In this work we simulate the full sequence of steps that are also typically performed in an experimental approach when studying photo-degradation of a polymer coating, namely, i) sample preparation, ...ii) photo-degradation and iii) thermo-mechanical analysis of the material during photo-degradation. In the current paper, we focus on performing several molecular dynamics simulations to study the thermo-mechanical properties of a virgin thermoset coating as well as degraded ones. Using an atomistic structure that is obtained by fine-graining the mesoscopic structure, we obtain consistent correlations between the simulated thermo-mechanical properties of the material and those measured experimentally. In addition, it is shown that by using oscillatory strain fields in MD - instead of the commonly applied linear tensile/compression strain fields – one can acquire greater knowledge on the structure-property relation of polymeric materials. Eventually, we show that our simulation approach gives rise to a remarkable insight into the mechanism of the photo-degradation process.
The effect of the addition of antimony doped tin oxide (ATO) nanoparticles on the electrical conductivity of acrylate films is described. To enable dispersing of ATO in acrylate matrices, ...3-methacryloxypropyltrimethoxysilane (MPS) was grafted on the surface of the filler. The amount of MPS used for this surface modification was found to strongly affect the electrical conductivity. Surface modification with a large amount of MPS resulted in colloidally stable dispersions of ATO, leading to a homogeneous distribution. Surface modification with small amounts of MPS led to instable ATO dispersions and aggregation of ATO into a fractal type network, which gives a much higher conductivity especially at low-volume fractions. For composites with a fractal type ATO network a second effect was found. Decreasing the amount of on ATO grafted MPS resulted in an increase of the electrical conduction between the ATO particles.
A Landau theory is presented for the structural transition of electrically stabilized colloidal crystals under shear. The model suggests that a structural transition from an ordered layered colloidal ...crystal into a disordered structure occurs at a critical shear stress. The shear induced structural transition is related to a change of the rheological properties caused by the variation of the microstructure which can be verified by scattering experiments. The theory is used to establish the shape of the flow curves. A good qualitative agreement with experimental results can be achieved, while a scaling relation similar to the elastic scaling is established.
•Adsorption of anionic polymeric surfactants on silica-modified Fe2O3 pigment with negative zeta potential.•This is due to the presence of positive oxydic iron sites.•Styrene ...oxide–ethyleneoxide–PO42− (SO–EO–P) adsorbs, only caused by electrostatics.•Polyacrylic acid sodium salt (PANa) also adsorbs; not lowered by SO–EO–P.•SO–EO–P adsorption is lowered by PANa.
The colloidal stabilization in waterbased paint is poorly understood due to its complexity in composition, usually containing mixtures of particles and of surface active agents (“dispersants”). In this study we make a step forward by analyzing the competitive adsorption of a few widely used dispersants on a typical inorganic pigment (70nm sized Fe2O3-based red pigment; surface treated with silica; negative zetapotential at pH∼7). The supposition is that any particle type in paint needs sufficient adsorbed dispersant in order to be stable. Thus, we investigate, for two combinations of two dispersants, how they mutually affect their adsorption at that pigment. Also the “single” adsorption of these dispersants was investigated, thus in the absence of the other. The dispersants are an anionic, polyacrylic acid sodium salt (“PANa”; MW=15,000Da) in combination with a MW=1500Da blockcopolymer of styrene oxide (SO) and ethoxylene (EO), either or not endcapped by a phosphate group (P). The adsorption behavior was analyzed by size exclusion chromatography of the processed supernatant of the pigment dispersion. PANa and SO–EO–P adsorb for electrostatic reasons while SO–EO has affinity only to an organic surface. PANa and SO–EO–P show regular single adsorption with a plateau starting at the critical micelle concentration (cmc). SO–EO shows single adsorption only beyond its cmc based on the adsorption of full micelles. When in competition, with SO-EP-P/PANa the adsorption of SO–EO–P is lowered by ∼65% while that of PANa is unchanged. With SO–EO/PANa the surface active species behave like in single adsorption below the cmc, but beyond the cmc a complicated phase separation occurs that cannot be based on mixed micelles. The adsorption data of PANa are compromised by depletion of PANa from interstices between particles. The anionic dispersants adsorb to the silicium oxide coated iron oxide pigment with negative surface potential because of the presence of a pH dependent relatively small number of positive iron oxide surface sites.
Polyester-urethane resins are important candidates for high performance, outdoor coating applications. Despite their relevance, quantitative information regarding the photodegradation of these ...materials is scarcely available. In the present study, a model polyester-urethane clearcoat without additives is artificially degraded and the changes in optical properties and chemical composition are studied by UV-VIS spectroscopy and FTIR-ATR microscopy, respectively. The change of the optical properties throughout the coating thickness is quantified and interpreted using a newly developed optical model. Chemical changes are quantified in a depth-resolved manner by combining FTIR-ATR microscopy with optical profilometry in order to visualise the time evolution of compositional gradients during photodegradation by accurate assignment of the correct depth position to all recorded ATR spectra. The rate of change for the concentration of several chemical entities in the model polyester-urethane was found to become constant after the initial stage of weathering. The loss of urethane crosslinks in the coating occurs faster and to a much larger extent as compared to ester bond scission. Results from the optical and the chemical characterisation are combined to propose a kinetic model for ester bond photolysis that provides an estimate of the quantum efficiency of this process.
In order to prevent a liquid epoxy cross-linker from premature, Arrhenius-law predicted, reaction with an acid-functional polyester resin, the liquid cross-linker has been physically separated from ...the resin by encapsulation while release is only possible by a temperature-controlled trigger. The glass transition temperature Tg of the polymeric encapsulant was used to trigger the softening of the polymeric capsule.
Epoxidized linseed oil (ELO) cross-linker was encapsulated as 0.1 μm diameter droplets in 16 μm diameter microparticles (poly(N-vinyl)pyrrolidone) (PVP) by means of spray-drying. The resulting nano-composite microparticles were used to cross-link the acid functional polyester in a powder coating.
It was found that below Tg the encapsulation considerably slows down the (premature) cross-link reaction. Beyond Tg also a slowdown was found but in this case it was caused by the mere presence of PVP rather than by the state of encapsulation of the cross-linker: PVP as a strong hydron bond acceptor slows down the reaction of epoxy with the acid groups of the polyester.
In conclusion, the Tg of the encapsulant was successfully used as a temperature trigger for realizing the controlled release of a liquid reactant in a reactive polymer matrix.
Display omitted
The mechanism of cross-linking of poly(neopentyl isophthalate) (PNI) by photo-degradation in nitrogen atmosphere was investigated. The exposure of PNI to UV light resulted in gel (insoluble material) ...formation. The gel material was collected and the morphology of the gel material was characterized with SEM. The gel has the highest density near the coating surface. To obtain information on the cross-linking at a molecular level the gel was decomposed by methanolysis and the decomposition products were analysed with LC-MS. Besides the expected “grafting” types of cross-links (phenyl-to-phenyl coupling) also “chain coupling” types of cross-links were detected (recombination of neopentyl glycol based moieties). Analysis of samples that had been exposed to UV light in air indicates that the phenyl-to-phenyl coupling also occurs in the presence of oxygen.
► Degradation of PNT – poly(neopentyl terephthalate) on exposure to UV. ► Identification of degradation products of PNT using MALDI-ToF. ► PNT degrades similar as PNI but 13× faster, due to subtle ...difference in structure. ► Degradation can be predicted quantitatively over 4 decades in (time×intensity).
In this paper we investigate the mechanism of photodegradation in simulated sun light (in a SUNTEST XXL+) of a polyester based on terephthalic units (poly(neopentyl terephthalate); PNT). The mechanisms of degradation were studied with MALDI-ToF MS, ATR-FTIR and SEC.
The mechanisms of the photodegradation are found to be very similar to those of the analogue polyester based on isophtalic units (poly(neopentyl isophthalate), PNI); in both cases the same type of degradation products were formed. However, all results indicate that PNT is much less UV stable than PNI, typically by a factor 13. This was explained in a quantitative way from the larger overlap of the spectrum of absorbance of PNT with the emission spectrum of the light source, as compared to the overlap in the case of PNI. In fact, a calculation indicates that the rate of degradation of both PNT and PNI under widely varying conditions is uniquely proportional to the totally absorbed amount of “photo-reactive” photons per unit of time, for a range of four decades in rate. No wavelength dependency of quantum yield was noticeable.
PDF
