Nucleation and Self‐Nucleation of Bio‐Based Poly(ethylene 2,5‐furandicarboxylate) Probed by Fast Scanning Calorimetry

The present work focuses on the influence of nucleation processes on the crystallization of bio‐based poly(ethylene 2,5‐furandicarboxylate) (PEF). Nuclei formation has been studied by means of fast scanning calorimetry (FSC) both when cooling from the melt (nonisothermal conditions) and when annealing at either low‐ or high‐temperatures (isothermal conditions). FSC results show that nucleation on cooling can be prevented by using fast rates allowing to keep the polymer in its amorphous state; whereas cooling at moderate rates results in sample nucleation with a subsequent increase of the crystallization rate. Isothermal pretreatment just above the PEF glass transition temperature (T_g) results in nuclei formation whose rate decreases when the nucleation temperature approaches PEF T_g. On the other hand, annealing below the PEF melting point allows determination of the sample self‐nucleation behavior which occurs in a very narrow temperature range, i.e., between 195 and 198 °C.

     

Improving Poly(ethylene terephthalate) Through Self‐nucleation

As‐received poly(ethylene terephthalate) (asr‐PET) may be reorganized by precipitation from trifluoroacetic acid upon gradual addition to a large excess of rapidly stirred acetone (p‐PET). Unlike asr‐PET, p‐PET repeatedly crystallizes rapidly from the melt, and can be used in small quantities (a few %) as an effective self‐nucleating agent to control and improve the bulk semi‐crystalline morphology and properties of asr‐PET. Nuc‐PET film has significantly increased hardness and Young's modulus and is much less permeable to CO₂, while its un‐drawn fibers exhibit higher tenacities and moduli. Because nuc‐PET contains no incompatible additives, it may be readily recycled.

     

Study of As‐Spun Poly(ethylene terephthalate) Fibers Subjected to Thermal and Mechanical Treatments

As‐spun poly(ethylene terephthalate) filaments, subjected to mechanical and thermal treatments have been studied. Structural peculiarities investigated by the methods of thermo‐mechanical analysis (TMA), differential scanning calorimetry (DSC) and wide‐angle X‐ray scattering (WAXS) are presented. The influence of simultaneously applied thermal and mechanical treatments on the structural changes of the studied samples is discussed. It was shown that the structures obtained could be semicrystalline or entirely amorphous depending on the mechanical treatment.     

Uniaxial Orientation and Crystallization Behavior of Amorphous Poly(ethylene terephthalate) Fibers

The effects of drawing conditions on the orientation and crystallinity of poly(ethylene terephthalate) (PET) fibers were investigated by using optical birefringence, sonic velocity, and wide-angle X-ray diffraction measurements, respectively. The preferred condition for preparation of uniaxially oriented amorphous PET fibers was suggested. The crystallization behavior of oriented PET fibers under relaxed and fixed length conditions was investigated by using differential scanning calorimetry (DSC). The multi-overlapping peaks were observed in the non-isothermal DSC curves of oriented PET fibers under relaxed condition. The kinetics of non-isothermal crystallization of oriented PET fibers under relaxed condition was analyzed by using an equation which takes the multi-crystallization processes into account. The kinetic parameters of every process were obtained and the crystallization mechanism was discussed. The crystallization behavior under fixed length condition differs from that under relaxed condition.     

Miscibility and Physical Properties of Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)/Poly(ethylene oxide) Binary Blends

In order to improve some inferior physical properties of bacterial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐co‐3HHx)] by blending with PEO, the miscibility, spherulite morphology, crystallization behavior and mechanical properties of P(3HB‐co‐3HHx)/PEO binary biodegradable polymer blends were investigated. A good miscibility between P(3HB‐co‐3HHx) with a 3HHx unit content of 11 mol‐% and PEO in the amorphous state was found when the PEO weight fraction was 10 wt.‐%, while the miscibility decreased dramatically when the PEO weight fraction exceeded 20 wt.‐%. Strongly depending on the blend composition, the mechanical properties of P(3HB‐co‐3HHx) was found to be significantly improved by blending with PEO with a weight fraction of ≈5–17.5 wt.‐%.

     

Sequence distribution,thermal properties,and crystallization studies of poly(trimethylene terephthalate‐co‐1,4‐cyclohexylene dimethylene terephthalate) copolyesters

A series of novel poly(trimethylene terephthalate‐co‐1,4‐cyclohexylene dimethylene terephthalate) (PTCT) with various compositions were synthesized by melt polycondensation of 1,3‐propanediol, 1,4‐cyclohexanedimethanol and dimethyl terephthalate. The resulting copolyesters were characterized using ¹³C and ¹H nuclear magnetic resonance. The average length of both trimethylene terephthalate (TT) and cyclohexylene dimethylene terephthalate (CT) sequences varies from 1 to 10, and the chain structure is statistically random. The crystallization was investigated using wide angle X‐ray diffractometer (WAXD) and differential scanning calorimeter. The WAXD patterns can be divided in two groups according to the composition: copolyesters with less than 35 mol % CT content exhibit PTT‐type lattice, and those with CT unit content higher than 42 mol % crystallize with the PCT‐type lattice. The crystallizability of CT sequence is higher than that of TT sequence. Thermodynamic analysis shows that the comonomer is excluded from the PTT‐type or PCT‐type crystal of the copolyesters. The thermal decomposition temperature of copolyesters increases with increasing CT content, and their thermal stability is improved as compared to that of PTT. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly[(N‐isopropylacrylamide)‐co‐(itaconic acid)] hydrogels with poly(ethylene glycol)

The aim of the work reported here was to investigate temperature‐ and pH‐sensitive hydrogels of N‐isopropylacrylamide (NIPAM) and itaconic acid (IA) and their semi‐interpenetrating polymer networks (semi‐IPNs) with varying contents of poly(ethylene glycol) (PEG). The stimuli responsiveness, swelling behaviour and mechanical properties of the hydrogels and semi‐IPNs were studied in order to investigate the effect of various amounts of PEG. Pulsed‐gradient spin‐echo NMR experiments were carried out to investigate the diffusion process. The pH sensitivity increased with an increasing amount of PEG in the semi‐IPNs, while the overall rate of water uptake was diffusion‐controlled (n < 0.5). For certain PEG contents (5 and 10 wt%), the semi‐IPNs exhibited better mechanical properties than the poly(NIPAM‐co‐IA) copolymer. The calculated values of the self‐diffusion coefficients of water indicated facilitated diffusion of water through the system with increased amounts of PEG, while the self‐diffusion coefficients of a model compound, metoprolol tartrate, showed no significant dependence on the amount of PEG. According to the results obtained and compared to results reported in the literature, the investigated semi‐IPNs may have potential applications in the controlled release of macromolecular active agents such as proteins and peptides. Copyright © 2009 Society of Chemical Industry     

Crystallization of 2‐methyl‐1,3‐propanediol substituted poly(ethylene terephthalate). I. Thermal behavior and isothermal crystallization

Differential scanning calorimetry (DSC) was used to evaluate the thermal behavior and isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) copolymers containing 2‐methyl‐1,3‐propanediol as a comonomer unit. The addition of comonomer reduces the melting temperature and decreases the range between the glass transition and melting point. The rate of crystallization is also decreased with the addition of this comonomer. In this case it appears that the more flexible glycol group does not significantly increase crystallization rates by promoting chain folding during crystallization, as has been suggested for some other glycol‐modified PET copolyesters. The melting behavior following isothermal crystallization was examined using a Hoffman–Weeks approach, showing very good linearity for all copolymers tested, and predicted an equilibrium melting temperature (T_m⁰) of 280.0°C for PET homopolymer, in agreement with literature values. The remaining copolymers showed a marked decrease in T_m⁰ with increasing copolymer composition. The results of this study support the claim that these comonomers are excluded from the polymer crystal during growth. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2592–2603, 2006     

Correlation between the fracture toughness and β‐crystal fraction in a β‐nucleated propylene‐based propylene–ethylene random copolymer

Propylene‐based propylene–ethylene random copolymer (PPR) has been widely used in the production of hot‐water pipes. To further improve its toughness and thermal resistance, β‐nucleating agents (β‐NAs) are frequently incorporated. In this study, PPR containing 5.6 mol % ethylene units was modified by two kinds of β‐NAs, that is, calcium pimelate and N,N′‐dicyclohexylterephthalamide. The notched Izod impact strength of PPR increased with the addition of the β‐NAs. Drastically different toughening effects were found between the two β‐NAs. The structure of PPR with and without a β‐NA was investigated by calorimetry, X‐ray diffraction, and thermomechanical analysis. The results indicated that the relative fraction of β crystals (k_β) in the injection‐molded specimens was determined by the type and content of β‐NA. The relationship between k_β and the impact toughness was summarized. A critical value for k_β (0.68) was identified for the brittle–ductile transition of PPR. PPR with β‐NA having a k_β greater than 0.68 displayed a higher impact strength than the other mixtures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42930.     

Preparation of Poly(ethylene terephthalate)/Poly(amino ether) Blends by means of the Addition of Poly(butylene terephthalate)

Summary: Blends based on poly(ethylene terephthalate), PET, with poly(amino ether) (PAE) contents up to 40% were obtained by the addition of 20% poly(butylene terephthalate) (PBT) to the PET matrix. PBT mixed with PET led to a decrease in the T_m of the matrix that was enough to produce homogeneous blends by mixing in the melt state. Despite the presence of a single peak observed by dynamic‐mechanical analysis, the blends were biphasic, with amorphous phases in which minor amounts of the other component, both reacted and mixed, were present. This presence of minor components gave a fine morphology and significant adhesion that, together with the higher orientation of PAE in the blends, produced blends with a clear synergism in the modulus of elasticity, notched impact strength similar to that of the neat components, and high ductility up to 30% PAE.

Young's modulus of the PET‐PBT/PAE blends.     

Poly(vinylidene fluoride)–acrylic rubber partially miscible blends: Phase behavior and its effects on the mechanical properties

A phase diagram of poly(vinylidene fluoride) (PVDF) and acrylic rubber (ACM) was plotted, and the effects of the extent of miscibility on the mechanical properties of the polymer blends were examined. A compressible, regular solution model was used to forecast the phase diagram of this blend. The model prediction, the lower critical solution temperature (LCST) over the upper critical solution temperature (UCST), was done qualitatively according to the experimentally determined phase diagram by differential scanning calorimetry (DSC), optical microscopy, and rheological analysis. These experimental methods showed that this system was miscible in ACM‐rich blends (>50% ACM) and partially miscible in PVDF‐rich blends. A wide‐angle X‐ray diffraction study revealed that PVDF/ACM blends such as neat PVDF had a characteristic α‐crystalline peak. The partially miscible blends displayed up to 350% elongation at break; this was a significant increment of this parameter compared to that of neat PVDF(20%). However, the miscible blends showed elongation of up to 1000% [again, a remarkable increase compared to chemically crosslinked ACM (220%)] and displayed excellent mechanical properties and tensile strength and a large elongation at break. For the miscible and partially miscible blends, two different mechanisms were responsible for this improvement in the mechanical properties. It was suggested that in the partially miscible blends, the rubbery depletion layer between the spherulite and the conventional rubber cavitations mechanism were responsible for the increase in the elongation at break, whereas for the miscible blends, the PVDF spherulite acted as a crosslinking junction. The stretched part of the tensile samples in the partially miscible blends showed characteristic β‐crystalline peaks in the Fourier transform infrared spectra, whereas that in the miscible blends showed α‐crystalline peaks. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1247‐1258, 2013     

Poly(dimethylsiloxane)‐toughened syntactic foams

The potential of preformed elastomers as a toughening agent for epoxy–glass syntactic foam has been explored. Poly(dimethylsiloxane) microspheres were prepared by suspension polymerization. The microsphere dimensions could be varied from 58 to 255 µm by tuning the reaction parameters, particularly the stirring speed and feed concentration. Rheological studies indicated that the introduction of microballoons led to an increase in the viscosity of the resin, with the extent being proportional to the microballoon content. The zero shear viscosity increased from ～10³ mPa s at 30 °C to 10⁵ mPa s as the microballoon loading was increased to 40%. Syntactic foams containing varying amounts of microballoons (40–60% v/v) were prepared, and an analogous set of toughened foams were also prepared, where a fraction of the microballoons was replaced with poly(dimethylsiloxane) microspheres (3–7%). The effect of increasing dimensions of the elastomeric microspheres on the mechanical properties was also studied. The improvement in properties was more pronounced when the microsphere size was equivalent to that of the constituent microballoons. An improvement of 40% and 185% in flexural strength and flexural toughness was observed upon the introduction of poly(dimethylsiloxane) microspheres of optimal dimensions (diameter ～63 µm, 5% loading), without any undesirable increase in foam density. However, the compressive properties remained practically unaltered. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45882.     

Some Mechanical Properties of Poly[(acrylic acid)‐co‐(itaconic acid)] Hydrogels

Two series of hydrogels of poly[(acrylic acid)‐co‐(itaconic acid)] have been prepared by copolymerization in solution using tetrafunctional N,N′‐methylenebisacrylamide (NMBA) as cross‐linker. The resulting polymer was swollen in water at 298 K to yield homogenous transparent hydrogels. These hydrogels were characterized in terms of swelling and compression‐strain measurements. The influence of the comonomer composition and concentration of cross‐linking agent on volumetric swelling and the mechanical properties of these hydrogels were investigated. Inefficient cross‐linking is indicated by the small values of ν_e relative to the theoretical cross‐linking densities.

Dependence of measured affective cross‐linking density (ν_e) on the theoretical cross‐linking density (ν_t) for acrylic acid/itaconic acid hydrogels prepared at a fixed composition of AA80/AI20 wt.‐%, but at different concentrations of NMBA.     

Improvement of microstructures and properties of poly(lactic acid)/poly(ε‐caprolactone) blends compatibilized with polyoxymethylene

Incompatibility of poly(lactic acid)/poly(?‐caprolactone) (PLA/PCL) (80:20) and (70:30) blends were modified by incorporation of a small amount of polyoxymethylene (POM) (≤3 phr). Impact of POM on microstructures and tensile property of the blends were investigated. It is found that the introduction of POM into the PLA/PCL blends significantly improves their tensile property. With increasing POM loading from zero to 3 phr, elongation at break increases from 93.2% for the PLA/PCL (70:30) sample to 334.8% for the PLA/PCL/POM (70:30:3) sample. A size reduction in PCL domains and reinforcement in interfacial adhesion with increasing POM loading are confirmed by SEM observations. The compatibilization effect of POM on PLA/PCL blends can be attributed to hydrogen bonding between methylene groups of POM and carbonyl groups of PLA and PCL. In addition, nonisothermal and isothermal crystallization behaviors of PLA/PCL/POM (70:30:x) samples were investigated by using differential scanning calorimetry and wide angle X‐ray diffraction measurements. The results indicate that the crystallization dynamic of PLA matrix increases with POM loadings. It can be attributed to the fact that POM crystals have a nucleating effect on PLA. While crystallization temperature is 100 °C, crystallization half‐time can reduce from 9.4 to 2.0 min with increasing POM loading from zero to 3 phr. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46536.     

Poly(ethylene glycol)‐based hydrogels as cartilage substitutes: Synthesis and mechanical characteristics

Cartilage substitutes are needed to replace cartilage tissue, damaged in accidents or by pathologies (e.g., osteoarthritis). Treatment by total hip replacement has disadvantages, particularly due to immunological reaction to the implant's wear debris. One promising alternative is to replace damaged cartilage with substitutes based on hydrogel‐type material, designed to mimic the structure and properties of cartilage. The development of such a substitute must consider a wide spectrum of requirements. In this study, we addressed one aspect of this development namely the preparation and investigation of hydrogels exhibiting the required mechanical characteristics. To this aim, poly(ethylene glycol) (PEG) hydrogels and amphiphilic interpenetrating polymer networks (IPNs) of PEG with poly(methyl methacrylate) (PMMA) were prepared and characterized for their mechanical and swelling properties. Twenty‐seven types of hydrogels were synthesized, differing in their composition: PEG molecular weight, crosslink density, and PMMA volume fraction. The properties measured were water content, compression modulus, strength, fatigue durability, and poroelastic properties (hydraulic permeability and equilibrium modulus). All were investigated as functions of hydrogel's composition. Results show that lower PEG M_w, higher crosslink densities and higher PMMA fraction, all lead to higher modulus and lower water content, and that these properties can be controlled independently by proper choice of ingredients. Introduction of IPN greatly improved the hydrogels' strength. No reduction in the compression modulus resulting from fatigue damage was evident. Poroelastic properties varied nonmonotonously with structural characteristics. Seven types of the hydrogels were found to fit cartilage in their water content, modulus, and poroelastic properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(3‐hydroxybutyrate)–thermoplastic starch–organoclay bionanocomposites: Surface properties

Bionanocomposites based on poly(3‐hydroxybutyrate) (PHB) and starch plasticized with glycerol and water [thermoplastic starch (TPS)] with organically modified montmorillonite clay as a nanofiller were obtained by melt‐blending. The influence of the clay and TPS on the thermal and mechanical properties of the resultant bionanocomposite was investigated by various techniques, such as X‐ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis, differential scanning calorimetry, and nanoindentation. The results obtained by AFM showed that bionanocomposites have a surface roughness of 30.88 nm, compared to 14.53 nm for processed PHB. This result is obtained due to the migration of clay layers to the surface. From XRD and TEM it was determined that the clay layers of the bionanocomposites are completely separated. The hardness and elastic moduli of bionanocomposites have values similar to those of PHB, improving the drawbacks of the PHB–TPS blends (65:35 weight ratio). The thermal properties do not present significant changes, and only the degree of crystallinity decreased with increasing clay content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45217.     

Miscibility,crystallization, and mechanical properties of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)/ poly(butylene succinate) blends

Naturally amorphous biopolyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) containing 21 mol % of 4HB was blended with semi‐crystal poly(butylene succinate) (PBS) with an aim to improve the properties of aliphatic polyesters. The effect of PBS contents on miscibility, thermal properties, crystallization kinetics, and mechanical property of the blends was evaluated by DSC, TGA, FTIR, wide‐angle X‐ray diffractometer (WAXD), Scanning Electron Microscope (SEM), and universal material testing machine. The thermal stability of P3/4HB was enhanced by blending with PBS. When PBS content is less than 30 wt %, the two polymers show better miscibility and their crystallization trend was enhanced by each other. The optimum mechanical properties were observed at the 5–10 wt % PBS blends. However, when the PBS content is more than 30 wt %, phase inversion happened. And the two polymers give lower miscibility and poor mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Relationships between crystalline structure and the thermal behavior of poly(ethylene 2,5‐furandicarboxylate): An in situ simultaneous SAXS‐WAXS study

Poly(ethylene 2,5‐furandicarboxylate) (PEF) is an emerging bio‐based polymer with interesting thermal and barrier properties. In this study, the melting behavior of PEF was investigated in situ by means of simultaneous wide and small angle X‐ray scattering (WAXS and SAXS) measurements coupled with DSC measurements. This study gives the first evidence of what happens from a structural point of view during the multiple melting behavior of PEF, which is composed of three distinct events, taking into account the nature of the initial crystalline phase present. The first result is that the α′ form, induced at low crystallization temperature, does not undergo any phase transformation upon heating revealing its stable character. Second, the comparison of the SAXS and WAXS results with the DSC ones showed that the multiple melting behavior observed is attributed to a melting–recrystallization–melting process. Third, this work also definitely shows that the low amplitude melting endotherm observed in the DSC thermograms is ascribed to the melting of secondary crystals. Finally, SAXS‐WAXS results led to the conclusion that the secondary crystals cannot be depicted by the commonly accepted lamellar insertion model. Another microstructural representation of these secondary crystals is proposed. In this model, the secondary crystals consist of bundles of macromolecules, which formed small crystalline entities located between the primary crystalline lamellae stacks. POLYM. ENG. SCI., 59:1667–1677 2019. © 2019 Society of Plastics Engineers