Flexible and deformable calcium carbonate (FCC) with a high aspect ratio was developed by forming calcium carbonate on the surface of nanocellulose through an in situ calcium carbonate formation process. Nanocellulose from wood fiber became a linear core of the newly formed calcium carbonate to result in the flexible inorganic material. When used in papermaking, FCC can make the paper bulky due to its large size and strong due to the creation of less surface area of calcium carbonate. It can also make the surface smooth due to its deformability. The property of FCC depends on the quality of the nanocellulose, the nanocellulose-to-calcium carbonate ratio, and the processing conditions. FCC demonstrated its potential to be the main component of paper by occupying more than 50% of the papermaking raw materials. FCC may change the history of paper in that major component of the paper materials becomes limestone rather than wood fibers. This could lead to the protection of the forest, reduced production costs, and energy savings in the manufacture of paper materials.

Hybrid calcium carbonate (HCC) was developed to simultaneously increase the bulk, stiffness, and strength of printing paper. It was prepared by the preflocculation of a mixture of ground calcium carbonate (GCC) and calcium oxide using ionic polymers in the first step. After which, carbon dioxide was injected to make semirigid agglomerates of the GCC and the precipitated calcium carbonate (PCC) that was newly formed from the calcium oxide. The final product became much larger than the original GCC and was called HCC. The HCC simultaneously improved the bulk, stiffness, and tensile strength of the paper sheets. The smoothness of a sheet containing HCC was observed to be much better than that of the large-sized GCC. It was believed that the HCC was slightly deformed by the pressure exerted during the papermaking process, which resulted in the smooth surface despite its large size. Due to its high stiffness and tensile strength without losing its smoothness, HCC has great potential for developing high-loaded printing paper that may lead to saving forest and reducing production costs.

Controlling the size and rigidity of calcium carbonate became possible. HCCs were developed and manufactured by the in situ reaction of carbon dioxide and calcium oxide, which were already preflocculated together with GCC using ionic polymers before the reaction. HCC is deformable under pressure during the papermaking process, and its degree of rigidity can be controlled by adjusting the fraction of calcium oxide. The size of HCC can be further controlled by adjusting shearing force. The more the fraction of calcium oxide, the more rigid the HCC and the smaller the diameter of the HCC. When used in papermaking, HCC increased the tensile strength and bulk of paper simultaneously without lowering other essential paper properties, and its deformable nature under pressure improved paper smoothness. Saving chemical pulp by 10% by replacing it with HCC, which is 3–4 times less expensive than the chemical pulp, was demonstrated successfully without lowering the essential properties of paper. Implementation of HCC in the paper mill may result in saving chemical pulp, drying energy, and production cost. The paper mill may utilize the carbon dioxide from the mill stack after purification for HCC preparation.

Flexible calcium carbonate (FCC) was prepared by attaching a large amount of calcium carbonate to cellulose nanofibrils (CNFs) by an in situ calcium carbonate formation method. FCC normally consists of CNFs and calcium carbonate at a 1:40 ratio by weight. FCC-containing papers resulted in a higher bulk, higher stiffness, and higher tensile strength than a commercialized ground calcium carbonate (GCC)-containing papers at the same ash content. However, there were speculations that calendering on FCC-containing paper might cause a large drop in bulk and no increase in smoothness due to the larger size of the FCC (avg. dia. 20–30 μm) than the GCC (dia. 2 μm). FCC-containing paper was shown to respond to the calendering process very effectively to increase the Bekk smoothness and to maintain high bulk. Furthermore, FCC-containing paper was so effective in increasing smoothness that it might need less calendering pressure to match the smoothness of GCC-containing paper. If so, there could be potential to increase the bulk and stiffness further in FCC-containing papers at the same smoothness as GCC-containing paper by applying reduced calendering pressure.

Wood flours (WFs) are bulky lignocellulosic materials that can increase the bulk and stiffness of paper. To be used in printing paper for replacing chemical pulp, WFs were first fractionated by a 200-mesh screen to improve smoothness; second, they were coated with calcium carbonate by an in-situ CaCO3 formation method (coated wood flours, CWFs) to improve brightness. The performance of CWFs for printing paper was compared to those of bleached wood flours (BWFs) and bleached chemical pulp. Equivalent brightness and much higher smoothness were obtained for the CWFs compared to the BWFs. Furthermore, BWFs caused a significant loss of yield and required wastewater treatment in the bleaching process, while the CWFs increased the yield greatly by attaching CaCO3 to the wood flours, and caused no wastewater burden. An accelerated aging test showed that the CWFs caused lesser brightness and strength loss than the bleached chemical pulp and BWFs. CWFs still had room for improvement to replace chemical pulp, but showed slower aging in optical and close strength properties.