14 Jan 2020

ETHACURE® 300 – the safe alter­native to MOCA

MOCA may still be used today as a crosslinker in polyurethane (PU) elastomers with special approval, but new legislation has called for an end to its distribution. Nordmann partner Albemarle Corporation supplies an alternative that gives PU elastomer systems higher flexibility as well as other attractive properties.

In November 2011, MOCA was defined by the International Agency for Research on Cancer (IARC) as a Class 1 carcinogen and classified as “a substance of very high concern” (SVHC) in the EU REACh Regulation. As a consequence, the trade of MOCA has required special approval from the European Commission ever since November 2017 and will be discontinued as of the year 2021.

A Safer Option for Users

ETHACURE 300 is a low toxicity, easy-to-handle liquid aromatic diamine widely known for its superior properties and extreme versatility in the polyurethane industry.

Polyurethane elastomers cured with E300 have demonstrated a broad range of properties such as high strength, hardness, modulus, and elongation at break point.

E300 formulated with TDI based prepolymers in cast elastomer delivers moderate reactivity, suitable working time, and ideal mechanical properties, making it an ideal alternative for MOCA users.

History of Proven Performance

Polyurethane elastomers cured with E300 have been proven to deliver similar performance to MOCA cured parts. In Figure 1,  at a 0.85 and 0.95 amine/iso ratio the split tear strength for E300 cured parts exhibit superior performance to MOCA parts. E300 tensile strength and elongation also both closely match MOCA performance. While MOCA cured parts have a minimally higher hardness at these ratios, E300 part hardness is competitive when optimization strategies outlined in the following sections are implemented.

Superior Thermal Aging Performance Compared to MOCA

Figure 2: E300 vs. MOCA Thermal Aging
  • In Figure 2, E300 and MOCA TDI systems were formulated using an amine/iso ratio of 0.95, and mold temperature of 100°C. Demolding took place after 1/2 hour, and then parts were post-cured at 100°C for 2 hours.
  • E300 cured systems demonstrated exceptional performance over MOCA cured polymers after exposure to high temperature over an extended period of time.
  • Tensile strength increases approximately 50% in the systems containing E300 during exposure. Whereas, MOCA-cured systems show general declines in tensile strength. After 50 days at 100 °C, MOCA parts exhibit less than half of original tensile strength.
     

Performance Optimization - Adjusting amine/iso ratio

Optimization is key to maximizing the potential benefits E300 offers formulators when utilized in systems.

When formulating, it is important to select the appropriate amine/iso ratio to generate performance characteristics that best meet user’s needs. Altering the amine/iso ratio is an advantageous modification that should be taken into consideration to improve part performance.

In Figure 3, using 4.1 % NCO TDI-PTMEG prepolymer it was demonstrated that E300 parts perform at optimal levels when an amine/iso ratio of 0.95 is used. This ratio gives the best balance of performance. Evaluations also showed that compression set is increased when a lower ratio is used.

Figure 3: Effect of Amine/Iso Ratio on E300 Elastomer Performance

Performance Optimization - Adjusting post-cure

A direct and powerful way to alter part performance is to adjust post-cure conditions. By Increasing the time and temperature of the post-cure, E300/TDI polymer performance is greatly increased, particularity tensile, tear, and compression strength. These performance characteristics are displayed in Figure 4.

Figure 4: Effect of Post-cure Conditions on Elastomers Cured with E300

Performance Optimization - Adjusting NCO content and temperature

Modifying the % NCO of a prepolymer allows formulators to control reaction speeds, as well as increase the hardness of E300 parts.  In Figure 5, increasing the % NCO from 4.05 % to 5.25 % caused hardness of the elastomer to increase from an 88 Shore A to an 91 Shore A. Utilizing a high % NCO prepolymer is also beneficial because it increases other polymer properties such as tensile, modulus, and tear strength.

E300 being a liquid at room temperature allows users to adjust prepolymer temperature processing. This adjustment is directly related to formulation pot-life.

Figure 5: Effect of NCO% on Elastomers Cured with ETHACURE 300

In Figure 6, E300/TDI systems were used to demonstrate that a 15 °C drop in prepolymer temperature nearly doubles the working time for formulators. During evaluation, when a 9.5 % NCO was used the pot-life is roughly 2 minutes at 80 °C. When the temperature is adjusted to 65 °C the pot-life doubles to 4 minutes. This trend repeats for prepolymers of lower NCO%.

Figure 6: Effect of Temperature on Pot-Life of E300 Systems