Ethylene-Vinyl Alcohol (EVOH) Copolymers

• Last time, the study focused on Polyethylene (PE), its varieties, Polypropylene (PP), and Olethane categories

Ethylene-Vinyl Alcohol (EVOH)

• Copolymers possess ethylene and vinyl parts, with two monomeric units linked.
• Copolymers have unique properties dependent on the concentration of the comonomers.
• Barrier properties, water vapor, oxygen, and aroma barrier properties are vital for packaging materials
• A unique feature of copolymers is the ability to provide a barrier to gases
• EVOH copolymers are highly crystalline.
• EVOH's properties heavily rely on the comonomers' concentration.
• As ethylene content rises, gas barrier properties diminish.
• Higher ethylene content improves moisture barrier properties and resin processability.
• EVOH's standout trait is its ability to block gases and odors
• The use of EVOH in packaging structures enhances flavor and quality retention by preventing O₂ penetration.
• EVOH has a low permeability coefficient for gases.
• EVOH effectively retains CO₂ or N₂ when used in gas-filled Modified Atmosphere Packaging (MAP) techniques.
• EVOH offers high resistance to oils and organic vapors, but this protection decreases with increasing penetrant polarity.
• EVOH is moisture-sensitive and unsuitable as a primary moisture barrier.
• EVOH functions as an excellent O₂ and aroma barrier at low water activity (aW).
• Sandwiched EVOH serves as an O₂ and aroma barrier in retort pouches, tubs (cans), and aseptic packages.
• EVOH is costly and never used alone.
• Ethylene vinyl alcohol provides protection against gases entering and prevents oxygen diffusion out of the package.
• In sandwich form, EVOH protects against oxidation.

Polystyrene (PS)

• Atactic configuration are random polymers, amorphous and grouped with structures of bulky styrene monomers

• Isotactic PS: free energy form isn't suitable for approaching sterene monomers, appearing as a result of melting

• When reacted with a suitable catalyst, ethylene and benzene form ethylbenzene

• Styrene, commonly known as vinyl benzene, is produced through catalytic dehydrogenation of ethylbenzene.

• Polystyrene (PS) is created through the addition polymerization of styrene, typically consisting of approximately 1000 styrene units.

• Normally atactic form is achieved, resulting in a completely amorphous polymer due to bulky benzine rings preventing chains from approaching

• Special catalysts and polymerization techniques can be used achieve a isotactic PS form, although often reverts to atactic form on melting

• Polystyrene's (PS) glass transition temperature (Tg) near 100°C can cause issues.

• Above room temperature, PS is glass-like thats why a cup can break

• When PS is subjected to high temperatures or stores really hot foods, it should be closely monitored.

• It's preferable to avoid phase transitions (glassy to rubbery or vice versa) when PS comes in contact with food.

• For example putting warm food into a PS cup, the Tg is very susceptible to change

• The polymer chains become more mobile in rubbery form, leading to additives migrating into the food.

• If styrene monomers are present, they could transfer to the food product, especially in creamy items.

• Microwaving PS isn't recommended due to its internal heating.

• Temperature can reach dangerous levels, which can result in a glassy to rubbery tranisition causing undesired chemical migration

• Due to its bulky side group, PS prevents close chain-chain interaction.

• PS is a totally amorphous polymer with a high Tg of approximately 100°C, and has bad barrier qualities.

• PS can be modified and used as many different applications

• Examples: Glossy/clear/stiff materials, cellular-formed EPS trays or containers

• PS is used to make:

  • Dairy product tubs
  • Clear trays for meat and prodice
  • EPS trays & cartons for meat and poultry
  • Clear/foamed cups, glasses and dinnerware

• When producing trays or cups with PS, additives are used to increase the glass transliton (Tg).

Polyvinyl Chloride (PVC)

• PVC is generally used in non-food applications as food packaging material

• Ethylene dichloride is the result of an addition reaction between chlorine and ethylene.

• The dichloride is then dehydrochlorinated and fractured, giving a VCM

• Polymerization of VCM produces PVC and ranges from 500 to 3500

• It was discovered in 1974, that VC polymerization plants in Britain, had fatal types of liver cancer diagnosed

• Food and Drug administrators focused on the VCM found in PVC and its use in food

• Likely to migrate in food, levels are now very low

• Can be used with non food applications such as window materials

• Inexpensive

• Stiff/brittle materials are made because of strong C-Cl polar interactions

• Can be improved by plasticizers

• Used for non-food applications such as piping, house siding/gutters, etc

• Addition of plasticizers increase mechanical properties

• Plasticized PVC acts as good H₂O barrier, but an ineffective O₂, CO₂, and aroma barrier

• Plasticized PVC stretches very well and provides cling

• It is self-extinguishing with a flame and inert in its chemical behavior.

• Plasticized PVC film is widely used for wrapping trays/containers for fresh produce and red meats

• It can be turned into bottles and jars

• Extremely glossy/transparent films can be made with high tensile strength/stiffness

• Density is very high and is around 1400 kg m⁻³

• High water vapor permeabiliy that's higher than polyolefins prevents condensation on the inside of the film

Polyvinylidene Chloride (PVDC)

• PVDC possesses strong C-Cl polar interactions.

• Copolymerization with PVC and the addition of a plasticizer enhances mechanical properties.

• PVDC/PVC acts as an effective barrier against H₂O, O₂, CO₂ & aroma.

• PVDC/PVC stretches and has cling properties.

• PVDC is expensive and is used as a coating, in laminations, or as a coextruded film.

• Another polymer is used to add stiffness and strength

• Polyvinylidene chloride (PVDC) was made in 1933 in Michigan

• Ralph Wiley, a lab worker for Dow

• Helped in this was by preventing beakers used in his process becoming very dirty, in an effort to develop a dry-cleaning product.

• Dow released Saran Wrap, a thin/clingy plastic wrap and was produced primarily for food wrapping

• Commonly used to preserve food products

• S. C. Johnson & Son acquired Saran Wrap later on

• Saran Wrap is no longer composed of PVDC due to halogenated materials, environmental concerns, and being comprised of ordinary polyethylene.

• Polyethylene enhances oxygen permeability which impacts food spoilage prevention.

Polyethylene Terephthalate (PET)

• Polyethylene terephthalate, can be written as poly(ethylene terephthalate)

• Commonly represented by PET, PETE, or the obsolete PETP or PET-P

• Most common thermoplastic of the polyester family

• Used in fibers for clothing and containers for liquids/foods

• Used for thermoforming during manufacturing

• In combination with glass fiber towards engineering resins

• Thermal and processing causes can cause polymers to exist as amorphous or semi-crystalline format

• Semi-crystalline can appear transparent depending on the particle size if under 500nm

• White and opaque features will show if the crystal and particle size is highter

• Ethylene alcohol can be synthesized in the esterification reaction for terephthalate

• For esterification terephthalic acid is used combined with ethylene glycol and water as byproduct

• Transesterification reaction requires ethylene glycol and dimethyl terephthalate to produce methanol as byproduct

• Polymerization can be achieved through condensatino reaction and is done after the esterification is complete

• PET's Tg (glass transition temperature) is ~80°C, Tm (melting temperature) is ~270°C and is not preferred for hot liquids

• PET must be oriented to achieve desired strength and barrier properties.

• High Tm; rubbery form;

• PET is tough, heat-resistant, glossy, clear and low cost

• Functions a good H₂O, O₂, CO₂, and aroma barrier

• Used mainly for beverage containers

• More commonly found in oil bottles and peanut butter jars

• Must be coated by PE/PVDC to produce pouches due to heat sensitivity

Polycarbonates (PC)

• Type of polyester that contains carbonated groups to form structure
• Synthesized through polymeriztion of sodium salts, bisphenolic acid and phosgene
• Transparent, very resistant to heat and very durable and strong
• Common alternative to glass for glazing and processing tools
• Used for large reusable water bottles (3 -6 liters)
• Employed towards sterilizing baby-bottles as a food-substitute
• PC shouldn't be mistaken for the variant in manufacturing contact lenses
• Can be applied towards returnable milk bottles and oven-safe trays
• Can be co-extracted with nylon to produce containers that can be used for carbonated drinks

Polyamides (PA)

• PAs are usually linear, thermoplastic condensation from monomers of carboxylic and amine acid

• Amide (-(C=O)-NH-) linkages result in the main polymer chain that provide mechanical strength and barrier properties.

• Highly permeable to water vapor due to amide group being polar

• Absorbed water causes a plasticizing effect, in turn lower tensile strangths

• Enhances increase in impact strength

• PAs are commercial for package films starting in the late 1950's

• Although films are considered 'special', food packages wouldn't be possible without PAs

  • Nylon-6
  • Nylon-11
  • Nylon-6,6
  • Nylon-6,10 (nylon 610)

• Often referred to as Nylons

• strong, heat-resistant, and barrier qualities similar to Ethylene Vinyl Alcohol (EVOH).

• Sandwiched nylon used as O₂ and aroma barrier towards retort pouches

• Also is used in tubs and aseptic packages

• Costly and often seldomly used alone

• Film that is Biaxially oriented improves flex-crack, and offers improved strength & properties

• Used to package natural cheese, processed food and frozen food types

• PAs can compete with biaxially PET, with improved gas barriers

• Improved softness and puncture resistant, with high rigidity

Additives in Plastics

• Additives enhance the qualities of base polymers

• Are added to an established based group

• Additives are auxiliary ingridients to increase/enhance polymer properties without alternation in its structure

• In food package additive have to receive clearance

• Main goal is to improve specifications such as processing, mechanical and stability

• Include agents such as plasticizers, anti-aging, surface property modifiers, foaming and optical property modifiers

Plasticizers

• Small molecules filling the positions between water and mud

• Increase flexibility and reduces hardness

• Enhance and improve bending

• Lowers temperatures for processing and decreases energy required

• Brittle polymers (ex PVC) must be plasticized to obtain film alternatives

• Gives materials found limps

• In "cling" film plasticizers

• In PVC 80% are plasticizers

• Pthalic esters that are epoxidized in low weight oils also do the job.

• Can be achieved through co-polymeriazation

• Vinyl with acetate and ethylene for additives

Anti-aging Additives

• With heat, O₂, water and agents modification in structure can occur

• Deterioration of material happens through aging and atmospheric radiation

• In food, it will preserve the products against oxidation and microbial contamination

• Necessary in polymeric films that degrade in atmosphete (PP)

• Can act as a free radical scavenger

• Has been cleared with the FDA

• Common to use with antioxidants together (synergistic effects)

• Act as peroxide decomposers

• Used when preventing deterioration

• UV stabilizers act and releasing high energy

Surface Property Modifiers

• Static occurs when rubbing

• Also in converting, film and fast operations

• Caused by fact that polymers are non-conducting

• Is generated on polymer surface

• Anti Static agents help prevent static

• Electrification in films leads from separation of ions/electrons

• Happens commonly when surfaces when separating with each other

• Addition of quaternary will help eliminate moisture/problems from occurring

• Also migrating to surface of conductive forms that absorb atmospheric moisture

• Moisture can condensation with food and packaging applications causing prevention when viewing content

• Form when polymer surface tension, and is lower than water tension

• Form continuous layers of water

• Compounds known as ethoxlyates with a levels from 0.5% to 4% will promote increase surface tension

• Can be applied internal or surface

• Used by levels that have a rance from 0.1-0.5%

• By incorporating compound to the polymer, blocking can be reduced in materials

• Block may occur under pressure so during storage it can be reduced with chemicals

• Anti-blocking help reduce block

Optical Property Modifiers

• Technological material with properties to transit light and colors

• Most food films arent pigmented, but pigments will be done for colors and are insolube

• Primary ones are black carbon, titanium dioxide and cadmium

• FDA has questioned pigments with food and contacting due with migrating

Foaming Agents

• Used for produce cellular and classified based on chemical and physical

• Occurs through either: decomposition reactions resulting from cell transition or evolution

• In modern times used for PS foams

• Hydrocarbons can be used as alternatives, with help of carbon dioxide

• PET and PVC use chemicals