Photodegradation of poly(vinyl alcohol) under UV and pulsed‐laser irradiation in aqueous solution

The photodegradation of poly(vinyl alcohol) (PVA) in aqueous solution was investigated under UV exposure and pulsed‐laser irradiation. The degradation under UV exposure was studied at different pH values and with the addition of potassium chloride and potassium dichromate. The pulsed‐laser degradation of PVA was investigated with a Nd : YAG laser, operating at a wavelength of 266 nm with about 6‐ns pulses. The pulsed‐laser degradation was studied at different polymer concentrations and light intensities. Samples were analyzed by gel permeation chromatography. The degradation rate coefficients were determined by the application of a continuous distribution model. The photodegradation rates under UV exposure were highest at extremes of pH and were greatly enhanced by the addition of potassium chloride and potassium dichromate. The pulsed‐laser degradation of the polymer decreased with increasing polymer concentration, although a threshold light intensity was required to initiate the degradation process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 958–966, 2006     

Enzymatic degradation of poly(D,L‐lactide) and its blends with poly(vinyl acetate)

The enzymatic degradation of poly(D ,L ‐lactide) (PLA) was investigated using two different lipases, Novozym 435 and Lipolase. The optimum temperature was 50°C for the enzymatic degradation of PLA. The effect of various solvents on the degradation of PLA was investigated at 50°C using Novozym 435, and toluene was found to be the best solvent among the solvents investigated. The enzymatic degradation of the blends of PLA and PVAc was investigated at 50°C in toluene. The enzymatic degradation of the blends of PLA and PVAc showed that there is an interaction between the polymers during degradation, which results in the reduction of degradation rate of both polymers in the blend. A continuous distribution model was used to determine the rate coefficients for polymer degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 657–680 2006     

Ultrasonic degradation of poly(acrylic acid)

The ultrasonic degradation of poly(acrylic acid), a water‐soluble polymer, was studied in the presence of persulfates at different temperatures in binary solvent mixtures of methanol and water. The degraded samples were analyzed by gel permeation chromatography for the time evolution of the molecular weight distributions. A continuous distribution kinetics model based on midpoint chain scission was developed, and the degradation rate coefficients were determined. The decline in the rate of degradation of poly(acrylic acid) with increasing temperature and with an increment in the methanol content in the binary solvent mixture of methanol and water was attributed to the increased vapor pressure of the solutions. The experimental data showed an augmentation of the degradation rate of the polymer with increasing oxidizing agent (persulfate) concentrations. Different concentrations of three persulfates—potassium persulfate, ammonium persulfate, and sodium persulfate—were used. It was found that the ratio of the polymer degradation rate coefficient to the dissociation rate constant of the persulfate was constant. This implies that the ultrasonic degradation rate of poly(acrylic acid) can be determined a priori in the presence of any initiator. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Degradation kinetics of poly (vinyl-pyrrolidone) under ultrasonic irradiation

Ultrasonicaton has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Solution of poly (vinyl-pyrrolidone) in chloroform with different concentrations and different molecular weights at a fined temperature were subjected to ultrasonic degradation. This study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The results were indicated that the polymers with height molecular mass degraded faster than the polymers laving low molecular mass thus the rate of ultrasonic degradation increased with increasing molecular weight. It was found that rate constant decreases as the concentration increases. The calculated rate constants correlated in terms of inverse concentration and relative viscosity of PVP solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased. The experimental results show that the viscosity of polymers decreased with ultrasonic irradiation time and approached a limiting value, below which no further degradation took place.     

Preparation and optimization of 2,4‐D loaded cellulose derivatives microspheres by solvent evaporation technique

Controlled release herbicide formulations were prepared by microencapsulation using solvent evaporation technique. 2,4‐D was chosen as core material, which was microencapsulated in two cellulose derivatives as matrices: cellulose acetate butyrate butyryl (CAB) and ethylcellulose (EC). The work is intended to produce systems containing the herbicide to reduce its risks by dermal contact, evaporation, or degradation and to control the release of the active agent. The microspheres loaded by 2,4‐D were characterized by scanning electron microscopy and infrared spectroscopy. We have obtained microparticles in the range of D₃₂ of 42–277 μm with CAB and 88–744 μm with EC by varying the process parameters. The drug entrapment was improved by controlling certain factors such as polymer/solvent ratio, pH of continuous phase, and organic phase solvent. The drug release was established in deionized water at pH = 5.5 and 25°C and the 2,4‐D concentrations were estimated by UV analysis. The release data were analyzed according to Fick's law and the results demonstrate that the release rate can be controlled by modifying the process parameters. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2742–2751, 2007     

Role of polymer–salt–solvent interactions in the electrospinning of polyacrylonitrile/iron acetylacetonate

Electrospinning is a process of producing ultrafine fibers by overcoming the surface tension of a polymer solution with electrostatic force. In this study, iron acetylacetonate was added to a polyacrylonitrile solution, and the role of polymer–salt–solvent interactions in the electrospinning of the ultrafine fibers was investigated. The polymer–salt–solvent interactions were characterized by Fourier transform infrared spectroscopy; and the solution viscosity, conductivity and surface tension were measured in solutions with different salt concentrations. The formation of polymer–salt–solvent interactions increased the solution viscosity, conductivity, and surface tension values at low salt concentrations. At high concentrations, the solution viscosity and surface tension decreased, but the conductivity remained relatively constant. The polymer–salt–solvent interactions influenced the structures of the electrospun fibers by changing the balance among the solution viscosity, conductivity, and surface tension. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Flow-assisted degradation in dilute polystyrene solutions

The flow-assisted degradation behavior of polystyrene was studied as a function of solvent, polymer concentration, molecular weight, and molecular weight distribution. To obtain data at concentrations as low as 100 parts per million by weight, turbulent drag reduction measurements were used to augment the usual analytical techniques of viscosity and gel permeation chromatography. Turbulent flow measurements were found to be a valuable technique for evaluating the effects of degradation: the drag reduction onset point provides information about the largest molecules in the sample while the flow rate dependence is related to the shape of the top part of the molecular weight distribution. For the polymers and flow conditions studied, the degradation causes a shift in the distribution to lower molecular weights with little change in the shape. This suggests a complex mechanism where the probability of bond scission is not random but varies along the polymer backbone.     

Application of degradation kinetics to the rheology of poly(hydroxyalkanoates)

The time‐dependent rheological behavior of a series of 3‐hydroxybuytrate‐based semicrystalline copolymers is employed to determine the expected rheological curves that would be generated in the absence of any polymer degradation. Both dynamic frequency sweep and shear rate sweep experiments were analyzed. A model for the degradation kinetics, coupled with standard rheological relationships, was employed to extrapolate the measured sweeps to predicted curves at time zero, prior to degradation. The model is broadly applicable over a wide range of frequencies or shear rates, and generates a single degradation rate constant k for each polymer studied. A similar, although ad hoc, procedure was applied to the dynamic storage and loss moduli. The model provides a method for determining the rheological behavior of degrading polymers over a time interval, typically found in processing applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1794–1802, 2006     

Effects of polymer concentration and zone drawing on the structure and properties of biodegradable poly(butylene succinate) film

To produce various biodegradable poly(butylene succinate) (PBS) films for particular use, the effects of initial polymer concentration and zone drawing on the structure, physical properties, and hydrolytic degradation of PBS film were investigated. PBS films were prepared from chloroform solutions with different initial concentrations of 8, 11, 14, 17 and 20 g/dl. In order to investigate the drawing behavior of the PBS films with different solution concentrations, the films were drawn under various zone drawing conditions. Through a series of experiments, it turned out that the initial concentration of PBS solution in chloroform caused significant changes in the draw ratio of the PBS film. That is, the zone draw ratios of the film at initial concentration of 14 g/dl exhibited its maximum values and gradually decreased at higher or lower concentrations. Thus, it was concluded that the initial concentration of 14 g/dl is the optimum polymer concentration to produce maximum draw ratio in this work. In addition, the crystal and amorphous orientations and tensile properties of PBS film having similar draw ratio and similar crystallinity were highest at 14 g/dl and surface crystal morphologies of these films were absolutely different. The hydrolytic degradation rate of the film at 14 g/dl was lowest, but with similar draw ratio, film dimension, and crystallinity, indicating that the degradation behaviors were greatly affected by the initial polymer concentration, orientation, and crystal morphology.     

Submicron copper‐low‐density polyethylene conducting composites: Structural,electrical, and percolation threshold

Copper‐embedded low‐density polyethylene (LDPE) composites were fabricated using different copper concentrations in the polymer matrix. The copper particles were spherical with a mean particle size between 200 and 300 nm. All the samples were compacted under pressure and melted. The LDPE matrix was analyzed using gel permeation chromatography (GPC) and it did not evidence degradation of the LDPE matrix. The microstructure of the composites was examined with scanning electron microscopy. The electrical conductivity was measured as a function of the copper content, and the composite fabricated with a 10 vol % copper presented a conductivity 15 orders of magnitude higher than that of pure LDPE. The enhancement in conductivity can be explained by means of segregated percolation path theory and the experimental results are in agreement with the theoretical law. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

γ‐Irradiation effects on the thermal and structural characteristics of modified,grafted polypropylene

The effects of both the degree of grafting and γ irradiation on the thermal stability and structural characteristic of polypropylene‐graft‐polyvinylpyrrolidone and polypropylene‐graft‐polyvinylpyrrolidone modified with α‐cyano‐δ‐(2‐thienyl) crotononitrile were investigated. The employed techniques were thermogravimetric analysis, differential thermogravimetry, and X‐ray diffraction. The thermal stability of various polymeric substrates was investigated through the determination of the degradation temperature and activation energy of degradation. The effects of different parameters on the structural characteristics of different films were investigated through the determination of possible changes in the degree of ordering of the polymeric substrates. The results revealed that the thermal stability of the trunk polymer, grafted polymer, and polymer modified by α‐cyano‐δ‐(2‐thienyl) crotononitrile increased progressively with an increasing degree of grafting. The increase was, however, more pronounced for the sample undergoing the lowest degree of grafting. The activation energy of the thermal degradation process remained almost unchanged, and this indicated that the degradation processes of the different films followed almost the same mechanism. The γ irradiation at a dose of 60 kGy of the sulfur‐treated polymeric films [i.e., the polymeric films treated with α‐cyano‐δ‐(2‐thienyl) crotononitrile] reduced their thermal stability. This conclusion was reached by the consideration of the changes observed in the pre‐exponential factor of the Arrhenius equation due to different chemical and γ‐irradiation treatments. The degree of ordering, evidenced by X‐ray diffraction measurements of the trunk polymer, grafted polymer, and modified polymer, suffered a significant drop. This drop was much more pronounced for the sulfur‐containing polymeric materials. The observed drop in the degree of ordering of the polymeric substrates was taken as a measure of the structure collapse due to a certain treatment (degree of grafting and sulfur inclusion). The γ irradiation of the sulfur‐containing polymeric materials greatly increased their degree of ordering, which reached a value greater than that measured for the trunk polymer. Therefore, it was concluded that the thermal stability increased as the degree of ordering decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 506–515, 2006     

Effects of the electrospray ionization parameters on the formation and morphology of colloidal microspheres of polyacrylonitrile

Polyacrylonitrile colloidal microspheres have been successfully prepared with different concentrations of electrospraying polyacrylonitrile solutions. The morphology of the colloidal spheres has two kinds of structures and is strongly affected by electrospray‐ionization parameters, such as the polymer concentration, applied voltage, and distance between the electrodes. The solvent can also affect the morphology of polyacrylonitrile. The optimum conditions for preparing colloidal spheres have been found, and differential scanning calorimetry results indicate that polyacrylonitrile colloid spheres are amorphous. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2889–2893, 2006     

Continuous distribution kinetics for ultrasonic degradation of poly(methyl methacrylate)

Ultrasonic degradation of poly(methyl methacrylate) (PMMA) was carried out in several solvents and some mixtures of solvents. The time evolution of molecular weight distribution (MWD), determined by gel permeation chromatography, is analysed by continuous distribution kinetics. The rate coefficients for polymer degradation are determined for each solvent. The variation of rate coefficients is correlated with the vapour pressure of the solvent, kinematic viscosity of the solution and solvent–polymer interaction parameters. The vapour pressure and the kinematic viscosity of the solution are found to be more critical than other parameters (such as the Huggins and Flory–Huggins constants) in determining the degradation rates. © 2001 Society of Chemical Industry     

Thermal degradation of water soluble polymers and their binary blends

The effect of five different metal oxides on the pyrolysis of poly(ethylene oxide) (PEO), polyacrylamide (PAM), and poly(vinyl alcohol) (PVA) was investigated using thermogravimetry. The presence of metal oxide did not influence the degradation of PEO while the order of metal oxide on the degradation rate of PAM and PVA was PbO > Co₃O₄ > CuO > ZnO > Al₂O₃. The miscibility and the decomposition of PEO–PAM and PVA–PAM blends were also investigated. The blends were found to be immiscible and the presence of one polymer did not influence the degradation of the other polymer in the polymer blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 233–240, 2006     

Porous polyphenylene sulfide membrane with high durability against solvents by the thermally induced phase‐separation method

Porous polyphenylene sulfide membranes were prepared as new solvent‐resistant membranes by the thermally induced phase‐separation (TIPS) method. Porous structures were either formed by solid–liquid phase separation (polymer crystallization) or liquid–liquid phase separation. The effects of solvents, cooling rates, and polymer concentrations on the porous structures were investigated. Various characteristics of pore structure can be obtained with suitable diluents and cooling rates using the TIPS method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2959–2966, 2006     

Phase separation phenomena of polysulfone/solvent/organic nonsolvent and polyethersulfone/solvent/organic nonsolvent systems

The precipitation values (PVs) of several organic nonsolvents in polysulfone (PSf)/solvent and polyethersulfone (PESf)/solvent systems were measured in temperatures ranging from 10 to 80°C by the direct titration method and compared with those of water in the same systems. The solvents used were N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAC); the organic nonsolvents employed were methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, ethylene glycol, and diethylene glycol as well as acetic acid and propionic acid. The compositions of nonsolvent, polymer, and solvent at the precipitation points for different polymer concentrations up to 10 wt % were also determined at 30°C with respect to both the polymers and six nonsolvents presented. These results were used to obtain the polymer precipitation curves in the polymer-solvent-nonsolvent triangular phase diagrams and to determine the theta composition of solvent-nonsolvent for a polymer. The results show that the precipitation value of nonsolvent in polymer/solvent systems depends on both the nature of polymer, solvent, and nonsolvent used and the temperature. The effect of temperature on the precipitation value was observed to be dramatically different for different polymer/solvent/nonsolvent systems. These results were explained on the basis of polar and nonpolar interactions of the polymer, solvent, and nonsolvent system. The results indicate that the precipitation values of the type presented in this paper not only give a relative measure of the nonsolvent tolerance of the polymer/solvent system involved and the strength of solvent and nonsolvent for the polymer, but also determine the relative location of the polymer precipitation curve in the triangular phase diagram. © 1993 John Wiley & Sons, Inc.     

Ultrasonic degradation of polyvinyl pyrrolidone in mixed water/acetone

The ultrasonic degradation of polyvinyl pyrrolidone solutions was carried out in mixtures water and acetone at 25°C to investigate the effect of solvent composition and solution concentration on the rate of degradation. The obtained limiting molecular weights indicate that the extent of degradation was decreased by increasing acetone volume fraction and solution concentration. The obtained limiting molecular weights were correlated in terms of concentration and acetone volume fraction. The calculated rate constants indicate that the rate of degradation was decreased by increasing acetone volume fraction and solution concentration. The calculated rate constants were correlated in terms of concentration, acetone volume fraction and molecular weight of polymer. This degradation behavior was interpreted in terms of vapor pressure of mixtures water and acetone, viscosity and concentration of polymer solutions. Vapor pressure of mixtures water and acetone were increased by increasing acetone volume fraction, and so the vapor easily entered the cavitation bubbles during their growth. This caused a reduction in collapsing shock because of a cushioning effect; therefore, the rate of degradation decreased. As the solution concentration increased, the viscosity increased and caused a reduction in the cavitation efficiency, and so the rate of degradation is decreased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Barrier properties of chlorobutyl nanoclay composites

Elastomeric materials are used as barriers to protect workers against exposure to chemicals. The effectiveness of a polymer as a chemical protective material depends on the rate of permeation of chemicals through it. The permeation rate is dependent on the type and amount of fillers added into the polymer matrix. In this study, Chlorobutyl nanoclay composites were prepared by addition of organically modified and unmodified nanoclays at different filler loadings. The nanocomposites were swollen in three solvents of varying cohesive energy density until equilibrium and desorption experiments were carried out. The data obtained from desorption experiments was used to determine the diffusion coefficients. The concentration‐dependent diffusion coeffecient (D) was calculated at high and low concentration regions and it was found that D is one‐order less in lower concentration region than in the higher concentration range. The aspect ratio of the nanoclay fillers in the composite was calculated by assuming square and disc shapes and it was found to vary with the type of solvent and the used and filler loading. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3630–3637, 2006     

Morphology and biodegradation of microspheres of polyester–polyether block copolymer based on polycaprolactone/polylactide/poly(ethylene oxide)

Porous microspheres of polyester–polyether block copolymer based on polycaprolactone/polylactide/poly(ethylene oxide) (PCEL) were prepared by an emulsification–solvent evaporation technique. The effect of hydrophilicity/hydrophobicity of the polymer on the morphology of the PCEL microspheres was studied and compared with that of polycaprolactone (PCL) and polycaprolactone/poly(ethylene oxide) block copolymer (PCE) microspheres. It was demonstrated by X‐ray photoelectron spectroscopy (XPS) that the enrichment of PEO segments on the surface of the microspheres occurred during solvent evaporation of the microdrops and lead to porous structure of the microspheres. The effects of the content and length of PEO segments of the PCEL polymer on the morphology of the microspheres were studied. The degradation behaviour of film‐like and microsphere‐like PCEL was investigated at pH 7.4 and 37 ± 1 °C. The shape of the PCEL samples had no obvious effect on the degradation rate of the material and homogeneous degradation was a main process. The degradation rate of PCEL microspheres was enhanced in the presence of the enzyme lipase. ¹H NMR measurements revealed that the PEO content reduced with degradation time because the PEO segment was broken down and dissolved in the medium during degradation. © 2000 Society of Chemical Industry     

Surface concentration effects in the drying of solvent-coated polymer films

The effect of changing the solvent surface concentration on the initial rate of solvent removal from solvent-coated polymer films is investigated. An analytical perturbation so-lution is developed for the nonlinear problem, and predictions are made for different surface concentrations and different diffusivity–concentration dependencies. © 1996 John Wiley & Sons, Inc.