Plastic Bottle Resin Materials
This section provides a brief description of common plastic container resin materials, their qualities, usages and limitations.
- High Density Polyethylene (HDPE)
HDPE is the most widely used resin for plastic bottles, both injection and extrusion blown. This material is economical, impact resistant, and compatible with a wide range of products (including acids and caustics) and provides a good moisture barrier. It is usually supplied in FDA approved food grade. HDPE is not compatible with aromatic hydrocarbons.
HDPE is naturally translucent and flexible. The addition of color will make HDPE opaque, resulting in the addition of extra weight to the bottle, which will yield a more rigid container.
HDPE packages must be either flame-treated, Lectro-Treated, or Corona discharge surface treated in order to lend themselves readily to silk-screen decoration. While HDPE provides good protection at above freezing temperatures, it cannot be used with products filled at over 160 degrees.
- Low Density Polyethylene (LDPE)
LDPE is similar to HDPE in appearance and characteristics, but is less rigid and in general less chemically resistant than HDPE.
LDPE is used primarily for squeeze applications. LDPE is more expensive than HDPE, but will yield a glossy bottle when produced in both natural or colors.
- Polypropylene (PP)
PP can be processed via injection molding (bottles, jars, and closures), or extrusion blow-molded (bottles and jars). One major advantage of polypropylene is its stability at high temperatures (max. fill temp. 200 to 210 degrees.); PP can be autoclaved by gas sterilization and is microwavable. PP's higher temperature resistance is the reason why its use with hot fill products such as pancake syrup.
PP has excellent chemical resistance, but provides poor impact resistance in cold temperatures. Oriented PP offers improved impact resistance at low temperatures.
Produced in color PP exhibits a glossy finish.
- Polyvinylchloride (PVC)
PVC is naturally clear, has extremely good resistance to oils and very low oxygen transmission. It provides an excellent barrier to most gases, but is vulnerable to solvents. PVC is a semi-rigid material which, when produced on extrusion blow-molding equipment, can accommodate handled designs.
Improvements in resin formulation have increased oxygen barrier properties and chemical resistance, with a 20-30% improvement in drop impact resistance. Advances in molding expertise, as well as in resin formulation, have also yielded an injection blow molding grade of rigid PVC.
PVC exhibits low temperature resistance and will distort at 160 degrees. It is not compatible with hot filled products. Because it provides a good oxygen barrier, PVC is an excellent choice for salad oil, mineral oil and vinegar. It is also commonly used for shampoos and cosmetic products.
PVC can also be molded via the stretch and blow process. These oriented bottles provide improved barrier properties while allowing light-weighting of the container. Chemical resistance is also improved due to the elimination of the PVC modifiers which are frequently attacked. Handled containers, however, cannot be produced via the stretch and blow process. Food grade and non-food grade resins must be specified.
- Polyester (PETG and PET)
PETG: Glycol modified Polyethylene Terephthalate is a tough, durable material with excellent gloss and clarity and the sparkle desired for clear bottles. PETG can be processed via conventional extrusion blow-molding methods, generally on machines designed to process PVC or Polycarbonate. Applications include shampoos, soaps, detergents and products not requiring high oxygen or moisture barriers.
PET: Polyethylene Terephthalate (PET) is a substance made from ethylene glycol and terephthalic acid which react at high temperature and pressure to create PET plastic and polyethylene Terephthalate (PET) bottles. PET is a strong, lightweight form of clear polyester, which is easily formed into containers for cosmetics, water, soft drinks, foods, and other non-food items such as household cleaners. PET is the most heat sensitive resin used in packaging, requiring special consideration for transport, shipping and storage conditions. Fill temperature not to exceed 120 degrees Fahrenheit for PET. Oriented PET provides very good alcohol and essential oil barrier properties, generally good chemical resistance (although acetones and ketones will attack PET) and a high degree of impact resistance and tensile strength. The orienting process also serves to improve gas and moisture barrier properties. Further the orienting process does not lend itself to the production of handled bottles.