This is the first time I have heard strawboard, it makes sense that the Cherry paper mill in Tama, Iowa, was making that product .
 In the late 40 the school toured the plant. They had many bales of straw, and paper all to be mixed together in huge kettles.
At the time the paper product was made into the folding egg separators in wood egg cases.
The plant changed hands several times and is still inspiration today. I believe it is now Tama Paperboard.
Doing a bit of research it was know as a strawboard plant
See the history at
https://books.google.com/books?id=N1UiAQAAIAAJ&pg=RA3-PA14&lpg=RA3-PA14&dq=history+tama+Cherry+paper+mill&source=bl&ots=8xT6qUY1No&sig=ACfU3U022vs7rAs8vXHXznBo2_VTf-6huw&hl=en&sa=X&ved=2ahUKEwiq4uqD4szqAhVDVc0KHbSZAqAQ6AEwAXoECAoQAQ#v=onepage&q=history%20tama%20Cherry%20paper%20mill&f=false
Probably too long to work I googled this   history tama Cherry paper mill
Ron Christensen