Corrugated plastic, often known by the brand name Coroplast, is a versatile product sometimes called twin-wall plastic or plastic cardboard, reflecting its structural similarity to corrugated fiberboard. Its widespread use stems from its balance of being lightweight and having inherent resistance to moisture and many chemicals.
The Core Material: Polypropylene
Corrugated plastic is constructed from polypropylene (PP) resin, a thermoplastic polymer derived from the monomer propylene. Polypropylene is chosen for this application because of its mechanical and chemical properties. It is classified as a semi-crystalline plastic, giving it a high melting point, typically between 160°C and 180°C, which makes it suitable for various environments.
The material is naturally resistant to moisture, oils, solvents, and acids, preventing it from degrading in harsh conditions or outdoor use. Polypropylene is significantly stiffer and more rigid than polyethylene (PE), allowing it to function effectively as a structural sheet that maintains its shape. It is also non-toxic, contributing to its use in packaging.
Understanding the Structure: Flutes and Walls
The term “corrugated” refers to the specific internal geometry of the sheet. The material features a twin-wall structure, consisting of two smooth, flat outer layers of plastic held apart by a series of parallel, vertical ribs. These internal ribs are known as flutes, creating channels that run the length of the sheet.
This fluted design is structurally analogous to an I-beam, allowing the sheet to resist bending and compression forces far better than a solid, flat piece of the same thickness and weight. The air trapped within these flutes serves as an insulator, offering a degree of thermal and acoustic dampening. This twin-wall construction provides the necessary rigidity, impact resistance, and durability while remaining lightweight.
Manufacturing Process and Additives
The production of corrugated plastic is achieved through a high-volume process known as extrusion. This process begins by feeding polypropylene resin pellets into a machine, where they are melted and homogenized under precise temperature control. The molten plastic is then forced through a specialized die shaped to form the continuous twin-wall profile, including the parallel flutes.
As the newly formed sheet exits the die, it is rapidly cooled and sized to lock in the intended dimensions and ensure a uniform structure. This continuous process creates a sheet with a fixed cross-sectional profile that is then cut to length. Additives are frequently blended into the resin mixture before extrusion to customize the final product. These modifications include UV stabilizers to prevent degradation from sunlight, colorants for aesthetic purposes, or flame retardants to meet safety standards.
Common Applications and Recyclability
The material’s weather resistance and printability make it the primary choice for temporary outdoor signage, such as yard signs and real estate advertisements. In construction, it is utilized as lightweight, protective sheeting for floors, walls, and countertops during renovation projects.
Its durability and light weight also make it ideal for packaging, particularly for reusable totes, dividers, and boxes in industrial and automotive supply chains. Corrugated plastic is a single-material plastic, coded with the resin identification number 5 (for polypropylene). While the material can be shredded and re-pelletized to create new plastic goods, its bulkiness often means that local curbside recycling programs do not accept it, requiring specialized facilities.