Page 39 - Plastics Engineering

22 General Roperties of Plastics
properties of plastics are given in Table 1.5. These are given for illustration
purposes. For each type of plastic there are many different grades and a wide
variety of properties are possible. The literature supplied by the manufacturers
should be consulted in specific instances.

Table 1.5
Short-term properties of some important plastics

Tensile Flexural %
Density strength modulus elongation
Material (kg/m3) (MN/m*) (GN/m2) at break Price*

ABS (high impact) 1040 38 2.2 8 2.1
Acetal (homopolymer) 1420 68 2.8 40 3.5
Acetal (copolymer) 1410 70 2.6 65 3.3
Acrylic 1180 70 2.9 2 2.5
Cellulose acetate 1280 30 1.7 30 3.2
CAB 1190 25 1.3 60 -
EPOXY 1 200 70 3.0 3 8.3
Modified PPO 1060 45 2.3 70 -
Nylon 66 1140 70 2.8 60 3.9
Nylon 66 (33% glass) 1380 115 5.1 4 4.0
PEEK 1300 62 3.8 4 42
PEEK (30% carbon) 1400 240 14 1.6 44
PET 1360 75 3 70 3.0
PET (36% glass) 1630 180 12 3 3.5
Phenolic (mineral filled) 1690 55 8 .O 0.8 1.25
Poly amide-imide 1400 185 4.5 12 67
Polycarbonate 1150 65 2.8 100 4.2
Poly etherimide 1270 105 3.3 60 -
Pol yethersulphone 1370 84 2.6 60 13.3
Poly imide 1420 72 2.5 8 150
Polypropylene 905 33 1.5 150 1
Poly sulphone 1240 70 2.6 80 11
Polystyrene 1050 40 3.0 1.5 1.1
Polythene (LD) 920 10 0.2 400 0.83
Polythene (HD) 950 32 1.2 150 1.1
rn 2100 25 0.5 200 13.3
PVC (rigid) 1400 50 3.0 80 0.88
PVC (flexible) 1300 14 0.007 300 0.92
SAN 1080 72 3.6 2 1.8
DMC (polyester) 1800 40 9.0 2 1.5
SMC (polyester) 1800 70 11.0 3 1.3
*On a weight basis, relative to polypropylene.

Material Selection for Strength
If, in service, a material is required to have a certain strength in order to per€orm
its function satisfactorily then a useful way to compare the structural efficiency
of a range of materials is to calculate their strength desirability factor.
Consider a structural member which is essentially a beam subjected to
bending (Fig. 1.7). Irrespective of the precise nature of the beam loading the