PKG 323 exam 2
As the VA content increases, the crystallinity decreases, but the density increases: results in____
-Better flexibility at low temperature -Increase in impact strength (related to amorphous region) -clarity improves -Adhesion strength and hot tack improve due to improved polarity with increasing VA content
Processing for PP copolymer
-Blow molding, extrusion and injection molding
Multilayer (with polyolefins) in pvdc
-shrinkable film (moisture or gas-sensitive food)
PP copolymer properties Ethylene (1.5-7%) --> prevents high crystallinity
-Lower crystallinity -Lower density -Improved clarity -Improved flexibility -Lower Tm -Good chemical resistance -Good moisture barrier
Properties of polypropylene
-Medium transparency -Low density (0.89-0.92 g/m^3) -Good resistance to chemicals -Good resistance to environmental stress cracking -Higher melting T (higher heat resistance) and stiffness than PE -Ease of orientation (improve barrier properties)
PVC: properties- strong affinity to additives
-because of the polar nature of PVC Types of additives: plasticizers, heat stabilizers, impact modifiers (ABS and MBS), lubricants, etc -PVC has wide stiffness range: from rigid containers to soft and flexible film
Properties of Ionomers
-better transparency, better toughness, higher melt strength, and lower crystallinity than the PE copolymers without neutralizaiton (EAA) -Poor barrier -High resistance to oils and aggressive products -Reliable seal -Good adhesion to corrugated board -Good resistance to puncture
Applications of LDPE
-containers and bags for clothing and food -Household products -Stretch wrap films -Shrink films -Agricultural films (For artificial green houses) In U.S. 55% of total LDPE is made into films (thickness < than 12 mils (300 microns)}
High Density polyethylene (HDPE) applications
-containers for milk, detergent, bleach, shampoo, deodorant -Flexible package for crackers, cereals, and snacks -Closures -Pharmaceutical bottles
Applications of EAA
-extruded tie layer between aluminum foil and other less polar polymers -Extrusion coating: toothpaste tubes, coated paperboard -blister packaging -Flexible packaging of meat, cheese, medical products (25% AA contact food) -Skin packaging -Adhesive lamination
Due to excellent adhesion and ease of processing, EVA is used
-in extrusion coating -As a coextruded heat seal layer with PET, BOPP (biaxially oriented PP), and cellophane, and for cheese wrap and medical films
Decomposition of PVC
-it produced HCL (very corrosive in the presence of moisture) -- heat -Tm and decomposition T very close (212C) -Difficult processing Solution: Addition of heat stabilizers (octyl tins)
Food packaging in PVDC
Barrier materials to moisture, gases, flavor, and odors
Polystyrene: Properties
Amorphous (Atactic) => for packaging uses -Highly transparent (exceptional clarity) -poor barrier to gases and H2O vapors -Chemical reactivity greater than that of PE and PP. -Stiff and brittle material (benzene ring), solution to the brittleness: biaxial orientation, improvement of properties -Not high T (liquid about 100C) -Low cost -petroleum based, non-biodegradable
Applications of Ionomers
Coating: skin packaging for electronics Films: Food packaging (frozen food (fish)) Laminations (multi-layer with Nylon, PET: tetra pack for fruit juice
Processing techniques for Ionomers
Coextrusion lamination and extrusion coating
PVC structure
Configuration of monomer: head-to-tail alignment -Has a slight degree of syndiotacticity which permits a very small degree of crystallinity -just enough to allow use to define a Tm -Mostly atactic
All commercially available PVDC resins are ??
Copolymers
Ionic bonds in Ionomers
Cross-linking between chains (but thermoplastic) heat
Films (blow processing) cooled down using water quench and not air (PE) because??
Crystallization too fast
EAA
Ethylene + Acrylic acid Ethylene Acrylic acid
HDPE is a _______ while LLDPE is a _____?
HDPE= homopolymer LLDPE = copolymer
Characteristic of linear PE
High Crystallinity (70-90%)
What is a linear PE homopolymer?
High density PE (HDPE)
What are the linear polyethylenes?
High density polyethylene (HDPE) Linear low density polyethylene (LLDPE) Metallocenes polymers
PVDC properties
Homopolymer has Tm (388-401C) but decomposes at 205C => impossible to process Solution: addition of comonomers (VC, methyl, acrylate) => decreases Tm (140-175C) -Decreases crystallinity: increased permeability -Plasticizers and heat stabilizers are also added
Monolayer in PVDC
Household wrap lamination: unit dose packaging, ... for moisture, oxygen, and solvent-sensitive products)
Compared to branched PE (LDPE) at the same density, LLDPE has:
Improved mechanical properties Increased Tm (Greater stiffness) Lower clarity and gloss Lower heat seal BC: increased regularity of the structure and narrower MW distribution in LLDPE
Processing of HDPE
Extrusion blow molding Blow and cast films Injection molding Injection blow molding
Polyethylene (PE) was the first olefinic polymer used in food packaging for?
Films, closures, moulded containers
Higher AA content in EAA?
Decreased crystallinity (decreased heat seal temp, increased clarity) Increased polarity (increased adhesion strength)
Metallocene PE
Different grades commercially available (depending on application) -Improved optical properties -Substitute for many LDPE/LLDPE blends
Example of a copolymer of a branched PE?
EVA (Ethylene + vinyl acetate)
Degree of branching effects properties for ____?
LDPE
What are the branched polyethylenes (PE)?
Low density polyethylene (LDPE) Ethylene vinyl acetate (EVA) Ethylene acrylic acid (EAA) Ionomers
Why PP is used for sterilizaiton purpose, but not HDPE?
Melting point of PP is high, HDPE will become soft
What is HDPE used for?
Milk containers
One of the key limitation of HDPE is it's low _____ barrier property and clarity
O2
What are polypropylene (PP)?
PP homopolymer PP copolymer
Polystyrene: structure
PS is the homopolymer of styfrene PS is a thermoplastic
Is PVC or PVDC more crystalline?
PVDC
PVC properties
Polar bond => attraction between neighboring molecules => -stiff and rigid material at room T -Difficult to process Solution: addition of plasticizers (additives that increase the flexibility of the material by virtue of a lubricating action at the molecular level) -Increase flexibility -Decrease processing T
Atactic PP hompolymer
Prepared by free radical polymerization Substituent group: placed randomly along the chain
Isotactic PP Homopolymer
Prepared with Ziegler Natta Cat Substituent group: always are on the same side of polymer chain
Syndiotactic PP homopolymer
Prepared with metallocene catalyst Substituent group: alternates sides in a regular pattern
PP more ________ than PE => chain scission (Solution: use of antioxidants in PP)
Sensitive to oxidation degradation (light and heat)
Properties of Ethylene Acrylic Acid
Similar to LDPE: Chemical resistance, barrier properties Superior to LDPE (H bond): strength, toughness, hot tack, adhesion
What are the result of the neutralization of PE copolymers such as EAA or EMAA by using cations?
Ionomers which are: Surlyn (DuPont) PE copolymers (Branched)
Why a catalyst used during polymerization?
To make linear polymers
The following properties increase as the average molecular weight of the resin for EVA increases?
Toughness Viscosity Heat seal strength and hot tack
PVC is the homopolymer of?
Vinyl chloride monomer
PVDC: Applications
Water- based latex coatings: PVDC + methyl acrylate Solvent-based coating: PVDC+acrylonitrile Paper and paperboard -water and grease barriers Plastic films- improved barrier to flavor and odor -coating on PET bottles(bad idea)!
Applications of PP homopolymer
Stretch film containers for sterilization in autoclave
Applications of LLDPE (PE copolymer)
Stretch/cling films Grocery bags Heavy duty shipping snacks
Tg of PVC is high because ______ secondary forces?
Strong
LLDPE is ____ flexible than HDPE?
more
LDPE is ____ homopolymer and prepared by _____ polymerization
branched radical
Branched PE characteristics compared to linear PE
non-linear (long branches) -lower crystallinity -lower density
PP are commonly oriented to improve??
optical, barrier and mechanical properties. Blown and cast methods
Use of ______ facilitates linear polyethylene
catalyst
Properties of HDPE
color (milky-white) because of high degree of crystallinity Barrier: good to moisture, bad to O2 and organic compounds Resistance to chemical compounds (acetone, alcohols, diluted acids) Environmental stress cracking
PVDC (polyvinylidene chloride) structure
homopolymer or copolymer of vinylidene chloride monomer SARAN is a thermoplastic polymer Addition polymerization
Is LLDPE a homopolymer or a copolymer?
copolymer
What are the three packaging resins for Polystyrene (PS)?
crystal PS, HIPS, PS foam
Example of a homopolymer of a branched PE?
low density PE (LDPE) (40-60% crystallinity and density of 0.910-0.940 g/cm^3)
VA is a _____ molecule. Its inclusion in the main chain of branched ethylene copolymer will:
polar decreased crystallinity increased density **compared to PE homopolymer
Preparation of linear PE
produced using a ziegler-natta stereospecific catalyst. Only terminal alkenes
EVA has limited thermal stability and low Tm, it has to be processed at low T
this results in toughness at low T, which is an asset for packages such as ice bags and stretch wrap for meat and poultry
Butene, hexene, octene create _____ which decrease ____ and makes it more flexible
tiny branches which decrease crystallinity
PP are not good barrier to oxygen, but good barrier to??
water
Properties of the PVC affected by amount and type of plasticizer
without plasticizer: good barrier properties with plasticizer: not good barrier (due to increase in Vf) -formulation to produce specific products made of PVC are mostly proprietary -Additives need to be approved by the FDA if the resin is used in food contact applications
We start with ethylene monomer, then why do we end with linear polymer (HDPE) in one case and branched (LDPE) in other case?
Linear PE is obtained by the use of catalyst Branched PE are obtained by free radicals Note: Some catalysts have been developed for branched PE
Polyolefin family consists of _____?
Linear PE, Branched PE and PP
What are the linear PE copolymers?
Linear low density PE (LLDPE) Ultra Low Density PE (ULDPE)
Why plasticizers are added during the processing of PVC and PVDC?
add plasticizers to increase flexibility & help processing temperature go lower
Health concerns of PVC
-Vinyl chloride monomer is carcinogen -Levels of residual vinyl chloride monomer in the material -Solution: vacuum of the resin to remove unreacted vinyl chloride monomer
Environmental concerns of PVC
Burning PVC ==> HCL ==> chlorinated dioxins Solution: PET
Why is LLDP flexible and clear?
Flexible b/c of branches clear bc copolymerization reduces crystallinity
PVDC is a great barrier to _____ and ___, meanwhile EVOH is not good barrier to moisture
Oxygen and moisture
Which one is more soluble in PP? oxygen or water?
Oxygen is more soluble due to P=D*S (density * sorption)
Polyolefin includes family of _____ and ____
PE and PP
High density polyethylene (HDPE) is a _____ homopolymer and is a ____?
PE homopolymer Thermoplastic (non-polar b/c of all the C-H frame work)
#1 most used plastic is _____
PETE
PS foam (crystal PS + blowing agent)
Required shock absorbing/ heat insulation Properties: reduced brittleness Applications: Egg cartons
HIPS
Required toughness and impact resistance Properties: opaque (due to polybutadiene presence) Applications: thermoformed containers for food
Crystal PS
Required: clarity Properties: amorphous and brittle Applications: bottle for pills, capsules
PVC types
Rigid: no plasticizer Semi-rigid: Up to 25 phr plasticizer Plasticized: > 25 phr plasticizer phr: parts per hundred resin
Atactic PP
Tacky byproduct Used mainly in adhesives Amorphous
PVC processing techniques
-Injection molding -Extrusion -Blown film -Blow molding
Iso-PP (Ziegler-Natta catalysis)
-Most common commercial form -CH3 groups on the same side of the chain lead to higher crystallinity and good heat resistance
PP copolymer applications
-Packaging for clothing -Packaging for bakery products
Properties of Low Density Polyethylene (LDPE)
-Transparency (clarity) -Flexibility -Good impact strength -Good oil resistance -Inferior water vapor and gas barrier than HDPE -Good heat sealing -Ease of processing (blown film, cast film, extrusion coating, injection molding and blow molding)
The larger the amount of comonomer, the lower the density why?
Adding branches & decreases crystallinity
Crystallinity decreases with _____?
Branched
EVA is prepared by radical addition, should it be branched or linear?
Branched
What is environmental stress cracking?
Failure of the plastic when exposed to both stress and a chemical substance. (Does not happen when exposed at each independently)
PVC applications
Food packaging: -flexible packaging films (food wraps): -fresh red meat (moderate O2 permeability) (bright red color indicates presence of oxymyoglobin in meat due to exposure to a certain amount of oxygen) -fresh fruit and vegetables -chilled poultry Pharmaceutical packaging: -bags for blood (hard to find acceptable substitutes Others: bottles for cosmetics, shampoo, many have been replaced with PET
Properties affected by HDPE?
Molecular weight (Mw)- the highter the Mw, the higher the tensile strength, impact strength Molecular weight distribution- narrow the distribution, higher the mechanical properties
LDPE properties values depend on:
Molecular weight, molecular weight distribution and branched LDPE properties due to chain branching
PVC is a _____ polymer
Thermoplastic