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Nanocomposites comprised of polyamide 6 (PA6) and cellulose nanocrystals (CNC) were prepared by solvent casting and subsequent melt pressing. The role of cellulose nanocrystals on morpholog...

Poly(ethylene naphthalate) (PEN) nanofiber membranes were prepared using hexafluoroisopropanol (HFIP) as a solvent. Crystallization and conformation of PEN nanofibers were characterized for the first time by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. SEM micrographs revealed that the size and uniformity of nanofibers depended on the PEN concentration in HFIP solution. DSC results showed that cold crystallization temperature (Tcc) decreased and the crystallinity of PEN nanofibers increased with increasing the concentration of spinning PEN/HFIP solution. FTIR and Raman spectroscopies showed that PEN nanofibers formed metastable β-crystals during electrospinning due to the fast evaporation of a solvent, while the concentration of spinning solution did not affect the crystal form of as-prepared PEN nanofibers. Upon annealing of PEN nanofiber membranes above 140 °C, metastable β-crystals were transformed into the thermodynamically most stable α-crystals. Our polarized FTIR spectroscopic studies revealed that no molecular orientation was developed when fibers were collected randomly.

Poly(trimethylene terephthalate) (PTT)/silica nanocomposite films were successfully fabricated using a novel sol–gel approach. The synthesis of these nanocomposites is being carried out by hydrolysis and condensation of tetraethoxysilane using trifluoroacetic acid with a small amount of water. The scanning electron microscopy and zetasizer result showed that the silica particles with a size range of 80–100 nm were homogeneously dispersed in the PTT matrix. The effect of different amounts of silica on crystallization of PTT was investigated using X-ray diffraction, differential scanning calorimetry (DSC), and optical microscopy. Polarized light microscopic results revealed that the spherulite size gradually decreased with increasing silica loading and increased with crystallization temperature for a given nanocomposite during isothermal melt crystallization. PTT with a small amount of SiO2 melt crystallized at low temperatures showed banded spherulites. DSC results revealed that nonisothermal cold crystallization temperature decreased with silica content, whereas no significant change in nonisothermal melt crystallization behavior was observed with silica content. The crystallinity of isothermally melt crystallized PTT increased with both crystallization temperature and silica loading.

Poly(trimethylene terephthalate) (PTT)/clay nanocomposite films have been prepared via a novel two-step approach. The resulting nanocomposites have been characterized by Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized light microscopy (PLM). XRD results showed this two-step process of preparation forms predominantly exfoliated structures. The effect of nanoclay on the isothermal and nonisothermal melt crystallization behaviors of PTT has been investigated and shown that the incorporation of clay accelerates the rate of crystallization and increases the total crystallinity of PTT nanocomposites compared to neat PTT. Nonisothermal melt crystallization kinetics of neat PTT and PTT nanocomposites was analyzed using crystallization isotherm. The Avrami analysis modified by Jeziorny was successfully used to describe the non-isothermal crystallization kinetics of neat PTT and PTT nanocomposites, shown by the decrease in half time ( t 1/2 ) of crystallization and increase in rate constant ( Z c ) as organoclay content increased up to 10%. FTIR spectroscopy has been utilized for the first time to monitor conformational changes during the melt crystallization of PTT nanocomposites. It was demonstrated that the amorphous trans conformation transforms into the crystalline gauche conformation with increasing clay content, which suggests that nanoclay accelerates the polymer chain conformational transition from trans to gauche conformation. No significant change in amorphous gauche conformation was observed either with crystallization temperature or clay content.

Poly(trimethylene terephthalate) (PTT) nanocomposites with two different clays were fabricated via a novel two-step process. Structure, morphology, and cold crystallization of these nanocomposites were studied using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). XRD results reveals that PTT-15A nanocomposites were fully exfoliated, whereas PTT-30B nanocomposites were partially exfoliated. Non-isothermal cold crystallization temperature and the crystallinity of non-isothermally cold-crystallized PTT-15A nanocomposites increased with increasing 15A content. The crystallinity of isothermally cold-crystallized PTT-15A nanocomposites was shown to increase with crystallization temperature and the clay content, but no clear trend in crystallinity was observed for PTT-30B nanocomposites. The combination of FTIR and DSC has been used to determine the conformational changes during isothermal cold crystallization. The results show that the crysta...

Sophorolipid (SL) purified from fermentation broth of Candida bombicola grown on oleic acid and glucose substrates was embedded at 0%, 9%, 17%, and 29% (%-total weight of final product) in solvent-cast films of poly(L-lactic acid) (PLLA), poly(e-caprolactone), and poly(hydroxybutyrate) (PHB). Growth-inhibition activity of the SL-biopolymers against Propionibacterium acnes, a causative agent of acne vulgaris skin condition, is dependent on the SL contents of the films; the degree of inhibition as determined from the width of the zone of inhibition in agar-plate assays follows the order of SL-PCL>SL-PLLA>SL-PHB. The release of SL from the films into aqueous medium after a 4-d shaking at 25 °C showed that SL-PLLA (30.1±1.7 wt% SL released) most readily released the embedded SL, followed by SL-PHB (11.4±4.3 wt%) and SL-PCL (4.3±1.4 wt%). Thermal properties as determined by differential scanning calorimetry showed that SL decreases the heat of fusion (ΔH) and the melting temperature (Tm) of the biopolymers, indicating for the first time its usefulness as a plasticizer to prevent crystallization. In summary, the study shows the feasibility of controlling the release of antimicrobial SL by varying the type of biopolymer used, with the added advantage of SL functioning as a plasticizer to improve the physical properties of the film in term of lower crystallinity. Future research could benefit the agricultural sector via new developments as varied as antimicrobial food packaging and algal bloom mitigation.

PHB-U-IC has been prepared for the first time by the cocrystallization method. The structure and conformation of poly(3-hydroxybutyrate) (PHB) chains encapsulated in urea (U) channels formed in the PHB-U inclusion complex (PHB-U-IC) were studied by DSC, FTIR, and solid-state NMR spectroscopy. The XRD pattern and FTIR spectroscopy demonstrated that PHB-U-IC takes a different crystal structure than the well-reported hexagonal and trigonal crystal structures of polymer urea inclusion compounds. PHB-U-IC takes an expanded tetragonal crystal structure. The conformation of PHB in the confined environment has been characterized by solid-state NMR spectroscopy and shown that PHB adopts a conformation similar to bulk PHB. The crystallization and thermal properties of as-received PHB and PHB coalesced from its U-IC were compared and demonstrated that the coalesced PHB crystallizes much slower than as-received PHB. Crystallinity of nonisothermally melt crystallized as-received PHB was found to be significantly highe...

A novel and simple surface modification of cellulose nanocrystals (CNC) was performed by chloroacetylation and subsequent reaction with tertiary amines to form quaternary ammonium modified CNCs. The acetylation of CNC and quaternary ammonium modified CNCs was confirmed using IR spectroscopy and solid state NMR spectroscopy. The 13C NMR spectrum of quaternary ammonium modified CNC showed several additional resonances ranging from 14.5 ppm to 58.0 ppm compared to 13C NMR spectrum of pure CNC, suggesting that alkyl chains have been added to the pure CNC. The disc diffusion method was used to evaluate the antimicrobial properties of quaternary ammonium modified CNCs. It was found that modified CNCs with alkyl chain longer than ten carbons are effective antimicrobial agents against Staphylococcus aureus and E. coli bacteria. These CNCs can be chemically modified to tailor the properties to improve dispersion in the polymer matrix. This will expand the application of CNC as a reinforcing material. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44789.

Poly(3-hydroxybutyrate) (PHB) is a microbially synthesized polymer, which is often purified by alkaline treatment. The effect of microstructure on alkaline hydrolysis has been studied by varying concentration of base and the temperature. The morphologies of PHB films before and after degradation were evaluated using DSC and FTIR spectroscopy. The hydrolytic degradation study by weight loss measurement revealed that the crystallinity of PHB greatly decreased the hydrolytic ability of PHB. The crystallization of PHB and the effect of base on hydrolysis was investigated by time dependent FTIR spectroscopy. The normalized absorbance of 3010cm-1 and 1183cm-1 were used to characterize the crystalline and the amorphous phases of PHB. FTIR spectroscopy reveal that the extent of hydrolysis decreased with increasing crystallinity. The crotonic acid was detected as a major product after hydrolysis, confirmed by UV/Visible and proton NMR spectroscopy. The normalized absorbance of the crystalline band at 3010cm-1 band remained constant, suggesting that there is no significant change in crystallinity with degradation. The normalized amorphous band at 1183cm-1 showed a decrease in absorbance ratio, suggesting degradation of the amorphous phase. Our data suggests that alkaline hydrolysis depends on concentration of base and the crystallinity of PHB.

Polyamide 6/SiO2 (PA6/SiO2) nanocomposites with varying amounts of SiO2 were prepared by using a novel sol-gel technique. These nanocomposites were formed in situ by hydrolysis and through the condensation of tetraethoxysilane (TEOS) using formic acid with a small amount of water as the solvent for PA6. Observations of TGA showed that the thermal stability of PA6 nanocomposite was significantly improved compared to that of neat PA6. Microstructure development during the thermally induced crystallization of PA6/SiO2 nanocomposites was investigated with a combination of differential scanning calorimetry (DSC), FTIR spectroscopy, scanning electron microscopy (SEM), and AFM. FTIR spectroscopy was used to determine the crystal form of these nanocomposites, and it was concluded that SiO2 nanoparticles have the γ-nucleating effect. The crystallinity of nanocomposites decreased with increasing TEOS loading as compared to that for neat PA6. SEM showed a very fine dispersion of nanoscale silica whereas SEM and Zetasizer proved the silica particle size was about 100-200 nm. The isothermal crystallization kinetics of these nanocomposites with increasing SiO2 content were investigated, and it was shown that the amount of SiO2 plays a significant role in crystallization kinetics.

The effect of molecular orientation on cold crystallization of amorphous crystallizable polymers was examined using poly(trimethylene terephthalate) (PTT) films drawn to different draw ratios and strain rates. A combination of differential scanning calorimetry (DSC) and polarized Fourier transform infrared (FTIR) spectroscopy was employed to examine structural evolution and nonisothermal crystallization kinetics. The cold crystallization temperature (Tc), cold crystallization exotherm (ΔHc), and subsequent melting temperature (Tm) were carefully correlated to the overall molecular orientation. For the first time, the overall molecular orientation was shown to have an inverse relationship to the cold crystallization temperature, as well as the cold crystallization exotherm. Nonisothermal cold crystallization has not occurred when the overall orientation exceeded the critical value of 0.43. The kinetics of nonisothermal cold crystallization of PTT with a different overall molecular orientation has been inve...

The structure development during the drawing of PTT films immediately above the glass transition temperature at two different strain rates (8.33 × 10–3 and 8.33 × 10–4 s–1) has been investigated us...

Poly(amidoamine) (PAMAM) (G3) dendrimer was modified into quaternary ammonium salts using tertiary amines with different chain lengths: dimethyldodecyl amine, dimethylhexyl amine, and dimethylbutyl amine using an efficient synthetic route. The antimicrobial activity of these dendrimer ammonium salts against Staphylococcus and Escherichia coli bacteria was examined using the disc diffusion method. It was found that quaternary ammonium salt prepared with the dimethyldodecyl amine exhibits antimicrobial efficacy against Staphylococcus and E. coli bacteria.

Poly(lactic acid) (PLLA) melt-pressed films with low crystallinity were crystallized by stretching at a constant strain rate. The strain-induced crystallization and enzymatic degradation of drawn PLLA films in the presence of proteinase K at 37 °C was investigated using weight loss measurements, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The results show that drawing has a significant effect on the crystallinity, molecular orientation, and enzymatic degradation. The absorbance ratio of the bands at 921 and 956 cm–1 (A921/A956) was chosen to determine the structural changes during strain-induced crystallization and hydrolysis. The DSC crystallinity and A921/A956 showed an increase with the draw ratio. Since we were unable to obtain the transition moment angle for the bands at 921 and 956 cm–1, the dichroic ratios were compared. It was found that the crystalline orientation develops rapidly at lower draw ratios whereas the amorphous orientation develops much...

Poly(L-lactic acid) (PLLA) films with different crystallinities were prepared by solvent casting and subsequently annealed at various temperatures (Ta) (80–110°C). The effects of crystallinity on enzymatic degradation of PLLA films were examined in the presence of proteinase K at 37°C by means of weight loss, DSC, FTIR spectroscopy, and optical microscopy. DSC and the absorbance ratio of 921 and 956 cm−1 (A921/A956) were used to evaluate crystallinity changes during thermally induced crystallization and enzymatic hydrolysis. The highest percentage of weight loss was observed for the film with the lowest initial crystallinity and the lowest percentage of weight loss was observed for the film with highest crystallinity. FTIR investigation of degraded films showed a band at 922 cm−1 and no band at 908 cm−1 suggested that all degraded samples form α crystals. The rate of degradation was found to depend on the initial crystallinity of PLLA film and shown that enzymatic degradation kinetics followed first-order kinetics for a given enzyme concentration. DSC crystallinity and IR absorbance ratio, A921/A956 ratio, showed no significant changes with degradation time for annealed PLLA films whereas as-cast PLLA film showed an increase in crystallinity with degradation; this revealed that degradation takes place predominantly in the free amorphous region of annealed PLLA films without changing long range and short range order © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Polymer science represents an important area in industrial and research laboratories for chemists and material scientists. However, experiments involving polymers are uncommon in chemistry and material science curricula; therefore, an experiment involving polymers has been developed. This experiment has been used to teach fabrication of polymer films and to investigate the structure–property relationships of polymers using a multi-instrumental approach. It also introduces principles of Fourier transform infrared spectroscopy (FTIR) and how it can be utilized for polymer characterization. This experiment has been introduced successfully in a graduate-level instrumental analysis course in the chemistry department, but is also appropriate for an upper-level undergraduate course. It is simple to conduct in a teaching laboratory and utilizes commonly used instrumentation. Students gain hands-on experience in using multiple instruments. The experiment is designed to be completed in two to three weeks.

Poly(L-lactic acid) (PLLA) intercalated nanocomposite films containing 1, 2, 5, and 10% organically modified montmorillonite (OMMT) have been synthesized by the solvent casting approach. The thermal characteristics, isothermal cold crystallization kinetics, and structural changes of neat PLLA and its nanocomposites during annealing were studied by using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. DSC observation showed that melting temperature and final crystallinity were not affected significantly with OMMT loading. PLLA films with increasing OMMT content exhibited higher crystallization rates than neat PLLA during annealing and suggested that the silicate platelets act as a nucleation agent during annealing. The effect of OMMT content on the isothermal crystallization kinetics of PLLA was analyzed using the Avrami equation. An Avrami constant of 1-2 was observed, suggesting that crystallization proceeds through one-dimensional growth with heterogeneous nucleation. FTIR investigation showed a band at 922 cm(-1) at all T(a), and no band at 908 cm(-1) suggested that all samples form α crystal regardless of OMMT content or T(a).

Dendrimers have been used as a vehicle to develop the antimicrobial properties of textile fabrics. We have taken advantage of the large number of functional groups present in the regular and highly branched three-dimensional architecture of dendrimers. In this study, the poly(amidoamine) (PAMAM) G-3 dendrimer was modified to provide antimicrobial properties. Following a procedure similar to what is suggested in the literature, PAMAM (G3) with primary amine end groups was converted into ammonium functionalities. The modification was then confirmed by FTIR and 13 C-NMR analysis. Dendrimers have unique properties owing to their globular shape and tunable cavities, this allows them to form complexes with a variety of ions and compounds; and also act as a template to fabricate metal nanoparticles. AgNO 3 -PAMAM (G3) complex as well as a MesoSilver-PAMAM (G3) complex were formed and these modified dendrimers were characterized by a UV-Visible spectrophotometer to study the complex formation. Modified dendrimers were applied to the Cotton/Nylon blend fabric. SEM and EDX analysis were performed to study the dispersion of silver nanoparticles onto the fabric. An antimicrobial test of the treated-fabric against Staphylococcus aureus exhibited significant biocidal activities for each type of modified-dendrimer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 716-722, 2010.

The effects of crystallinity and temperature on enzymatic degradation of poly-e-caprolactone (PCL) films and structural changes after degradation have been studied using weight loss, differential scanning calorimetry, and optical microscopy. The weight loss during the enzymatic degradation of PCL suggested that the extent of biodegradation and the rate of degradation strongly depend on the initial crystallinity. PCL films of lower crystallinity (24%) degraded much faster than films of higher crystallinity (45%). The crystallinity of low-crystalline PCL films increased with increasing degradation time, whereas the crystallinity of high-crystalline PCL films decreased with time. The spherulite size increased with increasing degradation time for low-crystalline samples but decreased with time for high-crystalline samples. These results revealed that degradation occurs first in the amorphous region where the degradation rate is much higher, and the crystalline region of the PCL film started to degrade simultaneously for those PCL with higher crystallinity. The enzymatic degradation of PCL proceeded from the free amorphous to restricted amorphous followed by lamellar edges, where PCL chains have higher mobility irrespective of hydrolysis temperature. Caproic acid was identified as the primary product formed after degradation and confirmed by proton nuclear magnetic resonance spectroscopy, suggesting that degradation occurs through the depolymerization mechanism. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 202–211, 2010

Structural changes during thermally induced crystallization and alkaline hydrolysis of Poly( l -lactic acid) (PLLA) films were investigated using differential scanning calorimetry (DSC), FTIR spectroscopy, weight loss, HPLC and optical microscopy. It was shown that crystallinity ( χ c ), glass transition temperature ( T g ) and melting temperature ( T m ) were found to be strongly annealing temperature ( T a ) dependent. The FTIR study of PLLA films suggested that the bands at 921 and 956 cm −1 could be used to monitor the structural changes of PLLA. An independent infrared spectroscopic method was developed for the first time to determine crystallinity of PLLA before degradation and it showed good qualitative correlation with DSC crystallinity. The higher crystallinity values determined by FTIR were attributed to the intermediate phase included in the IR crystallinity. Both the weight loss data and the percentage of lactic acid obtained by HPLC showed that the alkaline hydrolysis of PLLA films increased with increasing crystallinity. The DSC observation showed an increase in T g and no significant change in T m and heat of fusion, while IR showed an increase in IR crystallinity with increasing hydrolysis time. The increase in IR crystallinity and T g with hydrolysis time suggested that degradation progressed from the edges of the crystalline lamellas without decreasing lamellar thickness, but increased the intermediate phase and the short-range order.

Polyamide 66 fibers were thermoset in a torsion-bending deformation at various temperatures up to 240 °C. Some of the fibers were heat-set at constant length prior to the deformation at presetting temperatures of 150 °C and 200 °C to vary the structural state of the starting material. Fractional recovery was measured after various combinations of temperature and time. It was found that heat setting of PA66 is dominated by time-dependent stress relaxation exhibiting time-temperature equivalence. Increased crystallinity, and/or other molecular rearrangements occurring during presetting, impose additional constraints on molecular mobility, which delay onset of the flow regime and increase the time constant of relaxation at a given temperature. The thermosetting characteristics of PA66 fibers are very similar to those of poly(ethylene terephthalate) fibers. For both polymers, superposing the curves of fractional recovery vs. setting time at different temperatures produce satisfactory master curves, without the need for vertical shifting of the data. Arrhenius plots yield approximate activation energies for the thermosetting flow process of 35–65 kcal/mol in PA66 and 95–115 kcal/mol in PET.

A nylon 6,6 complex with GaCl 3 in nitromethane (4–5 wt% nylon 6,6) was prepared at 50–70 °C over 24 h for the purpose of disrupting the interchain hydrogen bonding between nylon 6,6 chains, resulting in amorphous nylon 6,6, and increasing the draw ratio for improving the performance of nylon 6,6 fibers. After drawing, complexed films and fibers were soaked in water to remove GaCl 3 and regenerate pure nylon 6,6 films and fibers. FTIR, SEM, DSC, TGA, and mechanical properties were used for characterization of the regenerated nylon 6,6 films and fibers. The amorphous complexed nylon 6,6 can be stretched to high draw ratios at low strain rates, due to the absence of hydrogen bonding and crystallinity in these complexed samples. Draw ratios of 7–13 can be achieved for complexed fibers, under low strain rate stretching. This study indicates that nylon 6,6 fibers made from the GaCl 3 complexed state, using a high molecular weight polymer, can reach initial moduli up to 13 GPa, compared to initial moduli of 6 GPa for commercial nylon 6,6 fibers. Lewis acid–base complexation of polyamides provides a way to temporarily suppress hydrogen bonding, potentially increasing orientation while drawing, and following regeneration of hydrogen bonding in the drawn state, to impart higher performance to their fibers.

The structure and dynamics of PEO chains encapsulated in thiourea (TU) channels formed in the PEO–TU-inclusion compound (PEO–TU-IC) were studied by XRD, FTIR and solid state NMR spectroscopy. XRD and FTIR observations clearly show PEO–TU-IC adopts a crystal structure different from neat thiourea, and the usual rhombohedral crystal structure of thiourea small molecule ICs. PEO chains in the channel adopt a conformation similar to bulk PEO, as confirmed by solid state NMR spectroscopy. Contact-time array (VCT) NMR profiles shows that PEO chains in the TU channels are considerably more mobile than in bulk PEO. Infrared bands for the PEO shift in the IC, and these were attributed to changes in the secondary forces.

Conformational changes occurring during thermally-induced crystallization of poly(trimethylene terephthalate) (PTT) by annealing have been studied using density measurement, differential scanning calorimetry (DSC), and mid-infrared spectroscopy (MIR). Infrared spectra of amorphous and semicrystalline PTT were obtained, and digital subtraction of the amorphous contribution from the semicrystalline PTT spectra provided characteristic MIR spectra of amorphous and crystalline PTT. The normalized absorbance of 1577, 1173, and 976 cm -1 were plotted against the crystallinity showing that these bands can be used unambiguously to represent the trans conformation while the band at 1358 cm -1 can be used to represent gauche conformation of methylene segment. The presence of a weak band at 1358 cm -1 in the amorphous spectrum suggested that a small amount of gauche conformation is present in the amorphous phase. Infrared spectroscopy has been used for the first time as a means to estimate the trans and gauche conformations of methylene segments in PTT as a function of T a . The amount of gauche conformation was plotted against the crystalline fraction and the extrapolation of this plot to zero crystalline fraction provided a value of 0.07, suggested that the pure amorphous phase consist of ∼ 7% gauche conformation. It was found that the amorphous and crystalline gauche conformation increases at the expense of amorphous trans conformation during thermally induced crystallization of PTT.

Crystallization of poly(trimethylene terephthalate) (PTT) by annealing was examined using density measurement, differential scanning calorimetry, and far-infrared spectroscopy (FIR). Crystallinity, measured by density, increased slowly up to the T a of 185 °C and increases rapidly once T a exceeds 185 ° C. It was found that thermally induced crystallization is mainly temperature-dependent above T a = 185 °C and temperature-and time-dependent below T a = 60 °C. Two melting transitions, T 1 m and T 2 m , were observed for those samples annealed above 120 °C. No significant change in T 1 m was observed as a function of T a while T 2 m showed strong dependency on T a . Digital subtraction of the amorphous contribution from the semicrystalline FIR spectra provided characteristic spectra of amorphous and crystalline PTT. The bands at 373, 282, and 92 cm -1 were assigned to the crystalline phase, while the bands at 525, 406, and 351 cm -1 were attributed to the amorphous phase. It was shown that FIR spectroscopy can be used as a means to estimate the degree of crystallinity of PTT. The band ratio of 373 and 501 cm - 1 was plotted against crystallinity measured by density and reasonably good correlation was obtained.

The morphology, mechanical properties, and dye diffusion of drawn and heat-set polyamide-6 (PA6) yarns were examined. Correlations between the microstructure of PA6 yarns and the dye diffusion coefficients and mechanical properties were established. The crystallinity of PA6 yarns was estimated with density and Fourier transform infrared spectroscopy measurements. A decrease in the γ crystallinity and an increase in the γ-crystallite size with the draw ratio were observed and attributed to the disappearance of small crystallites and an increase in the average γ-crystallite size population during the deformation process. The scouring treatment increased the total crystallinity, almost entirely as a result of an increase in the α fraction. Thermally induced crystallization involved increases in both crystalline phases (α and γ) and did not involve crystal-to-crystal transformation, whereas drawing PA6 yarns involved both crystallization of the amorphous phase in the α form and γ→α transformation. A sharp decrease in the diffusion coefficient with an increasing draw ratio of PA6 yarns was correlated with an increasing amorphous orientation. The influence of thermally induced crystallinity on the diffusion coefficient seemed exceptionally strong. The mechanical properties of PA6 yarns were examined and correlated with structural changes. It was demonstrated that the crystallinity had a direct correlation with the terminal modulus and extension at break, whereas there was no correlation with the initial modulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 349–357, 2007

Poly(L-lactic acid) (PLA) filaments were spun by melt-spinning at 500 and 1850 mm−1, and further drawn and heat-set to modify the morphology of these PLA filaments. PLA yarns were characterized by wide-angle X-ray diffraction (WAXD) and sonic method. WAXD reveals that PLA yarns spun at 500 mm−1 are almost amorphous while the PLA filaments spun at 1850 mm−1 have about 6% crystallinity. This is different from PET filaments spun at the same speed that have almost no crystallinity. Both drawn- and heat-set PLA filaments showed much higher crystallinity (60%) than do as-spun fibers produced at 500 and 1850 mm−1 speed, which is also higher than the usual heat-set PET yarns. It appears that crystalline orientation rapidly reaches a value in the order of 0.95 at 1850 mm−1 and that drawn- and heat-set yarns have almost the same crystalline orientation values. Molecular orientation is relatively low for as-spun PLA yarn, and molecular orientation increased to ∼0.5 after drawing or heat–setting or both. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1210–1216, 2006

Super high modulus polyethylene fibers can be created by converting high molecular weight flexible PE chains into highly oriented and extended chain conformations. However, unlike polyethylene, aliphatic polyamides have very high cohesive energy and therefore cannot be easily drawn and highly oriented. This review addresses this fundamental problem by analyzing various novel approaches that can be used to suppress hydrogen bonding in these types of polyamides. Plasticization of such polymers with ammonia, iodine, salts, and Lewis acids, as well as dry spinning, wet spinning, and gel spinning, are discussed. Specialized techniques that involve vibrational zone drawing and annealing as well as laser heating zone drawing and annealing are also reviewed. Some of these methods definitely lead to remarkable improvements in initial modulus and other mechanical properties. The development of recombinant spider silk proteins as well progress in spinning these materials is also reported. The advantages and disadvan...

In this study, PA 66 and PA 6 fibers are heat set at temperatures between 25 and 200°C. Fractional recovery ( f) depends on heat setting temperatures and crystallinity, which provides partial crosslinking that delays the onset of the flow regime and increases the time constant of relaxation at a given temperature. Mechanical properties are examined with an Instron tensile tester, and the effect of heat setting temperatures on mechanical properties is correlated with crystallinity changes. The terminal modulus and extension at break show a direct correlation with crystallinity, while there is no noticeable effect on initial modulus with crystallinity changes.

Polyamide 66 (PA66) has been complexed with the Lewis acid GaCl 3 for the purpose of disrupting the interchain hydrogen bonded network. FTIR and 13 C-NMR observations indicate that Ga metal cations form a 1:1 complex with the carbonyl oxygens of the PA66 amide groups. PA66–GaCl 3 films are amorphous and rubbery with a single relaxation, attributable to the glass transition temperature, at ∼−32 °C and a structure that appears by X-ray diffraction to be thermally stable to at least 200 °C. The complexed films could be drawn at room temperature to draw ratios (DR) up to ∼30, and could then be decomplexed, or regenerated, by soaking in water. GaCl 3 complexation and subsequent regeneration of PA66 was accomplished without changing its molecular weight, and all but ∼5 mol% of the amide groups in the regenerated PA66 were uncomplexed. The undrawn regenerated films regain levels of crystallinity much lower than possessed by the uncomplexed PA66 reference film. However, up to a DR of 8, drawing prior to regeneration increases the crystallinity, reaching crystallinity levels that are high for PA66, that has not been heat treated, and that are almost twice higher than in the uncomplexed (undrawn) reference film. It is intriguing that, in this DR regime, crystallinity increases quite sharply as the film is extended, despite the fact that molecular orientation does not appear to be increasing. For DR>8, the crystallinity decreases, but remains above that of the reference film. The level of crystallinity in PA66 can be controlled over a much wider range by the complexation-drawing-regeneration process than by conventional drawing processes.

Drawn polyamide 6 (PA6) fibers were characterized with X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, density measurement, and optical microscopy. The α and amorphous orientation functions were determined by polarized FTIR spectroscopy. It was demonstrated for the first time that the infrared band at 1124 cm−1 could be used to determine the amorphous orientation functions of drawn PA6 fibers and films. α, γ, and amorphous orientation functions increased rapidly at lower draw ratios and increased slowly at higher draw ratios. The amorphous orientation functions measured by polarized FTIR spectroscopy did not agree with those determined by a combination of wide-angle X-ray diffraction (WAXD) and optical birefringence measurements, attributed to possible error in the estimated birefringence. The α and γ crystallinity of undrawn fiber (DR = 1) were ∼24 and 6%, respectively, which increased to ∼13 and 39% at a draw ratio of 4 (DR = 4). The WAXD data suggested that γ crystal grew in the hydrogen-bonding direction as well as the van der Waals direction during deformation. The decrease in γ crystallinity and increase in γ crystallite size with the draw ratio were attributed to the disappearance of small crystallites and an increase in the average γ crystallite size population during the deformation process. The increase in density with the draw ratio was attributed to crystal-to-crystal transformation as well as strain-induced crystallization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2870–2877, 2003

The influence of molecular orientation on the “memory effect” of polyamides was investigated by differential scanning calorimetry. Melt crystallization of undrawn and drawn polyamide 6 (N6) and polyamide 66 (N66) fibers showed no difference either in the rate of crystallization or crystallization temperature. We demonstrated that hydrogen bonding does not play a major role in melt crystallization kinetics of polyamides (N6 and N66), and the “memory effect” is only retained for polymers, including N6 and N66, because of insufficient time spent above the melting temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 772–775, 2003

Our previous work showed that drawing polyamide 66 (PA 66) fibers at room temperature does not change the degree of crystallinity, but only increases the molecular orientation. We therefore have used a series PA 66 fibers with different draw ratios to establish a direct correlation between (noncrystalline) molecular orientation fa and the dye diffusion coefficient D. For both acid and disperse dyes, the relationship log D ∝ f provides reasonable fits to the data for PA 66 fibers, and a similar relationship appears to be applicable to PA 6 fibers. Heat-setting the fibers results in a continuous decrease in diffusion coefficient; unlike PA6 and PET fibers, no minimum in D was found in the region of 160°C. If this decrease in D is attributed to the increase in volume fraction crystallinity X taking place during heat-setting, it must be deduced that log D ∝ X6. This dependence is surprisingly strong, but is consistent with observations we have made on PET and PA6 fibers. It is possible that some other structural rearrangement is partially or largely responsible for the decrease in diffusion coefficient, but Fourier transform infrared, density, and X-ray diffraction measurements do not indicate any other structural changes taking place. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3803–3807, 2003

Structure development during drawing was studied for three sets of polyamide-66 (PA66) fibers with density, optical microscopy, wide-angle X-ray diffraction, and Fourier transform infrared spectroscopy. The crystallinity, estimated by density measurements, remained virtually constant with increasing draw ratios, indicating that stress-induced crystallization did not occur for the PA66 fibers drawn at room temperature, but there was a rapid transformation from a hedrite morphology to a fibrillar one. The absence of stress-induced crystallization differed from the behavior of polyamide-6, and this was attributed to the stronger hydrogen bonding between polyamide chains and the higher glass-transition temperature of PA66. Polarized infrared spectroscopy was used to measure the transition-moment angles of the vibrations at 936 and 906 cm -1 , which were found to be 48 and 60°, respectively. The crystalline orientation was estimated from the band at 936 cm -1 , and the increase with an increasing draw ratio was in close quantitative agreement with X-ray diffraction data; this showed that infrared spectroscopy could be used reliably to measure the crystalline orientation of PA66 fibers. Because we were unable to obtain the transition-moment angle of the amorphous bands, the amorphous orientation was obtained with Stein's equation. The amorphous orientation developed more slowly than the crystalline orientation, which is typical behavior for flexible-chain polymers.

First, we report the development of Fourier transform infrared (FTIR) spectroscopic methods to determine the α/γ-crystalline phase ratio of polyamide-6 fibers and, in combination with density measurements, the total crystallinity. Using density determinations of the crystallinity of pure α and pure γ samples, we found the absorption coefficient ratio for the 930 (α) and 973 cm−1 (γ) bands to be 4.4, from which we could obtain the α/γ ratio for any polyamide-6 sample. The application of this FTIR method to the quantitative analysis of phase changes during thermal treatment and the drawing of polyamide-6 was then made. We confirmed that crystallization during thermal treatments involved increases in both phases and did not involve crystal-to-crystal transformation, whereas drawing involved both crystallization of the amorphous phase in the α form and γ→α transformation. Finally, we revisited the band assignments for the amorphous phase of polyamide-6 and found that the band at 1170 cm−1 was not an amorphous band but, because its absorbance was independent of crystallinity, could be used as an internal reference band. The band at 1124 cm−1 was reliably attributed to the amorphous phase. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 536–547, 2001

Structural changes that occur during thermally induced and strain induced crystallization of polyamide 66 fibers were studied by infrared spectroscopy, density measurement and optical microscopy. Two bands at 924 and 1136 cm–1 were shown to arise from the amorphous phase and assignment of the bands at 936 and 1200 cm–1 to the crystalline phase were confirmed. We demonstrated that two different infrared spectroscopic methods could be used to determine the total crystallinity of polyamide 66 fibers. One is a calibration method in which the band ratio of 1200 and 1630 cm–1 is plotted against the crystallinity measured by density measurements. The other one is an independent infrared method. Crystallinity obtained by the independent infrared spectroscopic method showed good agreement with crystallinity observed by density measurement. Infrared dichroism was used to obtain the crystalline orientation using the band at 936 cm–1. The transition moment angle of 48° was found for the band at 936 cm–1 with respect to chain axis. Amorphous orientation was obtained using Stein’s equation.

Having found much ambiguity in the infrared band assignments for polyamide 66 (PA66), we revisited some of these assignments before using infrared spectroscopy to assess microstructure changes resulting from multiple thermal treatments. We discovered that earlier assignments of the 1144 and 1180 cm -1 bands to the amorphous (noncrystalline) phase were incorrect, whereas the bands at 924 and 1136 cm -1 can be attributed unambiguously to the noncrystalline phase. We also confirmed that PA66 bands at 936 and 1200 cm -1 are crystalline bands. The normalized absorbance of the 1224-cm 1 fold band increases in proportion to crystallinity, indicating that chain folding is the predominant mechanism of thermal crystallization in PA66. We demonstrated that infrared spectroscopy can be used to estimate the degree of crystallinity of PA66, and two methods were explored. One is a calibration method in which the band ratio of 1200 and 1630 cm -1 is plotted against crystallinity measured by density. The other is an independent infrared method based on the assumption that PA66 satisfies a two-phase structure model. The crystallinity determined by the independent infrared method showed good agreement with the crystallinity obtained from density measurements.

X-ray diffraction analysis demonstrated that a PEN film annealed from 160 to 260 °C crystallizes in the α crystal form while crystallization of PEN directly from the melt results in the β crystal form when Tc > 200 °C and in the α form at lower Tc. Infrared spectra from PEN samples containing α, β, and amorphous phases were obtained, and digital subtraction of the amorphous contribution from the semicrystalline spectra provided characteristic spectra of amorphous, α, and β crystalline spectra. The bands at 1004, 1332, and 814 cm-1 were attributed to the all-trans conformation in the α crystalline phase, and the bands at 975 and 1348 cm-1 were attributed to the β crystalline phase. Our infrared spectroscopic investigation suggests that the α crystal form adopts an all-trans conformation while the β crystal form adopts a conformation with appreciable gauche character. Conformational changes occurring in PEN not only are due to the rotation of the ethylene glycol unit but also arise from the rotation of the ...

We report the formation of crystalline inclusion compounds (ICs) between the small-molecule host urea (U) and two block copolymer guests: (i) poly(e-caprolactone)−polybutadiene (PCL−PBD) and (ii) ...

Inclusion compounds (ICs) can be formed between small-molecule hosts and guest polymers, where the crystalline host lattice confines the guest polymers to occupy narrow cylindrical channels. The included polymers are highly extended by the narrow channel diameters and are separated from neighboring polymer chains by the walls of the small-molecule host lattice. It is possible to coalesce the polymer chains from their ICs by exposure to a solvent for the small-molecule host which is not a solvent for the included polymer chains. When crystallizable polymers are coalesced from their ICs by solvent treatment, they are observed to crystallize in an extended-chain morphology accompanied by much less chain-folding than occurs when crystallization of the same polymers take place from their disordered melt or solution environments. In this report we outline our initial efforts to create polymer-polymer molecular composites based on the coalescence of polymer chains from their IC crystals with urea, which were previously embedded in a carrier polymer phase. Both film and fiber composites made with chemically identical or distinct IC-included and carrier polymers are described. Water vapor permeation, differential scanning calorimetry (DSC) and microscopic observations are used to probe these composites; and several applications are suggested. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 281–287, 1997

Isotactic (i) and syndiotactic (s) polypropylenes (PP) have been successfully incorporated into the channels of their inclusion compounds (IC) with urea (U). The IC's were obtained by cocrystallization following the addition of a warm toluene solution of polymer to a warm solution of urea in methanol. The white crystalline precipitates formed upon cooling were filtered and analyzed using X-ray diffraction, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) and 13C NMR spectroscopies. The results were compared with the components (urea and polypropylene) in their pure crystalline forms, the known hexagonal poly(e-caprolactone)−urea IC, and the known trigonal poly(ethylene oxide)−urea IC. X-ray diffraction data indicated that no free polymer was present in either sample, while FTIR showed that the i-PP−U and s-PP−U IC's were not the hexagonal and trigonal structures commonly observed. Instead the structure appears similar to a “large tetragonal” structure observed for the poly(et...

X-ray diffraction and FTIR and 13C NMR spectroscopies have been utilized to observe the inclusion compounds (ICs) formed by poly(ethylene oxide) (PEO) and low molecular weight poly(ethylene glycol) (PEG) oligomer with urea (U). We have confirmed that PEO-U-IC formed from solution has a trigonal crystal structure, while recrystallization from the melt produces a hexagonal PEO-U-IC. PEG-U-IC apparently adopts a crystal structure different from the trigonal and hexagonal forms of PEO-U-IC, and single crystals of PEG-U-IC are currently under investigation by X-ray diffraction. The conformations of PEO and PEG chains in their U-ICs appear similar to the TGT bulk crystalline conformation, while the all-trans conformer does not appear to be consistent with either the FTIR or the 13C NMR observations. For solution-formed PEO-U-IC in the trigonal crystal structure, where one-third of the urea molecules are hydrogen-bonded to the PEO chains and reside in the channels, the mobility of the included PEO chains is simi...

Combination of differential scanning calorimetry, x-ray diffraction, Fourier transform infrared, and C-13 nuclear magnetic resonance observations made on the crystalline inclusion compound (IC) formed between polytetrahydrofuran (PTHF) and urea (U), together with their comparison to identical observations performed on bulk semicrystalline samples of PTHF, have permitted an analysis of the conformations, motions, and environments available to PTHF chains in both solid-state phases. The isolated PTHF chains occupying the narrow channels of the PTHF-U-IC are highly extended, though small rotational deviations averaging 24° from the nearly all trans, planar zig zag conformation of bulk crystalline PTHF chains produce some significant differences in their behaviors. PTHF chains in PTHF-U-IC possess much greater mobility than bulk crystalline PTHF chains as evidenced by C-13 spin lattice relaxation times, T1, 50 times shorter (1.5 s) than observed for bulk crystalline PTHF chains (75 s). FTIR observations are consistent with very little specific interaction between guest PTHF chains and host urea matrix molecules and result in similar spectra for bulk and IC PTHF, except for the presence of the CH2 rocking vibration band at 745 cm−1 observed for bulk PTHF. The absence of this band in the IC PTHF can be understood by considering the symmetry of the all trans, planar zig zag conformation of bulk crystalline PTHF chains, which prevents the CH2 rocking mode from coupling with skeletal stretching and bending modes as occurs in the nonplanar, helical PTHF chains in PTHF-U-IC. © 1995 John Wiley & Sons, Inc.

We have successfully incorporated poly(L-lactic acid) (PLLA) into the narrow channels of its inclusion compound (IC) with urea (U). PLLA-U-IC was obtained by cocrystallization following the addition of a warm, saturated solution of urea in methanol to a warm, dilute chloroform solution of PLLA. DSC revealed that PLLA-U-IC melted at 131°C with an approximate enthalpy of 41 cal/g. Wide-angle X-ray diffractograms of PLLA-U-IC powders and FTIR spectra of their KBr pellets both strongly point to the formation of a hexagonal PLLA-U-IC structure very similar to that observed for the U-IC's formed with n-alkanes and polyethylene

Several small-molecule hosts form clathrates or inclusion compounds (ICs) with polymers. In these polymer-ICs the guest polymer chains are confined to occupy narrow channels in the crystalline matrix formed by the host. The walls of the IC channels are formed entirely from the molecules of the host, and they serve to create a unique solid-state environment for the included polymer chains. Each polymer chain included in the narrow, cylindrical IC channels (ca 5.5 A in diameter) is highly extended and also separated by the host matrix channel walls from neighboring polymer chains. The net result is a solid-state environment where extended, stretched (as a consequence of being squeezed) polymer chains reside in isolation from their neighbors inside the narrow channels of the crystalline matrix provided by the small-molecule host. Comparison of the behavior of isolated, stretched polymer chains in their crystalline ICs with observations made on ordered, bulk samples of the same polymer are beginning to provide some measure of the contributions made by the intrinsic nature of a confined polymer chain and the pervasive, cooperative, interchain interactions which can complicate the behavior of bulk polymer samples. Just as dilute polymer solutions at the θ temperature have been effectively used to model disordered, bulk polymer phases (both glasses and melts), polymer-ICs may be utilized to increase our understanding of the behavior of polymer chains in their ordered, bulk phases as found in crystalline and liquid-crystalline samples. Solid-state NMR observations of polymer-ICs can provide detailed conformational and motional information concerning the included, stretched and isolated polymer chains.

The melt crystallization of three epoxidized trans-1,4-polyisoprene was studied using DSC. The dependence of melting temperature on the amount of epoxidation and the crystallization temperature is discussed

The behavior of isolate poly(E-capro actone) (PEC) chains confined to the narrow channe l of their crystalline inclusion compound (IC) with urea is contrasted with the behavior of PEC chains observed in but, semicrystalline samples. DSC observations of bulk and IC-recovered PEC samples revealed that PEC recovered from PEC-U-IC via extraction with a nonsolvent for PEC produces crystals that melt 6°C higher than PEC samples recrystallized from solution or the melt. Presumably an extended chain morphology results when PEC crystals are obtained from the collapse of PEC-U-IC

Copolymers of trans-1,4-polyisoprene containing 2,2 mol-%, 5,0 mol-% and 9,8 mol-% epoxidized units were crystallized from the melt at temperatures (Tc) of 25 to 36°C. The progress of the crystallization was monitored, and final crystallinities at Tc and after cooling to 25°C were measured using Fourier-transform infrared spectroscopy. The morphology of samples, treated with OsO4 at 25°C after crystallization was complete, was observed using scanning electron microscopy. The crystallinity decreases linearly with increasing epoxy content at Tc = 25°C and 30°C and shows marked deviations from linearity at Tc = 36°C. Differences in morphology with epoxy content and Tc were observed. The differences in crystallinity between solution and melt crystallized samples are discussed.