THERMOPLASTIC POLYURETHANE (TPU)/POLYOLEFIN (PO) BLENDS

THERMOPLASTIC POLYURETHANE (TPU)/POLYOLEFIN (PO)
BLENDS

A THESIS
SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL

OF THE UNIVERSITY OF MINNESOTA
BY

Qi-Wei Lu

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

Christopher W. Macosko, Advisor

May 2003

Qi-Wei Lu
345 words

ABSTRACT

Thermoplastic polyurethane (TPU) is a very important material with high
versatility and superior physical properties. Melt blending TPU with metallocene
polyolefin (PO) can lower TPU cost and improve polyolefin properties like abrasion
resistance, adhesion, and paintability. Since TPU and non-polar PO blends are
completely immiscible, efficient compatibilizers become the key issue and remain
challenging. My main thesis work is to develop and study compatibilized TPU/PO
blends. Although reactive compatibilization is considered the most efficient method,
fast interfacial reactions between highly reactive functional groups are necessary to
generate compatibilizers within usually short processing time. It is known that the
urethane linkage (carbamate -NHCOO-) in TPU can reversibly dissociate to generate
highly reactive isocyanates at melt temperatures. To find out the best reactive
compatibilization, three approaches were employed on different molecular scales: (1)
model urethane compound (dibutyl & dioctyl 4,4′-methylenebis(phenyl carbamate))
and small functional molecule (primary amine, secondary amine, hydroxyl, acid,
anhydride, and epoxide) reactions at 200 °C monitored by nuclear magnetic
resonance and Fourier-transform infrared to examine the basic chemistry; (2) short,
model TPU’s with different chemical structures blended with functional polymers
including poly(ethylene glycol) and polybutadiene to explore the effect of interface in
immiscible mixtures; (3) melt blending of a commercial TPU with polypropylene
(PP), further involving more complicated morphology, using different types of
functionalized PP’s (note: amine functionalized PP’s were prepared by melt
amination) as compatibilizers followed by rheological, morphological, thermal, and
mechanical characterizations.

Besides the core thesis project on TPU blends, other related work that has
been accomplished includes: (1) adhesion between TPU and PP; (2) rheological
properties of TPU; (3) block copolymer formation by reactive coupling. In the first
work, the unique interfacial reactions were applied to promote TPU-PP adhesion that
was quantified by asymmetric double cantilever beam test. In the second study, the
abnormally high flow activation energy of TPU was explained by simultaneously
investigating the effect of temperature and thermal degradation on the melt viscosity.
In the third project, block copolymers were prepared by rapid reactive coupling of
amine and isocyanate functional polymers and the reaction kinetics were also studied.