Chemistry Reference
In-Depth Information
In summary, the final properties of thermoplastic articles depend both on the
molecular structure of the polymer and on the details of the fabrication opera-
tions. This is a disadvantage, in one sense, since it makes product design more
complicated than with other materials that are less history-dependent. On the
other hand, this feature confers an important advantage on plastics because fabri-
cation particulars are additional parameters that can be exploited to vary the costs
or balance of properties of the products.
PROBLEMS
4-1 Nylon-6,6 can be made into articles with tensile strengths around
12,000 psi or into other articles with tensile strengths around 120,000 psi.
What is the basic difference in the processes used to form these two differ-
ent articles? Why do polyisobutene properties not respond in the same
manner to different forming operations?
4-2
Suggest a chemical change and/or a process to raise the softening tempera-
ture of articles.
H
(
CH
2
C
)
x
4-3
(a) Calculate the fraction of crystallinity of polythylene samples with den-
sities at 20
C of 926, 940, and 955 kg/m
3
. Take the specific volume of
crystalline polyethylene as 0
.
989
10
2
3
m
3
/kg and that of amorphous
3
10
2
3
m
3
/kg. (b) What assumption did you make
polyethylene as 1
.
160
3
in this calculation?
4-4 The melting points of linear C
n
H
2n
1
2
molecules can be fitted to the empir-
ical equation
17
n
2
1
T
m
ð
K
Þ 5
1000
=ð
2
:
4
1
Þ
Plot the graph of
T
m
against
n
using the equation and compare the
observed values of
T
m
listed below with the curve. Determine the equilib-
rium melting point
T
m
0
for high-density polyethylene.
n
8
10
12
14
16
24
32
T
m
(
C)
2
56.8
2
29.7
2
9.7
2.5
14.7
47.6
67
