 |
GRP
is a composite material in which 3 major components can be identified:
1. The matrix
2. The reinforcement
3. The filler
The matrix is, generally, a polyester resin.
The overall performance of the laminate is strongly affected by the
type of resin used.
An acceptable
resin must have:
• Good adhesion to the glass fibers to increase the strength of
the laminate and its resistance to fatigue
• High purity to avoid migration of low molecular weight pollutants
into the potable water
• Low water absorption and good resistance to boiling water to
reduce the effects of ageing
• High elongation at failure.
These properties are normally found in isophtalic polyester resin such
as the one defined in the following tables:
|
Characteristics
|
Units
|
Orthophtalic
|
Isophtalic
|
Bisphenolic
|
Vinylester
|
|
Monomer
content
|
%
|
30-35
|
40 -45
|
50
|
45
|
|
Monomer
type
|
|
Styrene
|
Styrene
|
Styrene
|
Styrene
|
|
Viscosity,
25°C
|
Cps
|
+/-450
|
+/-450
|
+/-300
|
+/-500
|
|
Density,
25°C
|
g/cm3
|
1.1
|
1.1
|
1.1
|
1.1
|
|
Acid
number
|
MgsKOH/g
|
<42
|
< 18
|
< 15
|
<15
|
|
Hydroxyl
N°
|
MgsKOH/g
|
<30
|
<25
|
<25
|
<25
|
|
Heat
dist. Temp.
|
°C
|
>85
|
> 110
|
>90
|
>100
|
|
Hardness
|
Barcol
|
>40
|
>40
|
>35
|
>35
|
|
Elongation
at fail.
|
%
|
> 1
|
>2
|
>3
|
>3
|
|
Flexural
strength
|
N/mm2
|
>80
|
>80
|
>75
|
>75
|
|
Flexural
modulus
|
N/mm2
|
>3500
|
>3500
|
>2500
|
>2500
|
|
Volum
shrinkage
|
%
|
8+/-10
|
8+/-10
|
8+/-10
|
<5
|
|
Reactivity
|
|
High
|
High
|
Medium
|
Medium
|
The
reinforcement provides most of the mechanical and elastic properties of
the laminate and consists, normally, of glass fibers.
In the innermost portion of the pipe wall a veil of "C" glass
(chemical grade) shall always be included and a backing layer of chopped
strand mat is recommended.
The structural wall shall be made with continuous fibers.
The following tables show the typical composition and the physical properties
of structural glass:
Typical chemical composition (%)
| |
C glass
|
E glass
|
|
Si02
|
65
|
55
|
|
B203
|
5
|
7,3
|
|
CaO
|
14
|
18
|
|
MgO
|
3
|
3,3
|
|
F2
|
/
|
0,3
|
|
K20
|
/
|
0,2
|
|
Na02
|
8,5
|
0,3
|
|
A1203
|
4
|
14,8
|
|
Fe203
|
0,5
|
0,3
|
Physical and mechanical properties
| |
Unit
|
C
glass
|
E
glass
|
|
Tensile
strength at 22°C
|
N/mm2
|
1400-1500
|
1400-1500
|
|
Young's
modulus
|
N/mm2
|
70000
|
73500
|
|
Elongation
at break
|
%
|
4,5
|
3-4
|
|
Specific
gravity
|
kg/dm3
|
2,49
|
2,54
|
|
Creep
|
/
|
absent
|
absent
|
|
Isteresys
|
/
|
absent
|
absent
|
|
Poisson's
ratio
|
/
|
/
|
0,22
|
|
Filament
diameter
|
mm-3
|
10
|
10-23
|
|
Coefficient
of thermal expansion
|
m/m°C
|
7,1 xlO-6
|
5 xlO-6
|
The filler must be an inert material that does not absorb water nor does
modify the reaction kinetics of the resin.
Silica sand with 99% of silica containing no iron is ideal filler.
It is important that the filler is absolutely dry when it is used.
Other additives that are necessary for the cure of the resin and to facilitate
the removal of air bubbles must be selected by the pipe manufacturer strictly
observing the instructions of the resin supplier.
Back
|
