TEXTILE INSTITUTE OF PAKISTAN
Second Class Test – Spring 2008
Course Title: Fibre Science
Section(s): TS3A & B Instructor: Aasim Ahmed
Date: April 23, 2008
Course Code: TEXT-321
Max. Marks: 15
Max. Time: 1 hour
Name:
________________________________________________________________________
Registration Number:
________________________________________________________________________
Instructions for candidates
Please read the instructions carefully before beginning the paper.
1. Please ensure that you have entered your name and roll number in the space provided
on this paper.
2. There are 3 questions in this paper. All questions are compulsory.
3. This test carries a total of 15 marks
4. Candidates may carry with them provided handouts on Introduction to Fibre
Science by MA Wilding which they can consult during the examination.
5. Candidates will not be penalised for notes made on their handouts for purpose of study,
however, any attempt to write out related material from other sections of the course will
be considered as a violation of examination rules according to clause 2.29.1 (special
note) of studentsʼ handbook, and subject to action in accordance with the same.
6. Candidates are not allowed to carry out discussions during the examination.
7. All questions should be answered on this question paper, there are no extra sheets
required.
8. The number of points carried by each question is written in square brackets [ ] at the
end of the question.
9. All questions, except for those that require drawing must be answered in ink. Answers in
pencil will not be marked.
10.To answer multiple choice questions, the appropriate block next to the option should
either be marked with a tick, by shading or by placing an x in the block.
11.The solution to this paper will be posted online at the end of the examination.
Best of luck!
1/4
Question 1 [5]
Figure 1, shows a force extension curve.
B
E
F
Figure 1
D
C
A
Breaking strength
Tensile force at break
Tenacity
Extension at break
Extension at maximum tensile force
Tensile force at maximum compression
Initial modulus
Work of rupture
I. From the above list, choose the correct option which corresponds with each of the
following points on figure 1. [5]
i.Point A: Extension at break
ii.Point B: Breaking strength
iii.Point C: Extension at maximum tensile force
iv.Gradient from point D - E: Initial modulus v.Shaded area F: Work of rupture
Question 2 [6]
I. Explain the difference between strength and tensile strength [1]
While strength can vary in type, compressional, tortional, impact etc. the term tensile
strength specifically refers to strength determined by application of a uni directional
extension force applied along the axis of the fibre or yarn. II. Explain the difference between tenacity and tensile strength. [1]
Tensile strength is simple a measure of maximum force attained in breaking a fibre
however, tenacity is a measure the same forcein relation to the linear density of the fibre
or yarn.
2/4
III. What is the difference between tensile strength and breaking strength. [0.5]
No difference whatsoever, except in the name and spelling. Y
Stress
Figure 2
Strain
IV. Assuming that the stress strain curve shown in figure 2 above has a distinct yield point,
below which all deformation is elastic and above which any deformation is plastic. What
can be said about the changes taking place in the tested fibre on a molecular scale. [1.5]
a, Before the yield point, intermolecular bonds are subjected to strain but do not break.
b, After the yield point, intermolecular bonds are subjected to strain but do not break.
c, After the yield point, intermolecular bonds can break and adjust to more comfortable
positions.
II. List the following fibres in order of highest to lowest tensile strength under dry and wet
conditions. [2]
Cotton, Lyocell, Viscose Rayon and Modal.
i. Dry:
Highest
Lyocell -
Modal -
ii. Wet: Highest
Lyocell -
Cotton -
Viscose R. - Cotton
Lowest
Modal -
Lowest
Viscose R
Question 3 [4]
I. During the making of Viscose Rayon, harsh processing conditions lead to the
degradation of the cellulose chains. The degree of polymerization is thus reduced from
10,000 in native cellulose to about 500 in regenerated viscose rayon.
In the making of high wet modulus rayon, the losses in degree of polymerization are
reduced. Explain how this is achieved. [1.5]
By using a new process for development which utilizes a weaker concentration solution of
NaOH, omitting the ripening stage and applying the filament stretching more slowly.
3/4
II. Cellulose 1 and 2 are two forms of cellulose that exist in natural and regenerated fibres.
The difference in the two forms is said to exist in the parallel and anti parallel arrangement
of cellulose chains. In regenerated cellulose, typically in the case of viscose rayon, the
chains settle into an anti parallel arrangement as order is formed in accordance with the
lamellar theory.
However, an anomaly arises in the case of mercerized cotton in which cellulose 2 is said to
exist. Surely, in the case of mercerized cotton the chains could not have taken a 180o
summersault to switch to cellulose 2.
Use the space below to explain the change of cellulose 1 to cellulose 2 in mercerized
cotton in contrast to the changes that take place when natural cellulose is converted into
its regenerated form. [2.5]
When Cotton is mercerized, the crystallites rotate about their axis and the
structures swell up thus opening up from its original packed state. While all the
chains in emerging from a single centre of biosynthesis (enzyme), may have
chains pointing in a single outward direction, there can be several such units
present each with chains facing opposite directions. When the structure of
cotton opens up due to mercerization the chains from different enzyme centres
might begin to overlap one another thus giving the cellulose the appearance of
cellulose 2 or form 2 with alternating chains. 4/4