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Chemistry Project Reports on Acid & Bases of Tensile Strength of Fibres



Acid & Bases Effected on Tensile Strength of Fibres

(i) Compare the tensile strength of given samples of nylon and cotton fibers.

(ii) To investigate the Effect of Acids and Alkalies on the tensile strength of these fibers.



Depending upon the sources, the various types of fibers can be classified into the following three main categories :

(i) Animal fibers, e.g., Wool & Silk.

(ii) Vegetable Fibres e.g. Cotton & Linen.

(iii) Synthetic Fibres, e.g., Nylon & Polyester.


Besides their chemical composition and properties, the essential feature of these fibers is their tensile strength. Tensile strength means the extent to which a fiber can be extended without breaking, and it is measured regarding minimum weight required to break the fiber. To determine the tensile strength of any fiber, it is tied to a hook at one end, and weighted is slowly added to the other end until the fiber break.

Since bases than acids more easily hydrolyze peptide bonds, therefore wool and silk are affected by basis, not by acids. It is because of this reason that wool and silk threads break up into fragments and ultimately dissolve in alkaline.

In other words, alkaline decrease the tensile strength of animal fibers (wool & silk). Vegetable fibers (cotton & linen), on the other hand, consist of long polysaccharide chains in which either linkage joins the various glucose units. Since acids hydrolyze either and not by bases, therefore, vegetable fibers are affected by acids but not by stations. In other words, acids decrease the tensile strength of vegetable fibers. In contrast, synthetics fibers such as nylon & polyester practically remain unaffected by both acids and bases.

Experiment-1 [Acid and Bases]

Requirements :

(a) Apparatus: Hook, Weight hanger, and weights.

(b) Materials: Cotton, Silk and Nylon fibers.
Chemistry Experiment Acid and Bases Procedure

(i) Cut out equal lengths of a cotton fiber, nylon fiber and silk fiber from the given sample of nearly same dia.

(ii) Tie one end of the cotton fiber to a hook which has been fixed in a vertical plane. Tie a weight hanger to the other end. The thread gets straight.

(iii) Put a weight on the hanger and observe the thread stretch. Then, increase the weights gradually on the hanger until the breaking point reaches and note the minimum weight needed for breaking the cotton fiber.

(iv) Repeat the above experiment by tying nylon and silk fibers to the hook separately.

Sr.No.           Type of Fiber         Minimum Weight

1.                 Cotton                                 75 g.

2.                 Nylon                                375 g.

3.                 Silk                                   150 g.



(i) The thread must be of identical diameters.

(ii) Always take the same length of the threads.

(iii) Add the weights in small amounts very slowly.


Experiment – 2

Requirements :

(a) Apparatus: Hook, Weight Hanger and Weights.

(b) Materials and Chemicals: Wool, Cotton and Nylon Fibres, dilute solution of Hydrochloric acid and sodium hydroxide.


(i) Cut out identical lengths of wool, cotton and nylon threads from given pattern of almost equal diameter.

(ii) Determine the tensile power of every fibre as defined in test-1.
(iii) Soak the woolen thread in a dilute solution of sodium hydroxide for 5 minutes. Take it out from hydroxide solution and wash it very well with water after which dry either by retaining it inside the sun or in an over maintained at a temperature of about 400C. Determine its tensile power again as explained in

(iv) Now take another part of woolen thread of the identical size and diameter and soak it in a dilute solution of hydrochloric acid for just 5 min. Make it our from from there and wash it properly with  water and mesure the tensile power again.

(v) Repeat the above system for the samples of cotton and nylon fibre.




(i) The tensile strength of woolen fiber decreases on soaking in alkalies but practically remains unaffected by soaking in acids.

(ii) The tensile strength of cotton fiber decreases on soaking in acids but remains practically unaffected by soaking in alkalies.

(iii) The tensile strength of nylon fibers remains practically unaffected by soaking either in acids or alkalies.



(i) The thread must be of identical diameters.

(ii) Always take the same length of the threads.

(iii) Add the weights in small amounts very slowly.



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