystals into stable α-crystals can be suppressed by fast heating. Heating of α′-crystals of PLLA at a constant rate, faster than 30 K s−1, leads to its complete melting between 150 and 160 °C and suppression of formation of α-crystals on continuation of heating. Non-isothermal reorganization of α′-crystals into α-crystals only occurs when heating at a rate slower than 30 K s−1. It is evidenced that isothermal reorganization of α′-crystals into α-crystals at 150-160 °C proceeds via melting followed by recrystallization rather than a solid-solid phase transition. [ABSTRACT FROM AUTHOR]

The phase behavior of linear poly(N-isopropylacrylamide) (PNIPA), linear copolymer poly(N-isopropylacrylamide) and poly(sodium acrylate) (PNIPA-SA), and chemically cross-linked PNIPA in water has been determined by temperature modulated differential scanning calorimetry (TM-DSC). Experiments related to linear polymers (PNIPA and PNIPA-SA) indicated nontypical demixing/mixing behavior with a lower critical solution temperature (LCST), which do not correspond to the three classical types of limiting critical behavior. Some similarities and differences are observed in comparison to our literature data using standard TM-DSC for PNIPA/water. Furthermore no influence of composition cross-linked PNIPA/water system on demixing/mixing temperature was observed. [ABSTRACT FROM AUTHOR]

The influence of multilayer carton scraps (MC) on crystallization kinetics of high-density polyethylene (HDPE) is detailed in this contribution. HDPE/MC composites were prepared by melt mixing, and a maleated linear low density polyethylene (MAPE) was added as compatibilizer. The crystallization kinetics of HDPE/MC/MAPE was analyzed as function of composition both in isothermal and nonisothermal conditions. The multilayer carton scraps appear to promote the onset of crystallization of HDPE, acting as efficient nucleating agent. The presence of MAPE as compatibilizer slightly reduces the nucleating efficiency of MC: the compatibilizer induces a delay in the onset of crystallization, caused by the need to exclude the bulky pendant groups of maleated linear low-density polyethylene from the crystals, as HDPE and MAPE chains cocrystallize. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

This article presents a study regarding the miscibility and thermal and mechanical properties of poly(butylene terephthalate) blends. The blending of two or more polymers is a well-established plan for achieving a specified portfolio of physical properties. Polymer blending indicates one of the fastest growing segments of polymer technology.

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. [ABSTRACT FROM AUTHOR]

Bio-based composites made of poly(L-lactic acid) (PLLA) and β-cyclodextrin/d-limonene inclusion complex (CD-Lim) were prepared by melt extrusion. Encapsulation of volatile d-limonene molecules within β-cyclodextrin cages was proven to be a successful strategy to prevent evaporation during high-temperature processing. However, small amounts of limonene were released upon processing, resulting in the plasticization of the polymeric matrix. Morphological analysis revealed good dispersion of the filler, which acted as a nucleating agent, favoring the growth of PLLA crystals. The composites′ lowered glass transition temperature upon the addition of CD-Lim was also proved by thermomechanical analysis (DMA). Moreover, DMA revealed constant stiffness of modified materials at room temperature, which is crucial in PLLA-based formulations. [ABSTRACT FROM AUTHOR]

Bio-based composites made of poly(l-lactic acid) (PLLA) and pine wood were prepared by melt extrusion. The composites were compatibilized by impregnation of wood with γ-aminopropyltriethoxysilane (APE). Comparison with non-compatibilized formulation revealed that APE is an efficient compatibilizer for PLLA/wood composites. Pine wood particles dispersed within PLLA act as nucleating agents able to start the growth of PLLA crystals, resulting in a faster crystallization rate and increased crystal fraction. Moreover, the composites have a slightly lower thermal stability compared to PLLA, proportional to filler content, due to the lower thermal stability of wood. Molecular dynamics was investigated using the solid-state 1H NMR technique, which revealed restrictions in the mobility of polymer chains upon the addition of wood, as well as enhanced interfacial adhesion between the filler and matrix in the composites compatibilized with APE. The enhanced interfacial adhesion in silane-treated composites was also proved by scanning electron microscopy and resulted in slightly improved deformability and impact resistance of the composites. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including fermentation, polylactic acid and polymeric materials.

The manuscript details the preparation and characterization of binary blends of polyamide 11 (PA 11) and poly(butylene succinate) (PBS), with PA 11 as the major component. The blends are fully bio-based, since both components are produced from renewable resources. In addition, PBS is also biodegradable and compostable, contrarily to PA 11. In the analyzed composition range (up to 40 m% PBS), the two polymers are not miscible, and the blends display two separate glass transitions. The PA 11/PBS blends exhibit a droplet-matrix morphology, with uniform dispersion within the matrix, and some interfacial adhesion between the matrix and the dispersed droplets. Infrared spectroscopy indicates the possible interaction between the hydrogens of the amide groups of PA 11 chains and the carbonyl groups of PBS, which provides the compatibilization of the components. The analyzed blends show mechanical properties that are comparable to neat PA 11, with the benefit of reduced material costs attained by addition of biodegradable PBS. [ABSTRACT FROM AUTHOR]