Environmental Engineering Reference
In-Depth Information
Table 3.4
Characteristics of Common Classes of Polyethylenes
Property
HDPE
LDPE
LLDPE
VLDPE
PP
Density (g/
cm
3
)
0.94-0.97 0.915-0.935 0.90-0.94 0.905-0.915 0.90
55-77
30-54
22-55
0-22
30-50
Melting
temperature
(°C)
125-132
98-115 100-125
60-100 175
Shore
hardness
(type D)
66-73
44-50
55-70
35-55
80-102
Tensile
extensibility
(%)
100-650 100-950
100-600 100-600
10-1500
a
Measured calorimetrically. Polyethylene data based on data from Peacock (2000).
No significant fugitive emission problem is associated with the manufacture
of PE or PP, and in any event, the monomers (and the comonomers
generally used) are relatively nontoxic. The only exception might be where
solvents or diluents and catalysts are used in the manufacture.
3.5.2 Polypropylenes
PP is the lightest of common thermoplastics (density 0.905 g/cm
3
) and has
a useful combination of properties that include transparency, high stiffness,
good thermal resistance, chemical inertness, and good impact properties.
General-purpose PP (with
T
g
= −10°C and
T
m
= 173°C) is used in a wide
range of products including packaging materials (pails, containers bottle
caps and film) (~28%), textile fiber (~20%), molded products, housewares,
toys, auto parts, and extruded pipe. The annual world production is
approximately 52 MMT. Stereoregular grades of PP including syndiotactic
PP made using metallocene catalysts, or the m-PP, are commercially
available and gaining popularity in high-end applications. The low-pressure
polymerization of propylene employs either Ziegler-Natta or metallocenes
