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2014 Volume 32 Issue 9
2014, 32(9): 1119-1127
doi: 10.1007/s10118-014-1492-z
Abstract:
The intermolecular interaction between poly(vinylphenol) (PVPh) and polycaprolactone (PCL) and the crystallization behavior of PCL in PCL/PVPh blends with different compositions and under different conditions were investigated by Fourier transform infrared spectra (FTIR) and differential scanning calorimetry (DSC). It has been shown that the PCL in the blends with different blend ratios all exists in crystalline state after solution casting, even though the crystallinity decreases with increasing PVPh content. For the melt crystallized samples, PCL in its 80/20 PCL/PVPh sample can still crystallize. The crystallinity is, however, lower than that of the solution cast sample. For blends containing 50% or 20% PCL, the as-cast samples are semicrystalline and can change to compatible amorphous state after heat treatment process. FTIR analysis shows the existence of hydrogen bonding between PCL and PVPh and the fraction of hydrogen bonds increases remarkably after heat treatment process.
The intermolecular interaction between poly(vinylphenol) (PVPh) and polycaprolactone (PCL) and the crystallization behavior of PCL in PCL/PVPh blends with different compositions and under different conditions were investigated by Fourier transform infrared spectra (FTIR) and differential scanning calorimetry (DSC). It has been shown that the PCL in the blends with different blend ratios all exists in crystalline state after solution casting, even though the crystallinity decreases with increasing PVPh content. For the melt crystallized samples, PCL in its 80/20 PCL/PVPh sample can still crystallize. The crystallinity is, however, lower than that of the solution cast sample. For blends containing 50% or 20% PCL, the as-cast samples are semicrystalline and can change to compatible amorphous state after heat treatment process. FTIR analysis shows the existence of hydrogen bonding between PCL and PVPh and the fraction of hydrogen bonds increases remarkably after heat treatment process.
2014, 32(9): 1128-1138
doi: 10.1007/s10118-014-1512-z
Abstract:
Different inorganic salts, including NaSCN, NaCl, MgCl2 and Na2SO4, were added into the aqueous solution containing poly(-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) semicrystalline micelles. The effects of inorganic salt on the micellar size and morphology were investigated with TEM and DLS. It is found that addition of NaSCN leads to increase of the micellar size, but the micelles remain to be spherical. By contrast, the other three inorganic salts can induce sphere-to-cylinder or sphere-to-lamella transformations of the PCL-b-PEO semicrystalline micelles. The alteration rate of the micellar size with the time after addition of the inorganic salts decreases in the following order: Na2SO4 NaCl MgCl2 NaSCN. These results were interpreted in terms of the salting-out ability of the cations and anions. The anions SO42- and Cl- have a stronger salting-out ability, driving the morphological transformations of the micelles and leading to a rapid change in micellar size. By contrast, SCN- has a weaker salting-out ability. The cations Na+ and Mg2+ may associate with the PEO blocks, leading to a salting-out effect as well. However, the salting-out ability of cations is weaker than that of SO42- and Cl- anions, and the salting-out abilities of Na+ and Mg2+ are similar.
Different inorganic salts, including NaSCN, NaCl, MgCl2 and Na2SO4, were added into the aqueous solution containing poly(-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) semicrystalline micelles. The effects of inorganic salt on the micellar size and morphology were investigated with TEM and DLS. It is found that addition of NaSCN leads to increase of the micellar size, but the micelles remain to be spherical. By contrast, the other three inorganic salts can induce sphere-to-cylinder or sphere-to-lamella transformations of the PCL-b-PEO semicrystalline micelles. The alteration rate of the micellar size with the time after addition of the inorganic salts decreases in the following order: Na2SO4 NaCl MgCl2 NaSCN. These results were interpreted in terms of the salting-out ability of the cations and anions. The anions SO42- and Cl- have a stronger salting-out ability, driving the morphological transformations of the micelles and leading to a rapid change in micellar size. By contrast, SCN- has a weaker salting-out ability. The cations Na+ and Mg2+ may associate with the PEO blocks, leading to a salting-out effect as well. However, the salting-out ability of cations is weaker than that of SO42- and Cl- anions, and the salting-out abilities of Na+ and Mg2+ are similar.
2014, 32(9): 1139-1148
doi: 10.1007/s10118-014-1499-5
Abstract:
Poly(vinylidene fluoride) (PVDF) and poly(butylene succinate-co-24 mol% hexamethylene succinate) (PBHS), both crystalline polymers, formed melt-miscible crystalline/crystalline polymer blends. Both the characteristic diffraction peaks and nonisothermal melt crystallization peak of each component were found in the blends, indicating that PVDF and PBHS crystallized separately. The crystalline morphology and crystallization kinetics of each component were studied under different crystallization conditions for the PVDF/PBHS blends. Both the spherulitic growth rates and overall isothermal melt crystallization rates of blended PVDF decreased with increasing the PBHS composition and were lower than those of neat PVDF, when the crystallization temperature was above the melting point of PBHS component. The crystallization mechanism of neat and blended PVDF remained unchanged, despite changes of blend composition and crystallization temperature. The crystallization kinetics and crystalline morphology of neat and blended PBHS were further studied, when the crystallization temperature was below the melting point of PBHS component. Relative to neat PBHS, the overall crystallization rates of the blended PBHS first increased and then decreased with increasing the PVDF content in the blends, indicating that the preexisting PVDF crystals may show different effects on the nucleation and crystal growth of PBHS component in the crystalline/crystalline polymer blends.
Poly(vinylidene fluoride) (PVDF) and poly(butylene succinate-co-24 mol% hexamethylene succinate) (PBHS), both crystalline polymers, formed melt-miscible crystalline/crystalline polymer blends. Both the characteristic diffraction peaks and nonisothermal melt crystallization peak of each component were found in the blends, indicating that PVDF and PBHS crystallized separately. The crystalline morphology and crystallization kinetics of each component were studied under different crystallization conditions for the PVDF/PBHS blends. Both the spherulitic growth rates and overall isothermal melt crystallization rates of blended PVDF decreased with increasing the PBHS composition and were lower than those of neat PVDF, when the crystallization temperature was above the melting point of PBHS component. The crystallization mechanism of neat and blended PVDF remained unchanged, despite changes of blend composition and crystallization temperature. The crystallization kinetics and crystalline morphology of neat and blended PBHS were further studied, when the crystallization temperature was below the melting point of PBHS component. Relative to neat PBHS, the overall crystallization rates of the blended PBHS first increased and then decreased with increasing the PVDF content in the blends, indicating that the preexisting PVDF crystals may show different effects on the nucleation and crystal growth of PBHS component in the crystalline/crystalline polymer blends.
2014, 32(9): 1149-1157
doi: 10.1007/s10118-014-1501-2
Abstract:
Investigation on the folding mode of a single polymer chain in its crystal is significant to the understanding of the mechanism of the fundamental crystallization as well as the engineering of new polymer crystal-based materials. Herein, we use the combined techniques of atomic force microscopy (AFM) imaging and force spectroscopy to pull a single polyethylene oxide (PEO) chain out of its spiral crystal in amyl acetate. From these data, the folding mode of polymer chains in the spiral crystal has been reconstructed. We find that the stems tilt in the typical flat area, leading to the decrease in the apparent lamellar height. While in the area of screw dislocation, the lamellar height gradually increases in the range of several nanometers. These results indicate that the combined techniques present a novel tool to directly unravel the chain folding mode of spiral crystals at single-molecule level.
Investigation on the folding mode of a single polymer chain in its crystal is significant to the understanding of the mechanism of the fundamental crystallization as well as the engineering of new polymer crystal-based materials. Herein, we use the combined techniques of atomic force microscopy (AFM) imaging and force spectroscopy to pull a single polyethylene oxide (PEO) chain out of its spiral crystal in amyl acetate. From these data, the folding mode of polymer chains in the spiral crystal has been reconstructed. We find that the stems tilt in the typical flat area, leading to the decrease in the apparent lamellar height. While in the area of screw dislocation, the lamellar height gradually increases in the range of several nanometers. These results indicate that the combined techniques present a novel tool to directly unravel the chain folding mode of spiral crystals at single-molecule level.
2014, 32(9): 1158-1166
doi: 10.1007/s10118-014-1493-y
Abstract:
In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the subsequently dried poly(3-octylthiophene) (P3OT) film has been investigated by the combination of DSC, WAXD and FTIR techniques. When chloroform is employed as the solvent, it is unexpectedly found that form Ⅰ and form Ⅱ crystal modifications of P3OT could be respectively obtained by room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form Ⅱ, i.e. carbon disulfide (CS2) which is toxic and corrosive, chloroform is less toxic and corrosive and more suitable for solution processing of P3OT. Therefore, this finding provides an alternative way to obtain form Ⅱ. By temperature dependent IR spectroscopy, the structural evolution of P3OT during the form Ⅱ to form Ⅰ phase transition process has also been studied in detail.
In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the subsequently dried poly(3-octylthiophene) (P3OT) film has been investigated by the combination of DSC, WAXD and FTIR techniques. When chloroform is employed as the solvent, it is unexpectedly found that form Ⅰ and form Ⅱ crystal modifications of P3OT could be respectively obtained by room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form Ⅱ, i.e. carbon disulfide (CS2) which is toxic and corrosive, chloroform is less toxic and corrosive and more suitable for solution processing of P3OT. Therefore, this finding provides an alternative way to obtain form Ⅱ. By temperature dependent IR spectroscopy, the structural evolution of P3OT during the form Ⅱ to form Ⅰ phase transition process has also been studied in detail.
2014, 32(9): 1167-1175
doi: 10.1007/s10118-014-1465-2
Abstract:
-nucleated isotactic polypropylene (iPP) fibers with diameters less than 5 mm were prepared through melt electrospinning. The effects of electrospinning process and rare earth -nucleating agent (WBG) on the crystal structure of iPP fibers were investigated. The results indicate that the addition of WBG can improve the fluidity of iPP melt remarkably and help the formation of fine fibers with thinner diameter, while the electrostatic force applied on the iPP melt is not favorable for the formation of -crystal in iPP fibers. In addition, the morphology and crystalline structure of WBG/iPP electrospun fibers depended on the content of WBG. Both the crystallinity and the percentage of -crystal form of WBG/iPP electrospun fibers increase with the rise of the content of nucleating agent, which endows the prepared electrospun fibers excellent mechanical properties. The -nucleated iPP electrospun fibrous membranes prepared in this study can be used for protective clothing material, filtration media, reinforcement for composites and tissue engineering scaffolds.
-nucleated isotactic polypropylene (iPP) fibers with diameters less than 5 mm were prepared through melt electrospinning. The effects of electrospinning process and rare earth -nucleating agent (WBG) on the crystal structure of iPP fibers were investigated. The results indicate that the addition of WBG can improve the fluidity of iPP melt remarkably and help the formation of fine fibers with thinner diameter, while the electrostatic force applied on the iPP melt is not favorable for the formation of -crystal in iPP fibers. In addition, the morphology and crystalline structure of WBG/iPP electrospun fibers depended on the content of WBG. Both the crystallinity and the percentage of -crystal form of WBG/iPP electrospun fibers increase with the rise of the content of nucleating agent, which endows the prepared electrospun fibers excellent mechanical properties. The -nucleated iPP electrospun fibrous membranes prepared in this study can be used for protective clothing material, filtration media, reinforcement for composites and tissue engineering scaffolds.
2014, 32(9): 1176-1187
doi: 10.1007/s10118-014-1505-y
Abstract:
In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator (polyethylene glycol (PEG)) are investigated by wide angle X-ray diffraction (WAXD) and time-resolved Fourier transform infrared spectroscopy (FTIR). It is interestingly found that the presence of PEG could accelerate the formation of PLLA mesophase notably due to the enhanced chain mobility, giving rise to a substantially reduced half time (t0.5) of PLLA mesophase formation from 129 min to 8 min. The Avrami exponents (n) for the kinetics of mesophase formation are ~0.5 for neat PLLA and 1 for PLLA/PEG, respectively, indicating that 1D-rod growth through heterogeneous nucleation occurs during formation of PLLA mesophase. Tensile testing demonstrates that PLLA mesophase could increase the tensile strength and modulus but decrease the elongation at break.
In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator (polyethylene glycol (PEG)) are investigated by wide angle X-ray diffraction (WAXD) and time-resolved Fourier transform infrared spectroscopy (FTIR). It is interestingly found that the presence of PEG could accelerate the formation of PLLA mesophase notably due to the enhanced chain mobility, giving rise to a substantially reduced half time (t0.5) of PLLA mesophase formation from 129 min to 8 min. The Avrami exponents (n) for the kinetics of mesophase formation are ~0.5 for neat PLLA and 1 for PLLA/PEG, respectively, indicating that 1D-rod growth through heterogeneous nucleation occurs during formation of PLLA mesophase. Tensile testing demonstrates that PLLA mesophase could increase the tensile strength and modulus but decrease the elongation at break.
2014, 32(9): 1188-1198
doi: 10.1007/s10118-014-1506-x
Abstract:
Long-range ordered nanostructures are prepared in the poly(styrene)-block-poly(-caprolactone) diblock copolymer thin films using micromolding. We evaluated the change in crystallinity based on grazing-incidence X-ray diffraction and proved that the crystallinity increased with the decrease of the mold size. This means that ordered nanostructures with atomic length scale order can be adjusted by tuning the mesoscale confinement. The inherent mechanism was the cooperation of geometric confinement, microphase structure and surface-induced ordering of PS-b-PCL in the melt, which paved the way for the subsequent crystal growth. These findings establish a route to promote the cost-effective nanofabrication by combining the mature microfabrication technique with the emerging directed self-assembly of block copolymers.
Long-range ordered nanostructures are prepared in the poly(styrene)-block-poly(-caprolactone) diblock copolymer thin films using micromolding. We evaluated the change in crystallinity based on grazing-incidence X-ray diffraction and proved that the crystallinity increased with the decrease of the mold size. This means that ordered nanostructures with atomic length scale order can be adjusted by tuning the mesoscale confinement. The inherent mechanism was the cooperation of geometric confinement, microphase structure and surface-induced ordering of PS-b-PCL in the melt, which paved the way for the subsequent crystal growth. These findings establish a route to promote the cost-effective nanofabrication by combining the mature microfabrication technique with the emerging directed self-assembly of block copolymers.
2014, 32(9): 1199-1209
doi: 10.1007/s10118-014-1497-7
Abstract:
The crystallization behavior of PEOs with molecular weight of 10k and 200k as well as their blends was studied in details. The results show that the lower molecular weight PEO crystallizes with faster crystallization rate as judged from a shorter time for completing the crystallization. On the other hand, the higher molecular weight PEO crystallizes at relatively higher temperature, indicating an early start of crystallization compared with the lower molecular weight one. The blends of these two PEOs with different blend ratios always cocrystallize during the cooling processes. It is confirmed that mixing of the 10k PEO with the 200k one is in favor of the crystallization of the system. This is not only demonstrated by the early start of the crystallization at higher crystallization temperature, and also a faster crystal growth of the blend with respect to the 200k PEO. The crystallization of the blends at higher temperature is caused by an early start of nucleation and an increment of nucleus density. This may originate from the density fluctuation of the blend and a reduction in energy barrier for nucleation. Moreover, it is found that the crystallinity of the 10k PEO rich blends increases with increasing concentration of the 10k PEO. This is caused by the solvent effect of the 10k PEO toward the 200k PEO. On the other hand, the crystallinity of the 30/70 (10k/200k) PEO blend is decreased a little bit. This may be a balanced result of the improved crystallization of the 200k PEO at the expense of the high crystallization ability of the 10k PEO.
The crystallization behavior of PEOs with molecular weight of 10k and 200k as well as their blends was studied in details. The results show that the lower molecular weight PEO crystallizes with faster crystallization rate as judged from a shorter time for completing the crystallization. On the other hand, the higher molecular weight PEO crystallizes at relatively higher temperature, indicating an early start of crystallization compared with the lower molecular weight one. The blends of these two PEOs with different blend ratios always cocrystallize during the cooling processes. It is confirmed that mixing of the 10k PEO with the 200k one is in favor of the crystallization of the system. This is not only demonstrated by the early start of the crystallization at higher crystallization temperature, and also a faster crystal growth of the blend with respect to the 200k PEO. The crystallization of the blends at higher temperature is caused by an early start of nucleation and an increment of nucleus density. This may originate from the density fluctuation of the blend and a reduction in energy barrier for nucleation. Moreover, it is found that the crystallinity of the 10k PEO rich blends increases with increasing concentration of the 10k PEO. This is caused by the solvent effect of the 10k PEO toward the 200k PEO. On the other hand, the crystallinity of the 30/70 (10k/200k) PEO blend is decreased a little bit. This may be a balanced result of the improved crystallization of the 200k PEO at the expense of the high crystallization ability of the 10k PEO.
2014, 32(9): 1210-1217
doi: 10.1007/s10118-014-1494-x
Abstract:
Phase transition from form Ⅰ to form Ⅲ in syndiotactic polypropylene crystallized at different conditions during tensile deformation at different temperatures was investigated by using in situ synchrotron wide angle X-ray diffraction technique. In all cases, the occurrence of this phase transition was observed. The onset strain of this transition was found to be crystalline thickness decided by crystallization temperature and drawing temperature dependent. The effect of drawing temperature on this phase transition is understood by the changes in mechanical properties with temperature. Moreover, crystalline thickness dependency of the phase transition reveals that this form Ⅰ to from Ⅲ phase transition occurs first in those lamellae with their normal along the stretching direction which have not experienced stress induced melting and recrystallization.
Phase transition from form Ⅰ to form Ⅲ in syndiotactic polypropylene crystallized at different conditions during tensile deformation at different temperatures was investigated by using in situ synchrotron wide angle X-ray diffraction technique. In all cases, the occurrence of this phase transition was observed. The onset strain of this transition was found to be crystalline thickness decided by crystallization temperature and drawing temperature dependent. The effect of drawing temperature on this phase transition is understood by the changes in mechanical properties with temperature. Moreover, crystalline thickness dependency of the phase transition reveals that this form Ⅰ to from Ⅲ phase transition occurs first in those lamellae with their normal along the stretching direction which have not experienced stress induced melting and recrystallization.
2014, 32(9): 1218-1223
doi: 10.1007/s10118-014-1495-9
Abstract:
Network polymers in a rubber or a gel often contain non-uniform chain lengths. By means of dynamic Monte Carlo simulations of polymer mixtures with various compositions of two chain lengths, we investigated how the factor of polydispersity influences their strain-induced crystal nucleation. Under a high temperature and a high strain rate, the stretching of both polymers revealed that crystal nucleation is mainly accelerated by the presence of short-chain polymers; nevertheless, both polymers join together in the nucleation process. Further analysis proved that crystal nucleation is initiated from those highly stretched short segments, which are rich on the short-chain polymers.
Network polymers in a rubber or a gel often contain non-uniform chain lengths. By means of dynamic Monte Carlo simulations of polymer mixtures with various compositions of two chain lengths, we investigated how the factor of polydispersity influences their strain-induced crystal nucleation. Under a high temperature and a high strain rate, the stretching of both polymers revealed that crystal nucleation is mainly accelerated by the presence of short-chain polymers; nevertheless, both polymers join together in the nucleation process. Further analysis proved that crystal nucleation is initiated from those highly stretched short segments, which are rich on the short-chain polymers.
2014, 32(9): 1224-1233
doi: 10.1007/s10118-014-1502-1
Abstract:
In this study, recovery processes of isotactic polypropylene (iPP) melted spherulites at 135 ℃ after melting at higher temperatures (170 ℃-176 ℃) were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 ℃ and 174 ℃, the melted spherulite could recover back to the origin spherulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.
In this study, recovery processes of isotactic polypropylene (iPP) melted spherulites at 135 ℃ after melting at higher temperatures (170 ℃-176 ℃) were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 ℃ and 174 ℃, the melted spherulite could recover back to the origin spherulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.
2014, 32(9): 1234-1242
doi: 10.1007/s10118-014-1496-8
Abstract:
The poly(ethylene glycol) (PEG, with Mw 2000)-urea inclusion compound (IC) crystallized at high temperature region showed two typical orientations, flat-on and edge-on crystals. 2D-XRD and polarized FTIR spectroscopy revealed that the PEG chains within urea channels were perpendicular to the substrate in flat-on oriented crystals, while PEG chain axes were parallel to the substrate and lay along the growth direction in the edge-on crystals. FTIR absorption bands of PEG in the ICs are sensitive to orientation of the crystals. A scheme of PEG chain packing in the urea IC channel was proposed, which could explain the orientation of the crystal nucleus causing the two types of morphologies. Furthermore, functioning of PEG2000 chain end with analine had significantly influence on the morphology and orientation of the inclusion compound crystals, due to the defects caused by large terminal groups included in the urea channel.
The poly(ethylene glycol) (PEG, with Mw 2000)-urea inclusion compound (IC) crystallized at high temperature region showed two typical orientations, flat-on and edge-on crystals. 2D-XRD and polarized FTIR spectroscopy revealed that the PEG chains within urea channels were perpendicular to the substrate in flat-on oriented crystals, while PEG chain axes were parallel to the substrate and lay along the growth direction in the edge-on crystals. FTIR absorption bands of PEG in the ICs are sensitive to orientation of the crystals. A scheme of PEG chain packing in the urea IC channel was proposed, which could explain the orientation of the crystal nucleus causing the two types of morphologies. Furthermore, functioning of PEG2000 chain end with analine had significantly influence on the morphology and orientation of the inclusion compound crystals, due to the defects caused by large terminal groups included in the urea channel.
2014, 32(9): 1243-1252
doi: 10.1007/s10118-014-1503-0
Abstract:
Oriented and non-oriented Teflon films, which were found to have the same crystalline structure, but different surface morphologies, were used to sandwich poly(butylene adipate) (PBA) films during isothermal crystallization. It was found that both the Teflon surface structure and the PBA polymorphic structure are the determining factors to induce epitaxial crystallization. The oriented Teflon film was able to induce epitaxial crystallization of PBA crystal, while the non-oriented Teflon did not induce any epitaxial crystallization of PBA. Epitaxial crystallization did not occurred for PBA crystals between neither the oriented nor the non-oriented Teflon films. The enzymatic degradation rate of PBA films was not determined by the epitaxial crystallization, in fact it was still dependent on the polymorphic crystal structure of PBA. The morphological changes of PBA films after enzymatic degradation confirmed again that the epitaxial crystallization only occurred for the PBA film with crystal structure which was produced by being sandwiched between oriented Teflon films, and it happened only on the surface of PBA films.
Oriented and non-oriented Teflon films, which were found to have the same crystalline structure, but different surface morphologies, were used to sandwich poly(butylene adipate) (PBA) films during isothermal crystallization. It was found that both the Teflon surface structure and the PBA polymorphic structure are the determining factors to induce epitaxial crystallization. The oriented Teflon film was able to induce epitaxial crystallization of PBA crystal, while the non-oriented Teflon did not induce any epitaxial crystallization of PBA. Epitaxial crystallization did not occurred for PBA crystals between neither the oriented nor the non-oriented Teflon films. The enzymatic degradation rate of PBA films was not determined by the epitaxial crystallization, in fact it was still dependent on the polymorphic crystal structure of PBA. The morphological changes of PBA films after enzymatic degradation confirmed again that the epitaxial crystallization only occurred for the PBA film with crystal structure which was produced by being sandwiched between oriented Teflon films, and it happened only on the surface of PBA films.
2014, 32(9): 1253-1259
doi: 10.1007/s10118-014-1504-z
Abstract:
Poly(ethylene oxide) multi-layer crystals were obtained and the re-crystallization behavior was studied to give insight into how melt thickness and temperature affect the lamellar orientation. For a special re-crystallization temperature, there exists a critical transition thickness range for the occurrence of edge-on lamellar orientation. Below the critical thickness, only flat-on lamellae were observed. While above the critical thickness, both flat-on and edge-on lamellae were found and the proportion of the edge-on lamellae increases with thickness. At low re-crystallization temperatures (below 30 ℃), the critical transition thickness gradually increases from about 15 nm to 35 nm when the re-crystallization temperature was increased from 20 ℃ to 30 ℃. However, when the re-crystallization temperature is above 30 ℃, the critical transition thickness becomes constant. Our results demonstrated that the lamellar orientation could be specially modified by changing the melt thickness and re-crystallization temperature.
Poly(ethylene oxide) multi-layer crystals were obtained and the re-crystallization behavior was studied to give insight into how melt thickness and temperature affect the lamellar orientation. For a special re-crystallization temperature, there exists a critical transition thickness range for the occurrence of edge-on lamellar orientation. Below the critical thickness, only flat-on lamellae were observed. While above the critical thickness, both flat-on and edge-on lamellae were found and the proportion of the edge-on lamellae increases with thickness. At low re-crystallization temperatures (below 30 ℃), the critical transition thickness gradually increases from about 15 nm to 35 nm when the re-crystallization temperature was increased from 20 ℃ to 30 ℃. However, when the re-crystallization temperature is above 30 ℃, the critical transition thickness becomes constant. Our results demonstrated that the lamellar orientation could be specially modified by changing the melt thickness and re-crystallization temperature.
2014, 32(9): 1260-1270
doi: 10.1007/s10118-014-1500-3
Abstract:
A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly(ethylene-alt-propylene) (d-PE/PEP) blend films. And the band period is a function of initial d-PE concentration, quench depth and annealing time of phase separation. As Keith and Padden suggested, twisting of lamella is due to the unbalanced stress on its both sides, which can supply a satisfying explanation to banded spherulites formed in homogeneous systems. When it comes to d-PE/PEP blend system, in homogeneous 99% d-PE/PEP (weight fraction of d-PE) blend film, the formation of banded spherulite is observed as a result of uniform twisting of ribbon like d-PE lamellae along the radial direction. With the amorphous PEP piling up, it transfers into accelerated edge-on to flat-on twisting due to crystallization assisted phase separation. The mechanism can be interpreted as following: d-PE molecules must inter-diffuse to the twisting growth front to continue the secondary nucleation and growth process. Meanwhile, the amorphous PEP molecules are rejected and accumulated at the twisting growth front. Once the d-PE lamella begins to twist because of unbalanced stress on both sides, the accumulated rubber phase at the growth front strengthens the unbalance and accelerates the edge-on to flat-on twisting. The concentration wave propagates further away with constant speed, and leads to concentric ring pattern with periodic nonuniform twisting along the radial direction. Since this is a kinetic effect, the band period can be controlled through initial d-PE concentration, quench depth and annealing time of phase separation. Our result shows that crystallization assisted phase separation can modify lamella growth kinetic pathway, thereby assisting concentric ring pattern formation.
A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly(ethylene-alt-propylene) (d-PE/PEP) blend films. And the band period is a function of initial d-PE concentration, quench depth and annealing time of phase separation. As Keith and Padden suggested, twisting of lamella is due to the unbalanced stress on its both sides, which can supply a satisfying explanation to banded spherulites formed in homogeneous systems. When it comes to d-PE/PEP blend system, in homogeneous 99% d-PE/PEP (weight fraction of d-PE) blend film, the formation of banded spherulite is observed as a result of uniform twisting of ribbon like d-PE lamellae along the radial direction. With the amorphous PEP piling up, it transfers into accelerated edge-on to flat-on twisting due to crystallization assisted phase separation. The mechanism can be interpreted as following: d-PE molecules must inter-diffuse to the twisting growth front to continue the secondary nucleation and growth process. Meanwhile, the amorphous PEP molecules are rejected and accumulated at the twisting growth front. Once the d-PE lamella begins to twist because of unbalanced stress on both sides, the accumulated rubber phase at the growth front strengthens the unbalance and accelerates the edge-on to flat-on twisting. The concentration wave propagates further away with constant speed, and leads to concentric ring pattern with periodic nonuniform twisting along the radial direction. Since this is a kinetic effect, the band period can be controlled through initial d-PE concentration, quench depth and annealing time of phase separation. Our result shows that crystallization assisted phase separation can modify lamella growth kinetic pathway, thereby assisting concentric ring pattern formation.
