Study on the structure of nylon 6 films iodinated before forming. III. Fine structure variation of the amorphous film through deiodination

Amorphous nylon 6 film iodinated before forming with an aqueous solution of 1.0N iodine–potassium iodide (I₂/KI) was deiodinated by dipping in water/ethylene glycol (EG) solutions of sodium thiosulfate with various EG contents and temperatures, washed with water, and dried at ambient condition. Structural variation through deiodination and the effects of the deiodination conditions were investigated by X‐ray diffractometry and differential scanning calorimetry. The degree of swelling of the films immediately after deiodination and the time required to complete the deiodination were generally increased and decreased, respectively, with increasing temperature and EG content. The amorphous iodinated film was crystallized through deiodination. The α‐crystal formation became easier with increasing temperature and EG content in the solution. The crystallinity of the films was higher after drying than before drying, suggesting that the drying induced further crystallization without any significant conversion of crystal type. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure and processability of iodinated poly(vinyl alcohol) (III)‐structure of films iodinated in solution before casting

Films iodinated at solution before casting (IBC films) were prepared by casting aqueous solutions of 10 wt % poly(vinyl alcohol) (PVA) containing selected quantities of I₂/KI. The quantity of I₂/KI was controlled to obtain 15.2, 39.8, 83.2, 117.0, and 140.1%. The Thermogravimetry (TG) curves of the IBC film exhibited three distinct zones corresponding to the evaporation of H₂O and I₂ molecules (zone I), evaporation of I₂ and partial decomposition of side groups (? OH) (zone II), degradation of the remaining side groups and partial degradation of the main chain (zone III‐1), and degradation of the remaining main chain and the char zone corresponding to KI. The crystalline structure of the film with a weight gain of 15.2% was almost the same as that of the pure PVA, and the film with the weight gain of 140% was almost amorphous. The differential scanning calorimetry (DSC) thermograms of the IBC films with a weight gain of 15.2% and 39.8% indicated endothermic single or double peaks at around 180°C, corresponding to the crystal melting and degradation of side groups; those with weight gains of 83.2% and above indicated exothermic peaks at around 170°C, corresponding to crystallization, and broad endothermic peak at around 180–200°C, corresponding to the crystal melting and degradation of side groups. The dynamic mechanical α_a transition of the IBC film with the weight gain of 140.1% appeared at around 20°C. X‐ray diffraction and DSC analysis of deiodinated films show that the crystal structure, on deiodination of all the IBC films, regardless of crystallinity, returned to that of the pure PVA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3497–3502, 2006     

Effect of nanoclay on the thermal,mechanical, and crystallization behavior of nanofiber webs of nylon‐6

Nylon‐6 and nanoclay/nylon‐6 composite nanofibers were prepared by electrospinning technique, in which formic acid was used as a solvent for good solubility of nylon‐6. The diameter of nylon‐6 and nanoclay/nylon‐6 nanofibers was below 350 nm and had smooth surfaces. The DSC heating curves of nylon‐6 and composites nanofibers show two endotherm behaviors, T_m1 (about 214°C) and T_m2 (about 220°C), corresponding to the melting events of γ‐form and α‐form crystals, respectively. The WAXs study showed that the γ‐crystalline phase predominantly present in both nylon‐6 and nanoclay/nylon‐6 nanofibers. The mechanical properties of the nanoclay/nylon‐6 composite nanofibers were higher than neat nylon‐6 electrospun nanofibers, which was decreased as the quantity of the clay increased. It might be due to the aggregation of nanoclay at high concentration. The thermal properties of the composite nanofibers were higher than neat nylon‐6 nanofibers. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Crystal transition behavior of odd–odd nylon 11,11 under annealing and stretching

Nylon 11,11 is a new odd–odd polyamide with multiple crystalline structures. The wide‐angle X‐ray scattering indicated that the structure of quenched sample was not amorphous but a γ‐form crystal with a relatively low crystallinity. The α‐form and the γ‐form crystal of nylon 11, 11 could be obtained by annealing the quenched samples at high and low temperature, respectively. No crystal transition happened for the α‐form sample when annealed at any temperature before melting. However, the γ‐form would quickly transform into the α‐form when annealed above 145°C. Under the stretching conditions, the α‐form rapidly transformed into the γ‐form at low temperature, while the γ‐form changed into the α‐form only at high temperature. These results indicated that the stretching inducement was beneficial to produce the γ‐form, and the thermal inducement was favorable to forming the α‐form. POLYM. ENG. SCI., 54:2785–2790, 2014. © 2013 Society of Plastics Engineers     

Structure and processability of iodinated poly(vinyl alcohol). II. Drawability of iodinated films

The drawability of poly(vinyl alcohol) (PVA) films iodinated with 0.1, 0.3, 0.5, 1.0, and 2.0 mol/L I₂/KI aqueous solutions was examined with a tensile tester and a hand‐operated drawer at 30–150°C. The structure of the films drawn to a maximum draw ratio (MDR) and deiodinated was determined by X‐ray diffractometry, differential scanning calorimetry, and birefringence. Generally, the improvement of the drawability for the PVA film via iodination was ascertained by the increased breaking strain and decreased yield stress on the stress–strain curves when increasing the I₂/KI concentration of the aqueous solutions used in the iodination. The MDR was generally increased with the concentration of I₂/KI and the draw temperature. However, it diminished instead when close to the highest temperature and concentration of I₂/KI, which was likely due to molecular degradation by the action of iodine as an oxidizer. The variation of the structure of the films drawn and deiodinated seems to be dependent mainly upon the MDR rather than the concentration of I₂/KI. The greater the MDR was, the higher the degree of crystallinity, birefringence, and initial modulus were but the lower the melting temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95:1209–1214, 2005     

Detection of polymer transition temperatures by infrared absorption spectrometry

Infrared bands in the 900–1100 cm^?1 region are sensitive to thermal energy. These bands can result from intermolecular coupling, producing the crystal lattice, or from intramolecular coupling of the various atomic groups in a regular helix or coiled chain. In either case an increase in temperature will disrupt the coupling mode, resulting in a form of structural relaxation and a reduction in the integrated absorbance. It is proposed that the temperature at which the peak areas begin to decrease be assigned as the T_g. This is measured by continuously scanning a selected peak in the infrared spectrum of a polymer film while it is heated at a rate of about 1°C/min. Using this technique polyamides (nos. 6,66, and 610) exhibited transitions in the 30–50°C range, and by studying the increase in the free NH region (3440 cm^?1) of nylon 66 two other transitions were detected at 80 and 137°C; the latter represents a change in the nylon 66 crystal state. An amorphous film of poly(ethylene terephthalate) displayed a transition at 58–68°C (T_g) and at 85°C, which is the crystallization temperature. Films of poly(vinyl acetate) and polystyrene exhibited transitions at 25–37°C and at 70°C, respectively.     

Study on the structure and processibility of the iodinated poly(vinyl alcohol). I. Thermal analyses of iodinated poly(vinyl alcohol) films

To get more information on the structure of iodinated poly(vinyl alcohol) (PVA), thermal analyses of unoriented and oriented PVA films were conducted. Unoriented and oriented PVA films iodinated with aqueous solutions at selected concentrations were carried out by thermogravimetry (TG) and differential scanning calorimetry (DSC). The TG curves for the iodinated film shows four or five weight‐loss zones associated with degradation and evaporation of excess I₂ molecules and I₂ molecules from I, partial OH side groups on PVA, and I₂ from I, the remaining OH groups and the partial main chains, the remaining main chains, and a very small amount of residue from PVA. The char of KI salts remained. By investigating the TG results, it was identified that the amount of I ions increased with increasing I₂/KI up to 65%, but above that weight gain, the rate of increase diminished and the amount of I ions from the I ions increased. The TG curve for the oriented film was very similar to that for the unoriented film except for its greater weight loss at zone I due to narrow space in amorphous region. The DSC thermogram of iodinated films indicated two peaks at 145°C and 160–170°C, corresponding to the melting of crystals and the degradations of OH groups and main chains, respectively. The maximum temperatures of peaks were much lower than that of the untreated one. ©2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2407‐2415, 2004     

Structure and transformation of low‐temperature phases of 1,3‐distearoyl‐2‐oleoyl glycerol

Polymorphic transformations of 1,3‐distearoyl‐2‐oleoyl glycerol (SOS) at low temperatures (10 °C–30 °C) have been studied by time‐resolved synchrotron X‐ray diffraction (XRD) measurements at small and wide angles. Three structures have been identified: α‐phase structure forms by quenching to 10 °C from the liquid state, a metastable structure formed simultaneously with α‐phase and γ‐phase formed at 30 °C during α‐melt‐mediated crystallisation as well as at the pre‐melting temperature (22.5 °C) of the α‐phase when the coexistence of two phases (α and γ) is observed. The metastable structure produces three broad peaks in XRD patterns at small angles (one strong and two weak peaks corresponding to d‐spacings of ～4 nm, ～12 nm and ～1.5 nm respectively) and a peak in X‐ray diffraction patterns at wide angles (0.42 nm). A model is proposed for the metastable structure based on a combination of double‐ and triple‐chain packing of SOS molecules due to the similar length of alkyl chains (stearoyl and oleoyl) in the molecules.     

Self‐nucleation–induced nonisothermal crystallization of nylon 6 from the melt

The effect of thermal treatment over a wide range of temperature (130–280°C) on the crystallization behavior of nylon 6 was studied by using DSC, FTIR, and polarized light microscope equipped with a hot stage. The crystallization and the subsequent melting behavior of the nylon 6 samples treated at different temperatures (T_s) were classified into four types. When T_s was higher than 236°C or lower than 213°C, the crystallization behavior of nylon 6 was insensitive to the variation of T_s. When T_s was in the range of 213–235°C, the crystallization behavior was sensitive to the change of T_s. The polarized light microscopic experiments have demonstrated that a large amount of tiny ordered nylon 6 segments/cluster persisted when nylon 6 film are heated to 231°C. Consequently, the fastest crystallization speed was observed. As T_s was between 214 and 223°C, both the T_m and the ΔH_m were higher than those of the nylon 6 samples treated at other temperature. The polarized light microscopic investigations have also demonstrated that molten nylon 6 crystallizes by using the un‐molten nylon 6 crystals as nucleation center at 220°C. Crystallization at higher temperature produces nylon 6 with thicker crystalline lamella. The above results are helpful for rational design of thermal treatment procedure to obtain nylon 6 with different crystalline features. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42413.     

Effect of boric acid and heat treatment for the formation of poly(vinyl alcohol)/iodine complex films iodinated at solution before casting

This study examined the role of boric acid and the effect of heat treatment on PVA‐iodine polarizing films prepared in the solution state before casting (IBC) of PVA/iodine/boric acid films. The films were prepared by casting aqueous solutions of 10 wt % poly(vinyl alcohol) (PVA) containing boric acid with 0, 0.1, 0.3, and 0.5 mol/l of I₂/KI aqueous solution, and I₂/KI(1 : 2) with 5 wt % of PVA. The effect of boric acid and heat treatment on the durability of the IBC PVA polarizing sheet films was investigated by UV–vis absorption spectroscopy. Boric acid was found to be essential for the complex formation in PVA/iodine solutions at relatively low I₂/KI concentrations and high temperatures. The strength of the complex peak at ∼ 600 nm in UV–vis absorption spectra increased with increasing boric acid concentration. With increasing heating temperature over 90°C the intensity of the peak at 600 nm corresponding to the complex decreased due to the evaporation of I₂ decomposed from I₅⁻, but the peak at 355 nm corresponding to free I₂·I₃⁻ was remained unchanged. From heat treatment at 150°C, the intensity of the peak at 600 nm decreased but the intensity of the complex peak (600 nm) of the sample with 0.5 mol/l boric acid was unaffected. The transmittance and degree of polarization for the films increased and decreased with increasing heat treatment time under heat and a humid atmosphere, respectively. However, this tendency decreased with increasing boric acid concentration and heat treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of a synthetic ureido nucleating agent on crystallization behavior and mechanical properties of polyamide 6

A synthetic ureido mixture prepared from the reaction of 4,4′‐diphenylmethane disocynanate (MDI) and cyclohexylamine without using any harmful organic solvents, has been used as a nucleating agent (PNA) for polyamide 6 (PA6). The effect of PNA on the crystallization and mechanical properties of PA6 has been studied by means of differential scanning calorimetry (DSC), polarized optical microscopy (POM), tensile test, melt flow index (MFI), and X‐ray diffraction (XRD). The results show that PNA is an effective nucleation agent for PA6. PNA affects the nucleation mechanism of PA6, and substantially accelerates the crystallization rate of PA6 and gives rise to smaller crystal size. In comparison with PA6, the crystallization temperature (T_c) of PA6/PNA (100/0.5) increases 21.3°C and the degree of sub‐cooling (ΔT_c) decreases 23.7°C. Furthermore, because of the heterogeneous nucleation induced by PNA, the spherulites of PA6 become even and tiny based on POM observation. Polymorph transform has been obtained from XRD analysis. The virgin PA6 is free of γ‐phase crystals, presented as α‐phase crystals in this study, but γ‐phase crystal appears after the introduction of PNA. The mechanical and thermal properties of PA6 are obviously improved by the addition of PNA. POLYM. ENG. SCI., 55:2011–2017, 2015. © 2015 Society of Plastics Engineers     

γ‐Crystalline form of nylon‐10,10 in nylon‐10,10–montmorillonite nanocomposite

Wide‐angle X‐ray diffraction (WAXD) and variable temperature WAXD spectroscopy and Fourier‐transform infrared (FTIR) spectrometry were used to identify the γ‐crystalline form of nylon‐10,10 in the nanocomposite of nylon‐10,10 and montmorillonite. A new diffraction peak at 2θ = 22° was observed in the WAXD pattern of the nanocomposite as compared with nylon‐10,10, and the data of variable temperature WAXD indicated that it was the characteristic peak of γ‐crystalline form of nylon‐10,10. The amide VI band at 624 cm^?1 was also observed in the FTIR spectrum of the nanocomposite, which is characteristic of γ‐crystalline nylon. In addition, the shoulder peak at 1553 cm^?1 can be assigned to the amide II band of γ‐crystalline form of nylon‐10,10. Copyright © 2003 Society of Chemical Industry     

Preparation and Performance Study of Mullite/Al2O3 Composite Ceramics for Solar Thermal Transmission Pipeline

For lowering sintering temperature of mullite/Al₂O₃ composite ceramics for solar thermal transmission pipeline, kaolin, potassium feldspar, quartz, and γ‐Al₂O₃ were used as raw materials to in situ synthesize the composite ceramics with pressureless sintering method. Densification, mechanical properties, thermal expansion coefficient, thermal shock resistance, phase composition, and microstructure were investigated. The experiment results demonstrated that the introduction of potassium feldspar and quartz decreased the lowest sintering temperatures greatly to 1300°C. The optimum sample A3 sintered at 1340°C obtained the best performances. The water absorption, apparent porosity, bulk density, bending strength, and thermal expansion coefficient of A3 were 0.04%, 0.12%, 2.71 g/cm³, 94.82 MPa, and 5.83 × 10^?6/°C, respectively. After 30 thermal shock cycles (wind cooling from 1100°C to room temperature), no cracks were observed on the surfaces of the sample, and the bending strength increased by ?7.96%. XRD analysis indicated that the main phases of samples before and after 30 thermal shock cycles were consistently mullite, corundum, and α‐cristobalite, while the content of mullite increased after thermal shock. SEM micrographs illustrated that the mullite grains growth and micro‐cracks appeared after thermal shock endowed the composite ceramics with excellent thermal shock resistance.     

Effect of halide ions on the corrosion inhibition of aluminium in alkaline medium using polyvinyl alcohol

The corrosion inhibition of aluminum in NaOH in the presence of polyvinyl alcohol (PVA) at 30 and 40°C and the effect of addition of halides (KCl, KBr, KI) were studied using weight loss and hydrogen evolution methods. Results obtained showed that PVA acts as a corrosion inhibitor in the alkaline environment. The inhibition efficiency increased with increase in concentration of PVA and synergistically increased on the addition of the halides but however decreased with rise in temperature. The phenomenon of physical adsorption is proposed from the obtained E_a and Q_ads values. PVA was found to obey Freundlich and Frumkin adsorption isotherms. The increase in inhibition efficiency I (%), surface coverage θ values as well as synergistic parameter, S_I were found to be in the order I^? > Br^? > Cl^?, which clearly indicates that the radii and electronegativity of the halides play a significant role in the adsorption process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2810–2816, 2007     

Crystallization and melting behavior of multi‐walled carbon nanotube‐reinforced nylon‐6 composites

The crystallization and melting behavior of neat nylon‐6 (PA6) and multi‐walled carbon nanotubes (MWNTs)/PA6 composites prepared by simple melt‐compounding was comparatively studied. Differential scanning calorimetry (DSC) results show two crystallization exotherms (T_{CC, 1} and T_{CC, 2}) for PA6/MWNTs composites instead of a single exotherm (T_{CC, 1}) for the neat matrix. The formation of the higher‐temperature exotherm T_{CC, 2} is closely related to the addition of MWNTs. X‐ray diffraction (XRD) results indicate that only the α‐phase crystalline structure is formed upon incorporating MWNTs into PA6 matrix, independently of the cooling rate and annealing conditions. These observations are significantly different from those for PA6 matrix, where the increase in cooling rate or decrease in annealing temperature results in the crystal transformation from α‐phase to γ‐phase. The crystallization behavior of PA6/MWNTs composites is also significantly different from those reported in PA6/nanoclay systems, probably due to the difference in nanofiller geometry between one‐dimensional MWNTs and two‐dimensional nanoclay platelets. The nucleation sites provided by carbon nanotubes seem to be favorable to the formation of thermodynamically stable α‐phase crystals of PA6. The dominant α‐phase crystals in PA6/MWNTs composites may play an important role in the remarkable enhancement of mechanical properties. Copyright © 2005 Society of Chemical Industry     

Synergistic effect of halide ions on the corrosion inhibition of aluminum in acidic medium by some polymers

The corrosion inhibition of aluminum in H₂SO₄ in the presence of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) and the effect of addition of halides (KCl, KBr, KI) was studied using the hydrogen evolution technique at 30 and 40°C. Inhibition efficiency (%I) increases with concentration of PVA and PEG—‐but with PEG having higher %I. The %I decrease with increase in temperature from 30 to 40°C in the absence and presence of inhibitor and halides. PVA and PEG were found to obey Freundlish adsorption isotherm. Phenomenon of physical adsorption is proposed from the obtained E_a, ΔG_ads, and Q_ads values obtained. The synergism parameters (S_I) obtained were found to be greater than unity for both PVA and PEG, which indicates that the enhanced inhibition efficiency caused by the addition of halides is only due to synergism. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2889–2894, 2006     

Higher‐order structural analysis of nylon‐66 nanofibers prepared by carbon dioxide laser supersonic drawing and exhibiting near‐equilibrium melting temperature

Extended chains and/or extended chain crystals (ECC) are important structures for improving the mechanical properties of polymer fibers. ECC have so far been produced using specially prepared materials or manufacturing methods. In our study on the production of nanofibers by carbon dioxide (CO₂) laser supersonic drawing, we succeeded in producing nylon‐66 nanofibers having a high melting point near the equilibrium melting point (T_m⁰). Two melting points (T_m) of 260 and 276°C were observed for the nanofibers, with the latter temperature being close to the T_m⁰ (280°C) of nylon‐66. A nanofiber that was heat treated at 279°C for 10 min displayed a large stacked lamellar structure with an average crystal thickness of 140 nm. That value was close to the average molecular chain length of 212 nm, which was calculated from the average molecular weight of the nanofibers. It was inferred from these results that ECC corresponding to the average molecular chain length were present in the nanofibers. The CO₂ laser supersonic drawing process is applicable to general purpose thermoplastic polymers and uses a simple drawing system. It is expected that this drawing method will help to improve the fundamental performance of general purpose polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40361.     

Investigation of melting behaviors and crystallinity of linear polyamide with high‐aliphatic content

The melting behaviors and crystal structures of a long alkyl chain polyamide and nylon 18 18, were investigated under annealing and isothermal crystallization conditions. Nylon 18 18 showed multiple melting peaks in differential scanning calorimetry (DSC) thermograms depending on thermal history of the samples. The origin of the multiple melting peaks may be a result of a melting and recrystallization mechanism during DSC scans. Wide‐angle X‐ray diffraction patterns showed two new diffraction peaks, which appeared at 0.44 and 0.37 nm, and are characteristic peaks of α‐form (triclinic structure) of even–even nylons with increasing annealing temperature. The intensities of these peaks increased, and they split further apart, with elevated annealing temperatures. The solid‐state ¹⁵N CP/MAS NMR spectra of the nylon 18 18 samples that had been quenched and annealed also confirmed the α‐crystalline form. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Conductivity and structure of a polyamide/silver iodide nanocomposite

In this study, the structure and properties of an organic–inorganic composite material prepared from nylon 6 doped with fine particles of silver iodide (AgI) were examined. The preparation of the composite involved the complexation of nylon 6 with polyiodide ions such as I and I by immersion in an iodine/potassium iodide (I₂–KI) aqueous solution followed by reaction in a silver nitrate (AgNO₃) aqueous solution; this resulted in the in situ formation of β-AgI fine particles within the nylon 6 matrix. The AgI content formed in the composite was dependent on the immersion temperatures of the I₂–KI and AgNO₃ solutions. Lower solution temperatures resulted in larger amounts of AgI in the composite. This method readily provided a composite with a high content of AgI in nylon 6 and a conductivity of approximately 10⁻⁵ Ω⁻¹ cm⁻¹. In a uniaxially oriented nylon 6 matrix, AgI particles precipitated with anisotropic shape, which was caused by the orientation of the precursor polyiodide ions. The structure of the oriented composite provided the anisotropic conductivity. Additionally, the composite exhibited high antibacterial properties. The procedure used in this study is considered a unique method for the preparation of organic–inorganic composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of poly(lactic acid) multifilament yarns. I. The structure and thermal behavior

The structure and thermal behavior of poly(lactic acid) (PLA) multifilament yarns were studied by complementary techniques of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide angle X‐ray diffraction (WAXD). As for PLA filaments, notable differences in the WAXD patterns, DSC curves, and FTIR spectra were observed. The combination of the WAXD and FTIR results showed that PLA samples with different crystallinity contain α‐form crystal structure. The FTIR spectra of the filaments were analyzed to study their crystallinity and crystal structure. The total crystallinity of the PLA filaments was obtained from the percent area loss of the skeletal amorphous band at 955 cm^?1. Crystalline fraction from FTIR and DSC were comparable with each other. The C?O stretching region, which is sensitive to crystallization and dipole–dipole interactions, was evaluated to provide information about chain conformers and crystallinity of the samples. Depending on the processing conditions, double melting peaks were observed in the DSC curves of the samples. This exhibited the structural reorganization of the crystal phase during heating affected by heating and cooling rate. In the DSC curves of the nearly amorphous multifilament yarn, the exothermic peak observed right above the glass transition temperature (T_g) indicated two relaxed and deformed amorphous regions. However, the multifilament yarn with higher crystallinity showed just endothermic melting peak after its glass transition. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010