Temperature dependence of oxygen diffusion into polymer/carbon nanotube composite films

This study examines the transport properties of polystyrene (PS)/multiwalled carbon nanotube (MWNT) composite films taking into consideration both MWNT composition and temperature, via fluorescence technique. Three different (3, 15, and 40 wt%) MWNT content films were prepared from PS/MWNT mixtures by annealing them at 170°C, above the glass transition temperature of PS for 10 min. The diffusivity of the PS/MWNT composite was determined by performing oxygen (O₂) diffusion measurements within a temperature range of 24 to 70°C for each film and pyrene (P) was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined by the fluorescence quenching method assuming Fickian transport. Results indicated that D values are strongly dependent on both temperature and the MWNT content in the film and it was also observed that D coefficients obey Arrhenius behavior, from which diffusion energies were produced and increased along with increases of MWNT content. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Oxygen diffusion into polystyrene–bentonite films

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene–clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 °C above the glass transition (T_g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0, 5, 10, 20, 30, 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient, D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 × 10^− 10 to 26.9 × 10^− 10 cm² s^− 1 with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant, k_q and mutual diffusion coefficient, D_m values.     

Fluorescence quenching method for monitoring oxygen diffusion into PS/CNT composite films

Oxygen permeabilities of nanocomposite films consisting of multi wall carbon nanotubes (MWNT) and polystyrene (PS) were determined to investigate the oxygen diffusion depending on MWNT and temperature. A method which is based on quenching of an excited phosphorescent by oxygen was applied for the measurements. The composite films were prepared from mixtures of (MWNT) and surfactant-free pyrene (P)-labeled (PS) latexes of various compositions at room temperature. These films were then annealed at 170 °C which is well above the glass transition (T_g) temperature of polystyrene, for 10 min. Diffusion experiments were performed for eight films with different MWNT content (0, 1.5, 3, 5, 10, 15, 25 and 40 wt%) to evaluate the effect of MWNT content on oxygen diffusion. Diffusion coefficients were found to increase from 1.1 × 10⁻¹² to 41 × 10⁻¹² cm² s⁻¹ with increasing MWNT content. On the other hand, to examine the effect of temperature on oxygen diffusion, diffusion measurements were performed over a temperature range of 24–70 °C for three different MWNT contents (3, 15, and 40 wt%) within the films. The results indicated that the values of the diffusion coefficient D are strongly dependent on both temperature and MWNT content in the film. It was also observed that the diffusion coefficients obey Arrhenius behavior, from which diffusion energies were determined, which increased with increase of MWNT content and temperature.     

Effect of molecular weight on the dissolution properties of polystyrene latex films

An in situ steady-state fluorescence (SSF) technique was applied in order to study the dissolution process of polystyrene (PS) latex films. The effect of the molecular weight M _w of the PS on the dissolution rate was investigated. The PS chains were copolymerized with (1-pyrene)methyl methacrylate in order to make use of pyrene (P) as a fluorescent probe to monitor the dissolution process. Seven different films were prepared from P-labeled PS latex dispersions with different molecular weights at room temperature. These films were then annealed at 200 °C for 15 min to complete the film formation process before dissolution. The dissolution of PS films in a toluene (70 %)–cyclohexane (30 %) mixture was monitored in real time by watching the change in the fluorescence intensity of P, I _P. We used a model that included both case I and case II diffusion kinetics to interpret the results of the dissolution experiments. The relaxation constants k ₀ and the dissolution coefficients D _d of the polymer chains were measured. Two different dissolution coefficients were obtained, which were attributed to the small and long polymer chains in the film, considering the high polydispersity of the polymer. It was also found that both of the D _d values scaled with M _w according to the law D _d ≈ M ^?n .     

Optical percolation and oxygen diffusion in poly(divinylbenzene) doped poly(methyl methacrylate) latex flms

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into poly(methyl methacrylate) (PMMA) latex‐poly(divinylbenzene) (PDVB) composite films. Percolation model was used by using photon transmission (PT) technique to interpret the distribution of PDVB particles in PMMA lattice. Optical results were interpreted according to site percolation theory. The optical percolation threshold value and critical exponent were calculated as, R_c = 0.03 and, β = 0.34, respectively. PT measurements were performed for eight different PDVB content (0, 1.5, 3, 5, 10, 20, 40, and 60) wt%. Pyrene (P) functionalized PDVB cross‐linked spherical microspheres with diameters of 2.5 μm were synthesized by using precipitation polymerization technique followed by click coupling reaction. The diameter of the PMMA particles prepared by emulsion polymerization was in the range of 0.5–0.7 μm. PMMA/PDVB composite films were then prepared by physically blending of PMMA latex with PDVB microspheres at various compositions. The steady‐state fluorescence method was used to monitor oxygen diffusion into these (0, 5, 10, 20, and 40 wt%) latex films. Diffusion coefficients, D, of oxygen were determined by the fluorescence quenching method by assuming Fickian transport and were found to be increased from 1.8 × 10⁻¹¹ to 36.6 × 10⁻¹¹ cm² s⁻¹ with increasing PDVB content. This increase in D values was explained with formation of microvoids in the film by using PT technique. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Sorption and diffusion of water into melamine–formaldehyde‐incorporated poly(vinyl acetate)–polyester nonwoven fabric composites

A series of composites were fabricated by impregnating a polyester nonwoven fabric with melamine–formol (MF)‐incorporated poly(vinyl acetate) (PVAc) latex. The effect of different weight ratios of MF/PVAc, i.e. 0/100, 5/100, 10, 100, 15/100 and 20/100 (dry, wt/wt), on the water sorption and diffusion into the composites was evaluated. Water sorption studies were carried out at different temperatures, i.e. 30, 50 and 70 °C, based on the immersion weight gain method. From the sorption results, the diffusion (D) and permeation (P) coefficients of water penetrant were calculated. A significant increase in the diffusion and permeation coefficients was observed with an increase in the temperature of sorption. Drastic reductions in diffusion and permeation coefficients were noticed with increasing MF content in the composites. Attempts were made to estimate the empirical parameters like n, which suggests the mode of transport, and K, a constant which depends on the structural characteristics of the composite in addition to its interaction with water. The temperature dependence of the transport coefficients was used to estimate the activation energy parameters for diffusion (E_D) and permeation (E_p) processes from Arrhenius plots. Copyright © 2006 Society of Chemical Industry     

The effect of photodegradation of polystyrene on its permeability characteristics

The diffusion (D) and permeability (P) coefficients for ¹⁴CO₂ in polystyrene films which had been irradiated by short-wave ultraviolet (253.7 nm) radiation under vacuum and in oxygen were determined in the temperature range of 20° to 55°C. Both D and P decreased with increasing exposure, the vacuum-irradiated sample showing significantly greater decreases, presumably on account of a larger extent of crosslinking which was possible in the absence of oxidation. A good correlation was observed between crosslinking and decreasing P and D values. The solubility coefficients for all irradiated samples increase with increasing dose. Activation energies for diffusion increase with increasing irradiation, particularly for the vacuum-irradiated samples. Reductions in P and D values are interpreted in terms of free-volume decreases due to crosslinking and other modifications, while the increasing activation energies are attributed to the increasing energy requirements for creation of free volume in modified polymers.     

Polymer/carbon nanotube composite film formation: A fluorescence study

In this study, the effect of multi‐walled Carbon nanotube (MWNT) on film formation behavior of Polystrene (PS) latex film was investigated by using steady state fluorescence technique. Films were prepared by mixing of pyrene (P)‐labeled PS latex with different amounts of MWNTs varying in the range between 0 and 20 wt%. After drying, MWNT containing films were separately annealed above glass transition temperature (T_g) of PS ranging from 100 to 270°C for 10 min. In order to monitor film formation behavior of PS/MWNT composites, Scattered light (I_s) and fluorescence intensities (I_P) from P were measured after each annealing step to monitor the stages of film formation. At 0–20 wt% range of MWNT content films, minimum film formation (T_o), void closure (T_v), and healing, (T_h) temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It was observed that while void closure activation energies increased, backbone activation energies decreased as the percent of MWNT is increased in the composite films. POLYM. COMPOS., 35:817–826, 2014. © 2013 Society of Plastics Engineers     

Dielectric,transport and thermal properties of clay based polymer‐ nanocomposites

The polymer nanocomposite films (PNC) with varying amounts of organically modified sodium montmorillonite (DMMT) clay in poly(methyl methacrylate) (PMMA) based polymer matrix were prepared by solution cast technique. Dielectric measurements were carried out on these films as a function of frequency at 30°C and 100°C. The addition of clay significantly improved the ionic conductivity. Transport parameters, such as the diffusion coefficient (D), number density (n) and mobility (μ) of charge carriers were determined using a new approach, which is based on impedance spectroscopy. The temperature‐dependent dc conductivity, relaxation and mobility plots obey the Arrhenius rule. The results suggest that the higher ionic conductivity of these PNC films at elevated temperature is not only due to increased mobility of ions, but it is accompanied by a significant increase in carrier concentration. Analysis of DSC thermogram reveals a very high percentage of amorphous content for all samples. A good correlation among dielectric permittivity, carrier concentration, mobility and ionic conductivity has also been observed. POLYM. ENG. SCI., 58:220–227, 2018. © 2017 Society of Plastics Engineers     

Kinetic migration of PBS and PBSA biopolymers prepared by cast film extrusion and biaxial stretching: A combined experimental and modeling approach

The kinetic migration of poly(butylene succinate) (PBS) and poly(butylene succinate-co-adipate) (PBSA) biopolymers, prepared by cast film extrusion (thin film) and biaxial stretching (biaxially oriented [BO] film) techniques, were investigated based on experimental and mathematical modeling. MATLAB coding was used to fit the migration data to a diffusion model. BO films significantly reduced the migration rate compared with thin films, with reductions of 29% and 41% for BO-PBS and BO-PBSA, respectively, due to the increased degree of molecular crystallinity. Higher ethanol content increased the quantity of substance diffusing from plastic film. PBS and PBSA are more suitable for packaging hydrophilic foods than alcoholic beverages. PBS exhibited a lower migration rate than PBSA due to its more rigid polymer matrix. Remarkably, BO-films exhibited 31% and 41% lower diffusion coefficients (D) compared with thin films, but significantly higher partition coefficients (K_P,F) by 44% and 267% for BO-PBS and BO-PBSA, respectively. This suggests a stronger affinity of migrant for BO film matrix. However, at 70°C, PBSA films may be hydrolyzed with a high ethanol, resulting in an inadequate diffusion model. The diffusion–reaction concept should be implemented for a better fit. These findings provide valuable insights for selecting appropriate packaging materials and predicting migration under diverse conditions, ultimately promoting consumer safety.     

Gas transport in poly(vinylidene fluoride): Effects of uniaxial drawing and processing temperature

This paper reports on the gas sorption and transport properties of poly(vinylidene fluoride) (PVF₂) and on the effects uniaxial drawing and processing temperature have on these properties. Sorption and transport were first examined for “as-received” commercial Kynar PVF₂ film at 35°C. This film was 54% crystalline by weight. Solubility, diffusion, and permeability coefficients were measured for He, H₂, Ar, O₂, N₂, CH₄, and CO₂. The solubility coefficient and the diffusion coefficient D were correlated with the Lennard–Jones potential and mean molecular diameter of the gas, respectively. Uniaxial drawing of PVF₂ films was performed up to a draw ratio of 3.7 and over the temperature range 75–140°C. Transport properties were correlated with the extent of draw and drawing temperature. The permeability P and D were found to significantly decline with uniaxial drawing; the magnitude of this effect was dependent on both the drawing temperature and the molecular size of the penetrant considered. Roduetions in P and D became progressively more pronounced with increasing molecular diameter and with decreasing drawing temperature (down to a limit of about 75°C), which reflects an increase in effectiveness of drawing at low temperatures. PVF₂ films annealed above 75°C showed an increase in P and D as opposed to the effect of drawing. The solubility of various gases in PVF₂ was not found to be sensitive to processing treatments such as drawing and annealing, in agreement with the relatively small changes observed in free volume. PVF₂ films subjected to various treatments were characterized by DSC, density, birefringence, and dynamic mechanical measurements. Gas transport measurements appear to provide a more sensitive and hence more viable measure of the effectiveness of drawing than these other techniques. Drawing PVF₂ in the melt state was found to increase P and D, in contrast with the effects observed for solid-state drawing. The results have been interpreted in terms of existing theories on morphology and microstructure in semicrystalline polymers.     

Determination of oxygen diffusion coefficient of poly(methacrylonitrile) II and the calculation of diffusion activation energy

Poly(methacrylonitrile) (PMAN) samples in the shape of a cylinder used in this study were obtained from methacrylonitrile by bulk polymerization. The electron spin resonance (ESR) method has been used to calculate oxygen diffusion coefficient (D) into PMAN samples exposed to high‐energy radiation at different doses in vacuum by observing the ESR radical signal change. In order to calculate the dose‐independent diffusion coefficient (D₀), ln D values were plotted against dose values. The low dose region of this curve was extrapolated to a zero‐dose value, and D₀ was calculated as D₀ = 3.1 × 10⁻⁹ cm²/s. Although D₀ values were in very good agreement with the one obtained for the thin‐film sample of PMAN, the dose dependence of the oxygen diffusion into the cylindrical PMAN samples was observed as being converse of the thin‐film of PMAN,¹ as expected, because of the big difference of the surface/mass values between relatively big cylindrical PMAN samples and thin‐film of PMAN samples. The activation energy (E_a) values of the oxygen diffusion into PMAN were calculated as E_a1 = 27.9 kJ/mol for the 20–60°C temperature range E_a2 = 74.2 kJ/mol for the temperatures above 60°C of the 36 kGy gamma‐irradiated samples. The temperature value of the break point of activation energy was near to the T_g of PMAN.² © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1108–1118, 1999     

Mechanical,barrier, and interfacial properties of biodegradable composite films made of methylcellulose and poly(caprolactone)

Methylcellulose (MC) films were prepared by casting from its 1% aqueous solution containing 0.5% vegetable oil, 0.25% glycerol, and 0.025% Tween^®80. Poly(caprolactone) (PCL) films were prepared by compression molding from its granules. Biodegradable composite films were fabricated using MC film as reinforcing agent and PCL as the matrix material by compression molding. One layer of MC film was reinforced with two layers of PCL films. The MC content in the composites was varied from 10 to 50% by weight. Mechanical, barrier, and degradation properties of PCL, MC, and composite films were evaluated. The values of puncture strength (PS), puncture deformation (PD), viscoelasticity (Y) coefficient, and water vapor permeability (WVP) of the composites (50% MC content) were found to be 124.3 N/mm, 3.2 mm, 31%, and 2.6 g·mm/m²·day·kPa, respectively. Oxygen transmission rate (OTR) of PCL, MC, and composites (50% MC) were found to be 175, 25, 22 cc/m²/d, respectively, which indicated that composite films showed significantly lower OTR than PCL films. Degradation tests of the composite films (50% MC) were performed for 6 weeks in aqueous medium (at 25°C), and it was found that composites lost its mass slowly with time. After 6 weeks, mass and PS of the composites were decreased to 13.4 and 12%, respectively. Composite interface was studied by scanning electron microscopy (SEM). The MC film had good adhesion with PCL matrix during compression molding and suggested strong interface of the composite system. SEM image after 6 weeks of degradation showed some openings in the interface and revealed slow degradation of the MC films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of water on the oxygen barrier properties of poly(ethylene terephthalate) and polylactide films

The aim of this work was to study the variations in the oxygen diffusion, solubility, and permeability coefficients of polylactide (PLA) films at different temperatures (5, 23, and 40°C) and water activities (0–0.9). The results were compared with the oxygen diffusion, solubility, and permeability coefficients obtained for poly(ethylene terephthalate) (PET) films under the same experimental conditions. The water sorption isotherm for PLA films was also determined. Diffusion coefficients were determined with the half‐sorption time method. Also, a consistency test for continuous‐flow permeability experimental data was run to obtain the diffusion coefficient with the lowest experimental error and to confirm that oxygen underwent Fickian diffusion in the PLA films. The permeability coefficients were obtained from steady‐state permeability experiments. The results indicated that the PLA films absorbed very low amounts of water, and no significant variation of the absorbed water with the temperature was found. The oxygen permeability coefficients obtained for PLA films (2–12 × 10^?18 kg m/m² s Pa) were higher than those obtained for PET films (1–6 × 10^?19 kg m/m² s Pa) at different temperatures and water activities. Moreover, the permeability coefficients for PLA and PET films did not change significantly with changes in the water activity at temperatures lower than 23°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1790–1803, 2004     

Studies on sublimation of disperse dye out of dyed polymers. I. Rate of sublimation and amorphous transition points of poly(ethylene terephthalate)

Four samples of poly(ethylene terephthalate) film of various crystallinities and orientation were dyed with p-nitroaniline and disperse dyes. When these films were heated under a 2–3 × 10^?3 mm Hg vacuum at a specified temperature T, the dye sublimed out of the dyed specimen. The amount (M_t/M_∞) of sublimed dye is in linear proportion to the square root of the sublimation time, t^½, where M_t and M_∞ are the amounts of dye sublimed for times t and t = ∞. The diffusion coefficient D, calculated from the slope of the above plot, is independent of the dye concentration of the film. When log D is plotted against 1/T°K over the temperature range 320–520°K, the relation is composed of two to four intersecting lines with the slope decreasing with elevation of temperature and with the breaks at about 89°–98°, 122°–135°, 155° and 175°–176°C. These breaks are the amorphous transitions: the first is the glass transition temperature T_g, the second and the fourth are the amorphous transitions corresponding to the crystalline transition points, i.e., the cold crystallization temperature and the smectic–triclinic transition temperature. With some exceptions, these amorphous transitions are found also by dilatometry and electrical conductivity measurements. The apparent activation energy for diffusion decreases from about 100 kcal/mole for the glass state to 22–24 kcal/mole for the region above 180°C. The activation energy for each region changes slightly with the size of dye molecule and the crystallinity and orientation of the film.     

Synthesis of polystyrene/poly(butyl acrylate) core–shell latex and its surface morphology

A polystyrene (PS)/poly(butyl acrylate) (PBA) composite emulsion was produced by seeded emulsion polymerization of butyl acrylate (BA) with PS seed particles which were prepared by emulsifier‐free polymerization of styrene with potassium persulfate (KPS) under a nitrogen atmosphere at 70°C for 24 h with stirring at 60 rpm and swelled with the BA monomer in an ethanol/water medium. The structure of the PS/PBA composite particles was confirmed by the presence of the characteristic absorption band attributed to PS and PBA from FTIR spectra. The particles for pure PS and PS/PBA with a low content of the BA monomer were almost spherical and regular. As the BA monomer content was increased, the particle size of the PS/PBA composite particles became larger, and more golf ball‐like particles were produced. The surface morphology of the PS/PBA composite particles was investigated by AFM and SEM. The T_g's attributed to PS and PBA in the PS/PBA composite particles were found at 110 and ?49°C, respectively. The thermal degradation of the pure PS and PS/PBA composite particles occurred in one and two steps, respectively. With an increasing amount of PBA, the initial thermal decomposition temperature increased. On the contrary the residual weight at 450°C decreased with an increasing amount of PBA. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 595–601, 2003     

Fluorescence measurements of the diffusion coefficient for butylated hydroxyanisole in low-density polyethylene

Measurement of the diffusion coefficient (D) of butylated hydroxyanisole (BHA) in low density polyethylene at 31°C was made by two techniques. (1) Measurement of diffusion rate in the absence of solvent was made by use of a film stack with BHA-loaded discs on top and bottom. After a given diffusion time, the films were separated and the BHA extracted from the films into 1 -propanol. The fluorescence of the solutions provided values of BHA concentration as a function of film position in the stack, from which the value 3.4 (SD 0.3) × 10^?9 cm² s^?1 for D was calculated. (2) Fluorescence monitoring, under oxygen free conditions, was used to measure rate of BHA extraction from a film into 1 -propanol at 31°C, and gave the value 3.8 × 10^?9 cm² s^?1 for D which agrees well with the value determined by measurement in the absence of solvent.     

Dissolution of latex films after γ‐ray treatment

Latex films were prepared by annealing pyrene (Py)‐labeled poly(methyl methacrylate) particles at glass‐transition temperature (100°C). These films were then irradiated by γ‐rays from ⁶⁰Co in a gamma cell at room temperature at the same dose rate (rad/h) for 30 min. Before dissolution films were annealed at elevated temperatures for a 30‐min time interval to complete the film formation process. Steady‐state fluorescence (SSF) technique were used to monitor the dissolution of these irradiated latex films. The dissolution of films in chloroform–heptane (80–20%) mixture was monitored in real time by the Py fluorescence intensity change. Relaxation constants k₀ and desorption coefficients D_d of polymer chains were measured. It was observed that both D_d and k₀ values first increased and then decreased by increasing the annealing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 129–137, 2002     

Water absorption behavior of acrylonitrile‐butadiene (NBR) latex impregnated jute nonwoven fabric composites

Composites were fabricated by impregnating the jute nonwoven fabric in acrylonitrile–butadiene (NBR) latex. The effect of different pickup ratio (dry, wt/wt) of NBR latex to jute nonwoven fabric, viz., 0.5 : 1, 1 : 1.5, 1.5 : 1, 2 : 1, and 2.5 : 1 on the water absorption behavior of the composites were evaluated. Water absorption studies were carried out at different temperatures, viz. 30, 50, and 70°C, based on immersion weight gain method. From the sorption result, the diffusion (D) and permeation (P) coefficients of water penetrant have been calculated. Significant increase in the diffusion and permeation coefficients was observed with increase in the temperature of sorption experiments. Drastic reductions in diffusion and permeation coefficients were noticed with increase in the pickup ratio of NBR on to jute nonwoven fabric. Attempts were made to estimate the empirical parameters like n, which suggests the mode of transport, and K is a constant that depends on the structural characteristics of the composite in addition to its interaction with water. The temperature dependence of the transport coefficients has been used to estimate the activation energy parameter for diffusion (E_D) and permeation processes (E_p) from Arrhenius plots. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2045–2050, 2006     

Solubility and diffusion in latex films formed from high glass transition temperature particles

In situ steady-state fluorescence measurements were used to study the dissolution of polymer films. These films were formed from pyrene labeled poly(methyl methacrylate) (PMMA) latex particles that were sterically stabilized by polyisobutylene. Annealing was performed above the glass transition temperature at 180°C at 1-h time intervals for film formation. Desorption of pyrene labeled PMMA chains was monitored in real time by the change of pyrene fluorescence intensity. Dissolution experiments were performed in various solvents with different solubility parameters, δ, at room temperature. Diffusion coefficients, D, in various solvents were measured and found to be around 10⁻¹⁰ cm²/s. A strong relation between D and δ was observed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1493–1502, 1998