164
6
6.6 Processability of Commonly Used
Thermoplastic Matrices
Thermoplastic resins first melt and then solidify. Some of the commonly used thermoplastic resins and their processability factors are
described here.
1. Nylon—Nylon 6 and Nylon 6,6 are the major engineering
plastics being used in short fibre-reinforced thermoplastic
composites. Nylon 6 is manufactured from a ring-opening
reaction of caprolactam, and Nylon 6,6 is manufactured from a
polycondensation reaction of adipic acid with hexamethylenediamine. Water from the reaction comes as a condensate. The
properties of Nylon 6,6 are superior to Nylon 6. Nylon is made
available in the form of glass-reinforced granules, homopolymer films, and homopolymer sheets. The general properties of
Nylon 6 are given in . Table 6.3.
The major processability factors of nylons are listed here.
5 The melt viscosities are very low (i.e. 500 cps) due to its high
crystalline nature.
5 The processing temperature of nylons is quite high (250 °C).
Care must be taken to thermally process less stable natural
fibre-reinforced composites.
5 They are suitable for prepregging, and carbon, glass, and
Kevlar fibre-based nylon prepregs are used for vacuum
pressure moulding.
5 Nylon may be processed using either injection moulding or
compression moulding processes.
5 They have a low shrinkage (<0.5%).
5 Nylons are hygroscopic in nature due to the presence of an
amide group.
2. Polypropylene—Polypropylene (PP) is a commodity plastic that
is made into engineering plastic after reinforcement. It is
manufactured by addition reaction of propylene gas using a
Ziegler–Natta catalyst. The bulk manufacturing process for PP
is emulsion polymerization. PP is available in three basic
forms: isotactic (highly crystalline in nature), syndiotactic
Point to Ponder…
There are variety of grades in
nylon, such as Nylon 6; Nylon
6,6; Nylon 6,12; Nylon 6,11; etc.
However, the most commonly used
grades are Nylon 6 and Nylon 6,6.
Point to Ponder…
Polypropylene is one of the
wonder materials in the
manufacture of orthoses for
physically challenged persons.
PP’s low density, good mechanical
properties, lack of reaction from
the human body, and excellent
abilities to be both moulded
and machined make it the best
material for this purpose.
. Table 6.3 Properties of Nylon 6,6
Serial No.
Property
Value
1.
Density (g/cm 3 )
1.2
2.
Tensile strength (MPa)
65
3.
Young’s modulus (GPa)
4
4.
Elongation at break (%)
80
5.
Impact strength, notched (KJ/m)
0.07
6.
Glass transition temperature (°C)
45
7.
Processing temperature (°C)
240–350
Chapter 6 · Processability of Thermoplastic Composites
6
6.6 Processability of Commonly Used
Thermoplastic Matrices
Thermoplastic resins first melt and then solidify. Some of the commonly used thermoplastic resins and their processability factors are
described here.
1. Nylon—Nylon 6 and Nylon 6,6 are the major engineering
plastics being used in short fibre-reinforced thermoplastic
composites. Nylon 6 is manufactured from a ring-opening
reaction of caprolactam, and Nylon 6,6 is manufactured from a
polycondensation reaction of adipic acid with hexamethylenediamine. Water from the reaction comes as a condensate. The
properties of Nylon 6,6 are superior to Nylon 6. Nylon is made
available in the form of glass-reinforced granules, homopolymer films, and homopolymer sheets. The general properties of
Nylon 6 are given in . Table 6.3.
The major processability factors of nylons are listed here.
5 The melt viscosities are very low (i.e. 500 cps) due to its high
crystalline nature.
5 The processing temperature of nylons is quite high (250 °C).
Care must be taken to thermally process less stable natural
fibre-reinforced composites.
5 They are suitable for prepregging, and carbon, glass, and
Kevlar fibre-based nylon prepregs are used for vacuum
pressure moulding.
5 Nylon may be processed using either injection moulding or
compression moulding processes.
5 They have a low shrinkage (<0.5%).
5 Nylons are hygroscopic in nature due to the presence of an
amide group.
2. Polypropylene—Polypropylene (PP) is a commodity plastic that
is made into engineering plastic after reinforcement. It is
manufactured by addition reaction of propylene gas using a
Ziegler–Natta catalyst. The bulk manufacturing process for PP
is emulsion polymerization. PP is available in three basic
forms: isotactic (highly crystalline in nature), syndiotactic
Point to Ponder…
There are variety of grades in
nylon, such as Nylon 6; Nylon
6,6; Nylon 6,12; Nylon 6,11; etc.
However, the most commonly used
grades are Nylon 6 and Nylon 6,6.
Point to Ponder…
Polypropylene is one of the
wonder materials in the
manufacture of orthoses for
physically challenged persons.
PP’s low density, good mechanical
properties, lack of reaction from
the human body, and excellent
abilities to be both moulded
and machined make it the best
material for this purpose.
. Table 6.3 Properties of Nylon 6,6
Serial No.
Property
Value
1.
Density (g/cm 3 )
1.2
2.
Tensile strength (MPa)
65
3.
Young’s modulus (GPa)
4
4.
Elongation at break (%)
80
5.
Impact strength, notched (KJ/m)
0.07
6.
Glass transition temperature (°C)
45
7.
Processing temperature (°C)
240–350
Chapter 6 · Processability of Thermoplastic Composites