Page 167 - Engineering Plastics Handbook

140 Engineering Plastics

TABLE 7.4 Typical Properties of PBT and Blend Resins
PBT/PC PBT/PC PBT/ABS
Property Unit PBT* alloy † alloy ‡ alloy §

Specific gravity — 1.31 1.22 1.21 1.07
Tensile strength MPa 54 45 55 49
Elongation at break % 60 100 100 30
Flexural strength MPa 83 75 80 90
Flexural modulus MPa 2250 1950 2050 3230
Izod impact strength J/m 30 650 600 170
(notched)
HDT (1.82 MPa) °C 57 95 100 85
HDT (0.45 MPa) °C 154 110 115 95
Mold shrinkage % 1.2–2.1 0.7–1.0 0.7–0.9 0.5–0.8
* Lupox GP-2000 LG Chem, Ltd.
†
Lupox TE-5011 LG Chem, Ltd.
‡
Lupox TE-5000G LG Chem, Ltd.
§
Lumax HF-5008 LG Chem, Ltd.
SOURCE: Lupox PBT brochure and data sheets [20].

blends, the amorphous resin components reduce warpage of PBT. The
primary purpose in blending PBT with amorphous ABS is to combine
the good chemical resistance and mechanical properties of PBT and the
high impact strength and dimensional stability of ABS. These blends
may have the possibility of replacement of more expensive PC/ABS
blends in automotive and electronic applications. Typical properties of
PBT blends are summarized in Table 7.4.
Blends of PBT and PET are also commercially available, mostly as glass
fiber and/or mineral filler reinforced grades. Since PET has a much lower
crystallization rate than PBT, the molded products from these blends
show improved surface characteristics. The other advantages of PBT/PET
blends compared to general-purpose reinforced PBT include higher stiff-
ness and temperature performance with good cost performance. It is known
that exchange reactions take place between PBT and PC during high-
temperature melt processing [8–13]. Transesterification reaction is influ-
enced by many factors including residual catalyst and content of end
carboxyl groups of PBT. The reaction rate also increases with temperature
and residence time during the molding process. In general, addition of
certain stabilizers is used to suppress the transesterification reactions.
Table 7.5 summarizes some PBT blends with other polymers.

Chemical resistance
Chemical resistance of thermoplastics is dependent on a number of param-
eters, including temperature, time, residual mold stress, and external
stress to which the part is subjected in given use conditions. Generally,