Resins and Types of Packaging
Types of Resins
Plastic is often a more efficient material to choose than alternatives. That’s because plastics are incredibly energy efficient to manufacture and because they are lighter than alternative materials. Just two pounds of plastic can deliver 10 gallons of a beverage. You’d need three pounds of aluminum, eight pounds of steel, or over 40 pounds of glass to bring home the same amount of a beverage.
Rigid plastic packaging. commonly referred to in the industry as “rigids,” are a category of plastics generally made from #2 HDPE and #5 PP rigid.
Plastic films compose a broad category of materials that can be relatively simple or complex depending on the demands of a particular product or package. Like plastic bottles and containers, film can be made with different resins, each of which has a unique combination of properties that makes it ideal for certain applications.
This category of plastic packaging includes so much more than Polyethylene terephthalate (PET), the plastic used most commonly for soft drink bottles and other beverages. But a wide range of bottles—and even the closures used for PET bottles are made from other plastic resins.
High Density Polyethylene (HDPE)
HDPE is the most widely used type of plastic. It’s used to make many types of bottles and containers. Unpigmented bottles are translucent, have good barrier properties and stiffness, and are well suited to packaging products with a short shelf life such as milk. Because HDPE has good chemical resistance, it is used for packaging many household and industrial chemicals such as detergents and bleach. Pigmented HDPE bottles have better stress crack resistance than unpigmented HDPE.
- Excellent resistance to most solvents
- Higher tensile strength compared to other forms of polyethylene
- Relatively stiff material with useful temperature capabilities
- Bottles for milk, water, juice, cosmetics, shampoo, dish and laundry detergents, and household cleaners
- Bags for groceries and retail purchases
- Cereal box liners
Low Density Polyethylene (LDPE)
Includes Linear Low Density Polyethylene (LLDPE)
LDPE is used predominately in film applications due to its toughness, flexibility, and relative transparency, making it popular for use in applications where heat sealing is necessary. LDPE also is used to manufacture some flexible lids and bottles as well as in wire and cable applications.
- Excellent resistance to acids, bases, and vegetable oils
- Toughness, flexibility, and relative transparency; good combination of properties for packaging applications requiring heat-sealing
- Bags for dry cleaning, newspapers, bread, frozen foods, fresh produce, and household garbage
- Shrink wrap and stretch film
- Coatings for paper milk cartons and hot and cold beverage cups
- Container lids
- Squeezable bottles (e.g., honey and mustard)
Polyethylene Terephthalate (PET, PETE)
PET is clear, tough, and has good gas and moisture barrier properties. This resin is commonly used in beverage bottles and many injection- molded consumer product containers. Cleaned, recycled PET flakes and pellets are in great demand for spinning fiber for carpet yarns and producing fiberfill and geotextiles.
- Clear and optically smooth surfaces for oriented films and bottles
- Excellent barrier to oxygen, water, and carbon dioxide
- High impact capability and shatter resistance
- Excellent resistance to most solvents
- Plastic bottles for soft drinks, water, juice, sports drinks, beer, mouthwash, catsup, and salad dressing
- Food jars for peanut butter, jelly, jam, and pickles
- Ovenable film and microwavable food trays
PP has good chemical resistance, is strong, and has a high melting point making it good for hot-fill liquids. This resin is found in flexible and rigid packaging, fibers, and large molded parts for automotive and consumer products.
- Excellent optical clarity in biaxially oriented films and stretch blow molded containers
- Low moisture vapor transmission
- Inertness toward acids, alkalis, and most solvents
- Containers for yogurt, margarine, takeout meals, and deli foods
- Medicine bottles
- Bottle caps and closures
- Bottles for catsup and syrup
PS is a versatile plastic that can be rigid or foamed. General purpose polystyrene is clear, hard, and brittle. It has a relatively low melting point. Typical applications include protective packaging, food service packaging, bottles, and food containers. PS is often combined with rubber to make high impact polystyrene (HIPS) which is used for packaging and durable applications requiring toughness, but not clarity.
- Excellent moisture barrier for short shelf life products
- Excellent optical clarity in general purpose form
- Significant stiffness in both foamed and rigid forms
- Low density and high stiffness in foamed applications
- Low thermal conductivity and excellent insulation properties in foamed form
- Food service items, such as cups, plates, bowls, cutlery, hinged takeout containers (clamshells), meat and poultry trays, and rigid food containers (e.g., yogurt)
These items may be made with foamed or non-foamed PS.