Unsaturated polyester resins (UPRs) are
used widely in the fiber-reinforced plastics (FRPs) industry.
These resins have the disadvantages of brittleness and poor
resistance to crack propagation. In this study, hybrid polymer
networks (HPNs) based on UPR and epoxidized phenolic
novolacs (EPNs) were prepared by reactive blending.
A HPN is composed of a backbone polymer containing two
types of reactive groups that can take part in crosslinking
reactions via different mechanisms. EPNs were prepared by
glycidylation of novolacs using epichlorohydrin. The novolacs
had varying phenol: formaldehyde ratios. Blends of unsaturated
polyester with EPN were then prepared. The
physical properties of the cured blends were compared with
those of the control resin. EPN shows good miscibility and
compatibility with the resin and improves the toughness
and impact resistance substantially. Considerable enhancement
of tensile strength is also noticed at about 5% by
weight of epoxidized novolac resin. TGA, DMA, and DSC
were used to study the thermal properties of the toughened
resin and the fracture behavior was studied using SEM. The
blends are also found to have better thermal stability. Blending
with EPN can be a useful and cost-effective technique for
modification of UPR
Description:
Journal of Applied Polymer Science, Vol. 100, 457–465 (2006)
Unsaturated polyester resins (UPRs) are extensively
used by the fiber-reinforced plastic (FRPs) industry.
These resins have the disadvantages of brittleness and
poor resistance to crack propagation. In this study, UPRs
were chemically modified by reactive blending with polyurethane
prepolymers having terminal isocyanate groups.
Hybrid networks were formed by copolymerisation of unsaturated
polyesters with styrene and simultaneous reaction
between terminal hydroxyl groups of unsaturated polyester
and isocyanate groups of polyurethane prepolymer. The
prepolymers were based on toluene diisocyanate (TDI) and
each of hydroxy-terminated natural rubber (HTNR), hydroxy-
terminated polybutadiene (HTPB), polyethylene glycol
(PEG), and castor oil. Properties like tensile strength,
toughness, impact resistance, and elongation-at-break of the
modified UPRs show considerable improvement by this
modification. The thermal stability of the copolymer is also
marginally better
Description:
Journal of Applied Polymer Science, Vol. 100, 449–456 (2006)