Effect of morphology on the crack propagation of the semicrystalline polyester poly(1,4-dimethylene-trans-cyclohexyl suberate)

Crack propagation of the semicrystalline polymer poly(1,4-dimethylene-trans-cyclohexyl suberate) (MCS) was studied as a function of polymer morphology. MCS was characterized in terms of degree of crystallinity and crystal growth kinetics. Spherulitic band size and radius show similar temperature dependencies. The energy to propagate a crack was correlated with spheruliticr adius for a low-molecular-weight material (M_n = 24 500). Brittle fracture occurs in this material with little large-scale plastic deformation. What plastic deformation there is, however, correlated with spherulitic band orientation. A higher-molecular-weight sample (M_n = 38 000) shows plastic deformation over the entire temperature range studied. Energy to fracture agrees with a modified Griffith criterion in which the characteristic dimension is spherulitic radius. Annealing experiments show that energy to fracture is controlled by lamellar thickness, decreasing with increasing thickness. Fracture morphology shows little interspherulitic failure, with intraspherulitic failure (low-molecular-weight material) or plastic deformation (high-molecular-weight material) being the prevalent modes.     

Stress relaxation of poly(1,4-dimethylene-trans-cyclohexyl suberate)

Stress relaxation experiments were conducted on poly(1,4-dimethylene-trans-cyclohexyl suberate) (MCS) as a function of preparation condition and temperature. Deconvolution of the stress relaxations provides relaxation times, which can be plotted as a function of temperature to obtain an activation energy for the relaxation process. For an MCS sample of M_n=24.8 K, MWD=2, the activation energy varies from 12.7-5.0 kcal mol^?1 with forming temperatures varying from 45–90°C. These activation energies are associated with different populations of tie molecules between lamellae. We believe that these activation energies reflect the reorientation process in the amorphous segments of the polymer during stress relaxation.     

Miscibility, crystallization and melting behaviour, and semicrystalline morphology of binary blends of polycaprolactone with poly(hydroxy ether of bisphenol A)

Blends of poly(hydroxy ether of bisphenol A) (Phenoxy) with polycaprolactone (PCL) were prepared by the coprecipitation technique. The melt miscibility of the polymers was studied by optical microscopy, light transmission measurements and dynamic mechanical analysis. The crystallization kinetics of PCL in the miscible Phenoxy/PCL blends were studied using optical microscopy and the segregation behaviour of Phenoxy due to the crystallization of PCL was examined by means of optical microscopy and small-angle X-ray diffraction, while the melting behaviour of PCL in the blend was explored by differential scanning calorimetry. The polymers were found to be miscible over the entire composition and temperature range (up to 200°C), while Phenoxy is segregated interlamellarly as well as interfibrillarly and interspherulitically during the crystallization process of PCL.     

Crystallization kinetics and morphology of poly(ethylene suberate)

The crystallization kinetics and morphology of poly(ethylene suberate) (PESub) were studied in detail with differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray diffraction. The Avrami equation could describe the overall isothermal melt crystallization kinetics of PESub at different crystallization temperatures; moreover, the overall crystallization rate of PESub decreased with increasing crystallization temperature. The equilibrium melting point of PESub was determined to be 70.8°C. Ring‐banded spherulites and a crystallization regime II to III transition were found for PESub. The Tobin equation could describe the nonisothermal melt crystallization kinetics of PESub at different cooling rates, while the Ozawa equation failed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43086.     

Microscopic surface and bulk morphology of semicrystalline poly(dimethylsiloxane)–polyester copolymers

In this study, two series of semicrystalline poly(dimethylsiloxane) (PDMS)–polyester segmented copolymers with various PDMS contents were synthesized. One series was based on polybutylene adipate (PBA) as the polyester segment and the other was based on a polybutylene cyclohexanedicarboxylate ester (PBCH) segment. The copolymers were characterized using ¹H‐nuclear magnetic resonance, size exclusion chromatography, dynamic mechanical analyses, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). The microscopic surface morphology and the microscopic bulk morphology were investigated using atomic force microscopy (AFM) and transmission electron microscopy, respectively. The effects of the polyester type and the PDMS content on the crystallinity degree as well as the copolymer surface and bulk morphology at room temperature were investigated for each series. DSC and WAXD results showed the ability of the copolymers to crystallize, to various degrees, depending on the polyester type and the PDMS content. The results showed that the PDMS content had a greater influence on the crystallinity degree in the PDMS‐s‐PBCH (cycloaliphatic) copolymer series than in the PDMS‐s‐PBA (aliphatic) copolymer series. In the copolymers with a low PDMS content, the AFM images showed spherulitic crystal morphology and evidence of PDMS nanodomains in between the crystal lamellae of the ester phase on the copolymer surface. A heterogeneous distribution of the PDMS domains was also observed for these copolymers in the bulk morphology as a result of this segregation between the polyester lamellae. All the copolymers, in both series, showed microphase separation as a result of the incompatibility between the PDMS segment and the polyester segment. Three types of surfaces and bulk morphologies were observed: spherical microdomains of PDMS in a matrix of polyester, bicontinuous double‐diamond type morphology, and spherical microdomains of polyester in a matrix of PDMS as the PDMS content increases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Miscibility, crystallization and melting behaviour, and morphology of binary blends of polycaprolactone with styrene-co-maleic anhydride copolymers

Blends of polycaprolactone (PCL) and random copolymers of styrene and maleic anhydride (SMA) with different maleic anhydride contents were prepared by the coprecipitation technique. The miscibility of both polymers in the melt and in the solid state was studied by means of optical microscopy, light transmission measurements and dynamic mechanical analysis. The crystallization behaviour of PCL in the miscible blends was examined using optical microscopy and the morphology of the semicrystalline PCL/SMA blends was investigated by means of small-angle X-ray diffraction measurements. Their melting behaviour was studied by differential scanning calorimetry. SMA containing 14 and 25 wt% MA was found to be miscible with PCL over the entire composition and temperature range (up to 200°C). SMA appears to segregate interlamellarly during the isothermal crystallization of PCL. The double melting behaviour of PCL in the blends was attributed to a secondary crystallization process and not to a partial melting-recrystallization-remelting process.     

Influence of the morphology on the fire behavior of a polycarbonate/poly(butylene terephthalate) blend

Polycarbonate/Poly(butylene terephthalate) (PC/PBT) blends are used in various industrial sectors, particularly in the cable industry. In this work, the fire behavior of PC/PBT blends was studied for the entire range of blend composition to investigate the relation between fire properties and blend morphology. The morphology of the binary blends used presents a phase inversion point for 25–30 wt % PBT. Various tests have been performed to characterize the fire behavior [limiting oxygen index (LOI), epiradiator test, cone calorimeter, and pyrolysis combustion flow calorimeter (PCFC)]. A change in fire behavior has been observed when the PBT content increases from 20 to 30 wt %, corresponding to the phase inversion, from a continuous rich-PC phase to a continuous rich-PBT phase. Consequently, it can be suggested that the control of the morphology of binary polymer blends is crucial to improve their fire properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Temperature dependence of interaction parameters in electrolyte NRTL model

The electrolyte NRTL model captures the electrolyte solution nonideality over the entire concentration range with two binary interaction parameters. Here, the temperature dependence of the binary parameters is formulated with a Gibbs‐Helmholtz expression containing three temperature coefficients associated with Gibbs energy, enthalpy, and heat capacity contributions. We show the Gibbs energy term is correlated to the excess Gibbs energy of aqueous single electrolyte systems at 298.15 K. With the Gibbs energy term identified, the enthalpy term is correlated to the excess enthalpy at 298.15 K. With the Gibbs energy term and the enthalpy term identified, the heat capacity term is correlated to the excess heat capacity at 298.15 K. Once the temperature coefficients are properly quantified by regressing data of mean ionic activity coefficient, excess enthalpy, and heat capacity at 298.15 K or the equivalents, the model provides a comprehensive thermodynamic framework to represent all thermodynamic properties of electrolyte solutions. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1244–1253, 2016     

Temperature dependence of rheological properties of poly(methyl methacrylate) filled with silica nanoparticles

Creep-recovery experiments up to the steady state were performed on neat poly (methyl methacrylate) and on composites filled with 2.1 vol.% silica nanoparticles in order to get information on the long retardation times that occur due to polymer-particle interactions. The temperature dependence of the elasticity was investigated, varying the temperatures between 170 °C and 200 °C. For the neat polymer it was found that it behaves thermorheologically simple, whereas the composite exhibits a thermorheological complexity. An interpretation of these findings can be given, if the corresponding retardation spectra are regarded. The interactions between the polymer molecules and the particle surface is reflected by a particular maximum at longer retardation times, which exhibits a different temperature dependence compared to the spectra of the unfilled polymer matrix. This thermorheological complex behaviour is not seen in the usual dynamic-mechanical measurements down to angular frequencies of ω = 10⁻² s⁻¹. If the frequency range of the dynamic moduli is extended, however, by making use of the retardation spectra, a thermorheological complexity can be found, too. These results demonstrate that appropriate experimental time windows have to be applied to obtain a comprehensive picture of the rheological behaviour of nano particle-filled polymer melts.     

Optimization of poly(1,4-cyclohexylidene cyclohexane-1,4-dicarboxylate) (PCCD) preparation for increased crystallinity

A key factor, which affects the crystallization temperature on cooling (T_c) of PCCD is the cis/trans isomer ratio of the cyclohexyl diester in the polymer. Isomerization of pure dimethyl-trans-1,4-cyclohexanedicarboxylate can occur during the polymerization, and the T_c on cooling decreases along with the trans content. The isomerization reaction is enhanced with temperature, time and catalyst amount, and these variables should be minimized to prepare PCCD polymers with high T_c. However, these same variables also control the molecular weight growth of the polymer, and so a compromise between the best conditions for high T_c and those for high M_w must be made. A set of optimized conditions were obtained leading to PCCD polymers with M_w of 75,000-80,000 and T_c on cooling of 164-167 °C. Solid state polymerization was used to prepare high molecular weight PCCD with a high level of crystallinity (T_c on cooling ∼193 °C). It was also shown that adding small amounts of supplementary diols facilitates PCCD preparation by ensuring that high molecular weight PCCD polymers will be obtained even when the stoichiometry of monomer feed is off by >3%, i.e. conditions which would otherwise lead to low M_w. Finally, less crystalline PCCD's have been prepared via either incorporation of diethylene glycol or increasing the cis-diester amount in the polymer.     

Temperature dependence of distortion in poly(ethylene oxide) crystals

X-ray studies of poly(ethylene oxide) crystals have been made on integrated intensities of 31 Bragg peaks and the diffraction profile of 120 reflection, which gives information about lateral molecular packing, over the temperature range from ?150° to 50°C. Both the integrated intensities of 25 Bragg peaks and the integral breadth of 120 reflection have maxima in their temperature changes. These unusual temperature changes can be attributed to static crystal distortion: static displacement of atoms from their average positions over all crystals. Thermal vibration actually takes place around the displaced positions. Many Bragg peaks were required to be investigated in order to study the effect of the static distortion on the integrated intensities, since temperature changes of the displaced positions lead to changes of both the average positions (crystal structure) and magnitude of the static displacement. A model for the static displacement is proposed:; intermolecular interaction is the origin of the static displacement, which is decreased with increasing temperature by a smearing-out effect on the intermolecular interaction due to thermal vibration. Fourier analysis of the profile of 120 reflection suggests that crystalline order is maintained at short range, 20 molecules or more in diameter.     

Anaerobic biodegradation of the microbial copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate): Effects of comonomer content, processing history, and semi-crystalline morphology

Films of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB-co-3HHx) containing 3.8-10 mol% of 3-hydroxyhexanoate (3HHx) comonomer were subjected to anaerobic biodegradation to explore the effects of copolymer composition, crystallinity, and morphology on biodegradation. As biodegradation proceeded, samples with higher HHx fraction tended to have faster weight loss; on Day 7 of the degradation experiment, P3HB-co-10 mol%-3HHx lost 80% of its original weight, while P3HB-co-3.8 mol%-3HHx lost only 28%. Scanning electron microscopy (SEM) images revealed that the anaerobic biodegradation proceeded at the surface of the samples, with preferential erosion of the amorphous regions, exposing the crystalline spherulites formed inside the copolymer films. It was observed that copolymers with higher HHx fraction had smaller diameter spherulites, ranging from roughly 40 μm for P3HB-co-3.8 mol%-3HHx to 10 μm for P3HB-co-10 mol%-3HHx. A banded spherulite morphology was observed for P3HB-co-6.9 mol%-3HHx and P3HB-co-10 mol%-3HHx, with much wider band spacing (2 μm) for the former than the latter (0.3 μm). Different thermal history seemed to affect the morphological properties and, thus, the biodegradability of the P3HB-co-3HHx samples as well. When comparing copolymers with the same copolymer composition, P3HB-co-3HHx annealed at 70 °C had 5-30% more weight loss after the same duration of incubation in active sludge compared to the quenched samples. We suggest that annealing of P3HB-co-3HHx likely induces void formation in the semi-crystalline structure, facilitating the movement of water or perhaps enzymes to a higher degree of penetration into the sample and subsequently enhancing microbial degradation.     

Melting and crystallization behaviour of elastoplastic semicrystalline copolymers: poly(ether ester)

The melting and crystallization behaviour of an elastoplastic semi-crystalline poly(etherester) has been studied by differential scanning calorimetry. The shape of the melting endotherm is strongly dependent on heating rate and annealing time and results from the sum of simultaneous melting and crystallization phenomena. Samples prepared by different techniques, i.e. by solvent evaporation or by melt extrusion, behave very differently owing to specific crystal morphologies. By applying the Hoffman-Weeks plot, the equilibrium melting temperature has been extrapolated. The Avrami treatment allows the calculation of the index n and of the rate constant K from the isothermal kinetic data.     

增容剂对聚对苯二甲酸丁二酯/ 热塑性聚酰胺弹性体合金热性能和分散形态的影响

８０份聚对苯二甲酸丁二酯（ＰＢＴ）和２０份热塑性聚酰胺弹性体（ＴＰＡＥ）分别与９种含有环氧基（—ＧＭＡ）或无水马来酸酐基（—ＭＡＨ）或酯基的增容剂及它们的复合物进行熔融共混,得到ＰＢＴ／ＴＰＡＥ／增容剂合金。用动态粘弹性温度曲线、ＤＳＣ曲线、扫描电镜观察表明,含—ＧＭＡ或—ＭＡＨ或两者共存的增容剂能使ＰＢＴ与ＴＰＡＥ间的相互作用增强,使ＴＰＡＥ在ＰＢＴ中的分散更加均匀,但对软化温度影响很小。     

Phosphorescence emission from poly(di-n-hexylsilane) in a glass: Temperature dependence and optically detected magnetic resonance (ODMR) spectra

The low-temperature steady-state phosphorescence spectrum of poly(di-n-hexylsilane) (PDHS) in a 3-methylpentane (3MP) glass at 1.5 K has been measured. The temperature dependence of the phosphorescence decay was determined and zero-field optically detected magnetic resonance (ODMR) experiments were performed. Evidence of at least two distinct emitting species was found. A narrow phosphorescence spectrum with no distinct vibronic structure was observed for PDHS and interpreted as indicating a delocalized triplet state. The ODMR spectrum is dependent on the detection wavelength, indicating that the triplet splittings are sensitive to the conformation and local environment of the polysilane chains. The phosphorescence disappears completely above 30 K. This is attributed to the presence of a dissociative triplet state.     

Nonisothermal crystallization kinetics and morphology of poly(ethylene terephthalate) modified with poly(lactic acid)

The nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) copolymers modified with poly(lactic acid) (PLA) were investigated with differential scanning calorimetry, and a crystal morphology of the samples was observed with scanning electron microscopy. Waste PET (P100) obtained from postconsumer water bottles was modified with a low‐molecular‐weight PLA. The PET/PLA weight ratio was 90/10 (P90) or 50/50 (P50) in the modified samples. The nonisothermal melt‐crystallization kinetics of the modified samples were compared with those of P100. The segmented block copolymer structure (PET‐b‐PLA‐b‐PET) of the modified samples formed by a transesterification reaction between the PLA and PET units in solution and the length of the aliphatic and aromatic blocks were found to have a great effect on the nucleation mechanism and overall crystallization rate. On the basis of the results of the crystallization kinetics determined by several models (Ozawa, Avrami, Jeziorny, and Liu–Mo) and morphological observations, the crystallization rate of the samples decreased in the order of P50 > P90 > P100, depending on the amount of PLA in the copolymer structure. However, the apparent crystallization activation energies of the samples decreased in the order of P90 > P100 > P50. It was concluded that the nucleation rate and mechanism were affected significantly by the incorporation of PLA into the copolymer structure and that these also had an effect on the overall crystallization energy barrier. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Spherulite morphology and crystallization behavior of poly(trimethylene terephthalate)/poly(ether imide) blends

The spherulite morphology and crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(ether imide) (PEI) blends were investigated with optical microscopy (OM), small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS). Thermal analysis showed that PTT and PEI were miscible in the melt over the entire composition range. The addition of PEI depressed the overall crystallization rate of PTT and affected the texture of spherulites but did not alter the mechanism of crystal growth. When a 50/50 blend was melt-crystallized at 180 °C, the highly birefringent spherulite appeared at the early stage of crystallization (t < 20 min). After longer times, the spherulite of a second form was developed, which exhibited lower birefringence. The SALS results suggested that the observed birefringence change along the radial direction of the spherulite was mainly due to an increase in the orientation fluctuation of the growing crystals as the radius of spherulite increased. The lamellar morphological parameters were evaluated by a one-dimensional correlation function analysis. The amorphous layer thickness showed little dependence on the PEI concentration, indicating that the noncrystallizable PEI component resided primarily in the interfibrillar regions of the growing spherulites.     

Modelling the amorphous phase of a melt crystallized,semicrystalline polymer: segment distribution,chain stiffness,and deformation

The analogy between the Gambler's Ruin problem and the statistics of loops and bridges in the amorphous region of lamellar semicrystalline polymers was first recognized by Guttman et al. Results for the loop and bridge distribution compare very well with recent data from Monte Carlo calculations. However, when the molecular weight of the polymer is low, a substantial part of the amorphous region is filled by cilia and free polymer. We examined their relative importance by adapting the matrix formalism developed by DiMarzio and Rubin. The Gambler's Ruin results are recovered for high molecular weight polymer. In addition it will be shown that the effect of the temperature (chain stiffness) can be simulated by rescaling the steplength of a random walk chain. Mean field theories incorporate segment-solvent interactions and allow for non-uniform segment densities by weighting each step according to the local concentrations. Using these weighting factors, we find deformation to be controlled by energetic interactions rather than by entropy. At large strain a ‘necking’ process occurs. However, in the presence of a good solvent, the material is soft and flexible.     

Facile synthesis and properties of semicrystalline copoly(arylene ether ketone) containing hydroquinone and phthalazinone

Two series of novel copoly(arylene ether ketone) were successfully synthesized from hydroquinone or bisphenol A, bis(4‐fluorophenyl)ketone and 4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one with anhydrous potassium carbonate as the catalyst. The synthesized polymers exhibited high glass‐transition temperatures together with excellent thermooxidative stability. The chain structure of these polymers was studied by means of ¹³C‐nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD) techniques. The experimental results showed that these “as‐made” copolyaryleneketones containing hydroquinone moieties exhibited a multiblock chain structure with long segments that mainly consisted mainly of hydroquinone and bis(4‐fluorophenyl)ketone at the middle of the molecular chain. These long segments exhibited crystallites in the produced polymers. The synthesized copolyaryleneketone containing 90 mol % hydroquinone possessed a glass‐transition temperature higher than that of commercial PEEK. The synthesized polymers also exhibited either fair processability or solubility. The glass‐transition temperatures, solubility, and tensile strengths of the two series of copolyaryleneketones tended to increase with increasing phthalazinone moiety content. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2687–2695, 2001