Radiation-induced oxidative degradation of poly(vinyl chloride)

Gas evolution and oxygen consumption in the γ-irradiation of PVC were studied. The gas evolution and the oxidative degradation are retarded by the presence of plasticizers and stabilizers. The G(HCI) and G(H₂) and 8 and 0.24 for the irradiation of pure PVC under vacuum and 0.02 and 0.14 for that of plasticized PVC, respectively. Gas evolution increases in the presence of oxygen, specially for the pure PVC. The G(–O₂) values for the pure and plasticized PVC are 30 and 12, respectively. The dependence of gas evolution and oxygen consumption on the oxygen pressure is more pronounced for the plasticized PVC than pure PVC because the oxygen diffusion is controlled.     

Effects of gamma radiation on two aromatic polysulfones. II. A comparison of irradiation at various temperatures in air-vacuum environments

The aromatic polysulfone poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneiso-propylidene-1,4-phenylene) (I) showed no change in flexural yield strength after doses of γ-radiation up to 600 Mrad in vacuum at 35,80, and 125°C (T_g = 190°C)). However, the flexural strength decreased markedly with doses above 100 Mrad on irradiation in air, to 40–60% of the initial value after 200–400 Mrad, depending on the sample and the irradiation conditions. Chain crosslinking was predominant over scission for irradiation in vacuum at all temperatures; (G(X), G(S), and G(S)/G(X) increased with the irradiation temperature, but G(S)/G(X) decreased to zero above T_g. Poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) (II) behaved similarly, except that the flexural strength was found to be very dependent on the thermal treatment of the sample. This polymer showed a remarkable retention of its mechanical properties on irradiation up to 200°C (T_g = 230°C) in the absence of air, the flexural strength being retained up to 500 Mrad. Radiation annealing occurred at 35°C in vacuum and air and combined radiation and thermal annealing at 125 and 220°C. Progressive removal of surface layers from flexural test bars of I irradiated in air showed that the decrease in flexural strength with dose could be explained by a decrease in the molecular weight towards the surface resulting from radiation-oxidation reactions.     

Effects of gamma radiation on two aromatic polysulfones

Two aromatic polysulfones, poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneisopropylidene-1,4-phenylene) (I) and poly (oxy-1,4-phenylenesulfonyl-1,4-phenylene) (II), undergo crosslinking and chain scission at 30°C during γ-irradiation, the former being predominant in vacuum and the latter in air. Both processes occurred more readily in I, which contains isopropylidene linkages. Gel measurements gave G(crosslink) = 0.051, G(scission) = 0.012 for this polymer at 30°C in vacuum. Increased irradiation temperatures resulted in higher crosslinking and gas yields, especially above the glass transition temperature. The tensile strength, flexural strength, and modulus of I were unaffected by γ-irradiation up to about 50 Mrad in air, but the strength decreased markedly at higher doses. The elongation at break decreased progressively with dose. For both polymers, G(gas) = 0.04 at 30°C with the main products being SO₂, H₂, CO₂, CH₄, and H₂O.     

Degradation of polystyrene by gamma irradiation: Effect of air on the radiation-induced changes in mechanical and molecular properties

Irradiation of 3 mm polystyrene sheet in air at 30°C with γ rays caused a rapid decrease in the tensile and flexural strengths and strains to fracture. These properties were decreased to 50% of their initial values after ca. 80 Mrads and to 25% after ca. 200 Mrads, beyond which dose the rate of change was relatively small. These results contrast with the negligible changes that are observed after 600 Mrads in vacuum. The effect of irradiation in air has been correlated with decreasing molecular weight at the surface, even though crosslinking predominated over the complete sample so that a gel point was reached at a dose slightly in excess of 100 Mrads. Scission and crosslinking yields, G(S) and G(X), were determined as a function of depth by gel permeation chromatography of layers removed progressively from the surface. G(S) decreased and G(X) increased with depth, in accord with the concepts of increased scission by reaction with oxygen and a diffusion effect. Unusual transverse cracking to a limited depth occurred during tensile measurements, a phenomenon that is attributed to the nonuniform molecular weight profile.     

Gamma irradiation of polypropylene fibers in the presence of carbon tetrachloride

Polypropylene (PP) fibers have been irradiated with ⁶⁰Co γ rays in the presence of carbon tetrachloride, in the absence of oxygen. Irradiations have been carried out between dose rates of 0.078 and 0.664 Mrad/hr, and the effects of absorbed dose and temperature on the C? Cl formation in the PP fibers have been investigated. G(C? Cl) values were higher at lower dose rate. G(HCl) values were found to be much higher than the G(C? Cl) values, and IR absorption studied indicated increasing unsaturation with increasing dose. The number average molecular weights (M?_n) were evaluated from intrinsic viscosity measurements in decalin at 408 K and the M?_n values decreased with increasing dose and temperature. G(scission) ? G(crosslinking) values were calculated and it was found that the G_s ? G_x values are higher at lower doses and higher dose rates. The thermal characteristics of the irradiated fibers were investigated by thermogravimetry (TG) analysis in air or argon and with differential scanning calorimetric (DSC) studies. The TG data indicated slightly less thermal stability for the modified fibers both in air as well as argon. The DSC data indicated very little change in the melting points of the samples, the melting points being around 444 ± 2 K.     

Statistical evaluation of methylol-free melamine-formaldehyde oligomer distributions: Empirical formulae from elemental analysis

The problem of measuring quantitatively and reliably the proportions of methylene- and ether bridges in melamine-formaldehyde resins has resisted chemical and spectroscopic approaches. Such measurements are specially required for refining statistical models of the overall crosslinking reaction. Pregel samples contain oligomer mixtures which can be freed from pendent methylols by treatment with ammonia. They obey the empirical formula (C₃N₆H₆)₁(CH₂)_R(H₂O)_z, where R and z can be found by optimising over measurements of %C, %N and %H. The accepted structures lead to prediction of z = −0.5R if only ether bridges are present or z= −R if only methylene bridges are present. In principle, intermediate values of −0.5R>z>-R could allow the proportions of the two kinds of bridges to be determined. However, over a wide range of ratios R of formaldehyde to melamine, results are found to obey z = −0.2R, indicating retention of free water in the samples. Prolonged vacuum drying at room temperature may overcome the problem.     

γ‐Radiation‐Induced Graft Copolymerization of Ethyl Acrylate onto Hydroxypropyl Methylcellulose

Summary: Graft copolymerization of EA onto water‐soluble HPMC was carried out using γ‐radiation using both simultaneous and preirradiation in an aqueous medium. The effects of radiation environment, radiation dose, monomer concentration, and reaction temperature on percentage of grafting (G) and grafting efficiency (G_E) were investigated. For preirradiation, the observed values for G and G_E were higher in air than in a nitrogen atmosphere. G and G_E values are obviously higher for preirradiation; their maximum values were obtained for a radiation dose of 1.8 kGy. The grafting parameters increase for increasing monomer concentration up to 0.15 mol · L^?1, where they reach their saturation values. In the case of preirradiation, the largest grafting parameters are obtained at 65 °C. The graft copolymers obtained were characterized by FTIR spectroscopy, TEM, SEM, and XRD methods. The method of irradiation significantly affects the mechanical properties of the grafted HPMC samples. Samples prepared by simultaneous irradiation show superior mechanical properties. In addition, the equilibrium humidity adsorption behaviors of the grafted copolymers were also studied, and the humidity resistance behavior of HPMC was enhanced through the grafting copolymerization.

Transmission electron micrograph of the HPMC‐g‐PEA water dispersion.     

Unusual Elastic and Mechanical Behaviors of Copper Phosphate Glasses with Different Copper Valence States

Elastic and mechanical properties such as Young's modulus E, Poisson's ratio ν, Debye temperature θ_D, Vickers hardness H_v, fracture toughness K_c, and fracture surface energies γ_f of yCuO_x·(100−y)P₂O₅ glasses (y= 45, 50, 55) with different copper valence states, i.e., R(Cu⁺) = Cu⁺/(Cu⁺+ Cu²⁺), at room temperature (humidity 64%) have been examined. The following features have been found: (1) the glass transition temperature (218–434°C), H_v (2.7–4.4 GPa), E (50.6–78.2 GPa), and θ_D (358–434 K) decrease largely with increasing R(Cu⁺); (2) the mean atomic volume, K_c (0.56–1.14 MPa·m^1/2), and γ_f (1.9–11.2 J·m⁻²) tend to increase with increasing R(Cu⁺); (3) 50CuO_x·50P₂O₅ glasses with R(Cu⁺) = 0.42 and 0.55 have a high resistance against crack formation in Vickers indentation tests and no crack is observed in the 45CuO_x·55P₂O₅ glass with R(Cu⁺) = 0.57 under an applied load of about 98 N. The results demonstrate that elastic and mechanical properties of yCuO_x·(100−y)P₂O₅ glasses depend strongly on the copper valence state and the CuO_x/P₂O₅ ratio. The unusal mechanical and elastic properties of copper phosphate glasses are well explained qualitatively by considering unique oxygen coordination and bonding states of Cu⁺ ions, i.e., lower coordination number and more covalent bonding compared with Cu²⁺ ions.     

Synthesis and Surface Active Properties of tri[(N‐alkyl‐N‐ethyl‐N‐Sodium carboxymethyl)‐2‐Ammonium bromide ethylene] Amines

Trimeric betaine surfactants tri[(N‐alkyl‐N‐ethyl‐N‐sodium carboxymethyl)‐2‐ammonium bromide ethylene] amines were prepared with raw materials containing tris(2‐aminoethyl) amine, alkyloyl chloride, lithium aluminium hydride, sodium chloroacetate, and bromoethane by alkylation, Hoffman degradation reaction, carboxymethylation and quaternary amination reaction. The chemical structures of the prepared compounds were confirmed by FTIR, ¹H NMR, MS and elemental analysis. With the increasing length of the carbon chain, the values of their critical micelle concentration initially decreased. Surface active properties of these compounds were superior to general carboxylate surfactants C₁₀H₂₁CHN⁺(CH₃)₂COONa. The minimum cross‐sectional area per surfactant molecule (A_min), standard Gibbs free energy adsorption (ΔG_ads) and standard Gibbs free energy micellization (ΔG_mic) are notably influenced by the chain length n, and the trimeric betaine surfactants have greater ability to adsorb at the air/water interface than form micelles in solution. The efficiency of adsorption at the water/air interface (pC₂₀) of these surfactants increased with the increasing length of the alkyl chain. Their foaming properties, wetting ability of a felt chip, and lime‐soap dispersing ability were also investigated.     

硼酸盐热力学基元贡献模型及在MgBO2(OH)纳米晶须水热合成过程分析中应用

以MgCl₂·6H₂O、H₃BO₃、NaOH为原料,控制摩尔比Mg:B:Na=2:3:4,经室温共沉淀及水热转化(220～240℃,6.0～30.0 h)制得了单斜相MgBO₂(OH)纳米晶须。借鉴机械混合模型、基团贡献法思想,根据质量守恒原则将硼酸镁盐按照复盐分子式进行基元拆分,通过引入校正因子k,利用复盐基元的基础热力学数据拟合建立了Δ_fH_m及Δ_fG_m等硼酸盐热力学基础数据估算的基元贡献模型,估算了共沉淀产物Mg₇B₄O₁₃·7H₂O及水热产物MgBO₂(OH)不同温度下的Δ_fH_m、Δ_fG_m热力学数据,得到了25～100℃下共沉淀反应及25～250℃下水热转化的Δ_rH_m、Δ_rG_m。结果显示,共沉淀反应在室温条件下可自发进行,水热转化须借助一定温度条件方能自发实现,且反应趋势随水热温度升高时间延长而增大。该热力学基元贡献模型有望为其他结构复杂复盐化合物纳米结构的湿化学法控制合成分析及预测提供借鉴。     

γ-radiation-induced telomerization of vinyl acetate,styrene, and methyl methacrylate

Vinyl acetate (VAc), styrene (St), and methyl methacrylate (MMA) were irradiated in dilute solution at an absorbed dose rate of 0.5 Mrad/hr in the absence of oxygen at room temperature. In homogeneous systems, telomers are formed with a rate ∝ [M]¹ at monomer concentrations [M] > ca. 0.4M. The chain length (D.P. .n) increases with increasing [M]. (D.P. .n)^?1 depends over large ranges of [M] linearly on the ratio [S]/[M] (S = solvent) in accordance with the Mayo equation. These findings were obtained with VAc in methanol and with St in cyclohexane. In heterogeneous systems, telomer is formed at all monomer concentrations. The 100-eV yield for telomer formation passes a maximum of G_T(–M) = 40 (MMA in 2-propanol) and G_T(–M) = 27 (MMA in cyclohexane) at the onset of polymer formation ([M] ～ 3 vol-%). With the system St/2-propanol, G_T(–M) ～ 15 was found being independent of [M]. The molecular weight M _n (telomer) increased from ca. 600 to ca. 1200 by increasing [M] up to 100 vol-% (MMA/2-propanol). M _n (telomer) does not depend on [M] in the other two cases (M _n ～ 500, MMA/cyclohexane; M _n ～ 700, St/2-propanol).     

Sensor composites consisting of a ceramic substrate and thin films of TbOx oxides and (TbOx)0.5(YO1.5)0.5 solid solutions

A porous nanoceramic material based on aluminum magnesium spinel is synthesized. Films based on terbium oxide and the (TbO _x )_0.5(YO_1.5)_0.5 solid solution are prepared by the sol-gel processing and thermal vacuum evaporation onto a MgAl₂O₄ substrate. The temperature dependences of the electrical resistance of the films in air and CO₂ are investigated. The maximum values of the relative sensitivity coefficient of the films under investigation are determined.     

Application of radiation curing in the preparation of polycarbosilane-derived SiC fibers

Polycarbosilane fibers were irradiated by gamma-rays under vacuum and by electron beam in He gas flow or under vacuum at room temperature. Free radicals on Si and C atoms were produced. Most radicals reacted with each other, causing cross-links between polycarbosilane molecules. Some radicals, which did not contribute to cross-linking, were fairly stable under vacuum or in inert gas at room temperature but oxidized on exposure to air. The number of stable radicals under vacuum could be decreased by annealing. The remaining radical concentration was about 1% after annealing at 513 K. By a combination of radiation curing and annealing, SiC fibers with smaller quantities of oxygen were prepared. The mechanical properties of the SiC fibers showed a high tensile strength of 2.5 GPa after heat treatment at 1773 K. On the other hand, polycarbosilane fibers could be cured by radiation oxidation at room temperature, that is, gamma-ray or electron irradiation in oxygen, and the oxygen content could be well controlled by irradiation dose and dose rate. The SiC fibers obtained by the radiation oxidation had an oxygen gradient from the surface to the center which was dependent on the radiation oxidation conditions.     

Thermodynamic properties of methanol–benzene mixtures at elevated temperatures

The total pressure and the compositions of the vapour and liquid phases of the methanol–benzene system have been determined under equilibrium conditions at 100°, 120°, 140°, 160°, 180°, 200° and 220° for ten levels of concentration. The corresponding activity coefficients of methanol and benzene are reported; their values indicate that the equilibrium data are thermodynamically consistent. An azeotrope is found at all temperatures, its methanol content increasing as the temperature is increased. The relationship log P_az = 6·5098—(1,766/T) expresses the interdependence of the azeotrope vapour pressure P_az(lb/in² abs.) and temperature T(°K). Estimates of integral heat of mixing (H^E) and entropy change due to mixing (S^E) as functions of liquid composition (x_meth) have been made from the excess free energy of mixing G^E,(T) x_meth functions. Both H^E and S^E at a given x are positive increasing functions of temperature. These phenomena are discussed in terms of the dissociation of methanol ‘polymer’ and the formation of benzene–methanol ‘complexes’.     

Characterization of gamma irradiated polyethylene films by DSC and X‐ray diffraction techniques

The effect of gamma radiation on the thermal behavior and crystalline structure of low density polyethylene (LDPE) has been investigated using differential scanning calorimetry (DSC) and X‐ray diffraction techniques (XRD). Gamma irradiation was carried out in atmospheric air to a maximum dose of 883 kGy. DSC results of the heating run from room temperature up to 150 °C showed that the melting temperature (T_m), and onset temperature of LDPE film decrease linearly with increasing irradiation dose. However, upon cooling LDPE film from 150 °C to room temperature, the crystallization temperature (T_c) and onset temperature were found to decrease non‐linearly with increasing irradiation dose up to 500 kGy and then tended to level off. The change in heat of fusion (ΔH_f) with irradiation dose was found to proceed with different behaviour, two stages, with a kink at irradiation dose of about 500 kGy, being observed. This suggests the occurrence of degradation and crosslinking at low and high doses, respectively. However, parameters of the X‐ray diffraction pattern such as number of diffraction patterns, peak position (2θ) and width of the diffraction pattern, support the results of DSC measurements. © 2000 Society of Chemical Industry     

The antioxidant effect of natural substances on lipids during irradiation of chicken legs

Entire fresh chicken legs were subjected to three pretreatments (packaged in air; packaged under vacuum; or marinated in natural plant extracts and packaged in air) followed by irradiation (0, 3, or 5 kGy). The control and irradiated chicken legs were stored at 4°C and analyzed for FA composition and sensory quality at predetermined intervals. Irradiation dose had a significant (P<-0.01) effect on FA derived from phospholipid but less than on FA derived from a neutral lipid. In general, levels of unsaturated FA decreased as the radiation dose increased; however, for marinated chicken legs irradiated with 5 kGy, levels of linoleic acid (C_18∶2) and arachidonic acid (C_20∶4) derived from the phospholipid fraction were significanlty (P≤0.05) higher than those irradiated in air or under vacuum. The concentration of FA also decreased significantly (P≤0.05) as storage time increased. For chicken legs packaged in air or marinated and then packaged in air, significant (P≤0.01) inverse correlations existed between high-carbon-number PUFA and lower-carbon-number (≤17) saturated FA; this relationship was not apparent in samples irradiated under vacuum. A processing combination of marinating and vacuum packaging might better control lipid oxidation and degradation in irradiated chicken. Panelists found no significant difference (P>0.05) in the flavor and oder intensity of cooked irradiated chicken legs and their nonirradiated equivalents.     

Effects of various ester groups in γ-radiation degradation of syndiotactic poly(methacrylate)s

The γ irradiation of poly(methacrylate)s with various ester groups at room temperature was investigated by gel permeation chromatography and NMR techniques. The G values for scission and crosslinking for each of the polymers were estimated from the changes in the molecular weights and molecular weight distributions. The new structures formed during γ irradiation were examined by ¹H-NMR spectroscopy. All of the investigated poly(alkanemethacrylate)s were found to produce the alkane formates during γ irradiation, and for poly(2-methyl heptyl methacrylate) G(S) was less than 4G(X), indicating gel formation in this polymer. In the investigation of poly(benzyl methacrylate), no formate ester was found, but some small molecule compounds formed from the benzyl radical were detected. The benzyl group was also found to stabilize the polymer against radiation damage. © 1996 John Wiley & Sons, Inc.     

The Inclusion of Organometallic Derivatives of Cyclotriphosphazenes Inside SiO2 Matrix and Their Conversion to Nanostructured Metal-Oxides and Phosphates

Organometallic derivatives of the cyclotriphosphazene N₃P₃[OC₆H₄CH₂CN·TiClCp₂]₆ (1), N₃P₃(O₆H₅)₅[OC₆H₄N·W(CO)₅] (2), N₃P₃[OC₆H₄CH₂CN·Mo(CO)₅]₆ (3), [N₃P₃(O₆H₅)₅(OC₅H₄N·CpRu(PPh₃)₂)][PF₆] (4), [N₃P₃(O₂C₁₂H₈)₂OC₅H₄N·Ag(PPh₃)][OSO₂CF₃] (5), N₃P₃[OC₆H₅]₅ [OC₅H₄N·Cu][PF₆] (6) and N₃P₃[OC₆H₄CH₂CN·CuCl]₆[PF₆]₆ (7),were incorporated inside SiO₂ through the sol–gel method. The metal–organic nanocomposites of the general formula N₃P₃[OC₆H₄CH₂CN·TiClCp₂]₆·nSiO₂ (G ₁ ), N₃P₃[OC₆H₄N·W(CO)₅]·nSiO₂ (G ₂ ), N₃P₃[OC₆H₄CH₂CN·Mo(CO)₅]₆·nSiO₂ (G ₃ ), N₃P₃(O₆H₅)₅OC₅H₄N·CpRu(PPh₃)₂][PF₆]·nSiO₂ (G ₄ ), [N₃P₃(O₂C₁₂H₈)₂OC₅H₄N·Ag(PPh₃)][OSO₂CF₃]·nSiO₂ (G ₅ ), N₃P₃[OC₆H₅]₅[OC₅H₄N·Cu][PF₆]·(SiO₂) _n (G ₆ ), and N₃P₃[OC₆H₄CH₂CN·CuCl]₆[PF₆]₆·(SiO₂) _n (G ₇ ), were characterized by IR spectroscopy; ¹²C, ³¹ P and ²⁹Si MAS NMR measurements as well as UV–Visible diffuse reflectance spectra, indicating the presence of the respective organometallic derivatives of the cyclotriphosphazene incorporated into SiO₂. Pyrolysis of these nanocomposites under air at 800 °C gives rise to nanostructured metal-oxides and metal phosphates incorporated into amorphous SiO₂, with the presence in some cases of complexes phase mixtures. From some precursors, we obtained metal-oxides/phosphates nanoparticles separated from the SiO₂ nanoparticles instead the oxides/phosphates nanoparticles inside the SiO₂ matrix. Additionally and for comparison purposes, we used the compound N₃P₃[NH(CH₂)₃Si(OEt)₃]₆ as gelator. Nanocomposites (G′ ₁ ), (G′ ₂ ) and (G′ ₃ ) exhibited mainly morphological differences while in some cases composition differences when using TEOS as gelator. Some simple metal-containing compounds as (O₃SCF₃)Ag(PPh₃)(HOC₅H₄N), [CuCl₂·NC₅H₄OH] and [CuCl₂·NCCH₂C₆H₄OH]—which are useful models of the most complexes (G ₅ ), (G ₆ ) and (G ₇ ) were also prepared and incorporated in amorphous silica. Their pyrolytic products were compared with those of more complex cyclotriphosphazene analogous. Interestingly, the pyrolysis of the nanocomposite [(O₃SCF₃)Ag(PPh₃)(HOC₅H₄N)][SiO₂] _n affords the firstly-reported materials containing Ag₂O along with SiO₂ nanoparticles.     

Some effects of ionizing radiation on a polyhydroxyether

The behavior of the polyhydroxyether derived from bisphenol A and epichlorohydrin on exposure to electron irradiation (0–500 Mrads) in vacuum has been investigated. The polymer underwent chain scission, G = 0.20 (scission per 100 e. v.), with no evidence of crosslinking. Degradation was accompanied by the loss of H₂ together with smaller quantities of CO, CO₂, and CH₄. Spectroscopic studies are reported, and a mechanism of degradation is proposed. The tensile yield stress and fracture energy of molded specimens were also examined, and changes in these properties as functions of radiation dose and molecular weight are discussed.     

Vapor-liquid equilibrium,excess gibbs energy and excess enthalpy of 1, 3 dioxolane-methylcyclohexane at t = 313.15 k

Data on vapor-liquid equilibrium and enthalpy of mixing H^E are, obtained for the mixture 1, 3 dioxolane-methylcyclohexane at 313.15 K (40.0°C). Correlation of the data is given by using Redlich-Kister expressions and the excess functions G^E = RT(X₁ In γ₁ + X₂ In γ₂) and TS^E = H^E - G^E are thereby calculated. A comparison is made between this mixture and those formed by 1, 3 dioxolane with cyclohexanol and cyclohexanone.