Plastic Applications

Polyethylene (PE)

  • Produced by polymerizing ethylene gas under pressure and elevated temperature in the presence of metal catalysts

  • One of the most versatile and economical polymers

High-density Polyethylene (HDPE)

  • PE with a density between 0.941 and 0.959 g/cm³

  • Has small amounts of short-chain branching

  • Low-cost

  • Easy processibility

  • Good moisture barrier

  • Low oxygen-, hydrocarbon-, and flavor-barrier properties

  • Low softening poiint

  • Milky white appearance

  • Relatively high cold-flow properties (NOTE: Cold flow is the tendency of a solid material, typically a polymer, to slowly deform or change shape under a constant mechanical load.)

  • Used in most consumer and industrial blow-molded containers and bottles

  • For HDPE bottles that contains solvent compounds, fluorination is used to increase barrier properties. (NOTE: Fluorination is a process where the finished bottle’s interior is flooded with fluorine compounds.)

  • Used in many industrial boxes, crates, pallets, totes (specifically injection-molded HDPE)

  • Used in tubs for frozen products such as ice cream

  • Used in screw caps

Low-density Polyethylene (LDPE)

  • A material that is less crystalline and less dense

  • Has a density between 0.910 to 0.925 g/cm³

  • Has long-chain branching

  • Low cost

  • Easy processibility

  • Good moisture barrier

  • Have good heat sealability at temperatures as low as 106 to 112°C

  • Has the lowest softening point of conventional packaging polymers

  • Clarity

  • High elongation

  • Softness

  • Poor scuff resistance, high odor transmission, dust attraction, and low grease or oil resistance (NOTE: Scuff resistance is a material's ability to withstand surface wear, rubbing, or abrasion without showing unsightly marks or damage.)

  • Mostly used as film made by either blown (used for most light- and heavy-duty consumer and industrial packaging) or cast extrusion (used for pallet stretch wrap and overwrap)

  • Single largest user are trash bags

  • Has good heat-seal properties, readily sealed by various heat-sealing techniques

  • Used for injection- and blow-molded containers where softness, high flexibility, and squeezability is required

  • Used in snap-on or interference-fit closures

Linear low-density polyethylene (LLDPE)

  • A PE in which side-branching has been deliberately introduced by including monomers such as butene, hexene, or octene

  • Contains sufficient copolymer short-chain branching

  • Used in stretch and shrink films (used to overwrap product or bundle multiple units for shipping)

  • Used for injection- and blow-molded containers where softness, high flexibility, and squeezability is required

  • Used in snap-on or interference-fit closures

Metallocene polyethylene (mPE)

  • Has very narrow molecular weight spreads

  • Tougher (40% greater tensile strength, 10x higher impact strength)

  • Provide stronger heat seals than polyethylene

  • Better hot tack

  • High coefficient of friction

  • More difficult processing and higher cost

  • For tough, high-performance films and heat sealants

  • For high-oxygen or low-moisture permeable film for precut salads

Polystyrene (PS)

  • Produced by combining ethylene with benzene to form ethyl benzene and then converting this to styrene

  • Polymerized with the aid of oxygen, oxidizing agents, or light as a catalyst

  • Available as a hard, clear brittle homopolymer known as “crystal polystyrene”

  • Inexpensive and easily processed

  • Good dimensional stability

  • Superior opticals

  • Good chemical resistance to food acids and alkalis

  • Good printing characteristics

  • Poor resistance to many solvents

  • Used in boxes and containers used in hardware, toy, cosmetic, and jewelry applications (generally called as jewel boxes)

  • Used in clamshells

Homopolymer polystyrene (PS)

  • Has excellent clarity

  • Has high surface gloss

  • Can be brightly colored with opaque or transparent colorants

High-impact polystyrene (HIPS)

  • A polystyrene copolymer that has been modified with elastomeric molecules such as butadiene

Expanded polystyrene (EPS)

  • Made into a variety of trays, tubs, cups

  • Formed by incorporating a blowing agent with the PS that will expand the plastic into a low-density cellular foam

  • EPS foams are exceptional insulating materials

  • Thermoformed EPS food trays are the principal products made from extruded EPS sheet

  • EPS loose-fill bead products are used mostly for inner packing to protect fragile products from impact and vibration.

Unoriented polystyrene film

  • Low tear, impact, tensile, and heat-seal strengths

  • Has poor gas and water-vapor barrier properties

Polypropylene (PP)

  • Polymerized from propylene gas and processed into pellets

  • Has two general classifications: Isotactic PP (gives superior properties; used for most packaging applications), Atactic PP (yields a gummy PP; used as an adhesive base)

  • Very similar to PE in terms of some characteristics (barrier, cheap, easily processed, etc.)

  • Lower crystallinity than HDPE

  • PP clarity can be improved by incorporating nucleating agents

  • Easier to produce in an amorphous state

  • Has low UV light resistance; requires UV inhibitors for any application where there will be significant UV exposure

  • Brittle at low temperatures

  • Used for bottles where hot-filling or some other thermal exposure occurs

  • Has outstanding integral hinge (live hinge) properties

  • Oriented PP is not heat sealable and cannot be thermoformed.

Compared to PE, PP has:

  • Better resistance to cold flow

  • Reduced deformation at elevated temperatures

  • Has good stiffness, tensile strength, and surface highness

  • Has higher softening point

Polyethylene terephthalate (PET)

  • Formed by reacting ethylene glycol (base) and terephthalic acid

  • Melting point of 249°C is one of the highest of the common packaging plastics.

  • Formed by a condensation reaction

  • Subject to hydrolytic breakdown (NOTE: Hydrolytic breakdown, or hydrolysis, is a chemical reaction where water molecules break the chemical bonds of a polymer chain.)

  • May release acetaldehyde (AA) if thermal degraded

  • Highest tensile strength

  • Low elongation

  • High melting point

  • Excellent grease or oil barrier

  • Good gas and moisture barrier

  • Good printing characteristics

  • High use temperature, high impact strength, high scuff resistance

  • Dimensional stability

  • Not heat sealable

  • Poor machine performance, a propensity for generating static

  • Poor package openability

  • PET films are used as base films for cheese and luncheon meats packages.

  • PET’s heat resistance and microwave transparency makes it an ideal dual-ovenable film.

  • Largest single use - injection blow-molded carbonated beverage bottles

  • Used for strapping applications

  • Is recyclable (through methanolysis, a depolymerizing process that reverts back PET back to the original monomers)

Crystallized polyethylene terephthalate (CPET)

  • Used for dual-ovenable tray applications

Polyethylene terephthalate glycol (PETG)

  • Has very little tendency to crystallize

  • Can be EBM’ed or thermoformed

  • Has high melt strength

Polyvinyl chloride (PVC)

  • Produced by the suspension, or emulsion, polymerization of vinyl chloride

  • Is hard, brittle

  • Has low thermal stability

  • Unusable unless compounded with a number of additives

  • Has poor thermal processing stability

  • Compounded with additives

  • Most important additive is plasticizers (soften PVC)

  • Has high impact strength

  • Good scuff resistance

  • Good dimensional stability

  • Good opticals

  • Excellent grease- and oil-barrier properties

  • Is heat sensitive

  • More difficult to produce than PE or PP

  • Highly plasticized PVC films have excellent strength properties and unique “cling”.

  • Self-extinguishing, burns with difficulty

  • Preferred shrink material for many tamper-evident bands and for shrink-label stock

  • Used for most thermoformed shells for blister packaging

  • Has been targeted by environmental groups

Polyvinylidene chloride (PVDC)

  • Vinylidene chloride - a vinyl monomer with one more chlorine than a vinyl chloride monomer

  • Relatively high cost

  • Not made into dimensional parts

  • Often referred to as Saran (a Dow trade name)

  • Exceptional low permeability to water vapor and gases in a single material

Polyvinyl acetate (PVA/PVAC) and Ethylene-vinyl acetate (EVA/EVAC)

PVA

  • Highly polar, resilient thermoplastic that can be easily dispersed into water to make an emulsion

  • Used as glue or adhesive

EVA

  • A polyvinyl acetate copolymer of polyethylene

  • If close to PE, LDPE properties (used in stretch wrap films, ice bags, bag-in-box containers and heat-sealable films or coatings)

  • If close to PVA, it is usually used as a hot melt adhesive.

Polyamide (PA)

  • Aka Nylon (formerly a DuPont trade name)

  • Formed by condensing a diamine and a dibasic acid, or by the polymerization of amino acids

  • Identified by a number representing the number of carbon atoms in the basic amino acid (such as nylon type 6), or by the number of carbon atoms in the reacting amine and dibasic acid (such as nylon type 66)

  • Types 6 and 66 - commonly used for packaging purposes

  • Tough

  • Resist abrasion, puncturing, impact, cracking

  • Not resistant to strong inorganic acids

  • Not heat sealable

  • Has poor slip properties

  • Provide good barriers to aromatics, oxygen, nitrogen, and carbon dioxide

  • Poor water-vapor barrier properties

  • Used mostly in films, usually produced by extrusion casting

  • Can be monoaxially or biaxially oriented

  • Oriented nylon cannot be thermoformed.

  • Used for abrasive products like coffee granules

MXD-6

  • A semi-crystalline polyamide

  • Made by condensing m-xylene and adipic acid

  • Has higher heat resistance, stiffness, tensile strength, and lower moisture sensitivity

  • Used as an oxygen barrier in some PET bottles

  • Has better oxygen properties than EVAL when the humidity is higher than 80%

Nylon type 6

  • (Unoriented) Widely used in meat and cheese vacuum packaging

Polyvinyl alcohol (PVAL/PVOH) and Ethylene-vinyl alcohol (EVAL/EVOH)

PVAL/PVOH

  • Is water soluble

  • Used in water-soluble pouches like in detergent products

  • Has the theoretical highest oxygen barrier, but because of its water-soluble properties, it is impractical to use

EVAL/EVOH

  • Made by hydrolyzing the copolymer of ethylene and vinyl acetate

  • Has the highest usable oxygen barrier

Ethylene acid copolymers and ionomers

Ionomers

  • commonly known by the DuPont trade name Surlyn

  • Copolymers of ethylene and methacrylic acid that have been further modified by the inclusion of sodium or zinc ions

  • Can be made into tough, clear films that have properties particularly suitable for skin-packaging applications

  • Best sealing layer; can form a seal through fat contaminants

Cellulosics

  • Once the only clear packaging film choice

  • Based on wood cellulose rather than petrochemicals

  • Is a thermoset rather than thermoplastic

  • Has superior dead-fold properties and machinability

  • Generates lower static

  • Cost and performance cannot compete

  • Cellophane (a former DuPont trade name)

Epoxies

  • Are thermoset polymers based primarily on epichlorohydrin and bisphenol-A (BPA)

  • Form particularly strong bonds with many materials

  • Are found in adhesives and protective coatings

Polycarbonate (PC)

  • Made from carbonic acid and bisphenol-A

  • Particularly tough

  • Highest impact resistance or strength of packaging plastics

  • Has an unusually high use temperature

  • Major application is as a replacement for glass glazing in high risk areas

  • Used in returnable, large water bottles and returnable water jugs

  • High cost

Polyacrylonitrile (PAN)

  • An acrylonitrile-methyl acrylate copolymer from BP Chemicals

  • Trade name, Barex

  • Only resin marketed for packaging purposes

  • Has good oxygen- and gas-barrier properties but relatively poor water-vapor-barrier properties

  • Offers excellent resistance to many aggressive solvents not readily

  • Made into film and dimensional shapes

Polyurethanes (PUR)

  • Formed by a reaction between an isocyanate and a polyol

  • Can be blown in foams of varying densities, used as protective packaging forms

  • Used in “foam-in-place” systems, where the two reacting chemicals are mixed just prior to being spraying around an object to be protected

  • Used as cushioning and insulation

Polyethylene naphthalate (PEN)

  • A recently commercialized resin that can be used as blend with PET or as a PET/PEN copolymer

  • Monomer: dimethyl 2,6 naphthalate or naphthalene di-carboxylate (NDC)

  • Used for hot-fill and retort applications

  • Blocks out UV light entirely, a good candidate for beer, juices, pharmaceuticals, edible oils, and milk

  • Offers a high potential for replacing glass in some critical applications

  • Very very expensive

Styrene-butadiene

  • K-Resin - Chevron Phillips Chemical Company’s trade name

  • A high-clarity, tough, and easily processed styrene-butadiene copolymer

  • Low surface hardness, low stiffness, low resistance to organic solvents, UV sensitive

  • Relatively high gas permeation rates

Polytetrafluoroethylene (PTFE)

  • Teflon

  • Low coefficient of friction

  • Inert

  • Used for packaging machinery

Chlorotrifluoroethylene (CTFE) or Polychlorotrifluoroethylene (PCTFE)

  • Marketed under the trade name Aclar

  • Has the highest moisture barrier properties of packaging polymers

  • Has excellent optical properties

  • Readily thermoformed

  • Used in thermoformed blister packs for sensitive unit-dose pharmaceutical tablets

  • High cost

  • Tolerate cryogenic temperatures and ionizing radiation

Bioplastics

  • Developed from renewable sources, thus far including materials such as cellulose, starch, and other biopolymers

  • May not be biodegradable, but are recyclable

  • Other bioplastics: polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), Green PE, Bio-PET

Polylactide acid or polylactic acid (PLA)

  • Most used resin in the bioplastics market

  • A polymeric material derived from corn starch

  • A stiff, clear polymer

  • Sometimes mistaken as PS if thermoformed into a tray

  • Can be thermoformed easily at low temperatures (also its disadvantage)

Thermoset plastics

  • Examples: phenol-formaldehyde, urea-formaldehyde

  • Have superior solvent resistance, making them ideal for aggressive solvent contact materials

  • Have a particularly hard surface

  • Are not prone to developing sink marks

  • Used for specialty closures and applications