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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, 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
(PP)
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. |
 Polystyrene
(PS)
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.
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