Investigation of structure development in polyamide 11 and polyamide 12 tubular film extrusion

The processability of single bubble polyamide 11 and polyamide 12 films was investigated. The development of crystalline structure and chain orientation of polyamide 11 and polyamide 12 films in single bubble film blowing was studied by differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXS), infrared (IR) spectroscopy, and birefringence. DSC measurements of both films revealed a spontaneous increase in glass transition temperature (T_g) and cold crystallization temperature (T_c) during aging at room conditions, with crystallinity and melting point remaining constant. Single bubble polyamide 11 and polyamide 12 films exhibited triclinic α and monoclinic γ crystals, respectively. The level of biaxial orientation was evaluated by calculating White‐Spruiell biaxial orientation factors with pole figure data. We were not able to produce biaxially oriented double bubble films with either polyamide 11 or polyamide 12.     

Structures and properties of injection moldings of crystallization nucleator-added polypropylenes. I. Structure–property relationships

Flexural test specimens were injection-molded from polypropylenes added with 0.5 wt % of calcium carbonate, talc, p-tert- dibutyl-benzoic acid monohydroxy aluminum, or p-di-methyl-benzylidene sorbitol under cylinder temperatures of 200–;320°C. Properties such as flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, hardness, and mold shrinkage and higher-order structures such as crystalline texture, crystallinity, a^*-axis-oriented component fraction, and degree of crystalline orientation were measured and structure–property relationships were studied. By the addition of crystallization nucleators, the flexural modulus, flexural strength, heat distortion temperature, hardness, and mold shrinkage were increased and Izod impact strength was decreased. The degrees of crystalline orientation such as the orientation fraction OF and c-axis orientation function f_c were increased by the addition of nucleators. The degree of the increase was higher as the crystallization temperature was higher. Close relationships were observed between some properties and the degrees of crystalline orientation.     

Thermal transitions and stability of melt mixed TiO2/Poly(L‐lactic acid) nanocomposites

Poly(L‐lactic acid) (PLLA) nanocomposites containing 5, 10, and 20 wt% titanium dioxide (TiO₂), were prepared by mixing in a co‐rotating twin‐screw extruder. By X‐ray diffraction, a transformation of less ordered (α’‐form) to better organized crystalline (α‐form) structure of PLLA was observed with increasing TiO₂ content. Differential scanning calorimetry (DSC) tests revealed that cold crystallization was facilitated, as shown by the decrease of cold crystallization temperature (T_cc). The main melting peak of PLLA phase in nanocomposites, shifted towards higher temperatures and a shoulder appeared in the lower temperature flank of the curve, revealing a second peak for 20/80 w/w TiO₂/PLLA nanocomposites. The effect of TiO₂ on the isothermal crystallization of PLLA, in the temperature range T_ic: 100–120°C, was also investigated by DSC. At lower temperatures (T_ic: 100 and 110°C), the effect of TiO₂ nanoparticles is an increase of the crystallization rate, leading to lower time for the completion of crystallization, in comparison with that of pure PLLA. The inverse effect was observed at higher crystallization temperatures (T_ic: 115 and 120°C). The kinetic analysis of the crystallization behavior of the examined nanocomposites fits the Avrami equation quite well and gives values for exponent (n) varying between 2 and 3, suggesting a spherulitic crystalline morphology. POLYM. ENG. SCI., 59:704–713, 2019. © 2018 Society of Plastics Engineers     

Crystallization studies of semi-crystalline polymers under oscillatory shear using the rheometrics mechanical spectrometer

A method has been developed on the Rheometrics mechanical spectrometer using the eccentric rotating disks mode to study the crystallization kinetics of different semi-crystalline polymers (polyethylene, polypropylene, poly(butylene terephthalate) and Nylon 11) under oscillatory shear. Dynamic shear moduli (storage G′ and loss G″), loss tangent (tan δ), and dynamic viscosity (η′) were simultaneously, monitored during the crystallization process. The onset and completion of crystallization were characterized by the initial rise and final levelling off of G′, while the peak time, of crystallization (t_p) is calculated from the time elapsed between the onset and peak of crystallization which is indicated by the G″ or η′ maximum. In the case of polypropylene, going from a low frequency of ?0.1 rad/s, to higher frequencies of up to 10 rad/s, there is a monotonic decrease in peak time of crystallization (t_p) together with a progressive decrease in spherulitic morphology. The observed acceleration in crystallization is due predominantly to the increase in nucleation rate and orientation of chains in melt crystalline aggregate. The progressive disappearance of the spherulitic morphology is attributed to the disruption of the spherulite superstructure at higher frequencies of shear.     

Correlations between processing parameters,morphology, and properties of blown films of linear low‐density polyethylene/low‐density polyethylene blends. I. Crystalline biaxial orientation by IR and mechanical properties

The change of the processing parameters of a blown film operation alters the mechanical and optical properties of the films. This work studied the influence of some of these parameters on the properties of blown films made of blends of linear low‐density polyethylene (LLDPE) and LDPE. Correlations between the crystalline biaxial orientations of these films and the mechanical properties were found. The crystalline biaxial orientation was measured by IR following the Krishnaswamy approach. The a axis of the unit cell was oriented along the machine direction (MD) at all LDPE concentrations, and it was not affected by the blow‐up ratio (BUR). In contrast, the b axis changed its orientation from orthogonal to MD to along the transverse direction (TD), and it was affected by the BUR. Finally, the c axis changed its orientation from equiplanar between the MD and TD to along the thickness of the film, and it was influenced by the BUR. The decrease of the tensile mechanical properties along the MD with the increase in the amount of LDPE in the blends was attributed to the tilting of the c axis toward the film thickness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3161–3167, 2006     

Real‐time FTIR and WAXS studies of drawing behavior of poly(ethylene terephthalate) films

The development of molecular orientation and crystallization was studied during uniaxial drawing of poly(ethylene terephthalate) (PET) films, which was immediately followed by subsequent taut annealing at the drawing temperature. The behavior was monitored in real time throughout the drawing and annealing using dynamic FTIR spectroscopy and in situ WAXS measurements using the Daresbury Synchrotron Radiation Source. Films were drawn at 80 and 85°C at varying strain rates (0.001–0.7 s⁻¹). The true stress–strain behavior was determined at each of the drawing conditions and the density and optical anisotropy of unloaded samples was measured. The IR spectra were analyzed using curve reconstruction procedures developed previously, and they showed that orientation of the phenylene groups and the trans glycol conformers occurred before significant gauche–trans conformational changes could be seen. The onset of crystallization, defined as the point that the crystalline 1 05 reflection could be first observed using WAXS, was not found to correlate with any specific change in the proportions of trans and gauche isomers nor with any feature on the stress–strain curve. However, it was clear that, for these comparatively low strain rates, crystallization occurred during the drawing process while the crosshead was moving and the draw ratio was increasing. The orientation of the crystallites was calculated from the 1 05 reflection observed in a tilted film, transmission geometry. The crystallites were found to form at a draw ratio of about 2.5 with high orientation values (P₂ > 0.8) that increased during drawing and annealing to P₂ values of 0.95, irrespective of the drawing conditions. Semiquantitative measurements of crystallinity showed that the fraction of crystalline material that developed during drawing decreased with increasing strain rate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1825–1837, 2001     

Crystallization, hydrolytic degradation, and mechanical properties of poly (trimethylene terephthalate)/poly(lactic acid) blends

Crystallization, melting, hydrolytic degradation, and mechanical properties of poly(trimentylene terephthalate)/poly(lactic acid) (PTT/PLA) blends have been investigated. The blends show a single and composition-dependent glass-transition temperature (T _g) over the entire composition range, implying that these blends are fully miscible in the amorphous state. The observed T _g is found to increase with increasing PLA content and fitted well with the Gordon–Taylor equation, with the fitting parameter k being 0.91. The cold-crystallization peak temperature increases, while the melt-crystallization peak decreases with increasing the PLA content. Both the pure PTT and PTT/PLA blends cannot accomplish the crystallization during the cooling procedure and the recrystallization occurs again on the second heating. Therefore, on the thermogram recorded, there is exothermal peak followed by endothermal peak with a shoulder. However, to pure PLA, no crystallization takes place during cooling from the melt, therefore, no melting endothermic peak is found on the second heating curve. WAXD analysis indicates PLA and PTT components do not co-crystallize and the crystalline phase of the blends is that of their enriched pure component. With increasing PLA content, the hydrolytic degradation of the blend films increases, while both the tensile strength and the elongation at break of the blend films decrease. That is to say, the hydrolytic degradation of the PTT/PLA blends increases with the introduction of PLA at the cost of the decrease of the flexibility of PTT.     

Effect of prestrain on the subsequent thermal crystallization of a copolyester of lactic and glycolic acid

An investigation was carried out in order to study the effect of prestrain on the subsequent crystallization of a specific copolyester based on lactic and glycolic acid. This polymer, which can be easily quenched into an amorphous glass, has a T_g of 43°C and when in crystalline form has a melting point of 210°C. Using amorphous films, samples were prestrained to various levels at temperatures not far above T_g. In some cases films were immediately quenched at the prestrain level so as to retain the elongation while others were allowed to immediately retract whereby they showed a relatively small degree of permanent Set. Utilizing birefringence, quenched samples whose initial elongation was maintained showed linear behavior with prestrain while those that retracted showed essentially zero birefringence until a prestrain of about 150 percent after which a small degree of positive birefringence resulted. Wide angle x-ray diffraction (WAXS) showed no signs of crystallinity in all cases. These same films were then quickly taken to 150°C and rapidly crystallized. Again, one series of the prestrained samples were in the elongated state during crystallization whereas the second series was unrestrained during crystallization. Using microscopy and small angle light scattering (SALS), the morphological textures of these crystallized films were investigated. In all cases, spherulitic textures were observed of equivalent size up to a value of about 200 percent elongation the spherulite size systematically decreased with the prestrain an increase in clearly showing that prestrain had a pronounced effect upon the nucleation density. Increasing draw rate displayed a similar effect on nucleation density. Since spherulite size was noted to be the same in either series, it indicated that nucleation was induced as a result of the prestrain and remained irrelevant of whether the sample was allowed to relax or not. The morphology above the transitional state was similar to row structure common to polymers crystallized in the oriented state. WAXS and birefringence was applied to the crystallized materials and it was found that up until the transitional zone, no crystal orientation was observed in either series indicating that although nucleation density was strongly affected up until that point, no orientation was retained within the sample upon crystallization. A simplified model is used to explain the observed results.     

Crystallization, spherulite growth, and structure of blends of crystalline and amorphous poly(lactide)s

The effects of incorporated amorphous poly(dl-lactide) (PDLLA) on the isothermal crystallization and spherulite growth of crystalline poly(l-lactide) (PLLA) and the structure of the PLLA/PDLLA blends were investigated in the crystallization temperature (T_c) range of 90-150 °C. The differential scanning calorimetry results indicated that PLLA and PDLLA were phase-separated during crystallization. The small-angle X-ray scattering results revealed that for T_c of 130 °C, the long period associated with the lamellae stacks and the mean lamellar thickness values of pure PLLA and PLLA/PDLLA blend films did not depend on the PDLLA content. This finding is indicative of the fact that the coexisting PDLLA should have been excluded from the PLLA lamellae and inter-lamella regions during crystallization. The decrease in the spherulite growth rate and the increase in the disorder of spherulite morphology with an increase in PDLLA content strongly suggest that the presence of a very small amount of PDLLA chains in PLLA-rich phase disturbed the diffusion of PLLA chains to the growth sites of crystallites and the lamella orientation. However, the wide-angle X-ray scattering analysis indicated that the crystalline form of PLLA remained unvaried in the presence of PDLLA.     

The influence of TiO2 content on the properties of glass ceramics: Crystallization,microstructure and hardness

The effects of compositional variation, crystallization behavior, crystalline phases and microstructure formed in the SiO₂3Al₂O₃3CaO (SAC) glass system using various amounts of TiO₂ as nucleating agent were investigated by Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR) techniques. The crystallization kinetics and mechanical properties of SAC glass ceramics were studied using crystallization peak temperature (T_p) of three different glasses as obtained from DTA, the activation energy (E) and Avrami exponent (n) were also determined. The crystallization peak temperature (T_p) and activation energy (E) were found to increase with the increase in TiO₂ content. The major crystalline phases were anorthite and wollastonite along with gehlenite and titanite as the minor crystalline phases present in the glass ceramic system. The studies showed that the three dimensional crystalline structure and the microhardness increased with the increase of TiO₂ content in the glass ceramics system.     

Crystal structures and orientation development in tubular film extrusion of syndiotactic polypropylene and isotactic polypropylene

The differences in behavior of isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) in tubular film extrusion are qualitatively described. The crystalline form and orientation in the films were characterized using wide‐angle X‐ray diffraction (WAXD) patterns, pole‐figure analysis and birefringence. The sPP films had the crystalline form of the disordered Form I and the a‐crystallographic axis was found to be preferentially oriented in the film normal direction (ND) under the conditions of biaxial stresses. High transverse orientations were developed in the sPP films. In the iPP films, the monoclinic crystalline form was found and the b‐crystallographic axis was preferentially oriented in the ND. The birefringence of the films showed trends very similar to the crystalline orientations characterized by WAXD in both iPP and sPP films.     

Structure development and isothermal crystallization behaviour of compatibilized PET/expandable fluorine mica hybrid nanocomposite

Summary The compatibilized PET/expandable fluorine mica (ME) hybrid nanocomposite (CN) prepared by in situ polymerization technique showed a partially exfoliated structure of ME in PET matrix by XRD analysis, owing to its broad crystalline peak accompanied by an increase of d-spacing as compared to PET/ME uncompatibilized composite (UC). The analysis by TEM revealed a better dispersion of ME in PET for CN as compared to aggregates of ME in case of UC. Further, the isothermal crystallization behaviour studied using DSC for the same at different crystallization temperature (T _c,) revealed a significant decrease of crystallization half time and remarkable increase of crystallization rates (almost 2 times than pure PET) for CN in contrast to UC. The Avrami exponent n lowered to 2.3 for CN as compared to 3.1-3.4 for pure PET at various T _c. The activation energy (E _a) determined from Arrhenius equation reduced dramatically for CN. These various observations could be explained based on the nucleation efficiency by ME accompanied by different crystallization/growth process occurring in case of hybrid nanocomposite.     

Preparation and Characterization of high‐strength poly(ether ether ketone) films

High‐strength poly(ether ether ketone) (PEEK) films were prepared through melt extrusion followed by stretching. The tensile strength, orientation, and crystallization behaviors of PEEK films were characterized by universal testing machine, thermomechanical analysis, wide‐angle X‐ray diffraction, and differential scanning calorimetry. The results indicated that the tensile strength of PEEK films mainly depended on the stretching rate (ν), stretching temperature (T), and stretching ratio (λ_L). Moreover, the tensile strength of the stretched PEEK film (333 MPa) was almost four times higher than that of the unstretched PEEK film (87 MPa) under an optimized condition. This is attributed to a synergistic effect of orientation and crystallization in the stretching process, and the influence of orientation is stronger than that of the crystallization on the improvement of the tensile strength of PEEK films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40172.     

Effect of high-performance polymers on crystallization and multiple melting behavior of poly(phenylene sulfide)

The crystallization and multiple melting behavior of poly(phenylene sulfide) (PPS) and its blends with amorphous thermoplastic bisphenol A polysulfone (PSF) and phenolphthalein poly(ether ketone) (PEK-C), crystalline thermoplastic poly(ether ether ketone) (PEEK), and thermosetting bismaleimide (BMI) resin were investigated by a differential scanning calorimeter (DSC). The addition of PSF and PEK-C was found to have no influence on the crystallization temperature (T_c) and heat of crystallization (ΔH_c) of PPS. A significant increase in the value of T_c and the intensity of the T_c peak of PPS was observed and the crystallization of PPS can be accelerated in the presence of the PEEK component. An increase in the T_c of PPS can also be accelerated in the BMI/PPS blend, but was no more significant than that in the PEEK/PPS blend. The T_c of PPS in the PEEK/PPS blends is dependent on the maximum temperature of the heating scans and can be divided into three temperature regions. The addition of a second component has no influence on the formation of a multiple melting peak. The double melting peaks can also be observed when PPS and its blends are crystallized dynamically from the molten state. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 637–644, 1998     

Phase and Texture Evolution in Chemically Derived PZT Thin Films on Pt Substrates

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum‐coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO₂ adhesion layer. The Pt deposited on TiO₂ exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X‐ray diffraction at a synchrotron source. The intensity of the Pt₃Pb phase indicated that deposition on a highly oriented Pt/TiO₂ substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO₂ substrate than on the Pt/Ti substrate.     

Crystallization behavior and morphology of double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers

Double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers (PTT/PEOT), with PTT content ranging from 16.5 to 65.5 wt%, were synthesized by melt copolycondensation. The morphological transformation of samples from microphase separation to macrophase separation was investigated by gel permeation chromatography and transmission electron microscopy. Differential scanning calorimetry and in situ wide‐angle X‐ray diffraction suggested that all copolycondensation samples displayed double crystalline behavior. The melt‐crystallization peak temperatures (T_{m, c} values) of PTT chains monotonously increased with increasing PTT content and were higher than that of homo‐PTT when the content of PTT was above 30.6 wt%. Interestingly, T_{m, c} values of PEOT chains were also increased with increasing PTT content. Polarized optical microscopy revealed that all copolycondensation samples studied could form ring‐banded spherulites and band spacing increased with increasing T_c values. In addition, band spacing decreased with increasing PTT content at a given T_c. Strangely, although PEOT was the main component in all copolycondensation samples, spherulitic morphology formed by the advance crystallization of PTT did not change after PEOT crystallization. Only a subtle change of quadrant tones was detected. © 2012 Society of Chemical Industry     

Effect of annealing and orientation on microstructures and mechanical properties of polylactic acid

Two types of polylactic acid (PLA) films (one amorphous and one semi‐crystalline) were produced by sheet extrusion. Talc was used as a nucleation agent for the semi‐crystalline PLA. The films were annealed above their T_g or were uniaxially orientated in two ways: (1) via a drawing system in front of the extruder and die or (2) via a three‐roller stretching system. The slower crystallization rate and lower melting stress of the PLA resulted in amorphous film using the drawing system. Annealing above T_g increased crystallinity and polymer chain relaxation, which resulted in increases in both strength and toughness. Stretching above T_g also produced simultaneous crystallization and chain relaxation, which resulted in increases in both modulus and toughness. Both modulus and tensile strength in the stretching direction were higher than in the crosswise direction. Talc acted not only as a rigid filler to reinforce the PLA, but also as a nucleation agent for the PLA, especially during annealing. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Rapid Microwave Annealing of Amorphous Lead Zirconate Titanate Thin Films Deposited by Sol‐Gel Method on LaNiO3/SiO2/Si Substrates

The heating behavior of LaNiO₃ (LNO) films on SiO₂/Si substrate heated by 2.45 GHz microwave irradiation in the microwave magnetic field was first investigated, and then amorphous Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were deposited on LNO‐coated SiO₂/Si substrates by a sol‐gel method and crystallized in the microwave magnetic field. The crystalline phases and microstructures as well as the electrical properties of the PZT films were investigated as a function of the elevated temperature generated by microwave irradiation. The perovskite PZT films with a highly (100)‐preferred orientation can be obtained by microwave annealing at 700°C for only 180 s of total processing time, and have good electrical properties. The results demonstrated that conductive metal oxide LNO as a bottom electrode layer is an advantage for the crystallization of PZT thin films by microwave irradiation in the microwave magnetic field.     

Oriented structure of PP/LLDPE multilayer and blends films

Polypropylene/linear low-density polyethylene (PP/LLDPE) multilayer and blends blown films are investigated in terms of crystalline morphology and orientation. The crystalline structures were probed using microscopy, infrared trichroism and X-ray pole figures. Two different PPs were used, one was a homopolymer and the other was a copolymer. Similar orientation characteristics were observed for both PP components in the blends and multilayer films, the PE component, however, showed very different structure, especially for the crystalline a- and b-axes orientation. The row-nucleated structure, epitaxial crystallization and transcrystallization observed in the films are discussed.     

Effect of the Amount of H2O on the Crystallization of TiO2 Films Prepared from Alkoxide Solutions Containing Acetylacetone

Sol–gel‐derived TiO₂ films were prepared by dip‐coating from Ti(OC₃H₇ⁱ)₄–CH₃COCH₂COCH₃–HNO₃–H₂O–C₂H₅OH solutions, and the effect of the H₂O content in solutions on the crystallization of TiO₂ films during the heat treatment at 800°C was discussed. The crystalline phase, crystallite size, grain size, and refractive index of the TiO₂ films depended on the H₂O/Ti(OC₃H₇ⁱ)₄ mole ratios (x) in the coating solutions. Highly dense and crystalline rutile films were obtained at x = 0.5–10, where the crystallites and grains became larger with increasing x. The further increase in x from 10 to 50 reduced the crystallite size and refractive index of the films, where anatase phase appeared at x = 30–50.