samples were found to break up like a flexible polymer when exposed to 500 h of
UV radiation, and the reduction in its intrinsic viscosity (or molecular weight) due
to γ-ray irradiation is lower than that for i-PP.
7.5.2 Injection Blow Molding
Syndiotactic polypropylene resins allow the production of small flexible containers
with very good γ-radiation resistance and a degree of transparency never achieved
before with any polypropylene. Moreover, the final objects transmit a feeling by
contact that has been qualified as “soft and warm.” Only some highly expensive
specialty and engineered polymers can achieve the same combination of properties,
but require a significantly longer cycle time.
7.5.3 Films
Syndiotactic polypropylene can be heat-sealed at a lower temperature than
conventional i-PP copolymers containing high levels of ethylene (sealing initiation
temperature of around 100
C versus 110–120
C). s-PP films can be heat-sealed at a
lower temperature than conventional ethylene/propylene copolymers containing 6%
ethylene, e. g., <113
C versus >~119
C to develop a seal strength of 500 g/in.,
When compared with conventional i-PP, cast and blown films extruded from s-PP
have much lower haze, much higher gloss, slightly higher elongation at yield, and
comparable tensile strength at yield. Bi-axially oriented polypropylene (BOPP)
films with improved shrink versus conventional BOPP films are obtained by
blending a few wt% of s-PP into i-PP. The tensile, elongation, and optical properties
and the impact strength of s-PP cast films are influenced by the melt temperature and
chill roll temperature. Lowering the chill roll temperature leads to production of
films with slightly higher tensile strength and elongation. Film extruded from an
s-PP-modified random propylene copolymer has much lower haze, much higher
gloss, slightly higher elongation at yield, comparable tensile strength at yield,
slightly lower Elmendorf tear strength, and much lower Dart drop impact than
that extruded from a ultra-low-density polyethylene (ULDPE)-modified random
copolymer. It also has higher haze, gloss, Elmendorf tear strength, Dart drop impact,
and elongation, and lower tensile strength at yield than films extruded from a
propylene copolymer containing 2% ethylene and a conventional homopolypropylene.
7.5.4 Fibers
Addition of a few wt% of s-PP to i-PP before spinning dramatically improves the
bulk and the softness of spun laid or staple nonwovens, two important techniques in
fiber application. Moreover, the thermal bonding temperature is lowered by about
5–10
C, whereas the mechanical properties of the nonwovens are retained or
slightly improved.
106
A. Razavi
UV radiation, and the reduction in its intrinsic viscosity (or molecular weight) due
to γ-ray irradiation is lower than that for i-PP.
7.5.2 Injection Blow Molding
Syndiotactic polypropylene resins allow the production of small flexible containers
with very good γ-radiation resistance and a degree of transparency never achieved
before with any polypropylene. Moreover, the final objects transmit a feeling by
contact that has been qualified as “soft and warm.” Only some highly expensive
specialty and engineered polymers can achieve the same combination of properties,
but require a significantly longer cycle time.
7.5.3 Films
Syndiotactic polypropylene can be heat-sealed at a lower temperature than
conventional i-PP copolymers containing high levels of ethylene (sealing initiation
temperature of around 100
C versus 110–120
C). s-PP films can be heat-sealed at a
lower temperature than conventional ethylene/propylene copolymers containing 6%
ethylene, e. g., <113
C versus >~119
C to develop a seal strength of 500 g/in.,
When compared with conventional i-PP, cast and blown films extruded from s-PP
have much lower haze, much higher gloss, slightly higher elongation at yield, and
comparable tensile strength at yield. Bi-axially oriented polypropylene (BOPP)
films with improved shrink versus conventional BOPP films are obtained by
blending a few wt% of s-PP into i-PP. The tensile, elongation, and optical properties
and the impact strength of s-PP cast films are influenced by the melt temperature and
chill roll temperature. Lowering the chill roll temperature leads to production of
films with slightly higher tensile strength and elongation. Film extruded from an
s-PP-modified random propylene copolymer has much lower haze, much higher
gloss, slightly higher elongation at yield, comparable tensile strength at yield,
slightly lower Elmendorf tear strength, and much lower Dart drop impact than
that extruded from a ultra-low-density polyethylene (ULDPE)-modified random
copolymer. It also has higher haze, gloss, Elmendorf tear strength, Dart drop impact,
and elongation, and lower tensile strength at yield than films extruded from a
propylene copolymer containing 2% ethylene and a conventional homopolypropylene.
7.5.4 Fibers
Addition of a few wt% of s-PP to i-PP before spinning dramatically improves the
bulk and the softness of spun laid or staple nonwovens, two important techniques in
fiber application. Moreover, the thermal bonding temperature is lowered by about
5–10
C, whereas the mechanical properties of the nonwovens are retained or
slightly improved.
106
A. Razavi