This code below leaves it aligned below if the content fills the entire page, otherwise it stays in the middle of the body.
Note: I have already read the materialize manual until it has been aligned but has not altered the side menu.
I've also tried style='vertical-align=bottom;'
to no avail.
<!-- INÍCIO DO RODAPÉ -->
<footer class="page-footer">
<div class="footer-copyright">
<div class="container">
</div>
</div>
</footer>
<!-- FIM DO RODAPÉ -->