Plastics Exam Study Guide Questions with
Correctly Solved Answers
Polyolefin
polypropylene, LDPE, and HDPE - very cheap, but petroleum based
olefin = oil-forming
polyethylene
first olefinic polymer used in food packaging
used for films, closures
addition polymerization
linear polyethylene
high crystalinity
homopolymer - high density (HDPE)
copolymer - linear low density (LLDPE) and ultra low density (ULDPE)
branched polyethylene
non-linear (long braches) - lower crystalinity and lower density than linear PE
homopolymer ex LDPE
copolymer ex EVA (ethylene and vinyl acetate)
HDPE
,thermoplastic (non-polar) --- can be heated and shaped again
properties affected by molec wt (higher the Mw, the higher the tensile and impact strength),
molec wt distribution (the narrower the distribution the higher the mech prop)
properties: color (milky white), barrier (good to moisture and bad to O2 and organic
compounds), resistant to chem compounds, environmental stress cracking (failure of plastic
when exposed to stress and chem substance)
second most used plastic (PET is #1) - containers for milk, bleach, shampoo
processing: extrusion blow molding, blow and cast films, injection molding, injection blow
molding
linear low density polyethylene (LLDPE)
applications: stretch/cling film, grocery bags, heavy duty shipping sacks
when compared to brached PE: increased mech prop, increased Tm (greater stiffness), lower
clarity and gloss, lower heat seal
metallocene polymers
PE polymers based on metallocene catalysts
metallocene catalysts - more uniform incorporation of copolymers
, improved optical properties, substitute for many LDPE/LLDPE blends
LDPE
branched PE homopolymer
properties: transparency (clarity), flexibility, good impact strength, good oil resistance, inferior
water vapor and gas barrier than HDPE, good heat sealing, ease of processing
LDPE properties are due to chain branching
applications: containers and bags for clothing/food, stretch wrap films, shrink films
55% of total LDPE is made into films in US
ethylene vinyl acetate (VA)
branched PE copolymer
as VA content increases, crystallinity dec but density inc - better flexibility at lower temp,
increase in impact strength, clarity improves, adhesion strength and hot tack improve due to
improved polarity
toughness, viscosity, and heat seal strength and hot tack inc as avg molec wt of resin increases
used in extrusion coating
Correctly Solved Answers
Polyolefin
polypropylene, LDPE, and HDPE - very cheap, but petroleum based
olefin = oil-forming
polyethylene
first olefinic polymer used in food packaging
used for films, closures
addition polymerization
linear polyethylene
high crystalinity
homopolymer - high density (HDPE)
copolymer - linear low density (LLDPE) and ultra low density (ULDPE)
branched polyethylene
non-linear (long braches) - lower crystalinity and lower density than linear PE
homopolymer ex LDPE
copolymer ex EVA (ethylene and vinyl acetate)
HDPE
,thermoplastic (non-polar) --- can be heated and shaped again
properties affected by molec wt (higher the Mw, the higher the tensile and impact strength),
molec wt distribution (the narrower the distribution the higher the mech prop)
properties: color (milky white), barrier (good to moisture and bad to O2 and organic
compounds), resistant to chem compounds, environmental stress cracking (failure of plastic
when exposed to stress and chem substance)
second most used plastic (PET is #1) - containers for milk, bleach, shampoo
processing: extrusion blow molding, blow and cast films, injection molding, injection blow
molding
linear low density polyethylene (LLDPE)
applications: stretch/cling film, grocery bags, heavy duty shipping sacks
when compared to brached PE: increased mech prop, increased Tm (greater stiffness), lower
clarity and gloss, lower heat seal
metallocene polymers
PE polymers based on metallocene catalysts
metallocene catalysts - more uniform incorporation of copolymers
, improved optical properties, substitute for many LDPE/LLDPE blends
LDPE
branched PE homopolymer
properties: transparency (clarity), flexibility, good impact strength, good oil resistance, inferior
water vapor and gas barrier than HDPE, good heat sealing, ease of processing
LDPE properties are due to chain branching
applications: containers and bags for clothing/food, stretch wrap films, shrink films
55% of total LDPE is made into films in US
ethylene vinyl acetate (VA)
branched PE copolymer
as VA content increases, crystallinity dec but density inc - better flexibility at lower temp,
increase in impact strength, clarity improves, adhesion strength and hot tack improve due to
improved polarity
toughness, viscosity, and heat seal strength and hot tack inc as avg molec wt of resin increases
used in extrusion coating
