Experiment #1
Impact Strength of Plastics
Mickey Mouse (1232456)
Section VN
Submitted on January 21, 2009
Lab Group Members:
Donald Duck
Minnie Mouse
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1. Objective
The objective of this lab is to understand the influence of temperature on impact strength of various types of
plastics in common use.
your own words showing understanding
of the issue and its importance
2. Introduction
Plastics are frequently used in many areas of Building and Civil Engineering. Building components including
roofing, flooring, insulation and window frames can be manufactured from various polymers. In Civil
Engineering, geotextiles are only one of several instances of relevant applications.
Buildings and civil infrastructure can experience a wide range of temperature in service. It is important to know
the behavior of the intended polymer over the range of temperatures that are likely to be encountered. For
example, certain polymers are intended to remain flexible over a wide range of temperatures, such as caulking
around windows. Other materials are intended to remain strong, such as a window frame.
Changes in the properties of a material from a brittle solid to a vicous liquid are temperature dependent. For
polymers, the temperature at which brittle behavior ceases is termed the glass transition temperature. The
determination of this temperature is often carried out by examining the mechanical behavior at various
temperatures.
not the best quality
Figure 1: Effect of Temperature on Impact Energy (Nass and Heiberger, 1992)
page numbers
1
reference!
indicates that you understand and can
find relevant published information
Figure 1 schematically shows brittle failures occur at low temperatures and result in relatively low impact
strengths. As the temperature increases, more energy is required for fracture due to the greater deformations
occurring in ductile behavior. Purely ductile performance results in slight increases in impact resistance with
temperatures. At intermediate temperatures, a sharp significant increase in impact energy is measured.
3. Procedures
In this experiment, the Izod test was used to measure the impact energy per unit cross‐sectional area of three
types of plastics. The polymers tested were the following:
•
•
•
Polystyrene (white)
Polyvinylchloride (grey)
Poly(methyl methacrylate) (clear).
no need to repeat details of
standard, just deviations (means
that you read the standard)
Testing was carried out according to ASTM D256 ( Standard Test Methods for Determining the Izod Pendulum
Impact Resistance of Plastics) Method C using both notched and unnotched specimens. Polymer samples were
exposed to four different conditions, dry ice (‐56°C), a standard freezer (0°C), room temperature (23.5°C) and in
an oven (50°C). For each of these conditions, the specimens were exposed for a minimum of 15 minutes prior to
testing for temperature equalization. One specimen was tested for each polymer at each of the four
temperatures. (According to the standard 5 to 10 specimens should be used.)
4. Results
refer to Figures (or
Tables) in the text
The net strength was determined from subtracting the tossing strength from the total strength. The numerical
results of the tests are given in the Appendix. The effect of temperature on the net strength of the three
polymers studied is shown in Figure 2. The results show that for two of the polymers, PVC and PMMA, impact
strength is not significantly dependent on temperature in the range investigated in this experiment. However,
polystyrene (PS) did show a consistent increase in net strength with an increase in temperature. In general,
poly(methyl methacrylate) (PMMA) showed the lowest impact resistance, while PS showed the highest.
From the measured data and the values determined, it is likely that PVC and PMMA are well below the glass
transition temperature for the temperatures investigated. Evidence of this fact could have been verified from
the fracture surface. Typically, smooth, glassy fractures indicate brittle fracture; while white surface would
indicate a ductile failure. Unfortunately, the condition of the fracture surface was not noted. For the PS samples,
the transition from brittle to ductile behavior can be seen clearly.
admit to your
limitations
2
axis labels and
units
Figure number and
description
Figure 2: Net strength
vs. Temperature for Notched Specimens
Figure 3 shows the results for the same polymers and temperatures for solid (unnotched) specimens. In general,
it can be seen that the net strength was approximately one order of magnitude higher than the results of the
notched specimens. This outcome is expected for two reasons; firstly, the cross‐sectional area to fracture was
cusing the energy of fracture at a specific
less and secondly, the notch creates a stress concentration fo
location rather than distributing the energy over a larger portion of the specimen.
In the case of the solid specimens, the polyvinyl chloride specimens exhibited very high net strength. In fact, at
the three higher temperatures, sufficient energy could not be generated to fracture the samples. PMMA
exhibited the lowest impact resistance of the three polymers tested as was also observed in the notched
specimens.
For PVC and PMMA there was not a significant influence of temperature on the resulting net strength measured
by the Izod tests.
use correct descriptive
language
3
Figure 3: Net Strength vs. Temperature for Solid Specimens
5. Discussion
Table 1 gives the published values of ASTM D 256 tests. Compared to the measured results given in Figure 2, the
published results are higher than those measured. However, the published results do not state weather the test
was carried out using Method A or Method C. In Method C, the tossing strength is determined and subtracted
from the total strength, while Method A includes only the total strength. In this experiment, the tossing strength
was approximately 8 J/m for the notched specimens. If the tossing strength is not taken into account, the
measured results agree reasonably well with the published data.
compare to published
Table 1: ASTM D 256 data at room temperature for notched specimens (www.boedeker.com)
Polymer Type
Polystyrene (PS)
results (referenced, of
course)
Izod (ft‐lb/in)
Izod (J/m)
0.8‐2.0
42.67‐106.7
Polyvinylchloride (PVC)
0.52
27.75
Poly(methyl methacrylate) (PMMA).
0.3
16
The glass transition temperatures of the three polymers are similar; 373, 354 and 378 K for PS, PVC and PMMA
respectively (CRC, 1996). These temperatures are above the maximum temperature of the experiments carried
out during this investigation. It is surprising that the temperature sensitivity of PS was apparent for these
experiments given this fact.
4
show your
understanding
6. Conclusion
The impact resistance of three types of polymers were measured and compared with literature values. The total
strength as determined by notched specimens using ASTM D 256 was in reasonable agreement with published
values when disregarding the tossing strength.
The Izod test was also carried out with solid specimens. This arrangement is not one of the methods discussed in
the ASTM standard. Regardless of this fact, the net strength was considerably higher than that measured with
the notch. This indicates that small defects in these polymeric materials can significantly effect the impact
resistance. In practice, small imperfections exist and therefore the values obtained using the notched specimens
may better reflect reality.
As for applications in Building and Civil Engineering for these three polymers, it can be indicated from the data
measured during this experiment, the highest impact resistance was observed in PS followed by PVC and PMMA.
The disadvantage of PS in some applications might be the increasing ductility observed in the temperature range
studied. This temperature range certainly encompasses the variability of the Montreal climate. Both PVC and
PMMA behave in a brittle manner throughout the entire range measured. In this case, they will retain consistent
properties during the extremes of annual exposure. Residential window frames can be constructed on PVC,
while PMMA is sometimes used as a glass replacement in greenhouse applications.
7. References
boedeker.com, accessed January 24, 2009
CRC, Handbook of Chemistry and Physics, D. Lide Editor, 76th Edition, 1995‐1996.
Nass, Leonard I. and Charles A. Heiberger, Encyclopedia of PVC: Compounding Processes, Product Design,
and Specifications ‐ Volume 3 of 4 (Print), Edition: 2, 1992
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Appendix
don't include all detailed data in
report, unless requested
PS
Notched
Temperature
(°C)
‐56
0
23.5
50
Solid
Total
Tossing
Net
Total
Tossing
Net
Strength Strength Strength Strength Strength Strength
(J/m)
(J/m)
(J/m)
(J/m)
(J/m)
(J/m)
42.21
8.53
33.68
411.48
8.28
403.20
66.36
8.65
57.71
335.99
8.15
327.84
87.96
8.28
79.68
362.18
7.53
354.65
100.84
8.16
92.68
346.52
7.53
338.99
PVC
Notched
Temperature
(°C)
‐56
0
23.5
50
Solid
Net
Total
Tossing
Net
Total
Tossing
Strength Strength Strength Strength Strength Strength
(J/m)
(J/m)
(J/m)
(J/m)
(J/m)
(J/m)
32.16
13.55
18.61
857.22
5.32
851.90
31.89
12.41
19.48
did not break
31.21
10.52
20.69
did not break
30.40
10.77
19.63
did not break
PMMA
Notched
Temperature
(°C)
‐56
0
23.5
50
Solid
Net
Total
Tossing
Net
Total
Tossing
Strength Strength Strength Strength Strength Strength
(J/m)
(J/m)
(J/m)
(J/m)
(J/m)
(J/m)
15.38
10.32
5.06
212.81
10.58
202.23
14.55
11.09
3.47
192.48
9.06
183.42
12.24
10.58
1.66
238.77
27.79
210.98
13.39
10.96
2.44
212.24
8.55
203.69
where is the signed
data sheet?
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