Bio-Resin: A comparison of bio-based casting resins

Bio-resins – bio-based casting resins – replace some petroleum-based raw materials with plant-based resources such as vegetable oils, cashew nut shells, or tree resins. The market for sustainable resin systems is growing rapidly, particularly in the arts and crafts sector (resin art, river tables), but also in technical applications such as composites and mold making. This guide explains the different types of bio-resins, compares them with conventional resins, and helps you choose the right system.

SILITECH bio-resin range: Biothan & Biodur

SILITECH AG markets a comprehensive range of bio-based polyurethane casting resins from the German manufacturer Bioresin Products under the SILIRESIN brand. The system consists of Biothan resins (component A) and Biodur hardeners (component B). All products are based on renewable raw materials and are non-toxic.

Biothan – Bio-based PU casting resins (Component A)

Biothane resins are divided into different application groups:

Bio-resin in technical applications

Composite manufacturing and boat building

Surfboard and boat manufacturing were among the first sectors to use bio-resins commercially. Sicomin (GreenPoxy) and Entropy Resins (Super Sap) were specifically developed for fiberglass and carbon fiber laminates.

Advantages of composite construction:

• Fiber wetting and impregnation behavior comparable to conventional systems
• Infusion and vacuum procedures possible
• Reduced styrene gas content in bio-polyesters
• Marketing advantage: "Green" label for the final product

Mold making

Bio-epoxy resins are suitable for mold making, particularly for prototypes and small production runs. The slightly lower glass transition temperature should be taken into account when molds are used for hot curing processes.

Processing bio-resin: Practical tips

The processing of bio-resins is largely identical to conventional resin systems. Some special features:

Mix

• Adhere to the exact mixing ratio (typically 2:1 or 100:45 by weight)
• Stir thoroughly for at least 3–5 minutes
• Repot and mix again for bubble-free results
• Processing temperature: 20–25 °C ideal

Pour

• Pour thinly and build up in layers if the pouring depth is >2 cm (unless using a deep-pour system)
• Remove bubbles with a hot air gun or gas torch (briefly and carefully)
• Dust-free environment for clean surfaces
• Apply release agent to the mold (silicone oil or wax)

Curing

• Room temperature curing: 24–72 hours (depending on the system)
• Post-curing at 60–80 °C improves Tg and mechanical properties by 20–30%
• Avoid curing below 15 °C (significantly extends curing time, can lead to cloudy results)

Buying bio-resin: What to look out for?

The market for bio-resins is confusing. Pay attention to the following points:

1. Bio-based share (%)

Reputable manufacturers specify the bio-based carbon content according to ASTM D6866. Values ​​of 20–56% are realistic. Products claiming to be "100% bio" or "completely natural" should be critically examined – a fully bio-based, high-performance casting resin does not currently exist.

2. Certifications

• USDA BioPreferred: US standard for bio-based products
• ASTM D6866: Measurement of bio-based carbon content via radiocarbon method
• ISO 16620: International standard for bio-based plastics

3. Intended Use

• Deep Pour Resin: Low exothermicity, high pouring height
• Laminating resin: Low viscosity, good fiber wetting
• Coating resin: Self-leveling, UV-stable
• Structural casting resin: High mechanical strength, defined Tg

4. Price-performance ratio

Bio-resins typically cost 20–50% more than conventional resins. For art and hobby applications, this price difference is less significant (small quantities). For large industrial quantities, however, the price difference can be substantial.

Frequently Asked Questions (FAQ)

Is bio-resin biodegradable?

No. Cured bio-resin is a thermoset and behaves like conventional epoxy or polyester resin. It does not decompose under normal environmental conditions. "Bio" refers to the raw material base (plant-based), not to disposal.

Is bio-resin as strong as regular epoxy resin?

Largely yes. Mechanical properties typically reach 90–95% of conventional resins. The glass transition temperature (Tg) may be somewhat lower (50–80 °C vs. 60–120 °C), which limits the maximum operating temperature. For most art and hobby applications, this is not a disadvantage.

Can I use bio-resin for river tables?

Yes, there are special deep-pour bio-resins with low exothermicity that allow pouring heights of 5–10 cm per layer. Make sure to choose a system with low exothermicity (low heat generation) to avoid cracking and yellowing with large pour volumes.

What is the actual organic content?

Typically, 20–56% of the carbon content is bio-based (measured according to ASTM D6866). The remaining 44–80% still comes from petrochemical sources. A 100% bio-based high-performance casting resin does not currently exist.

Can I color bio-resin with regular pigments?

Yes. Bio-resins are compatible with standard resin pigments (epoxy pigment pastes, mica powders, alcohol inks). Processing is identical to conventional systems.

Where can I buy bio-resin in Switzerland?