A yogurt cup, a carton of milk, and maybe even a bag of chips are three common products at the supermarket. While they contain different kinds of foodstuffs, all three items are confined within practical packaging that helps protect their freshness until they safely reach your hands. Little did you know that these three products are made from the same material: polypropylene.
Polypropylene (PP) is a commonly used thermoplastic material used to pack food, medicine, automotive, textile, and other various products. It is created by chemically combining propylene monomers into a chain-like sequence using a process called polymerization. This method is the reason why PP film has its unique physical properties.
So, how are packaging films made from polypropylene processed? How does it conform to the strict food regulations and standards without compromising the quality and price of the final product?
Arlene, PT Argha Karya Prima Industry Tbk's PP film product
From Polymer to Packaging
According to the patented process by Huang Hwang-Wen, PP films are made using homopolymers, random and block copolymers of propylene, and other olefins. Other additives such as acid acceptors, heat stabilizers, antioxidants, antistatic agents, colorants, and so forth are later added to increase the material’s strength. These materials are introduced into the extruders before they are melted and heated at 200-230°C.
After these polymers have properly melted, they are fed into the extrusion head where they will emerge as foil. The foil is cooled by rolling them on a chilled cylinder and submerging them in a water bath. Then they are stretched using multiple rollers that spin at increasing speeds and multiple temperatures.
Increasing PP Film Strength: Biaxial Orientation
To increase the packaging’s barrier properties and strength, PP films are then processed using a method known as biaxial stretching. This process helps align the polymer molecules in particular directions before it is frozen in place to quench their molten state. Stretching films using this technique will allow them to be highly tensile, have great gloss and clarity, be flex-crack resistant, oil and grease resistant, water vapor resistant, and will not wrinkle or shrink easily.
The biaxial stretching process is done by stretching the film in machine direction (MD), which means the film flows through the machine from start to finish, and the transverse direction (TD). In the same paper, DeMeuse explains two different biaxial orientations: sequential and simultaneous. In the sequential process, films are crystalized through the MD step before temperatures rise and the films are stretched using the TD step. Thanks to the different stretch ratio, this process yields a film with different physical properties.
On the other hand, in the simultaneous process, the film is stretched at the same time in MD and TD in a single step. This process will stretch the films in equal ratios, resulting in films with similar physical properties and a balanced quality.
Read more about Advantages of Metalized Film for Food Packaging
In conclusion, PP films used for packaging have to undergo a meticulous process that allows them to be thin, transparent, and strong. These processes have proven to optimize the film's ability to protect food products during transportation and keep them fresh for a longer time. For more information on biaxially oriented PP films for your food products, visit PT Argha Karya Prima Industry Tbk (https://arghakarya.com).
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