Bio-based alternative to petrochemical unsaturated polyester resins

For the first time, Schill + Seilacher offers an unsaturated polyester resin in industrial scale, based on more than 99 % bio-based raw materials

Unsaturated polyester resins (UPR) are among the most important resins in the field of fiber reinforced polymer composites (FRPC). This is founded on their favourable price, their good processing properties and their possibility to adapt the material properties. UPR are processed on a polycondensation reaction of carboxylic acids and alcohols. So far, the use of bio-based raw materials in UPR failed due to price requirements.

For the first time, the business unit Reactive Polymers and Flame Retardants of Schill + Seilacher “Struktol” GmbH succeeded in processing a bio-based polyester resin in industrial scale and favourable price, which is based for more than 99 % on bio-based raw materials. This is faciliated on a corresponding selection of raw materials and a decreased price of these. Brand name of this resin is Polyvertec 3830. Schill + Seilacher received positive feedback from the end consumer market (automotive, transportation, horticulture and agriculture). In these fields of application, an annual growing rate of 21 % to 27.9 billion USD within the next five years in the field of bio-based resin systems is expected.

Polyvertec 3830 offers the possibility for far-reaching customization. With a change in styrene content (reactive diluent) of 0 to 40 wt.-%, the viscosity of the resin system can be adapted from 260 to 1 Pa∙s. Current research activities target at the use of bio-based reactive diluents, though, their application is not feasible yet. Customer specific systems with longer or shorter processing times can be realised using different accelerators and hardener systems. Styrene content also has tremendous influence to the achievable mechanical properties. With a styrene content of 20 to 30 wt.-%, Polyvertec 3830 achieves a bending modulus > 2500 MPa and a bending strength > 65 MPa (according to DIN EN ISO 14125). With increasing content of styrene, glass transition temperature increases to a maximum of 180 °C at 40 wt.-% styrene.

First test series showed the practicality of the resin system. In combination with natural fibers Polyvertec 3830 was processed to furniture and writing devices (see fig. 1). Furthermore, natural fiber organic sheets were produced in hand lay-up process (see fig. 2). Those samples reached 2/3 of the mechanical properties – at same fiber mass content – as organic sheets based on epoxy resin.

Leibniz-Institut für Verbundwerkstoffe used Polyvertec 3830 resin system in a Sheet Molding Compound (see fig. 3). After adapting the recipe, Polyvertec 3830 could be processed to a SMC semi-finished material and demonstrator parts under conventional SMC process parameters. At same fiber mass content, Polyvertec 3830-SMC achieves same mechanical properties as SMC materials consisting of petrochemical unsaturated polyester resins. The biggest difference is the thickening effect of the material: thickening process for conventional SMC semi-finished materials takes four to six days, whereas Polyvertec 3830-SMC semi-finished products need up to fourteen days.

Based on these results, Schill + Seilacher is currently working on an adapted version of the resin system which allows faster thickening via magnesium oxide. Furthermore, the use of bio-based reactive diluents will be investigated.

Contact:
Dr.-Ing. Florian Gortner
Press & Joining Technologies
Leibniz-Institut für Verbundwerkstoffe GmbH
Erwin-Schrödinger-Straße 58
67663 Kaiserslautern
Telephone: +49 631 2017-439
E-Mail: florian.gortner@ivw.uni-kl.de