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Mineral filler pore structure and paper properties.

Application: Knowing filler and paper porosity characteristics, one can adjust a papermaking process to control structural and optical properties of paper.

Mineral fillers scatter light by virtue of the light-scattering surfaces that become available when filler is incorporated in the dried fiber web. This capacity is the filler's opacifying efficiency, which is a function of particle size, shape, and refractive index.

Our goal was to assess how different mineral fillers influence light-scattering capacity as well as bulk, air permeability, and burst strength. Therefore, we carried out porosity studies on mineral fillers that have different particle shapes and different degrees of particle aggregation.

Results

The mineral fillers studied did show scattering coefficients over a wide range, which was expected since they have different morphologies, particle size distributions, and specific surface areas.

Internal voids determine the light-scattering ability of the filler. In this study, we found that the pore size range of 1.0-0.01 [micro]m corresponds best with light scattering. This result means that the number of pores of small size is decisive. The synthesis of a PCC scalenohedral or rhombohedral filler could be controlled to increase the amount of internal voids in the range of 1-0.01 [micro]m in order to achieve higher light-scattering capacity.

Conclusions

Mercury-intrusion porosimetry is a useful tool for evaluating mineral fillers and paper porosity. Data obtained for commercial paper fit well with data obtained for papers produced in the laboratory, which means that pore size distributions of commercial and lab papers are similar.

Precipitated calcium carbonate (PCC) fillers having scalenohedral habit were particularly effective in producing pores of acceptable size. The two PCC fillers studied were optically superior to the PCC rhombohedral filler. Ground calcium carbonate filler was less effective because it has a great number of pores of large sizes.

Valho and Games are professors in Departamento de Geociencias, Universidade de Aveiro, 3810 Aveiro, Portugal, Santos is a professor in Departamento de Engenharia Quimica Industrial, Institute Politecnico de Tomar, 2300 Tomar, Portugal. Address correspondence to Velho by email at jvelho@clix.pt
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Article Details
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Title Annotation:Fillers
Author:Gomes, Celso
Publication:Solutions - for People, Processes and Paper
Date:Dec 1, 2001
Words:340
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Next Article:Removal of manganese from pulp fibers with MgS[O.sub.4] in a displacement system.


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