It is a costly material compared with other bottle-making polymers, so its use is restricted primarily to high-end reusable bottles such as nursing bottles or those found on water coolers or in lab settings. Polycarbonates are manufactured by polymerization of bisphenol A (C 15H 16O 2) and phosgene (COCl 2). Its low viscosity at melt temperatures makes it well suited to extrusion and molding applications, including blow molding.įor more information about PP, please see our polypropylene resins article. Polypropylene cannot match the optical clarity of polymers such as polycarbonate, but it does quite well. For bottles, It competes primarily against polyethylene and can be made transparent for see-through applications, while polyethylene can only be made translucent, as in milk jugs, for example. Polypropylene resin is a usually opaque, low-density polymer with excellent thermoforming and injection molding characteristics. Polyethylene is more expensive than polypropylene – the cheapest of the thermoplastics – though the two share many applications.įor more information about HDPE, please see our polyethylene resins article. LDPE is amorphous while HDPE is crystalline which accounts for LDPE’s greater ductility and HDPE’s higher rigidity. Polyethylene is composed of a single monomer, ethylene, making it a homopolymer. Suppliers can adjust formulation to increase tear strength, transparency, formability, printability, or other parameters. The material in its natural form is usually white or black and becomes translucent when thinned to the dimensions of milk bottles and the like. HDPE is used for many forms of pourable bottles. LDPE was one of the first plastics to be blow molded and today it is still used for making squeezable bottles, as it has high ductility compared with HDPE, but lower strength. Both LDPE and HDPE can be thermoformed, blow-molded, injection-molded, etc. LDPE/HDPE (Low- and High-Density Polyethylene)Īnother thermoplastic, polyethylene is used for manufacturing blow-molded milk and water jugs, detergent bottles, ketchup bottles, spray bottles, and other products. Other factors, such as transparency, gloss, shatter resistance, thickness, and pressure resistance, are also carefully monitored.įor more information about PET, please see our polyester resins article. To ensure that the plastic is appropriate for use, numerous tests are done post-manufacturing to check that the bottles are impermeable by carbon dioxide (which is important for bottles that carry soda). Once the plastic itself has been manufactured, the PET bottle manufacturing process can begin. A large amount of acetaldehyde in PET used for bottle manufacturing can give the beverage inside an odd taste. Although diethylene glycol is generally not produced in high enough amounts to affect PET, acetaldehyde can not only be produced during polymerization but also during the bottle manufacturing process. Typically, two kinds of impurities are produced during polymerization: diethylene glycol and acetaldehyde. Polymerization itself can be a complicated process and accounts for many of the inconsistencies between one batch of manufactured PET and another. The PET is polymerized to create long molecular chains, which allows it to produce PET bottles later on. As with most plastics, PET is produced from petroleum hydrocarbons, through a reaction between ethylene glycol and terephthalic acid.
Polyethylene Terephthalate is a thermoplastic polymer that can be either opaque or transparent, depending on the exact material composition. We'll be examining how each material affects the bottle manufacturing process below. PE is often referred to as LDPE (Low-Density Polyethylene) or HDPE (High-Density Polyethylene). What are Plastic Bottles Made of?Īs mentioned above, plastic bottles are commonly made of PET, PP, PC, and PE. You can also learn more about how glass bottles are made and types of glass bottles in our other guides. To understand the manufacturing process, it is helpful to first examine the compositions of the materials they're made from. Polycarbonate (PC) is used for refillable water bottles and similar reusable containers. Polypropylene (PP) is used for pill bottles and the like. Polyethylene (PE) in its high-density form is used for making rigid plastic bottles such as detergent bottles and in its low-density form for making squeeze bottles. Typically, the plastic bottles used to hold potable water and other drinks are made from polyethylene terephthalate (PET), because the material is both strong and light. Plastic bottle manufacturers generally use one of four types of plastic to create bottles. Plastic bottle manufacturing takes place in stages.
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