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Lignin-Free - referes to paper made with less than 1% lignin, which is most accuratly called low-lignin. Papers having a high-lignin content (including papers made using a mechanical pulping process) should not be used for archival applications. Lignin an organic substance that, with cellulose, forms the chief part of woody tissue -- it is the bonding element which holds wood fibers together. Its presence causes paper to change color and become brittle. Paper can be made lignin-free by its removed during the papermaking process which makes paper archival safe.
Paper mills buy their pulp based on properties such as lignin content. Paper mills use specific test methods to measure lignin content. One common method is KAPPA. A KAPPA number of 5 or less is sometimes used to determine lignin-free.
SPS Definition Lignin-free: the term used to describe a paper/paperboard with a lignin content of less than 1%. Below 1%, the test results become too inaccurate to rely on. So, technically, it is "low-lignin" instead of "lignin-free." But consumers may not be ready for that. low-lignin papers cost more than high-lignin papers.
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