You can try to create a custom class inheriting sf::Drawable, and in the Render function, after the renderer->SetTexture(), you add
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
It will ensure the extremities of your drawable won't be transparent.