Nylon-6 also serves as the matrix for advanced nanocomposite films, in which microscopic plate-like clay particles are dispersed at low levels (less than 6% by weight) in a resin carrier. Because such composite films exhibit anywhere from three to six times the oxygen barrier and stiffness properties of the unfilled nylon, food processors can use the composites to down-gauge the thickness of their packaging. In the food industry, nanocomposite nylon 6 films are being used in boil-in bags, standup pouches and vacuum packs. Nanocomposite films for packaging are also made with polyester and PP base resins.
Polyolefins
Films made of oriented polypropylene (OPP), particularly biaxially oriented polypropylene (BOPP), are receiving much attention from food packagers because of their exceptional moisture and oxygen barrier properties and improved economics over metal foil packaging. They are useful for enclosing such products as corn chips, cookies, crackers and pet foods. Unlike foils, the OPP films are transparent and can be designed for useful configurations such as stand-up pouches.
OPP films can be metallized for further improvement in barrier properties. Such films are already in use for packaging such foods as powdered beverages, nutritional drinks, soup, rice and dried cheeses. Some grades of metallized OPP films are heat sealable. Others are intended as the inner layers of coextruded packaging laminates containing other polymers such as plain OPP or PET.
Biaxially oriented polypropylene (BOPP) films are key elements of a growing variety of food packaging applications.
Figure 3: Biaxially oriented polypropylene (BOPP) films are key elements of a growing variety of food packaging applications.
Source: Toray Plastics.
The adoption of metallocene catalyst technology has enabled resin producers to develop grades of polypropylene (PP) packaging films possessing unique combinations of stiffness, toughness and clarity. Such films allow downgauging of packaging containers so that thin-wall injection molded food containers are now possible. For thermoformed packaging, the new PP grades offer superior heat resistance with improved clarity and gloss. Targeted application for the thermoformable grades are plastic trays for fresh foods, and microwaveable ready-meal packaging.