Info

EVOH (0% R

H)

° 0 1 10 100 WVTR (g mil/100 in2/day) at 38°C, 90% RH

° 0 1 10 100 WVTR (g mil/100 in2/day) at 38°C, 90% RH

Figure 2. Gas barrier properties of some common food-packaging polymers.

Compared to LDPE, HPDE has a higher melting point (typically 135°C vs 110°C), greater tensile strength and hardness, and better chemical resistance. HDPE is used mostly to make blow-molded bottles for the packaging of products such as milk and water. It is also used for food containers, bags, films, extrusion coating, bottle closures, and the like.

LDPE has a density between 0.91 and 0.93 g/cm3. It is a polymer with many long side-chain branches. LDPE is used mostly as film for packaging fresh produce and baked goods, as an adhesive in multilayer structures, and as waterproof and greaseproof coatings for paperboard packaging materials. The packaging film made from LDPE is soft, flexible, and stretchable. The film also has good clarity and heat sealability.

LLDPE has a density about the same as that of LDPE. LLDPE is a copolymer with many short side-chain branches. LLDPE has similar clarity and heat sealability to that of LDPE, as well as the strength and toughness of HDPE. With its superior properties, LLDPE has been replacing LDPE in many food-packaging applications. In recent years, many development efforts have focused on using single-site or metallocene catalyst to produce LLPDE films with superior heat seal and hot tack properties, clarity, abuse resistance, and strength (10,11).

Table 2 Barrier Properties of Some Common Packaging Plastics

Plastics

permeability"

C02 permeability"

WVTR6

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