Untersuchung der ursachen für das auftreten mehrerer schmelzpeaks in den DSC-thermogrammen von hochverstreckten und getemperten folien aus isotaktischem polypropylen

Isotactic polypropylen films were highly stretched and annealed during 20 s under stretching tension at temperatures up to 206°C at maximum. The melting behaviour of these films was investigated by using a differential scanning calorimeter (DSC — 1 B). Two melting peaks at about 165 and 174°C respectively, were observed. The heat of fusion of the former peak predominates, if the film temperature during annealing exceeds 190°C. Its position is independent of the stretching ratio. This melting peak is assigned to crystalline domains, which show a long identity period of 140 to 160 Å and corresponds to an amorphous orientation factor of 0 to ?0.2. The higher melting peak appears during stretching. This peak is assigned to crystalline domains, which show a long identity period longer than 200 Å and corresponds to an amorphous orientation factor of 0.4 to 0.5. This fraction refers obviously to the paracrystalline building blocks of the microfibrils, which are transformed at a film temperature higher than 190°C to a greater part into smaller lamellaforming paracrystallites. The transformation of the fibrillar into a lamellar texture was visualised by transmission electronmicroscopy.     

Structure and thermal behaviour of nylon 6 nanocomposites

In this article, nylon 6/clay nanocomposites with 5 wt % clay (NCN5) were prepared by a twin screw extruder. The effects of annealing including solid‐state annealing (170 and 190°C) and melt‐state annealing (240°C) on the polymorphic behavior and thermal property of NCN5 and nylon 6 have been comparatively studied as a function of annealing time using modified differential scanning calorimetry (MDSC) and wide‐angle X‐ray diffraction. It was demonstrated that NCN5 and nylon 6 exhibit a similar polymorphic behavior when they were annealed at 190°C for different time durations. As the annealing temperature was elevated to 240°C, significant differences in thermal behavior and polymorphism between NCN5 and nylon 6 could be found. For example, the α crystal became the absolutely dominating crystalline phase for NCN5 sample independent on the annealing durations, whereas the formation of γ crystal is greatly enhanced in neat nylon 6 with increasing annealing time. Moreover, a small endothermic peak is observed around 180°C in both nylon 6 and NCN5 samples annealed at 170 and 190°C, which might be related to the melting of microcrystals formed in the amorphous regions during annealing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3116–3122, 2006     

Effect of annealing on the structure and properties of polyvinylidene fluoride hollow fiber by melt‐spinning

Polyvinylidene fluoride hollow fibers were prepared by melt‐spinning technique under three spinning temperatures. The effects of annealing treatment on the structure and properties of hollow fiber were studied by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), tensile test, and scanning electron microscopy (SEM) measurements. DSC and WAXD results indicated that the annealing not only produced secondary crystallization but also perfected primary crystallization, and spinning and annealing temperature influenced the crystallinity of hollow fiber: the crystallinity decreased with the increase of spinning temperature; 140°C annealing increased the crystallinity, and hardly influenced the orientation of hollow fiber; above 150°C annealing increased the crystallinity as well, and furthermore had a comparative effect on the orientation. The tensile tests showed that the annealed samples, which did not present the obvious yield point, exhibited characteristics of hard elasticity, and all the hollow fiber had no neck phenomenon. Compared with the annealed sample, the precursor presented a clear yield point. In addition, the annealed samples had a higher break strength and initial modulus by contrast with the precursor, and the 140°C annealed sample showed the smallest break elongation. SEM demonstrated the micro‐fiber structure appeared in surface of drawn sample. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 935–941, 2007     

The influence of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers

An investigation was carried out on the effects of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers annealed in an air heated environment at temperatures ranging from 60 to 140°C. Analysis of the equatorial X‐ray diffraction traces showed the presence of a three phase system of amorphous‐smectic‐monoclinic forms and revealed the transformation of the metastable smectic form to the highly stable monoclinic form as the annealing temperature is increased, resulting in an enhanced degree of crystallinity and the crystallite size. The improvements in the degree of crystallinity and the crystallite size became more remarkable above 120°C. Evaluation of the crystallinity was carried out using an analysis of density, infrared spectroscopy, and X‐ray diffraction methods whereas the state of the molecular orientation was evaluated using polarized infrared spectroscopy measurements only. Polarized infra‐red spectroscopy measurements after the curve fitting procedure showed a slight increase of the molecular orientation of the helical chain segments present in the crystalline phase represented by the IR bands at 841 and 998 cm^?1 whereas the amorphous structure represented by the IR band at 974 cm^?1 showed no significant change with increasing annealing temperature. The improvement in the molecular orientation of the crystalline phase became more remarkable above 120°C. Tensile strength of the annealed fibers increased with increasing annealing temperature but the elongation at break and the initial modulus were not affected as much as the tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Crystal structure transformations and orientation in crosslinked elastic fibers of an ethylene‐octene copolymer in response to deformation and heat treatment

Crosslinked elastic fibers, made from a low density (0.875 g/cc) ethylene‐octene copolymer, were studied after constrained at 300% elongation and annealed at different temperatures (40–80°C) to simulate conditions encountered in yarn and textile processing. It is surprisingly found that the transition from pseudo hexagonal to orthorhombic structure is much faster under simultaneously constraining and annealing than that without strain. Almost a neat orthorhombic structure can be produced when the fiber is annealed at 60°C. Annealing above 60°C leads to mixed orthorhombic and pseudo‐hexagonal structures. The average melting point increases with an increase in the fraction of orthorhombic phase. It is also surprisingly noted that the simultaneously constraining and annealing of the fiber can produce highly oriented crystals, even annealed at 80°C (above the average melting point of 65°C). The unique effect of annealing under large strain can be attributed to the crosslinking of the fiber, which makes it possible for the fiber to have strong chain orientation (even in molten state) under large strain. The strong chain orientation in melt leads to a faster structural transition from pseudo hexagonal to more stable orthorhombic structure. The strong chain orientation is also very likely the reason why highly oriented crystal and amorphous phases are formed, including the case where the fiber is annealed above melting point. These findings could be leveraged for improving thermal and mechanical properties of the fabrics made with such fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3565–3573, 2013     

The effects of annealing (solid and melt) on the time evolution of the polymorphic structure of polyamide 6

To understand whether and how the thermal history, especially the melting annealing, affects the polymorphism and thermal property of polyamide 6 (PA6), the temperature‐modulated differential scanning calorimetry technology was used to investigate the effects of thermal histories, including annealing temperature, annealing time, and cooling rate, on the polymorphic behavior and thermal property of PA6. It was found that longer annealing time and faster cooling rate favored the formation of α crystal when PA6 samples were annealed in the solid‐state at 175°C. As the annealing temperature was elevated to 195°C, faster cooling rate also favored the formation of α crystal, whereas longer annealing time was more favorable for the formation of γ‐form crystals. When PA6 samples were annealed in the melt‐state (245°C), however, although the α crystal was dominating crystalline phase, the formation of γ crystal was greatly enhanced with increasing annealing time and cooling rate. Moreover, a small endothermic peak was observed in the low‐temperature region in PA6 samples annealed at 175°C and 195°C, which might be related to the melting of microcrystals formed in the amorphous regions during annealing. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystalline structure and morphology of poly(L‐lactide) formed under high pressure

The poly(l ‐lactide) (PLLA) samples were prepared by the annealing under 100 MPa at 75–145^°C and 200 MPa at 105–145^°C for 6 h, respectively. The crystalline structures, thermal properties and morphology were investigated using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and scanning electron microscopy (SEM). On the basis of the DSC and WAXD results, it can be seen that the α′ form was formed by the annealing under 100 MPa at 85–95°C but not found under 200 MPa at 105–145°C. A phase diagram of PLLA crystal form under high pressure was constructed under the given experimental conditions, which displayed the α′ form was formed at limited temperature and pressure range. Besides, SEM suggested that the PLLA samples annealed under 100 MPa crystallize to form lamellar‐like crystals due to the low growth rate and the confined crystallization behavior under high pressure. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40637.     

Morphology and molecular mobility of plasticized polylactic acid studied using solid‐state 13C‐ and 1H‐NMR spectroscopy

MAS ¹³C‐NMR measurements were used for the study of morphology and molecular mobility in amorphous quenched and triacetine‐plasticized PLA samples and PLA samples which underwent cold crystallization during annealing at 80 and 100 °C. The single pulse MAS ¹³C‐NMR spectra indicate that plasticizer promotes cold crystallization which results in the decrease of the temperature of crystallization and formation of more perfect crystalline domains. The T₁(¹³C) spin‐lattice relaxation times show that the presence of plasticizer molecules leads to an increase of local mobility in PLA chains but plasticized PLA after annealing at 100 °C shows more rigid structure. The series of broad line ¹H‐NMR spectra performed at temperatures up to 100 °C provided information on the changes in relaxation processes and morphology of the studied samples. The interpretation of the results obtained using the techniques of NMR spectroscopy were supported by WAXD and DSC measurements. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43517.     

NEW-TPI thermoplastic polyimide: Structure and relaxation using SAXS and TSDC

The thermoplastic polyimide Regulus^TM NEW-TPI has been studied using small-angle X-ray scattering (SAXS) and thermally stimulated depolarization current (TSDC). SAXS was used to study the development of lamellar structure during isothermal or nonisothermal crystallization. The one-dimensional electron-density correlation function was used to determine structural parameters. The long period, lamellar thickness, and amorphous layer thickness increase as crystallization temperature increases from 300 to 360°C. By combining melting-point data with SAXS results, we report the side and fold surface free energies of NEW-TPI crystals, which are 29 ± 3 and 41 ± 3 erg/cm², respectively. Real-time SAXS was carried during nonisothermal cold-crystallization at 5°C/min. The long period decreases, while lamellar thickness, linear crystallinity, and interphase thickness increase, with increasing temperature. These changes are explained by a crystal-insertion model. TSDC was used as a more sensitive probe of the amorphous phase structure below 300°C. Both semicrystalline and amorphous NEW-TPI exhibit complex TSDC behavior. Above the glass transition, amorphous NEW-TPI has a strong TSDC peak attributed to short-range-ordered structures, which may serve as nucleation sites for subsequent crystallization. This peak was not seen in semicrystalline material. At the glass transition, both amorphous and semicrystalline NEW-TPI have a strong TSDC peak. In the semicrystalline polymer, relaxation of the amorphous dipoles is slightly restricted by the crystals, which results in a smaller relaxation peak and a shift to higher temperature. Below T_g, another TSDC peak occurs which is not due to dipolar relaxation. This peak is attributed to the combined effects of space charge, electrode type, ionizable species, and interfacial charges. © 1995 John Wiley & Sons, Inc.     

Morphology and physical properties of nanocomposites based on poly(methyl methacrylate)/poly(vinylidene fluoride) blends and multiwalled carbon nanotubes

Nanocomposites of blends of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) with multiwalled carbon nanotubes (CNTs) were prepared by melt mixing and hot press molding followed by quenching or annealing (120°C, 24 h). PMMA‐rich nanocomposites showed higher electrical conductivity than PVDF‐rich samples at identical CNT loading. At a specific composition, the quenched nanocomposites showed electrical conductivity values three to four orders of magnitude higher than those observed in annealed samples. Measurement of the dielectric constants also supported the electrical conductivity results. In the annealed samples, agglomerated CNTs located mainly in the PVDF crystalline phase were observed. Addition of CNTs promoted the crystallization, and especially, the formation of β‐crystals, which was confirmed by X‐ray diffraction. The thermal behavior of nanocomposites from differential scanning calorimetry (DSC) analysis was explained in terms of the three‐phase model involving the presence of the rigid amorphous fraction, the mobile amorphous fraction, and the crystalline phase. POLYM. COMPOS., 36:1195–1204, 2015. © 2014 Society of Plastics Engineers     

Effect of crystallinity on enthalpy recovery peaks and cold‐crystallization peaks in PET via TMDSC and DMA studies

Poly(ethylene terephthalate) (PET) sheets of different crystallinity were obtained by annealing the amorphous PET (aPET) sheets at 110°C for various times. The peaks of enthalpy recovery and double cold‐crystallization in the annealed aPET samples with different crystallinity were investigated by a temperature‐modulated differential scanning calorimeter (TMDSC) and a dynamic mechanical analyzer (DMA). The enthalpy recovery peak around the glass transition temperature was pronounced in TMDSC nonreversing heat flow curves and was found to shift to higher temperatures with higher degrees of crystallinity. The magnitudes of the enthalpy recovery peaks were found to increase with annealing times for samples annealed ≤30 min but to decrease with annealing times for samples annealed ≥40 min. The nonreversing curves also found that the samples annealed short times (≤40 min) having low crystallinity exhibited double cold‐crystallization peaks (or a major peak with a shoulder) in the region of 108–130°C. For samples annealed long times (≥50 min), the cold‐crystallization peaks were reduced to one small peak or disappeared because of high crystallinity in these samples. The double cold‐crystallization exotherms in samples of low crystallinity could be attributed to the superposition of the melting of crystals, formed by the annealing pretreatments, and the cold‐crystallizations occurring during TMDSC heating. The ongoing crystallization after the cold crystallization was clearly seen in the TMDSC nonreversing heat flow curves. DMA data agreed with TMDSC data on the origin of the double cold‐crystallization peaks. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structure and properties of poly(ethylene terephthalate) crystallized by annealing in the highly oriented state. 3. Dynamic- and static-mechanical properties

Commercial undrawn and cold drawn (5 × ) poly(ethylene terephthalate) (PETP) fibers and bristles have been annealed with fixed ends for 6 h in vacuum at different temperatures between 60 and 260°C. With these samples static- and dynamicmechanical measurements have been carried out. It has been found that the α-and β-processes as well as the moduli depend on the annealing temperature (T_a) in different way, for undrawn and drawn material. The temperature position of the β-peak evaluated from tg δ and loss modulus as well as the step height of α- and β-processes are unsensitive to the T_a for the undrawn material in contrast to the drawn one for which maxima are observed. The appearance of these maxima is explained by the dominating role at the corresponding crystallization temperature of one of the two concurrent processes - crystallization and disorientation, reflected in the change of the effective density of amorphous regions. The dynamic and static measured moduli as well as the stress at break for drawn PETP decrease with the increase of annealing temperature as generally observed. The predominating significance of orientation and the state of amorphous phase in comparison with crystallinity is demonstrated. An extremely high deformation ability at room temperature (up to 200%) of previously drawn and annealed at 255 or 260°C bristles is observed. This originates from the solid state postcondensation and premelting phenomena taking place during annealing in vacuum.     

The Crystallization of Amorphous Aluminum Oxide Thin Films Grown on NiAl(100)

The crystallization of amorphous aluminum oxide thin films formed on NiAl(100) has been investigated using in‐situ low energy electron microscopy, low energy electron diffraction, and scanning tunneling microscopy. It is found that both the annealing temperature and annealing time play crucial roles in the crystallization process. A critical temperature range of 450°C–500°C exists for the crystallization to occur within a reasonably short annealing time. The initially uniform oxide film first becomes roughened, followed by coalescing into amorphous‐like oxide islands; further annealing results in the conversion of the amorphous oxide islands into crystalline oxide stripes. The density of the crystalline oxide stripes increases concomitantly with the decrease in the density of the amorphous oxide islands for annealing at a higher temperature or longer time.     

Effects of annealing on the hierarchical crystalline structures and mechanical properties of injection‐molded bars of high‐density polyethylene

The effect of annealing on the microstructural evolution and mechanical properties of high‐density polyethylene parts molded via gas‐assisted injection molding was investigated using scanning electron microscopy, differential scanning calorimetry, two‐dimensional wide‐angle X‐ray diffraction and tensile testing. The results indicated that a variety of annealing temperatures could induce considerable variations in the hierarchical structures, crystallinity, lamellar thickness and yield stress of the molded bars. According to these results, the annealing temperatures could be divided into three regions. In the low‐temperature region of annealing at 80 °C, the spatial variation of the superstructure developed along the thickness direction and mechanical properties of the annealed sample were mainly unchanged and similar to those of the original specimen. At 100 and 120 °C, the intermediate temperature region of annealing, the thickness of the crystals, degree of orientation and yield stress of annealed samples were greatly improved. Finally, at 127 °C, the degree of orientation decreased and yield stress slightly improved, an indication of the high‐temperature annealing region being characterized by increasing melting/recrystallization and causing relaxation of oriented molecular chains. A model is proposed to interpret the mechanism of the annealing treatment of the samples at various temperatures. © 2013 Society of Chemical Industry     

Creep behaviour of annealed UPVC and PMMA

The 20°C creep compliance of UPVC is temporarily increased by prior annealing at temperatures above ～45°C and below T_g. This effect increases with decreasing annealing time. Similar behaviour is observed with PMMA which suggests that this may be a general phenomenon shared by polymers in the ‘glassy amorphous state’. The temporary, and therefore unstable nature of the annealed state is inappropriate for a test specimen, particularly for tests of long duration. It is suggested that volume relaxation in UPVC below 45°C proceeds by short range separation into regions of molecular order and disorder. This state is rapidly disrupted at temperatures above 45°C.     

Annealing effect on the microstructure of poly(vinyl chloride)

The effect of annealing on the microstructure of commercial grade poly(vinyl chloride) was investigated by calorimetric, X-ray and viscoelastic measurements. The degree of crystallinity increases with increasing annealing temperature from above the glass transition temperature up to 130°C, at which point the degree of crystallinity takes on a maximum value. Also, the crystal melting temperature increases with increasing annealing temperature. Thermal analysis and X-ray study suggest that the crystallite of poly (vinyl chloride) decomposes by thermal degradation when annealed, above 170°C. The isothermal crystallization process is analyzed using Avrami's equation employing the degree of crystallinity as a function of annealing time at various annealing temperatures. The crystallization rate has a maximum value at around 140°C. It is expected that the crystalline texture grows in the shape of a lineal-like habit, judging from the magnitude of Avrami's constant and from a study of the X-ray intensity distribution. The α_f-transition was observed to occur at temperatures 5 to 10°C lower than the crystalline melting temperatures for annealed specimens of poly(vinyl chloride) using a dynamic spring analysis. The α_f-transition may be attributed to thermal molecular motions with a long time scale, resulting from the cross-link points introduced by the small crystallites.     

Microstructural Development of Uniaxial Stretched Anneal-Oriented Syndiotactic Polystyrene and its Blend with Poly (2,6-dimethyl-1,4-phenylene oxide): DSC,WAXD, SAXS and FTIR Studies

Studies have been done on strain-induced microstructure development in syndiotactic polystyrene (s-PS) and its blends with poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) in 70/30 and 50/50 compositions of stretched annealed samples. Wide-angle X-ray showed that crystal orientation is less in annealed blend samples compared to annealed pure s-PS for a higher draw ratio. It increases with annealing, and relaxation occurs after a certain annealing temperature at above 180° for both s-PS and s-PS/PPO 70/30 blends. No crystal orientation was observed in the blend of s-PS/PPO 50/50 stretched samples. Small angle X-ray scattering (SAXS) shows the inclusion of amorphous PPO chains in between s-PS crystals lamella. Fourier transform infrared (FTIR) spectroscopy shows that the s-PS molecular chain packing band at 905 cm^?1 is enhanced due to annealing in oriented samples and saturates to around 0.63. The crystal chain relaxation is lower than amorphous chains of s-PS. The molecular chains of amorphous PPO are less oriented into the blend matrix, whereas its relaxation is enhanced during heat treatment and reaches an optimum value after full relaxation. The different behaviors of orientation and relaxation of s-PS and PPO chains into the blend matrix produce superstructures.     

Enhancing mechanical properties of aromatic polyamide fibers containing benzimidazole units via temporarily suppressing hydrogen bonding and crystallization

The copolymerization modified poly(p‐phenylene terephthalamide) containing 2‐(4‐aminophenyl)?5‐aminobenzimidazole (PABZ) units in the main chain was synthesized and the corresponding poly‐p‐phenylene‐benzimidazole‐terephthalamide (PBIA) fibers were prepared by wet spinning. The HCl, the by‐product released during polymerization, can complex with PABZ units to prevent the formation of hydrogen bonding between PABZ units, resulting in amorphous PBIA fibers and a lower glass transition temperature (T_g). Therefore, for the purpose of gaining strong hydrogen bonding and high orientation degree at the same time in PBIA fibers, two‐step drawing–annealing processing was adopted. The as‐spun PBIA/HCl complex fibers were drawn first at 280°C, higher than the T_g of the PBIA/HCl complex fibers and lower than the decomplexed temperature of HCl, which temporarily suppresses the formation of hydrogen bonding and crystallization. Subsequently, the fibers were annealed to reform hydrogen bonding between PABZ units and crystallization via decomplexation of HCl at 400°C. However, when the drawing is above the decomplexed temperature of HCl, the decomplexation of HCl begins to occur which leads to the reform of hydrogen bonding and crystallization, and the tensile strength of the drawn‐annealed PBIA/HCl complex fibers decreases with a decrease in the HCl content of fibers. The tensile strength of two‐step drawn‐annealed fibers increased by approximately 15% compared to that of one‐step drawn PBIA/HCl complex fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42482.     

Thermal and crystalline properties of water‐borne polyurethanes based on IPDI,DMPA, and PEBA/HNA

A series of water‐borne polyurethanes (WPUs) with different soft segments, various COOH contents, and various hard segment contents were prepared through a prepolymerization process. Thermal and crystalline properties of their films were studied by the measurement of differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and thermogravimetry (TG), respectively. Two T_g areas in DSC of WPUs with polyethylene‐butylene adipate glycol (PEBA) as the soft segment were found; an endothermic peak at ～ 33°C was also found with polyhexane neopentyl adipate glycol (HNA) as the soft segment. The DSC of WPUs with the mixture of PEBA/HNA as soft segment was investigated to show similarity to those from HNA, but with a relatively smaller endothermic peak at ～ 34°C. Three sharp diffraction peaks at 2θ = 20.50°, 21.72°, and 24.54° in XRD of water‐borne PUs from HNA were found to indicate the crystallization of soft segments, which was disrupted by the addition of polyacrylate (PA), as evidenced by the amorphous shoulder at ～ 2θ = 20°. TG analysis and differential thermogravimetric (DTG) analysis were measured to indicate that the films lost weight in two stages, and the decomposition temperatures of the films depended on the COOH content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1936–1941, 2007     

An optical investigation of high‐tenacity polyester (H‐T PET) fibers annealed at different temperatures

A two‐beam “Interphako” interference microscope was used to study the effect of annealing on the physical properties of high‐tenacity poly(ethylene terephthalate) H‐T PET fibers. The PET fibers were annealed with free ends for 1 h at temperatures ranging from 100 to 200°C. The shrinkage, refractive indices, and orientation angle of the PET fibers were determined for different annealing temperatures. The measured birefringence and orientation function were found to have decreased with increasing temperature, whereas the degree of crystallinity and the onset temperature (DSC) increased. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers