What are plastic bags made out of? A process called extrusion is the first step in making a plastic bag. The Norrköping site remains a plastics production site, however, and is now the headquarters of Miljösäck, a manufacturer of waste sacks manufactured from recycled polyethylene. Another blow molding technique is to injection mold an intermediate shape called a preform and then to heat the preform and blow the heat-softened plastic into the final shape in a chilled mold. Starch, obtained from corn or potatoes, can be converted into lactic acid, which can be polymerized to the biodegradable plastic known as polylactide.
Once the plastic bag is placed onto the spindle, it is sent to what is known as a conversion department. This team unwraps the film roll and cuts it with a heated knife that also seals each of the sides of the bags together. Once this is completed, the conversion also adds all of the special characters of the bag. Next, handles are cut out using a heat process, and logos, designs and text is added to the bag.
As you can see from the information above, creating plastic bags is a fairly simple and easy process that a company can do quickly and without a lot of trouble. Thousands of bags can be produced in only a minute of time, and since the process is so easy, it keeps the cost of the plastic bags down to an affordable price. Plastic bags are very easy to create and they have so many different purposes that make them handy in our everyday lives. Now that you know how the bags are created you can feel so much better about using them!
Bakelite was used to produce many items, including telephones, cameras, and even ashtrays. Although a key component in these items, plastics did not become really popular until after World War I, when petroleum, a more easily processed substance than coal, became readily available. Petroleum and natural gas are the primary sources of the key ingredients in plastic.
Plastics are composed of polymers--large molecules consisting of repeating units called monomers. In the case of plastic bags, the repeating units are ethylene, or ethene. When ethylene molecules are polymerized to form polyethylene, they form long chains of carbon atoms in which each carbon also is bonded to two hydrogen atoms. Many kinds of polyethylene can be made from ethylene. Plastic bags typically are made from one of three basic types: The major difference between these three materials is the degree of branching of the polymer chain.
Branching can influence a number of physical properties including tensile strength and crystallinity. The more branched a molecule is, the lower is its tensile strength and crystallinity. That's why garment bags from the dry cleaner are so weak and flimsy. They are made from highly branched LDPE. Another difference among these types of plastics is the method in which they are made. For a long time, Ziegler-Natta polymerization was the only way to produce linear unbranched polyethylene.
Teflon contains attached fluorine atoms. How the links in thermoplastics are arranged can also change the structure and properties of plastics. Some plastics are assembled from monomers such that there is intentional randomness in the occurrence of attached elements and chemical groups. Others have the attached groups occur in very predictable order.
Plastics will, if the structure allows, form crystals. Some plastics easily and rapidly form crystals, such as HDPE—high density polyethylene. HDPE can appear hazy from the crystals and exhibits stiffness and strength.
Other plastics are constructed such that they cannot fit together to form crystals, such as low density polyethylene, LDPE.
An amorphous plastic typically is clear in appearance. By adjusting the spatial arrangement of atoms on the backbone chains, the plastics manufacturer can change the performance properties of the plastic.
The chemical structure of the backbone, the use of copolymers, and the chemical binding of different elements and compounds to a backbone, and the use of crystallizability can change the processing, aesthetic, and performance properties of plastics.
The plastics can also be altered by the inclusion of additives. When plastics emerge from reactors, they may have the desired properties for a commercial product or not.
The inclusion of additives may impart to plastics specific properties. Some polymers incorporate additive during manufacture. Other polymers include additives during processing into their finished parts. Additives are incorporated into polymers to alter and improve basic mechanical, physical or chemical properties. Additives are also used to protect the polymer from the degrading effects of light, heat, or bacteria; to change such polymer processing properties such as melt flow; to provide product color; and to provide special characteristics such as improved surface appearance, reduced friction, and flame retardancy.
Thermosets are valued for their durability and strength and are used extensively in automobiles and construction including applications such as adhesives, inks, and coatings. The most common thermoset is the rubber truck and automobile tire.
Some examples of thermoset plastics and their product applications are:. A Thermoplastic is a polymer in which the molecules are held together by weak secondary bonding forces that soften when exposed to heat and return to its original condition when cooled back down to room temperature.
When a thermoplastic is softened by heat, it can then be shaped by extrusion, molding, or pressing. Ice cubes are common household items which exemplify the thermoplastic principle. Ice will melt when heated but readily solidifies when cooled.
Like a polymer, this process may be repeated numerous times. Thermoplastics offer versatility and a wide range of applications. They are commonly used in food packaging because they can be rapidly and economically formed into any shape needed to fulfill the packaging function. Examples include milk jugs and carbonated soft drink bottles. Other examples of thermoplastics are:. There are a variety of different processing methods used to convert polymers into finished products.
Extrusion - This continuous process is used to produce films, sheet, profiles, tubes, and pipes. Plastic material as granules, pellets, or powder, is first loaded into a hopper and then fed into a long heated chamber through which it is moved by the action of a continuously revolving screw.
The chamber is a cylinder and is referred to as an extruder. Extruders can have one or two revolving screws. The plastic is melted by the mechanical work of the screw and the heat from the extruder wall. At the end of the heated chamber, the molten plastic is forced out through a small opening called a die to form the shape of the finished product. As the plastic is extruded from the die, it is fed onto a conveyor belt for cooling or onto rollers for cooling or by immersion in water for cooling.
Examples of extruded products include lawn edging, pipe, film, coated paper, insulation on electrical wires, gutter and down spouting, plastic lumber, and window trim. Thermoplastics are processed by continuous extrusion.
Thermoset elastomer can be extruded into weatherstripping by adding catalysts to the rubber material as it is fed into the extruder. Calendering — This continuous process is an extension of film extrusion. The still warm extrudate is chilled on polished, cold rolls to create sheet from 0.
The thickness is well maintained and surface made smooth by the polished rollers. Calendering is used for high output and the ability to deal with low melt strength. Heavy polyethylene films used for construction vapor and liquid barriers are calendered. High volume PVC films are typically made using calendars. Film Blowing — This process continuously extrudes vertically a ring of semi-molten polymer in an upward direction, like a fountain. A bubble of air is maintained that stretches the plastic axially and radially into a tube many times the diameter of the ring.
The diameter of the tube depends on the plastic being processed and the processing conditions. The tube is cooled by air and is nipped and wound continuously as a flattened tube.
The tube can be processed to form saleable bags or slit to form rolls of film with thicknesses of 0. Multiple layers of different resins can be used to make the tube. Injection Molding - This process can produce intricate three-dimensional parts of high quality and great reproducibility. It is predominately used for thermoplastics but some thermosets and elastomers are also processed by injection molding.
In injection molding plastic material is fed into a hopper, which feeds into an extruder. An extruder screw pushes the plastic through the heating chamber in which the material is then melted.
At the end of the extruder the molten plastic is forced at high pressure into a closed cold mold. The high pressure is needed to be sure the mold is completely filled. Once the plastic cools to a solid, the mold opens and the finished product is ejected.
What are plastic bags made out of? "Plastic" refers to different materials made from carbon (which is usually drawn from petroleum), used in anything from milk jugs to vinyl jackets. Household products, including shopping bags, are typically printed with a number to make sorting and recycling easier. Plastic bags are made from crude oil, which is made into a hard or a soft material. Plastic bags have only existed for one generation. In this short time, their extreme convenience has made them widespread all aspects of life, making them the synonym of waste. Most plastic carrier bags are made from polyethylene, a kind of plastic. Polyethylene, or polythene as it is known in the UK comes in different forms. The top three used in bag manufacture are. High Density PolyEthylene – HDPE- is used to make supermarket type carrier bags.