A Brief Introduction of Filter Paper

Definition of filter paper

Filter paper, made of cotton fiber, is a filter tool commonly found in chemical laboratories to separate liquids and solids. A filter paper is an effective filter medium and has been widely used in various fields. Different fiber filter papers have different performances and usages, as there are normal ones for general occasions, glass fiber filter papers for high temperatures, and polypropylene filter papers for ultra-clean, etc. It provides an effective means for removing as many contaminating particles as possible from liquids and air and has a small resistance limit.

Chromatography of filter paper

Paper chromatography uses an inert support of filter paper. The filter paper fiber has a strong affinity with water and can absorb about 22% of water, and 6~7% of the water is combined with the hydroxyl group of cellulose in the form of a hydrogen bond, which is difficult to remove under normal conditions. While the affinity of the filter paper fiber to the organic solvent is very weak, the general paper chromatography actually takes the combined water of the filter paper fiber as the stationary phase, with the organic solvent as the mobile phase.

When it passes the sample through the paper, the solute at the sample point is continuously distributed between the water and the organic phase. A part of the sample moves with the mobile phase, enters the solute-free region, and is redistributed at this time, and a part of the solute enters the stationary phase(aqueous phase) from the mobile phase. As the mobile phase moves, the various parts are continuously distributed according to their respective partition coefficients and moved along the mobile phase, thereby separating and purifying the material.

filter-paper

Principle of filter paper

In the actual design of the filter paper, every effort must be made to balance the various indicators to protect the system being filtered effectively. Then the filtration principle of filter paper is reflected in the following aspects:

1. Filtering agglomerates – As the dirt particles accumulate on the surface of the filter paper, they form a filter layer itself, thereby capturing smaller particles in the pores between the large particles. As the particles continue to increase, the resistance also increases continuously until it is completely blocked or reaches the pressure difference.

2. Adsorption – When the filtered fluid passes through the labyrinth, although some of the particles are much smaller in diameter than the pore size, these small particles are adsorbed onto the filter paper by electrostatic attraction. Therefore, static electricity is specially added to some filter materials during the manufacturing process.

3. Fall-into – In this process, due to the flow rate, the particles directly fall into the surface of the filter paper fiber rather than staying in the pores of the filter paper and are held by the adsorption force and the fluid force of the fluid, thereby blocking some smaller particles

Types of Filter Papers

There are three kinds of filter papers, which are made of different materials with different properties for different purposes. One is a cellulose filter paper for general occasions. Two is a glass fiber filter paper for high-temperature conditions. There is a polypropylene filter paper for ultra-clean.

Filter paper equivalent to Whatman Cellulose Filter Papers Filter Paper in Chemistry

Classification of filter paper

In general, the filter paper is divided into qualitative and quantitative. In analytical chemistry applications, the residue collected on the filter paper after the separation of the inorganic compound by filtration can be used to calculate the rate of wastage during the experiment.

Qualitative filter paper is filtered to produce more cotton fibers, making it only suitable for qualitative analysis; Quantitative filter paper, especially ashless filter paper, is more effectively resistant to chemical reactions after special treatment procedures with fewer impurities, which can be used for quantitative analysis.

  • Qualitative filter paper – used for general laboratory applications to filter out particles without needing precise measurements of residue.
  • Quantitative filter paper – ashless and highly pure, ideal for gravimetric analysis where accuracy is essential.

Besides the filter paper for general laboratory applications, there are many filter paper applications in daily life and engineering. For example, coffee filter paper provides high softness and high wet strength. Others use air filter paper for testing suspended particles in the air and fiber filter paper for various industrial applications.

Technical indicators

The technical indicators of the filter paper can be mainly divided into two aspects: filter characteristics and physical characteristics. Filtration characteristics include air permeability, air resistance, maximum pore size, and average pore size. Physical properties include basis weight, thickness, stiffness, corrugation depth, burst strength, resin content, and the like.

Application of Filter Papers

Filter paper is frequently seen in various industries. Paint filter papers can effectively filter the paint, oil, glass raw materials, epoxy, tar, liquefaction of workpieces, plastic, ceramic, dye, painting, and porcelain. The filtering effect is 99.99%.

High-efficiency filter papers, made of glass fiber, are ideal for air filter selection with the characteristics of uniform fiber distribution, large dust capacity, small resistance, and high strength, which are widely used in the defense industry, electronic instruments, medicine, food industry, and other fields.