The effect of a thermal treatment, i.e. annealing, on the adhesion of a thermoplastic polyurethane overmolded on a precoated steel substrate was evaluated. The hybrid part was subjected to three different annealing temperatures after the overmolding process. Adhesion of the thermoplastic elastomer was achieved by using an in-house-developed, two-step curable organic powder coating, which was selectively crosslinked to a polyallophanate state. The powder material was applied to the steel substrate by electrostatic charging followed by molecular crosslinking in an oven. The influence of the metal surface pretreatment was also evaluated regarding adhesion. The effects of the postthermal treatment were assessed through mechanical peel test, differential scanning calorimetry, atomic force microscopy, and scanning electron microscopy. Interesting results were obtained regarding strong adhesion between the precoated metal sheets and thermoplastic polyurethane after injection molding, especially in hybrids that were annealed at higher temperatures with the in-house adhesive coating.

The use of plastic films with specific diffusion or permeation properties for industrial applications has grown at a considerable rate. Some useful applications are found in medical devices, bioreactors, and combustible fuel storage where polymer films function as separation membranes that allow permeation of different gases at different rates. In this work, the permeation and diffusion properties of a polyester-based thermoplastic polyurethane (TPU) were investigated. TPU injected and extruded specimens were subjected to thermal treatment (annealing) at 100 C for 20 h. Injected samples were exposed to certain hygrothermal conditions and films were prepared to evaluate the influence of annealing on the permeation of gases. In order to achieve a complete analysis, tests such as differential scanning calorimetry, tensile tests, and Fourier transform infrared spectroscopy were conducted to examine the morphological changes. These were then correlated to the TPU permeation behavior after annealing. Water uptake by the polymer-measured as weight gain-likely indicates an increase in the free volume in the amorphous domains. Similarly, in permeation and water immersion tests, the diffusion rate of gases and H 2 O through the TPU was higher for the annealed samples when compared to those without treatment, indicating that diffusion within the polymer is dependent on the postprocessing thermal treatment.

No abstract

In this work, surface analysis and failure of rigid polyurethane (PUR) near to the metal interface of an insulating district heat pipe were evaluated. The hybrid composite consists of a steel tube surrounded by a rigid and thick PUR layer for thermal isolation. Accurate life spam approximation of district heat pipes based on PUR and steel is a complex task because of a number of variables involved in the service life of the composite, such as corrosion on the metal pipe, unexpected variations in humidity and temperature, and the quality of raw materials. In this work, artificial aging, mechanical tests, thermogravimetric, and surface analysis were conducted to determine the failure mechanisms at the polymer-metal interface. From thermogravimetric data, different methods were applied to identify parameters of the kinetics of solid decomposition, and subsequently, the lifetime of the product was estimated. From the methods evaluated, the Chang analysis gave the best approach when compared to results attained by mechanical tests and predictions established by the standard EN 253.