151-0548-00L
Manufacturing of Polymer Composites FS 17
Exercise 2
Exercise 2: Solution
MATRIX SYSTEMS
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Task 1:
Manufacturing of Polymer Composites FS 17
Exercise 2
Polymeric materials
a) What part of the composite determines its thermal properties?
The matrix is the component limiting the thermal range where a composite can be used.
b) What is the difference between glass transition temperature and melting temperature?
In polymer science, the melting temperature is the temperature at which the melting of the
crystalline part of a semi-crystalline polymer takes place. The glass transition temperature
is the temperature at which a polymer passes from a glass state (hard and relatively brittle)
into a rubber-like state. While the melting represents an effective phase transition (first order transformation, involving a heat exchange with the external environment to break up
the inter-chains bonds), the glass transition is second order transformation that involves only the amorphous region of the polymer and entails the passage into a state with higher
(rubber-like) or lower (glass-like) mobility of the polymeric chains (regulated by the available thermal energy from the environment). The glass transition temperature is always
lower than the possible melting temperature.
c) Draw the qualitative behavior of the stiffness as a function of temperature for the following
classes of polymers and comment on the curves (The glass transition temperature TG is the
same for all three polymers)
• Partially crystalline thermoplastic
• Amorphous thermoplastic
• Thermoset
Range I: It is found bellow Tg, and is also known as glass state. The polymer chains remain frozen in space, as they have not enough energy to undergo any type of motion.
Range II: It is found between Tg and Tm, and can also be called rubber-elastic state.
Thermal energy activates additional molecular degrees of freedom. The polymer chains are
now free to rotate, inducing a loss of stiffness in the polymer. This effect is less pronounced for semicrystalline thermoplastics: only the amorphous regions soften at TG. The
crystalline regions still contribute substantially to the overall stiffness of a component.
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Laboratory of Composite Materials and Adaptive Structures
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151-0548-00L
Manufacturing of Polymer Composites FS 17
Exercise 2
Range II: Shortly ahead of the melting temperature stiffness begins to drop drastically. The
polymer is in the melting range, where the first crystallites start to melt.
Interesting remark: in contrast to metals, which exhibit an almost fixed defined melting
point, semicrystalline thermoplastics do not feature a unique melting point, but an interval
or a range of melting,
d) What is the degree of polymerization and what influence has on the final properties of the
resin?
The degree of polymerization is the number of times a monomer is repeated on a polymer
chain. It is defined as the ratio between the number-average molecular weight (Mn) and the
molecular weight of the monomer unit (Mo).
𝐷𝐷𝐷𝐷 =
𝑀𝑀𝑛𝑛
𝑀𝑀0
The higher the degree of polymerization is the better thermal and chemical resistance of
the polymer as we have more intermolecular bonds. However, very high viscosities (almost
solid state) are also obtained at room temperature, which make the processability of the
material more difficult. High temperatures (above the melting points) or solvents are in this
case needed.
e) Discuss also the influence of the crosslink density on the material properties.
Following the same reasoning, the higher the crosslink density is the higher the number of
intramolecular bonds on a polymer. The chains cannot slide or rotate because they are
fixed into position. There are less available degrees of freedom and hence higher Tg.
f) How does the branching of the molecules affect the glass transition temperature?
The “free volume” of a molecule is the space between this molecule and the ones surrounding it. Branching increases the distance between molecules, resulting in a reduction
of the intermolecular forces. Therefore, less energy is necessary to release some degrees of
freedom, so the Tg reduces.
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Laboratory of Composite Materials and Adaptive Structures
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151-0548-00L
Manufacturing of Polymer Composites FS 17
Exercise 2
Consider the reaction, taking place in alkaline medium, between bisphenol-A and epichlorohydrin.
g) If the resin has a degree of polymerization of 0 (1 bisphenol-A + 2 epichlorohydrin) and is
cured with a diamine hardener, with a molecular weight of 82g/mol and 4 reactive hydrogens. What is the mass of hardener necessary to cure 450g of resin?
𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐻𝐻 𝑒𝑒𝑒𝑒 𝑤𝑤𝑤𝑤 =
𝑀𝑀𝑀𝑀 ℎ𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎
82
=
= 20.5𝑔𝑔/𝑚𝑚𝑚𝑚𝑚𝑚
𝑛𝑛𝑛𝑛. 𝑜𝑜𝑜𝑜 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 ℎ𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦
4
𝑀𝑀𝑀𝑀 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 = 21 ∙ 12 + 24 ∙ 1 + 4 ∙ 16 = 340𝑔𝑔/𝑚𝑚𝑚𝑚𝑚𝑚
𝐸𝐸𝐸𝐸𝑣𝑣 =
𝑛𝑛𝑛𝑛. 𝑜𝑜𝑜𝑜 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 ∙ 100 2 ∙ 100
=
= 0.588
𝑀𝑀𝑀𝑀 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
340
𝑀𝑀ℎ𝑎𝑎𝑎𝑎𝑎𝑎 = 𝐸𝐸𝐸𝐸𝑣𝑣 ∙ 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐻𝐻 𝑒𝑒𝑒𝑒 𝑤𝑤𝑤𝑤 ∗ 4.5 = 0.588 ∙ 20.5 ∗ 4.5 = 54.2𝑔𝑔
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Laboratory of Composite Materials and Adaptive Structures
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151-0548-00L
Manufacturing of Polymer Composites FS 17
Exercise 2
Task 2: Thermomechanical properties
a) A table with polymer material data is given to you at the end of this exercise. Why for
some polymers the maximum service temperature is above its glass transition? Why this is
not the case for amorphous polymers?
Using semicrystalline polymers above their glass transition temperature permits to improve
their ductility without a critical impact on their thermomechanical properties (stiffness for
example), as the glass transition takes place only in their amorphous regions. However,
amorphous polymers cannot be used above their glass transition temperature as this critically lowers their thermomechanical properties.
b) Two well-established techniques in thermomechanical analysis are DSC and TGA. What
are the parameters that can be obtain through each of these analyses?
DSC: Tg, Tm, enthalpy, degree of crystallinity and heat capacity.
TGA: fiber volume content and type of fibers.
c) You are given a unidirectional composite having an unknown composition with the following information:
1.
2.
A DSC curve of the unknown material;
Two TGA curves obtained at different operating conditions:
• O2 atmosphere (A complete combustion of the material is observed.)
• Ar atmosphere (Ar is a noble gas and the atmosphere is considered to be inert.)
3. The properties of the most common composite materials.
What material is the matrix composed of?
According to the DSC, TG is 190°C. This is most likely true for PSU.
- What material is the fibre?
From the TGA we know on the one hand that the fibres can be burnt in oxygen, on the
other hand that they stay stable up to 2500°C under inert conditions (Argon atmosphere).
This condition can only apply for carbon fibres.
-
What is the fibre volume content?
Composite mass = 10 g, Fibres mass = 7g and Matrix mass = 3g
V
=
f
mf
=
ρf
7g
4.02 cm3
=
3
1.74 g cm
mm
=
3g
=
2.45 cm3
3
ρ m 1.24 g cm
Vf
4.02 cm3
V=
=
= 0.621
= 62 %
f .cont
V f + Vm 4.02 cm3 + 2.45 cm3
V
=
m
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Manufacturing of Polymer Composites FS 17
Exercise 2
TGA (Ar)
TGA (O2)
DSC
151-0548-00L
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1)
Manufacturing of Polymer Composites FS 17
Fibres
3
Density [g/cm ]
E-Modulus [GPa]
Elongation at break [%]
Tensile strength [GPa]
2)
Carbon
1.74
240
1.5
3.6
Glass
2.55
73
4.5
3.5
PP
Semicryst.
0.94
1.9
120
36
-18
85
No break
PET
Semicryst.
1.32
2.7
130
55
77
74
No break
Thermoplastic polymers
Structure
3
Density [g/cm ]
E-Modulus [GPa]
Elongation at break [%]
Tensile strength [MPa]
Gass transition temperature [°C]
Max. Service temperature [°C]
Impact strength (IZOD, unnotched)
[J/m]
-1
Coefficient of thermal expansion [K ]
Chemical resistance
Fire behaviour
Structure
3
Density [g/cm ]
E-Modulus [GPa]
Elongation at break [%]
Tensile strength [MPa]
Glass transition temperature [°C]
Max. Service temperature [°C]
Impact strength (IZOD, unnotched)
[J/m]
-1
Coefficient of thermal expansion [K ]
Chemical resistance
Fire behaviour
3)
Exercise 2
-6
150•10
Good
-6
70•10
High
PBT
Semicryst.
1.31
2.5
120
56
60
70
No break
-6
130•10
High
PA 6
Semicryst.
1.12
1.9
94
73
50-60
100
No break
-6
PA 66
Semicryst.
1.12
2.1
83
73
50-60
100
No break
-6
70•10
Good
70•10
Good
Flammable at
345°C
Flammable
without additives
Flammable
without additives
Flammable
without additives
Flammable
without additives
PES
Amorphous
1.4
3.7
30
99
230
200
No break
PSU
Amorphous
1.24
2.5
10-75
75
190
170
No break
PEI
Amorphous
1.35
3.7
42
100
220
200
1300
PPS
Semicryst.
1.43
3.6
4
87
88
160
900
PEEK
Semicryst.
1.33
4.5
37
110
140
260
No break
-6
55•10
High
-6
54•10
Good
-6
62•10
High
-6
49•10
High
Barely flammable
Barely flammable
Barely flammable
Flame retardant
Epoxy
Amorphous
1.2
3.2
1.5-8.0
73
65-175
130
5-15
Polyester
Amorphous
1.2
3.9
1.0-6.5
63
70-120
150
10-20
Vinyl ester
Amorphous
1.1
3.2
2.0-8.0
76
70
100
-
BMI
Amorphous
1.3
4.1
1.5-3.3
79
230-345
190
24-33
31•10
High
-6
47•10
High
Barely flammable
Thermosetting polymers
Structure
3
Density [g/cm ]
E-Modulus [GPa]
Elongation at break [%]
Tensile strength [MPa]
Glass transition temperature [°C]
Max. Service temperature [°C]
2
Fracture toughness [J/m ]
-1
Coefficient of thermal expansion [K ]
Chemical resistance
Fire behaviour
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-6
-6
45•10
Good
54•10
Limited
Good
Flammable
without additives
Fire retardant
-
-6
Barely flammable
Laboratory of Composite Materials and Adaptive Structures
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151-0548-00L
Manufacturing of Polymer Composites FS 17
Exercise 2
Task 3: Composition of the fibres
Discuss which type of fibres would be more convenient for each case.
1- Bulletproof vest
A Bulletproof vest requires high impact strength, because it must transfer the kinetic energy
of the projectile to the vest without failure at the impact point.
The suitable material is Kevlar: It is a long molecule. The summation of all Van der Walls
forces gives a high material strength. Carbon would be in this case too brittle for impact resistance. Another good point is the protection from high temperatures as it is not thermal conductive.
2- Nose of an airplane.
The airplane nose is usually accommodates communication and navigation instruments.
Glass fibres: they are radiolucent, which means they permit the radiations to pass through
them.
3- Aerospace structures.
Two important parameters on aerospace are stiffness and lightweight design.
Carbon fibres: they offer the best specific stiffness and strengths, so they are ideal for high
performance lightweight design in an industry that is willing to pay a premium price for a
small increase in performance.
Sources: (1) and (3) Airbus, (2) Dupont.
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