The main crisis for hemp arose in America during the 1930’s due to propaganda created from companies with vested interest from the new petroleum based synthetic textile companies and
the large and powerful newspaper and lumber barons who saw hemp as the biggest threat to their businesses. The 1930s coalesce unsurprisingly, with DuPont patenting their new “plastic fibre”. By the 1930s, new machinery, which separated the fibre from the rest of the plant, was available and affordable.
From < https://www.totalhemp.co.uk/history-of-hemp/>