Paper making can be trace back long time ago. I did notice there is a saying that Egyptians first invented paper; however based on the education I received, it is a Chinese named Cai Lun who invented paper at the time around 100 AD. Anyway, modern paper making is much more complicated and different from these ancient process. The following is a short history of paper making.
Paper making is to extract wood fibers or cellulose fibers from forestry or other products and then, combined with other additives into a formulation, convert into solid paper sheets or rolls.
A log wood includes, as shown in above figure, bark, cellulose, and lignin. Bark needs to be removed in the debarking process. Wood has a composite structure: Cellulose functions as reinforcing fibers which provide extension strength; Lignin functions as resin, providing compressive strength. Lignin has conjugated structures which is called chromophores; chromophores, like dyes, can absorbs visible lights and present colors. Lignin is not thermally or optically stable either. With large amount of lignin in the pulp, the paper will turn to yellowish with aging. That is reason why lignin should be removed in high quality paper making.
Pulping process can be divided by two categories: mechanical and chemical. In the mechanic process, wood is simply ground down together with cellulose fibers and lignin. Due to the existence of lignin, mechanically made paper can easily turns to yellowish with time. Besides, mechanical grinding process breaks long fibers in to short ones; The resulted paper has low mechanic strength.
Meanwhile, chemical methods use chemicals, either acid or base, to degrade cross-linked lignin to water soluble phenoxide segments. The side effect is that it also degrade the cellulose more or less depending on specific conditions.
The comparison of paper making is made between technical and chemical methods
Even in chemical process, e.g. Kraft process, lignin is not completely removed from pulp. A bleaching step is needed to oxidize the remaining lignin and destroy the conjugation structure of the chromophores; then it will not absorb visible light any more. typical oxidants are Cl or ClO2, and O2/O3/H2O2. After the addition of bleaching agent, NaOH is added to solubilise oxidised lignin fragments. This bleaching step is the key to determine the longevity of the final paper products. Acidic paper has shorter lifetime then basic paper with basic fillers.
Fillers including Clay, CaCO3, and TiO2 are added into pulp to improve optical and physical properties, e.g. making paper denser, brighter, softer, and smoother, in addition to cost reduction. CaCO3 is also helpful in keeping paper slightly basic.
Cellulose surface is hydrophilic in nature, which facilities water or ink to penetrate into paper bulk. The sharpness of lines in writing or printing will be limited; therefore, tuning cellulose surface from hydrophilic to hydrophobic is needed in some paper production process. The process is called sizing. Rosin is one of good sizing agents.
During dewatering stage in paper making, fillers or short cellulose fibers may not able to stay on top of the mesh or they may block the pores between fibers, leading to poor drainage. To solve the problems, a special high molecular weight cationic polymer is developed to “bond” the fillers or short fibers to long fibers.
After pulp formulation is made, starts the paper making step.
As shown in the above figure, the process include 4 steps: wet end, wet press, drying, and calendaring. Some other articles in internet has a lot more details. Reference 1, Reference 2.