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.     

Biodegradable poly (butylene succinate‐co‐cyclohexanedimethylene succinate): Synthesis,crystallization, morphology,and rheology

Poly (butylene succinate‐co‐cyclohexanedimethylene succinate) (PBCSs), which are composed of various amounts of cyclohexanedimethylene succinate (CS) with butylene succinate (BS) were synthesized via polycondensation. The composition of PBCSs was analyzed by a ¹H‐nuclear magnetic resonance (¹H‐NMR). Crystallization, morphology, and rheological properties of PBCSs were investigated by a polarized optical microscopy (POM), a differential scanning calorimetry (DSC), a X‐ray diffraction (XRD), and a parallel‐plate rheometer (PPR). The studies revealed that the composition of PBCSs played an important role in controlling their properties. Only one T_g can be seen for PBCSs by DSC, which demonstrate they are miscible copolymers. PBCSs exhibited lower crystallization capacity than its homopolyesters either Poly (butylene succinate) (PBS) or poly (cyclohexanedimethylene succinate) (PCS). It also proved that the cyclohexyl group of CHDM not only affected the crystalline formation, but also changed spherulitic morphology during crystallization. The spherulitic size gradually decreased with an increase of CS content. When CS content approached 50 wt %, the crystallization ability reached minimum. By comparing the effect of temperature with shear rate, it concluded that the viscosities of PBCSs were more sensitive to temperature rather than shear rate, and flow activation energies of PBCSs linearly increased with an increase of CS content. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40103.     

Poly(styrene‐co‐maleic anhydride) ionomers as nucleating agent on the crystallization behavior of poly(ethylene terephthalate)

Poly(styrene‐co‐maleic anhydride) (SMA) ionomers were synthesized and designed as a new kind of nucleation agent according to the crystallization theory for improving the crystallization of poly(ethylene terephthalate) (PET). The crystallization behavior of PET with the addition of nucleation agents was investigated by differential scanning calorimetry, polarized‐light microscope, and X‐ray diffraction (XRD). Avrami equation and Hoffman–Lauritzen theory are adopted for analyzing isothermal and non‐isothermal crystallization kinetics, respectively. The results show that the addition of 1 wt % SMA ionomers effectively accelerates the crystallization rate and reduces the fold surface free energy of PET at high temperature regions. PLM results also indicated that the crystals impinge on each other, thus decreasing the spherulite size for PET/SMA ionomers samples compared with PET. XRD measurement revealed that the introduction of SMA ionomers does not change the crystal structure but indeed accelerates the crystallinity of PET. The results clearly demonstrate that our synthesized SMA ionomers are an efficient nucleating agent for PET. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41240.     

Crystallization kinetics and crystalline morphology of poly(ethylene naphthalate) and poly(ethylene terephthalate‐co‐bibenzoate)

Copolymers of ethylene glycol with 4,4′‐bibenzoic acid and terephthalic acid are known to crystallize rapidly to surprisingly high levels of crystallinity. To understand this unusual behavior, the isothermal crystallization of poly(ethylene bibenzoate‐co‐terephthalate) in the molar ratio 55:45 (PETBB55) was studied. Poly(ethylene naphthalate) (PEN) was included in the study for comparison. The kinetics of isothermal crystallization from the melt and from the amorphous glass was determined using differential thermal analysis. The results were correlated with the crystalline morphology as observed with atomic force microscopy (AFM). Crystallization of PEN exhibited similar kinetics and spherulitic morphology regardless of whether it was cooled from the melt or heated from the glass to the crystallization temperature. The Avrami coefficient was close to 3 for heterogeneous nucleation with 3‐dimensional crystal growth. The copolymer PETBB55 crystallized much faster than did PEN and demonstrated different crystallization habits from the melt and from the glass. From the melt, PETBB55 crystallized in the “normal” way with spherulitic growth and an Avrami coefficient of 3. However, crystallization from the glass produced a granular crystalline morphology with an Avrami coefficient of 2. A quasi‐ordered melt state, close to liquid crystalline but lacking the order of a recognizable mesophase, was proposed to explain the unusual crystallization characteristics of PETBB55. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 98–115, 2002     

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     

Reversible selectivity of water/organic solvent mixtures in poly(lactic acid) film

The separation properties of water/organic solvent mixtures in poly(lactic acid) (PLA) films were investigated. The organic solvent flux increased linearly as the feed concentration increased, whereas the water flux was almost constant up to a feed concentration of 30 wt %. Interestingly, the permselectivity of PLA films was reversed from organic solvent selectivity to high water selectivity depending on the type of organic solvent. The permselectivity was strongly correlated with the solution concentration at which the solvent‐induced crystallization of the PLA films occurred. The selectivity of permeation, solution, and diffusion in water/organic solvent mixtures was determined by the expanded free volume of the PLA films as a result of the interaction between PLA and the water/organic solvent mixture. The permeability behavior of water/organic solvent mixtures in PLA films was very complex. However, it was found that this behavior could be predicted through immersion tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43822.     

Effects of crystallinity and molecular weight on crack behavior in crystalline poly(L‐lactic acid)

The crack behavior and spherulitic morphology in melt‐crystallized poly(L ‐lactic acid) (PLLA) were found to be molecular weight (MW) and crystallinity dependent, along with other key factors. With increasing MW in PLLA, the size of spherulites, band spacing of ring‐banded spherulites, and degree of crystallinity decreased, whereas cracks were increasingly less likely to occur. Multiple types of cracks, that is, circumferential and/or radial cracks, were massively present in low‐MW PLLA (PLLA‐11k), which had a high crystallinity. Upon cooling, in PLLA‐11k at most crystallization temperatures (T_c's), cracks formed, and the crack patterns were dependent on the lamellar morphology within the spherulites. Hexagonal, rather than circular, cracks occurred spontaneously during the cooling process of PLLA of a medium‐MW grade (PLLA‐120k) in PLLA film samples crystallized only at high T_c (135–138°C) and cooled to ambient temperature. However, no cracks of any types at all were present in PLLA films of high enough MWs (PLLA‐152k and PLLA‐258k) upon either slow air cooling or quench cooling when the samples were dipped into liquid nitrogen. Apparently, cooling‐induced contraction differences in different directions were invalid or not sufficient to address the complex cracking behavior in PLLA. In addition, for PLLA‐11k with a substantially high crystallinity, cracks were so prone to occur that even cover constraint imposed another factor in determining the crack and ring‐band patterns. More plausible mechanisms and correlations between the cracks, MW, crystallinity, spherulite size, and spherulite lamellar patterns of PLLA were analyzed in detail and proposed in this study. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Crystallization and Morphology of Poly(ethylene 2,6‐naphthalene dicarboxylate) Containing Additives

The influence of nucleating agents (AClyn^®, Surlyn^® and sodium benzoate (SB)) alone and together with nucleating promoter (Ceraflour^® 993 and Ceraflour^® 991 and poly(1,4‐butylene sebacate)) on the crystallization and morphology of poly(ethylene 2,6‐naphthalene dicarboxylate) (PEN) was investigated by means of differential scanning calorimeter, polarized optical microscopy and small angle light scattering. It was revealed that AClyn, Surlyn and SB effectively accelerate nucleation and crystallization of PEN with increasing the ratio of nucleating agent up to 1 wt.‐%. A combination of nucleating agent and nucleating promoter leads to further increase in crystallization rate at low temperature, but only a slight change at high temperature. Hedrites were obtained in pure PEN and the addition of SB and Ceraflour 993 produces small crystals with poor perfection upon crystallization in high temperature region. When crystallization temperature was below 210 °C, spherulites were observed in pure PEN and also in the samples of PEN/Ceraflour 993 and PEN/SB but with smaller size.

Crystal morphology of PEN crystallized at 240 °C for 40 min.     

Poly(ethylene terephthalate)/expanded graphite conductive composites: Structure,properties, and transport behavior

Poly(ethylene terephthalate)/expanded graphite conductive composites were prepared by the melt‐blending method. The relationships between the preparation methods, microstructures, and conductivity properties of the composites were studied with scanning electron microscopy and conductivity measurements. The results showed that the composites presented a low percolation threshold and strong anisotropic conductivity. The epoxy resin had a strong intercalation effect on the expanded graphite that led to the easy formation of the conductive network. With classical statistical percolation theory, the conductivity behaviors of the composites were investigated. The results indicated that the nonuniversal critical exponent should be attributed to the anisotropy of conductivity, the tunneling conduction, and the particular structure. In addition, preliminary studies on the crystallization and dynamic mechanical behavior of the composites were performed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Water vapor solubility of poly(lactic acid) films modified the surface by vacuum ultraviolet irradiation

Surface modification of poly(lactic acid) (PLA) film is performed via 172 nm excimer lamp irradiation. Effects on water vapor solubility and physical properties via vacuum ultraviolet (VUV) irradiation are studied systematically. After VUV irradiation, water vapor solubility increases approximately 11–43% in the low‐pressure region and approximately 20–38% in the high‐pressure region as surface hydrophilicity increased. The increase is attributed to hydrogen bonding with the carboxyl groups because of VUV radiation. The modified layer is significantly swelling after water vapor sorption. The hydrophilic layer forms a thickness of 2–3 μm from the irradiated surface via VUV radiation, but no changes are observed inside the irradiated film. Therefore, PLA film solubility after irradiation is enhanced by hydrophilicity and the swelling effect of the surface. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42200.     

Influence of the thin‐film thickness and crystallization temperature on the spherulitic structure of polymer thin films

The spherulitic structure and morphology of poly(3‐hydroxybutyrate) (PHB) thin films crystallized from the melt were observed with a polarizing optical microscope. Depending on the thickness of the PHB thin film and crystallization temperature, banded and nonbanded spherulites could form. Reducing the thin‐film thickness and crystallization temperature was favorable for the formation of the banded structure. The morphology transition from banded spherulites to nonbanded spherulites was related to the ratio of the crystallization rate to the diffusion rate. The formation mechanism of the banded structure was examined with the discontinuity growth theory. A depletion zone was considered to appear periodically at the crystal growth front because of the slow diffusion rate, and this may have resulted in the banded spherulites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystallization of poly(tetramethylene succinate) in blends with poly(ϵ‐caprolactone) and poly(ethylene terephthalate)

The crystallization behavior of polymer blends of poly(tetramethylene succinate) (PTMS) with poly(?‐caprolactone) (PCL) or poly(ethylene terephthalate) (PET) was investigated with differential scanning calorimetry under isothermal and nonisothermal conditions. The blends were prepared by solution casting and precipitation, respectively. The constituent polymers were semicrystalline materials and crystallized nearly independently in the blends. The addition of the second component to PTMS showed that PCL did not significantly influence the crystallinity of the constituents in the blends under isothermal conditions, whereas the crystallization of PTMS was slightly suppressed by crystalline PET. Nonisothermal crystallization under constant cooling rates was examined in terms of a quasi‐isothermal Avrami approach. In blends, the rates of crystallization were differently influenced by the second component. The rate of the constituent that crystallized at the higher temperature was barely influenced by the second component being in the molten state, whereas the rate of the second component, crystallizing when the first component was already crystalline, was altered differently under isothermal and nonisothermal conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 149–160, 2004     

In situ AFM study of near‐surface crystallization in PET and PEN

The surface crystallization behavior of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6‐naphthalate) (PEN) spin‐coated thin films was compared by means of atomic force microscopy (AFM) with an in situ heating stage. As the films were heated up stepwise, characteristic surface crystals appeared at a crystallization temperature (T_c) in the near‐surface region which is about 15 °C under the bulk T_c, and were replaced by bulk crystals when the temperature was increased to the bulk T_c. In the case of films whose thickness is less than 70 nm (PET) and 60 nm (PEN), significant increases in the bulk T_c were observed. Scanning force microscopy (SFM) force‐distance curve measurements showed that the glass transition temperature (T_g) of the near‐surface region of PET and PEN were 22.0 and 26.6 °C below their bulk T_g (obtained by DSC). After the onset of surface crystallization, edge‐on and flat‐on crystals appeared at the free surface of PET and PEN thin films, whose morphologies are very different to those of the bulk crystals. Although the same general behavior was observed for both polyesters, there are significant differences both the influence of the surface and substrate on the transition temperatures, and in morphology of the surface crystals. These phenomena are discussed in terms of the differences in the mobility of polymer chains near the surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44269.     

Permeability of ethanol solution through poly(lactic acid) film

The permeation properties of ethanol solution through poly(lactic acid) (PLA) films were investigated. The total flux of ethanol solution through PLA films was strongly depended on the flux of water. In addition, the diffusion coefficient of water was 1000 times higher than that of ethanol, and decreased with increasing feed concentration. After the permeation measurement, crystallization (X_C‐DSC = 1–2%) was observed. However, the crystallinity was not dependent on the feed concentration. On the other hand, the mole ratio of ethanol and water molecules in the PLA film strongly depended on the feed concentration. Based on the results, we concluded that the interaction with ethanol molecules caused the decrease in diffusion coefficient of water in PLA film. Thus, the permeation mechanism of the ethanol solution to the PLA film was investigated in detail. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42031.     

Thermal,optical, and electrical characterization of thin film coated RTV 655 bilayer system

Adhesion of thin films to hydrophobic elastomeric substrates is of particular interest in the area of flexible electronics and nano‐sensor technology. Here, nanometer‐thick Au films were deposited directly onto hydrophobic RTV 655 substrates by means of sputtering, thermal evaporation, and electroless techniques without an adhesion‐promoting layer. The bilayer system was exposed to repeat thermal cycling and changes to the surface morphology of the thin film were monitored electrically and optically. Buckle formation in the as‐deposited film was attributed to stress in the film and substrate stiffness rather than thermal coefficient mismatch between films. The Au‐RTV 655 interface was water tight and maintained a strong adhesion despite repeated thermal cycles. Sputtered and thermally evaporated carbon‐coated RTV 655 substrates were also studied in parallel for comparison. Periodic arrays of buckles formed in pre‐strained RTV 655 samples showed reproducibility in their optical properties demonstrating good adhesion between the two layers without an interfacial layer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41396.     

Isothermal and nonisothermal crystallization kinetics of poly(ϵ‐caprolactone)

With increasing environmental awareness, evaluating the potential of biopolymers as a substitute for traditional materials has been of great interest. Crystallization kinetics provides fundamental knowledge required for evaluation, playing vital role in determining the final properties of the product. In this study, the isothermal and nonisothermal crystallization kinetics of poly(?‐caprolactone) (PCL) were investigated with the help of various models. The Avrami model best described the isothermal crystallization kinetics, suggesting three‐dimensional spherulitic growth, which was in agreement with the morphology studies; whereas the Liu model fit well under nonisothermal crystallization conditions. The failure of the Kissinger model to determine the activation energy was overcome with the Friedman model. The kinetic crystallizability determined by the Ziabacki model indicated a higher crystallization ability of PCL at lower cooling rates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and mechanical properties of semi‐interpenetrating polymer networks composed of diisocyanate‐bridged,four‐armed,star‐shaped ε‐caprolactone oligomers and poly(ε‐caprolactone)

Semi‐interpenetrating polymer networks (S‐IPNs) were prepared by the reactions of hydroxyl‐terminated four‐armed, star‐shaped ε‐caprolactone oligomers with degrees of polymerization per one oligocaprolactone chain (ns) of 3, 5, and 10 and 2,4‐tolylene diisocyanate (TDI) in the presence of poly(ε‐caprolactone) (PCL). In the dynamic mechanical analysis of the S‐IPN [2,4‐tolylene diisocyanate bridged hydroxyl‐terminated four‐armed, star‐shaped ε‐caprolactone oligomer (TH4CLO)/PCL], only one tan δ peak was observed; its temperature increased with increasing TH4CLO content and with decreasing n value. Differential scanning calorimetric analyses of the TH4CLOs and TH4CLO/PCLs revealed that the TH4CLOs with ns of 3 and 5 were amorphous, whereas TH4CLO with an n of 10 was semicrystalline and that the crystallization of the PCL chain for TH4CLO/PCLs was more strongly disturbed with increasing TH4CLO content and decreasing n value. Although the tensile strength, modulus, and elongation at break of TH4CLO were much lower than those of PCL, those values increased with the n value. Although the tensile strength and modulus of the TH4CLO/PCLs decreased with increasing TH4CLO content, TH4CLO (n = 3)/PCL 50/50 showed the highest elongation at break (314%) among the S‐IPNs because of the suppression of crystallization of the polycaprolactone chain. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4229–4236, 2013     

Size control of poly(2‐oxy‐6‐naphthoyl) whiskers by the addition of oligomers during polymerization

The method of controlling the size of a poly(2‐oxy‐6‐naphthoyl) (PON) whisker was examined with a focus on lengthening the whisker. PON whiskers were prepared by the polymerization of 2‐acetoxy‐6‐naphthoic acid in liquid paraffin at 330°C. The whiskers were very symmetrical. and both tips were very sharp. Growth of the whiskers along the length took place by which oligomer lamellae piled up along the long axis of the needlelike crystals with spiral growth. During steady growth until 8 min, the tip angle of the whiskers was constant at 80°. However, it became significantly sharper (22°) at 30 min, and later the trunk part of the whiskers stopped increasing. To depress the sharpening of the tips and to extend the steady‐growth period for longer whiskers, oligomers were added to the polymerization system after 8 min, just before the tip angle became sharper, to keep the concentration of the oligomers in the polymerization system constant. The addition of the oligomers extended the steady‐growth period, and the length increased from 12.5 to 17.3 μm. Although the width of the whiskers increased very slightly with the addition of the oligomers, the axial ratio of the whiskers increased from 19.4 to 24.7. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1320–1327, 2003     

Analysis of surface structure with regard to interfacial delamination in polyester films with incompatible polymers

Poly(ethylene terephthalate) (PET) films containing incompatible polymer particles were analyzed, with particular reference to the relationship between the PET particle interfacial tension and the microvoids, or the protrusion that were formed when the composite material was stretched at 90°C. A model was developed to simulate void formation and surface protrusion due to interfacial delamination between PET and three types of dispersed incompatible polymers, poly(4‐methyl‐1‐pentene), polypropylene, and polystyrene. The numerical results, obtained with the finite element method, were compared with experimental data of the blends for both the internal and subsurface regions. The experimental measurements showed that the increase in the difference in the surface tension between PET and the added incompatible polymer was associated with the formation of larger voids. The protrusions were also generated in the stretching and delamination between PET and the incompatible polymers, but a decrease in the interfacial tension agreed with the formation of a larger protrusion. Modeling studies showed that increasing the interfacial tension between the two components in a blend causes a decrease in the critical stress for delamination. Interfacial tension values related qualitatively to the critical stress for void formation and protrusion calculated with the numerical analysis. A concavity was also necessary for understanding the surface structure of the films, along with protrusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1243–1251, 2004     

Non-isothermal Crystallization of Poly(ethylene terephthalate) with Poly(oxybenzoate-p-trimethylene terephthalate) Copolymer

The influence of a poly(oxybenzoate-p-trimethylene terephthalate) copolymer, designated T64, on the non-isothermal crystallization process of poly(ethylene terephthalate) (PET) was investigated. All samples were prepared by solution blending in a 60/40 by weight phenol/tetrachloroethane solvent at 50°C. The solidification process strongly depended on cooling rate and composition of system. The crystallization rate of blends was estimated by crystallization rate parameter (CRP) and crystallization rate coefficient (CRC). From these results of CRP and CRC, it was predicted that the overall non-isothermal crystallization rate of PET would be accelerated by blending with 1–15 wt% of T64. The acceleration of PET crystallization rate was most pronounced in the PET/T64 blends with 5 wt% T64. The observed changes in crystallization behavior are explained by the effect of the physical state of the copolyester during PET crystallization as well as the amount of copolymer in the blends. An Ozawa plot was used to analyze the data of non-isothermal crystallization. The obvious curvature in the plot indicated that the Ozawa model could not fit the PET/T64 blend system well, and there was an abrupt change in the slope of the Ozawa plot at a critical cooling rate.