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.     

On the relation between surface texture and gloss of injection‐molded pigmented plastics

The relation between the surface topography of injection‐molded plastic objects with deliberately imposed textures and their gloss, measured by means of a conventional glossmeter at incident angles of 20°, 60°, and 85°, was investigated. A modification of the general scalar Kirchhoff approximation, which accounts for geometrical features of the glossmeter, is used to describe the experimental gloss values of the textured surfaces. The agreement between the measured and the calculated values for incidence angles of 20° and 60° confirms the usefulness of the approach, though several of the textured surfaces used here are too rough for the Kirchhoff theory to be strictly valid. A poorer agreement, however, was noted at higher incidence angles (85° in this case). For very smooth surfaces (without any texture), the classical Bennett‐Porteus theory could in many cases describe the gloss level with sufficient accuracy. The influence on the measured gloss of the polymer material (in terms of its refractive index) and the color of the injection‐molded object is also discussed. Light beige specimens in three different polymeric materials (acrylonitrile‐butadiene‐styrene, acrylonitrile‐butadiene‐styrene/polycarbonate blend, and polypropylene) as well as three acrylonitrile‐butadiene‐styrene products with different colors were used. The refractive index of the polymer had no major influence on the measured gloss. The gloss level increased slightly with increasing lightness of the specimens, which can be associated with an increased contribution from the bulk scattering. However, the surface texture governed most of the gloss variations. POLYM. ENG. SCI., 45:1343–1356, 2005. © 2005 Society of Plastics Engineers     

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.     

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.     

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.     

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.     

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     

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.     

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.     

Degradation profiles of polyester–urethane (hydroxylated polyester/diphenylmethane diisocyanate) and polyester–melamine (hydroxylated polyester/hexamethoxymethylmelamine) coatings: An accelerated weathering study

The successful material performance of coatings depends on the environmental conditions to which they are exposed. The effects of the diol structure and acetoacetylation on the weathering degradation of hydroxylated polyester (HP)/hexamethoxymethylmelamine and HP/diphenylmethane diisocyanate clear coatings were studied. The acetoacetylation of HPs led to better performance for higher application solids than the acetoacetylation of their base counterparts. Weathering degradation profiles were investigated with dynamic mechanical thermal analysis, scanning electron microscopy, and X‐ray photoelectron spectroscopy. The structural variations of the building blocks and acetoacetylation were found to be important for enhancing the stability of coatings at higher application solids. Polyester–urethane coatings were more stable toward weathering than polyester–melamine coatings. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1069–1081, 2005     

Augmenting the performance of acrylonitrile–butadiene–styrene plastics for low‐noise dynamic applications

The main objective of this study was to enhance the performance of acrylonitrile–butadiene–styrene (ABS) plastics for dynamic structural applications, including those of automobile relevance. First, ABS was modified by blending with maleic anhydride grafted styrene–ethylene–butadiene–styrene block copolymer (MA‐g‐SEBS) in various proportions. Squeaking noise characteristics were evaluated by measurement of the frictional behavior in an in‐house fabricated friction testing apparatus, and the results are explained on the basis of the change in surface energy upon modification. Detailed dynamic mechanical analyses (strain, frequency, and temperature sweep) revealed significant improvements in the damping characteristics of the modified ABS, especially that modified with 10 wt % MA‐g‐SEBS, without much sacrifice in its mechanical strength. The modulus values predicted with Kerner's model of the blends were well correlated with the morphological changes upon modification. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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⁺).     

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.     

Oxidation kinetics in olive oil triacylglycerols under accelerated shelf‐life testing (25–75 °C)

A kinetic study of the autoxidation reaction in olive oil triacylglycerols stored in darkness at different temperatures (25, 40, 50, 60 and 75 °C), in absence of pro‐ and antioxidant compounds to avoid confounding effects, is described. After the induction period (IP) the decrease in the oxidizing substrate and the formation of primary oxidation products followed a pseudo‐zero‐order kinetic, and the calculated E_a from the Arrhenius equation for the formation of hydroperoxides was 32.1 kJ·mol^?1. The formation of secondary oxidation products followed a pseudo‐first‐order kinetic whose rate reaction constant also increased exponentially with temperature. The first oxidation index to exceed the upper limit in the EU regulations was PV, followed by K₂₃₂ and K₂₇₀. The time required reaching these limits and the rancidity threshold showed a potential dependence on temperature, and therefore with accelerated storage at 75 °C, POO shelf‐life in ambient conditions (25 °C) can be predicted. Finally, there was a good linear relationship between the time required to reach the rancidity threshold and the IP of the formation of the 2,4‐decadienal, and hence this instrumental determination could be useful to measure sensory recognition of the rancid defect in POO.     

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。     

Synthesis of 5‐sulfosalicylic acid‐intercalated layered double hydroxide and its effects on wood flour/polypropylene composites during accelerated UV weathering

In this study, 5‐sulfosalicylic acid (SA) anions have been intercalated into Mg₃Al‐NO₃ layered double hydroxide (LDH) to synthesize SA‐intercalated Mg₃Al‐NO₃‐LDH (LDH‐SA) by ion‐exchange reaction. Then, the effects of LDH, SA, and LDH‐SA on the photostability of wood flour/polypropylene (WF/PP) composites during accelerated ultraviolet (UV) weathering were investigated. The surface color, surface gloss, and mechanical properties of the composites during weathering were tested, accompanied by characterizations using SEM, ATR‐FTIR, and TG. The results showed that (1) SA anions completely replaced the anions in LDH and the thermal stability of LDH‐SA was considerably enhanced; (2) composites with LDH or LDH‐SA exhibited less color change, fewer surface cracks, better thermal stability, and less losses of mechanical properties than the control group; (3) LDH‐SA showed a long‐term efficiency and alleviated the photo‐oxidation of WF/PP composites successfully; (4) LDH‐SA blocked UV light by physical shield effect of the layer sheets, as well as the chemical absorbability of the interlayer anions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44597.     

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.