Miscibility and Crystallization Behavior of Poly (Ethylene Terephthalate)/Phosphate Glass Hybrids

Fundamental studies on miscibility and crystallization behavior of poly (ethylene terephthalate) (PET) and inorganic phosphate glass (Pglass) hybrids were conducted. The Flory–Huggins interaction parameter (χ) value of ?0.075 for the PET/Pglass hybrids was obtained using the Nishi–Wang equation, demonstrating that the Pglass and PET components were miscible in the melt state. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the phase separation occurred during quenching from the melt. The phase boundaries between PET and Pglass were blurred, which indicated partial compatibility of the components in the solid state. Contact angle measurements indicated the interfacial tension of PET/Pglass hybrids was 1.5 mN/m, and the work of adhesion was 78.0 mN/m at 28 °C. Based on the Hoffman–Lauritzen theory, the nucleation constant (K_g) and fold surface free energy (σ_e) of PET/Pglass hybrids were less than those of neat PET.     

Isothermal Melt Crystallization Kinetics for Poly(Trimethylene Terephthalate)/Poly(Butylene Terephthalate) Blends

The kinetics of isothermal melt crystallization of poly(trimethylene terephthalate) (PTT)/poly(butylene terephthalate) (PBT) blends were investigated using differential scanning calorimetry (DSC) over the crystallization temperature range of 184–192°C. Analysis of the data was carried out based on the Avrami equation. The values of the exponent found for all samples were between 2.0 and 3.0. The results indicated that the crystallization process tends to be two‐dimensional growth, which was consistent with the result of polarizing light microscopy (PLM). The activation energies were also determined by the Arrhenius equation for isothermal crystallization. The values of ΔE of PTT/PBT blends were greater than those for PTT and PBT. Lastly, using values of transport parameters common to many polymers (U*=6280 J/mol, T _∞=T _g – 30), together with experimentally determined values of T _m ⁰ and T _g, the nucleation parameter, K _g, for PTT, PBT, and PTT/PBT blends was estimated based on the Lauritzen–Hoffman theory.     

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T _m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.     

Toughening of Poly (Butylene Terephthalate) with Epoxy-Filled Poly (Ethylene–Octene) Copolymer

Toughened poly (butylene terephthalate) (PBT) with triglycidyl isocyanurate (TGIC)-filled poly (ethylene–octene) (POE) was prepared by melt reaction extrusion. For retarding the reaction extent between PBT and the epoxy component, the TGIC was first blended with POE to enwrap its reactive epoxy groups. Then, the TGIC-filled POE was used to melt blend with PBT. The Fourier transform infrared (FTIR) spectra showed that no other peaks appeared in the POE/TGIC specimens except for those originally existing in pure POE and TGIC. The rheological results further confirmed that no reaction occurred between the epoxy and the POE matrix. When the POE/TGIC was blended with PBT, a distinct increase of the viscosity suggested that the migration of the TGIC from POE to PBT during the melt processing induced chain extension reactions of PBT. The results obtained from DSC and DMA revealed that the chain extension of PBT induced by the reaction with TGIC restricted the mobility of PBT chains leading to a limitation of the recrystallization-remelting process and an increase of the glass transition temperature of PBT. The mechanical tests showed that the presence of TGIC in the POE phase distinctly improved the toughness of PBT. Compared to the case of a PBT/POE (80/20, wt%/wt%) blend, the elongation at break and impact strength of the system filled with 5 phr TGIC were increased more than three and six times, respectively.     

Study on the Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride)/Tributyl Citrate Blends Via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly (vinylidene fluoride) (PVDF) in PVDF/tributyl citrate (TBC) blends having undergone thermally induced phase separation were investigated through differential scanning calorimetry measurements. Ozawa theory, Mo's method and Kissinger model were used to analyze the kinetics of the nonisothermal crystallization process. The Ozawa theory failed to describe the crystallization behavior of PVDF in the PVDF/TBC blends, whereas the Mo model was able to describe the nonisothermal crystallization process fairly well. The crystallization activation energy was determined by the Kissinger method, and was in the range of 90–165 kJ/mol.     

Nonisothermal Crystallization Kinetics of Poly(lactic acid)/Nanosilica Composites

Poly(lactic acid) (PLA)/nanosilica composites were prepared by blending the PLA and nanosilica in chloroform and then evaporating the solvent to form the composite films in a dish. The Ozawa and Mo equations were used to characterize the nonisothermal cold crystallization kinetics of the PLA/nanosilica composites. The results indicated that the Ozawa equation was not successful while the Mo equation was successful to describe the nonisothermal crystallization kinetics of PLA/nanosilica composites. The values of crystallization activation energy (E _c) of the samples were calculated by the Kissinger method. Although the sample crystallization rates were enhanced with the increase of nanosilica content, the samples exhibited increased E _c in the presence of nanosilica. The results showed that nanosilica had an effect on both the nucleation and the crystal growth of PLA, promoting the nucleation but interfering with the molecular motion of PLA in the crystallization process.     

Crystallization Behavior of Poly(Trimethylene Terephthalate)/Polycarbonate Blends

The crystallization behavior of poly(trimethylene terephthalate (PTT) in compatibilized and uncompatibilized PTT/polycarbonate (PC) blends are investigated in the research reported in this paper. The differential scanning calorimetry (DSC) results showed that the crystallization behaviors of PTT/PC blends were very sensitive to PC content. The onset (T_ci) and the peak (T_c) crystallization temperatures shifted to lower temperatures whereas the area of the exotherm decreased quickly as the PC content was increased. The Avrami exponent, n, decreased from 4.32 to 3.61 as the PC content was increased from 0 to 20 wt %, and the growth rate constant, Z _c , decreased gradually as well. This suggests that the nucleation mechanism exhibits the tendency of changing gradually from a thermal nucleation to an athermal mode although the growth mechanism still remains three‐dimensional. When epoxy (2.7 phr) was added as a compatibilizer during melt blending, the T_ci and T_c shifted slightly to higher temperature (≤2°C), and the crystallization enthalpy, however, exhibited an increased crystallinity with the exception of the 90/10/2.7 phr PTT/PC/Epoxy. This suggests that the epoxy make a positive contribution to the PTT crystallization. Moreover, the influences of epoxy on the crystallization behaviors of PTT/PC blends are related to the epoxy content. By contrast, the compatibilizer of ethylene‐propylene‐diene copolymer graft glycidyl methacrylate (EPDM‐g‐GMA, ≤6.3 phr) had little effect on the crystallization behavior of PTT/PC blends. For PTT/PC/Epoxy (2.7 phr) blends, the Avrami exponent, n, decreased to near 3, while the growth rate constant, Z _c , increased slightly as PC content was increased from 0 to 20 wt %. It is suggested that epoxy accelerated the process of the nucleation mechanism changing from thermal nucleation to an athermal mode. The EPDM‐g‐GMA had little effect on the nucleation mode and spherical growth mechanism. The PTT spherulite morphologies in PTT/PC blends were very sensitive to blend composition. Completely different morphologies were observed in pure PTT, PTT/PC, PTT/PC/Epoxy, and PTT/PC/EPDM‐g‐GMA blends.     

Kinetics of Isothermal and Nonisothermal Crystallization of Poly(ethylene oxide) (PEO) in PEO/Fatty Acid Blends

In this work, isothermal and nonisothermal crystallization kinetics of poly(ethylene oxide) (PEO) and PEO in PEO/fatty acid (lauric and stearic acid) blends, that are used as thermal energy storage materials, was studied using differential scanning calorimetry (DSC) data. The Avrami equation was adopted to describe isothermal crystallization of PEO and nonisothermal crystallization was analyzed using both the modified Avrami approach and Ozawa method. Avrami exponent (n) for PEO crystallization was in the range 1.08–1.32 (10–90% relative crystallinity), despite of spherulites formation, while for PEO in PEO/fatty acid blends n was between 1.61 and 2.13. Hoffman and Lauritzen theory was applied to calculate the activation energy of nucleation (K_g) – the lowest value of K_g was observed for pure PEO, despite of heterogeneous nucleation of fatty acid crystals in PEO/fatty acid blends. For nonisothermal crystallization of PEO in PEO/lauric acid (1:1 w/w) and PEO/stearic acid (1:3 w/w) blends, secondary crystallization occurred and values of the Avrami exponent were 2.8 and 2.0, respectively. The crystallization activation energies of PEO were determined to be ?260 kJ/mol for pure PEO, ?538 kJ/mol for PEO/lauric acid blend, and ?387 kJ/mol for PEO/stearic acid blend for isothermal crystallization and ?135,6 kJ/mol, ?114,5 kJ/mol, and ?92,8 kJ/mol, respectively, for nonisothermal crystallization.     

Crowding-Induced Crystallization of Poly(Ethylene Terephthalate)

Samples of poly(ethylene terephthalate) (PET) extracted from three-component systems with different ratios among PET, phenol, and poly(ethylene glycol) (PEG) were prepared. As a crowding agent, PEG can greatly increase PET crystallinity. The crystal and thermal behaviors were characterized by wide-angle x-ray scattering and differential scanning calorimetry. There were two endothermic maxima of the crowding-induced crystallization process as molecular weight and concentration of PEG increased. The theory of crowding can interpret the phenomena well.     

Crystallization of Lightly Sulfonated Poly(ethylene terephthalate) Ionomer. I. Isothermal Crystallization from the Melt

Thermal properties and overall rates of isothermal crystallization from the melt of a commercial ionic copolyester (K‐X/SPET) based on poly(ethylene terephthalate) (PET) were analyzed in detail over a composition range from pure PET to a copolymer containing 10.1 mol% of potassium‐neutralized sulfonated PET. For measurements, differential scanning calorimetry (DSC) was used. Copolyesters with the ionic group content of 4.4 mol% or more were unable to crystallize. The isothermal melt crystallization of the copolyesters was analyzed using both the Avrami and the modified Lauritzen‐Hoffman equations. It was found that both the overall rate constant, as well as the Avrami parameter for the primary crystallization stage, varied with the sulfonated unit percentage—but surface free energy and work of folding were practically independent of them. The observed changes in the thermal properties and the kinetic parameters of crystallization were attributed to the comonomer effects and the intermolecular aggregation of the ionic groups.     

Surface Effect of Two Different Calcium Fluoride Fillers on the Non-Isothermal Crystallization Behavior of Poly(ethylene Terephthalate)

Two different types of calcium fluoride (CaF₂) particles were incorporated into a poly(ethylene terephthalate) (PET) matrix, fine particles (～350 nm), and nanoparticles (～70 nm). Both of them were synthesized by a chemical precipitation method using triethanolamine (TEA) as stabilizer. To obtain the nanoparticles, a greater amount of TEA was added during the synthesis in order to limit their growth. Therefore, unlike the fine particles, nanoparticles contained a greater amount of the stabilizer. Once CaF₂ particles were obtained, the composite materials were prepared by melt-blending PET and particles at different filler loadings. The influence of both kinds of particles on the non-isothermal crystallization behavior of PET was investigated by using differential scanning calorimetry and field emission scanning electron microscopy. The Jeziorny-modified Avrami equation was applied to describe the kinetics of the non-isothermal crystallization, and several parameters were analyzed (half-crystallization time, Avrami exponent, and rate constant). According to the results, it is clear that CaF₂ particles act as nucleating agents, accelerating the crystallization rate of PET. However, the effect on the crystallization rate was more noticeable with the addition of the fine particles where the surface plays an important role for epitaxial crystallization, while the addition of the nanoparticles with an organic surface coating resulted in a crystallization behavior similar to the observed for PET.     

Effect of Organoclay Platelets on Crystallization of PTT/EPDM-g-MA Blends: Nonisothermal Melt Crystallization Kinetics

PTT/EPDM-g-MA (80/20 w/w) nanocomposites were prepared by melt mixing of poly(trimethylene terephthalate) (PTT), ethylene-propylene-diene copolymer grafted with maleic anhydride (EPDM-g-MA), and organoclay. The blend nanocomposites show typical sea-island morphologies. The nonisothermal crystallization kinetics of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay were extensively studied by differential scanning calorimetry (DSC). The Avrami, Ozawa, and Mo methods were used to describe the nonisothermal crystallization process of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay. Avrami analysis results show that the crystallization rates of 80/20 (w/w) PTT/EPDM-g-MA blends with the clay were faster than those of pure PTT or PTT/EPDM-g-MA blends without clay, which indicates that the clay particles promote crystallization effectively, in agreement with the Mo analysis results. Ozawa analysis can describe the nonisothermal crystallization of pure PTT very well but was rather inapplicable to the 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay.     

The Effect of Poly(Ethylene Succinate) on Mechanical Properties of PLLA/PES Blend Prepared by Melt-Blending

Fully biodegradable poly(L-lactide) and poly(ethylene succinate) (PLLA/PES) blends were prepared via melt-blending using PLLA and PES as reactants in a stainless steel chamber. The prepared PLLA/PES blend, as well as neat PLLA and PES, was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) to confirm the structure and the crystallization of PLLA in the blend. The mechanical properties of PLLA/PES blends were determined by bending and tensile tests and the effects of PES content on the mechanical properties of PLLA/PES blends were investigated. It was found that blending some amount of PES could significantly improve the elongation at break while still keeping considerably high strength and modulus. With increasing PES content, both strength and modulus gradually decreased; however the elongation at break significantly increased. SEM was used to examine the morphology of fracture surfaces of PLLA/PES blends.     

The Nucleation Effect of Grafted Carbon Black on Crystallization of Poly(Ethylene Terephthalate)/Grafted Carbon Black Composite

Poly(ethylene terephthalate)/grafted carbon black (PET/GCB) and poly(ethylene terephthalate)/carbon black (PET/CB) composites were prepared by melt blending. The nucleating effect of CB and GCB were investigated using differential scanning calorimetry (DSC) analysis. The morphologies of the spherulites in PET, PET/CB and PET/GCB composites were observed by means of scanning electron microscopy (SEM). All results showed that GCB had higher nucleating activity than CB in PET and PET/GCB composite had higher rate of nucleation and crystallization. The melting behaviors of neat PET, PET/CB and PET/GCB composites after non‐isothermal crystallization were investigated as well. It was evident that the melting behavior of PET is greatly influenced by addition of CB and GCB.     

Isothermal Crystallization Kinetics and Melting Behavior of Poly(ethylene terephthalate)/Attapulgite Nanocomposites Studied by Step-scan DSC

The crystallization kinetics of poly(ethylene terephthalate)/attapulgite (AT) nanocomposites and their melting behaviors after isothermal crystallization from the melt were investigated by DSC and analyzed using the Avrami method. The isothermal crystallization kinetics showed that the addition of AT increased both the crystallization rate and the isothermal Avrami exponent of PET. Step-scan differential scanning calorimetry was used to study the influence of AT on the crystallization and subsequent melting behavior in conjunction with conventional DSC. The results revealed that PET and PET/AT nanocomposites experience multiple melting and secondary crystallization processes during heating. The melting behaviors of PET and PET/AT nanocomposites varied in accordance with the crystallization temperature and shifted to higher temperature with the increase of AT content and isothermal crystallization temperature. The main effect of AT nanoparticles on the crystallization of PET was to improve the perfection of PET crystals and weaken its recrystallization behavior.     

Effects of Montmorillonite on the Nonisothermal Crystallization Behavior of the Poly(trimethylene terephthalate)/Polypropylene/Montmorillonite Nanocomposites

Organic montmorillonite (MMT) reinforced poly(trimethylene terephthalate) (PTT)/ polypropylene (PP) nanocomposites were prepared by melt blending. The effects of MMT on the nonisothermal crystallization of the matrix polymers were investigated using differential scanning colorimetry (DSC) and analyzed by the Avrami equation. The DSC results indicated that the effects of MMT on the crystallization processes of the two polymers exhibited great disparity. The PTT's crystallization was accelerated significantly by MMT no matter whether PTT was the continuous phase or not, but the thermal nucleation mode and three-dimensional growth mechanism remained unchanged. However, in the presence of MMT, the PP's crystallization was slightly retarded with PP as the dispersed phase, and was influenced little with PTT as the dispersed phase. When the MMT content was increased from 2_wt% to 7_wt%, the crystallization of the PTT phase was slightly accelerated, whereas the crystallization of the PP phase was severely retarded, especially at lower temperatures. Moreover, the nucleation mechanism for the PP's crystallization changed from a thermal mode to an athermal one. In the polypropylene-graft-maleic anhydride (PP-g-MAH) compatibilized PTT/PP blends, with the addition of 2_wt% MMT during melt blending, the T _c (PTT) shifted 7.8°C to lower temperature and had a broadened exotherm, whereas the T _c (PP) shifted 17.1°C to higher temperature, with a narrowed exotherm. TEM analysis confirmed that part of the PP-g-MAH was combined with MMT during blending.     

Large‐Scale Fluctuation Behavior Prior to the Crystallization of Poly(ethylene terephthalate) Glass: A Small‐Angle Light Scattering Study

The crystallization processes of amorphous, glassy‐state poly(ethylene terephthalate) (PET) at two temperatures, a low temperature near T _g where PET has a slow crystallization speed and a middle temperature (about 55°C above T _g ) where PET crystallization is rapid, were monitored in situ by a time‐resolved small‐angle light scattering (SALS) device. It was found that large‐scale fluctuations happened prior to the crystallization at both temperatures, but the kind of fluctuation had a temperature dependence: at the middle temperature, pure density fluctuation took place during the induction period, whereas at low temperature, both density fluctuation and orientation fluctuation occurred, but the latter was the dominant factor. Analyses of the kinetics of these two kinds of fluctuation processes demonstrated that the spinodal decomposition (SD) type of phase‐separation character was undistinguishable in the SALS scale, while the nucleation‐growth (NG) type of phase behavior could describe the scattering results as well.     

Influence of Blend Composition on Crystallization of Poly(L-Lactic Acid)/Poly (Ethylene Oxide) Crystalline/Crystalline Blends

The effect of blend composition on crystallization morphology and behavior of a crystalline/crystalline blend, poly(l-lactic acid) (PLLA)/poly(ethylene oxide) (PEO), during slow, non-isothermal crystallization was studied by polarized light microscopy (PLM) connected with a hot-stage and differential scanning calorimetry (DSC). The results showed that all of the PLLA/PEO blends produced spherulites which gradually became bigger and looser, as well as coarser, with the increment of the PEO content, indicating that the PEO crystals was resided in the interlamellar or interfibrillar (between clusters of commonly oriented lamellae) regions of the PLLA spherulites. In the (25/75) and (10/90) blends, the nucleation and growth processes of the PEO spherulites could be clearly observed in the pre-existing PLLA spherulites. The onset crystallization temperature and the melting point of one component decreased with increasing the content of the other one owing to the good miscibility of the two components in the non-crystalline state and the interaction between their macromolecules, indicating that the crystallization of each component was influenced by the other one.     

Isothermal Crystallization and Miscibility of Isotactic Polypropylene/Poly(cis-butadiene) Rubber Blends

Isotactic polypropylene/poly(cis-butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. Isothermal crystallization and miscibility for neat iPP and blends of iPP/PcBR were investigated by differential scanning calorimetry. The presence of PcBR remarkably affected isothermal crystalline behaviors of iPP. An addition of PcBR caused shorter crystallization time and a faster overall crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak was broader and the supercooling decreased as the crystallization temperature increased. The Avrami equation was suitable to describe the primary isothermal crystallization process of iPP and blends. The addition of PcBR led to an increase of values of the Avrami exponent n, which we suggest was because the blends had a stronger trend of instantaneous three-dimensional growth than neat iPP. The equilibrium melting point depression of the blends was observed, indicating that the blends were partly miscible in the melt.     

Miscibility and Isothermal Crystallization Behavior of Poly (Butylene Succinate-co-Adipate) (PBSA)/Poly (Trimethylene Carbonate) (PTMC) Blends

Poly(butylene succinate-co-adipate) (PBSA)/poly (trimethylene carbonate) (PTMC) blend samples with different weight ratios were prepared by solution blending. The morphologies after isothermal crystallization and in the melt were observed by optical microscopy (OM). Differential scanning calorimetry (DSC) was used to characterize the isothermal crystallization kinetics and melting behaviors. According to the OM image before and after melting, it was found that the blends formed heterogenous morphologies. When the PTMC content was low (20%), PBSA formed the continuous phase, while when the PTMC contents was high (40%), PBSA formed the dispersed phase. The glass transition temperatures (T_g) of the blends were determined by DSC and the differences of the T_g values were smaller than the difference between those of pure PBSA and PTMC. In addition, the equilibrium melting points were depressed in the blends. According to these results, the PBSA/PTMC blends were determined as being partially miscible blends. The crystallization kinetics was investigated according to the Avrami equation. It was found that the incorporation of PTMC did not change the crystallization mechanism of PBSA. However, the crystallization rate decreased with the increase of PTMC contents. The change of crystallization kinetics is related with the existences of amorphous PTMC, the partial miscibility between PLLA and PTMC, and the changes of phase structures.