The numbers don’t lie. Increasingly, business owners are shifting away from traditional blown film packaging and choosing cast film instead. With improved efficiency and sustainability standards, cast film is used by around 70-80% of the industry globally.
Yes, the popularity of cast film may be enough to convince you to make the switch. However it’s worth understanding how these films are made too. In this way you can make an informed decision on which way to go…
Blown Film. This is the traditional way of producing film and takes its name from the process used to create it. Heated resin is blown through a circular die, and a thick layer of extruded film emerges as a large bubble. The bubble can be many feet tall – and it is this height that allows the film to gradually cool before rollers collapse the bubble and flatten the material for shaping onto rolls.
The very nature of blown film makes it a pre-stretched product, and the thickness of blown film is adjustable dependent on the diameter of the tube from which it comes.
Cast Film. Cast film is created by feeding a sheet of heated resin through a flat die. The molten material emerges from the die and out onto larger chilling rollers which cool and solidify the material. It is then ready for trimming and rolling.
Cast film is minimally pre-stretched compared with blown film giving it improved depth of drawing for thermoforming operations. The cooling process can be used to produce different characteristics in the final product. Cast film can be thinned by winding the film out of the roller faster than it is extruded.
There are likely to be many factors to consider when choosing which film to use. These may include the environmental conditions (is it cold or frozen?) storage and transportation processes, and what level of pre-stretch is needed. Here is a quick breakdown of the pros and cons of each type of film.
Blown Film
Has a higher resistance to puncture; preferred for wrapping sharp-edged products and heavy loads such as masonry and construction materials
Film offers less clarity due to crystallisation which occurs during manufacture
Has a high level of cling
Cast Film
Comes off the roll easily and is quieter than blown film
Often used for lighter products, and loads stacked on pallets
Very clear product making it easy to scan barcodes through the film
Requires less force to stretch
High tear resistance
How much energy is used to make a plastic bag?
The plastic carry bag is an established part of Australian shopping. The nation consumes approximately 6.9 billion plastic bags, or 36,850 tonnes of plastic, each year - this equates to just under one bag per person per day. About 53% of plastic bags are distributed from supermarkets, while 47% come from other retail outlets such as fast food shops, liquor stores, and general merchandising. One of the main methods of managing the use and disposal of plastic bags is the voluntary National Code of Practice for the Management of Plastic Retail Carry Bags (Australian Retailers Association 2002).
Plastic bags are popular with consumers and retailers because they are a functional, lightweight, strong, cheap, and hygienic way of transporting food and goods. Additionally, the manufacture of plastic bags uses little energy. However, research has shown that energy use and greenhouse gas emissions can be reduced by switching from the commonly used bags to larger, reusable bags, by expanding the Code, and introducing a levy. These options are discussed briefly below.
The two main types of plastic bags used in Australia are the 'singlet' bag made of high density polyethylene (HDPE) and the 'boutique' bag made of low density polyethylene (LDPE). The HDPE bags are mainly used in supermarkets and take-away food shops, whereas the LDPE are commonly used in department and fashion stores. In 2001-02, 66% (or four billion) of all HDPE bags and 25% (or 225 million) of all LDPE bags used in Australia were imported.
Around 0.48 megajoules (MJ) of energy is consumed to make one HDPE singlet bag including the energy content of the bag (the embodied energy). Another way of considering this is that the energy consumed by driving a car one kilometre is the equivalent of manufacturing 8.7 plastic bags (Nolan-ITU 2002).
By comparison, it is estimated that the making of a plastic bag uses up to 70% less energy and produces around half the greenhouse gas emissions than a paper bag (National Plastic Shopping Bags Working Group 2002). However, the amount of energy used and greenhouse gases emitted in the manufacture of plastic bags does not compare favourably to other alternatives, as shown in table S17.1. Over one year, using woven HDPE bags consumes 9% of the energy and produces 10% of the greenhouse gas emissions compared with using standard HDPE bags (Nolan-ITU 2002).
Further, modelling has shown that significant energy savings are possible with the introduction of a plastic bag levy. Under the current Code, plastic bag manufacturing uses 2,540 gigajoules (GJ) of energy per year. If the Code is expanded and a legislated levy of, say, 15 cents per bag is introduced, energy use could be cut by 54.9% (to 1,160 GJ a year). If a 25 cent levy was introduced, energy use could be reduced by over 60% (to 940 GJ per year; Nolan-ITU 2002).
