4.3.1 Classification

Fibers are classified by their source as follows:

1. Natural fibers

   1. wood pulp,

   2. vegetable fibers,

   3. cotton,

   4. animal fibers (wool).

2. Synthetic polymer fibers

   1. polyester,

   2. rayon (regenerated cellulose),

   3. nylon (polyamide),

   4. polyaramid (e.g. Kevlar ),

   5. polyphenylene sulfide,

   6. nomex,

   7. polypropylene,

   8. polyethylene,

   9. polyacrylic,

   10. polyimide.

3. Inorganic and mineral fibers

   1. glass,

   2. ceramic,

   3. carbon,

   4. asbestos,

   5. basalt.

4. Binder fibers

   1. bi-component high melt/low melt polymer,

   2. polyester copolymer,

   3. polyvinyl chloride,

   4. polyvinyl acetate/polyvinyl chloride copolymer,

   5. polyamide copolymer,

   6. polyvinyl alcohol.

5. Bi-component fibers

6. Nanofibers

   1. electro spun,

   2. carbon (graphite),

   3. microglass.

4.3.2 Physical Characteristics

The following physical characteristics of fiber that are important for their use in filter media.

1. Diameter

2. Length

3. Aspect (length to diameter) rati

4. Density

5. Linear density

6. Cross-section shape

7. Length characteristics

   1. crimp,

   2. curl,

   3. kinkiness.

8. Internal structure (cellular or solid)

9. Strength properties

   1. tensile strength and breaking length,

   2. stretch or elongation,

   3. Young's modulus,

   4. stiffness,

   5. bending modulus.

4.3.3 Physical Chemical Characteristics

The following are chemical and physical chemical properties of fibers to be considered in their choice for use in filter media:

1. Glass transition temperature.

2. Melting point.

3. Additives, components, contaminants, and impurities.

4. Bonding properties.

5. Chemical composition.

6. Chemical resistance.

7. Corrosion resistance.

8. Electrostatic charge.

9. Water and moisture resistance.

10. Moisture absorption.

11. Moisture content.

12. Dimensional stability.

13. Polymer structure.

14. Temperature and heat resistance.

15. Surface properties.

16. Surface size.

17. Surface tension and energy.

18. Volatile components.

4.3.4 Fiber Properties for Filtration Media

The choice of fibers for nonwoven filter media depends on the properties of the filter medium to be produced, the process by which it is produced, and the application.

Table 4.2 provided by MINIFIBERS, Inc., compares the properties of several fibers...