Control release of some pesticides from starch/(ethylene glycol‐co‐methacrylic acid) copolymers prepared by γ‐irradiation

Starch/(Ethylene glycol‐co‐Methacrylic acid) [Starch/(EG‐co‐MAA)] hydrogels were designed for controlled delivery of pesticides, such as Fluometuron (FH); Thiophanate Methyl (TF) and Trifluralin (TI) which are use in the agricultural field. The delivery device was prepared by using γ‐irradiation and was characterized by FTIR, DSC, and SEM. The swelling behavior of hydrogels as a function of copolymer composition and irradiation dose was detected. This article discusses the swelling kinetics of polymer matrix and release dynamics of Trifluralin from hydrogels for the evaluation of the diffusion mechanism and diffusion coefficients. The values of the diffusion exponent ‘n’ for both the swelling of hydrogels and the release of Trifluralin from the hydrogels have been observed between 0.56 and 0.86 when the MAA content in the polymers was varied from 20 to 80 wt %, respectively. It is inferred from the values of the ‘n’ that non‐Fickian diffusion mechanism has occurred for different EG/MAA compositions. The release rate from matrices prepared under different conditions was studied to determine which factors have the most affect and control over the hydrogel matrix release property. The preparation conditions such as EG/MAA hydrogel composition, pesticide concentration, type of pesticide and irradiation dose greatly affect the pesticide release rate, which also influenced by the pH and temperature of the matrix‐surrounding medium. The pesticide release rate decreased as the irradiation dose and pH increased, but it increased as the MAA content, pesticide concentration and temperature increased. The release rate of Trifluralin is the highest one, whereas the Fluometuron is the lowest. The properties of the prepared hydrogels may make them acceptable for practical use as bioactive controlled release matrices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Determination of diffusion coefficient of oxygen into polymers by using electron spin resonance spectroscopy. I. Poly(methyl methacrylate)

A simple technique has been proposed for the measurement of the diffusion coefficient of oxygen into polymeric spheres. The technique is based on the scavenging of radicals produced by high energy radiation by oxygen. The diffusion coefficient of oxygen determined for poly(methyl methacrylate) has shown an inverse dependency on the dose received. Diffusion coefficient determined for low doses (D = 3.4 × 10^?8 cm²/s) as well as that determined after extrapolation to zero dose (D₀ = 3.7 × 10^?8 cm²/s) are in excellent agreement with the values reported in the literature.     

A simulation of gas transport in polymeric membranes. Application to heterogeneous aging

A simplified mechanism of polymer aging has been proposed to simulate the effect of diffusion on degradation processes. Simple observations have been made on different events simulated using a modelization of the diffusion of low mass species: (1) the bulk oxidation rate, in the case of heterogeneous oxidation, is proportional to the square root of the initiation rate (formation of radicals). (2) The relative oxidation profile (relative to the surface oxidation) as a function of aging time is not constant. (3) The initial concentration of oxygen has, in some cases, a large influence on the apparent bulk oxidation rate during all the degradation processes. (4) The same observation is made for model samples stored in air and aged in inert atmosphere. (5) When heterogeneous oxidation occurs in samples containing antioxidant additives, the concentration of antioxidant has an effect on the induction period and on the bulk oxidation rate (this is not the case for homogeneous oxidation). (6) When heterogeneous oxidation occurs, the effect of antioxidant mobility can be practically neglected when D_oxygen/D_antioxidant (D = diffusion coefficient) varies from to 100 to 1. (7) The time required to reach a pseudostationary state (corresponding to the egality of oxidation rate and oxygen diffusion rate) can be interpreted by a simple induction period (antioxidant consumption and/or hydroperoxide accumulation). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 435–444, 1997     

Self-diffusion coefficient studies in polystyrene/polystyrene/ toluene solutions: Dynamic light scattering and fluorescence recovery after photobleaching experiments

The dynamical behavior of a polystyrene (M_w1)/polystyrene(M_w2)/toluene ternary mixture has been investigated by Dynamic Light Scattering (DLS) and Fluorescence Recovery After Photobleaching (FRAP). The experiments were made at several total polymer concentrations C_T from dilute to semi-dilute range of concentration. In FRAP experiments, the dynamic of such a system is characterized by the existence of one relaxation mode identified to the self-diffusion coefficient D_s of the labelled polymer. This mode has been compared to the corresponding extracted D_s value from the two relaxation modes observed in DLS. The comparison between the results shows that in the semi-dilute range of concentration the agreement is good between both D_s values. As the concentration decreases, the agreement becomes less and less satisfactory, showing the limitation of the theory used to extract D_s from DLS measurements to the semi-dilute regime. Received: 27 March 1997/Revised: 2 May 1997/Accepted: 3 May 1997     

Room Temperature Radiolytic Synthesized Cu@CuAlO2-Al2O3 Nanoparticles

Colloidal Cu@CuAlO₂-Al₂O₃ bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a ⁶⁰Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO₂-Al₂O₃ nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO₂-Al₂O₃ nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation.     

ESR study on the effect of temperature on the diffusion of oxygen into PMMA and PVAC polymers

The free radicals produced by γ irradiation in the polymer network are formed with ionizing radiation. The decay rates of radicals in the temperature range were used to estimate the diffusion coefficient of oxygen into polymeric spheres by an electron spin resonance (ESR) technique. The ESR results showed that the activation energy of the diffusion of oxygen into poly(methyl methacrylate) (PMMA) in the temperature range 10–40°C is 29.6 kJ/mol. There are two activation energies of the diffusion of oxygen into poly(vinyl acetate) (PVAc) in the temperature range 25–50°C. The activation energies below and above 35°C, which is the glass transition temperature of PVAc, were found to be 16.8 and 82.5 kJ/mol, respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1203–1207, 1999     

Diffusion in polyacrylamide gels

Using a novel sorption technique, the diffusion of some series of solutes in polyacrylamide gels has been investigated with regard to: (a) molecular size of solute; (b) concentration of solute and gel polymer; and (c) temperature. The approach used also yields the partition coefficient pertaining to sorption equilibrium. The ratio, $\text{D}\text{D}{}_{\mathrm{o}}$, where D_o refers to diffusion in the pure solvent, is found to reflect in part the characteristic interactions between solute and gel polymer. The temperature results indicate that the apparent activation energy for solute diffusion is approximately independent of the polymeric component for dilute gels.     

Concentration dependence of the diffusion coefficient in polymer solution and molecular weight distribution determined by the diffusion method

The effects of the concentration dependence of the diffusion coefficient of a polymer solution (polystyrene in benzene and cyclohexane) in determining molecular weight distribution by the diffusion method are briefly discussed. The value of the ratio D_m0/D_A0 in a good solvent was found to be close to 1.0 for a polydisperse polymer and less than 1.0 for monodisperse polymers. Molecular weight distribution curves of the polydisperse sample were obtained by the diffusion method in cyclohexane and benzene, respectively. The molecular weight distribution curve obtained for the polymer used in benzene solution looked as if the polymer had a narrow molecular weight distribution. The phenomena cited above were interpreted in the light of the concentration dependence of the diffusion coefficient of polymer solutions.     

Studies of the smoke emission from burning poly-(vinylchloride) plasticized with diisooctylphthalate

Smoke evolved from burning poly-(vinychloride) plasticized with diisooctylphthalate has been studied using a light absorption method. It has been shown that the quantity of smoke produced depends upon the oxygen concentration of the oxidizing gas as well as on the concentration of diisooctylphthalate present in the polymer. The results of this work have been analysed using an empirical equation proposed by the authors, which correlates the maximum smoke density (σ_max) with oxygen concentration. This equation may be written where No₂ is the molar concentration of oxygen in the oxidizing gas, and LOI refers to the limiting or critical concentration of oxygen at which at the polymer will just burn, as defined by the ASTM test 2863. The effect of various additives, particularly organic iodine compounds, as smoke suppressants has also been investigated.     

Der Einfluß des Photoinitiators auf die radikalische Härtung von Siliconacrylaten, 9

The photo-induced, free-radical network formation of silicone acrylates has been investigated in the presence of several photoinitiators containing benzoyl groups. The crosslinking process can be described by means of a free-radical chain process. From calorimetrical measurements it is inferred that oxygen inhibits and terminates the chain propagation process. Both the reaction rate and the inhibition time of the crosslinking are proportional to the air pressure, to the intensity of the incident light, and to the quantum yield of the initiator photolysis. The reaction starts when all oxygen is consumed in the silicone layer. Using Fick's 1st diffusion law it can be show that only oxygen, which diffused into the system, determines the final conversion. Contrary, O₂ influences the reaction rate, the inhibition time, and the final conversion. The network density does not depend on the oxygen concentration. The negative influence of oxygen on the reaction rate, on the inhibition time, and on the final conversion can be reduced by means of a high rate of the start reaction which depends on the incident light intensity, light absorption, and the quantum yield of the initiator photolysis. By means of two kinetical methods it is possible to show that any initiator used exhibits a different initiating efficienty; their relative order has been estimated.     

Surface modification of PTFE by 60Co γ-ray irradiation

Surface carboxyl groups were formed during the ⁶⁰Co γ-ray irradiation of poly(tetrafluoroethylene) (PTFE) in air. Fourier transform infrared spectroscopy enables the detection of surface carboxyl groups. The contact angles were used to calculate the dispersive and polar components of the surface free energy according to a two-liquid method. The γ-ray irradiation of PTFE mainly caused degradation of the polymer. The concentration of carboxyl groups, the wettability, the friction, and the dispersive and polar components of the surface energy and the crystallinity on PTFE surface were increased, while the particle size of PTFE decreased with increasing irradiation dose. A highly modified PTFE was used to reduce the aqueous liquid repellent properties of PTFE. A 20 kGy dose for modified PTFE surface was suitable in air additivity in antifriction, anticorrosion, antifouling, lubrication, and noise reduction coatings. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 435–441, 1998     

Plasma polymer deposition from mixture of tetramethoxysilane and oxygen on PET films and their oxygen gas barrier properties

Plasma polymerization of silane compounds has been discussed for deposition of SiOx positron emission tomography (PET) films at room temperature. A mixture of tetramethoxysilane (TMOS) and oxygen containing 60 mol % O₂ is a preferable raw material for SiOx formation by plasma polymerization. The deposited plasma polymers consist mainly of Si(SINGLE BOND)O networks with small amount of Si(SINGLE BOND)OH and Si(SINGLE BOND)C groups. A part of Si(SINGLE BOND)O networks in the plasma polymers is distorted by the Si(SINGLE BOND)OH and Si(SINGLE BOND)C groups. The oxygen permeability coefficient for the plasma polymer itself is 2.1 × 10⁻¹⁵ (STP) cm³/cm/cm²/s/cm Hg, which is lower than that for hydrolyzed ethylene-vinylacetate copolymer (Eval) and poly(vinylidene chloride) (Saran). Conclusively, the plasma polymer deposited from the mixture of TMOS and oxygen containing 60 mol % O₂ is a material with good oxygen barrier properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1031–1039, 1997     

AN EXPERIMENTAL STUDY OF POLYMER DIFFUSION IN CONCENTRATED SOLUTION: IMPLICATIONS FOR DIFFUSION IN POLYMERIZATION

The Trommsdorf or gel effect in free radical polymerization is due to the fact that the termination reaction becomes strongly diffusion controlled above a critical concentration associated with the onset of molecular entanglements. Therefore, an understanding of polymer self-diffusion in entangled systems becomes essential to understanding the Trommsdorf effect. Our group has previously proposed a molecular model for the gel effect which uses a specific theory for polymer diffusion (reptution). The present work represents an experimental attack on the same problem Experimental studies of polymer self-diffusion in entangled systems are scarce. Quasielastic light scattering from ternary systems composed of solvent(l)-polymer(2)-polymer(3), in which species (3) is isorefractive to the solvent (i.e. 0n/0c ₃ = 0), offers an attractive way to study the tracer diffusion coefficient of species (2) in a binary mixture of composition c ₃. In regimes of low momentum transfer (qR _G < 1,) where q is the scattered wave vector and R _G is the polymer radius of gyration, we have shown that the correlation function of the scattered electric field should decay with a single exponential decay time, given by (D₂₂ q ²)^?1 where D ₂₂(c ₂, c ₃) is the main ternary diffusion coefficient of component (2). Extrapolation to zero concentration of 2) at fixed concentration of (3) yields the tracer diffusion coefficient of (2) in the binary mixture of (1) and (3). The systems toluene(l)-polystyrene(2)-polymethylmethacrylate(3) (0n/0c ₃ ≈ 0.007 at 25°C) and toluene(l)-polystyrene(2)-polyvinylmethylether (3) (0n/0c ₃ ≈ 0.012 at 60°C) very nearly satisfy the above criteria. In both systems, we have found that the tracer diffusion coefficient of the polystyrene decreases with increasing concentration of the isorefractive polymer. Further studies have focused upon the dependence of the tracer diffusion coefficient upon polystyrene molecular weight, and upon the effect of incomplete index matching.     

Properties of biodegradable hydrogels prepared by γ irradiation of microbial poly(ϵ-lysine) aqueous solutions

Poly(?-lysine) (PL) hydrogels have been prepared by means of γ irradiation of PL produced by Streptomyces albulus in aqueous solutions. When the dosage of γ irradiation was 70 kGy or more and the concentration of PL in water was 1–7 wt %, transparent hydrogels (opaque hydrogels for 1–3 wt % PL concentration) could be produced. In the case of 70 kGy of γ irradiation and 5 wt % PL concentration, the specific water content (wt of absorbed water/wt of dry hydrogel) of the PL hydrogel was approximately 160. Specific water contents of PL hydrogels decreased markedly with an increase in the dosage of γ irradiation. The specific water contents were increased with an increase in PL concentration in the irradiated solution. This result indicates the presence of a radical scavenger in the PL solution. Swelling equilibria of PL hydrogels were measured in water or in aqueous solutions of various pHs or concentrations of NaCl, Na₂SO₄, and CaCl₂. Under acid conditions, the PL hydrogel swelled due to the ionic repulsion of the protonated amino groups in the PL molecules. The degree of deswelling in electrolyte solution was smaller than that of other ionic hydrogels [poly(γ-glutamic acid), poly(acrylic acid) etc.]. In addition, the enzymatic degradations of PL hydrogel were studied at 40°C and pH 7.0 in an aqueous solution of the neutral protease [Protease A (Amano)] produced from Aspergillus oryzae. The rate of enzymatic degradation of the respective PL hydrogels was much faster than the rate of simple hydrolytic degradation. The rate of enzymatic degradation decreased with the increase in γ-irradiation dose during preparation of the PL hydrogel. © 1995 John Wiley & Sons, Inc.     

Oxygen Transport in Aluminum Nitride Substrates

The diffusion of oxygen in commercially available aluminum nitride substrates has been studied by performing interdiffusion-type experiments. The diffusion of oxygen both within AlN grains and along grain boundaries was investigated. By using as-received AlN substrates and an electron microprobe as an analytical tool, it was found that the rate of oxygen diffusion along grain boundaries was strongly influenced by the presence of impurities and/or other phases at these boundaries. The diffusion of oxygen within AlN grains was studied between 1600° and 1900°C in a flowing nitrogen atmosphere by using secondary ion mass spectrometry (SIMS) for determining oxygen concentration profiles. The chemical diffusion coefficient of oxygen in the AlN lattice as a function of temperature is described by the equation The oxygen concentration profiles determined by SIMS also show a contribution from diffusion along grain boundaries. Therefore, it was possible to determine values for the product δD'_o (δ= width of grain boundaries, D'_o= grain boundary diffusion coefficient of oxygen).     

Electrical conductance of irradiated NBR/LDPE conductive blend during swelling in benzene

The effect of γ-irradiation on both the electrical conductance, Y, and diffusion coefficient, D, of acrylonitrile butadiene rubber mixed with different concentrations (1, 3, and 5 phr) of low-density polyethylene (LDPE) that was swollen in benzene, have been studied. The diffusion coefficient decreases with increasing the γ-irradiation dose for loaded samples with 1 and 3 phr of LDPE content, while samples with 5 phr of LDPE show a significant increase of diffusion coefficient with the increase of the radiation dose. The electrical conductance was found to be highly affected by the γ-irradiation dose. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1639–1645, 1997     

The effect of casting solvent and water on gas permeability of poly(γ-methyl L-glutamate) membrane

Gas permeability of poly(γ-methyl L-glutamate) (PMLG) membranes prepared by using dichlorethane, trifluoroacetic acid, and formic acid as solvents was studied. The membranes prepared by casting dichloroethane and trifluoroacetic acid solutions of the polymer, designated as PMLG—DCE and PMLG—TFA, respectively, had α-helical structures according to infrared absorption spectra, while the membranes prepared by allowing the PMLG—TFA membranes to swell in formic acid, designated as PMLG—FA, had mainly a β-sheet structure. The diffusion coefficients of each gas studied for PMLG—DCE, PMLG—TFA, and PMLG—FA decreased in that order, and the apparent activation energies of diffusion increased in that order. The apparent heats of solution for Ne,O₂, N₂, and CO₂ were negative in PMLG—FA. These results were discussed in connection with the molecular conformations of PMLG in the membranes. It is suggested that the diffusion of gases in PMLG—DCE takes place in the side-chain regions between helices, while in PMLG—FA the diffusion occurs across the polymer main chain whose mobility is depressed by the intermolecular hydrogen bonds. The effect of water on oxygen permeability of PMLG—DCE was small; on the contrary that of PMLG—FA was very large. Furthermore, it is assumed that the random-coil conformation partly exists in PMLG—TFA.     

Aggregation in solutions of poly(γ-benzyl-l-glutamate) monitored by static and dynamic light scattering

We have studied dilute and semidilute solutions of poly(γ-benzyl-l-glutamate) in 1,2-dichloroethane by static and dynamic light scattering. The aggregational behaviour of the semiflexible polymer is evidenced in both static and dynamic scattering, and is sensitive to the temperature and the polypeptide molecular weight. In particular, both the reciprocal specific scattering intensity and the effective decay rate of the dynamic correlations exhibit a minimum as a function of the concentration. The slope of effective diffusion coefficient versus the square of the scattering vector displays an anomalous maximum as a function of the concentration which can also be attributed to aggregation. The experimental evidence is compatible with head-to-tail dimerization of the polymer as the concentration increases.     

Dye-sensitized photopolymerizations of acrylic monomers in the presence of fibrous proteins

Dye-sensitized photopolymerizations of low concentrations (1–5%) of acrylic monomers proceed at 40°C., if fibrous proteins (keratin, fibroin or collagen) are suspended in solution. In the absence of dye (riboflavin or fluorescein) or fibrous protein no appreciable photopolymerization of monomer is observed at the short irradiation times (120 min.). Graft products containing 0.5–23% polymer are found. The quantity of grafted polymer introduced into the protein depends on the chemical nature and concentration of monomer, dye, and fibrous protein. Homopolymerization of monomer is observed to some extent in each graft polymerization. In the presence of oxygen an induction period ia found, but removal of oxygen from solution greatly retards these photo-polymerizations. Chemical and physical characterization of the protein–polymer products suggests that only a small number of initiation and grafting sites are present in the protein and that the grafted polymer partially resides within the protein matrix. We believe these photopolymerizations proceed via a free-radical pathway involving radicalabstraction of hydrogen from the protein by dye intermediates.     

A study of the contact angle on RTV-silicone treated in a hydrogen glow discharge

A hydrogen glow discharge surface treatment followed by exposure to the atmosphere has been used to decrease the contact angle for distilled water on RTV-silicone. The change in contact angle has been studied in terms of vacuum ultraviolet irradiation, metastable bombardment, free-radical bombardment, and electrostatic charging. The study demonstrates that the decrease in the contact angle is caused by the interaction of the hydrogen atoms produced in the glow discharge with the polymer surface.