Nataša Čuk, Miha Steinbücher, Nejc Vidmar, Martin Ocepek,
Peter Venturini – HELIOS RESINS
In Helios Resins different activities are going on towards producing more sustainable resins. The company produces intrinsic bio-based alkyds, high-solid resins, water-based resins and BPA-free resins for food packaging. Using recycled and new bio-based raw materials, Helios Resins participates as a partner in various European initiatives.
In this study, a new development of 100% bio-based and solvent-free polyester resin is presented, which can be used as a drop-in replacement for one of the commercially polyester. Novel resin is intended to be used in two-component polyurethane coatings for metal surfaces. This resin exhibits properties such as high gloss and UV light, heat and weathering resistance and can be used as such or in combination with hydroxyl acrylic resins to increase solids content in industrial finishes, protective coatings and plastic coatings.
There are two main approaches when introducing a bio-based raw material: a) conventional substance is substituted with bio-based alternative, for example terephthalic acid can be replaced with 2,5-furandicarboxylic acid, and b) so-called drop-in approach where fossil-fuel derived raw material is substituted with the chemically identical substance which is derived from biomass, for example fossil-based adipic acid can be replaced with adipic acid derived from biomass. In addition, biomass balance approach according to ISCC PLUS (International Sustainability and Carbon Certification) certification can be used. Since 2021 our company is ISCC PLUS certified and the mass balance approach is used for raw materials such as glycols, (meth)acrylates and isocyanates.
In this research, a fully bio-based version of fossil-based polyester polyol was successfully synthesized to be used in combination with acrylic polyol for high solid two-component polyurethane protective coatings for metal surfaces. 
Tab. 1 – Properties of fossil-based (Domopol 6046) and bio-based (Domopol 7046) polyester polyo
Domopol 6046 which is HeliosResins’ commercial product was used as a reference and compared to newly developed bio-based polyester polyol Domopol 7046 where synthetic raw materials were replaced with bio-based alternatives. The bio-based raw materials used in this work are already being produced on a large scale and were obtained from commercially available sources.
Fig. 1 – Appearance of fossil-based (Domopol 6046) and
bio-based (Domopol 7046) polyester polyols
Properties of polyester polyols were determined and measured. They were characterized by the determination of acid number, hydroxyl number and glass transition temperature; and measurement of viscosity, colour and molecular weight. The results are presented in Table 1 together with the standard requirements for Domopol 6046. The appearance of the materials is presented in Figure 1. It is clear from the presented data, the materials are a very close match and fulfill same specifications.
As the polyester polyols in question are primarily meant as a modifier of acrylic polyols we tested their basic mechanical and optical properties in high-solids two-component polyurethane top coat aimed for the ACE segment. The formulations were based on Domacryl 5845 and either of Domopol 6046 or Domopol 7046, without use of any HALS and/or UV-absorbers. The coatings were produced in RAL 7005 shade with total solids content of 72.6 % (w/w).
Tab. 2 – Wet and dry film properties of top coats based on
Domacryl 5485 and Domopol 6046 or Domopol 7046
The difference between the coatings viscosity was well within the error of measurements. Both materials were applied by means of air-spraying to cathodic epoxy e-coat Elecron LB-400 (Kansai Helios) primed zinc phosphated CRS panels and tested with standard methods for ACE coatings. The results of basic testing of both, wet and dry film properties, of both coatings are presented in Table 2.
Comparison show no significant difference between the coatings. One of the most important, if not the most important property of a top-coat, is its weathering resistance. The coatings were exposed to Xenon artificial weathering according to ISO 16474-2, Method A, cycle no. 1. The results are presented in Table 3.
Tab. 3 – Gloss retention and color change after 504, 1008, 1512 and 2016 h Xenon exposure according to ISO 16474-2, Method A, cycle no. 1 of top coats based on Domacryl 5485 and Domopol 6046 or Domopol 7046
The data clearly shows no practical difference between the tested coatings and shows their remarkable weathering resistance, even with omission of both HALS and UV-absorbers. Eventhough top-coat is not the primary corrosion resistance determining layer in the system, neutral salt spray test and water condensation tests were performed. No defects were observed after 1008 h of water condensation tests. After 1008 h of neutral salt spray tests, both coatings show 1 mm delamination along the scribe and 0.5 mm corrosion along the scribe with no other defects. The chemical resistance of the materials was tested by a spot method with exposure times denoted in brackets. The following media was used: unleaded gasoline (6 h), diesel fuel (6 h), 50% aqueous solution of an antifreeze (6 h), 2-propanol (1 h), grease (24 h) and 10W30 motor oil (24 h). The results were determined immediately after exposure and show no degradation in all cases.
The company can safely conclude that the newly developed fully bio-based Domopol 7046 is a drop-in replacement for the established petrol based Domopol 6046. Both polyester polyols enable production of very high performance high-solids polyurethane coatings. Domopol 7046 enables a significant decrease of carbon footprint of the coatings.
