Smart Molding International 2-2025

30 smart_molding international 2/2025 molding technologies SACMI investigates the potential of PET caps SACMI has recently presented a comparative analysis and a new prototype of a 29 mm PET water cap, manufactured and tested on a pilot line Is it possible to produce a PET cap for beverage packaging at the current state of technological development? Should it replace HDPE (polyolefins), and under what conditions? Do the performance and functional characteristics align? But above all... Could this represent a genuine advantage in terms of total cost of ownership (TCO) and environmental sustainability? The new 29 mm PET cap for water In May, SACMI unveiled a 29 mm PET water cap. This standard was not selected at random — it's the most commonly used opening worldwide for this category of beverage. The cap features segmented, hinged flaps at the base of the band for easier application; a segmented thread for simpler moulding and opening, reducing removal torque; and an ogive plug to ensure a proper seal. Produced on a CCM press with a cycle time of 2.7 seconds, the cap is fully transparent and performs comparably to an HDPE cap at room temperature. The subsequent processing stages, such as cutting and folding, also show good stability and repeatability at the experimental level. PET cap and HDPE cap: advantages and disadvantages The cap is a key component of the packaging, forming the first point of contact between the consumer and the product. The cap is responsible for the sealing and, consequently, the safety and freshness of the contents. In terms of chemical and physical properties, polyolefins have proven particularly well-suited to this type of application. All beverage caps are currently made from polyolefins — primarily HDPE — which is highly efficient from both an economic and environmental perspective. In fact, over the past two decades, the main drivers have been reducing virgin resin consumption (with a reduction of more than 50% in total weight between cap and relative opening) and energy use. More recently, the cap2cap recycling chain has begun to emerge on some markets. From a recycling standpoint, separating HDPE (used for caps) from PET (used for bottles) is relatively straightforward and cost-effective: by grinding the materials, HDPE floats away from PET, enabling the recovery and reuse of both materials. In terms of production, it should be noted that PET may require a cycle time over 70% longer than HDPE, and—under the same conditions — the cap may be heavier than its polyolefin counterpart. So, why switch to PET? This would create mono-material packaging, thereby increasing the PET yield during the recycling process. In addition, PET caps are transparent, offering a more aesthetically pleasing appearance. Performance, technological and process challenges SACMI’s project centres on the chemical and physical properties of PET, cap performance, and the economic and environmental impact of the same. Compared to HDPE, PET presents some significant challenges: chief among them are its amorphous structure and hygroscopic nature, which together cause the material to deform under stress (despite PET’s theoretically superior mechanical properties). A detailed comparison of the two materials helps define the "process window", highlight relative differences, and assess cost implications. • PET has a density approximately 40% higher than HDPE;