What are the different commercial grades of PSF available?
Following are the four commercially available grades:

• First (I)
• Standard(STD)
• Print Quality(PQ)
• Sub-standard (S/S)

Which are the important physical characteristics of PSF tested for regular gradation of product?

1. DENIER & TENSILE PROPERTIES
   Denier is the weight in grams of 9000meters length of a filament. Denier or Fineness is first tested on VIBROMAT-ME based on the principle of vibration under a fixed pre-tension and then the same fibre is elongated (at constant rate) to break (under specified conditions) on FAFEGRAPH-HR. From the sress-strain curve obtained Tenacity (strength of fibre) Elongation (ability to get stretched) and T-10 (tenacity at 10% elongation) are calculated automatically.
   
   
2. CRIMP PROPERTIES
   The crimp properties are tested on the instrument CRIMP BALANCE. CPCM - the number of crimps per centimeter length of fibre is obtained by counting the number of crimps on a given length and then dividing the number with the length in centimeter.
   
   
3. DRY HEAT SHRINKAGE
   The original length of the fibre under a fixed pre-tension is first determined on SHRINKAGE TESTER and subsequently the sample is exposed to dry heat in an Oven at 1800C for 30minutes. The shrunken length is measured and from the difference in lengths percentage shrinkage is calculated.
   
   
4. FINISH ON FIBRE
   The surface finish on a particular mass of fibre sample is extracted with methanol and collected on a pan kept on a heater where methanol gets evaporated and the finish oil remains as residue. From the wt. of residue oil and the fibre sample weight, the percentage Finish is calculated.
   
   
5. L,a,b COLOUR
   "L"(total reflectance) "a" (red-green) and "b" (yellow-blue) colours are measured directly on HUNTER Lab COLORIMETER or Lab SCAN by putting a fixed weight of air blended fibre sample in the sample cup.
   
   
6. DYEABILITY
   It is the relative dyeability of a fibre compared to a control.

   Thoroughly blended fibre samples are prepared and dyed along with control samples under specified conditions in HTHP dyeing machine. The "Y" colour values of the individual sample balls are measured on HUNTER Lab and a relative dyeability value in percentage with respect to the control sample is calculated.

7. FUSED FIBRE
   Fused fibres are unoriented, coarse, hardened fibres. They dye deeper than normal polyester fibre.

   About 2 kg composite bale sample of a creel is processed on a CARDING Machine and from the flat strip obtained the fused fibres are sorted out under magnifying glass and counted/weighed. The fused fibres are expressed as Numbers/Kilogram and as weight/weight per cent.

8. OVER LENGTH / MULTI LENGTH
   Over length fibres are fibres longer than the nominal cut length plus 10mm.

   Multi length fibres are fibres whose lengths are in multiples of nominal cut length.

9. FIBRE BULK
   Bulk indirectly represents the openness of the fibre.

   A particular mass of fibre is inserted in to a 1000 millilitre measuring cylinder without handling it much. Specific load is applied on fibre by a piston, and the volume occupied is read out from the cylinder.

10. CUT LENGTH
    Cut length is the average length of fibre at which the fibre is cut. The fibre is made straight on a greasy surface and the length is measured.