Morphological, mechanical and thermal properties of Amorphous Copolyester/ Polyoxymethylene blends
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Date
2005
Authors
Kok Loon, Lam
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Abstract
The research on amorphous copolyester/polyoxymethylene (POM) blends consists of
two parts. The first part was to study the effects of blend composition on the
morphological, mechanical and thermal properties of amorphous copolyester/POM
blends. Poly(ethylene glycol-co-cyclohexane-1, 4-dimethanol terephthalate) (PETG)
was selected as copolyester. PETG/POM blends were produced by melt blending
covering the whole composition range. The specimens of the blends were prepared
using injection and compression molding. Properties such as melt flow index (MFI),
density, tensile and flexural stiffness of these incompatible PETG/POM blends followed
the additivity rule as a function of composition. However, the elongation at break,
energy absorbed until tensile failure, flexural strength, notched Izod impact strength
and static fracture toughness, Kc showed lower values than either of the neat blend
components. This was traced to the poor interfacial adhesion between PETG and
POM. The degree of crystallinity of the PETG/POM blends decreased with increasing
the PETG concentration. This was attributed to the amorphous nature of PETG. A cocontinuous
morphology was ascertained by the combination of selective extraction and
SEM for the blends PETG/POM 60/40 and 50/50 wt%/wt%. The tensile fracture surface
of the 50/50 blend exhibited a fibrillar morphology owing to the injection moldinginduced
distortion of the initial co-continuous phase structure. The elongation at break,
energy to tensile failure, notched Izod impact strength and fracture toughness of the
co-continuous PETG/POM blends were slightly higher than those blends with
dispersed phase structure. However, the values were still below the corresponding
values of the neat PETG and POM. The second part of the research involves the usage of thermoplastic
polyurethane (TPU) as a compatibilizer in PETG/POM blends. Two types of TPU (i.e.
polyester based and polyether based) were used to compatibilize the blends system.
The co-continuous PETG/POM (50/50 wt%/wt%) blends were prepared. The
mechanical properties of the co-continuous PETG/POM blends were studies through
flexural and single-edge notch tensile test (SEN-T). The flexural strength of the
PETG/POM blends was decreased in the presence of TPU. This was attributed to the
elastomeric nature of the TPU. The compatibilizing effects of TPU on the PETG/POM
blends were proven by moderate improvement in the fracture toughness and confirmed
by the SEM observation. The SEN-T fractured surface of the compatibilized blends
showed gross matrix shear yielding as compared to the uncompatibilized system. The
Kc values of the PETG/POM blends decreased with the increasing of testing speed.
The optimum toughening effect was observed in PETG/POM blends compatibilized
with polyether based TPU at testing speed of 100mm/min. The polyether based TPU is
a more efficient compatibilizer as the amount required being 1/2 to that of the polyester
based counterpart to achieve the same Kc value. This was attributed to the elastomeric
nature of the polyether based TPU. The softer nature of polyether based TPU could
provide better toughening effect than the polyester based TPU, which is relatively
harder in nature.
Description
Master
Keywords
Materials and Mineral Resources Engineering , Amorphous Copolyester