Co-reporter:Anusha Krishnama and Nadarajah Vasanthan
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 33) pp:8183-8192
Publication Date(Web):August 11, 2015
DOI:10.1021/acs.iecr.5b01913
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 crystalline gauche and amorphous gauche conformations increased and the amorphous trans conformation decreased with crystallization temperature and clay content for PTT-15A nanocomposites, whereas no trend was observed for PTT-30B nanocomposites.
Co-reporter:Lawrence Smith, Nadarajah Vasanthan
Thermochimica Acta 2015 Volume 617() pp:152-162
Publication Date(Web):10 October 2015
DOI:10.1016/j.tca.2015.08.035
•PTT/clay exfoliated nanocomposites films were prepared by novel two-step approach.•It has been shown that the incorporation of clay accelerates the rate of crystallization and increases the total crystallinity of PTT nanocomposites compared to neat PTT.•FTIR results showed that the amorphous trans conformation transforms into the crystalline gauche conformation with increasing clay content and crystallization temperature.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 (t1/2) of crystallization and increase in rate constant (Zc) 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.
Co-reporter:Pavithran Ravindran and Nadarajah Vasanthan
Macromolecules 2015 Volume 48(Issue 9) pp:3080-3087
Publication Date(Web):April 30, 2015
DOI:10.1021/acs.macromol.5b00387
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 higher than the crystallinity of nonisothermally melt crystallized coalesced PHB, indicating that coalesced PHB is not easily converted into semicrystalline PHB.
Co-reporter:Fatima Zohra Rafique and Nadarajah Vasanthan
The Journal of Physical Chemistry B 2014 Volume 118(Issue 31) pp:9486-9495
Publication Date(Web):July 15, 2014
DOI:10.1021/jp505046v
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.
Co-reporter:Nadarajah Vasanthan and Naga Jyothi Manne
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 35) pp:12596-12603
Publication Date(Web):August 12, 2013
DOI:10.1021/ie401783y
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 using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. It was found that both the melting temperature and the crystallinity development are dependent on the strain rate. The cold crystallization peak decreases with increasing draw ratio and disappears completely beyond a draw ratio of 2.5. DSC results showed that the decreasing strain rate delays crystallization and reduces the rate of crystallization. The bands at 1358 and 976 cm–1 were chosen to determine the gauche and trans conformations of methylene segments in PTT as a function of the draw ratios and strain rates. It was found that the crystalline gauche conformation increases at the expense of the amorphous trans conformation during the strain-induced crystallization of PTT. The conversion of the amorphous trans conformation into the crystalline gauche conformation is also delayed at lower strain rate, which is consistent with our DSC observation. Polarized IR spectroscopy was used to measure the crystalline and the amorphous orientation functions separately with draw ratios and strain rates, and it was demonstrated that the crystalline orientation develops rapidly with strain-induced crystallization and that the amorphous orientation stays constant up to draw ratio of 2.5 and increases slowly above a draw ratio of 2.5, which is typical behavior for flexible chain polymers.
Co-reporter:Nadarajah Vasanthan, Naga Jyothi Manne, and Anusha Krishnama
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 50) pp:17920
Publication Date(Web):November 26, 2013
DOI:10.1021/ie402860t
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 investigated and the Avrami equation has been applied to evaluate the kinetic parameters. An increase in the rate constant and a decrease in the Avrami exponent suggested that cold crystallization is faster for a PTT film with a high overall molecular orientation and a change in growth geometry with orientation. This study demonstrates that overall molecular orientation affects the cold crystallization kinetics of amorphous–crystallizable polymers.
Co-reporter:Nadarajah Vasanthan;He Gezer
Journal of Applied Polymer Science 2013 Volume 127( Issue 6) pp:
Publication Date(Web):
DOI:10.1002/app.38015
Abstract
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
Co-reporter:Shakira Charles, Nadarajah Vasanthan, Dong Kwon, Gabriela Sekosan, Subhas Ghosh
Tetrahedron Letters 2012 Volume 53(Issue 49) pp:6670-6675
Publication Date(Web):5 December 2012
DOI:10.1016/j.tetlet.2012.09.098
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.
Co-reporter:N. Vasanthan
Journal of Chemical Education 2012 Volume 89(Issue 3) pp:387-390
Publication Date(Web):January 11, 2012
DOI:10.1021/ed200398m
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.Keywords: Analytical Chemistry; Crystals/Crystallography; Graduate Education/Research; Hands-On Learning/Manipulatives; IR Spectroscopy; Laboratory Instruction; Phases/Phase Transitions/Diagrams; Polymer Chemistry; Upper-Division Undergraduate; UV−Vis Spectroscopy;
Co-reporter:Deepika Rangari and Nadarajah Vasanthan
Macromolecules 2012 Volume 45(Issue 18) pp:7397-7403
Publication Date(Web):September 4, 2012
DOI:10.1021/ma301482j
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 more slowly. The enzymatic degradation of annealed PLLA films was reported, and surprisingly, quite different results were observed for the enzymatic degradation of oriented PLLA films. The extent of degradation was lower for the drawn PLLA film than for the undrawn melt-pressed PLLA film. The DSC crystallinity and A921/A956 of drawn PLLA films increased with the degradation time, suggesting an increase in the crystalline phase with degradation. This reveals that degradation occurs in both the free and the restricted amorphous region in the case of drawn PLLA films, whereas it occurs only in the free amorphous region in annealed unoriented PLLA films.
Co-reporter:Gabriela Sekosan
Journal of Polymer Science Part B: Polymer Physics 2010 Volume 48( Issue 2) pp:202-211
Publication Date(Web):
DOI:10.1002/polb.21889
Abstract
The effects of crystallinity and temperature on enzymatic degradation of poly-ε-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
Co-reporter:Nadarajah Vasanthan, Onah Ly
Polymer Degradation and Stability 2009 Volume 94(Issue 9) pp:1364-1372
Publication Date(Web):September 2009
DOI:10.1016/j.polymdegradstab.2009.05.015
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 (χc), glass transition temperature (Tg) and melting temperature (Tm) were found to be strongly annealing temperature (Ta) 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 Tg and no significant change in Tm and heat of fusion, while IR showed an increase in IR crystallinity with increasing hydrolysis time. The increase in IR crystallinity and Tg 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.
Co-reporter:Mustafa Yamen;Sabahattin Ozkaya
Journal of Polymer Science Part B: Polymer Physics 2008 Volume 46( Issue 14) pp:1497-1504
Publication Date(Web):
DOI:10.1002/polb.21485
Abstract
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 Ta. 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. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1497–1504, 2008
Co-reporter:Nadarajah Vasanthan;Mustafa Yaman
Journal of Polymer Science Part B: Polymer Physics 2007 Volume 45(Issue 13) pp:1675-1682
Publication Date(Web):22 MAY 2007
DOI:10.1002/polb.21196
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 Ta of 185 °C and increases rapidly once Ta exceeds 185 °C. It was found that thermally induced crystallization is mainly temperature-dependent above Ta = 185 °C and temperature- and time-dependent below Ta = 60 °C. Two melting transitions, T and T, were observed for those samples annealed above 120 °C. No significant change in T was observed as a function of Ta while T showed strong dependency on Ta. 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. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1675–1682, 2007
Co-reporter:N. Vasanthan
Journal of Polymer Science Part B: Polymer Physics 2007 Volume 45(Issue 3) pp:349-357
Publication Date(Web):19 DEC 2006
DOI:10.1002/polb.21057
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 γα 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
