A Guide to Plastic Resins
Polyethylene Terephthalate (PET)
PET is one of several resins in the polyester family. The major raw materials used to manufacture PET bottles include ethylene glycol, terephthalic acid or dimethyl terephthalate and small quantities of additives such as catalyst and stabilizers. Bottles made from PET are injection blow molded, unoriented or injection stretch blow molded, biaxially oriented. PET bottles have outstanding clarity, good impact and scratch resistance, high gloss finish and good barrier properties. They are lightweight and safe compared to glass (no breakage on filling lines, in transit, retail stores and in homes). Containers manufactured with PET resin are ideal for packaging a wide range of food product, toiletries, cosmetics and household and pharmaceutical products. Each application should be tested to ensure that the product is compatible with the container.
High Density Polyethylene (HDPE)
HDPE is the most widely used resin for plastic bottles. 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. When fluorine treated, HDPE becomes an effective package for solvents (aromatic hydrocarbons) and oxygen sensitive extracts. HDPE is naturally translucent and flexible. The addition of color will make HDPE opaque although not glossy. Adding extra weight to the bottle will yield a rigid container. HDPE is supplied surface-treated on a stock basis and lends itself readily to silkscreen decoration. While HDPE provides very good protection at temperatures below freezing, it cannot be used with products filled at over 180º F or products requiring a hermetic seal.
Vinyl / Polyvinyl Chloride (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. PVC exhibits low temperature resistance and will distort at 160º F. 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.
Low Density Polyethylene (LDPE)
LDPE is similar to HDPE in composition. It is less rigid and generally less chemically resistant than HDPE, but is more translucent. LDPE is used primarily for squeeze applications. LDPE is significantly more expensive than HDPE, but will yield a glossy bottle when produced in colors.
Polypropylene is a naturally translucent material which provides contact clarity and an excellent moisture barrier. One major advantage of polypropylene is its stability at high temperatures (maximum temperature = 230-260º F); it is autoclavable and offers the potential for steam sterilization. PP’s compatibility with high filling temperatures is responsible for its use with hot fill products such as pancake syrup. PP has an excellent chemical resistance, but provides poor impact resistance in sub-freezing temperatures. Produced in color, PP exhibits a glossy finish.
Styrene offers excellent clarity and stiffness at an economical cost. It is commonly used with dry products including vitamins, petroleum jellies and spices. Styrene does not provide good barrier properties and exhibits poor impact resistance. It can be screen printed without being flame treated and lends itself well to offset printing.
Can be any combination of plastics. Usually one of the above plastics mixed with an additive or barrier plastic to enhance the properties of the final container.