Fathimathul Suhara, P P; Dr.Sunil,Narayanankutty K(Cochin University of Science And Technology, February 20, 1998)
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Abstract:
The work presented in this thesis is regarding the
development and evaluation of new bonding agents for
short polyester fiber - polyurethane elastomer composites.
The conventional bonding system based on
hexamethylenetetramine, resorcinol and hydrated silica was
not effective as a bonding agent for the composite, as the
water eliminated during the formation of the RF resin
hydrolysed the urethane linkages. Four bonding agents
based on MDI/'I‘DI and polypropyleneglycol, propyleneglycol
and glycerol were prepared and the composite recipe
was optimised with respect to the cure characteristics and
mechanical properties. The flow properties, stress
relaxation pattern and the thermal degradation
characteristics of the composites containing different
bonding agents were then studied in detail to evaluate the
new bonding systems. The optimum loading of resin was 5
phr and the ratio of the -01 to isocyanate was 1:1. The cure
characteristics showed that the optimum combination of
cure rate and processability was given by the composite
with the resin based on polypropyleneglycol/ glycerol/
4,4’diphenylmethanediisocynate (PPG/GL/MDI). From the
rheological studies of the composites with and without
bonding agents it was observed that all the composites
showed pseudoplastic nature and the activation energy of
flow of the composite was not altered by the presence of
bonding agents. Mechanical properties such as tensile
strength, modulus, tear resistance and abrasion resistance
were improved in the presence of bonding agents and the
effect was more pronounced in the case of abrasion
resistance. The composites based on MDI/GL showed
better initial properties while composites with resins based
on MDI/PPG showed better aging resistance. Stress
relaxation showed a multistage relaxation behaviour for the
composite. Within the-strain levels studied, the initial rate of relaxation was higher and the cross over time was lesser
for the composite containing bonding agents. The bonding
agent based on MDI/PPG/GL was found to be a better
choice for improving stress relaxation characteristics with
better interfacial bonding. Thennogravimetirc analysis
showed that the presence of fiber and bonding agents
improved the thennal stability of the polyurethane
elastomer marginally and it was maximum in the case of
MDI / GL based bonding agents. The kinetics of
degradation was not altered by the presence of bonding
agents
Description:
Department of Polymer Science and Rubber Technology,
Cochin University of Science and Technology