Cause and effect in the weathering of plastics

In most instances, the study of the weatherability of plastics follows empirical schemes that show little correlation with the actual effects of outdoor exposure. A more reliable analysis must be based on a knowledge of the factors in the weather which affect plastic properties and of the modes of interaction between these factors and the plastic material. It is shown that both the factors of the weather and the kinetics of polymer degradation may be expressed in a quantitative manner suitable for analytical treatment. Furthermore, it is shown that the analytical approach yields predictions which are in qualitative agreement with the results of actual outdoor exposure. Finally, some new techniques are proposed for more reliable predictions of long-term outdoor weatherability on the basis of laboratory studies.     

The use of new blockcopolymeric dispersing agents for waterborne paints — theoretical and practical aspects

Newly developed blockcopolymeric dispersing agents are evaluated in their performance with a number of pigments in order to obtain a deeper understanding of the dispersing process and of the factors that affect the stability of waterborne binder free pigment concentrates. Special attention is paid to the variation of the amphiphilic ionic/non-ionic and hydrophobic/hydrophilic properties of these new dispersants. By measuring particle surface charges and particle size distributions of pigment pastes and by determining relevant properties of the films obtained after application the effect of a number of binders and other paint components on the stability of dispersions is also evaluated. Guidelines for efficient and economically optimum preparation of pigmented waterborne paints are given.     

Substituent Effects on the Colour,Dyeing and Fastness Properties of Trisubstituted 4–N–β–Hydroxyethyl–N–β–Cyanoethylaminoazobenzenes

School of Chemistry and Chemical Technology University of Bradford Bradford West Yorkshire BD7 1DP The synthesis of a series of 2′, 4′, 6′-trisubstituted derivatives of 4–N–β–hydroxyethyl–4– N–β–cyanoeth ylaminoazobenzene is reported, and the effect of the nature of the substituents on the colour, dyeing and fastness properties of these dyes is described. The dyes coloured synthetic–polymer fibres well, with the exception of those containing a methylsulphonyl group, which gave weaker dyeings on polyester. Dyes substituted by 2′-nitro groups tended to have poor light fastness, and reasons for the variations in the light fastness of monoazo dyes of this type are discussed.     

Effect of variables in artificial weathering on the degradation of selected plastics

Artificial weathering devices are used extensively by the plastics industry to aid in the prediction of the weatherability of plastic matrials. Correlations between the results of outdoor and artificial weathering, however, are poor for lack of control and understanding of the exposure variables in these devices. This work summarizs some of the results of an experimental program designed to analyze the effects of variables in artificial weathering on the preoperies of selected commercial plastics. In addition to the presentation of data establishing the importance of each of the variables in artificial weathering, a discussion of the significance of these data with regard to the selection of optimum exposure cycles is given. Furthermore, some new approaches are proposed with regard to obtaining inproved correlations between the results of outdoor and artificial exposure. Model calculations based on the proposed approaches yield a surprisingly high degree of correlation between the two types of exposure.     

Investigation of the rheological behavior of titanium dioxide pigmented acrylonitrile–butadiene–styrene polymer

Titanium dioxide (TiO₂) pigments may be surface‐modified by hydrous oxides, such as alumina (e.g., Cristal 134) or by organic compounds, such as organophosphate (e.g., Tiona 188). In this investigation, the effects of these pigments on the rheological properties of acrylonitrile–butadiene–styrene (ABS) polymer were investigated. With the oscillatory rheometry method in the linear viscoelastic region, the storage and loss moduli versus frequency graph of ABS in the molten state showed two crossover points (COPs) when the surface of the ABS components, that is, poly(styrene‐stat‐acrylonitrile) and poly[(styrene‐stat‐acrylonitrile)‐graft‐polybutadiene] or g‐ABS, had good interaction. The first COPs increased when the TiO₂ content rose to 0.5 and 1.5% in Tiona 188 and Cristal 134 pigmented ABS samples, respectively. With the addition of TiO₂ up to these contents, the polymer–pigment interaction becomes stronger so that the dispersion of the pigments was good. With increasing TiO₂, the first COPs dramatically decreased because of agglomeration of the pigments. The shifting of the first COP may be applied as a criterion to specify the dispersion of TiO₂ particles in the ABS matrix. Scanning electron micrographs showed that the pigments had no effect on the size of the polybutadiene particles. Also, transmission electron micrographs proved that agglomerates of Tiona 188 and Cristal 134 particles were formed above 0.5 and 1.5% TiO₂ contents, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Performance of zinc molybdenum phosphate in anticorrosive paints by accelerated and electrochemical tests

This work studied the anticorrosive behaviour of micronized zinc molybdenum phosphate (zinc phosphate modified with zinc molybdate). It was proposed to evaluate its efficiency in solvent borne paints with 30 and 15% of the pigment by volume and a pigment volume concentration/critical pigment volume concentration ratio (PVC/CPVC) of 0.8. The behaviour of paints formulated with different binders such as epoxy, chlorinated rubber, vinyl and alkyd resins, was assessed by accelerated (salt spray cabinet and accelerated weathering) and electrochemical tests. Epoxy and chlorinated rubber paints showed the best anticorrosive performance. The inhibitive action of zinc molybdenum phosphate was confirmed. Good correlation was obtained between salt spray and electrochemical tests.     

The Photofading of 1 –Arylazo–2–naphthols in Solution.

1–(Substituted phenylazo)–2–naphthols with a nitro group positioned para– or ortho– to the azo group, show anomalous photofading behaviour in methanol, i. e., their fastness to light is very much lower than that of similar compounds. On the other hand, although 1 –(o–nitrophenylazo)–2–naphthol (II) in alcoholic solvents faded to give similar products via photooxidative and/or photoreductive reactions, little photoreduction of the nitro group was detected, and the rate of photofading of II was lower than that of la. The contribution of intramolecular interaction, such as intramolecular bifurcated hydrogen bonding, involving the o–nitro group, azo group and o–hydroxy group of 1–(o–nitrophenylazo)–2–naphthol, are also discussed. Photochemical reaction of 1–(p–nitrophenylazo)–2–naphthol (la) in methanol, ethanol or 2–propanol produces not only oxidative but also reductive products, while photochemical reaction of la in acetone gives only oxidative products. From these results and earlier observations, it is suggested that the anomalous photofading of la is a substrate–specific phenomenon, and may be caused by photo–reduction of the nitro and azo groups to amino groups by the substrate, instead of the normal photo–oxidation of the hydrazone tautomer by singlet oxygen.     

Concurrent physical aging and degradation of crosslinked coating systems in accelerated weathering

Coating degradation is a combination of both chemical and physical processes; however, physical processes have not received much attention. Physical aging has a non-negligible effect on coatings’ mechanical properties and permeability etc. through the densification that continues as a polymer approaches its thermodynamic equilibrium below the glass transition temperature, T _g. Observations in recent work showed that physical aging affects coatings’ mechanical property response during accelerated weathering and is, itself, affected by the associated chemical degradation. Two crosslinked coating systems were studied in order to compare different chemical compositions, their T _g, and their thermal response in accelerated weathering. During thermal cycling, physical aging measured by enthalpy recovery exhibited different trends in the two coatings. A “rejuvenation” mechanism was observed in the coating with a T _g between the top and bottom limits of the exposure cycle; continued aging was observed for the coating with a high T _g. Stress relaxation tests detected aging and “memory” behavior over periods comparable with accelerated weathering cycles. Both thermal and mechanical responses changed in complicated and different ways as the coatings degraded. Different degrees of coating thickness reduction were observed in both isothermal relaxation and degradation. When various coatings are evaluated, simply judging their performance under the same weathering environment is not reliable since polymer relaxation behavior depends on the relationship between the exposure temperatures and the T _g of each polymer. This paper was awarded First Place in the 2007 Gordon Awards technical paper competition, held as part of the FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in Toronto, ON, Canada, on October 3–5, 2007.     

Contact angle measurements to determine the rate of surface oxidation of artists’ alkyd paints during accelerated photo-ageing

The rate of surface photo-oxidation and changes in polarity of the surfaces of artists’ alkyd paint films were studied by a rapid and novel approach using sessile drop contact angle measurements. The contact angles of distilled water and diiodomethane drops on the film surfaces were measured over a period of 25–2000 h of artificial ageing at 40 °C under an indoor light filtered Xenon light source. Chemical changes on the surfaces of the films were also followed using Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Titanium white artists’ paint samples from three different manufacturers were investigated: Winsor & Newton, Ferrario and Da Vinci Paint Co. As the films aged, there was a decrease in the contact angle and an increase in the polar component of the free surface energy of the paint film surfaces indicating the formation of photo-oxidation products. Such changes correspond well to the chemistry of oil paints, and suggested chemistry of long-alkyd paints, because of their relatively high weight percent of fatty acids.     

Thermal and chemical stability of Cu–Zn–Cr-LDHs prepared by accelerated carbonation

Layered double hydroxides Cu_xZn_6 − xCr₂(OH)₁₆(CO₃)·4H₂O with different molar ratios of Cu/Zn/Cr were synthesized by accelerated carbonation. The products were characterized by XRD, SEM, FT-IR and TG-DTG-DSC-MS. The chemical stability was tested by the modified Toxicity Characteristic Leaching Procedure (TCLP). The results showed that the products were the mixture of Cu_xZn_6 − xCr₂(OH)₁₆(CO₃)·4H₂O and (CuZn)₂(CO₃)(OH)₂, with similar thermal behavior. All products were chemically stable with reduced leaching at pH > 6 (Cu²⁺, Zn²⁺) or > 5 (Cr³⁺).     

Factors Influencing the Stability of AFm and AFt in the Ca–Al–S–O–H System at 25°C

The stabilities of Al₂O₃–Fe₂O₃‐mono (AFm) and ‐tri (AFt) phases in the Ca–Al–S–O–H system at 25°C are examined using Gibbs energy minimization as implemented by GEM‐Selektor software coupled with the Nagra/PSI thermodynamic database. Equilibrium phase diagrams are constructed and compared to those reported in previous studies. The sensitivity of the calculations to the assumed solid solubility products, highlighted by the example of hydrogarnet, is likely the reason that some studies, including this one, predict a stable SO₄‐rich AFm phase while others do not. The majority of the effort is given for calculating the influences on AFm and AFt stability of alkali and carbonate components, both of which are typically present in cementitious binders. Higher alkali content shifts the equilibria of both AFt and AFm to lower Ca but higher Al and S concentrations in solution. More importantly, higher alkali content significantly expands the range of solution compositions in equilibrium with AFm. The introduction of carbonates alters not only the stable AFm solid solution compositions, as expected, but also influences the range of solution pH over which SO₄‐rich and OH‐rich AFm phases are dominant. Some experimental tests are suggested that could provide validation of these calculations, which are all the more important because of the implications for resistance of portland cement binders to external sulfate attack.     

Modelling of multi gas/solid reactions – effect of structural parameters

A unified gas/ solid reaction model has been formulated for multi reactions with multi gas and solid species. The transient formulation has been followed by finite-difference method and subsequent solution via an iterative procedure. The simulation produces intermediate results for concentration profiles of various components and pressure and temperature distribution, in addition to various structural parameters within a reacting pellet. The effect of structural parameters is analysed. The general formulation allows homogeneous and heterogeneous reactions. Solid state processes can also be accommodated.     

Thermodynamic Stability of Spinel Phase at the Interface Between Alumina Refractory and CaO–CaF2–SiO2–Al2O3–MgO–MnO Slags

The interfacial reaction between alumina refractory and CaO–CaF₂–SiO₂–Al₂O₃–MgO–MnO slag was observed at 1873 K to estimate the stability of the spinel phase using computational thermodynamics under refining conditions of Mn‐containing steels. The concentration of MnO formed by the slag–steel reaction in the CaO–CaF₂–SiO₂–Al₂O₃–MgO melts generally increased by decreasing the CaO/SiO₂ ratio of the initial melts. No intermediate compounds were formed at the refractory–slag interface when the initial CaO/SiO₂ ratio was 0.5, whereas CaAl₁₂O₁₉ (CA6) and Mg(Mn)Al₂O₄ (spinel), identified from TEM analysis using EDS mapping and SAED patterns, were observed at the refractory–slag interface when the CaO/SiO₂ ratio was 1.0 or greater. The (at.%Mg)/(at.%Mn) ratio in the spinel solution increased by increasing the CaO/SiO₂ ratio, which originated from the fact that MgO activity continuously increased as the CaO/SiO₂ ratio increased. From thermodynamic analysis considering the equilibrium constant (K_SP) and activity quotient (Q_SP) of the spinel formation reaction at the slag–refractory interface and the bulk slag phase, the precipitation–dissolution behavior of the spinel phase was predicted, which exhibited good consistency with the experimental results. Hence, the dissolutive corrosion mechanism of alumina refractory into the CaO–CaF₂–SiO₂–Al₂O₃–MgO–MnO slag was proposed.     

A Proton–magnetic–resonance Spectroscopic Investigation of Intramolecular Hydrogen Bonding in 4–Substituted–2–nitrodiphenylamine Disperse Dyes

Detection of long–range coupling constants, JNH, H5, in 100–MHz proton–magnetic–resonance spectra confirms the presence of intramolecular NH ON hydrogen bonding in some 2–nitrodiphenylamine disperse dyes. Measurements in polar and non–polar solvents on 2–nitrodiphenylamine and on twelve 4–substituted derivatives indicate weakening of the bonding, which is related to light fastness, when the 4–substituent is a strong electron acceptor.     

Patterns of erosion from acrylic and fluoropolymer coatings in accelerated and natural weathering tests

Commercial poly (vinylidene difluoride) (PVDF)/acrylic coatings show minimal gloss loss or bulk chemical change even after sustained Florida or accelerated weathering testing. Previously, we showed that “QUV-B” weight loss rates can be used as an early predictor of the weatherability of fluoropolymer/acrylic blend clearcoats. In this work, we study the microscopic basis for differences seen between various blends and pure acrylic coatings. Scanning electron microscopy (SEM) images reveal different characteristic patterns of degradation. 900 First Ave., King of Prussia, PA 19406.     

Foam application from a closed system – a study of machine and foam parameters

An attempt has been made to gain a greater insight into the interaction between foam and a moving textile substrate. The effects of changing wet pick–up, fabric velocity, liquid viscosity, foam density and mode of application on penetration have been studied. Application from a closed system makes it possible to apply an exact amount of liquid, and reflectance measurements revealed that between 10 and 60% wet pick–up the actual level of wet pick–up is of major importance. The amount of liquid available determines the likelihood of capillary transport. The results obtained in terms of fabric speed and foam density still leave questions to be answered on the mechanisms of foam flow and degradation in the textile.     

Compositional effects on the crosslink density of Ca–(Mg)–(Y)–Si–Al–oxyfluoronitride glasses

The effects of fluorine and nitrogen substitution for oxygen in aluminosilicate glasses, effectively oxyfluoronitride (OFN) glasses, modified by calcium, calcium–yttrium or calcium–magnesium on thermal and physical/mechanical properties have been compared. Thus, 42 glasses in the Ca–(Mg)–(Y)–Si–Al–O–(N)–(F) system have been prepared and characterized with respect to density (ρ), molar volume (MV), compactness (C), free volume (FV), glass transition temperatures measured by DTA (T_g,DTA) and dilatometry (T_g,dil), dilatometric softening point (T_DS), microhardness (μHv) and Young's modulus (E). Gradients of property variation with nitrogen or fluorine substitutions for oxygen are similar for all three different oxyfluoronitride glass systems and are comparable with those reported for other OFN glasses, again indicating independent and additive effects of nitrogen and fluorine. In attempting to further understand how fluorine affects the cross‐link density (CLD) in OFN glasses, it becomes apparent that it is necessary to allow for a greater contribution by aluminum in a modifier role as fluorine content is increased. This modified calculation of CLD values results in good linear fits between T_g and CLD values. This analysis clearly demonstrates and endorses the concepts that thermal properties are related to CLD while physical/mechanical properties are dependent on glass compactness.     

塑料的滚塑成型及结构泡沫塑料成型新工艺

本文简要介绍了滚塑成型工艺过程、发展历史、优点,对用该工艺进行结构泡沫塑料生产新工艺的过程、机理及需注意的有关问题也进行了简明阐述。