Wood-free paper

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Wood-free paper is paper created exclusively from chemical pulp rather than mechanical pulp.^[1] Chemical pulp is normally made from pulpwood, but is not considered wood as most of the lignin is removed and separated from the cellulose fibers during processing, whereas mechanical pulp retains most of its wood components and can therefore still be described as wood.^[2][3][4] Wood-free paper is not as susceptible to yellowing as paper containing mechanical pulp. Wood-free paper offers several environmental and economic benefits, including reduced deforestation, decreased energy consumption, and improved waste management.^[5][6] The term Wood-free paper can be rather misleading or confusing for someone unfamiliar with the papermaking process because paper is normally made from wood pulp derived from trees and shrubs.

However, wood free paper does not mean that the paper in question is not made from wood pulp but it means that the lignin in the wood fiber has been removed by a chemical process. Paradoxically, lignin is the complex polymers containing aromatic groups that provide much of the tree strength. In its natural form, it gives rigidity and resilience to the tree, but its presence causes paper to weaken and turn yellow as it ages and eventually disintegrate. The reason for this is that as the paper ages, lignin releases acid which degrades the paper.^[7] Wood is technically a lignocellulosic material and a xylem tissue that comes from shrubs and cambium, the inner bark of trees made up of extractives, lignin, hemicellulose and cellulose.^[8] Pulp consists of wood and other lignocellulosic materials that have been broken down chemically and physically and filtered and mixed in water to reform into a web.^[8][9] Creating pulp by breaking down the materials chemically is called chemical pulping, while creating pulp by breaking them down mechanically is called mechanical pulping.

In chemical pulping, chemicals separate the wood fibers. The chemicals lower the lignin content because chemical action solubilizes and degrades components of wood fibers, especially hemicelluloses and lignin. Chemical pulping yields single unbroken fibers that produce strong quality papers because the lignin that interferes with hydrogen bonding of wood fibers has been removed. Chemical pulps are used to create wood free paper that is of high quality and lasts long, such as is used in arts and archiving.^[8] Chemical pulping processes take place at high pressures and temperatures under aqueous alkaline, neutral or acidic conditions, with the goal of totally removing the lignin and preserving the carbohydrates. Normally, about 90% of the lignin is removed.^[9]

Mechanical pulping, in contrast, converts raw wood into pulp without separating the lignin from the wood fiber.^[9] No chemicals other than water or steam are used. The yield is about 90% to 98%. High yields result from the fact that lignin is retained. Mechanical pulps are characterized by low cost, high stiffness, high bulk, and high yield.  Mechanical pulp has low strength because the lignin interferes with hydrogen bonding between wood fibers. The lignin also makes the pulp turn yellow when exposed to light and air. Mechanical pulps are used in the production of non-permanent papers such as newsprint and catalog papers. Mechanical pulps made up 20% to 25% of the world production and this is increasing because of the high yield of the process and increasing competition for fiber resources. Advances in technology have also made mechanical pulp increasingly desirable.^[8]