To Know the Features of Filter Paper Well, Understand the Cotton Fiber First

Filter paper is a porous material that is commonly used in laboratories for various filtration applications. It is composed of fibers that create a matrix with a specific pore size, allowing the passage of liquids while retaining solid particles. Understanding the characteristics of the fibers used in filter paper, including cotton fibers, is essential for appreciating the features of filter paper. Here are some key features of filter paper, with a focus on cotton fibers:

1. Material Composition:

  • Cotton Fibers:
    • Filter paper is often made from cellulose fibers derived from wood pulp or cotton. Cotton fibers are known for their purity, high cellulose content, and natural properties that make them suitable for filtration.

2. Pore Size and Porosity:

  • Defined Pore Structure:
    • Filter paper is manufactured to have a specific and uniform pore size, allowing for precise filtration.
  • Porosity:
    • The porosity of filter paper is a measure of the open space between fibers. It determines the flow rate and the capacity of the filter paper.

3. Particle Retention:

  • Selective Particle Retention:
    • Filter paper is designed to selectively retain particles of a certain size while allowing liquids to pass through. The particle retention is determined by the pore size and composition of the paper.

4. Purity and Low Extractables:

  • High Purity:
    • Cotton fibers contribute to the high purity of filter paper, making it suitable for applications where minimal interference or contamination is crucial.
  • Low Extractables:
    • Filter paper is often treated to reduce extractables, ensuring that it does not introduce unwanted substances into the filtrate.

5. Chemical Compatibility:

  • Chemically Inert:
    • Filter paper, including types made with cotton fibers, is generally chemically inert. This allows it to be used with a variety of chemical solvents without significant degradation.

6. Thickness and Weight:

  • Variable Thickness:
    • Filter paper comes in various thicknesses, allowing users to choose the appropriate grade for their specific filtration needs.
  • Weight Categories:
    • Filter papers are often categorized by weight (grams per square meter), indicating the density of fibers and thickness.

7. Wet Strength:

  • Enhanced Wet Strength:
    • Cotton fibers, when properly processed, contribute to the wet strength of filter paper. This is important to prevent disintegration or tearing when the paper is wet.

8. Fast Filtration:

  • High Flow Rate:
    • Filter paper, including those made with cotton fibers, is designed for fast filtration while maintaining effective particle retention.

9. Application-Specific Grades:

  • Qualitative and Quantitative Grades:
    • Filter papers come in qualitative and quantitative grades. Qualitative grades are used for general-purpose filtration, while quantitative grades are used for precise gravimetric analysis.

Filter paper is one of the most frequently used tools in many experiments. Filter paper manufacturers are divided into qualitative and quantitative filter papers. If you would like to know the filter paper better, you should know the raw material first-cotton fiber.

Composition properties

The main component of cotton fiber is cellulose. Cellulose is a natural polymer compound. The chemical structural formula of cellulose consists of repeatingαglucose as the basic structural unit. Its elemental composition is carbon 44.44%, hydrogen 6.17%, and oxygen 49.39%. The degree of polymerization of cotton fiber is between 6000 and 11000. In addition, cotton fiber also has about 5% of other substances, called companion organisms, which have an impact on spinning technology, bleaching, printing, and dyeing.

The surface of cotton fiber contains fat wax, commonly known as cotton wax. Cotton wax has a protective effect on cotton fiber, which is one of the reasons for the good spinning performance of the cotton fiber. Therefore, the cotton cloth is easy to wind around the roller and the rubber roller. After degreasing treatment, the moisture absorption of raw cotton increases, and the water absorption capacity can reach 23~24 times its own weight.

The linear density of cotton fiber refers to the thickness of the fiber, which is one of the important quality indicators of cotton fiber, and it is closely related to the maturity and strength of the cotton fiber. The linear density of cotton fiber is also one of the main factors that determine the spinning characteristics and yarn quality.

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Folding strength and elasticity

If the fiber strength is high, the yarn strength is also high. The strength of the cotton fiber is often expressed by breaking strength and breaking length. Because of the large difference in the strength of individual cotton fibers, the strength of cotton bundle fibers is generally measured and then converted into a single fiber strength index.

Folding moisture absorption

Cotton fiber is a porous substance, and there are many hydrophilic groups (-OH) on its cellulose macromolecule, so its moisture absorption is good. Under normal atmospheric conditions, the moisture regains rate of cotton fiber can reach about 8.5%.

Acid and alkali resistance

Cotton fiber has weak resistance to inorganic acids. Cotton fiber has greater resistance to alkali, but it will cause lateral expansion. Dilute alkali solution can be used to “mererify” cotton cloth. In addition, there are impurities and defects in the cotton fiber. The impurities include sand, leaves, bell shells, etc., and the defects include neps and ropes. They affect not only the amount of cotton used in textiles but also the processing and yarn quality, so inspections and strict control must be carried out.

Chemical stability

Since the main component of cotton fiber is cellulose, it is more alkali-resistant but not acid-resistant. Caustic soda can cause the cotton fiber to swell violently, increase the diameter and shorten the length, which causes the strong shrinkage of cotton products. At this time, if tension is applied to restrict its shrinkage, the surface of the cotton product will become smooth and bright and greatly improve the dyeing performance.

This processing is called mercerizing; if it is allowed to shrink without tension, it is called alkali shrinkage. Knitted fabrics will become compact and elastic after alkali shrinkage, and have good shape retention. Acid can make the strength of cotton fiber worse, and especially strong acid and concentrated acid should be avoided. It can be dissolved in more than 70% concentrated sulfuric acid. Concentrated hydrochloric acid and concentrated nitric acid also have a serious impact on their strength.