Hi guys,
Holidays are never
enough and the unexpected sun in Nantes looks like a divine punishment! For my
return to work I would prefer rain and wind. Then, if right now you are going
to work, I wish you a little storm! At least you will not envy the people who
still enjoy the sun.
But now let’s go back
to my project, do you remember its name? mmm… it looks no! Well, it is RA2ROAD.
Do you remember the topic?.... ok, please go back to my previous post ahah!
Great, finally you are
ready to know something more.
During the last months,
I worked on the design of the semi-transparent layer and for my tests I used 4 polyurethane
binders and 3 glass fractions.
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| Figure 1. How much glass do you need? |
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| Figure 2. Part A and part B of a polyurethane binder. |
The first step was to
study the viscous-elastic behavior of the polyurethanes and to determine their
curing time. For this purpose, I performed the dynamic shear rheometer test (DSR) at
different temperatures and I evaluated the variation of phase angle according
to the time. The phase angle represents the lag between the applied shear
stress and the resulting shear strain. Remember that the larger the phase
angle, the more viscous the material. This
assumption is the key for determine the state of the polymerization process,
because the curing of the polyurethane is linked to a stable value of phase
angle.
As for any
“self-respecting chemical reaction”, also the polymerization is strictly
dependent on the temperature. It means
that, if you plan to realize your pretty semi-transparent layer during the
winter, this is not a good idea! The results show that the curing time at 10°C is more of 2 days. But
don’t worry, because the polymerization follows an exponential trend and at 30°C you can reduce the
curing time of 80%.
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| Figure 3. The first DSR test is never forgotten... |
I also worked on the
mechanical and the optical performance of the semi-transparent layer. The goal
was to optimize the glue content and the grading curve of the glass aggregates
in order to improve the strength of the mixture and at the same time maintain a
good transparency. Unfortunately (or maybe fortunately) this is a big issue,
because if I improve the mechanical performance, adding for example fine
particles, at the same time I reduce the optical performance of the layer
because of the interference between the fine aggregates and the sunlight
wavelengths. It means that the “truth is in the middle” and if I want optimize
both mechanical and optical properties, I’ll have to find a compromise. I will keep you
updated!
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| Figure 4. Ugly picture of my first samples. |
Another problem is that my dear polyurethanes are not eternal, on the
contrary they are affected by the sunlight. For this reason, I studied the aging
effect on the glues putting my samples on the roof of my office!!!
The idea is to study
the evolution of the mechanical and the optical performance. About this topic I
think to write a new post. So, if you want know what happen to my samples and
if they didn’t fly away from my roof, please continue to follow by blog!!!
See you soon
Domenico
“The research presented in this
report/paper/deliverable was carried out as part of the H2020-MSCA-ETN-2016.
This project has received funding from the European Union’s H2020 Programme for
research, technological development and demonstration under grant agreement
number 721493”