Rigid Amorphous Fraction Research Articles

Estimations of the Thicknesses of Smectic Layer and Rigid Amorphous Layer in Mesomorphic Isotactic Polypropylene with Synchrotron Small‐Angle and Wide‐Angle X‐Ray Scattering

AbstractDespite extensive research, the stabilization mechanism of mesomorphic isotactic polypropylene (iPP) at room temperature has not been elucidated completely. To address this issue, nanoscale structural information is indispensable. In this study, mesomorphic‐α phase transition is studied with synchrotron wide‐angle diffraction and small‐angle X‐ray scattering. It is found that during phase transition, the mobile amorphous content remained unchanged, while rigid amorphous fraction (RAF) decreased constantly, accompanied by an increase in long period. Assuming that the increase in long period is induced by the extension of the rigid amorphous coil (RAC), the thickness of RAF (RRAF) is estimated, which is found to be 2.2 nm. This value is greater than the length of b axis in α crystal cell, which can be the reason that folded‐chain iPP clusters in mesomorphic iPP cannot approach closer to form α crystal at room temperature. Besides, with RRAF, the thickness of smectic layer is estimated, which is found to be 0.9 nm. At this thickness, bulk‐free energy cannot compensate for the folded‐surface free energy, which can be the other reason that mesomorphic iPP chains cannot transit into α crystal at room temperature. The information obtained in this study is favorable for understanding the stabilization mechanism of mesomorphic iPP.

Dependence of the crystal structure on the d-units amount in semi-crystalline poly(lactic acid)

The study investigates the impact of the d-lactic acid units content on the crystallinity and crystal structure of commercial poly(lactic acid) (PLA) grades, which are copolymers of poly(l-lactic acid) (PLLA) containing a minor amount of d-units. As the d-units content increases, a detectable decrease in crystallinity was observed along with a simultaneous rise in mobile amorphous fraction (MAF) and a reduction in rigid amorphous fraction (RAF). The percentage of d-units was found not to significantly affect RAF thickness, suggesting that the d-units are not completely excluded from the crystals. The inclusion of d-units as defects in the PLA crystal lattice was confirmed by XRD analysis, which disclosed that the crystal phase gets gradually richer of d-units as the crystallization time evolves. FT-IR analysis proved that the incorporation of d-units in the crystal phase is promoted by the formation of local CH3···O=C interactions, similar to those massively active between PLLA and poly(d-lactic acid) (PDLA) in the stereocomplex. The establishment of these interactions leads to a contraction of the interplanar distances and a decrease in the crystal cell volume with increasing the crystallization time and the d-units percentage. In summary, the study proves that for PLA copolymers containing a d-units percentage at least up to about 8 %, d-units are included in the crystal lattice.

Molecular origin of the plasticizing effect difference of glycerol with other polyols on plasticizing polyvinyl alcohol (PVA) as elucidated by solid-state NMR

Glycerol has been proved to be an effective plasticizer for polyvinyl alcohol (PVA), which can significantly increase PVA’s processability and ductility, whose molecular origin remains unclear. In current study, the physical structure and chain dynamics of polyol plasticized PVA were studied in detail, including ethylene glycol, glycerol, erythritol, xylitol, and sorbitol under the same addition level. The glycerol plasticized PVA exhibits the most significant reduction in Young’s modulus, enhanced superior toughness, and the lowest melting temperature (195 °C) as compared with other polyols. The molecular mechanism was elucidated through comprehensive analysis, with a particular focus on solid state NMR (SS NMR) results. The physical structure was first elucidated by the Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS). The crystallinity of the glycerol plasticized PVA was the lowest 29 % by WAXS and the thickness of the amorphous layer was the largest 7.76 nm by SAXS among different plasticized PVA films. This suggests the significant influence of glycerol on structure change of PVA. The molecular dynamics information was further accessed by Low Field Nuclear Magnetic Resonance (LF NMR), where two key features are obtained: i) Different dynamics dimensionality. The 1H spin diffusion NMR was used to check the dimensionality from the aspect of chain dynamics. Compared with other plasticizers, LF NMR result shows that glycerol plasticized PVA has a two-dimensional (2D) structure; ii) Chain dynamics heterogeneity in the interphase. With respect to the chain dynamics heterogeneity in the interphase, the glycerol plasticized PVA shows the most heterogeneous dynamics, with the lowest ratio of the rigid amorphous fraction (RAF) of 0.507 in the interphase. Current study provides a versatile analytical strategy to quantify the plasticizing effect.

Influence of semi-crystalline microstructure on gas permeability of Poly(Ether-Ketone-Ketone)

In a context of ecological transition, aeronautics is moving towards the development of hydrogen-powered aircraft for which lightweight, long-lasting and tough storage tanks must be developed. Among other properties, the tightness of tanks made of polymer and composite materials is of prime importance. This study thus aims at understanding the permeation phenomena through Poly-Ether-Ketone-Ketone (PEKK), which is one of the thermoplastic polymers considered for tank manufacture. In order to better understand the phenomena governing gas permeability, tests were carried out on different PEKK grades of different T/I ratios and degree of crystallinity. The results show that the crystallinity ratio is not the only factor that governs gas diffusion and solubility, but that permeability also depends on PEKK semi-crystalline microstructure. Even if considering crystallites organization through a tortuosity factor improves permeability predictions, permeability can be better understood using a 3 phases description of PEKK microstructure considering distinct contributions of the rigid and mobile amorphous fractions (RAF and MAF). It appears that the MAF permeation does not depend on PEKK T/I ratio, but that gas diffusion and solubility increase for RAF when increasing T/I ratio, thus counterbalancing the blocking effect of crystallites.

Recyclability of elastomer toughened recycled poly(ethylene terephthalate): The effect of grinding-extrusion-injection moulding on the mechanical and morphological properties of the blend

Reprocessing potential of recycled poly(ethylene-terephthalate) (RPET)/ethylene-butyl-acrylate-glycidyl methacrylate (EBA-GMA) blends was investigated. PET flakes from food packaging were compounded with 0, 5, 10, 15 and 20 % EBA-GMA. Injection moulded specimens were produced, and some of the specimens were grinded, and reproduced to simulate real reprocessing. It was revealed by scanning electron microscopy that the distribution and particle size of the elastomer did not change notably after recycling. Noticeable degradation of the polymer matrix was observable after every processing step. Such deterioration of PET resulted in higher crystallinity and rigid amorphous fraction, as found by differential scanning calorimetry, which ultimately led to higher storage modulus, while the notched impact strength and elongation at break decreased. Nevertheless, the mechanical performance of the reprocessed RPET/EBA-GMA blends still significantly outperforms that of the neat PET recyclate. The degree of chain breakage was found to be the primary factor determining the recyclability of RPET/EBA-GMA blends.

Hydrolysis of biobased stereocomplex polylactide: Polymorphism dependent crystals degradation and evolution of three-phase crystalline composition

The hydrolytic degradation behavior of stereocomplex polylactide (SCPLA) with distinct polymorphisms (α, αʹ, SC) and SC fractions (the ratio of SC crystallinity to total crystallinity) was first investigated in the present study. The evolution of three-phase crystalline compositions was quantified using modulated differential scanning calorimetry. Hydrolytic degradation commenced in the mobile amorphous fraction (MAF), while both the crystal (CF) and rigid amorphous fraction (RAF) began degradation on Day 3. By the 26th day, the MAF was consumed entirely, followed by the CF and RAF degraded at similar rates, primarily through the cleavage of chains with free ends on the folding surface of the remaining lamella. This work further discussed the influence of polymorphism on homochiral (HC) and SC crystal degradation during hydrolysis. Given racemic helices' participation in SC crystallization, SC-crystal lamellae may possess a higher number of amorphous chains with free ends than HC-crystals. This attribute could account for the faster degradation of HC-crystals in samples with a higher SC fraction.

Constrained amorphous interphase in plasticized poly(lactic acid): Composition and tensile elastic modulus estimation

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 α-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 α-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.

Modulating Barrier Properties of Stereocomplex Polylactide: The Polymorphism Mechanism and Its Relationship with Rigid Amorphous Fraction.

The barrier properties of semicrystalline polymers are crucial for their performance and their use as packaging materials. This work uncovers the mechanism of polymorphism modification (α, α' and stereocomplex-crystals) and its combined effect on the oxygen and water vapor barrier properties of semicrystalline stereocomplex polylactide (SCPLA). A polymorphic selective filler-type nucleator was employed to eliminate the temperature effect on the development of polymorphism and rigid amorphous fraction (RAF), allowing correlations of barrier properties with different crystal forms and RAF combinations under the same amorphous composition (SCPLA). The oxygen and water vapor barrier performances strongly correlated with crystallinity and crystal form but were not monotonically related to the RAF quantity. The study proposes that the chain conformation of intermediate phases between the crystalline and amorphous phases differs with the associated crystal forms, thereby leading to different RAF "qualities" and contributing to different gas diffusion and solubility coefficients of the amorphous regions. RAF's per unit excess free volume may be varied with crystal forms, for instance: α' ≫ SC > α. Therefore, SCPLA with α' crystals exhibited high oxygen and water vapor permeabilities. Those with high SC and α crystals showed similar barrier behaviors governed by Henry's law dissolution and followed a linear "two-phase" relationship with total crystallinity.

Hydrolytic degradation of poly(lactic acid): Unraveling correlations between temperature and the three phase structures

Hydrolysis significantly influences both the properties and degradability of poly(lactic acid), PLA. This work investigates the hydrolysis kinetics of PLA films as affected by degree of crystallinity and temperatures by considering the three-phase model structures (i.e., mobile amorphous, rigid amorphous, and crystalline). Molecular weight and three-phase fraction analyses were performed during hydrolysis to estimate the kinetic rates using phenomenological models. Results revealed that temperature significantly impacted PLA degradation, with distinct characteristics observed for each of these three phases. Above the glass transition temperature, the hydrolysis rates of PLA were comparable among samples with different crystallinity due to rapid water-induced crystallization of the amorphous phases, coupled with accelerated hydrolysis. In contrast, at below the glass transition temperature, the higher crystallinity sample exhibited a faster hydrolysis rate attributed to the presence of the rigid amorphous fraction. An increase in crystallinity introduced more defects due to limited mobility in the rigid amorphous fraction, influencing hydrolysis. The study provides valuable insights into the crucial relationship between temperature, crystallinity, and hydrolysis kinetics which are expected to be useful for predicting PLA degradation behavior during its intended applications and at its end of life.

Poly (butylene succinate): Low-temperature nucleation and crystallization, complex morphology and absence of lamellar thickening

Melt-crystallization of poly (butylene succinate) (PBS) at largely different melt-supercooling was analyzed by X-ray scattering techniques, direct imaging using microscopy, and by fast scanning chip calorimetry, with the latter employed to achieve high melt-supercooling. Crystallization at 100 and 20 °C, representing structure formation at low and high melt-supercooling, respectively, yields lamellae with thicknesses of around 8 and 4 nm. In both cases, lamellar thickening is excluded as main mechanism of isothermal secondary crystallization, suggesting that absence of intracrystalline chain-sliding diffusion is not dependent on the absolute value of the thickness of lamellae. The wide-angle X-ray pattern of PBS crystallized at low temperature shows less and broader peaks than in case of PBS crystallized at high temperature, pointing to presence of crystal defects, and causing an enlargement of the unit cell. Secondary crystallization leads to an increase of the melting temperature, being distinctly larger (per unit annealing time) for low-temperature crystallized PBS. Since lamellar thickening is absent, and imperfection of the bulk crystal structure persists even on long-term annealing, merging of crystalline blocks and lateral crystal growth at the crystallization temperature, for explaining the observed increases of the crystallinity and melting temperature, are suggested. Though there is detected a large rigid amorphous fraction in PBS crystallized at high supercooling, vitrification only occurs continuously on cooling, after the isothermal crystallization process.

Rigid amorphous fraction in isotactic polystyrene induced by cold crystallization: Characterization by differential scanning calorimetry and ellipsometry

AbstractRigid amorphous fraction (RAF) in bulk and thin‐film states of isotactic polystyrene (iPS) was studied as a function of crystalline fraction (CF). The CF increased with isothermal cold crystallization in initially amorphous, melt‐quenched bulk iPS samples. Assessed by differential scanning calorimetry, RAF in bulk iPS increased and then decreased with increasing crystallization time and CF. Specific RAF, that is, RAF/CF, decreased with increasing CF. Using ellipsometry, similar behaviors of RAF and specific RAF as functions of CF were observed in initially amorphous iPS thin films. These results indicate that specific RAF in iPS exhibits a continuous decrease from slightly below 2 at very low CF to ~0.2 at the maximum CF, independent of sample type and characterization method. This trend of decreasing specific RAF is consistent with a progression of crystal perfection during cold crystallization which is associated with lamellae thickening and decoupling between crystalline and amorphous regions. Qualitatively similar behaviors of RAF and specific RAF have been reported in other semi‐crystalline polymers and in our recent studies of syndiotactic polystyrene, indicating that this trend of decreasing specific RAF with increasing CF is general for many semi‐crystalline polymers. Finally, maximum CF is strongly reduced by nanoscale confinement in thin iPS films.

Investigation of the correlations between the microstructure and the tensile properties multi-scale composites with a polylactic acid matrix, reinforced with carbon nanotubes and carbon fibers, with the use of the fiber bundle cell theory

In this paper, we established a relationship between the microstructure and the tensile properties of nano- and hybrid composites with a thermoplastic, semi-crystalline poly(lactic acid) (PLA) matrix, reinforced with carbon fibers and carbon nanotubes, using the fiber bundle cell model. The microstructure of the matrix and the volume ratio of the mobile amorphous, rigid amorphous and crystalline fractions were determined by differential scanning calorimetry and the elastic modulus of these fractions was measured by atomic force microscopy. These data served as input parameters for the fiber bundle cell model, in which each structural unit corresponded to a single bundle of fibers. For the parameters for which no experimental method was available, we determined structure-independent constants. With these model parameters, we fitted a fiber bundle cell model curve to the averaged tensile curves of each material. By analyzing the fitted model, we concluded that the mobile and the rigid amorphous fraction of the matrix has a key role in the properties of the initial, load-carrying section of the tensile curve. The crystalline fraction and the carbon nanotubes elongated the failure section. By examining the damage maps, we found that overlapping interphases in the vicinity of carbon fibers and carbon nanotubes improved the load transfer between the carbon fiber and the matrix, thus allowing better utilization of the reinforcing effect of the carbon fibers.

The cytisine-enriched poly(3-hydroxybutyrate) fibers for sustained-release dosage form

The polymeric cytisine-enriched fibers based on poly(3-hydroxybutyrate) were obtained using electrospinning method. The biocompatibility study, advanced thermal analysis and release of cytisine from the poly(3-hydroxybutyrate) fibers were carried out. The nanofibers' morphology was evaluated by scanning electron microscopy. The formation and description of phases during the thermal processes of fibers by the advanced thermal analysis were examined. The new quantitative thermal analysis of polymeric fibers with cytisine phases based on vibrational, solid and liquid heat capacities was presented. The apparent heat capacity of fibers was measured using the standard differential scanning calorimetry. The quantitative analysis allowed for the study of the glass transition and melting/crystallization process. The mobile amorphous fraction, degree of crystallinity and rigid amorphous fraction were determined depending on the thermal history of semicrystalline polymeric fibers. Furthermore, the cytisine dissolution behaviour was studied. It was observed that the kinetic of the release from polymeric nanofiber is delayed than for the marketed product. The immunosafety of the tested polymeric nanofibers with cytisine was confirmed by the Food and Drug Agency Guidance as well as the European Medicines Agency. The polymeric matrix with cytisine seems to be a promising candidate for the prolonged release formulation.

Fold Surfaces of Polymer Crystals Are Nucleation Sites: The Link between Polymer Decoration, Secondary Crystallization, and the Rigid Amorphous Fraction (RAF)

The fold surfaces of polymer crystals may become suitable nucleating sites for uncrystallized material left over during the primary crystallization process. This “nucleation by the folds surface” (NFS) ability is highlighted in the so-called polymer decoration technique in which vapors of polyethylene condense and crystallize on a cold fold surface substrate to form edge-on lamellae that reveal the folds and loops orientations in different growth sectors. In bulk materials, the primary crystallization leaves confined and uncrystallized material between lamellae. NFS, based on epitaxy-type interactions, is expected to take place in these confined and supercooled melt fractions before “true” homogeneous nucleation sets in. The insights provided help elucidate the structural features of the interlamellar layers of crystalline polymers, which overcomes the limits of global, indirect investigation techniques (e.g., differential scanning calorimetry (DSC)) used in attempts to analyze their structure in situ. The interlamellar layer is known to be divided into a rigid amorphous fraction (RAF) located in contact with the fold surfaces and a mobile amorphous fraction (MAF) at its center. The nature of the RAF─amorphous but rigid above its Tg, or crystalline─is still debated. The NFS provides a structural identity for the RAF that associates conformation disorder with stem orientation: the RAF is actually a “condis oriented” fraction. On heating, the small endotherm observed in DSC curves corresponds to its isotropization. The RAF is also a protonucleus for secondary crystallization and induces the growth of edge-on lamellae on top and in the interlamellar spaces of the primary crystals. As such, the RAF has also a layered lamellar structure. Polymer decoration, the “condis oriented” RAF, and the specific edge-on lamellar secondary crystallization are manifestations of the nucleation by the fold surfaces.

A Relatively Simple Look at the Rather Complex Crystallization Kinetics of PLLA.

This work demonstrates that, despite the existence of a significant number of works on PLA crystallization, there is still a relatively simple way, different from those already described, in which its complex kinetics can be observed. The X-ray diffraction (XRD) results presented here confirm that the PLLA under study crystallizes mostly in the α and α' forms. An interesting observation is that at any temperature in the studied range of the patterns, the X-ray reflections stabilize with a given shape and at a given angle, different for each temperature. That means that both α and α' forms coexist and are stable at the same temperatures so that the shape of each pattern results from both structures. However, the patterns obtained at each temperature are different because the predominance of one crystal form over the other depends on temperature. Thus, a two-component kinetic model is proposed to account for both crystal forms. The method involves the deconvolution of the exothermic DSC peaks using two logistic derivative functions. The existence of the rigid amorphous fraction (RAF) in addition to the two crystal forms increases the complexity of the whole crystallization process. However, the results presented here show that a two-component kinetic model can reproduce the overall crystallization process fairly well over a broad range of temperatures. The method used here for PLLA may be useful for describing the isothermal crystallization processes of other polymers.

Block copolymer interfaces investigated by means of NMR, atomic force microscopy and dielectric spectroscopy

Self-assembly of block copolymers (BC) is a key feature for bottom-up patterning that is applied in the fabrication of templates for nanostructured membranes, photonic nanodevices, or solar cells. The wide range of possible BC applications is because the dissimilar blocks can be appropriately selected to form distinct domains with controllable dimensions and functionalities. An important representative of these materials is polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymer. This copolymer is of considerable academic interest and therefore it is examined by a plethora of experimental techniques to elucidate its structure and molecular dynamics. Particularly worth investigating is the interphase, consisting of polymer chains located at the interface of crystallite-amorphous and inter-domain regions, which codetermines the properties of such a system. It is shown that below the melting point of the PEO, the majority of the amorphous PEO are occupying interfacial sites and are represented by the rigid amorphous fraction (RAF) which can be monitored by dielectric and nuclear magnetic resonance spectroscopies. Moreover, two independent NMR spin-diffusion experiments reveal the asymmetrical nature of PS-PEO interface indicating a significant fraction of the PEO phase under the influence of stiff, adjacent polystyrene. An analysis of complementary thermal calorimetry and X-ray scattering data confirms the presence of microphase-separated morphology as well as the semicrystalline nature of PEO component. Lamelar domain architecture was confirmed by atomic force microscopy data acquired in the case of thin copolymer film.

Microstructural consequences of isothermal crystallization in homo- and co-polyesters based on 2,5- and 2,4-furandicarboxylic acid

Different position isomers of furandicarboxylic acid (FDCA) can be obtained from the biomass by a Henkel disproportionation reaction. 2,5- and 2,4-FDCA are obtained in amounts that are large enough to be used for the synthesis of polyethylene furanoate (PEF). The homopolyesters obtained with ethylene glycol (EG) and either 2,5- or 2,4-FDCA have a completely different crystallization behavior, for 2,5-PEF can crystallize whereas 2,4-PEF cannot, even after very long annealing times. The synthesis of random copolyesters with EG and different ratios of 2,5/2,4-FDCA may therefore allow to tune PEF crystallization ability. The partial replacement of 2,5-FDCA by its position isomer could help disrupting crystallinity analogously to what happens when EG is partially replaced by cyclohexane dimethanol (CHDM) in glycol-modified polyethylene terephthalate (PETg). This work investigates the thermal behavior of the homopolyester 2,5-PEF and the microstructural consequences of copolymerization (replacement of small amounts of 2,5-FDCA with 2,4-FDCA). Crystallization is performed in isothermal conditions after cooling down from the molten state, and investigated with both conventional DSC and Fast Scanning Calorimetry (FSC). When the amount of 2,4-FDCA-based repeating units is low (10 and 15 mol %), crystallization still occurs but with an increased induction time. Neither the crystalline nor the rigid amorphous fractions are significantly affected by copolymerization. Due to multiple and complex microstructural reorganizations observed at relatively slow heating rates, conventional DSC is inaccurate and does not provide a reliable microstructural depiction of these polyesters. The use of FSC is recommended, for it allows to obtain a better characterization of the quality and thermal stability of the formed crystals.

High-performance and durable fibrous poly(glycolic acid)/poly(butylene adipate-co-terephthalate) blends by reactive compatibilization and solid-state drawing

The application of poly(glycolic acid) (PGA) is limited by its inherent brittleness and easy to hydrolysis. Herein, we demonstrate an effective strategy to make fibrous PGA/poly (butylene adipate-co-terephthalate) (PBAT) blends with high strength, toughness and better hydrolysis resistance by reactive compatibilization and subsequent solid-state drawing. The enhanced chain entanglement due to the compatibilization restricts the chain relaxation during drawing process, leading to a predominance of stress-induced orientation. Meanwhile, it also facilitates the immobilization and transformation of extended chains into rigid amorphous fraction (RAF). As a consequence, the combination of strong interfacial bonding, high orientation and abundant RAF results in superior comprehensive properties of the fibrous PGA/PBAT blends, e.g., the drawn compatibilized PGA/PBAT exhibit a tensile strength as high as 700 MPa and a tensile toughness of 385 MJ/m3. Moreover, the tensile strength retention of the drawn compatibilized PGA/PBAT is 20 % higher than uncompatibilized sample after hydrolysis for 5 days. Therefore, this work provides a feasible strategy to make robust and durable fibrous PGA-based blends, which may broaden the application range of PGA.

Polymer/Layered Clay/Polyurethane Nanocomposites: P3HB Hybrid Nanobiocomposites-Preparation and Properties Evaluation.

This paper presents an attempt to improve the properties of poly(3-hydroxybutyrate) (P3HB) using linear aliphatic polyurethane (PU400) and organomodified montmorillonite (MMT)-(Cloisite®30B). The nanostructure of hybrid nanobiocomposites produced by extrusion was analyzed by X-ray diffraction and transmission electron microscopy, and the morphology was analyzed by scanning electron microscopy. In addition, selected mechanical properties and thermal properties were studied by thermogravimetric analysis, TGA, and differential scanning calorimetry, DSC. The interactions of the composite ingredients were indicated by FT IR spectroscopy. The effect of the amount of nanofiller on the properties of prepared hybrid nanobiocomposites was noted. Moreover, the non-equilibrium and equilibrium thermal parameters of nanobiocomposites were established based on their thermal history. Based on equilibrium parameters (i.e., the heat of fusion for the fully crystalline materials and the change in the heat capacity at the glass transition temperature for the fully amorphous nanobiocomposites), the degree of crystallinity and the mobile and rigid amorphous fractions were estimated. The addition of Cloisite®30B and aliphatic polyurethane to the P3HB matrix caused a decrease in the degree of crystallinity in reference to the unfilled P3HB. Simultaneously, an increase in the amorphous phase contents was noted. A rigid amorphous fraction was also denoted. Thermogravimetric analysis of the nanocomposites was also carried out and showed that the thermal stability of all nanocomposites was higher than that of the unfilled P3HB. An additional 1% mass of nanofiller increased the degradation temperature of the nanocomposites by about 30 °C in reference to the unfilled P3HB. Moreover, it was found that obtained hybrid nanobiocomposites containing 10 wt.% of aliphatic polyurethane (PU400) and the smallest amount of nanofiller (1 wt.% of Cloisite®30B) showed the best mechanical properties. We observed a desirable decrease in hardness of 15%, an increase in the relative strain at break of 60% and in the impact strength of 15% of the newly prepared nanobiocomposites with respect to the unfiled P3HB. The produced hybrid nanobiocomposites combined the best features induced by the plasticizing effect of polyurethane and the formation of P3HB-montmorillonite-polyurethane (P3HB-PU-MMT) adducts, which resulted in the improvement of the thermal and mechanical properties.

Strong, ductile and durable Poly(glycolic acid)-based films by constructing crystalline orientation, entanglement network and rigid amorphous fraction

Poly(glycolic acid) as a promising substitution for traditional petroleum-based polymers suffers from its inherent brittleness and rapid hydrolysis. The improvement of toughness and hydrolysis resistance is usually accompanied with a sacrifice of strength and stiffness. In the present work, we propose a simple and effective strategy to address this obstacle by introducing poly (butylene adipate-co-terephthalate) (PBAT) and combining extensional stress and temperature field. The robust, ductile and durable PGA/PBAT films are fabricated via “high temperature melting-quenching-stretching-annealing” (QSA) process. Highly oriented crystallites constructed by stretching and annealing lead to the improvement of strength and stiffness. Stress-induced strengthened entanglement network contributes to stabilization of craze growth and slipping, thus leading to the ductile behavior. As the result, the QSA films exhibit 89 MPa and 131% in tensile strength and the elongation at break, which are increased by 195%, 126% respectively compared to the unstretched film. More impressively, stretching resulted in abundant rigid amorphous chains, which worked with oriented crystallites to impart enhanced heat and hydrolysis resistance for the films. This work paves an avenue toward a wider range of applications for PGA materials and might be guidance for other semi-crystalline polymer blends.