Glass Transition Temperature Of PVA Research Articles

Thermal, Mechanical and Chemical Analysis of Poly(vinyl alcohol) Multifilament and Braided Yarns.

Poly(vinyl alcohol) (PVA) in multifilament and braided yarns (BY) forms presents great potential for the design of numerous applications. However, such solutions fail to accomplish their requirements if the chemical and thermomechanical behaviour is not sufficiently known. Hence, a comprehensive characterisation of PVA multifilament and three BY architectures (6, 8, and 10 yarns) was performed involving the application of several techniques to evaluate the morphological, chemical, thermal, and mechanical features of those structures. Scanning electron microscopy (SEM) was used to reveal structural and morphological information. Differential thermal analysis (DTA) pointed out the glass transition temperature of PVA at 76 °C and the corresponding crystalline melting point at 210 °C. PVA BY exhibited higher tensile strength under monotonic quasi-static loading in comparison to their multifilament forms. Creep tests demonstrated that 6BY structures present the most deformable behaviour, while 8BY structures are the least deformable. Relaxation tests showed that 8BY architecture presents a more expressive variation of tensile stress, while 10BY offered the least. Dynamic mechanical analysis (DMA) revealed storage and loss moduli curves with similar transition peaks for the tested structures, except for the 10BY. Storage modulus is always four to six times higher than the loss modulus.

Fabrication and chemo-physical characterization of CuO/chitosan nanocomposite-mediated tricomponent PVA films

Copper oxide/chitosan nanocomposite (CCNC) specimens were fabricated via a simple solvent evaporation route. The presence and intercalation of chitosan and CuO within the nanocomposites were explored using advanced analytical techniques of X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray analyses and the scanning electron microscopy. The prepared nanocomposite was then incorporated into poly(vinyl alcohol) (PVA) matrix to fabricate a tricomponent composite. The resultant tricomponent composite was characterized for various chemo–physical and mechanical properties using differential scanning calorimetry (DSC) and the mechanical testing. The DSC results indicated that the glass transition temperature of PVA decreased on incorporating the CCNC into the PVA matrix; this also enhanced the tensile strength and flexibility of the resulting films. The prepared tricomponent films may find potential applications in sensing and catalysis.

Composite (PVA/Cu nano) films: Two yield points, embedding mechanism and thermal properties

Direct embedding of Cu nanoparticles into the PVA surface is detected by AFM and a fresh embedding mechanism submitted via the change of the annealing temperatures (Tannealing). When the Tannealing goes above the glass transition temperature of PVA, Cu nanoparticles are rapidly sinked by a thin wetting layer of PVA. In order to it makes capillary pressure on a Cu nanoparticles, suggested, this wetting layer is accountable for Cu embedding. Also, study of the thermal and mechanical properties of the nanocomposites during the embedding of Cu into the PVA. The XRD patterns show that the presence of the Cu nanoparticles in the PVA matrix. The DSC studies show an increase in the glass temperature (Tg) from 344.4 K for the green PVA to 354.2 K for the annealing temperature 423 K. Also shows two melting points for the composites (PVA/Cu nano) with thermal annealing temperature below the glass temperature (Tg) and one melting point with annealing above the glass temperature (Tg). The study shows that Young’s modulus (Y) increases with increasing the thermal annealing temperatures from 0.20 × 109 Pa for the green PVA to 3.75 × 109 Pa for the annealing temperature 423 K. In addition to, the strength at the break increases, while the elongation at break decreases with increasing the thermal annealing temperatures.

Anisotropy in Third-Order Nonlinear Optical Susceptibility of the Stretch-Oriented Chrysophenine-Doped Poly(vinyl alcohol) Films

Stretch-oriented chrysophenine-doped poly(vinyl alcohol) (PVA) films were prepared at temperatures above the glass transition temperature of PVA. The optical absorption spectra of the stretch-oriented films exhibited a very high anisotropy (anisotropy ratio = 13). The third-order nonlinear optical properties of chrysophenine in stretch-oriented PVA films were measured by the resonant femtosecond degenerate four-wave mixing (DFWM) technique. The anisotropy ratio of the DFWM signal intensity was greater than 1000. The value of third-order nonlinear optical susceptibility of a uniaxially stretch-oriented chrysophenine-doped PVA film was 6.9×10-13 esu.

The plasticizing effect of calcium nitrate on poly(vinyl alcohol)

AbstractCalcium nitrate (Ca(NO3)2) was used as the plasticizer to improve the properties of Poly(vinyl alcohol) (PVA). The interaction between Ca(NO3)2 and PVA was investigated by Fourier transform infrared (FTIR) spectroscopy. The influence of Ca(NO3)2 on the crystalline, thermal, and mechanical properties of PVA was studied by X‐Ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing, respectively. FTIR studies showed that Ca(NO3)2 could strongly interact with PVA molecule and reduce the intensity of the hydrogen bonding between PVA molecules. The crystallization of PVA was interrupted and the degree of crystallinity of PVA decreased due to the strong interaction between Ca(NO3)2 and PVA. DSC studies showed that the glass transition temperature of PVA decreased with the addition of Ca(NO3)2. However, the thermal stability of PVA decreased with the addition of Ca(NO3)2. The mechanical properties of PVA was improved with the addition of Ca(NO3)2, PVA film became soft and ductile, with lower tensile strength and higher elongation at break compared with original PVA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Resonant Third-Order Optical Nonlinearities of the Stretch-Oriented Cyanine-Dye-Doped Poly(vinyl Alcohol) Films

Stretch-oriented cyanine-dye-doped poly(vinyl alcohol) (PVA) films were prepared at temperatures above the glass transition temperature of PVA. The optical absorption spectra of the stretch-oriented films exhibited an anisotropy. The third-order nonlinear optical susceptibilities of the stretch-oriented films were measured parallel and perpendicular to the stretching direction by the resonant femtosecond degenerate four-wave mixing (DFWM) technique, and a high anisotropic X(3) was observed for the uniaxially stretch-oriented cyanine-dye-doped PVA films.

Reinforcement on Properties of Poly(vinyl alcohol) Films by Embedding Functionalized Carbon Micro Coils

Carbon micro coils (CMCs) were hybridized with poly(vinyl alcohol) (PVA) through esterification reaction. The mixing of as-prepared CMC hybrid with polymer (PVA) matrix was effective to prepare PVA film where the functionalized CMC was homogeneously dispersed and embedded. The presence of CMCs in PVA film heightened the glass transition temperature of PVA. Results of tensile stress and electrical conductivity indicated that overall mechanical and electrical properties of PVA film were enforced by embedding CMC, depending on increase of the CMC concentration. These properties were further reinforced by prefunctionalization of CMC by PVA, because CMC can have an affinity to PVA in matrix through PVA immobilized on CMCs. However, mechanical and electrical properties for both nonfunctionalized and functionalized composites were depressed above a certain CMC concentration, indicating the self-orientation of CMC in the matrix, different from the behavior of carbon black.

Preparation and Characterization of Poly (vinyl alcohol)/Antimony-Doped Tin Oxide Nanocomposites

Nanocomposites of poly (vinyl alcohol) and antimony-doped tin oxide (ATO) were prepared by solution blending. The PVA composites were characterized by FTIR, TGA, DSC, WXRD and stress-strain testing. It has been found that adding ATO to the matrix has great influence on the crystallization behavior and glass transition temperature of PVA. The mechanical properties of PVA changed with the filler content, exhibiting an initial increase in these properties due to polymer-filler interactions. After a maximum value, at about 5 wt%, the mechanical properties decreased. Thermal stability of the nanocomposites was found to be remarkably enhanced by the incorporation of ATO.

Synthesis and characterization of hybrid nanocomposites comprising poly(vinyl alcohol) and colloidal silica

AbstractOrganic–inorganic hybrid composite films were developed using poly(vinyl alcohol) (PVA) and an aqueous dispersion of colloidal silica of initial particle size of 15–30 nm. The hybrid films, prepared with varied proportion of colloidal silica (10–90 phr), were found to be transparent, indicating the nanolevel dispersion of the inorganic component over the polymer. Morphological studies further revealed no significant agglomeration of the silica domains embedded into the polymer matrix. A depression in glass transition temperature of PVA is observed with increasing proportion of silica. The degree of crystallinity also showed a decreasing trend with increasing amount of silica. However, the composite films demonstrated superior mechanical performances, higher resistances to dissolution in boiling water, and lower permeability compared with virgin PVA, owing to the better interaction between PVA and silica as well as the reinforcing action of nanosilica particles in the polymer matrix. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:152–162, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20129

Thermal transitions of poly(vinyl alcohol) hydrogel sensed by a fluorescent probe

Fluorescence from the fluorescein molecule has been used to study of phase transition processes in five poly(vinyl alcohol) (PVA) hydrogels in the temperature range 75–350 K. These hydrogels were prepared with PVA with molecular weight = 124,000–186,000, 99+% hydrolyzed, by repeated freezing–thawing cycles in five compositions: 9.9, 11.1, 13.3, 16.5, and 20.9 PVA w/w %. Plots of total fluorescence intensity versus temperature, normalized with the fluorescence signal at 75 K, and of the emission wavelength maximum versus temperature indicated that the dynamic of the guest deactivation was dependent on the hydrogel thermal transitions. These thermal transition processes were compared to three model systems: uranine (fluorescein di-sodium salt) in water, fluorescein in water/ethanol (85%/15% v/v), and fluorescein/PVA homopolymer. Small spectral shifts were obtained for these model systems over the entire temperature range attributed to the hot band effect. Nevertheless, larger spectral shifts were obtained for hydrogels, indicating that shifts of the chemical dissociation equilibrium was occurring in this last case. Slope changes of both intensity and wavelength maximum plots versus temperature occurred at the same temperature values, and we attributed the onset of the hydrogel thermal transition as the sol–gel transition occurring at T ≅ 370 K; at 320 K we observed the glass transition temperature of PVA plasticized by water molecules; at T ≅ 240 ± 5 K we attributed the melting point of water molecules bonded to the PVA chains (freezable bond molecules); at T ≅ 270 ± 5 K we observed the melting point of free water molecules (bulk water); and, at 135–145 K the water glass transition. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 815–824, 2000

Understanding isothermal semicrystalline polymer drying: Mathematical models and experimental characterization

The drying mechanism of semicrystalline poly(vinyl alcohol) (PVA) was investigated. PVA samples of various molecular weights were crystallized by annealing at temperatures slightly above the glass transition temperature of PVA, and swollen in water for different time periods. The water volume fraction in the sample was measured using a buoyancy technique. The samples were dried in air at constant temperatures, and the drying kinetics were investigated using thermogravimetric analysis. The change in degree of crystallinity of the swollen polymer during drying was measured by differential scanning calorimetry (DSC) as well as by Fourier transform infrared spectroscopy (FTIR). The degree of crystallinity of the samples increased during drying, which in turn was found to alter the drying rate. The drying kinetics were faster at higher temperatures, for lower molecular weights, and for lower degrees of crystallinity. A mathematical model was developed to predict drying rates of semicrystalline polymers by considering the crystallization kinetics during drying. The model predictions included the thickness of the polymer sample, the degree of crystallinity of the polymer, and the water weight loss as functions of drying time. Model predictions were found to agree reasonably well with the experimental results.

Understanding isothermal semicrystalline polymer drying: Mathematical models and experimental characterization

The drying mechanism of semicrystalline poly(vinyl alcohol) (PVA) was investigated. PVA samples of various molecular weights were crystallized by annealing at temperatures slightly above the glass transition temperature of PVA, and swollen in water for different time periods. The water volume fraction in the sample was measured using a buoyancy technique. The samples were dried in air at constant temperatures, and the drying kinetics were investigated using thermogravimetric analysis. The change in degree of crystallinity of the swollen polymer during drying was measured by differential scanning calorimetry (DSC) as well as by Fourier transform infrared spectroscopy (FTIR). The degree of crystallinity of the samples increased during drying, which in turn was found to alter the drying rate. The drying kinetics were faster at higher temperatures, for lower molecular weights, and for lower degrees of crystallinity. A mathematical model was developed to predict drying rates of semicrystalline polymers by considering the crystallization kinetics during drying. The model predictions included the thickness of the polymer sample, the degree of crystallinity of the polymer, and the water weight loss as functions of drying time. Model predictions were found to agree reasonably well with the experimental results. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2771–2780, 1998