PLASTIC PACKAGING SYSTEMS

Cradle-to-virgin conventional PET resin production is based on a life cycle inventory Franklin Associates conducted for the Plastics Division of the American Chemistry Council (2010).99

This data represents the most recent LCI data for plastics production in North America. These data are publicly available through the US LCI database (www.nrel.gov/lci) and include production of the investigated resins:

• Low-Density Polyethylene (LDPE)

• High-Density Polyethylene (HDPE)

• Polypropylene (PP)

• Polyvinyl Chloride (PVC)

• Polystyrene (PS)

• Expanded Polystyrene (EPS)

• Polyethylene Terephthalate (PET) 3.3.2. Plastic Converting Processes

This analysis uses plastic converting LCI data from Franklin Associates’ Private LCI Database.

3.3.2.1. Film & Sheet Extrusion

Plastic film is made by the extrusion of resin followed by the pulling and cooling of film. Plastics extrusion is a manufacturing process in which raw plastic material is melted and formed into a continuous profile. In the extrusion of plastics, resin is gravity fed from a top-mounted hopper into the barrel of the extruder. The material enters through the feed throat and comes in contact with the screw. The rotating screw (turning at approximately120 rpm) forces the resin into a heated barrel. The molten plastic leaves the screw and travels through a screen that removes contaminants. The molten plastic is then

99

American Chemistry Council. 2010. Cradle-to-Gate LCI of Nine Plastic Resins and Two Polyurethane Precursors. Franklin Associates, A Division of ERG.

Chapter 3. Life Cycle Inventory

forced through an annular slit die, usually vertically, to form a thin walled tube. Air is blown through a hole in the center of the die to blow up the tube. A high-speed air ring is on top of the die and blows onto the hot film to cool it. The tube of film then continues upwards, continually cooling, until it passes through nip rolls where the tube is flattened. The edges of the tube are slit to produce two flat film sheets. The film is then wound onto reels. Data for film extrusion are based on confidential industry data collected from 1992 through 2005 and APME data collected in the 1990s.100,101

3.3.2.2. Blow Molding

Hollow plastic parts are formed by a process called blow molding. Melted plastic is extruded into a hollow tube (a parison) and captured by closing it into a cooled metal mold. Low-pressure air (typically 25 to 150 psi) is blown into the parison, inflating it into the shape of the desired container. Once the plastic has cooled, the mold can be opened and the part ejected. Data for extrusion blow molding are based on confidential industry data collected from 1992 through 2005 and APME data collected in the 1990s.102,103

3.3.2.3. Injection Stretch Blow Molding

The first step in the injection stretch blow molding (ISBM) process is production of a preform using the injection mold process (see Injection Molding). The preform is made up of a fully formed bottle/jar neck with a thick tube of polymer attached, which eventually forms the body. The preform is heated above the glass transition temperature and stretched mechanically with a core rod. First, low pressure air is introduced to blow a bubble. After the stretch rod is fully extended, high-pressure air blows the expanded plastic bubble into the shape of the blow mold. Injection stretch blow molding is commonly used to produce polyethylene terephthalate (PET) beverage bottles, as the polymer is strengthened when stretched, allowing it to keep its shape under pressures e.g., created by carbonated beverages. ISBM data are based on confidential industry data collected from 1992 through 2005 and APME data collected in the 1990s.104,105

3.3.2.4. Thermoforming

Like injection molding, thermoforming is a principal fabrication technique for rapidly creating large quantities of plastic articles. This technique is relatively simple and well established. A sheet of extruded plastic is fed, usually on a roll or from an extruder, into a heated chamber where the plastic is softened. The sheet is then clamped over a negative

100

Franklin Associates, A Division of ERG. Data from industry sources collected from 1992 through 2005.

101

Boustead (1997). Eco-Profiles of the European Plastics Industry, Report 10: Polymer Conversion. Association of Plastics Manufacturers in Europe (APME).

102

Franklin Associates, A Division of ERG. Ibid.

103

Boustead (1997). Ibid. 104

Franklin Associates, A Division of ERG. Data from industry sources collected from 1992 through 2005.

105

Boustead (1997). Eco-Profiles of the European Plastics Industry, Report 10: Polymer Conversion. Association of Plastics Manufacturers in Europe (APME).

mold while in a softened state and then cooled. A punch loosens the plastic forms and eliminates sheet webbing that may be recycled back into the process. Thin-gauge sheet or film is used in thermoforming to produce disposable/recyclable food, medical and general retail products such as containers, cups, lids, and trays. Thick-gauge sheet is used to produce larger, usually more permanent, items such as plastic pallet, truck beds, and spas. Thermoforming data are based on primary data compiled for the Rigid Plastics Packaging Group (RPPG) of the Plastics Division of the American Chemistry Council (ACC) and available through the US LCI Database.106

3.3.2.5. Injection Molding

Injection molding is one of the primary fabrication techniques for rapidly creating large quantities of plastic articles ranging from disposable food containers to high precision engineering components. For this manufacturing process, plastic is fed by a rotating screw under high pressure into a mold that is the inverse shape of the desired product shape. The melted plastic solidifies when it comes into contact with the cooled wall of the mold. The mold opens and the finished part is ejected, completing the cycle. Injection molding data are based on primary data compiled for the Rigid Plastics Packaging Group (RPPG) of the Plastics Division of the American Chemistry Council (ACC) and available through the US LCI Database.107

3.4. NON-PLASTIC PACKAGING SYSTEMS