Properties and interfacial bonding of regenerated cellulose films coated with polyurethane–chitosan IPN coating

Water-resistant films were prepared by coating a castor oil-based polyurethane–chitosan (PU–CH), in which grafted interpenetrating polymer networks (IPNs) were produced, on a regenerated cellulose (RC) film. The tensile strengths of the coated films cured at 90°C for 5 min reached 853 kg cm⁻² (dry state) and 503 kg cm⁻² (wet state) and were obviously higher than those of the films of uncoated and coated with PU coating. Moreover, the coated films have excellent water resistivity, low vapor permeability, and good size stability, and their optical transmittance is even better than that of the RC film in the range of 400–800 nm. The interfacial structure of the coated films was investigated by using spectroscopy infrared, ultraviolet spectroscopy, transmission electron microscopy, and electron probe microanalysis. It was shown that the strong interfacial bonding with chemical and hydrogen bonds between the RC film and the coating exists. The PU prepolymer in the IPN coating penetrated through the interface into the RC film and partly crosslinked with the cellulose, forming a semi-IPNs. The chitosan in the PU–CH coating plays an important role not only in accelerating the cure of the coating but also in improving the mechanical properties and biodegradability of the coated film. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1313–1319, 1998     

Structure and properties of semiinterpenetrating polymer networks based on polyurethane and nitrochitosan

Two semiinterpenetrating polymer networks (semi‐IPNs) based on trihydroxyl methylpropane–polyurethane (T‐PU) or castor oil–polyurethane (C‐PU) were prepared by curing the mixed solution of the polyurethane prepolymer and nitrochitosan (NCH). During the curing process, crosslinking and grafting reaction between the molecules of the PU prepolymer and NCH occurred, because of the high reactivity of remaining hydroxyl groups in the NCH with ? NCO groups of PU. The structure of the original semi‐IPN sheets and the sheets treated with acetone were studied by infrared, ¹³C‐NMR, scanning electron microscopy, and dynamic mechanical analysis, showing interpenetration of NCH molecules into the PU networks. When nitrochitosan content (C_NCH) was lower than 10 wt %, the semi‐IPN sheets T‐PU and C‐PU had higher density and tensile strength (σ_b) than the systems with C_NCH more than 20%. The trihydroxymethyl propane‐based PU reacted more readily with nitrochitosan to form the semi‐IPNs than castor oil‐based PU. The semi‐IPN coatings T‐PU and C‐PU were used to coat cellophane, resulting in intimate interfacial bonding. The mechanical strength and water resistivity of the cellophane coated with T‐PU coating were improved remarkably. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3109–3117, 2001     

Mechanical properties of blocked polyurethane/epoxy interpenetrating polymer networks

The mechanical properties of blocked polyurethane(PU)/epoxy interpenetrating polymer networks (IPNs) were studied by means of their static and damping properties. The studies of static mechanical properties of IPNs are based on tensile properties, flexural properties, hardness, and impact method. Results show that the tensile strength, flexural strength, tensile modulus, flexural modulus, and hardness of IPNs decreased with increase in blocked PU content. The impact strength of IPNs increased with increase in blocked PU content. It shows that the tensile strength, flexural strength, tensile modulus, and flexural modulus of IPNs increased with filler (CaCO₃) content to a maximum value at 5, 10, 20, and 25 phr, respectively, and then decreased. The higher the filler content, the greater the hardness of IPNs and the lower the notched Izod impact strength of IPNs. The glass transition temperatures (T_g) of IPNs were shifted inwardly compared with those of blocked PU and epoxy, which indicated that the blocked PU/epoxy IPNs showed excellent compatibility. Meanwhile, the T_g was shifted to a higher temperature with increasing filler (CaCO₃) content. The dynamic storage modulus (E′) of IPNs increased with increase in epoxy and filler content. The higher the blocked PU content, the greater the swelling ratio of IPNs and the lower the density of IPNs. The higher the filler (CaCO₃) content, the greater the density of IPNs, and the lower the swelling ratio of IPNs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1826–1832, 2006     

Semi‐interpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. II. Dielectric relaxation and thermal behaviour

Semi‐interpenetrating polymer networks (semi‐IPNs) based on crosslinked polyurethane (PU) and linear polyvinylpyrrolidone (PVP) were synthezised, and their thermal and dynamic mechanical properties and dielectric relaxation behavior were studied to provide insight into their structure, especially according to their composition. The differential scanning calorimetry results showed the glass transitions of the pure components: one glass‐transition temperature (T_g) for PU and two transitions for PVP. Such glass transitions were also present in the semi‐IPNs, whatever their composition. The viscoelastic properties of the semi‐IPNs reflected their thermal behavior; it was shown that the semi‐IPNs presented three distinct dynamic mechanical relaxations related to these three T_g values. Although the temperature position of the PU maximum tan δ of the α‐relaxation was invariable, on the contrary the situation for the two maxima observed for PVP was more complex. Only the maximum of the highest temperature relaxation was shifted to lower temperatures with decreasing PVP content in the semi‐IPNs. In this study, we investigated the molecular mobility of the IPNs by means of dielectric relaxation spectroscopy; six relaxation processes were observed and indexed according the increase in the temperature range: the secondary β‐relaxations related to PU and PVP chains, an α‐relaxation due to the glass–rubber transition of the PU component, two α‐relaxations associated to the glass–rubber transitions of the PVP material, and an ionic conductivity relaxation due to the space charge polarization of PU. The temperature position of the α‐relaxation of PU was invariable in semi‐IPNs, as observed dynamic mechanical analysis measurements. However, the upper α‐relaxation process of PVP shifted to higher temperatures with increasing PVP content in the semi‐IPNs. We concluded that the investigated semi‐IPNs were two‐phase systems with incomplete phase separation and that the content of PVP in the IPNs governed the structure and corresponding properties of such systems through physical interactions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1191–1201, 2003     

Thermal Degradation of p-Hydroxybenzoic Acid in Macadamia Nut Oil,Olive Oil,and Corn Oil

p-Hydroxybenzoic acid (PHBA) plays a significant role in sustaining the oxidative stability of macadamia nut oil (MNO). However, PHBA undergoes thermal decarboxylation and loses its bioactive antioxidant properties. In this study, we determine PHBA degradation kinetics in oils at various heating temperatures, which provides fundamental understanding of PHBA thermal degradation in oils and oil quality changes during high-temperature processing. PHBA degradation kinetics in MNO, olive oil, and corn oil were evaluated at temperatures typical for cooking and frying. PBHA headspace concentration was measured using selected ion flow tube mass spectrometry. PHBA decarboxylation followed a zero-order reaction, where degradation could be affected by factors such as the type of oil matrix having different FA compositions, antioxidants, and component interactions. PHBA degradation activation energies (E _a) showed that PHBA was more stable against thermal decarboxylation in MNO (85 kJ mol^–1) than in olive oil (40 kJ mol⁻¹) or corn oil (22 kJ mol⁻¹). The higher enthalpy () of decarboxylation in MNO (82 kJ mol⁻¹) indicates that PHBA is more inhibited from decomposition than olive oil (37 kJ mol⁻¹) or corn oil (19 kJ mol⁻¹). Moreover, the negative entropy values () of PHBA degradation from MNO (−192 J mol⁻¹ K⁻¹), olive oil (−277 J mol⁻¹ K⁻¹), and corn oil (−325 J mol⁻¹ K⁻¹) indicates that these oils impart some inhibitory properties against PHBA thermal decarboxylation.     

Semiinterpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. I. Thermodynamic state and dynamic mechanical analysis

Semiinterpenetrating polymer networks (semi‐IPNs) based on polyurethane (PU) and polyvinylpyrrolidone (PVP) have been synthesized, and their thermodynamic characteristics, thermal properties, and dynamical mechanical properties have been studied to have an insight in their structure as a function of their composition. First, the free energies of mixing of the two polymers in semi‐IPNs based on crosslinked PU and PVP have been determined by the vapor sorption method. It was established that these constituent polymers are not miscible in the semi‐IPNs. The differential scanning calorimetry results evidence the T_g of polyurethane and two T_g for PVP. The dynamic mechanical behavior of the semi‐IPNs has been investigated and is in accordance with their thermal behavior. It was shown that the semi‐IPNs present three distinct relaxations. If the temperature position of PU maximum tan δ is invariable, on the contrary, the situation for the two maxima observed for PVP is more complex. Only the maximum of the highest temperature relaxation is shifted to lower temperature with changing of the semi‐IPNs composition. It was concluded that investigated semi‐IPNs are two‐phase systems with incomplete phase separation. The phase composition was calculated using viscoelastic properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 852–862, 2001     

Simultaneous full‐interpenetrating polymer networks of blocked polyurethane and vinyl ester. II. Static and dynamic mechanical properties

Simultaneous full‐interpenetrating polymer networks (full‐IPNs) based on blocked polyurethane (PU) and vinyl ester (VE) have been prepared. The static and dynamic properties of these IPNs have been examined. Results show that the tensile strength and flexural strength of IPNs increased with blocked PU content to a maximum value at 7.5 wt % PU content and then decreased. The tensile modulus, flexural modulus, and hardness of IPNs decreased with increasing blocked PU content. The impact strength of IPNs increased with increasing blocked PU content. The tensile strength, flexural strength, tensile modulus, and flexural modulus of IPNs increased with filler (kaolin) content to a maximum value at 20 to 25 phr filler content and then decreased. The higher the filler content, the greater the hardness, and the lower the impact strength of IPNs. The tensile strength, flexural strength, tensile modulus, flexural modulus, and hardness of IPNs increased with increasing VE initiator content. The dynamic technique was used to determined the damping behavior across a temperature range. Results show that the glass transition temperature (T_g) of IPNs are shifted inwardly compared with pure PU and VE, which indicated that the blocked PU–VE IPNs showed excellent compatible. Meanwhile, the glass transition temperature was shifted to a higher temperature with increased filler content. The dynamic storage modulus (E′) of IPNs increased with increasing VE and filler content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1977–1985, 1999     

Viscoelastic Behavior of Synthesized Liquid Soaps and Surface Activity Properties of Surfactants

In the present work, a rheological study of liquid soaps prepared from different mixture of surfactants as a function of surfactant type and concentration was performed. The curves of shear stress vs. shear rate and viscosity vs. shear rate were recorded at constant temperature, 294 ± 0.1 K. The surface activity properties were also studied. The results of the study showed that values of surface tension, γ, were in the range 31–40 mN m⁻¹ and the critical micelle concentration (CMC), was of the order 10⁻⁴ mol L⁻¹. The calculated maximum surface excess, Γ_max, varied from 2.40 to 3.66 μmol m⁻², while minimum area per molecule, A_min, varied from 41.1 (for amphoterics) to 81.4 Ų (for nonionic surfactants). The standard free energy of micellization, −29.8 and −29.3 kJ mol⁻¹ for anionic and amphoteric surfactants, respectively, were while values for nonionic surfactants varied between −31.8 and − 30.3 kJ mol⁻¹. The free energy of adsorption, was the lowest for amphoteric surfactants (−37.9 kJ mol⁻¹), followed by anionics (−40.4 kJ mol⁻¹) and nonionics (−43.34 to −46.84 kJ mol⁻¹), indicating that micellization process is spontaneous in the examined medium. The synthetized liquid soaps show pseudoplastic behavior and they achieved pipe flow. The results of this research indicate that flow behavior was affected significantly by the ionic charge of the surfactant and the ionic strength of the formulation, suggesting that the flow behavior could be changed by manipulating the choice of the surfactant and salinity. The pH value of all liquid soaps examined were weakly acidic, in the range of 5.0–6.4.     

Effects of nitrolignin on mechanical properties of polyurethane–nitrolignin films

Polyurethane‐nitrolignin (PUNL), a new network polymer, was synthesized from a castor oil based–polyurethane (PU) prepolymer and nitrolignin (NL) with a weight‐average molecular weight of 20.6 × 10⁴ and a content of 1.4–10%. The structure and miscibility of PUNL films prepared by solution casting were investigated by infrared spectroscopy and transmission electron microscopy. The results indicated that PUNL2 film, which had a 2.8% NL content, was the most miscible, and its tensile strength (σ_b) and breaking elongation (?_b) were 2 times higher than that of PU film. The crosslink densities of PUNL films increased with the increase of NL content until about 3%, similar to the variety of the mechanical properties. Thermogravimetric analysis revealed that the thermal stability of PUNL films was slightly higher than that of PU. Covalent bonds occurred between PU prepolymer and the NL in the PUNL films, forming crosslink networks, which resulted in the enhancement of mechanical properties and thermal stability. NL has a far higher reactivity with PU than nitrocellulose. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1213–1219, 2001     

Water sorption in amorphous poly(ethylene terephthalate)

The water sorption characteristics of poly(ethylene terephthalate) (PET) amorphous samples of 250 μm thickness have been studied at various temperatures in a saturated atmosphere. Concerning diffusivity, one can distinguish the following two domains characterized by distinct values of the activation energy: E_D ≈ 36 kJ mol⁻¹ at T > 100°C, and E_D ≈ 42 kJ mol⁻¹ at T < 60°C, with a relatively wide (60–100°C) intermediary domain linked to the glass transition of the polymer. The crystallization of this latter occurs in the time scale of diffusion above 80°C but doesn't change the Fickian character of sorption curves. The equilibrium concentration m_∞ is an increasing function of temperature, but the solubility coefficient S decreases sharply with this latter, with the apparent enthalpy of dissolution ΔH_s being of the order of −28 kJ mol⁻¹ at T < 80°C and −45 kJ mol⁻¹ at T > 80°C. Density measurements in the wet and dry states suggest that water is almost entirely dissolved in the amorphous matrix at T < 80°C but forms partially a separated phase at T > 80°C. Microvoiding can be attributed to crystallization-induced demixing. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1131–1137, 1999     

Interpenetrating polymer networks from polyurethanes and poly(methyl acrylate)

Simultaneous two-component interpenetrating polymer networks (IPNs) of polyurethane (PU)–poly(methyl acrylate) (PMA) were prepared, as well as the corresponding pseudo-IPNs. A comparison was made between the full IPNs, pseudo-IPNs, and the respective homopolymers. Their ultimate mechanical properties were obtained and the dynamic glass transition temperatures (T_g's) were found using a thermomechanical analyzer. At all compositions, a single T_g(except 50–50 wt %) was found.     

Effect of polyurethane molecular weight on the properties of polyurethane–poly(butyl methacrylate) hybrid latex prepared by miniemulsion polymerization

Polyurethane (PU) prepolymer was first prepared via introducing double bonds on‐to the PU chains, and then polyurethane–poly (butyl methacrylate) (PU–PBMA) hybrid latex was prepared via miniemulsion polymerization. Transmission electron microscopy, Differential scanning calorimeter (DSC), Fourier transform infrared, and dynamic mechanical analysis were adopted to characterize the hybrid latex and its coating film. Both the coating property and the miscibility of PU–PBMA emulsion have been greatly improved through introducing double bonds into PU prepolymer. With an increase in the molecule weight of PU (M_PU), the increase in the particle size of PU–PBMA emulsion was observed plus decreases in the stability of the hybrid latex and conversion of methacrylate. Besides, as M_PU increased, the final dried coating film of the hybrid latex showed decreased water resistance, weakened miscibility, and improved mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal characteristics of IPNs composed of polyallylamine and chitosan

Interpenetrating polymer network (IPN) hydrogels composed of polyallylamine and chitosan were synthesized by radical polymerization using 2,2‐dimethyl‐2‐ phenylacetophenone (DMPAP) and methylene bisacrylicamide (MBAAm) as initiator and crosslinker, respectively. The IPNs thus obtained were characterized by using Fourier transform infrared (FT‐IR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dielectric analysis (DEA). The melting temperatures of IPNs were observed with increasing chitosan content by DSC. DEA was employed to ascertain the glass transition temperature (T_g) of IPNs. From the result of DEA, IPNs exhibited two T_gs indicating the presence of phase separation in the IPN. The thermal decomposition of IPNs was investigated by TGA and appeared at near 270 °C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1956–1960, 2002     

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     

Properties and interfacial bonding for regenerated cellulose–polyurethane/amylose acetate sipn composite films

Composite films were obtained by placing a polyurethane/amylose acetate semi‐interpenetrating polymer network (SIPN) coating onto the surfaces of regenerated cellulose (RC) film. The properties of the composite film, such as tensile strength, 79.9 MPa (in dry state), 49.5 MPa (in wet state), water resistance (R), 0.62, dimensional stability (S_c), 3.0%, and water vapor permeability (P), 5.96 × 10⁻⁵ Kgm⁻²h⁻¹, are better than those of the uncoated RC film or RC film with PU coating. The interfacial strength was characterized with infrared spectroscopy (IR), ultraviolet spectroscopy (UV), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA). The results showed the existence of covalent and hydrogen bonds between the SIPN coat layer and the RC layer. It was also found that the PU prepolymer in the coating layer penetrated into the cellulose bulk, and reacted with the cellulose molecules, which formed another SIPN.     

A Shock Tube Study of the Reactions of H Atoms with COS,CS2, and H2S

Reactions of H atoms with COS, CS₂, and H₂S were studied behind reflected shock waves at temperatures between 1170 K and 1830 K and pressures around 1.0 bar by applying atomic resonance absorption spectroscopy (ARAS) for time-resolved measurements of H atoms at L_α. The thermal decomposition of a few ppm ethyl iodide (C₂H₅I) was used as a H-atom source. In the presence of a large excess of the molecular reactant COS, CS₂, or H₂S, a consumption of H was observed which follows a pseudo first-order rate law. Rate coefficients for the reactions: were determined to be: k₁ = 2.4 × 10¹⁴exp(–3415 K/T) cm³mol⁻¹s⁻¹ k₂ = 1.4 × 10¹⁵exp(–9250 K/T) cm³mol⁻¹s⁻¹ k₃ = 2.5 × 10¹⁴exp(–2890 K/T) cm³mol⁻¹s⁻¹     

Reaction of Silane with Atomic Oxygen at High Temperatures

The reaction of silane with atomic oxygen (³P) was investigated by the shock-tube–laser-photolysis method over the temperature range of 900–1170 K. Oxygen atoms were produced by the ArF laser photolysis of SO₂ behind reflected shock waves and monitored with atomic resonance absorption spectroscopy. The rate constant for the SiH₄ + O reaction was evaluated by taking the possible contribution of the consecutive reaction into consideration. The Arrhenius temperature coefficient was determined to be E_a= 26.6 kJ mol⁻¹, which is much higher than the experimental activation energies obtained at lower temperatures. Rate constants calculated by a transition state theory with the reaction barrier height of E₀= 10.2 kJ mol⁻¹ agreed well with both the present and the previous experimental results for a wide temperature range.     

Synthesis of polymer materials by low energy electron beam. III. Effects of polymerization temperature in EB solid-state polymerization of semicrystalline urethane-acrylate film

In an electron beam (EB) polymerization of a urethane-acrylate prepolymer, the polymerization temperature greatly affected the structure and properties of the resulting gel film. Urethaneacrylate, which was synthesized by the reaction of poly(butylene adipate)diol, 4,4′-diphenylmethane diisocyanate, and 2-hydroxyethyl acrylate, was used as a prepolymer. The prepolymer was semicrystalline and showed a melting point in the region of 50–60°C. The maximum polymerization rate of the prepolymer was obtained when the prepolymer film was irradiated in the temperature range of 25–40°C. EB polymerization below the melting point (T_m) of the prepolymer produced semicrystalline polyurethane-acrylate gel films with a spherulitic texture. On the other hand, EB polymerization above the T_m destroyed the crystalline phase of the prepolymer to give transparent gel films. The gel film cured below the T_m had higher stress at yield, Young's modulus, and tensile strength than those cured above the T_m. Such temperature effects are attributed to whether or not the EB polymerization proceeds with retention of crystalline structure of the prepolymer.     

Humid aging of polyetherimide. I. Water sorption characteristics

The sorption and desorption kinetics of water into polyetherimide (ULTEM 1000) were studied at various temperatures ranging from 20 to 100°C. The water equilibrium concentration increases slightly with temperature from 1.39% (by weight) at 20°C to 1.50% at 100°C. The solubility coefficient, S, calculated from these data, and the water vapor pressure decrease with temperature. The calculated heat of dissolution H_s is close to −43 kJ mol⁻¹, which explains the low effect of temperature on the equilibrium concentration. The diffusion coefficient, D, varies from about 1.10⁻¹² m² · s⁻¹ at 20°C to about 16.10⁻¹² m² · s⁻¹ at 100°C. The apparent activation energy of diffusion, E_D, and the heat of dissolution, H_s, of water in the polymer have opposite values (respectively, +43 and −42 kJ · mol⁻¹). From this observation and a comparison of these data with water diffusion characteristics in other glassy polar polymers, it is hypothesized that the transport rate of water is kinetically controlled by the dissociation of water–polymer complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1439–1444, 2000     

Thermal Behavior and Thermolysis Kinetics of the Explosive Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD)

Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD), a cyclic nitroamine, has been studied with regard to the kinetics and mechanism of thermal decomposition, using thermogravimetry (TG), IR spectroscopy, and pressure differential scanning calorimetry (PDSC). The IR spectra of TNAD have also been recorded, and the kinetics of thermolysis has been followed by non‐isothermal TG. The activation energy of the solid‐state process was determined by using the Flynn‐Wall‐Ozawa method. Compared with the activation energy obtained from the Ozawa method, the reaction mechanism of the exothermic process of TNAD was classified by the Coats‐Redfern method as a nucleation and nuclear growth (Avrami equation 1) chemical reaction (α=0.30–0.60) and a 2D diffusion (Valensi equation) chemical reaction (α=0.60–0.90). E_a and ln A were established to be 330.14 kJ mol⁻¹ and 29.93 (α=0.30–0.60) or 250.30 kJ mol⁻¹ and 21.62 (α=0.60–0.90).