Paberimassi

Paberimassi, or pulp, is the primary raw material used in papermaking. It consists of cellulose fibers liberated from plant material and suspended in water. Pulp can be produced from wood fibers (softwood and hardwood), non-wood sources, or from recycled paper. It serves as the fiber network that becomes paper after forming, pressing, and drying.

There are several main categories of paberimassi. Mechanical pulp is produced by physically grinding or refining wood, yielding high fiber weight but retaining much of the original lignin. This results in high yields and good opacity but lower strength and brightness. Chemical pulps are made by chemically digesting lignin and hemicelluloses, producing stronger, brighter fibers; kraft (sulfate) pulps are the most common, with sulfite pulps also used. Semi-chemical pulps combine elements of chemical and mechanical processing. Recycled pulp is obtained from recovered paper and often undergoes deinking and cleaning to remove inks and contaminants before refining.

Non-wood sources, such as cotton linters, bagasse, hemp, and straw, are used to make specialized pulps with particular properties. The choice of pulp depends on the intended end product, with long-fiber pulps providing strength (as in packaging grades) and short-fiber pulps contributing to smoothness (as in printing papers). Dissolving pulps, a subset of chemical pulps with very high cellulose content, are used to manufacture regenerated fibers and specialty textiles.

Processing steps typically include preparation (size reduction and washing), pulping, washing of the pulp, bleaching (for chemical pulps), refining, deinking and cleaning for recycled pulp, and preparation for sheet formation. Environmental considerations involve energy and chemical use, effluent management, and recycling rates, with certifications guiding sustainable sourcing.