Copolyesters are formed when modifications are made to polyesters. These modifications can considerably modify the performance profile of the polyester in question. Case in point: PEIT.
Polyethylene terephthalate, or PET, as this polyester is more familiarly called consists of the two main building blocs ethylene glycol and terephthalic acid, which are then combined to form a polymer chain. Strong and food-safe, PET has become one of the mainstay materials of the packaging industry and is used in everything from bottles and trays to blisters and clamshells.
There are, however, areas where the material performs less well. A good example is in hot-fill applications. Marked improvement can be achieved through the incorporation of an alternative comonomer, which modifies the performance profile of the material. More specifically, it has long been known that replacing the monoethylene glycol as a diol with isosorbide benefi- cially modifies the properties of PET, boosting, among other things, its glass transition temperature and the optical properties of finished packaging. Ethylene glycol is still predominantly a petrochemical feedstock so (partial) substitution by plant-based isosorbide is also potentially appealing from the perspective of the material’s environmental impact.
Isosorbide – what is it?
“Isosorbide is a really versatile, safe, environmentally benign performance chemical with great potential as a co-monomer,” said Bruno Plancke, head of Global BU Industry, at Roquette, the France-based leading producer worldwide of plant-based ingredients such as isosorbide for the performance plastics and chemistry markets.
Isosorbide is produced from annually renewable plant feedstocks by a process of sequential hydrolysis and hydrogenation. Hydrolysis converts plant starches to glucose which are subsequently converted to sorbitol; the hydrogenation of sorbitol to isosorbide is the final step. Isosorbide production technology has been optimised over the last two decades, to minimise carbon footprint and deliver consistently high purity.
Since starting production at a modest scale in 2002 in Lestrem, France, Roquette has continued to expand its isosorbide activities. Today, the company operates a large-scale production facility at its Lestrem site, using its patented sorbitol-based process to produce isosorbide which is marketed under the brand name Poly- sorb. The different purification steps in the production process produce isosorbide grades of very high purity—over 99.5% isosorbide content—which enables Roquette to comply with all quality requirements of its customers, as well as to support the development of innovative high-performance solutions for the global plastics and chemistry industry. Its Polysorb is a REACH compliant, non-toxic, non-endocrine disrupting, valuable feedstock for multiple applications; moreover, it is suitable for food contact, and compatible with cosmetic and pharmaceutical requirements.
Previously, the availability of a consistent supply of high-purity isosorbide tended to be uncertain, but now, having successfully put a reliable, high purity industrial-scale are free to exploit its full potential, said Plancke.