The Main Function, Classifications, and Properties of Filter Paper

The main component of filter paper is cotton fiber. There are many small holes on the surface of the filter paper that allow liquid particles to pass freely, while those larger solid particles, will be blocked outside and cannot pass through the filter paper. It is precise because of this property of filter paper that it can separate liquid and solid substances very well. In addition to the experimental analysis, filter paper is also widely used in our daily life. Today, HAWACH will discuss the function of filter paper, classifications, and some basic properties.

Filter paper function

The main function of the filter paper – chromatography: because the cotton fibers in the filter paper have a good affinity with water, it can absorb about 22% of the water, of which the water combined with cellulose in the form of hydrogen bonds has 6% to 7%.


Compared with the affinity with water, the affinity of cotton fibers in filter paper with organic solvents is weaker, so in most cases, paper chromatography is to remove the filter paper fibers. The combined water is used as the stationary phase, and the mobile phase is mainly the organic solvent. When the mobile phase of the organic solvent passes through the sample, the water, and the organic phase are continuously distributed, and then with the continuous movement of the mobile phase, the substances of various components are continuously redistributed, which further enables the substances to be separated. and purification. Filter paper is frequently used in chemical laboratories.

Filter paper classification

The main classification of filter paper: In general, filter paper can be divided into two types, one is qualitative filter paper and the other is quantitative filter paper. Qualitative filter paper generally refers to the formation of cotton fibers on its surface after filtration, which is generally only suitable for qualitative analysis. Quantitative filter paper is generally aimed at ashless filter paper. It must undergo special treatment procedures during use. To a certain extent, it can effectively resist certain chemical reactions, so impurities generated on its surface are generated. will be much less, usually, it is generally used in quantitative analysis. In addition to the application of filter paper in chemical experiments, we also have the application of filter paper in our lives. For example, coffee filter paper is one of the widely used ones. Generally, this filter paper has a high degree of softness, while in industry filter paper It is generally used to adsorb suspended particles in the air.

1. Basis Weight:

Filter paper can be categorized by its basis weight, which refers to the weight of a standard sheet of paper. Common weights include lightweight, medium weight, and heavyweight filter paper.

2. Porosity:

Filter paper can be classified by its porosity, which determines the size and number of pores in the paper. This affects the flow rate and retention capacity. Common porosity classifications include:
Fast (coarse) filter paper: Large pores for fast filtration.
Medium filter paper: Balanced porosity for general-purpose filtration.
Slow (fine) filter paper: Small pores for fine particle retention.

3. Composition:

Filter paper can be made from various materials, each suitable for specific applications. Common compositions include:
Cellulose filter paper: Made from cellulose fibers and is widely used for general filtration.
Glass fiber filter paper: Composed of borosilicate glass fibers and is known for its high retention capacity and resistance to chemicals.
Qualitative filter paper: Used for general qualitative analysis.
Quantitative filter paper: Designed for quantitative analysis and is typically ash-free to minimize residue.4. Retention Capacity:

Filter paper can be classified based on its retention capacity for particles of different sizes. This is often indicated in micrometers (µm) or nominal pore size ratings, such as 1µm, 5µm, etc.

5. Shape and Size:

Filter paper is available in various shapes and sizes, including circular sheets, rolls, pre-cut discs, and folded filters.

6. Grade or Series:

Many manufacturers assign grades or series to their filter papers to indicate specific properties, applications, or compositions.

Filter paper properties

The basic properties of the filter paper: the selection of the appropriate filter paper must be determined by the following four factors. The first is hardness. The filter paper will be wet during filtration, so in the long-term filtration process, you should Choose a tougher filter paper. The second is its filtration efficiency. The filtration efficiency is mainly determined by the tightness of the water seepage pores on the filter paper and the size of the pores. Then there is the capacity. The capacity is mainly determined by the density of the water seepage pores. The denser the pores, the higher the capacity. The last is applicability. The production steps of some filter papers are very special, so we must pay attention to them when applying them. It should be noted that the filter paper cannot filter zinc chloride, because it will corrode and damage the filter paper.

The above is a brief introduction to the function of filter paper, classifications, and some basic properties. If you would like to learn more about the filter paper, contact HAWACH directly.