Introduction: One-component waterborne wood coatings are easy to apply and affordable, but hardness and chemical resistance are often unsatisfactory. How can simple “external crosslinking” raise performance? This report uses measured data to show what aziridine crosslinkers do well, and where they fall short.

01 Why Is a Crosslinker Needed?

One-component waterborne acrylic wood lacquers hold a large market share, but wood cannot be baked at high temperature and can only be crosslinked at room temperature. Many emulsions include “self-crosslinking”, but only to a limited degree.

An external crosslinker is an effective way to raise film performance further. Aziridine compounds react with carboxyl groups in waterborne acrylic resins and form a network at room temperature, which improves the coating.

Structural formula of the aziridine crosslinker:

02 How Was the Experiment Run?

The study used three waterborne acrylic emulsions with different minimum film-forming temperatures (MFFT) — A1, B1 and C1 — and added an aziridine crosslinker.

Table 1 Basic properties of the three waterborne acrylic emulsions

The crosslinker was added at 0%, 0.5%, 1%, 1.5%, 2%, 2.5% and 3% of the solid resin weight, and the change in each film property was then tested.

03 Key Finding: The Crosslinker Cuts Both Ways

The results show that an aziridine crosslinker does not improve every property. It has clear strengths and clear limits.

✅ Strength 1: Blocking resistance rises sharply (the standout benefit)
Waterborne acrylic coatings tend to re-tack in summer, a serious problem for wood lacquers. After the crosslinker was added, blocking resistance improved markedly:
At 1% addition, the two A1 coated panels did not block at all.
At 3% addition, B1 and C1 also separated on their own.

Conclusion: The crosslinker overcomes the poor blocking resistance of waterborne acrylic coatings.

✅ Strength 2: Alcohol resistance improves markedly
Alcohol resistance matters on wood surfaces that often come into contact with alcohol.
As the crosslinker level rises, swelling of the film in ethanol falls clearly.
Ethanol rub resistance increases sharply. C1 withstood only 25 rubs with no crosslinker, but stayed intact after 100 rubs at 2.5% addition, with no change in gloss.

❌ Limitation: A negative effect on strong-alkali resistance
One important warning from the experiment:
In 2% sodium hydroxide solution, swelling of all three acrylic films rose as the crosslinker level increased.

Conclusion: Adding the crosslinker lowers strong-alkali resistance. The end use needs careful attention when the formula is designed.

Gloss:
The crosslinker is compatible with the resin and has no effect on gloss.

Hardness:
Crosslinking can raise film hardness and also lifts the glass transition temperature (Tg).

Water resistance:
In a standard water-resistance test, the difference within 48 hours was small. For resins that already had poor water resistance, such as B1 and C1, the crosslinker reduced whitening and flaking after water immersion.

Summary: effect of aziridine crosslinkers on waterborne acrylic wood coatings