Polymer Properties and Uses Quiz

Packaging Materials

• Diverse materials used in packaging, each with unique properties.
• Key properties of paper and paperboard: Low-density materials, poor barriers to light (unless coated), poor barriers to liquids, gases and vapors, grease resistant, good stiffness, crease/fold/glue ability, tear easily, not brittle, excellent substrates for inexpensive printing.
• Key properties of plastics: Wide range of barrier properties, permeable to varying degrees of gases and vapors, low density materials, variable tensile and tear strengths, functional over a wide range of temperatures, low stiffness, flexible.
• Plastic packaging: Thermoplastic, i.e. reversibly fluid at high temperatures. Characteristics modified by co-polymerization, blending, additives, alloying, surface treatment.

Paper Packaging

• Cellulose fibers: strength and mechanical properties vary depending on the fiber sources and processing treatment; additives, surface coatings, and laminations used to modify properties.
• Primary or secondary packaging: includes paperboard folding cartons, composite paperboard cans (laminated paperboard), distribution cases.

Plastic Packaging Types

• LDPE (low-density polyethylene): slightly cloudy, high tensile strength, good moisture barrier properties, high gas permeability. Used for shrink and stretch bundling, pallet wrapping, packaging of bread, fresh vegetables, fruit, and stable food products.
• LLDPE (linear low-density polyethylene): higher tensile and elongation at break; higher heat-seal temperature; higher impact and puncture resistance than LDPE; similar moisture and gas-barrier properties to LDPE as LDPE.
• HDPE (high-density polyethylene): more translucent, stiffer, higher gas and moisture permeability than LDPE; high melting point. Used for bottles.
• PP (polypropylene): excellent water vapor barrier, medium gas barrier, excellent clarity; good heat-seal properties; often oriented – improved heat resistance and other physical properties. Heat-set (packaging bakery products, pouches); non-heat-set (transparent, moisture barrier enhancing aesthetic appeal); coating, vacuum metallization.
• PVC (polyvinyl chloride): transparent, soft, high gas permeation, low water vapor transmission. Used for packaging fresh red meat, poultry, and vegetables. Plasticized PVC films are limp, tacky (slightly sticky), stretchable.

Other Packaging Materials

• Cellophane: transparent, protection against oxygen and aroma, wrinkle resistance, stiff. Coated to be moisture proof.
• PET (polyethylene terephthalate): Good gas and water vapor properties, very high tensile and impact strengths. Properties improved with coating or metallization. Used in soft drink bottles and vacuum-metallized films.
• Nylon (polyamide): Good oxygen barrier, tough, thermoformable; fair moisture barrier; high melting point; chemical resistance. Lamination with other materials can improve properties.
• Polystyrene (PS): Amorphous polymer with excellent clarity. Used as films (windows in paperboard boxes), solid PS (clear, low gas barrier, hard, low impact strength); expanded polystyrene (EPS) for cups, bowls, plates, meat trays, clamshell containers, egg cartons.
• High Impact Polystyrene (HIPS): An immiscible blend of polystyrene, polybutadiene, and grafted polystyrene-polybutadiene copolymer. More resilient and impact resistant than standard PS.
• Polyvinylidene chloride (PVDC): Trade name Saran, copolymer of vinylidene chloride and vinyl chloride; excellent oxygen and moisture barriers; used in films, containers, coatings; monolayer (household wraps); multilayer films (packaging food that requires good oxygen barrier); used co-extruded with polyolefins in shrinkable films; for tight closure of meat and cheese products.
• Ethylene vinyl alcohol copolymer (EVOH): Crystalline copolymer of ethylene and vinyl alcohol; exceptional high oxygen barrier in multilayer structures; laminated or coextruded with other polymer layers to form barrier layers; more expensive among packaging polymers.
• Ionomer: Trade name Surlyn, contains small but significant portion of ionic units; chemical structure: nonpolar ethylene groups, polar methacrylic acid group, carboxylate ionic pairs; good sealing performance, formability, clarity, and oil/grease resistance. The ionic crosslinks reversibly diminish with heating, enabling the polymer chains to move.
• Ethylene vinyl acetate (EVA): High versatility in hot-melt formulations used for packaging, bookbinding, label sticking, glue sticks; EVA resins for packaging film, heavy duty bags, extrusion coating, wire and cable jacketing; hot melt adhesives; cross-linked foam; and as a lidding sealing layer, used in applications with PE, PP, PET, and PS.
• Polyamides (Nylons): amide groups (-CO-NH-) in the backbone chain. Common types: nylon 6,6 and nylon 6. Nylon 6 synthesized using monomer caprolactam; Nylon 6,6 synthesized using adipic acid and hexamethylene diamine. Nylon has good gas barrier, puncture resistance, and heat resistance.
• Polycarbonate (PC): Amorphous thermoplastics; injection, blow-molded, thermoformed; Good replacement of glass (clear & tough, but lighter); withstands temperatures above 200 °C; used in 5-gallon reusable water bottles.
• Styrene butadiene (SB): Co-polymer; tough, transparent, high-gloss surface finish; relatively low density; high permeability to water vapor and gases, ideal for fresh produce packaging; used in blow-molded food and confectionery containers.
• Acrylonitrile butadiene styrene (ABS): Copolymer of acrylonitrile, butadiene, and styrene; varied properties by altering the monomers' proportions; tough, good impact strength; good tensile strength; flexing properties, can be either translucent or opaque; thermoformable; and can be molded. In large shipping and storage containers, and thin-walled margarine tubs and lids.
• Polymethyl pentene (PMP): Co-polymer methyl pentene; Low density; clear; heat resistant up to 200°C; excellent transparency and gloss; used as trays, extrusion coating on paperboard, in baking applications.
• High nitrile polymers (HNP): Co-polymers acrylonitrile, good gas and odor barrier properties; good flavor protection; chemical resistance; clear, tough, rigid; used as inner layer in blow-molded bottles with HDPE; can be film/sheet/laminated with PE, PP, and foil for flexible packaging.
• Fluoropolymers: related to ethylene; High performance, highest water vapor barrier, highest gas barrier; high resistance to chemicals at low temperatures; transparent, heat sealable, can be laminated, thermoformed, metalized, and sterilized; used for blister packs, laminated with PVC; expensive.
• Polyethylene naphthalene dicarboxylate (PEN): Relatively new condensation polymer; higher gas and water vapor barrier and strength compared to PET; UV resistant and has higher temperature resistance; used in one-trip beer/soft drink bottles, returnable/refillable beer/mineral bottles.