Disposable Straw

Plastic compounding
The polypropylene resin must first be mixed with the plasticizers, colorants, antioxidants, stabilizers, and fillers. These materials, in powder form, are dumped into the hopper of an extrusion compounder that mixes, melts, and forms beads of the blended plastic. This machine can be thought of as a long, heated, motor driven meat grinder. The powders are mixed together and melted as they travel down the barrel of the extruder. Special feeder screws are used to push the powder along its path. The molten plastic mixture is squeezed out through a series of small holes at the other end of the extruder. The holes shape the plastic into thin strands about 0.125 inch (0.3175 cm) in diameter. One compounding method ejects these strands into cooling water where a series of rotating knives cut them into short pellets. The pellet shape is preferred for subsequent molding operations because pellets are easier to move than a fine powder. These pellets are then collected and dried; they may be further blended or coated with other additives before packaging. The finished plastic pellets are stored until they are ready to be molded into straws.

Straw extrusion
The pellets are transferred to another extrusion molder. The second extruder is fitted with a different type of die, which produces a hollow tube shape. The pellets are dumped in a hopper on one end of the machine and are forced through a long channel by a screw mechanism. This screw is turned in the barrel with power supplied by a motor operating through a gear reducer. As the screw rotates, it moves the resin down the barrel. As the resin travels down the heated channel, it melts and becomes more flowable. To ensure good movement and heat transfer, the screw fits within the barrel with only few thousands of an inch clearance. It is machined from a solid steel rod, and the surfaces almost touching the barrel are hardened to resist wear. By the time the resin reaches the end of the barrel, it is completely melted and can be easily forced out through the opening in the die.

The resin exits the die in a long string in the shape of a straw. It is then moved along by a piece of equipment known as a puller which helps maintain the shape of the straw as it is moved through the rest of the manufacturing process. In some processes, it is necessary to pull the straw through special sizing plates to better control the diameter. These plates are essentially metal sheets with holes drilled in them. Eventually, this elongated tube is directed through a cooling stage—usually a water bath. Some operations run the plastic over a chilled metal rod, called a mandrel, which freezes the internal dimension of the straw to that of the rod. Ultimately, the long tubes are cut to the proper length by a knife assembly.

Packaging
Straws are typically packaged in individual paper sleeves after manufacturing. This packaging is widely used for applications where each straw must be kept sanitary. One method of packaging involves loading the finished straws into a supply funnel. At the bottom of the hopper is a wheel with straw receiving grooves cut in it around its outer edge. The straws drop out of the hopper and are picked up one at a time by this rotating wheel. As the wheel rotates, it moves the straws along to a second wheel, which has grooves connecting to a vacuum source. Sheets or packaging material (paper wrap) are moved onto this wheel from a supply roller. The vacuum holds the paper in place while the main wheel feeds straws on top of the paper. Another layer of paper is guided over the first and the assembly then passes through a sealing roller. The two layers of paper are then crimped together with the application of pressure or otherwise sealed together. The sealed sheet of straws then travels along the conveyor to a punching region where a die presses down and cuts out individual flexible grooves can be cut into the straws in a two step process. As the straws rest in slots, they are gripped by a pair of semi-circular steel jaws, which crimp a series of rings into the straw. The die cut pieces then move along a conveyor to a collection area. The individual straws can then be bundled together and packed in boxes or pouches for shipping.