Stabilization of low‐density polyethylene films containing metal stearates as photodegradants

The effect of various stabilizer additives on Low‐Density Polyethylene films with a thickness of ca. 40 μm and containing metal stearates was studied. The films were subjected to accelerated aging in a QUV Weatherometer. The apparatus was fitted with A320 lamps and operated on a dry cycle at 63°C and an irradiance of 0.67 W/m². A phosphite (Naugard P) and a phosphate (Alkanox 240P) antioxidant provided good stabilization against UV degradation accelerated by transition metal photocatalysts such as cobalt stearate. These compounds outperformed HALS‐based UV stabilizers and a metal deactivator (Irganox MD 1024) at the concentrations tested. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Cinnamylidene-amine-sensitized photodegradation of polyethylene

The activity of Schiff's bases of cinnamic aldehyde and aromatic amines in the controlled photodegradation of polyethylene (PE) was studied. N-cinnamylidene anilines containing different substituents in the amine ring (methyl group, halogen, or amine group) and N-cinnamylidene α-naphthyl amine were synthesized and introduced into the polyethylene films by compression molding or extrusion, and they were exposed to the filtered ultraviolet light produced by mercury lamp. The changes in molecular weight, tensile strength, and characteristic IR absorptions were followed during irradiation to control the processes undergoing in the polymer films. It was discovered that N-cinnamylidene anilines containing methyl or halogen substituents and N-cinnamylidene α-naphthyl amine accelerated the photodegradation of polyethylene. Their sensitizing activity increased when the mixtures of Schiff's bases and stannous laurate were introduced into the polymer. PE films containing these additives became brittle after 600 h exposure to the artificial UV light which was the equivalent of 1.5–2 years exposure to the natural sunlight in the medium geographic latitudes. The mechanism of the initial step of photodegradation is discussed.     

Catalytic action of metal salts in autoxidation and polymerization. X. The effect of various metal stearates on the thermal oxidation of 2,6,10,14-tetramethylpentadecane

The various metal stearate-catalyzed thermal oxidations of 2,6,10,14,-tetramethylpentadecane (TMPD, a model compound of polypropylene) and the decomposition of TMPD hydroperoxide (TMPD-HPO) were carried out. The results obtained were compared with those of the oxidation of polypropylene reported previously;¹⁸ and the initial tion process of the oxidation of the polymer is discussed. The catalytic activity of metastearates in the oxidation of polypropylene differed from that in the oxidation of pure TMPD and was fairly similar to that in the oxidation of TMPD with TMPD-HPO. The more effective the catalyst for the decomposition of TMPD-HPO, the more effective it was for the oxidation of both TMPD with TMPD-HPO and polypropylene. The results apparently indicate that metal catalysts enhance the decomposition of hydroperoxides which presumably contaminate the polymer and form during the oxidation, and also imply that the initiation of the oxidation of polypropylene is primarily affected by the presence of hydroperoxide contamination of the polymer.     

Study of the degradation of polyurethanes. I. The effect of various metal acetylacetonates on the photodegradation of polyurethanes

Photodegradation of polyurethanes based on polyester diol-diphenylmethane-p,′p-diisocyanate in the absence and presence of various metal acetylacetonates (Ti, V, Cr, Mn, Co(II), Co(III), Fe, Ni, Cu, Zn, Mg, Al, and Sn) was carried out; and the effect of these metal compounds on the degradation was examined by investigating the changes in the stress–strain properties and infrared- and ultraviolet-visible spectra of the polymer. The results obtained were as follows: Co(III), Co(II), Cu, Ti, and Sn acetylacetonates substantially enhanced the photo-oxidation of the polyurethane; and Al, Ni, and Zn acetylacetonates scarcely affected, or slightly retarded, it. The other metal acetylacetonates accelerated more or less the photo-oxidation of the polymer. Co(III), Co(II), and Cu acetylacetonates extremely degradation. Wavelength of the irradiated light was responsive to photochemical reactions of functional groups in the polymer. C? N and C? O bonds of urethane groups were very accessible to the photo-irradiation both without and with a glass filter, while methylene groups were rather stable to the irradiated light longer than 300 nm, through a glass filter. The effect of the metal compounds on the coloration of the polymer was also consistent with that of mechanical strength and infrared spectral changes.     

The ductile-brittle transition of low-density polyethylene

The impact behavior of a low-density polyethylene was studied with an instrumented Charpy tester. A change from elastic or ductile response to brittle fracture was observed over a small temperature interval, usually within 1°C. This characteristic impact transition temperature (ITT) was highly sensitive to shallow, sharp notches. Whereas an unnotched test bar had a very low impact transition temperature of ?94°C, a razor cut with a depth of only 5 percent of the total thickness raised it to ?4°C. The impact transition temperature was effectively reduced by increasing the cooling rate during specimen preparation and by the addition of nonpolar liquids, On the other hand, impact properties were adversely affected by aging, annealing, and adding other thermoplastics.     

The effect of dissolved transition metal complexes on the rate of yellowing of linseed oil

A number of metal complexes were examined as potential antiyellowing additives for linseed oil-based coatings. Yellowing was measured as the rate of increase of the absorbance at 400 nm of solutions of 20% linseed oil in toluene. Most metal complexes increased the yellowing rate, but 1,1-bis(diphenylphosphino)ferrocene retarded the rate by 50% over a wide concentration range, and some complexes caused nonlinear changes that might make them useful as additives.     

The effect of chemical element on hardness in high-entropy transition metal diboride ceramics

The relationship between the chemical elements of high-entropy boride (HEB) ceramics and their hardness is important for the prediction of high-hardness HEB ceramics. In this work, by designing four HEB ceramics with different chemical elements, the effect of lattice parameter difference factor (δ, represents the difference-degree in lattice parameters among the five individual constitute diborides) on phase composition and lattice-distortion, and the effect of rule of mixture (ROM) average hardness and lattice-distortion on HEB ceramics hardness were studied. The results indicated that, as δ value increases, more severe lattice-distortion occurs inside the HEB ceramics, and a single solid-solution is difficult to be formed. Furthermore, lattice-distortion and the ROM average hardness codetermine the HEB ceramics hardness. The greater lattice-distortion brings about significantly higher hardness for HEB ceramics than their ROM average hardness. Among the four HEBs, (Hf_0.2Zr_0.2Ta_0.2V_0.2Nb_0.2)B₂ exhibits the high hardness of 26 GPa measured using a load of 9.8 N.     

The effect of photodegradation of polystyrene on its permeability characteristics

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

Radiation-modified atactic polypropylene as a sensitizer for photodegradation of polyethylene

Atactic polypropylene (APP) was dissolved in CCl₄ and irradiated with ⁶⁰Co gamma rays in various gas atmospheres (air, O₂, N₂, and Cl₂). A small amount of the irradiated APP was blended with polyethylene (PE) as a sensitizer for photodegradation of PE. There was no significant acceleration of decrease in yield strength of PE with UV exposure when oxidized APP or chlorinated APP was used. On the contrary, the use of the APP which was both oxidized and chlorinated caused a considerable acceleration of decrease in both yield strength and elongation. From the fact that the amount of carbonyl groups formed in the matrix PE with UV light exposure was closely related to both the amount of carbonyl groups and the amount of C? Cl bonds existing in the APP before the UV exposure, it was concluded that the combined action of carbonyl groups and C? Cl bonds in the sensitizer is important in the promotion of the photodegradation of the matrix polymer.     

The effect of anions of transition metal salts on the structure of modified mesostructured silica films and monoliths

The structure of the preformed LC mesophase of water:transition metal salt ([M(H₂O)₆]X₂):acid (HX):oligo(ethylene oxide) (or Pluronics):tetramethylorthosilicate (TMOS) mixture during hydrolysis and partial polymerization of the silica source is maintained upon further polymerization and condensation of the silica species in the solid state. The liquid mixture in early stage of the silica polymerization could be casted or dip coated to a surface of a glass or silicon wafer to produce mesostructured silica monoliths and films, respectively. The silica species and ions (metal ions and anions) influence the structure of the LC mesophases (as a result, the structure of silica) and the hydrophilic and hydrophobic balance in the reaction media. The silica structure can be changed from hexagonal to cubic by increasing, for example, the nitrate salt concentration in the nitrate salt systems. A similar transformation takes place in the presence of very low perchlorate salt concentration. The salt concentration in the mesostructured silica can be increased up to 1.1/1.0 salt/SiO₂ w/w ratio, in mesostructured silica materials by maintaining its lamella structure in P123 and cubic in the C_nEO_m systems. However, the materials obtained from the P123 systems undergo transformation from lamella to 2D hexagonal upon calcinations. The method developed in this work can be used to modify the internal surface of the pores with various transition metal ions and metal oxides that may find application in catalysis.     

Synthesis and photodegradation behavior of polyethylene containing side-chain keto ether groups

The synthesis and photochemical behavior of the polymers obtained by grafting diazoacetophenones and p-substituted diazoacetophenones onto an ethylene–vinyl alcohol copolymer were studied. Photodegradation proceeds through a primary process with generation of acetophenone (or the p-substituted acetophenone) and “in chain” keto groups. A secondary photochemical process sensitized by these two units leads to oxidative photodegradation. The degradation leads to lowering of the molecular weight in prevalence to crosslinking. The effect of the p-substitution on the acetophenone with electron-withdrawing substituent has little effect on the degradation rate.     

Thermal and crystallization behaviors of polyethylene blends synthesized by binary late transition metal catalysts combinations

A series of reactor blends of linear and branched polyethylenes have been prepared, in the presence of modified methylaluminoxane, using a combination of 2,6‐bis[1‐(2,6‐dimethyphenylimino) pyridyl]‐cobalt(II) dichloride ( 1 ), known as an active catalyst for producing linear polyethylene, and [1,4‐bis(2,6‐diidopropylphenyl)] acenaphthene diimine nickel(II) dibromide ( 2 ), which is active for the production of branched polyethylene. The polymerizations were performed at various levels of catalyst feed ratio at 10 bar. The linear correlation between catalyst activity and concentration of catalyst 2 suggested that the catalysts performed independently from each other. The weight‐average molecular weights , crystalline structures, and phase structures of the blends were investigated, using a combination of gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, and small angle X‐ray scattering techniques. It was found that the polymerization activities and MWs and crystallization rate of the polymers took decreasing tendency with the increase of the catalyst 2 ratios, while melting temperatures (T_m), crystalline temperatures (T_c), and crystalline degrees took decreasing tendency. Long period was distinctly influenced by the amorphous component concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4188–4198, 2007     

The alpha-sulfonation of alkyl palmitates and stearates

Methyl, ethyl, and isopropyl esters of palmitic or stearic acid werea-sulfonated directly by the dropwise addition of a 2.4 molar ratio of liquid sulfur trioxide to the ester, with or without solvent, at 0C. Scission of the ester apparently takes place during sulfonation. Yield of the ester RCH-(SO₃Na)CO₂R was increased, and yield of by-product disodium salt was decreased by reesterification with methyl, ethyl, or isopropyl alcohol prior to neutralization. Direct sulfonation of the ester by sulfur trioxide, without solvent, gave 70-80% yields, increased 10% by the presence of a small amount of CCl₄ as the solvent (1 ml/g of ester). Mixtures of thea-sulfo ester and the disodium salt can be analyzed by infrared spectra. 1 Presented at the AOCS Meeting in Philadelphia, October 1966 2 E. Utiliz. Res. Dev. Div., ARS, USDA.     

The nucleation effect of linear polyethylene lamellae over the crystallization of branched polyethylene

Summary The polyamides with aromatic rings in the main chain were synthesized by the solution polymerization of 4,4-diphenylmethane diisocyanate and aliphatic dicarboxylic acid in the presence of catalyst. The thermal properties and the miscibility behaviours with polyamide-6,6 of these aromatic polyamides were studied. The aromatic polyamides synthesized with one kind of dicarboxylic acid had typical thermal properties of crystalline polymers, whereas those synthesized with the mixtures of dicarboxylic acids were not easily crystallized. The observed miscibility behaviours showed some differences from those predicted by binary interaction model.     

The effect of polar groups on the dielectric loss of polyethylene

The dielectric loss tangent for polyethylene with low dielectric loss was approximated by tan δ = C_f Σ(nμ²), where n and μ are the number and dipole moment of polar groups, respectively, and C_f is a parameter. The type and number of polar groups in the polyethylenes were mainly determined from infrared spectra obtained with a Fourier transform spectrometer. It was found that the contribution of hydroxyl and carbonyl groups to tan δ was significantly large, but the contribution of double bond groups was less significant. The tan δ was observed to decrease with a decrease of methyl group density although the overall contribution of methyl groups to tan δ was small. This suggests that tan δ is closely related to the secondary structure of polyethylenes, thus indicating the methyl groups seem to play an important role in the secondary structure.     

The effect of colorants on the properties of rotomolded polyethylene parts

An experimental study is reported on the effect of colorants on the warpage, shrinkage, and mechanical properties of rotomolded polyethylene (PE) parts. Five pigments were investigated (titanium dioxide white, cadmium oxide yellow, iron oxide red, carbon black, and phthalocyanine blue). Their concentration was in the range of 0.11 to 0.36 wt%. The pigments were added to the linear low-density polyethylene (LLDPE) by various techniques, dry blended in low intensity or high intensity mixer or compounded with a single-screw extruder. Some blends also contained 0.077 wt% zinc stearate as surfactant. It was found that zinc stearate surfactant in the dry blend increases warpage by about a factor of 2 and shrinkage by ˜ 30%, but color quality and powder handling properties are improved. The dry-blended pigments concentrate along the fusion lines of the PE particles in rotomolded parts, which results in >50% decrease of impact strength with some pigment-surfactant combinations. Mold pressurization minimizes warpage and shrinkage, but causes no significant improvement in impact resistance. Impact resistance can be improved by using compounded pigments or making two-layer parts with a pigmented outer and unpigmented inner layer.     

The effect of heterogeneity on the flow behavior on high density polyethylene

The effect of heterogeneity on the flow behavior of high density polyethylene (HDPE) has been studied by systematically homogenizing heterogeneous blends and observing the effect on the basic rheological parameters and on the extrudate surface appearance. Ample evidence is presented to show that heterogeneity causes substantial changes in the flow behavior although molecular parameters obtained through solution studies are unchanged. A simplified mathematical model which clearly illustrates the effects of the size of these flow units on the flow behavior is presented.     

表面活性剂与仿生光催化氧化的协同效应

仿生光催化剂磺酸铁酞菁在可见光的照射下,能很好地发挥催化作用,使H2O2更有效地氧化孔雀绿模拟的印染废水,而废水中所含的表面活性剂,会与仿生光催化氧化产生协同作用.实验研究了三种不同的表面活性剂对仿生光催化氧化的影响,实验结果表明聚乙烯醇(PVA)、十二烷基苯磺酸钠(DBS)以及聚氧乙烯醚(OP-10)均与仿生光催化氧化产生协同效应.     

过渡金属磷化物催化剂综述

过渡金属磷化物催化剂具有特殊的晶体结构,在催化加氢脱硫、加氢脱氮及电化学制氢反应中具有优异的催化活性。主要简述过渡金属磷化物催化剂的结构、制备方法和应用。多金属、复合多功能型过渡金属磷化物催化剂将在催化制氢反应中受到更多的关注。