predicted to contain nearly three times the number of entanglements as i-PP, due
primarily to tacticity differences alone! This would begin to explain many of the
effects observed.
7.5 Market Applications
Although s-PP resins were originally designed for specialty markets, not yet served
by conventional i-PP, it has the potential to compete against conventional i-PP,
low density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and
polyvinyl chloride (PVC) in certain markets because of its toughness, impact
strength, transparency, and low heat-seal temperature. As pure polymer, s-PP has
found new applications and as a blend with i-PP it yields new properties that can be
exploited in existing applications as a substitute for other polymers. Potential
application areas include: (1) adhesives such as hot melt and functional graftingtype adhesives; (2) clear containers for sub-zero temperature usages; (3) preparation of color and/or additive concentrates; (4) elastomers; (5) extrusion products,
especially those that must be sterilized by radiation, such as flexible bags and
tubing; (6) fibers; (7) films, especially those requiring high clarity, toughness, and
a low heat-sealing temperature, such as for snack food packaging; (8) injection
molded products, especially those that must be sterilized by radiation, such as
containers, rigid bottles, and syringes for medical use; (9) modifier and/or clarifier
for resins such as i-PP; (10) modifier for polypropylene film; and (11) transparent
sheets. A few important applications are reviewed below.
7.5.1 Injection Molding
The cycle time in injection molding with s-PP is significantly increased compared
to that for i-PP. Because s-PP polymer thins less than i i-PP under shear, s-PP
requires a longer boost time in injection molding and has a lower die swell than
i-PP. Injection-molded s-PP samples and articles have lower haze, higher gloss,
much higher notched Izod impact strength, lower flexural modulus (thus higher
flexibility), lower Vicat softening temperature, and lower heat distortion temperature than similarly molded i-PP and copolymer containing 2% ethylbenzene. Their
tensile properties are lower than that of i-PP and are comparable to that of the
copolymer. s-PP homopolymer and clear impact resin also have higher Gardner
impact at room temperature, higher light transmittance, and lower flexural modulus
and haze than i-PP, i-PP copolymer, and s-PP-modified i-PP copolymer. After aging
at room temperature, the tensile properties and flexural modulus of s-PP increases
during the first 48 h, then the tensile properties begin to decrease and the flexural
modulus begins to level off. s-PP also has a higher percentage decrease in elongation with time than i-PP homo- and copolymer at room temperature, probably due to
the more pronounced secondary crystallization effect. The elongation at break of
s-PP remains relatively stable at 130
C up to about 1,000 h. Injection-molded s-PP
Syndiotactic Polypropylene: Discovery, Development, and Industrialization. . .
105
primarily to tacticity differences alone! This would begin to explain many of the
effects observed.
7.5 Market Applications
Although s-PP resins were originally designed for specialty markets, not yet served
by conventional i-PP, it has the potential to compete against conventional i-PP,
low density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and
polyvinyl chloride (PVC) in certain markets because of its toughness, impact
strength, transparency, and low heat-seal temperature. As pure polymer, s-PP has
found new applications and as a blend with i-PP it yields new properties that can be
exploited in existing applications as a substitute for other polymers. Potential
application areas include: (1) adhesives such as hot melt and functional graftingtype adhesives; (2) clear containers for sub-zero temperature usages; (3) preparation of color and/or additive concentrates; (4) elastomers; (5) extrusion products,
especially those that must be sterilized by radiation, such as flexible bags and
tubing; (6) fibers; (7) films, especially those requiring high clarity, toughness, and
a low heat-sealing temperature, such as for snack food packaging; (8) injection
molded products, especially those that must be sterilized by radiation, such as
containers, rigid bottles, and syringes for medical use; (9) modifier and/or clarifier
for resins such as i-PP; (10) modifier for polypropylene film; and (11) transparent
sheets. A few important applications are reviewed below.
7.5.1 Injection Molding
The cycle time in injection molding with s-PP is significantly increased compared
to that for i-PP. Because s-PP polymer thins less than i i-PP under shear, s-PP
requires a longer boost time in injection molding and has a lower die swell than
i-PP. Injection-molded s-PP samples and articles have lower haze, higher gloss,
much higher notched Izod impact strength, lower flexural modulus (thus higher
flexibility), lower Vicat softening temperature, and lower heat distortion temperature than similarly molded i-PP and copolymer containing 2% ethylbenzene. Their
tensile properties are lower than that of i-PP and are comparable to that of the
copolymer. s-PP homopolymer and clear impact resin also have higher Gardner
impact at room temperature, higher light transmittance, and lower flexural modulus
and haze than i-PP, i-PP copolymer, and s-PP-modified i-PP copolymer. After aging
at room temperature, the tensile properties and flexural modulus of s-PP increases
during the first 48 h, then the tensile properties begin to decrease and the flexural
modulus begins to level off. s-PP also has a higher percentage decrease in elongation with time than i-PP homo- and copolymer at room temperature, probably due to
the more pronounced secondary crystallization effect. The elongation at break of
s-PP remains relatively stable at 130
C up to about 1,000 h. Injection-molded s-PP
Syndiotactic Polypropylene: Discovery, Development, and Industrialization. . .
105