textile science
6. FIBER TESTING METHODS
Fiber Testing
It is an important part of textile production, distribution, and consumption. It is the process of determining the properties of different kinds of Textile substances.
Purpose of fiber testing
1) Performance requirement - It involves verification that a particular product confers to the national standards hence certification mark. This is to the interest of the consumer and textile industry. So as:
· To ensure consumer protection and safety
· To ensure good quality of raw material e.g. test the average fiber length so as to adjust the spinning machine accordingly.
2) Product and production quality control - Examines the quality of the product attributes and ensures the products meet the specification requirements and in the production control wastes and breakage minimized
· Helps in production, planning and organization as well as machinery replacement
· Ensures good quality material is produced
3) Research –It is used in the development of new methods, product and appropriate technology in use for testing
Fiber Testing Conditions
· Most fibers are hydroscopic in nature i.e. they absorb the moisture from an environment and conversely loose water in a dry atmosphere
· There are many physical features of a fiber that are affected by the amount of moisture they absorb and this are dimensions, tensile strength, elastic recovery, electrical properties, resistance moisture constant and regain rigidity
· According to the Kenya bureau of standards on condition for testing is that all textile articles should be conditioned for sufficient time to reach moisture equilibrium
· It’s said to be rigid when a sample or specimen during free exposure to moving air controlled at specified condition change in weight of the sample weighed successfully at interval of 2 hrs. In less than 0.05%
· Fiber testing involves scrutiny of characteristics/attributes that certain textile possess. Tests that may be carried out involves both optical and reactive investigations of fiber testing
· Testing is an important activity because it’s used to ascertain if the quality is good enough for the fiber to be put into textile use
· Since most fibers are hygroscopic in nature, the relative humidity and atmospheric temperature affect both their mechanical and physical properties and therefore allow the textile material to remain in conditioning room for sufficient time to allow it reach the moisture equilibrium
· Fiber testing is done by bringing the material to relatively low moisture content between 10-25% relative humidity with temperatures not exceeding 50 degrees Celsius
· Standard atmosphere for textile testing should be relative humidity of 65% and temp. of 20%
· The atmosphere in which physical tests are done on textile fibers are of a relative humidity of 65% minus or plus 2 with temperatures of 20 plus or minus 2 degrees Celsius
Sampling of fibers
Sampling operation must be done with great care and must be well understood by satisfying the following three main conditions
· Must be representative of all population to test items in the lot in order for the results to inferred
· Sample must be randomly selected to avoid biasness. If the sample is biased it should be indicated when the data is reported
· Must be obtained in a form suitable for the measuring instrument being used and the type of test being carried out
Properties to be tested
In testing the textiles you need to focus on the following properties:
1) Properties relating to the usage e.g. Tensile strength, tear strength, burst strength, resistant to abrasions, dimension stability, stretch recovery and pulling
2) Properties related to aesthetic acceptability e.g. drape, easy care, and appearance, retention and color fastness
3) Properties important in garment manufacture e.g. sew ability, free from static electricity, seam slippage
4) Properties relating to special application e.g. Water proof, resistance to acid, resistant to toxic acid, flame resistant
Fiber identification tests
There are basically 5 methods for identification. They include:
1) Thermal reaction
2) Staining test
3) Microscopic analysis
4) Solubility
5) Visual examination
1) Thermal test
The aim of this test is to identify the thermal reaction of textile. This shows the behavior of textile samples at various temperatures which determine the use and care of particles that remain from it, it’s also important for fiber identification in general categories. The behavior of the sample is noted as temperature is increased
2) Staining test
It takes advantage of the fact that dye stuffs and other chemicals not usually for dyeing, stain fibers differently. One of the most popular methods is Shyla stain where the sample is thoroughly wetted then immersed in the stain for one minute and washed with cold water
3) Microscopic analysis
Both longitudinal and cross-sectional view are examined. This examination is important for the combination with other fibers. Fiber shape and surface contours are among the important features that are noted. Cross sectional also contributes to characteristics e.g. hand feel, surface texture, body and covering power
4) Solubility analysis/test
A large number of tests could be noted under this section. The variables to be observed include: swelling and dissolution, dissolution without swelling, disintegration, color reactions and change, dimensional change etc.
It’s important because chemical reaction are utilized in the manufacture of fibers, cleaning and chemical finishing and in textile dyeing. Some of the chemicals used is Sulphuric acid, nitric acid, caustic soda and sodium hypochlorite. Caustic potassium of 5% will dissolve wool and silk but won’t dissolve cotton. Concentrated hydrochloric acid 30-40% dissolves silk and colors jute red-brown but does not dissolve wool
5) Visual examination/Analysis/Test
It’s done without the use of any visual aids, variables observed include Texture, luster, and natural color.
This does not provide any reliable information but can be used for general categorization. Other tests must be used alongside visual examination to be certain of the conclusions
How to identify fiber properties
a) Fiber length
· This vary considerably in natural fibers in their physical characteristics in a given sample due to different conditions under which they are grown or produced
· Variation in terms of co-efficient variation may be as high as 40% for cotton and about 50% for wool
· Man –made fibers may be produced in any length to meet the requirements of spinners and to soot the existing machine design
Methods of measuring fiber length
i. Hand stapling method
- It’s done by manipulating a turfed fiber between the thumb and the 1st finger to align the fibers and therefore allow official assessment of the fiber length distribution
- Its subjective and therefore unreliable
ii. Shirley Comb Sorter method
- A turfed is prepared with all fibers aligned to one end
- The fibers are then separated in order of decreasin length with their lower lengths aligned along the horizontal base line e.g. cotton fibers of standard mass are taken
- The fibers are manipulated by tweezers and a depressor on a bed of combs which are hitched side by side and spaced ¼ inch apart
- The combs are dropped successfully exposing the tips of the longest fibers which are pulled out by tweezers and arranged on a velvet pad in a decreasing order of length
iii. Fabric strength
- Samples of fabric tests should be taken at least one yard from the piece and for general the samples should be obtained along the centerline.
- 10 strips should be tested both warp and weft ways and at times it’s important to compare strength of strip at warp and selvedges
iv. Twist
- It’s a measure of spiral turns given in a yarn in order to hold the constituent fibers as threads together.
- The direction of the twist may be either ‘S’ or ‘Z’ twist
- An increase in twist results to an increase in strength but there is an optimum point beyond which an increase of twist causes decrease in strength
- The number of turns per inch usually depends on type of fiber and the yarn count.
Tools, materials and equipment used in fiber testing
1. Microscope Slides and Coverslips
2. Microscope Slide Boxes
3. Teasing Tools
4. Water
5. Stains
6. Mounting Media
7. Marking Pens
8. Reference Samples
9. Chemicals
10. Heating source
11. Different samples of fabrics and fibers
12. Measuring tools
13. Thermometers etc.
Safety measures to observe during fiber testing
1. All employees performing the testing activities should always wear safety glasses with side shields.
2. The experiments should be performed in a well-ventilated and lit area.
3. Workers must avoid smoking while working with fiber optics.
4. Food and beverages should be kept out of the work area.
5. Workers can wear disposable aprons to keep fiber particles off their clothing.
6. Before leaving the work area, an employee should always check their clothing for pieces of stray fiber, and if any are found, they can remove it with double-sided tape.
7. A worker should wash their hands thoroughly before touching their eyes, and contact lens
8. Workers should also read all instructional material before handling chemicals.
9. A disposable container that can be tightly closed must be used for fiber scraps.
10. When finished with a fiber optic job, all cut fiber pieces should be disposed of properly along with any used chemicals and containers.
11. The work area should be thoroughly cleaned when job is completed.