Pulping

Pulping is the process of converting wood or lignocellulosic nonwood material to separated pulp fibers for papermaking. Processes range from purely mechanical, in which the wood is ground into fibers by disk refiners or grindstones, to chemical, in which the fibers are separated by chemically degrading and dissolving the lignin that binds them together in the tree. Mechanical pulping is energy intensive. The dominant chemical process, the Kraft process, uses a solution of sodium hydroxide and sodium sulfide to dissolve the lignin.

Book pulping

A more specialized use of the term "pulping" is to refer to the system of destroying unsold books (usually but not always mass market paperbacks). If a book is not selling well, the publisher may not only allow it to go out of print by ceasing to print more copies, but (for tax purposes) destroy any copies they cannot sell by the end of the fiscal year. Bookstores strip the front covers from paperbacks that do not sell, and return them to the publisher as evidence they have been destroyed rather than sold. The books are then burned or recycled into paper or cardboard products.

This system of pulping paperback books evolved from the rise of the mass market distribution system following World War II when paper was cheaper than the cost of transport. Coverless paperbacks are often found for sale in thrift stores, charity libraries (in hospitals, for instance), flea markets, and the like; sometimes even in used bookstores. In the 1990s, publishers began an information campaign to alert book buyers to the fact that these books have been reported as destroyed, to mixed results. Many paperbacks from this period contain a warning notice in the indicia, to the effect that "If you purchased this book without a cover, it has been reported to the publisher as 'unsold and destroyed', and neither author nor publisher have received payment for this book."

Unsold hardbacks or trade paperbacks are more commonly remaindered (sold off at reduced prices). Remaindered books that still fail to sell may then be pulped.

The practice of pulping, as opposed to remaindering, has the long term effect of diminishing the number of copies of a given print run or edition and of making the surviving copies more valuable in the book collecting market.