Molecular relaxation phenomena during accelerated weathering of a polyurethane coating

Fernando, Brianna M.; Shi, Xiaodong; Croll, Stuart

doi:10.1007/s11998-007-9077-1

Cited by 13 publications

(12 citation statements)

References 24 publications

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“…The same heating and cooling rate was maintained for all the testing. 1,8 As one should expect, aging is seen to occur even at room temperature and this must be taken into account in making enthalpy change measurements. Dynamic mechanical thermal analysis (DMTA) was used to measure and calculate the crosslink density from the storage modulus at 130°C 5 and TGA was used to measure the amount of water absorbed during exposure.…”

Section: Thermal Analysismentioning

confidence: 99%

“…Studies on coatings' protective properties and their durability have most often been concerned with ultraviolet irradiation spectra and ultraviolet absorption, but moisture absorption and temperature variation can be very important also. 1,2 Structural relaxation, known as physical aging, is a kinetic phenomenon wherein glassy polymers tend to relax since they are not in an equilibrium situation when stored at a temperature lower than the glass transition temperature (T g ). It is well known that physical aging is always accompanied with densification and reduction in fractional free volume, and reduction of segmental mobility.…”

Section: Introductionmentioning

confidence: 99%

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

2008

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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.

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Section: Thermal Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2008

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“…During the curing stage of a coating, mechanical stresses can arise, which have been identified as a major cause for failure of the coating. [12][13][14][15][16][17] If the coating is applied on a metal substrate, an important cause of stress is the differential thermal contraction between the coating and the substrate. Other factors also contribute to the stress, including an increase in density upon crosslinking and shrinkage due to the evaporation of solvent.…”

Section: Introductionmentioning

confidence: 99%

Preemptive Healing through Supramolecular Cross-Links

et al. 2009

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The ability of highly cross-linked thermoset materials to relax stresses by network chain segment mobility above or just below T g is generally limited. We describe materials in which some of the crosslinks have been replaced by dimers of quadruple hydrogen-bonding ureidopyrimidinone (UPy) moieties, which act as reversible cross-links. Materials based on mixtures of ε-caprolactone and L-lactic acid, and containing different ratios of covalent and UPy dimer cross-links, were synthesized, and their thermal and mechanical properties were tested by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The presence of reversible cross-links results in superior relaxation of stresses even below T g , as witnessed by the creep and stress relaxation behavior. These properties bode well for potential applications, e.g., in coatings technology.

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“…1 Particularly interesting is how the physical changes are linked to the chemical evolution of the coating as a result of degradation. [2][3][4][5] Specifically, the mechanical stability of a coating is an important factor which is expected to be preserved during its service life.…”

Section: Introductionmentioning

confidence: 99%

Degradation of a polyester‐urethane coating: Physical properties

Makki

Adema

Peters

et al. 2015

J Polym Sci B Polym Phys

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In this article we studied the evolution of thermomechanical properties of a polyester-urethane coating during degradation under different degradation conditions, i.e., aerobic and anaerobic conditions with and without dry/wet cycling during degradation. Dynamic mechanical and thermal analyses show that under aerobic conditions the coatings become stiffer and more brittle in the glassy state. This stiffening is probably due to the increase in the amount of hydrogen bonding and the formation of oxidized groups which increase the polarity of the material and enhance the interactions of the polymer segments. However, oxidation reactions result in a considerable decrease in cross-link density and stiffness in the rubbery state. Both changes, in the glassy and rubbery states, give rise to development of internal stresses. These stresses increase as the degradation process proceeds. Nevertheless, for samples exposed to anaerobic conditions, the stiffness remains constant in the glassy state and the cross-link density slightly increases as a result of degradation. This reconfirms the dominance of the effect of oxidation reactions on the mechanical failure of the coatings. Oxygen permeation measurements show a more-or-less time-independent diffusion coefficient and a gradual decrease in solubility of oxygen as a function of exposure time. This results in a slight decrease in oxygen permeation (mainly in the early stage of the degradation) as degradation proceeds.

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Molecular relaxation phenomena during accelerated weathering of a polyurethane coating

Cited by 13 publications

References 24 publications

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

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

Preemptive Healing through Supramolecular Cross-Links

Degradation of a polyester‐urethane coating: Physical properties

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