Additives: Special Stabilizer Boosts Rate of Scrap Reused in Polyolefin Films

A special stabilizer intended for use with polyolefin film packaging of such fresh products as cookies and pasta is said to substantially boost the rate of scrap reused in the polyolefin film. Developed by Clariant’s Business Unit Additives (U.S. office in Charlotte, N.C.),   PKG 906 Circle is the latest addition to the company’s proprietary AddWorks additives.

The company notes that most plastic films are made by melting down pellets of PE or PP resin and casting or blowing them into large sheets and tubes, or using a special process to make biaxially oriented PP or PE (BOPP and BOPE, respectively). But some of the machines used, which actually resemble huge pasta rollers, collect manufacturing waste when films are slit and trimmed, or when production startups, shutdowns and changeovers create leftovers and off-spec material.

Clariant worked with a global film maker who was already grinding up and reusing some of this scrap – both for the sake of sustainability and costs. However, the addition of scrap affected the texture and quality of the films. The problem was that the leftover scrap had already been ‘baked’ during production, which degrades the polymer chains and networks. Add too much of this post-manufacturing waste to virgin resin, and the mixture will no longer flow properly. It can also develop gel streaks, black spots or break at high line speeds, and have a yellow tinge in the final product.

AddWorks PKG 906 Circle was shown to minimize these effects. Building on an existing solution from the AddWorks range, Clariant  additive experts created a polymer stabilizer that allows reintroducing reground scrap at a rate of 20% and higher into virgin PP and PE resins without notable loss in quality or process efficiency. The stabilizer additive consists of free-flowing white granules that are approved for food contact.

Similar to human cells, polymers are damaged when they form free radicals under heat, stress and oxidation – and AddWorks PKG 906 Circle catches these radicals and also prevents certain chemical alterations in other ways. An addition of 0.1% to 0.2% of this stabilizer has been shown to be enough to greatly reduce the risk of gels, spots and breakage, maintain high line speeds, and obtain clear, untainted product in the end.

Clariant tests showed this stabilizer even worked at scrap contents of up to 30%, and the additive also proved better at ensuring good melt flow of BOPP resins than similar products. While being particularly suited for BOPP films, AddWorks PKG 906 Circle also works with cast and blown film, and can easily be dosed to fit different scrap rates and resin qualities. It allows film makers to not only substantially reduce waste and use of virgin resin, but also to cut costs without compromising quality. Due to these benefits, the product is specially featured in Clariant’s new EcoCircle initiative, with which the company supports the shift to a circular plastics economy and is the first to carry the “Circle” designator, indicating advantages for reuse and recycling.